Sunday, July 28, 2013

Gold and Silver Refining At the Phoenix Company

Gold and Silver Refining At the Phoenix Company 


I'm grateful for all of our hard working team of employees who busted their butts for the business and not just a paycheck. Their hard work, loyalty and enthusiasm was a great inspiration for me.  

We started out with 3 of us in the garage and grew to around 27- 30  employees in a building just outside of town in Modesto, CA in a little over a year and a half.

Our business was in it's infancy as a  manufacturer of very simple silver charms. We started in our garage in a rented home in Modesto, California.
My father traveled all over the country building relationships with buyers and sellers while my girlfriend and I worked about 16 hours a day - 7 days a week manufacturing the silver and gold charms using the lost wax casting process. This lasted a year until our garage was full of employees and we had to move into a commercial building near the edge of town. In the next few months we rapidly grew to casting up to 72 - 4 X 6 inch flasks 2 to 3 days a week which  would produce about 3,8880 small charms. The process creating a great deal of polishing dusts, floor sweeps and grindings which we eventually decided to refine ourselves. In the beginning I tried to follow instructions from what we were able to read and repeatedly failed to achieve the purity and complete return of precious metals from our scrap. Finally my father decided to hire a professional refiner and a chemist to help us get everything going properly. The information found in this blog are the exact processes that we developed with the help of 2 refiners, 2 chemists and a PhD metallurgist. 

I hope this becomes a valuable reference for you and sparks your entrepreneurial spirit.

Best of Success For You!
ΩPhoenix Consulting
Copyright ©2012 All rights reserved.








Natural Untreated Loose Gemstones

Tuesday, April 2, 2013

Back In the Day - Operating Gold and Silver Refineries













I was born in Alaska and I grew up in Central California.
Over 33 Years Ago I trained with and helped to manage "The Phoenix Company" in Modesto California a Jewelry Charm manufacturing company that evolved into a Commercial Gold and Silver Refinery - The Phoenix Smelting and Refining Co.


My father and I built the jewelry charm manufacturing company, (The Phoenix Co.) with the help of my girlfriend and we worked about 16 hours a day in the garage then soon expanded to the outskirts of town growing our business to 30 employees. We worked our butts off for a year before we finally became well recognized as a  wholesale jewelry manufacturing company located in Modesto, CA USA. Our business grew rapidly and soon we needed to recover all of the gold and silver from our floor sweeps, grindings and polishing dusts. We then hired chemists and metallurgists to train us in assaying , smelting, recovery and refining.



At this time we learned about a company through a refiner in Oregon that manufactured heat processing equipment. We contacted them with a proposal for the construction of a furnace that would reduce x-ray film to ash without losing silver at high temperatures.



They put their team of top engineers in the industry to work on it and with our combined ideas and the help of a German scientist designed a machine that would recover silver from pre 1980's X-ray film at a capacity of 500 pounds of film per hour producing an end product of approximately 100 Troy Ounces of 99.99% Pure Silver per Hour with only trace silver losses due to volatilizing. The company that helped us design and build the Pyrolysis Machine is Kleen Air USA. The process which is used widely today is more commonly referred to as Bio-Mass Reduction.  



Our gold and jewelry charm company production rose and fell with the gold and silver prices rising to their highest prices in history up to 1980. Gold refining became more lucrative when Gold peaked in 1980 then prices took a downturn which led us to selling the jewelry/refining companies at a good exit point for our situation. We then moved to Hong Kong, (http://www.companies-hongkong.com/jkl-industries-h-k-limited-3myw/ ) where we built rotating cathode electro winning, (reverse electroplating), units for hospitals and plating shops. These units recovered silver from fixer solutions utilized in X-ray film production and gold from cyanide solutions used in gold plating operations. Later we moved to Thailand where we exported jewelry for about a year. Then my father and his lovely Thai wife started a boat building business in Terrenganu, Malaysia and went on to operating a resort on Kenyir Lake in Kuala Terengganu. As organizing chairman of the local Lions Club dad was able to organize fun trips for orphans and children of single parents. The two of them continued to operate the resort for 8 yrs. until his health issues forced them to return to the U.S. I came back to California and went to work in the technical metal alloys industry producing technical brazing alloys for medical, automotive, aircraft and other highly specialized purposes.

  I am currently living in Oregon USA and I interested about helping you if you are serious about starting a gold or silver refinery and partnering with you or providing you with consultation. I can't provide all of the knowledge that would be required to start this kind of business with  continuously changing City, County, State, Federal industrial, environmental, employee, etc. regulations. As with starting any business you have to employ specialists as needed. But I can provide a smooth transition for you from your first "back yard" melting and pouring of a 3 gram button of silver or gold to your first 1000 troy Ounce Bar of .9995 Fine Silver or Gold.








ΩPhoenix Consulting
Copyright ©2012 All rights reserved.
Be Happy - Hang_Loose







Wednesday, March 27, 2013

Refining to 99.95% Gold


by Steve Looser


Before using this information and education site you should agree that you alone are responsible for your own health and safety and that you will not hold the author of this site or any contributing authors and publishers responsible for any of your decisions or actions resulting from any information contained herein. You agree to do your research and accept full responsibility for your actions. If you agree to the statement above then continue reading and enjoy, if not we advise you to leave now or continue reading for learning only. I strongly recommend that you take a laboratory safety study course or lab safety class before proceeding with processes described in this book and do not work alone. I also suggest that you start with simple and basic refining methods before you attempt some of the more complicated ones. Also be easy on yourself, perfecting your skill comes with practice.

Preparing Scrap Gold for Refining
When precious metal bearing material is received from a customer it is weighed and copies of the gross weight received with the customer name and date, an order number, processing instructions and lot number are produced. Samples are taken and the material is sealed in a drum with a metal seal and identification. Processes for sampling vary depending on the material. Several samples are taken from the material. Samples are given to the customer, some are sent out for an independent assay analysis and some for your in house assay. In the case of raw metal it is melted homogenized and poured into and ingot so drilling's can be taken as samples. If it is solutions you will need to draw liquid samples. If it is sweeps that must be incinerated it will have to go through a lengthy process that is described below. Before dissolving gold in aqua regia, (1 part nitric acid & 3 parts hydrochloric acid) make sure it is free from waxes, oils plastics, tar, any organic materials, sulfides, chemicals, etc. "Sweeps" material is often full of crushable materials like old broken crucibles, clay and glass as well as combustible materials like polishing dust, paper, waxes, common garbage and sometimes even food. Incinerating is often done first before any of the separating of the materials mentioned above.
The incinerator is designed to allow air to pass over the material so as to completely oxidize all of the organic material and convert it to a carbon less ash. During the incineration the material is turned mechanically in some types of barrel incinerators and in others the incinerator doors are opened and the material is raked to expose it to oxygen. These incinerators are exhausted into smoke and dust collection systems. Back in the day they called them Bag Houses. After it has finished roasting to ash it is allowed to cool to room temperature and then it can be crushed into a fine powder in a crusher or ball mill. After removal of the material from the ball mill or other type of crusher a magnet is then used to remove steel and other magnetic materials. It is then screened to remove certain materials that will not crush. After screening to a uniform size it can be thoroughly mixed so that multiple samples can be taken for assays. Analysis on this dust is normally done using the fire assay method.
2 Preparing scrap gold for refining
Silver will not dissolve in aqua regia except in very small quantities as a dissolved chloride. When silver is introduced into aqua regia it quickly forms a hard impermeable layer of silver chloride, (AgCl) on the surface and stops reacting with the acid. The same thing occurs when trying to dissolve gold if the silver percentage in the gold reaches near 15% or more. It's a common procedure to reduce the silver percentage in your gold alloy to 12% before refining by melting it and stirring copper into the melt. Old school called this "Inquarting" because they added 4 times the weight to the gold using copper or silver. Inquarting silver was often used making the gold 25% or less of the alloy and then it was dissolved in nitric acid to leave the pure gold remaining as a brown residue in the bottom of the beaker. But the term has evolved to mean adding copper or any base metal to gold scrap to make the gold one fourth of the total weight so that the silver will sluff off during the digestion with aqua regia.
This Video Below Is One Of A Series Of Fantastic Training Videos That I Highly Recommend

Gold Refining Complete Process for the Home Refiner  Subscribe to Streetips YouTube Channel for More Videos

In gold refining you will find silver to be your enemy but save your silver sludges for the end of the year and process them near tax time because they will be your friend. When tax time rolls around each year for large jewelry manufacturers and other precious metal industries the settlement for their floor sweeps and polishing dusts can often pay their taxes. The same goes for a refinery with their silver chloride sludges and their slags from smelting

3 Preparing scrap gold for refining

The gold is melted in zirconia crucible using a hydrogen-oxygen torch. The crucible must be capable of withstanding the high temperature produced by the torch without cracking. Wesgo Platinum Crucibles are what we used to use at The Phoenix Smelting and Refining Co.
If the gold is clean and free of foreign material such as gold received as pendants, rings, and chains, it can be added directly into the aqua regia for dissolving but usually it is melted and poured into a tank of cold water to create shot. It's good to do this for a couple of reasons. One is that it gives you a uniform and homogeneous alloy that will dissolve at an even rate. Two is that you can introduce copper and zinc into the melt to effectively lower the silver content in the alloy. If the content of silver is too high in the alloy it forms a barrier to the acid and slows or stops the acid from dissolving the gold. When melting gold scrap and alloying gold a carbon rod is used to stir the molten metal.
*Also remember to always preheat your carbon stir rod before sticking it in molten metal unless you want instant dental caps and a gold faceplate. Graphite always seems to attract moisture out of the air and if you don't dry them prior to placing them into a melt they will cause the metal to explode.
I did it once with a long rod in a blast furnace and ate silver. It fused silver in my clothing and shoes and there were pieces of silver stuck in the cracks between my teeth. I'm Lucky I was wearing safety glasses. *Always preheat your carbon rod before touching it to molten metal. Stirring of the molten metal must be done very thoroughly using circular motions and contacting all areas for the molten metal for several minutes.

4 Preparing scrap gold for refining
Borax or boric acid is used as flux. The addition of a light sprinkle of flux to the molten metal cleans the surface of the metal and helps remove oxides. The molten flux forms a glass like substance called slag and will contain impurities as well as some of the original melt in the form of tiny or even microscopic particles. This is why you never dispose of your slag. If the metal is to be poured into water, any excess slag which might pour out with the metal into the water should be removed with a carbon stir rod. The rod is swept across the surface of the molten metal and all around the inner edges of the crucible with a twirling motion which creates a slag ball on the tip. Slag removal is more important when pouring shot than when pouring bar although it's always a good thing to do. If you are pouring scrap into bars it is not necessary to remove slag before pouring as it is easily tapped off after the bar cools, whereas with shot it would be very difficult to remove slag.

5 Preparing scrap gold for refining and pouring shot
Your shot tank should be filled with cold water to 1.5 inches from the top of the tank. When the metal is molted the crucible is held with crucible tongs balancing it on the edge of the shot tank and tilted very slowly. The metal should have poured slow enough to cause the stream of molted metal to break into individual droplets, breaking just below the water line. If the metal is too cold it will solidify before the pouring is completed. If the metal is too hot or poured too fast it can explode into powder and dust in the water. It's helpful to have an assistant play a torch flame over the molten metal while pouring. a hydrogen flame with the oxygen turned on low to give a feather like reducing flame works well for this.
Once the pouring is completed the water is emptied from the tank and the tank is tilted over a clean container and the shot is washed out of the tank by spraying with water. If the shot is to be weighed it must be dried thoroughly. You can do this by putting it in ceramic dishes and placing it in a drying kiln at a low temperature that will not discolor the shot. You will only want to heat it just over the boiling point of water around 250°C will do but make sure all the water is eliminated.
You don't want to calculate an alloy charge with wet metal.

6 Dissolving Gold
Before you begin handling the acids and chemicals be sure to put on your PPE, personal protective equipment such as a rubber apron, rubber boots, a pair of splash proof goggles or a face shield, and rubber gloves. Also you should have a 5 gallon pail of neutralizing material handy that you pre make by mixing sand with sodium carbonate. If you have a spill you cover it with this. You should have a good water supply and plenty of paper towels available.
After the gold bench filings and scrap are prepared for refining the metal is placed in a heavy beaker on a hot plate. Hydrochloric acid is added to the beaker amounting to 4 to 5 times the weight of the gold. Nitric acid is added very slowly to the hydrochloric acid amounting to 1.5 times the weight of the gold. This acid solution is Aqua Regia and dissolves the gold. The reaction of the dissolving gold will generate heat and it is only necessary to turn on the hot plate at the lowest setting after the reaction has slowed down an hour after starting. It is important to do all of your work with acids under a good fume hood or ventilation system working at all times with backup electrical power in case of a power outage. At times the gold scrap or filings can react violently with the acid and generate too many fumes. This is why you should only add half of the nitric acid in the beginning and wait for the initial reaction to subside before adding the remainder. Aqua regia is 3 parts HCL and 1 part HN03. An example would be 600mls HCL and 200mls HN03 but my suggestion is to place your 600ml HCL in the beaker first then carefully and slowly add your gold scrap in shot or sheet form to the acid and then only add 100ml of the HNO3 VERY SLOWLY to the HCL and let it react until there is no more reaction before adding the remaining 100mls. You must always be cautious of a possible boil over of your acids causing a potential loss or injury as well as damage to your equipment. The amount of acid is added in small portions to control the rate of reaction is based on the size of the batch being dissolved and the capacity of the acid scrubber equipment to handle the amount of gases being generated.

7
The average small size lot we processed was between 5 and 10 troy ounces and took up to 3 hours to dissolve. The scrap needed occasional stirring and the use of a plastic stir rod to break up the silver chlorides which held to the metal. Most gold scrap has silver as part of the alloy and this silver converts to silver chloride when under attack by aqua regia forming a cake or crust like layer on the gold. Before you begin to dissolve your scrap you can melt zinc and copper into your gold to lower the silver content ratio in your scrap then pour it into shot. Then when you dissolve your scrap the silver chloride will easily fall off the gold and settle to the bottom of the beaker. You want the silver to be no more than 10-12% of the alloy you are going to dissolve. By having your silver content in the gold alloy low enough the silver will fall away from the gold as it is dissolving and form a powder in the bottom of the beaker. It's a good idea to have a stirrer hotplate to speed the dissolving process but not necessary. A large lot is sometimes processed overnight. When all of the gold is dissolved you should feel no pieces or particles with your stir rod and there will be no more bubbling and fuming.
Now it is time to let the solution cool and pour it off into a plastic tank to chill by adding cold distilled or deionized water to double its volume. Add about 20 milliliters of sulphuric acid to the cooling aqua aqua regia to precipitate lead. After you double the volume you then set up your filter funnel with its adapter and filtrate bottle. Note* you can pay a lot of money for laboratory vacuum flasks or you can use a 6 gallon water bottle, the same kind home brewers use for beer making.
8
The filtration system is made up of a 240cm Buchner porcelain filter funnel and a 5 gallon glass filter bottle, a rubber filter adapter to fit the funnel to the bottle or flask vacuum tight and a Tygon plastic hose which connects from the filter flask to a vacuum pump. All of these items can be purchased at a laboratory supply company. The adaptors and filter flasks can be found at Amazon and large filter flasks up to 20 liters can be very expensive at laboratory supply companies so we just used 5 gallon water bottles. The adaptors fit into the neck of the flask or bottle and the funnel fits through the adaptor into the flask. A vacuum is drawn and a filter paper is laid down over perforations in the funnels plate wetting it with a stream of water from a wash bottle while laying it down. Then the gold solution is slowly poured into the funnel filling it close to the top. The first 500mls can be emptied from the flask and re-filtered to help the paper be more retentive by clogging the pores in the paper. This helps to make a clearer filtrate. Filter all of the gold solution this way and wash all of the undissolved silver chloride and other insoluble material onto the filter paper also. When all of the solution has passed through the filter, wash the remaining insolubles by pouring a dilute 1% nitric acid solution over it and allowing the vacuum to pull it through the paper. Repeat this about 5 times until the solution exiting the stem of the funnel is clear. That is the way you filter rinse. The small amount of nitric acid is necessary to prevent the silver chloride from dispersing, (called peptization) into fine particles that will pass through the filter paper and contaminating the filtrate.

9

After filtering turn off the vacuum and carefully remove the funnel. Then remove the paper from the funnel and place it in a bucket to save along with other chlorides for processing at a later date when the value makes it profitable to spend time on it. Also take a wash bottle and wash away the chlorides adhering to the funnel into the same bucket. Then take the funnel to a wash basin and wash it thoroughly with a sponge and powdered cleanser before placing it in a safe place.

Note* I want to mention here the "Old School Refining Method

After dissolving gold scrap and filtering out the chlorides we used to evaporate the filtrate to a crystal and rehydrate with HCL repeating this 3 or more times to a crystal until no brown nitric oxide fumes appeared. We used Coors Evaporation Dishes:


Doing this eliminated the use of urea to sequester the HNO3 and allowed for easier precipitation of the gold with Ferrous Sulfate without the interference of the nitric acid.
You then pour the filtrate into a clean container such as a 5 gallon plastic bucket and dilute it to double the volume with water. Now you are ready to add urea to chelate the nitric acid. When you are adding and stirring in the urea you will get a fizzing reaction. You will want to continue adding urea until the fizzing stops or at least diminishes. When the fizzing slows or stops it's time to precipitate your gold using one of the following precipitation reagents,
Ferrous Sulfate, (my favorite), Sulfur Dioxide Gas, Sodium Sulfite or Sodium Meta Bisulfite. You will need to add about 1.5 times the weight of the gold to precipitate all of the gold. If the filtrate foams while adding the reagent you should dilute it more and dissolve the reagent in water before adding it to the filtrate. The gold will begin to precipitate as a light color, then turn dark brown.
When the precipitate turns dark brown the precipitation is complete but it doesn't have to turn dark to be complete. When you think the precipitation is complete let it stand about 30 minutes then filter it through a Whatman # 2, 40 or 52 filter paper. You can test the clear filtrate to see if there is any gold left in it with a solution of stannous chloride by placing a couple of drops of the filtrate on a spot plate and taking an eye dropper and dropping 1 drop of stannous chloride into the filtrate. It it turns purple the precipitation is complete. Another way is to take a 100ml sample of your filtrate and add more sodium sulfite to it letting it set overnight.

Filter rinsing greatly speeds the rinsing process over trying to rinse and let settle before decanting or pumping the solution off of the settled contents. You just add your precipitate into the Buchner funnel filter and begin pulling water and rinse solutions through it letting the vacuum speed the process. It can literally save you hours or even days on big projects.
Filter rinsing removes trace impurities which may still be in your gold. Pass all of the solution through the filter paper and wash all the precipitate onto the paper. Some of the precipitate will stick to the container and can be removed with a nylon scouring pad which can be easily rinsed clean using a wash bottle. When all to the precipitate is on the paper a step by step rinsing and washing procedure is done as follows.

1. Filter wash and rinse the precipitate with distilled water allowing the vacuum to draw the water through. Repeat this a minimum of 5 times.

2. If a Whatman #52 glazed hardened filter paper is used, you can remove the gold from the paper and place it in a beaker. Then cover the precipitate with hot 1:1 nitric acid and water. Stir it occasionally and allow it to stand for at least 5 to 10 minutes.

3. Filter rinse the precipitate 5 more times with distilled or deionized water.

4. Cut the vacuum and cover precipitate with hot 1:1 HCL / water and let stand for 5 minutes. Then turn on vacuum and pull the solution through filter paper.

5. Filter rinse the precipitate 5 times with hot distilled water containing approximately10 to 30 ml per liter HCL.

6. Allow the vacuum to continue running to dry or semi- dry the precipitate.
Then sprinkle a very small covering of borax or boric acid on the surface of the precipitate. Gather up the paper and precipitate and place it in a zirconium oxide crucible for melting. The crucible must be new or one that has only been used to melt 999+ fine gold. Take a camel hair brush and brush all of the precipitate which adheres to the edge of the porcelain funnel into the crucible

7. Melt the gold with a hydrogen-oxygen torch. Bring the metal to a white glowingtemperature and turn off the hydrogen, blowing pure oxygen on the metal until it cools to a solid. This will sometimes produce discolorations and what could be oxides of trace metal impurities like copper. Don't worry and think that you have failed to produce pure gold. I have melted the most popular 9999 fine gold coins down in new crucibles and seen this occur. Nevertheless repeat this melting and blowing pure oxygen over the molten metal until all of this discoloration no longer appears. If you have a clean crucible and done everything correctly up to this point you shouldn't have any problem doing this final cleaning of your gold. If it will not clean up then assay it and it will probably be at least 999 Fine. Like I said I have melted the most popular 9999 Fine

Gold coins and still found this. Hey that tells you that I get my stuff pretty darn clean don't it. I want to mention also that if you did your last filtration's of your precipitate on a glazed hardened filter paper then you can brush your precipitate off of it into your crucible and re-use the paper for more filtration's instead of burning it. Here is another method you might prefer For these procedures you may want to use reagent grade acids for your final acid washes and rinses. I am not sure if it really helps to use reagent rather than industrial grade or technical grade chemicals. You will spend a whole lot less money if you stick with industrial grade. I don't think you want to get too cheap and use farm grade though. If you have the time and money to go through a lot of testing and lab work you might find that you can save a lot of money and use the cheapest chemicals for certain applications. I used to go to a company just outside of Modesto, California by the name of Snowden Chemical. They supplied the wine industry in that area with bottled SO2, (pressurized sulfur dioxide gas) which precipitates gold nicely after chelating the nitric acid with Urea prills, Urea can be farm grade. Sodium Meta Bisulfite or Sodium Sulfite is producing SO2 as soon as it enters aqua regia so any of these will work well.

1• The gold is dissolved in aqua regia then diluted in cold water and a small amount of sulfuric acid is added to precipitate lead. Then it is filtered.

2• Potassium nitrite is added to the filtrate solution using about 2 to 5 grams per ounce of the gold you expect to recover. This is to chelate trace platinum group metals.

3• The pH of the solution is adjusted to 1.5 using Potassium Hydroxide.

4• Then the gold is precipitated using sodium or potassium sulphite, sodium metabisulphite or sulfur dioxide gas....By the way, it is not okay to breath sulfur dioxide because it will eventually cause you to have allergies to sulphites and then you're really screwed because you won't be able to enjoy wine or dried fruit again without getting a sore throat from the sulphites. SO2 and or sodium sulfite is used in the wine industry to stop the fermentation before bottling and on dried fruit to stop bacteria growth during the drying process or to speed the drying.

5• The precipitate is transferred to the filter and filter rinsed as before using distilled or deionized water. Wash it thoroughly on the paper covering the gold precipitate and letting the vacuum pull the water through it five times or more. Use a Whatman® #40 or #52 filter paper that you can get at a laboratory supply. If you don't have a vacuum filter funnel arrangement then you will have to be much more patient and double up on the rinsing.

6• Remove the precipitate from the paper and place it in a beaker on a stirrer hotplate and covered with 1:1 HNO3 / distilled water and allowed to simmer just below boiling on a low heat and stir for about 1 hour.

7• Then the precipitate is filter rinsed with distilled water 10 times. You should shop around to find the lower cost filter papers. I always used Whatman to be safe but I see people using coffee filters and claiming to get a result of 999 gold. I really didn't know at the time and just used Whatman papers to be on the safe side but  pick the least expensive filter papers on the market that get the job done and won't contaminate.

8• Place the precipitate back into a beaker on a stirrer hotplate and cover with 50/50, (1:1) solution of ammonium hydroxide and distilled water and add 2.5 grams per liter of EDTA, (ethylenediamine tetra acetic acid) for 1 hour cold and stir. It's important that you don't breath that ammonia hydroxide because it causes chronic damage to the thyroid glands with prolonged exposure. Ever wonder why some housekeepers have a weight problem? It's their exposure to ammonia cleaners every day that's messing up their thyroids. Sorry housekeepers, you need to be careful also.

9• Filter rinse the precipitate 10 times more with distilled water.

10• Return the precipitate to a beaker and this time cover with a 1:1 solution of HCL/distilled water and let it leach out trace contaminants at near boiling for another hour or so.

11• Then the precipitate is filter rinsed 10 more times with hot deionized or distilled water containing approximately 10 ml per liter HCL. Now I hope that you realize you've messed around with this gold long enough and you know deep down inside yourself that it's pure! You have done all that you can other than repeating the process. If you want to produce 9999 or 99999 you have to employ the Wohlwill process
 of electroplating the gold
through a gold chloride and hydrochloric acid bath.
12• Allow it to dry on the paper and sprinkle a little boric acid on it then gather it into you clean crucible and melt it. After pouring your bar wash it in hydrochloric acid, rinse it, dry it, weigh it, and stamp it for identification. Buy yourself a little numbers and letters stamp set at the hardware store if you don't have one. The gold that you pour should assay at 9995+Fine.
If you have an electric kiln you may want to gather the gold withthe filter paper and place it in a ceramic dish to dry it and burn off the paper to ash before you melt it. You will find that some crucibles work much better than others. I had good results using a quartz silica crucible for small pours because they didn't crack as often as some other types. But zirconia cruciblesare by far the best type you can buy in my opinion for the big melts. What you really are looking to do here is build yourself a good reputation as a refiner who knows his shit so don't ever try to cut corners and keep your end product consistent. Then after you have refined some jewelers scrap and sold a few of your bars you will start to get word of mouth advertising and people will come to you to refine their gold or buy yours. Take you time, make sure everything is clean practice safety always and do it right. It will pay. Refine 100 Kg Gold to 9995 Fine Daily. Visit: GOLD AND SILVER REFINING SYSTEMS
12• Allow it to dry on the paper and sprinkle a little boric acid on it then gather it into you clean crucible and melt it. After pouring your bar wash it in hydrochloric acid, rinse it, dry it, weigh it, and stamp it for identification. Buy yourself a little numbers and letters stamp set at the hardware store if you don't have one. The gold that you pour should assay at 9995+Fine.

If you have an electric kiln you may want to gather the gold withthe filter paper and place it in a ceramic dish to dry it and burn off the paper to ash before you melt it. You will find that some crucibles work much better than others. I had good results using a quartz silica crucible for small pours because they didn't crack as often as some other types. But zirconia crucibles
are by far the best type you can buy in my opinion for the big melts. What you really are looking to do here is build yourself a good reputation as a refiner who knows his shit so don't ever try to cut corners and keep your end product consistent. Then after you have refined some jewelers scrap and sold a few of your bars you will start to get word of mouth advertising and people will come to you to refine their gold or buy yours. Take you time, make sure everything is clean practice safety always and do it right. It will pay. Refine 100 Kg Gold to 9995 Fine Daily. Visit: GOLD AND SILVER REFINING SYSTEMS
12-13 Gold Refining to 9995+ Fine Gold

The method below was originally posted on pg.48 and I moved it to this more appropriate post.

This method produced 999.54 fine gold Dissolve scrap in aqua regia and precipitate with sodium sulfite. Filter wash the precipitate with deionized or distilled water by pouring the water over the precipitate in the funnel and letting the water pull through completely before adding more water. Repeat this about 20 times. Next pour hot nitric acid 1: 3 water over the precipitate and observe it lighten in color. Next repeat rinse procedure with water as stated above. Then wash with weak HCL and again as indicated above with water. Gather to dry in kiln and burn off filter paper at 1100° F and then place in a clean crucible and melt with hydrogen oxygen torch. Play the hydrogen over the bar as it is being poured and cooling. Drop a pinch of ammonium chloride on the bar immediately after pouring while still glowing red. To further complicate things if you are totally anal you can use the process below. 100 ounce Refining procedure Dissolve scrap with 1 gallon nitric acid and 3 gallons hydrochloric acid. After it's finished dissolving carefully add urea until fuming subsides. Filter on a #40 or #52 Whatman filter paper with pulp. Stir in 100 grams ammonium sulfate and double the

volume of the filtrate with deionized water. Let stand for 2 hours then filter again with a #40 Whatman filter paper and pulp. Rinse paper once with 1% nitric acid. Add more urea to the filtrate. Very carefully stir in a solution of 1 liter deionized water and 200 grams sodium nitrite for complexing platinum groups. Then carefully add 1 oz. ammonium sulfite for every ounce of 99.9% gold you will precipitate. Let it settle for 2 hours. Then filter the gold with a #52 Whatman filter paper. Rinse with deionized water. Dry in the filter with the vacuum pulling all the water out until

dry. Take the gold off the filter and place it in a glass beaker and cover it with a 1:1 HCL and deionized water. Stir for 3 hours on stirrer hot plate or let stand for 24 hours. Pour off and rinse thoroughly with deionized water ,( check pH) then cover with a 1:1 solution of ammonium hydroxide, (see footnote) and deionized water with 2-3 grams of EDTA. Stir for 3 hours or let stand for 24 hours. Gather the precipitate into the filter funnel and vacuum filter dry it then gather it and place in porcelain drying dish in an electric kiln. Set the temperature and 1100° F and roast it until all the filter paper is disintegrated. Remove the gold sponge and gather into a Zirconium crucible. Melt with a hydrogen oxygen torch using a rosebud torch tip. Pour into a preheated cast iron mold or graphite mold and sprinkle a pinch of ammonium chloride on the red hot bar immediately after pouring. Your bar should receive an assay result of .999 to .999.5 Fine Gold.

If either of these methods doesn't get you what you want in terms of purity even after taking the metal through the process 2 times. You have got contamination entering your process somewhere like on your crucibles, stir rods, molds etc. Too further refine the gold to 999.9 fine and higher you will need to set up Wohlwill gold cells. An excellent summary of this process can be found her http://en.wikipedia.org/wiki/Wohlwill_process.
I would also like to mention that the methods described above only work well for gold scrap containing 25% gold or higher. If you are refining gold that is 25% or less it is best to part it with HNO3, (nitric acid) first and then after washing the remaining residue and rinsing with distilled water you then take that gold and re-dissolve it in aqua regia and follow the process described above. Finally I highly advise not to use the aqua regia refining methods described above on circuit boards or other low grade gold bearing materials that contain high amounts of lead, and other base metals. It is near impossible from my experience to recover the gold. The gold will become trapped in solution. That is why large operations use various types of leaching on low grade scraps and ores such as weak cyanide solutions with a buffered pH of 10.5 I have leached gold plated and gold filled scrap with hot/very weak cyanide solutions with the addition of hydrogen peroxide 35% to introduce the oxygen necessary to strip the gold. This is the same procedure jewelers use that is called "Bombing" and it strips a tiny layer of gold off the jewelry to leave a bright and shiny surface. We used to do this with gold charms after casting in quantities of 50 ounces or more. They were placed in a casserole in a deep wash basin
and covered with hot water then a sodium cyanide egg was dropped into the hot water and allowed to dissolve after pouring one ounce of 35% hydrogen peroxide into the casserole and the glass lid was quickly placed on top and held tight. Almost as soon as you get the lid on it goes poof bang and shoots the hot liquid out under the lid even though you try to hold it shut. That's why they call it Bombing, because it goes Boom! All this must be done with heavy rubber gloves , face mask and apron of course. The gold from leaching and bombing solutions can be recovered by vacuuming out the oxygen then stirring in zinc powder which will precipitate the gold. The gold/zinc is then is rinsed free of the cyanide and the excess zinc can be dissolved away with HCL. Then the remaining gold can be refined to 999 or higher with the aqua regia method.
I processed one batch of 37 pounds of gold filled jewelry with cyanide and recovered about 3.5 ounces of 999 Fine Gold. There are many good books on cyanide extraction of gold.                 
   
This assay of 999.54 parts per thousand 
                                    from methods described above.








Note: Do not breath Ammonia Hydroxide.

You should do all of this under a fume hood with face

shield, rubber apron, rubber gloves and rubber boots.

Always remember that you are handling corrosive and toxic

chemicals, hydrochloric acid is corrosive and nitric acid is

toxic and corrosive, people have been seriously injured when not

following safety operating procedures and wearing all appropriate

personal protective equipment , (PPE).




See More by clicking the link below.








Steve Looser
Phoenix Consulting
Copyright ©2012 All rights reserved.








 

PGM REFINING






14
If the gold contains platinum and palladium amounting to quantities that are profitably recoverable like some of the dental alloys, the gold is digested and the solution is evaporated to a syrup using evaporation dishes. A small amount of sulfuric acid is used to help prevent the acid from spattering when it has evaporated to a syrup. The thick syrup is diluted with 1:1 HCL and water and filtered if necessary.
Then before rinsing the paper, remove the filtrate from the filtering flask and place it in a clean container. Then rinse the chlorides in the filter paper 3 to 5 times with dilute, (10ml per liter) HNO3 to water. Evaporate this rinse filtrate down to a syrup or crystal and add it to the rest of the filtrate. This filtrate is evaporated again to a crystal and re diluted with HCL and evaporated 3 times again until no brown fumes of nitrogen oxides are expelled out of the crystals when they are re dissolved in HCL. Usually 3 evaporation's are sufficient to remove all of the nitrates. The nitric acid and nitrates must be removed from the solution in order for the platinum and palladium to be precipitated.
When all of the nitric has been expelled the crystals are dissolved in HCL again and the solution is filtered if necessary and the platinum is then precipitate with a concentrated solution of ammonium chloride and distilled water. The solution should be cool and allowed to set for 3 to 5 hours before filtering. Then it is filtered and rinsed with a solution of ammonium chloride 20% and water 75% and alcohol 5% for 10 rinses. The ammonium chloroplatinate precipitate is gathered dried and covered while hot with formic acid to convert it to metallic platinum sponge. It is then roasted in a kiln at 600°C and can be melted or sold as is. It is usually better than 90 % pure at this point.
15
Then the filtrate still contains gold and palladium. Gold is precipitated with ferrous sulphate using 4.5 ounces per ounce gold that is in the filtrate in order to precipitate all of gold. The gold is filter rinsed as mentioned earlier but may only achieve a purity of 999 fine and you might want to re refine it to produce 999.5 Fine or better. After platinum and gold have been precipitated and removed by filtration the remaining filtrate may contain palladium and after it has cooled to room temperature it is precipitated with an a 1% dimethylglyoxime made alkaline by the addition of sodium hydroxide. You will need 2.2 grams dimethylgloxime per gram of palladium. It will quickly separate from the solution and can be filtered and washed with hot distilled or deionized water and dried at 220°F and ignited at 750°F.
Then it can be converted to metal by moistening with formic acid or bathing in a pure hydrogen flame.
Caution> You Must Were Special Platinum Melting Eye Protection Goggles When Melting Platinum With A Torch Or Pouring Out Of A High Temperature Melting Furnace...
These can be purchased at jewelry manufacturing supply dealers.


Steve Looser
ΩPhoenix Consulting
Copyright ©2012 All rights reserved.









Steve Looser
stevelooser55@gmail.com
ΩPhoenix Consulting
Copyright ©2012 All rights reserved.




Natural Untreated Loose Gemstones



Alloying Karat Gold




16


I like to use an accurate scale with an accuracy to .01 gram. Use pure metals and a clean melting crucible that has only been used for melting the same alloy. Use a consistent melting and stirring technique to provide repeatable results. For alloying gold you should have a supply of Pre-Made alloy ready to add to 24 karat gold for producing the lower karats.
For alloying silver to sterling, keep on hand a supply of pure copper.
The copper is melted, poured into shot and dried for later use. Be careful to dry completely to avoid weight variations and possible explosions when introduced into a melt.
Many alloy formulas for karat gold alloys can be found online and in jewelry manufacturing textbooks. A good alloy for making yellow gold of various karat content that I used to use is: 57% Copper 33% Silver and 10% Zinc. More sophisticated alloys containing silicon can be purchased from precious metal suppliers.
When preparing the metals to melt, the zinc is placed in the bottom of the crucible and the silver is placed on top of the zinc and the copper is place on top of the silver. It is done that way because the zinc melts at a very low temperature and if place on top of the melt it will burn off before it has a chance to alloy with the other metals. When placed on the bottom it will melt in easily with the silver and create a higher melting point alloy before alloying into the copper.


17

Melt the metals with a torch or furnace. A small amount of flux is added before and during the melt to keep the metal fluid and absorb oxides of trace contaminates. When the metal is almost molten begin stirring it with a carbon rod and playing the torch on it at the same time when it is completely molten. Continue stirring for about 30 seconds. If a furnace is used, a graphite rod can be used to stir with or a quartz rod. If you don't have a stir rod you can grab the crucible with a pair of tongs and swirl the metal around  carefully in the crucible because it is Very Easy to Spill this way and Dangerous!
Fill a shot tank with water to use before the melting begins. You can have an assistant help you holding a flame from a torch on the tip of the crucible as you are pouring into the shot tank or have a torch mounted to aim the flame on your pouring spout. If you are melting the metal with a torch you can easily handle the small crucible with the tongs in one hand and the torch in the other. After the metal is fluid and you have finished stirring, notice the surface of the metal where it comes in contact with the crucible. If the metal surface is not mirror like then add a small amount of boric
acid flux, like 1 or 2 pinches and continue to melt until you have a convex mirror surface.


18


Continue to heat and stir making sure, (if you are using a torch), that you are directing the flame onto the metal and not on the crucible wall. Hold the tip of the torch approximately 2" from the metal surface, pointing towards the center of the metal pool. Remove the excess flux as you are heating the molten metal. When you see a convex mirror look the metal should be ready to pour.

If you are pouring finished karat gold or sterling silver, ( .925 fine), refer to the section on making shot to produce a more attractive product. Once you have made a supply of your pre made alloys, you can alloy your pure gold or silver as needed. If for example you have 10 ounces of 999.5 gold shot you want to alloy to 14 karat, you first need to find what the decimal equivalent of 14 karat is. To do this you simply divide 14 by 24, 14/24 = .5833 You then divide the weight of the pure gold by the karat you want to make into .5833 so 10 / .5833 = 17.14 ounces.

You should run an analysis on your end product always of course. You should actually multiply your beginning weight of pure gold by the actual fineness , Example: 10 troy ounces X .999 = 9.99 oz. and then calculate 9.99 / .5833 = 17.12. Bottom line is always get a lab analysis on your finished product so that you are not giving away gold or producing under karat. You should do your own lab work and get an outside assay also before you sell your alloy shot or pure bar.


19

Here is a list of Karat Decimal Equivalents


9 karat = .375


10 karat = .4167


12 karat = .500


14 karat = .5833


16 karat = .667


18 karat = .750


20 karat = .8333


22 karat = .9167


23 karat = .9583


24 karat = .999+



The term fine or fineness means parts per thousand. This means a bar marked 9999 or .9999 Fine Gold is 99.99% gold. The same is true for silver.


When alloying 10 ounces of 99.9 fine gold you take 10 X .999 = 9.99 / .5833 = 17.12

So you add 7.12 ounces of alloy shot to your gold to produce 17.12 ounces of 14 Karat.

If you are using a gram scale there are 31.10348 grams to a troy ounce rounded to 31.1035 or 31.104 grams per troy ounce.


In Asian countries gold is sold in Taels.

There are 37.80 grams to a Tael and 1.2036 troy ounces to a Tael.


In China, there were many different weighting standards of tael depending on the region or type of trade. http://en.wikipedia.org/wiki/Tael



Sometimes gold is sold in Kilograms, (1000 grams). There are 32.15 troy ounces to a Kilo.


For Kindle  view all chapters on Amazon Kindle Here :How To Refine Precious Metals

Steve Looser
ΩPhoenix Consulting
Copyright ©2012 All rights reserved.



Natural Untreated Loose Gemstones

                                                                              

Pouring Gold and Silver Bars




Pouring Gold and Silver Bars 

Pg.  20 - 21

Here are some inside Diameter Specs. for graphite ingot molds I just used a bench drill press to cut them out. I think a router could get messy and create to much dust with the high speed.









20

Once you have added the alloy to the 24 karat gold you then
melt, flux, and stir the molten alloy using the procedure
mentioned previously. then pour the molten alloy into shot.
When you are ready to pour bars make sure the bar molds
are very clean. If you are going to pour into a graphite ingot
mold be sure to preheat the mold to drive off any moisture
it contains or the metal will explode when it contacts the mold.
Graphite molds will absorb water from the air so they have 
to be heated prior to pouring molten metal into them. Be
sure not to pour any boric acid or borax slag into the graphite
molds or it will stick to the mold and you will damage the
mold chipping it out.  Heat the graphite molds enough to
drive off the moisture but not to red heat because this will
will make the mold weak and porous. No oil or lubricant
should ever be used in a graphite mold like you can do with
an iron mold. Iron molds should never be too hot when
pouring gold or silver into them or the metal will fuse to
the mold. Warm the iron mold just to hot to the touch and
it is ready to pour into. Slag can be poured into iron molds
with no damage being done to the mold.  It's important to
keep a different mold for each metal or alloy that you pour.
For instance don't use a mold that you have been pouring
silver into for pouring 999.9 gold bars . It's okay to pour
any alloy of scrap into the same bars prior to refining but
if you are producing 999 silver, 999 gold or karat alloys
for sale them you should have a separate mold for each.


21

The torch flame should be feather like and completely cover the surface
of the metal. The oxygen should not be turned down far enough to allow
the metal to cool below the desired pouring temperature of the metal when
you are pouring. When you have completed the pour, turn off the oxygen
and play the hydrogen flame on the bars surface as it cools and solidifies.
You should be able to develop some skill handling the oxygen - gas
controls with the hand you hold the torch with because you will be holding
the crucible with your other hand. I like using hydrogen gas better than
other gasses because it produces a very hot flame with no contaminating
properties and you can use an oxygen regulator fit with an adaptor to fit
the hydrogen cylinder.
When pouring from a blast furnace the air should be reduced or the
gas increased to produce a flame extending 6' to 8' above the hole of the
furnace for approximately 3 to 5 minutes before pouring. You should have
an assistant stand by with a torch fitted with a rosebud tip and play a
hydrogen flame on the bars as you pour them. If you are pouring 500oz.
or 1000oz. bars you will be using 2 man tongs and you'll need a third
person to handle the torch and bars.
When the oxygen in the heat source is enough to form oxides on the
metals surface you have an oxidizing flame and it  is creating an
oxidizing atmosphere. When the oxygen is reduced  or eliminated
in the heat source and is low enough to reduce oxides on the molten
metals surface back to metal it is called a reducing flame or reducing
atmosphere.





Steve Looser
http://goldrefineryprocess.com/
ΩPhoenix Consulting
Copyright ©2012 All rights reserved.

Testing and Assaying Gold and Silver Pg. 22 - 36


Testing and Assaying Gold and Silver

by Steve Looser


Pg. 22 – 36




You need to assay scrap before refining to determine it's purchase value.

Customer lots are sometimes assayed to determine the exact value so that they can be combined and refined as one lot.

Test silver with nitric acid. The silver item is given a notch with a file before testing with the acid to determined if it is solid silver or only plated. Small acid bottles with ground glass stoppers can be purchased from laboratory supply companies.






One type of acid bottle has a lid which allows dispensing of one drop at a time. Another type has a glass rod which can run a streak of acid across the metal. It's important to know that there are a lot of types of silver markings and a lot of counterfeit silver passed around as well as legitimate names such as nickel silver and German silver which don't have any silver at all in their alloy. So it's important to develop the ability to recognize silver from various imitations and look-alikes. The same holds true for gold. You should develop the ability to see the difference in most cases. It's a good idea in the beginning to have small samples of other metals to comparewith gold and silver and to observe the way the acid reacts on the different metals. As far as scrap silver there are three common types you will run into. They are .750, .800, coin silver, ( 900 fine) and Sterling is .925 to .950.

23

Before using the acid be sure the metal you are testing does not have varnish, lacquer, was, or other substances on it's surface which will form a barrier for the acid to come into contact with the metal. Then place a drop of acid on the metal surface where you made the notch. Wait for the acid to react with the metal for a few seconds and observe the color of the acid. If the acid turns green means the silver is below coin silver 90% or it is possibly white bronze. If it turns green in the notch but the metal surrounding the notch turns grey white it is silver plate. some white metals cause the acid to become milky and it's good to compare with silver look a likes to help with you decision. If the silver turns dark grey it is approximately 90%. If the silver turns light grey it is approximately 92.5% , 900 fine, (925 sterling) and if it turns white if is pure. Rinse the metal with distilled water using a wash bottle and observe the color of the metal after the acid is washed off. If you are buying hallmarked jewelry, flatware,and decorative silver, calculate a margin of error before making payment.

If you are receiving metal to refine to pure and return to the customer you can melt the entire lot into 1 bar and take a drilling sample of it to verify the gold and silver content. You can send some of the drilling samples to laboratory for an independent assay analysis.

24

In testing gold jewelry a quick test is possible using nitric acid which

can be used to determine if the item is gold, gold plate, low karat, or a base metal, ( bronze, brass, copper, pewter, tin, etc.) The article must be clean on the spot where the acid touches it.

A notch is made with a file and one drop or streak is placed on the metal. If after a few seconds, no change takes place, the article is probably gold but if the item is a white metal it could be platinum, stainless steel or some other non reacting metal. if the metal slowly turns brown it's around 10 karat or below. If it quickly turns brown it could be any percentage gold up to 10 karat. Brass or silver with gold content less than 1% will turn brown. A test kit for gold that contains a series of gold topped needles with karats 10 to 22 karat can be purchased at Amazon.com or jewelry manufacturing supply companies.



In this case a flat smooth black test stone is used to rub a streak of gold from the item onto the stone and from the test needles onto the stone. A small amount of aqua regia is placed on each gold streak and the karat value is estimated by comparing the reaction and color of the acid after it has attacked the alloys. I always used fire assay or wet gravimetric analysis to test the gold I received so I am not able to explain the test stone method in detail. I do know that it is accurate enough to purchase gold from the public and be profitable. I have met many buyers that use that method. The most exciting method of analysis and testing that I have seen so far is the x-ray gun gold tester. I really don't know how accurate it is but the company that I worked for used xray to analyze metal alloys and it was accurate. Go here to see it:





25

A very old but still considered the most accurate method for testing gold and silver is the fire assay.

The equipment and supplies needed are listed below. 1 ea. Electric or gas fired kiln with an accurate pyrometer capable of controlled temperatures from 100°C to 1100°C . If an electric kiln is purchased it should be one that the heating elements are not exposed to the open interior of the kiln, (a muffle furnace) or one with elements made of a non oxidizable material.

1 ea. Roll silver free pure lead foil.

1 ea. 25kg bag Borax, ( sodium tetraborate)

1 case (100 ea. ) 1 1/4" bone ash cupels from Denver Fire Clay

D.F.C. Ceramics Denver, Colorado U.S.A.

2 to 3 ounces 9999 Fine silver shot.

12 ea. Tall form 100ml glass graduated beakers.

2 ea. Pair stainless steel forceps.

1 Pair beaker tongs.

1 Pair cupola tongs 30" length D.F.C Ceramics

1 Pair of half round pliers

1 Stainless steel brush

1 Ball peen hammer

1 ea. .5" thick flat steel block

1 2.5 liter 65-70% nitric acid

1 water filtration system or supply of deionized water.

1 drill or drill press

2 ea. 250ml plastic wash bottles

26

1 or more variable temperature stirrer hot plates

1 fume hood or ventilation system with acid fume scrubber

12 ea. Watch glass 3" Diameter

1 Balance Bench

1 bench 3' tall X 2' deep X 7' long (heavy construction)

Paper Towels

2 - 3 ea. 5 gallon plastic buckets

1 large wash basin.

1 25kg Salt

1 25kg sodium Hydroxide

1 case 64 ea. Assay Crucibles 30 gram.  D.F.C. Ceramics Denver, CO

1 small blast furnace

2 #4 Clay graphite crucibles

2 #8 Clay graphite crucibles

2 #12 same

2 #20 same

1 Pair large crucible tongs for Clay graphite crucibles

4 10 ounce cast iron ingot molds D.F.C Ceramics

4 50 ounce cast iron ingot molds

4 100 oz. same

1 3" X 5" sheet of 16 gauge stainless sheet

27

Silver assays are the easiest to accomplish. After the silver is received and the weight is recorded the silver is melted in the blast furnace or in the electric kiln. Then the silver is stirred when molten to homogenize, (completely blend) the metal. A small amount flux is used, and when the silver is ready to pour the crucible is rocked to swirl the silver and collect all the small beads of silver that cling to the inner walls of the crucible. Then the metal is poured into the ingot mold. the silver bar is immediately dumped from the iron mold when it solidifies and is quenched in cold water. It is a good idea to only cool the bar a little and pull it from the quench water while it is still hot so that any water that might be on the bar or trapped in tiny holes in the bar will be boiled off and not change the weight of the bar. After the bar cools it is them weighed and the weight is recorded.

28

*Note if the bar is dirty with oil film and slag, the slag must be chipped off and the oil washed of with a heavy detergent and rinsed thoroughly then heated to drive off any moisture before weighing. After weighing the bar place it on clean piece of paper and drill it on a slow speed with a small bit, drilling the hole on a clean area of the bar. Keep your hands and drill bit clean and free from oils to prevent contamination of the sample. The drilling's are then mixed on the paper and samples are gathered with tweezers and weighed on watch glasses on the scale. Two samples weighing .2 gm are needed. At this time the kiln should be preheated to 875°C with 2 bone ash cupels placed inside for 10 minutes to eliminate organic compounds in them and expel gasses which would cause losses. Two 3" X 3" sheets of lead foil are folded into pouches and the silver samples are brushed into them. One of the silver samples is the drilling's and the other is a .2 gm sample of 999.5+ fine silver. The pouches are then folded into small wafers, small enough to fit into the curvature of the cupel. When the kiln temperature has stabilized at about 875° C for 10 minutes place the wafers in the hot cupels and immediately shut the door to avoid heat loss. A small hole apx. .5" in the top or back of the kiln is and one at the bottom front of the kiln or the door should be be left ajar about 1/16" to create a draft. After about 1 to 2 minutes, check the lead.

It should have opened up and become a molten pool. If it hasn't opened and pooled, one trick that I was taught is to place a matchstick over the top of it, holding it with a pair of tongs and when the match lights it will open up and drop into a pool. This may seem strange but is something to do with the oxidation present on the pouch preventing it from reducing.

29

After the 2 lead pouches melt, oxygen in the kilns atmosphere causes the lead to oxidize and become PbO2, the other metals except precious metals, in this case silver , oxidize with it and absorb into the porous cupel and vaporize. About 20 % vaporizes and the remainder absorbs into the cupel. The cupelling takes about 15 to 20 minutes and towards the last 5 minutes the kiln temperature should be elevated to about 960° C to help remove the last of the lead. the cupels should be checked often because silver volatilizes and the cupels should be pulled from the kiln and covered as soon as the oxidation is complete. The surface of the lead button during cupelling has visible droplets of litharge PbO2 or PbO3 floating on it's surface. this is what oxidizes other metals in the silver and absorbs with them into the cupel. When almost all of the lead is oxidized away from the silver the surface of the silver pool begins to form rainbow like colors then very soon after it becomes shinny and mirror like. At this point the silver is pure unless gold or platinum group metals are present. If the kiln temperature is just below the melting point of silver,(960 ° C) the silver button will brighten for a second then cool and solidify. This is when you should immediately remove cupels from the kiln and cover with a sheet of graphite to prevent the loss of silver.

30

Silver absorbs up to 20 times it's volume in oxygen in the molten state if exposed to oxygen when molten and releases it when it cools to a solid often spitting silver out of the cupel in fine particles.

When the silver beads cool, take the half round pliers and crimp the beads to release the silver from the cupel and adhering cupel material from the silver using the stainless steel brush along with the pliers. Then weigh the bead which is pure. If the weight of the return bead is .1959 gm and the beginning weight was .2 gm you use the formula .1959 / .2 = .9795 You know that you started with .9995 so .9995 - .0795 = .02 or 2% That is your loss factor so you add 2% to the weight result of the other sample, ie: The sample result weight is .1958 / .2 = .9790 + .o2 = .9990 = 999.0 fine silver the loss factor is due to silver vaporizing in the melt which always occurs.

31

Watchglasses are placed on top of the beakers to contain the fumes. In approximately 20 minutes the silver in the button will have dissolved into the nitric acid and the gold will remain in the bottom of the beaker as a gold powder residue or a lump, in which case it should be broken up completely with a glass stir rod or stainless spatula and allowed to steep in the acid until all the silver has dissolved and none of the gold particles show visible signs of reaction with the acid.Then acid is carefully poured out of the beaker and the gold residue is thoroughly rinsed in distilled water with the use of a wash bottle, directing the stream of water back and forth through the gold residue. After the gold residue is rinsed with approximately 30 ml of distilled water the rinse water is carefully poured off of the gold residue making sure none of the gold particles accidentally pour out with it.

The residue is washed this way 5 times and then covered again with nitric acid only this time using 1:1 nitric and distilled water. This solution is brought to a higher temperature , (near boiling) and allowed to digest until the dark brown residue becomes light beige. At this point the gold residue is pure unless platinum group metals are present.

32

If the residue is light beige it is rinsed as in the first digestion and carefully dried taking care not to allow any of the gold to spatter out of the beaker from heating it too fast. When the residue is dry the temperature is increased to near read hot in order to burn off traces of acid and organic material in the sample. then it is allowed to cool before weighing. In weighing, a camel hair brush is used to carefully brush the gold out of the beaker onto a tared watchglass. The weight of the residue is divided by the weight of the original sample to find the percentage of gold present also known as fineness or karat. No vitalization loss occurs as in silver assays and no loss factor is calculated.

Examples:

.1 / .2 = .50 or 50% gold, 500 Fine or 12 Karat gold

.08333 / .2 = .4166 or 41.6% or 10 Karat gold

.11666 / .2 = .5833 or 58.3% or 14 K gold

.1999 / .2 = .9995 or 99.95% or 999.5 fine or 24 Karat gold

If the gold residue did not turn light beige during the second digestion in hot nitric acid it contains platinum group metals in which case it is rinsed completely and then digested in boiling concentrated sulfuric acid 90% . This will dissolve all to the metals and trace elements present except gold and when the residue turns light beige it is ready to rinse, dry, heat and weigh. Be extremely careful rinsing sulfuric acid. Let it cool down completely then add diluted sulfuric before starting to rinse.

33

For nitric acid that may contain silver you will use a small 100ml beaker and add salt water to the acid to precipitate a white curdy precipitate called silver chloride. Rinse the chlorides with hot water and let them settle to the bottom of the beaker. Decant the rinse water and repeat with more rinsing and decanting the rinses until you have completed 5 rinses. After the 5th rinse add a few drops of HNO3 to the chlorides and repeat the rinsing 15 times. If the hot water dissolves that precipitate it is lead chloride. The few drops of nitric acid keeps the chlorides from dispersing and allows them to settle quickly. If the silver will not settle, it is contaminated and will be easier to filter rinse than wash rinse in a beaker. The white precipitate that is left behind after repeated rinsing is silver chloride.

Silver chloride is photo-sensitive and if you take a spatula and spread a small amount on a white piece of paper it will darken in a few minutes.

To achieve a quantitative result start with an exact amount , like: 100, 300, 1000ml etc. Precipitate the chlorides and rinse as previously described. then after the final rinse cover the chlorides with cold water and stir in small portions of zinc powder. Then while stirring add a few drops of HCL. continue to stir in zinc until all of the white chlorides have converted to silver. Add small amounts of HCL to keep the reaction going. The zinc reduces the silver chloride to silver in a grey color grainy metallic state called cement silver that looks like fresh mixed cement.

34

When all of white chloride has converted to cement silver add more HCL in small portions to dissolve all of zinc. The cement silver will stop bubbling when all of zinc is dissolved. Sometimes zinc will take a long time to dissolve and precipitate should be left to digest, stirring it and checking for bubbles occasionally until all bubbling stops. Then rinse silver in hot water 15 to 20 times then dry it, heat it to burn off acid and organic residues at cherry red, let it cool, then brush it onto a watch glass with a camel hair brush for weighing on a milligram balance accurate to .00001 gram. Weight of this precipitate can be calculated into grams per liter , ounce per liter etc.

Example:

Sample vol. 100 ml

Result wt. 5 gms

There are 1000 mls per liter so 5 X 1000 / 100 = 50 gm per liter.

If you have a large amount of solution ie: 236 liters and you draw 100 ml samples and

produce 5 gm results your equation is as follows

5 X 236000 / 100 = 11800 grams / 31.1034 = 379.38 troy ounces.

For photographic fixer solutions, a sample is drawn ie:, 500 ml and heated in a beaker on a hot plate to improve precipitation. Then zinc powder is stirred into solution using enough to precipitate all of silver. To my knowledge the most silver contained in fixer is 20 to 22 gm/l. The solution is heated for a few minutes and occasionally stirred, then taken off the heat and allowed to settle. When excess zinc settles, decant solution & rinse with distilled water using a wash bottle.

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After rinsing zinc and decanting rinse water 5 times, add small portions of HCL to dissolve away zinc. Then when all zinc is dissolved rinse again 10 times, then dry, heat to 600° C, cool and weigh result. Calculate for grams per liter (gpl) same as mentioned before.

Result X 1000ml ./ mls of sample = gm per liter.

Example:

Sample volume 500ml

Result wt. 3 gm

3 X 1000 / 500 = 6 gm per liter

Cyanide solutions are tested using zinc with same method used for photographic fixer solutions except cyanide must be made alkaline to a pH of 10.5-11 using potassium or sodium hydroxide and temperature must be at least 60°C (140°F) and a few grams per liter excess cyanide is added to sample. The zinc must be left in the 140° F sample for 30 minutes before allowing solution to settle and finishing process using same methods as mentioned

for fixer solutions. If cyanide is known to contain only gold or only silver, result can be weighed and calculated as is. If cyanide contains gold and silver or gold and silver combined with other metals, resulting residue can be wrapped in lead foil with 4.5 times it's own weight in pure silver and fire assayed. The bead is weighed after cupelling and if you subtract weight of silver you added to residue, remaining wt. of the bead is gold or silver or both gold and silver. The bead is then parted dissolved in nitric acid and resulting residue is gold..

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The difference between weight of gold residue and wt. of bead minus silver added , plus silver volatilising equals weight of silver present in solution sample. Example: You drew 200mls. cyanide solution for testing. The resultant residue was gold and silver you decided to fire assay it. It weighed .5 gram so you added 4.5 times that weight in silver , 2.25 gm. and cupelled it. The bead weighed 2.7 grams so you subtract 2.25 gm. and that gave you .45 gm gold and silver. the bead was then parted, the gold residue rinsed, dried and weighed and the weight was .15 gm. So you subtract .15 gm gold from .45 gm gold/silver and that left you with .3gm silver. If a proof sample of similar alloy composition was cupelled side by side with sample cupel, silver volatilizing loss factor could be added. Usually silver loss during cupellation amounts to about 2%

Example:

.3gm Ag / .98 = .306

.306 X 1000 / 200 = 1.53 gm per liter silver

.15gm Au X 1000 /200 = .75 gm per liter gold






Hang Loose

Steve Looser

ΩPhoenix Consulting

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