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high copper in gold bullion base metal analysis (7 replies and 2 comments)
Hello Mashudu, see https://www.911metallurgist.com/electrowinning-smelting/is-there-a-specific-flux-recipe-or-extra-additive/
Adding oxygen also helps lower copper content from bullion https://www.911metallurgist.com/blog/oxygen-air-refining-gold-bullion and https://www.911metallurgist.com/electrowinning-smelting/gold-refining-using-oxygen-and-flux/
Very scanty information exists on systems containing copper oxides but the indications aro that slags containing considerable amounts of boric oxide would possibly prove to be the best solvents for cuprous and cupric oxides. This is attributed to the fact that the activities of copper oxides are much lower in boric oxide slags than in slags in which silica is the main network former. The number of possible slags containing boric oxide was limited by consideration of liquidus temperature, viscosity, corrosive action on refractories, volatilization, and ultimately cost (for industrial application). Slags in the systems soda-boric oxide-silica and lime-boric oxide-silica were selected paying due attention to the above limitations.
Review the 2 PDFs at bottom of https://www.911metallurgist.com/blog/gold-refining-process and the attached PDF.
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There was a process developed by old Gold room operators around Kalgoorlie in Western Australia to remove copper from bullion bars. It however a bit tricky as it involved granulating the dore by melting it and pouring into a well stirred drum of water. The granulated dore was then mixed in a crucible with sulphur and heated until the sulphur started to burn then the furnace was turned off. Once it had stopped burning the mixture was then melted and poured into a conical mould. This converted a lot of the copper into a matte which floats on top of the molten bullion. Once cooled the matte normally separates from the dore allowing the button to be re-melted and cast into bars. I have used this method and it works but there are inherent risks particularly in granulating the dore by pouring molten metal into water. It is crucial to keep the water stirred and pour slowly to minimise the risk of explosion. Additionally there is a risk that some gold could be lost in the copper matte. Unless there are huge refining penalties it is far better to send the dore out as it is and let the refiner worry about it. I can provide more information if requested.
I have melted the bullion very high in copper and poured it from a height into water to bead the metal. You can then dissolve the copper in nitric acid giving you near pure gold, which can be filtered, and fired into bullion. This is kind of like parting a bead in fire assaying.
Attached is a bit more information on the removal of copper from bullion with sulphur as well as matte treatment and smelting of silver chloride. Most of this was developed for a treatment high silver Merrill Crowe. The silver chloride was formed by adding salt after aciding to remove excess zinc. In this case smelting was carried out in a small rotary furnace.
What fluxes are you using, and what is your ratios. The ore that you treat at your plant does it have high copper content? At what Amps do you run your electrowining cells rectifier.
Do, you also find it hard to clean your electrowining cells during harvest? How many Anodes and Cathodes do you have in your E/W cell?
Your circuits, is it CIL, CIP or Gravity?
I can't advise you on a flux recipe, smelting time, and smelting temperature which could minimize the copper in bullion and increase purity >80%. Please answer the above questions
hi thanks. here are the answers to the questions
1. fluxed used: -Borax(60%), silica(20%) and Manganese(10%)
2. Amps running at 800-950
3.no difficulties expireince during harvest
4. we are using 2 sludge reactors each consist of 1 cathode and 8 anodes.
5. our circuit is CIL
6. the sludge us acid treated with 50% nitric acid.
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our final gold bullion contains about 19% of copper whist gold fines is 65%. i would like to ask as to what flux composition can we use to reduce such high copper in the final bullion