The thermodynamics of polysulfide leaching of gold was reported by Soviet scholar Kakowski in 1962. The treatment target is As-Sb-Au sulfide concentrate (containing As up to 4.5%), and the recovery rate of gold can reach 80%. ~99%. The method has the advantages of high selectivity, no pollution, and is suitable for processing low grade ore. The Murchison Graflot plant was built into a 5t test workshop, and the indicators obtained were consistent with the small test. Only after the factory closed down, the work could not continue.
The principle flow of the multi-sulfide method leaching gold process multi-sulfide method for gold extraction is shown in the figure below. In the gold extraction method, sulfur can form SS bonds such as S 4 2- - and S 5 2- - like polysulfide ions like carbon, and such ions have a strong complexing ability to Au(I), so The polysulfide can effectively dissolve gold with the cooperation of a suitable oxidizing agent or by self-disproportionation. If elemental sulfur can be produced during the leaching process, the sulfide can also leach gold because the sulfide and elemental sulfur are easily converted into polysulfide. was gold sulfide concentrates containing arsenic and antimony is particularly suitable for treatment by this method.
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The most commonly used polysulfide leaching gold is an ammonium polysulfide solution containing about 8% by mass of NH 3 , 22% of S, and 30% of (NH 4 ) 2 S 2 . The solution is a red clarified liquid. There is a hydrogen sulfide smell, and sulfur is resolved in the presence of acid. The polysulfide process is primarily proposed for refractory arsenic-bearing gold deposits because traditional cyanidation processes are not economical or safe. For gold ore containing arsenic or antimony up to 4.5%, it is leached with an aqueous solution containing 40% ammonium polysulfide at 25 ° C under normal pressure. Gold is selected in the form of NH 4 AuS together with hydrazine [NH 4 ) 3 SbS 4 ]. Sex leaching, arsenic remains in the slag. The experimental results show that for a specific ore, the method can extract more than 80% of gold, and the dissolved gold in the leachate can be adsorbed by activated carbon, or can be precipitated from the solution by steam heating. At this time, Sb 2 S 3 and sulfur are produced. , release NH 3 , H 2 S and sublimed sulfur, depending on the composition of the leachate. After the gold removal, the ammonium polysulfide can be regenerated and returned for immersion gold.
The polysulfide method is characterized by strong selectivity, fast leaching speed (usually a leaching period of several hours), high leaching rate, no pollution, and also suitable for low-grade ore. Some ore can be treated by this method. Elemental sulfur. South Africa is a country with early research on polysulfide. It has carried out semi-industrial tests. In China, the process conditions for treating gold-containing waste slag from lead and antimony in this process were studied. The leaching temperature, leaching time and pharmacy were investigated. The effect of consumption, liquid-solid ratio, slag particle size and gold occurrence state on the recovery rate. The gold in the immersion liquid can be enriched by solvent extraction and activated carbon. The main disadvantage of the polysulfide method is the heat of the polysulfide itself. Poor stability and decomposition of H and NH 3 will deteriorate the production conditions, and the sealing of the equipment is highly demanded in industrial applications. In addition, the concentration of the drug is required to be quite high, and the consumption is also large, and the small leaching rate of gold is only 80%, which is difficult to guarantee in actual production.
One of the advantages of hydrometallurgical treatment of sulfide minerals by ammonium sulfide and sodium sulfide gold leaching is that elemental sulfur can be obtained. Obviously, as a variant of the ammonium polysulfide leaching process, the wet leaching slag containing gold sulfide minerals with (NH 4 ) 2 S is a two-way method for simultaneously recovering elemental sulfur and gold. Alkali metal sulfides can dissociate S 2- ions like ammonium sulfide, and have the same force as ammonium polysulfide in leaching gold and elemental sulfur. Central South University studied the treatment of arsenic, antimony and gold sulfide ore leaching residues by gold-containing wet-process lead slag and sodium sulfide by ammonium sulfide method.
1) Thermodynamic analysis The polysulfide leaching gold reaction reported in numerous literatures is:
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Compositions containing gold-lead slag and slag: The main chemical compositions of the gold-containing wet slag and wet slag used in the test are shown in the table below. Antimony (I) as well as part of the slag and arsenopyrite pyrite decomposition Not arsenic removal process.
Sample name | Au/(g·t -1 ) | Ag/(g·t -1 ) | S/% | Fe/% | Cu/% | Pb/% | Zn/% | As/% | Sb/% |
Wet method lead slag Wet refining slag (I) Wet refining slag (II) | 17.4 142.58 152.17 | - 13.84 <1 | 51.07 8.33 7.66 | 16.61 2.00 0.06 | 16.61 2.00 0.06 | 1.19 0.0017 0.0012 | 1.96 0.021 0.020 | - 2.58 0.054 | —0.001 0.001 |
2) Gold leaching from the ammonium smelting lead slag. In the test, ammonium sulphide was used as the leaching agent. To prevent the escape of H 2 S and NH 3 , the leaching system needs to be sealed.
When the temperature, leaching time and the amount of (NH 4 ) 2 S added to the gold leaching rate were investigated, it was observed that the leaching rate of gold increased with the increase of temperature, but when the temperature exceeded 70 ° C, elemental sulfur was precipitated. In order to obtain the high gold recovery rate of S at the same time, the temperature should not be higher than 70 ° C, the leaching time exceeds 6 h, the gold leaching rate not only increases but decreases, which may be caused by the loss of ammonia volatilization. As the amount of ammonium sulfide is increased, the leaching rate of gold is significantly increased. The composition of the leachate was observed by the temperature test at 50 °C and the leaching time of 6 h. It was found that the addition of ammonium polysulfide had little effect on the leaching rate of gold. This is because the polysulfide formed by elemental sulfur in the slag can satisfy the leaching. The reason for the request. The addition of ammonia can significantly increase the leaching rate of gold. This may be because the addition of ammonia increases the pH of the solution and inhibits the proton reaction of the polysulfide, thereby increasing the free polysulfide of the solution. The leaching rate of elemental sulfur in the slag is greater than 98%, and the leaching rate of gold is about 95%.
3) Sodium sulfide leaching gold from the wet refining slag
The leaching rate of gold in the slag (I) slag concentration below 116g/L was increased with the increase of sodium sulfide concentration at a fixed temperature of 90 ° C, liquid-solid ratio of 7:1, and time of 6 h, and the sodium sulfide concentration was continuously increased. The gold leaching rate is basically unchanged. When the molecular ratio of sulfur content S to Na 2 S is 3:1, the effect of NaOH concentration on gold leaching rate is observed. When the NaOH concentration is less than 0.25 mol/L, the leaching rate of gold can be improved by adding NaOH, but continue The addition does not help to leach gold, as long as the NaOH concentration is greater than 0.5 mol/L, the sulfur can be completely dissolved. Under such conditions, the gold leaching rate of sodium sulphide (I) slag is 90%, while for bismuth (B) slag without pyrite and arsenopyrite, the leaching rate of gold can reach 97.47%.
It can be seen that both ammonium polysulfide and sodium polysulfide are used as leaching gold reagents to obtain a higher gold leaching rate. The use of these and the sulfur in the slag can form polysulfide characteristics, which can recover gold and recover sulfur.
4) Example of gold-bearing sulphide ore leaching gold The main composition of gold concentrate in Zhaoyuan Gold Mine, Shandong Province: Au 92.8 g/t, Ag 36.0 g/t, S 31.4%, Cu 0.018%; Guangdong Hetai Gold Mine Gold Concentrate Main Composition: Au 54.6 g/t, Ag 28.0 g/t, S 18.5%, Cu 4.4%.
It is observed in the leaching test that the concentration of polysulfide is the key factor affecting the leaching of gold. The sum of S x 2- concentration is about 2 mol/L. The polysulfide leaching out of Guangdong Hetai gold sulfide concentrate can get 80. The leaching rate of gold above 100%, while the leaching rate of Shandong Zhaoyuan Gold Mine is over 90%. When the leaching temperature is raised and the S/S 2- ratio in the polysulfide system is increased, the leaching of gold is favorable, but the temperature of the leaching process should not be too high. Too high will increase the volatilization amount of polysulfide and easily cause multi-vulcanization. The oxidation of the substance lowers the sum of the concentrations of S x 2- and is counterproductive to the leaching of gold, so the leaching temperature is generally about 60 °C. When the polysulfide is leached out of the sulfide ore, the S/S 2- ratio is about 1.0.
For polysulfide leaching systems, mainly controlled by chemical reactions, mass transfer in solution is a secondary factor in the gold leaching process. The addition of CuS to the ammonium polysulfide system significantly reduced the leaching rate of gold, while the addition of FeS had no significant effect on the leaching of gold.
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