Experimental Study on New Process for Extraction of Gold, Silver, Copper and Lead by Calcination of Copper, Lead and Arsenic Gold Concentrates

At present, copper, lead to extract gold from gold concentrate containing silver cyanide usually roasting. The process not only can effectively extract gold and silver, but also comprehensively recover sulfur and copper. However, the content of lead and arsenic is relatively strict. Because lead is present in the acid leaching slag in the form of lead sulfate in the process, in addition to increasing the cost of cyanide leaching, it also directly affects the cyanide leaching rate of gold and silver. How to recover lead from acid leaching residue has always been a topic of great concern.

According to the data, there are two ways to recover lead from the acid leaching residue in the roasting cyanidation process: 1. slurry electrolysis method, 2. wet method lead removal method. Due to the large investment in the pulp electrolysis equipment, the high cost and the technical methods are not yet mature, the wet method for removing lead is still one of the current methods to be selected.

Based on the work of the predecessors, this paper has developed a new process for the comprehensive recovery of gold, silver, copper and lead from the copper and lead gold concentrates by roasting cyanidation. The method is to add a certain amount to the ore sample. The NaOH, Na ₂ S mixed additive is calcined. After the calcined slag is immersed in dilute sulfuric acid, the lead is leached with a weakly acidic solution of 25% NaCl at room temperature, and then gold and silver are extracted by cyanidation. The test shows that the method not only comprehensively recovers copper, lead and sulfur, reduces the cost of cyanide leaching, improves the cyanide leaching rate of gold and silver, and allows the existence of higher arsenic content, broadens the utilization range of the source, and has a larger Economic and social benefits.

First, the nature of the sample

The ore sample used in this test was provided by Henan Zhongyuan Gold Smelter. Mineral composition mainly pyrite, arsenopyrite, chalcopyrite, galena, sphalerite and other sulfide minerals, gold, silver isomorphous places distributed sulfide minerals. The main chemical components of the ore samples are shown in Table 1.

It can be seen from Table 1 that in addition to gold and silver, the content of copper, lead and sulfur is high, and a certain amount of arsenic is also contained. The ore sample belongs to the type of refractory gold and silver concentrate, and the current roasting is adopted. The cyanidation method is difficult to obtain a high gold, silver cyanide leaching rate and achieve the purpose of comprehensive recovery of valuable elements.

Second, direct cyanidation leaching test

The ore sample was leached by direct cyanidation leaching method, the leaching condition; sodium cyanide concentration: 0.5%, liquid-solid ratio: 2:1 leachate PH>11 (lime adjustment), leaching time: 42h, leaching results are shown in the table 2.

Table 1 Chemical composition of the ore sample

Note: Au and Ag units are 1×10 ^-6

Table 2 Direct cyanidation leaching results

It can be seen from Table 2 that the cyanidation leaching rate of gold and silver is low under normal temperature conditions, especially the cyanidation leaching rate of silver is lower, mainly due to the high content of copper and arsenic in the ore sample. It affects the cyanide leaching of gold and silver, and the presence of a large amount of sulfur causes encapsulation of particles and ultrafine particles of gold and silver. The cyanidation reaction of gold and silver is difficult to carry out.

Third, roasting cyanide leaching test

The ore sample is subjected to gold and silver recovery by a roasting cyanidation leaching process. Calcination conditions: temperature 630 ° C, time 60 min. Copper sulphate leaching conditions: sulfuric acid concentration: 2%, temperature: 7O-80 ° C, leaching time: 2 h. Cyanide leaching conditions: sodium cyanide concentration 0.2%, liquid-solid ratio 2.1, leachate PH=9.5 (sodium carbonate adjustment), leaching time: 36 h. The test results are shown in Table 3.

Table 3 Roasting cyanide leaching results

It can be seen from Table 3 that the calcination cyanidation method can greatly improve the gold and silver cyanide leaching rate compared with the conventional cyanidation method, but the gold and silver content in the cyanide residue is still high, especially silver, and the leaching rate is only 26.28. %, most of the silver is not leached.

Fourth, adding additives roasting cyanide leaching test

The author has studied the improvement of silver recovery rate in the cyanide leaching process of gold concentrate roasting, and also discussed the recovery rate of gold and silver in the roasting cyanide leaching process of arsenic-containing gold concentrate. This test combines two processes. The characteristics of the method were carried out by using the Na0H+N aS mixed additive to carry out the roasting cyanide leaching test of the ore sample. The process conditions: the amount of the mixed additive (NaOH + NaS) was 0.5% of the ore sample, the calcination temperature was 63O ° C, and the roasting time was 1 h. The process conditions of cyanidation of gold and silver by leaching copper and acid leaching of sulfuric acid solution are the same as those of calcination cyanide leaching. The test results are shown in Table 4.

Table 4 Calcination cyanide leaching results with mixed additives

It can be seen from Table 4 that the addition of NaOH + Na ₂ S mixed additive to the ore sample for calcination cyanidation can greatly increase the cyanidation leaching rate of gold and silver. Compared with the roasting cyanidation method, the cyanidation leaching rates of gold and silver are respectively Increased by 4.53% and 36.11%.

5. Leaching lead test from acid leaching residue

The lead in the gold concentrate mainly exists in the form of galena. When the ore sample is calcined at a high temperature and the copper is dilute with sulfuric acid, the lead is mainly present in the acid leaching residue. In this paper, the acidic sodium chloride solution is used to dissolve the nature of lead sulfate. Under normal temperature conditions, the acid chloride solution is used for leaching, and the lead sulfate is converted into a soluble chloride ion solution. The reaction formula is as follows:

Pb ^{2 +} +NaCl ^- →PbCln ^{(n -2)-}

At 13 ° C, when the concentration of sodium chloride is 300g / L, the concentration of lead ions in the solution can reach 20g / L, increasing the concentration of sodium chloride is conducive to the leaching of lead. At 20 ° C, the saturated sodium chloride concentration in the water was 360 g / L. The process conditions used in this test: NaCl concentration 25%, liquid-solid ratio 5:1, leachate PH=2, leaching time 4h, leaching temperature: normal temperature. The test results are shown in Table 5.

Table 5 Results of acid leaching leaching lead test

It can be seen from Table 5 that the lead leaching rate calculated according to the test results is 91.36%, and the gold and silver in the salt leaching slag can be used as a protective base for sodium cyanide in the cyanidation leaching, and the lead in the salt immersion liquid can be carried out. Recycling.

6. Recovery of lead in salt immersion liquid

The salt immersion liquid mainly contains lead and a small amount of metals such as copper, iron and zinc, and is recovered by the following process.

(1) Lead precipitation by sodium carbonate

Add solid sodium carbonate to the salt immersion liquid under normal temperature conditions. Adjust to pH=5 of the solution. At this time, the precipitation rate of lead is over 90%, and metals such as copper and iron are simultaneously precipitated. The filtrate is returned to the recycling after solid-liquid separation. .

(2) Leaching copper from sulfuric acid solution

Lead precipitates are leached with 5% sulfuric acid, lead carbonate is converted to lead sulfate, and copper and iron are formed into sulfate. After solid-liquid separation, lead sulfate precipitation is obtained, and copper in the solution is recovered.

(C) 3 ammonium bicarbonate conversion

The ammonium sulfate solution is used to leach the lead sulfate precipitate, and the lead sulfate is converted into lead carbonate in an alkaline medium, and the solid phase is separated to obtain lead carbonate.

(4) Dissolving lead carbonate in a nitric acid solution

With a nitric acid solution dissolved at normal temperature lead carbonate, lead nitrate to prepare a solution of lead nitrate as the raw material can be synthesized more than ten kinds of chemical products, such as red lead, yellow lead, lead acetate, lead chromic acid.

Tests show that for the lead-containing 2%, copper O.6% acid leaching residue can be recovered by the above process, 5kg of copper and 20kg of lead chemical products.

Seven, comparative test

Take two ore samples, one part is treated according to the following process: mineral sample plus mixed additive roasting - sulfuric acid immersion copper - acid leaching cyanide leaching gold, silver (using sodium hydroxide, ammonium bicarbonate as pH adjuster). The other part is treated according to the following process: mineral sample plus mixed additive roasting - sulfuric acid immersion copper - acid leaching leaching lead - leaching lead slag cyanidation gold, silver (with CaO as pH adjuster). The test results are shown in Table 6.

Table 6 Comparison test results

It can be seen from Table 6 that the new process method (lead removal process) is beneficial for cyanide leaching of gold and silver, and the cyanide leaching rate of gold and silver is increased by 2.46% compared with the unlead process. And 14.47%. Since the new process adopts cheap CaO as the pH adjuster, the cost of cyanide leaching can be greatly reduced, and the economic and social benefits are remarkable.

Eight, conclusion

(I) Tests show that the calcination cyanide leaching with the addition of a mixture (NaOH + Na ₂ S) can increase the recovery of gold and silver, and allow the presence of higher levels of arsenic in the calcined raw materials, thereby broadening the source of raw materials.

(2) The test showed that the acid leaching residue was leached with sodium chloride solution (25%, PH=2) under normal temperature conditions, and the lead leaching rate reached 91.36%. As a raw material, chemical products such as lead nitrate and lead chromate can be prepared, and the economic benefits are remarkable.

(3) The test shows that the acid leaching residue is immersed in lead and then cyanidated, which is beneficial to gold and silver cyanide leaching of Au. The cyanide leaching rate of Ag is increased by 2.46% and 14.47%, respectively. Due to the use of cheap CaO as a pH adjuster, the cost of cyanide leaching is greatly reduced, and its economic and social benefits are remarkable.

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