Gold-arsenic ore and its concentrate processing method

Native gold - arsenic ore containing 1-2% to 10-12% arsenic pyrite. In other sulfides, there are often pyrite and sometimes pyrrhotite. In rare cases, minerals do not contain particulate gold. Such ores can be treated by cyanidation or by flotation followed by cyanidation of the flotation concentrate. Most of the gold in the ore is often encapsulated in sulfides in the form of fine particles. For this type of ore, mixed flotation can be carried out to select gold-arsenic concentrate or gold-arsenic-pyrite concentrate. The concentrate is calcined, and the calcined slag is treated by cyanidation or sent to a smelting plant for smelting. An arsenic-containing product is obtained during the firing. However, the current demand for such products is small. If the waste tailings cannot be obtained after the mixed flotation, the flotation tailings may be cyanated or the ore may be cyanated, and the gold-containing sulfides may be recovered from the cyanide tailings by flotation.
When flotation of gold-arsenic ore, it is necessary to test the known methods, namely, stage flotation, flotation of ore and slime separately, flotation in soda medium, etc., in order to improve the flotation process of gold-arsenic ore. Various indicators. When flotation of arsenopyrite, oxygen must be added to the slurry. The broken iron formed during the grinding process acts as an absorbent for oxygen. When soda ash is present, the oxidation of iron and the absorption of oxygen proceed slowly. Therefore, when formulating flotation conditions, the amount of soda added in the mill should be tested (consumption of 1~2 kg/ton) so that the pH of the mill can reach 10~10.2, and then Reduce it to 8.5~8.8 when flotation. Copper sulfate is very advantageous as an activator in an amount of 100 to 200. g / ton. This medicine should be added to the sweep. In individual cases, the recovery of gold and arsenic will increase as the slurry and the mixing time of the collector increase (up to 20 to 30 minutes).
Sometimes it is appropriate to use a preferential flotation to sort gold-containing pyrite concentrates and arsenic concentrates, or a single gold-pyrite concentrate. If the gold in the pyrite concentrate and the arsenic concentrate is recovered by different methods or if a high-crystal arsenic concentrate is required, it is advantageous to separately select the pyrite concentrate and the arsenic concentrate. Only a single gold-pyrite concentrate can be selected under the following conditions:
When the flotation tailings meet the requirements of the scrap gold grade, and arsenic has no industrial value;
The gold in the flotation tailings is not the same as the gold in the pyrite concentrate, which can be recovered by cyanidation.
Using lime or lime with air in an oxidation medium, inhibition arsenopyrite soft manganese ore and potassium permanganate, can arsenopyrite and pyrite separation. In many cases, the effectiveness of the oxidant depends on how well the oxidant use system is formulated and adhered to. The amount of oxidant used is too large, and the contact with the slurry for too long will cause the activation of arsenopyrite.
Difficulties in flotation of mud ore and carbonaceous ore. Mineral deposits usually contain carbonaceous materials, various shale and carbonates. When flotation of sulfides, these components enter the concentrate, which increases the yield of the concentrate and reduces the quality of the concentrate. In addition, the slime can absorb the flotation agent and hinder the flotation of the sulfide. In order to study argillaceous ore, it is first necessary to determine the gold content in the ore and to test the following methods according to its quality:
Desliming of ore and its processed products (rough selection of tailings, intermediate products, sweeping concentrates). If necessary, the separated slime should be subjected to adsorption cyanidation;
Use different agents (KMLI, IIAA, aniline dyes, starch, etc.) to inhibit slime floatation in rough, sweep or select operations;
Flotation and treatment of the ore portion with the agent.
The industrial utilization of arsenic pyrite concentrate and pyrite-arsenic pyrite concentrate containing fine particle impregnated gold has not yet been resolved. This problem is difficult to solve due to the limited demand for various compounds of arsenic and the toxicity of these compounds.
Arsenic is a harmful component in the pyrometallurgical process, so it is sent to concentrates in smelters; there are strict limits on the content of arsenic.
In foreign production practice, the gold-arsenic concentrate is generally calcined, and then the calcine is treated by cyanidation. When using this method, it is necessary to carefully collect the god from the gas phase. If the sales of arsenic products are not good, it will cost an expensive storage or burying. It is preferable to use two-stage calcination: the temperature of the first stage calcination is 500 to 580 ° C, and a small amount of air is supplied, and the calcination temperature of the second stage is 600 to 620 ° C and a large amount of air is supplied. Only in this way, it is possible to form a fusible compound at the time of firing, and to obtain a calcine having good porosity. The arsenic grade in the accompanying sand should not exceed 1~1.5%. If a portion of the calcination is carried out at a higher temperature and under an excess of air, the arsenic grade in the calcine will be increased by the formation of a less volatile arsenate such as FeAsO ₄ . Arsenate covers the surface of gold and hinders the dissolution of gold during cyanidation. When roasting a material containing realgar (AsS) and orpiment (As ₂ S ₃ ), iron arsenate is formed to a large extent. The second stage of calcination at a temperature of 600 to 620 ° C is mostly chlorination roasting or oxidation-chlorination roasting. In most cases, the gold encapsulated in pyrite or arsenopyrite can be more fully exposed by this calcination.
When calcining a carbon-containing gold-arsenic concentrate, it is preferably carried out in two stages: the first stage of calcination is carried out at a temperature of 500 to 600 ° C and an insufficient air supply, at a temperature of 650 to 700 ° C and A second stage of calcination is carried out under excess air. The first stage of calcination should burn arsenic to the calcined less than 1%, while the second stage of roasting should burn off the activated carbon and sulfur. In order to burn off the activated carbon, it is necessary to feed not only excess air but also a relatively high temperature, and it takes a considerable amount of time. When calcined in a boiling roaster, the calcination process proceeds faster and the calcination is more complete. In order to achieve self-ignition roasting without fuel in the roaster, the concentrate should have a sulfur content of 22 to 24%.
If the calcined slag is sent to the smelting, a calcination can be carried out. The content of arsenic in this calcined slag is allowed to reach 2%. [next]
When the gold arsenic concentrate or the calcined calcined cyanide is treated, it has different characteristics. When the concentrate is cyanated, it should be treated with alkali in advance, cyanized in stages, and leached with a cyanide solution of low-concentration calcium oxide. If a simple sulfide (or estrogen yellow realgar) ore or a concentrate containing arsenic, it must be treated with the test method of antimony ores and concentrates containing at cyanide. The calcination after calcination usually requires washing with water, followed by cyanidation and maintaining the concentration of NaCN in the cyanide solution at 0.08% or more. The consumption of cyanide and lime can be greatly reduced by rinsing. For calcined sand containing difficult to recover gold, it can be treated with two or three stages of cyanidation, and if necessary, intermediate treatment with alkali. The base dissolves the oxides of arsenic (especially iron arsenate) and exposes the gold encapsulated in these compounds. When processing the calcine, an alkali solution having a NaOH concentration of 6 to 8% is required. The slurry is heated to 80~90% °C, and the treatment time is 2~3 hours. The material is then dewatered, and finally cyanidation is carried out and the gold in the liquid phase is examined and analyzed. By adding a hydroxide or calcium oxide to the solution, the alkali solution containing Na ₃ AsO ₄ can be regenerated. Arsenic precipitates as calcium arsenate and the solution is concentrated with NaOH.
Incomplete oxidative roasting followed by chlorination volatilization is a viable method for recovering gold from gold-arsenic concentrates. The conditions of the chlorination volatilization test are as follows: the sulphur content in the calcine is 3.5 to 4%, the NaCl consumption is 7.5 to 10% of the calcine weight, and the chlorination volatilization temperature is 1000 °C. Under these conditions, about 96 to 98% of the gold is transferred to the volatiles and recovered.
The autoclave-alkali leaching method for decomposing gold-arsenic concentrates deserves further study. Under the condition of temperature of 100 ° C and partial pressure of oxygen in the gas phase of 10 atm, the concentrate can be decomposed very completely by using a 150 ~ 180 g / liter NaOH solution for 2 hours of heat treatment. 98 to 99% of arsenic and sulfur enter the liquid phase. The gold in the leaching slag after rinsing can be recovered by cyanidation (without adding lime). The autoclave can be achieved in an aqueous medium by passing oxygen in the air through an autoclave at 50 atm. Under these conditions, arsenic is oxidized to form iron arsenate and sulfuric acid.
Bacterial leaching is a promising method for oxidizing gold-arsenic concentrates. This method can expose gold quite completely. The arsenic compounds (mainly arsenate and calcium arsenite) obtained after bacterial leaching are poorly soluble in water and have little toxicity. This is unmatched by the arsenic compound formed during the roasting process and the pyrometallurgical smelting process.
In order to oxidize arsenic pyrite, it is recommended to use artificially cultured Thiobacillus ferrooxidans in a concentration of 106-107 cells/ml in the original solution. Bacterial leaching tests are carried out under static conditions and the best values ​​for the following main parameters must be determined:
The pH of the original bacterial solution;
The concentration of ferric iron;
Liquid to solid ratio in the original slurry;
The time of bacterial leaching.
The original values ​​of these parameters are: pH; 1.8~2; the concentration of Fe ³⁺ is 3~4g/L, the ratio of liquid to solid is 30~50, and the time is 300~400 hours. The bacteria are then adapted to the specific conditions, the solution is subjected to intermediate arsenic removal (adding lime milk to a pH of 3 to 3.5), and the bacterial leaching test is organized according to a downstream process in an effort to shorten the time of bacterial leaching and to be thicker. This method is implemented in the slurry. For some gold-arsenic concentrates, the optimum conditions for the initial oxidation of arsenopyrite are: liquid to solid ratio = 5:1, leaching time is 120 to 150 hours. While the arsenic pyrite is oxidized, part of the pyrite (about 30 to 40%) is also oxidized.
The leaching residue after the leaching of the bacteria is washed with water, and then the leaching residue is cyanated. In addition to the cyanidation method, it is also possible to carry out tests using a thiourea method, a water chlorination method, or the like.
In order to expose gold from pyrite and arsenopyrite, there are some relatively new methods (such as mechanochemical and electrochemical methods) that should be taken seriously.
Part of the arsenic contained in the partially oxidized ore is present in the form of scorodite and other oxidized minerals. The gold in this ore is covered by a scorodite film, making it difficult to perform flotation and cyanidation. The scorodite can be floated with a fatty acid collector.
In order to recover gold and arsenic from partially oxidized ore, it can be tested using a process that includes the following operations:
The flotation gold and sulfide are collected by a sulfhydryl group, and the concentrate is calcined and calcined to cyanide;
Flotation tailings are treated with NaOH solution to leach arsenic and remove the film on the surface of the gold particles;
The residue is treated by cyanidation;
Arsenic is precipitated from an alkaline solution with lime or a high concentration of NaOH solution. Lime can precipitate and also regenerate NaOH. The regenerated NaOH can be recycled.

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