The way and progress of arsenic treatment in gold-bearing ores

At present, many are gold plant processing gold ore containing arsenic, but also from the development prospects of view, the amount of arsenic gold ore will be greatly increased. The increasing number of arsenic-containing wastes requires a good solution to the problems of arsenic removal, preservation and as comprehensive utilization as possible.

Or cyanide flotation process for the production of mineral processing plants, the main issue is how to calculate the number of waste containing arsenic and cyanide final flotation tailings, analyze its toxic effects on the surrounding environment and seek to reduce the toxicity of effective method. For new companies that will use concentrates with high levels of arsenic as their main raw material, they need to develop special methods for producing arsenic and arsenic from arsenic-containing waste or to develop economically viable arsenic removal and storage. method.

In conventional gold plant treated ore discretion, arsenic is usually not so large (see Table), and often is present in the form of sulfide mineral, such as arsenic, pyrite, realgar, orpiment, tetrahedrite copper ore. The distribution of arsenic in the process cycle depends first on the symbiotic characteristics of gold and metal minerals. However, most of the arsenic will be transferred to the flotation or re-elected sulphide concentrate (about 35%) and to the final tailings of the beneficiation or cyanidation (65%). The arsenic entering the sewage does not exceed 1-2%, and the arsenic in the qualified products (quality gold, zinc precipitate) entering the gold selection plant is very small.

Sulfide minerals of arsenic are very stable in sodium cyanide solution, and most of the arsenic is transferred to the tailings in the form of raw minerals, so there is no special requirement for tailings filling. In the cyanidation process, arsenic minerals may be partially dissolved by increasing the alkalinity of the cyanide slurry or during long-term storage, under certain natural factors that can convert arsenic to water.

In the sewage and slurry discharged into the tailings, the concentration of dissolved arsenic can reach 0.04~0.2 mg/L (the maximum allowable concentration is 0.05 mg/L), and the total amount of arsenic in the sewage can reach 300 kg per year. Although this value is small in the total balance of arsenic, care should be taken to prevent the danger of tailings filling the filtered water from contaminating the groundwater.

Based on the results of research on the removal of arsenic from pulp and sewage, some very effective methods have been developed. The main basis of these methods is that arsenic is precipitated as an insoluble arsenic compound [Ca3(AsO4)2, As2S3, etc.] and arsenic is adsorbed on the active surface of activated carbon or resin, arsenic and Fe(OH)3 or Al(OH). ) 3- from flocculation. With chlorine or NaOCl oxidation of pre As8 + CaO added to maintain the pH and the optimum value can be obtained arsenic concentration was 0.46 mg / l tailings, and after addition of sodium hydrogen phosphate, ammonium acid may have its concentration of 0.03 Mg/L of waste tailings. Among the known methods, iron sulfate, ferrous sulfide, aluminum sulfate, polyacrylamide, and the like are also used.

Under certain conditions, the above various methods can be applied to the gold mining industry, and the main task at present is to rationally adopt these methods in order to more completely exclude the environmental pollution of arsenic around the enterprise.

One of the most effective ways to solve arsenic contamination is to implement a fully circulated water supply and an optimal purification scheme in the concentrator.

For example, in a concentrator, a process for dearsenicization of tailings has been developed for the adsorption of calcium hypochlorite and ferrous sulfate and for the use of purified water in a circulating water supply. By using this process, the arsenic content in the slurry liquid phase can reach the specified emission standard, even lower (≤0.05 mg/L). The amount of ferrous sulfate can vary between 1.32 and 2.33 kg/ton depending on the arsenic content in the slurry. The selection-method is also suitable for other companies that process minerals whose mineral composition is similar to that of the plant.

The second important task is to further accumulate information on the quantity and distribution of various arsenic compounds in the pulp and sewage of each concentrator and mine, and to develop various comprehensive measures to reduce the toxic effects of arsenic. Permitted standards for each business and each compound.

The most feasible solution for the use of arsenic-containing waste tailings is to use these abandoned tailings for hydraulic filling of underground wells or to incorporate them into special concrete for filling. It can also be used for industrial construction and road construction. Filled in. In any case, special studies must be conducted when determining the toxicity of arsenic in tailings and determining the method of arsenic removal in tailings.

The behavior and distribution of arsenic in the flotation concentrate and re-election concentrate depends on the treatment of these concentrates. In the case of cyanidation of concentrates, the behavior of arsenic minerals is similar to that of cyanidation of ore, except that the content of arsenic in abandoned tailings is slightly higher than that of ore cyanide tailings (up to 2.513%) .

However, there are some such concentrates. Because the ultrafine gold and arsenic pyrite coexist very closely and other factors (such as high carbon content), these concentrates cannot be treated by cyanidation. Can be sent to the copper smelter for processing. In this case, arsenic is distributed to various products of copper smelting (such as matte, slag, dust, crude metal, copper-containing scum, arsenic bismuth compounds, etc.). In this case, a large amount of arsenic is accumulated in the circulating material, which results in a more complicated main production process, resulting in additional loss of copper and contamination of the surrounding environment. Therefore, it is necessary to add an auxiliary process to recover arsenic from the dust and to treat the unqualified calcium arsenate.

All of the above limits the possibility of handling arsenic-containing gold concentrates at the copper smelter. According to the technical conditions (Ty48-16-6-75), the maximum content of arsenic in gold-containing concentrates should not exceed 2%. In the future, as the requirements for product quality continue to increase, it is clear that these technical conditions will become more stringent. Therefore, the task of the project is to develop some effective processes in order to be able to treat the arsenic gold concentrate on site, transfer the arsenic into the desired product or reliably store the arsenic.

Various methods of treating such concentrates require prior arsenic removal and subsequent recovery of the precious metals from arsenic-free products by pyrometallurgy or hydrometallurgical methods.

The simplest way to remove arsenic from concentrates has proven to be very effective - one method is oxidative roasting. In this way, arsenic, sulfur and carbon can be very completely excluded from the concentrate and provide a good possibility for cyanidation or some kind of pyrometallurgical treatment of such concentrate.

The process of calcining concentrates with a multi-layer calciner to obtain acceptable arsenic trioxide (and subsequent acquisition of metal arsenic and arsenic-based alloys and intermediate alloys) has been practically applied in some gold-sorting companies. The calcine containing arsenic is 0.8~1.0% and sent to the copper smelter for treatment. The system for collecting As2O3 (cleaning chamber, condenser and electrostatic precipitator) can make As2O3 in the atmosphere through the chimney no more than 0.2 tons / year.

In addition to the oxidative roasting method, some other methods of arsenic removal have been developed, including oxidative oxidative leaching, bacterial leaching, electrolysis, vacuum pyrolysis, volatilization from the melt, and the like.

The Irkutsk branch of the National Institute of Rare Metals of the Soviet Union, the Institute of Metallurgy of the Soviet Academy of Sciences (HMeT) and other units jointly studied the comprehensive treatment of refractory gold-containing arsenic concentrates and conducted semi-industrial tests. These methods are based on oxidative calcination, chemically treating the calcine, followed by cyanidation or electrosmelting under the conditions of adding chloride. The latter method enables high recovery of various valuable components and allows for the comprehensive utilization of raw materials, wherein the smelting slag can be used to produce rock castings or insulating materials. The dust containing high arsenic can be treated by the heterogeneous refining method to obtain high purity (99.5~99.9%) arsenic trioxide and gold-containing slag. The industrial device manufactured to achieve this method was tested in a gold mining company in the Soviet Union. In the future, the refining method and the reduction method of arsenic trioxide can be combined into a continuous process cycle. This makes it possible to mass produce high-purity, inexpensive metals. The incidental production of arsenic in a metallic state from a dense, high-purity compound promotes God's new use and wider use.

Therefore, the widespread use of oxidizing roasting in gold-removing companies is an indispensable prerequisite for the treatment of refractory sulfur-containing arsenide concentrates.

The production practices and observational data of oxidative roasting in the Soviet Union and abroad are the basic materials for designing and constructing the arsenic removal process.

Obviously, in the special case of large-scale gold-mining companies, it is very reasonable and feasible to require these companies to produce high-quality and easy-to-transport products (elemental sulfur, arsenic trioxide, high-purity metals or high-purity sulfides).

In order to completely solve the problem of arsenic removal and detoxification utilization in the gold selection industry, the following work must be done in recent years:

1. Check whether the calculation of the quantity and distribution of arsenic in each gold selection enterprise is correct.

2. Expand research on the chemical properties of arsenic, including studies on the properties of low-solubility compounds, so that they can be preserved without the need for expensive construction facilities.

3. Expand research on new ways to apply arsenic and arsenic-containing waste in national economic sectors, for example, to make alloys, building materials or to fill mine roadways.

4. Accelerate the development and adoption of advanced methods for the treatment of arsenic-containing materials, including oxidative roasting based on oxidative roasting or hydrometallurgy of arsenic trioxide, elemental sulfur and sulfuric acid from exhaust gases and arsenic trioxide Sublimation refining and other methods.

5. Accelerate the development of advanced processes for the production of metal arsenic from arsenic trioxide and arsenic sulfides and other compounds.

6. Ensure that the gold mining enterprises realize the circulating water supply without sewage as soon as possible, so that the problem of arsenic discharge and environmental pollution with sewage can be completely solved.

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