Extraction of silver from mineral waste and tailings using environmentally friendly leaching method

Abstract

As well as causing environmental problems, mining waste can also be used as a secondary source for the production of valuable metals such as silver, and these valuable metals can be recovered and used in industry. The recovery process is used when the cost of recovery is much lower than the value of the precious metals, and given the increasing price of silver in the world, recovering this valuable element from mining waste will be economically viable. In this regard, silver present in tailings and mineral wastes, especially waste from acidic zinc dissolution in zinc processing plants, is dissolved by leaching and then recovered from the solution by precipitation. One of the important points of this method is the use of materials and methods that are compatible with the environment.

Description

Description of the invention Title of the invention Extraction of silver from mineral waste and tailings using environmentally friendly leaching method Technical background of the relevant invention This invention is related to the extraction of silver from waste and mineral tailings from lead and zinc processing plants, which is environmentally friendly. Technical problem and stating the objectives of the invention Waste from lead and zinc processing plants, as well as causing environmental problems, also contains a significant amount of valuable elements, especially silver, whose recovery is economically viable due to the increasing price and applications of silver in the world. Also, due to the environmental impacts of cyanide and pyrometallurgical methods and the depletion of silver resources, it is important to develop a method that is both environmentally friendly and economically viable. A description of the state of the prior art and the history of developments related to the claimed invention. Increased recovery in zinc plants is achieved by the acid leaching process. This process is universally designed to maximize zinc extraction, resulting in elements such as copper, cadmium and iron being extracted to a large extent simultaneously. However, these leaching processes are not designed to extract minor elements such as silver, tin, germanium, selenium etc., and these elements remain in solution as waste. Therefore, these wastes not only contain minor elements of commercial value, but also contain valuable amounts of zinc, copper and cadmium that are not fully extracted. In patent number EP0010365A1, which was filed by Michel Freeman in 1978 on the recovery of elements in the leach solution of a zinc processing plant, after the silver precipitated in the form of silver chloride, 65% of the silver chloride was separated from the leach solution by filtration and could be purified and recovered. In patent number CA1321077C, which was carried out by Lucia in 1987 on the recovery of silver from zinc acid leach waste using thiourea, an acidic sulfate solution containing 0.1-20 g / l of thiourea at a temperature of 30-85°C and a pH of 1-5 was used to dissolve more than 85% of the silver, and the recovery of the dissolved silver was carried out by adsorption on activated carbon, ion exchange resin or cementation with zinc or iron dust. In this process, by adding metabisulfite to the conventional sodium thiosulfate-copper sulfate system and in some cases ammonia, we achieve an efficiency of over 80% silver dissolution in leaching. In addition to being environmentally friendly, adding metabisulfite is also more economical than other cyanide methods and reduces and improves thiosulfate consumption. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention In this method of silver extraction, a combination of two methods, hydrometallurgy and pyrometallurgy, has been used. The method of silver extraction is carried out by the leaching process by adding chemical compounds to the pulp obtained from the mixture of soil and water. As a result of this process, an efficiency of 80% can be achieved. The silver content in the soil or waste entering the silver extraction process is about 50 to 150 grams per ton, which after completing the first stage reaches the base cake silver content of about 3 to 5%. In a specific case, the silver content in the waste entering the silver extraction process is equal to 62 grams per ton (Table 1). In the silver extraction process, the hydrometallurgical method is first used as follows: In the leaching process used, chemicals are added to the pulp (waste from zinc ingot production industries or other mineral waste containing silver) to dissolve silver. In the first stage, considering the soil moisture content and the desired pulp concentration, the soil and water are mixed in a specific ratio, and then copper sulfate - ammonia - sodium thiosulfate and sodium metabisulfite are added to the resulting pulp, and the process is carried out for 4 hours and at a temperature of 55 degrees Celsius to complete the dissolution of silver. The leaching process is carried out with an efficiency of 80% silver dissolution. The desired pulp is filtered after 4 hours. In the second stage, zinc dust is added to the filtered solution (containing silver) and it is given 3 to 4 hours to complete the cementation reaction. After the desired time has passed and the solution has been analyzed and the silver concentration has decreased to below 1 ppm, the mixture is filtered. The filtered solution is sent to the beginning of the leaching process for recharge. The filter cake, known as the base cake, contains about 6% silver (Table 2). The resulting base cake was melted in a furnace and the purity of the silver ingot was 99.53% (Table 3). Explanation of shapes, maps and diagrams Figure 1) Flowchart shows the production of silver bullion from the process of extracting silver from mineral waste and tailings. Table (1) shows the analysis and amount of silver present in the tailings entering the silver extraction process. Table (2) shows the analysis of the base cake and the amount of silver present in this base cake. Table (3) shows the analysis of the purity of the silver ingot prepared. A clear and precise statement of the advantages of the claimed invention over prior inventions. The process of leaching silver from low-grade soils or tailings and mineral wastes using sodium thiosulfate along with metabisulfite to increase efficiency has not been carried out so far. According to the studies and investigations carried out, various laboratory tests were carried out to achieve optimal conditions for selective leaching of silver, and this process using metabisulfite in pilot, semi-industrial and industrial scales has achieved significant results and efficiency. Also, the cost price of the ingot produced from this process is estimated at 120 million rials per kilogram, which means that this product can be sold for 180 million rials per kilogram. Description of at least one implementation method for implementing the invention In this process (Figure 1), first, zinc industry waste is fed as input feed (No. 1) into the tank with a mechanical stirrer (No. 2) and by adding an activator (No. 9) that helps in the dissolution process of the existing elements, these materials are leached into the tank for 5 hours at 55°C (No. 3) and silver enters the solution phase, which is separated from each other by filtration (No. 4), the liquid phase (No. 10) and the solid phase (No. 11), and the silver in the solution is precipitated in the next step by adding zinc dust (No. 12) with the cementation process (No. 5) and the filtered solution (No. 6) and the liquid phase resulting from this step (No. 13) is returned to the beginning of the process. The base cake resulting from this step (No. 14), which is also known as cement cake, contains 3 to 6 percent silver. The resulting base cake is melted in a furnace (No. 7) and by adding slag-forming agents, the impurities in the melt are removed (No. 15), and finally a silver ingot with a purity of 99.53% is obtained (No. 8).Using this process increases the efficiency of dissolving silver in waste and mineral tailings in the leaching process to 80%. Also, due to the innovative use of sodium metabisulfite in the process, the consumption of thiosulfate is reduced and it can be returned to the process. Explicit mention of the industrial application of the invention Due to the progress and development of the mining industry, the demand for valuable metals and elements is increasing rapidly, but high-grade ore reserves are decreasing, and therefore the need to discover alternative sources has received more attention than ever before. Metal production industries have produced various types of industrial waste that cause environmental problems. Among these wastes, waste from the production and processing of minerals is a major waste of industrial production. In zinc production, some elements are present in the ore along with zinc, which remain in the waste after zinc processing, one of which is silver. Also, large amounts of waste are produced annually in lead and zinc factories in Iran and the world, and as a result, their recycling is economically and environmentally beneficial. Pyrometallurgical and hydrometallurgical processes are usually used to process such secondary resources. A major drawback of the pyrometallurgical method is the need for high energy and the need for a dust collection system and toxic gas filter.The waste from the zinc hydrometallurgy process produces a large amount of acid leaching waste, containing a significant amount of valuable elements, especially silver, whose recovery is economically viable due to the increasing price of silver in the world and can be considered in this field. Silver is considered one of the precious metals and most of its applications are due to its capabilities as a precious metal and its high conductivity. In recent years, the highest consumption of silver has been in the industrial sector (especially the electronics industry), the manufacture of jewelry and decorative accessories, the production of coins and medals, photography, and the manufacture of tableware and utensils. Other uses of silver include the manufacture of mirrors and cameras, as a catalyst for chemical processes, dental fillings, and the manufacture of some musical instruments. In addition, silver coins and bars are also used for investment. Generally, silver is recovered from some natural sources or from the wastes of other metal mining. Therefore, the development of processes for recovering high-purity silver from secondary sources is of great importance. Summary of the invention Zinc industry waste, as well as causing environmental problems, can be used as a secondary source for the production of valuable metals such as silver, and these valuable metals can be recovered and used in industry. The recovery process is used when the recovery cost is much lower than the value of the precious metals, and given the increasing price of silver in the world, recovering this valuable element from the waste of zinc production industries will be economically viable. In this regard, the silver in the tailings and mineral waste, especially the waste from acidic zinc dissolution in zinc processing plants, is dissolved by leaching and then recovered from the solution by precipitation, which is one of the important points of this method is the use of materials and a method that is compatible with the environment. In this context, the use of sodium thiosulfate has been used in some articles, but the silver dissolution efficiency when using thiosulfate is about 20% and when using cyanide is about 80%. In this invention, a combination is used in addition to thiosulfate that increases the silver dissolution efficiency to 80%.

Claims

Claim What is claimed: Claim 1) A process for recovering silver from mineral waste and tailings comprising: extracting silver by a leaching process by adding sodium metabisulfite together with sodium thiosulfate, copper sulfate, and ammonia to a mineral waste and tailings; adding zinc dust to the silver extracted from the pulp in order to carry out a cementation reaction; filtering the product from the cementation reaction to obtain a base cake; and melting the base cake to obtain a silver ingot. Claim 2) The silver extraction process according to claim 1, wherein the mineral waste and tailings comprise a pulp obtained from a mixture of soil and water. Claim 3) The silver extraction process according to claim 1 or 2, wherein the leaching process is carried out for 4 hours and at a temperature of about 55 degrees Celsius, in which case about 80 percent of the silver present in the waste and mineral tailings is dissolved. Claim 4) The silver extraction process according to claim 1, wherein the base cake contains 3 to 6% silver. Claim 5) The silver extraction process according to claim 1, wherein the cementation reaction takes place over a period of between 3 and 4 hours. Claim 6) The silver extraction process according to claim 1, wherein the purity of the silver ingot is 99.53 percent.

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