Optimization of slag bioleaching process of Sarcheshme copper complex using response surface method

Academic thesis for receiving a master's degree in the field of chemical engineering with a focus on biotechnology

Abstract

      This research was conducted in order to optimize the operational parameters for the use of bioleaching technology in the extraction of copper from the slag produced by the reflective smelting furnaces of Sarchesheme copper complex. Wide applications of bacterial leaching technology of low-grade sulphide ores have received attention in recent years due to the reduction of environmental pollution and acceptable economic justification compared to other metal extraction methods. The slag in two dumps has been stored with a total of 6 million tons and an average grade of 1.15% by weight of copper. More than 90% of the copper sulphide minerals in the composite sample are chalcocite and chalcopyrite. Preliminary investigations were conducted in shaking containers in a period of 15 days for different types of microorganisms and the parameters of solid percentage, pH and inoculum percentage were investigated for mesophilic and thermophilic bacteria. The highest recovery of copper and iron in vibrating containers was obtained for mesophilic bacteria at 35 °C, 75% and 30%, respectively, and for moderate thermophilic bacteria at 45 °C, 78% and 36%, respectively. While for the control sample, at a temperature of 35 degrees Celsius, the highest recovery of copper and iron was 34.5% and 7.5%, respectively. At a temperature of 45 degrees Celsius, the highest recovery of copper and iron was achieved, respectively 38% and 9.7%. Conducting the column bioleaching test showed that at a pH of 1.5 and a flow rate of 3 ml/min of the spray solution, in the column of mesophilic bacteria with a temperature of 35 degrees Celsius, recovery of 51.2% for copper and recovery of 10.7% for iron, and in the control column (without bacteria), recovery of 32.5% for copper and 1.7% for iron in the column of thermophilic bacteria with a temperature of 45 degrees Celsius, recovery of 57% for copper and 13.7% for Iron in the witness column recovered 38% for copper and 2.9% for iron metal.

Key words: bioleaching - copper slag - mesophile - thermophile - response surface method

High-grade reserves have gradually decreased and the grade of minerals has decreased. One of the problems of recovering materials from low-grade ores with conventional techniques is that it is expensive due to high energy consumption and the need for high capital costs. Another problem is environmental costs due to the high level of pollution with the use of these technologies. Biotechnology is one of the most promising methods to solve these problems compared to pyrometallurgy, and the current century is the century of prosperity of this type of technology. Technologies that are used to provide comfort facilities and take into consideration the preservation of the environment. Willingly or unwittingly, human activities lead to the production of environmental pollution, which causes irreparable damage to the environment and the human being. Industrial factories contribute the most to this pollution. Metal mining also fuels an important part of these pollutions. Since the middle of the last century, many researchers have started their efforts in order to find ways to reduce these pollutions that are obtained in the metal mining sector. In the copper mining industry, where thermal methods are usually used, hydrometallurgical, electrical, etc. methods have been proposed to reduce these pollutions. In the last few decades, the knowledge of biotechnology as a key technology has made a tremendous change in the field of human life. The most important tools of this science are microorganisms. Using microorganisms, various food, pharmaceutical, chemical, and mineral products are produced on an industrial scale [1].

Bioleaching is one of the methods of extracting metals from minerals using microorganisms in an aqueous environment with air. In this method, minerals containing iron and sulfur (pyrite, chalcopyrite, etc.) are dissolved by certain types of mesophilic bacteria such as Acidi Thiobacillus ferrooxidans, Acidi Thiobacillus thiooxidans and Leptospirillium ferrooxidans, moderate thermophilic species such as Sulfobacillus and absolute thermophilic species such as Sulfolobus and Acidianus brierli. Such microorganisms provide their biological energy from ferrous ion oxidation or sulfur oxidation along with the required carbon dioxide.. In the dissolution of sulphide minerals by microorganisms, two main mechanisms, direct and indirect, are confirmed by researchers. In the first mechanism, i.e. direct, the activity of the bacteria and its binding to the mineral surface causes dissolution, and in the second mechanism, the activity of the bacteria in the dissolution is indirect and is done through the conversion of ferrous iron to ferric (oxidation). The process of microbial dissolution (bioleaching) and microbial oxidation (biooxidation) have replaced conventional methods (in low-grade ore processing) due to their environmental, technological and economic advantages over other methods of extracting elements from sulfide and even non-sulfide minerals (smelting, etc.)[2]. Copper extraction is usually done using two methods: pyrometallurgy and hydrometallurgy. in the pyrometallurgy method using smelting and refining processes; Cathode copper is produced with a grade of 99.99%, but the high pollution of these processes, which mainly leads to the production of toxic gases and acid rain and is released into the environment without any restrictions, has caused this industry to be reviewed in recent decades and to look for alternative methods to produce copper and other metals. Hydrometallurgy can help a lot in this regard. Hydrometallurgical methods are carried out in two ways, chemical and biological. The biological method is suitable for low grade sulfide minerals as well as resistant minerals [3 and 4].

Bioleaching is the extraction of metals from minerals or sulfide metal compounds or concentrates using components that are easily found in the environment, including water, air and bacteria. The leaching rate of insoluble or poorly soluble sulphide minerals in acid, such as chalcopyrite, is accelerated by the activity of certain types of bacteria that are able to obtain energy through the oxidation of these minerals. rtl;">Hydrometallurgical extraction (leaching) of copper from ore and depositing copper from the leaching solution by metallic iron (cementation) is an old technology. The Chinese experience in using this technology goes back to 100-200 years BC and even before that. The fact that copper can be extracted from a blue solution must be an accidental discovery that the contact of metallic iron with such a solution causes copper precipitation [5].

Perhaps leaching was the only method of extracting copper from sulphide ores in the past, because in the past, smelting was done in open furnaces and this technology is only effective for copper oxide and carbonate ores. But today, by using new smelting furnaces, sulfide minerals can also be melted [6]. furnace slag in Sarcheshmeh copper mine. The existing slag is composed of two dumps with the capacity of 6 million tons and with the average grade of 1.15% Cu. More than 90% of the copper is in the forms of Chalcocite and Chalcopyrite. The first part of the experiments performed in the shake flasks with different species of microorganisms. The effect of pulp density, pH and the amount of inoculation (for the Mesophilic and Thermophilic bacteria) on the bioleaching were studied. The maximum recovery of copper and iron was 75% and 30% for mesophilic bacteria respectively. These figures were 78.5% and 36% for thermophilic bacteria respectively. The control experiments were performed without bacteria at the temperature of 35C and 45C. The highest copper and iron recovery were 34.5% and 7.5% at the temperature of 35C and 38% and 9.5% at the temperature of 45C respectively. The bioleaching experiments were also performed in columns loaded with the slag. With mesophilic bacteria the Cu and Fe recovery were 51.2%, 10.7% respectively. The temperature, pH and the flow rate of the trickling medium were 35C, 1.5 and 3 mm/min. With thermophilic bacteria the Cu and Fe recovery were %57, %13.7 respectively