Thermoacidophilic bioleaching of copper sulfide concentrate in the presence of chloride ions

The role of chloride ion in the performance of extreme thermophiles bacterium Sulfolobus acidocalarius in bioleaching process of copper sulfide concentrate at Midouk Shahr-e-Babak Complex was investigated. The gradual adaptation of bacteria to chloride ions at pH=۱.۵ showed that the presence of chloride ions in solution reduced the reproduction and growth rate of bacteria but did not prevent their growth. Results indicated that the effect of decreasing pH from ۲.۰ to ۱.۵ on bioleaching of copper sulfide concentrate is to increase the recovery of copper in the first few days, and nearly ۱۰۰% of copper was extracted after ۹ d. As the solid content in solution increases from ۱% to ۳%, about more ۶ d was required to extract copper. Bioleaching of copper sulfide concentrate revealed that the dissolution of copper sulfide concentrates at constant pH=۱.۵, ۱% solid content, and concentration of ۰.۵ mol/L and ۱.۰ mol/L NaCl after ۹ d, was ۹۸% and ۸۰%, respectively; and after ۲۱ d, it reached nearly ۱۰۰% and ۹۰%, respectively. Under the same conditions without microorganisms, copper extraction reached ۶۲%.BACKGROUND AND OBJECTIVESSince common and traditional methods for extraction of heavy metals from ore are no longer economically feasible, and using pyrometallurgical methods for copper production from copper sulfide minerals leads to environmental problems and pollutant generation, using alternative methods, such as hydrometallurgy and biohydrometallurgy, is gaining interest. Biohydrometallurgy is applicable to production, extraction, and recycling of different metals from minerals and industrial wastes [۱-۴]. There are many reasons to consider biohydrometallurgy as a suitable method for extracting metals from low-grade ores and sulfide concentrates, such as copper grade reduction in ore, less energy consumption and less pollution to the environment. Hydrometallurgy and biohydrometallurgy need a lot of water. However, in many cases, supplying low-salinity water is difficult for industries. Usually, the water used contains large amounts of different ions including chloride. In this paper, bioleaching tests were conducted on sulfide concentrate produced at the Midouk Copper Complex in Shahr-e-Babak City located in a dry area in Southern Iran. The Midouk Copper Complex must use underground water resources which contain chloride ions. An alternative water supply being considered is۳۷the piped Persian Gulf seawater. A case study was done to investigate the effects of chloride concentrations and pH on dissolution of copper from the copper sulfide concentrate. The unique feature of this research is that the copper sulfide concentrate has different kinds of copper sulfide minerals, such as chalcopyrite, covellite, and bornite. Moreover, bioleaching of copper sulfide concentrate was carried out using the native extreme thermophile bacteria Sulfolobus acidocaldarius, which was adapted in the presence of high chloride concentrations. The bacteria were isolated from acid mine drainage of the Sarcheshmeh Copper Complex located near the Midouk Copper Complex.MATERIALS AND METHODSSome tests were designed to determine the effects of different parameters on bioleaching copper sulfide concentrate from Shahr-e-Babak, Midouk Copper Complex. Two different levels of parameters such as initial pH, solid content, and sodium chloride concentration were studied. pH value of the samples aided by concentrated sulfuric acid was measured daily for ۲۱ d using Soil pH meter PRN-۴۱. After sampling, ۵ mL of distilled water was added to keep the volume of the solution constant. Tests ۱۲ and ۱۳ were done without chloride ions using the same method as tests ۲, ۴, ۵, and ۶, with the exception that sampling was done only at the end of the ۲۱st day. Samples were poured to ۱۵ mL falcon tubes, where the solid material was separated using a centrifuge (Sigma ۲− ۱۶ PK, Germany) at ۶۰۰۰ r/min in ۳ min. The sample solutions were also filtered using a syringe and ۰.۲۲ μm syringe filter (Biofil, Canada) to ensure sample clarity. The concentration of copper in each sample was determined with ICP-OES analyzer. The leaching tests were done to compare the results of chemical leaching and bioleaching of the Midouk copper sulfide concentrat. In test ۹, ۱ g of copper concentrate (۱% w/v) and ۳ g of NaCl (۰.۵ mol/L) were added to ۲۵۰ mL Erlenmeyer flask containing ۱۰۰ mL of distilled water. pH of solution was set at ۱.۵ using concentrated sulfuric acid. Then ۵۰ mg/L of thymol and ۵ g/L of citric acid were used as antibacterial agent to prevent microorganism from growth in the solution. The Erlenmeyer flask was put inside the shaker-incubator at ۶۰ ℃ and under agitation rate of ۱۵۰ r/min for ۲۱ d. Sampling and other steps were similar to previous bioleaching tests ۱ − ۸. Tests ۱۰ and ۱۱ were carried out using the same method as test ۹ but without chloride, and sampling was done only at the end of the ۲۱st day.RESULTS AND DISCUSSION۱- Effect of solid content on bioleachingThe bioleaching tests were carried out with ۱% and ۳% solid content, ۰.۵ and ۱.۰ mol/L NaCl, and initial pH=۱.۵ and ۲.۰ (Figure ۱). According to Figure ۶, Cu extraction increased with time and reached faster its maximum value (۹۰% to ۱۰۰%) in the tests with ۱% solid content compared to the tests with ۳% solid content, and then remained constant with time. It may be because chalcopyrite dissolves faster in the lower solid content tests. However, the tests with ۳% solid content needed more time to reach the maximum Cu extraction (about ۶ d). Since increasing solid content also means increasing tension on the cell walls of the bacteria, Sulfolobus acidocaldarius dissolved more copper in the ۱% solution compared to the ۳% solution, in a shorter period of time. It is also noted that during these tests, a reduced mass۳۸transfer coefficient because of the low agitation in the shaker, especially oxygen transfer coefficient, was another factor for decreasing copper dissolution [۲۳].CONCLUSIONThe main conclusions from this study are as follows: ۱) During bacterial adaptation with different concentrations of chloride ions at pH ۱.۵, increasing chloride ions concentration reduced the bacterial count but did not prevent the bacterial from reproducing. ۲) Increasing pH in the bioleaching from ۱.۵ to ۲.۰ decreased copper dissolution. Therefore, pH=۱.۵ was more effective for Cu extraction than pH=۲.۰. ۳) The inoculation of bacteria to leaching process of copper sulfide concentrate with pH=۱.۵, ۱% solid, and ۰.۵ mol/L NaCl increased copper dissolution from ۶۲% to ۹۸% after ۹ d. ۴) In bioleaching copper sulfide concentrate, high concentrations of chloride ions (۱.۰ mol/L) can reduce jarosite formation if solution ORP is controlled. ۵) Despite formation of jarosite and elemental sulfur, copper sulfide concentrate dissolution using Sulfolobus acidocaldarius bacteria in the presence of chloride ions (۰.۵ mol/LNaCl) reached approximately ۱۰۰% after ۱۴ d, which indicated the important role of chloride ions in bioleaching copper dissolution. Less jarosite formed in the bioleaching compared to the leaching process. ۶) Higher solid content (۳%) requires more time for Cu extraction in leaching and bioleaching processes than low solid content (۱%) reported by most researchers. ۷) Generally, the bioleaching process for dissolution of copper sulfide concentrates in the presence of chloride ions is efficient at the Midouk Copper Complex in Shahr-e-Babak City. Therefore, using underground water (or piped seawater) can be a suitable option in the bioleaching process of copper extraction.

کلیدواژه ها:

bioleaching ، Sulfolobus acidocalarius ، copper sulfide concentrate ، chloride ion