Zinc Sulfide Concentrates Is Associated With The Biological Leaching Of Indium - Extraction Processes Study

Indium is one of China's preponderant scattered metals;it is often associated with polymetallic zinc ores and enriched into zinc sulfide concentrates after beneficiation.Thus,zinc sulfide concentrates become the best part of charge resources of indium.Study on extracting indium from zinc sulfide concentrates has attracted much attention home and abroad.The traditional ways for extracting indium are not only long processes that need huge investment in a good many equipments,but also ineffective techniques result in a large volume of ferrovanadium slag and low recovery of indium mostly below 50 percent.The enrichment and comprehensive recovery of indium becomes a thorny issue for which there is still not an ideal metallurgical process.Thus,it is very urgent and meaningful to research and develop clean and effective ways for indium extracting industry.Bio-hydrometallurgical technique may paly as a candidate process owing to its adavantages such as short technological process,environment friendliness,simple equipment,less operation capital,low production cost and ability to deal with complex multi-metal minerals.The paper systematically introdued the existing methods and techniques as well as the latest research developments of extracting indium from zinc sulfide concentrates, made a concrete study on the mineral preatreatment and bacterial culture, demonstrates the feasibility of bioleaching indium through thermodynamic analysis, and initiated the pilot experiments on the bioleaching of indium from zinc sulfide concentrates.The leaching yield of indium reached 65.84%by using adapted strains conducted at 33℃,pH value of 1.8,rotation speed of 175 r/min,minerals by fine grinding for 3 minute,pulp density of 5%and bacterial inoculum of 20%,nearly two and a half times than by sterile acid leaching.A disscusion about the kinetics of the bioleaching process was given here based on the observation of the change of the number of bacterium,the concentration of Fe³⁺and Fe²⁺,pH value and Eh value.Then,the enrichment and separation of indium from the leachate was studied.It compactly stated the reason why direct extraction of indium using di-2-ethylhexyl phosphoric acid(D2EHPA)after reduction of Fe³⁺.Sphalerite concentrate was chosen as reducing agent in virtue of its easiness to obtain and handle,low price and would not bring other impurities.When the reduction test was made at 95℃,the amount of sphalerite concentrate 1.6 times of its theoretical amount,mechanical agitation for 2.5 h,the reuction yield of Fe³⁺is 97.6%,it produced a solution contained Fe³⁺＜0.5 g/L which could be used as feed solution for the following solvent extraction.Orthogonal experiment designs were employed to optimize the conditions of indium extraction by D2EHPA.The effects of D2EHPA concentration,pH value, phase ratio O/A(organic phase/aqueous phase)and extraction time were studied by a four-level orthogonal array designed with an L₁₆(4⁵)matrix.The results of orthogonal experiments showed that D2EHPA is highly selective and very efficient in the extraction of indium,and analysis of variance indicates that the sequence of parameters according to their influence on the separation efficiency is D2EHPA concentration＞phase ratio O/A＞pH value＞extraction time.The optimal condition for copper extraction is obtained as 20%of D2EHPA concentration,1 min of extraction time,1:8 of phase ratio O/A and pH 0.6,at which the extraction yield of In is 98.4%and the extraction yield of Fe is quite low.In and Fe were primarily separated.Further absertation and counter-extraction were investigated on the basis of the present research achievements and successful experiences.Aiming at washing off the iron from the loaded organic phase,a mixture of 0.5mol/L sulfuric acid and 0.1mol/L oxalic acid was employed and gained a favorable result:the elution yield of Fe ionic approached 99%.More than 99%of indium was stripped in one stage back washing procedure with 6mol/L hydrochloric acid when phase ratio O/A is 12:1 and back washing time is 10 minute.From the above study,the bioleaching-Fe³⁺reduction-solvent extraction process for indium metallurgy was brought forward and recommended.