The Impact Of Extracellular Polymer In Chalcopyrite Leaching By Acidithiobacillus Ferrooxidans

The interaction between bacteria and minerals involves a series of the electrochemical,biochemistry and surface chemical processes. Bacteria are entrapped in the Extracellular polymeric substances(EPS) layer of their own,which mediates the contact between the bacterial cell and the sulfidic energy source.EPS plays a pivotal role in organic film formation and bacterium-substratum interaction.Now, "EPS-contact-leaching mechanism" is extentively accepted by researchers.Howerver,the reasearch of EPS-related leaching mechanism has been basically focused on pyrite so far,and the most of studies were only limited to the initial stage of adsorption between bacteria and minerals,and the exact role of bacterial extracellular polymers(EPS) in the process of mineral extraction has still been unkown,while the study of EPS on chalcopyrite remained in observation phase.The research on the relationship of ferrous and ferric irons in EPS and the passivation of minerals is fewly.In the present study,we builded a simulation EPS solution system according to extracellular polymers(EPS) component of Acidthiobacillus ferrooxidans from past researchs to study bacterial leaching kinetics of chalcopyrite and influencing factors in order to understand further the role and the mechanism of EPS in the process of mineral extraction by the use of cyclic voltammetry,tafel curve,spectral analysis and other methods.In the same time,as agar(C₁₂H₁₈O₉)_n has these characteristics of favorable affinity for biological materials and good passageway for ions and water freely and accumulating EPS formed in the bioleaching process in the agar-phase,the behaviors of bacteria in agar-bacteria -chalcopyrite system were also investigated.The results indicated that:(1) EPS makes bacteria adherence to chalcopyrite surface easily,plays an important role in protecting bacteria against disadvantage environment,and reduces the time to adapt to environment;(2) in the experiments(â…°) with different Fe³⁺/Fe²⁺,while the total iron ions is 5 g/L,and(â…±) with different total Fe,while the ratio of Fe³⁺/Fe²⁺ is 1,the redox potential and concentration of Fe²⁺ reach an equilibrium with the value of approximate 850 mV vs.SHE and 0.4 g/L, respectively.In the condition of EPS,the initial addition of 5g/L total iron ions is reasonable suggested to reduce the precipitation of jarosite,and favors for the dissolution of chalcopyrite when the redox potential less than 650 mV vs.SHE;(3) EPS which contains -OH and -COOH chelates Fe³⁺ and releases H⁺ into the solution causing the drop of the pH.EPS film layer with jarosite and its deposits on the surface of chalcopyrite gradually creates the high redox potential space,at the same time,results in the change of effect of the original battery between chalcopyrite and pyrite,which favor for the dissolution of pyrite;(4) the presence of bacteria and EPS leads to the most corrosion potential shift of chalcopyrite electrode.The EPS on the surface of chalcopyrite increase the anodic oxidation of chalcopyrite by concentrating H⁺ and chelating Fe³⁺;the limiting current appearence in cathode indicates that the EPS film layer containing jarosite on the surface of chalcopyrite results in the passivate of chalcopyrite by restricting oxygen transportation,and favors for the dissolution of pyrite;The results of agar experiments indicates that in the natural case without Fe²⁺ added,EPS formed by A.ferrooxidans creates a suitable environment for bacterial living and sulfide oxidizing,maintaining higher potential and suitable pH about 1.8 for bioleaching;in the presence of Fe²⁺ ions,jarosite precipitation formed by hydroxylation gradually covers the surface of chalcopyrite and hinders further bioleaching chalcopyrite.