Study On Bioleaching Behavior And Mechanism Of Pb/Zn Smelting Slag

Study on bioleaching behavior and mechanism of Pb/Zn smelting slag was the main aim in this paper. Pb/Zn smelting slag contains high-dose Zn, Pb, In, Ag, Cd and As. Using a kind of economically effective, safe and environmental processing technology to realize its harmless and recycling is of great significance. Owing to the advantages of smaller acid consumption, lower costs, higher leaching rate, safety and eco-friendly traits, bioleaching technology has caused wide public concern. Limited reports were available about releasing valuable/toxic metals from Pb/Zn smelting slag by heterotrophic bioleaching using expensive yeast extract as energy source, leading to high leaching cost. In this work, autotrophic bioleaching using cheap sulfur/pyrite as energy matter was firstly applied to tackle the slag: to explore the optimization conditions through changing the experimental conditions; to explain the mechanism and analyze potential toxicity of residues after bioleaching, which were designed to obtain the basic data for the practical application of bioleaching technology.The studies showed that Acidithiobacillus thiooxidans, Leptospirillum ferriphilum and the mixed culture had strong tolerance of Zn, Pb, In, Ag, Cd and As, which always maintained good growth during bioleaching, playing an important role. Through changing bacterial style, solid-liquid ratio, substrate concentration, initial pH value, and adding chemical acid during leaching period, the optimization of conditions were determined as in the bioleaching system of mixed culture; 10% solid liquid ratio; 16 g/L energy substrate; the initial pH value of 1.0; and keeping pH ca.2.0 by chemical acid. Under the condition, the autotrophic bioleaching was capable of solubilizing valuable/toxic metals from the slag, harvesting the maximum extraction efficiency of 98.2% for Zn, 90.9% for Cd, 80.8% for In, 28.4% for As, 13.2% for Pb, despite poor performance with Ag.According to chemical simulation, BCR extraction experiment, SEM and XRD characterization, the sole acidic dissolution by biogenic H2SO4 as the non-contact mechanism was responsible for extraction of Zn, Pb and Cd unrelated with oxidation reduction and direct effect of microorganism; for In, while the extraction was due to both contact mechanism and non-contact one. The combined action of acidic and oxidation dissolution is the main cause; As achieved poor efficiency with high concentration of iron ion, confirming the formation of FeAsO4 caused lower extraction through the XRD experiment; Ag existed as refractory, so extraction did not occur.Using the domesticated bioleaching strains cultured in the acidic waste water which discharged by Nitrocellulose production can effectively improve the dissolution performance of Zn, Pb, In, Ag, Cd and As. Metal elements in residue after bioleaching mainly existed as residual state, it is difficult to dissolve them out again, so its potential harm to environment reduced significantly.