Bioaugmentation With Moderately Thermophilic Acidophiles For The Promotion Of Chalcopyrite Concentrate Bioleaching

Chalcopyrite is the most important source of copper in the world, and accounts for70%of the world’s known copper reserves. Extensive research in the field of bioleaching, one of the most effective ways for metal extraction, has been conducted to develop an efficient process to extract copper from chalcopyrite. However, because of slow leaching kinetics and low extraction rate, the industrial application of bioleaching for the recovery of copper is still limited. Hence, it will be beneficial for alleviating the copper resource crisis of China and the world to carry out the effective and economical research of promoting the chalcopyrite oxidation. In this study, bioaugmentation, originating from the field of bioremediation, was utilized as a biological monitoring technology for promoting copper extraction. With the purpose of the feasibility of bioaugmentation, effects of bioaugmentation of three different moderately thermophilic microorganisms with different bioaugmented inoculum periods and amounts on the recovery of copper in the chalcopyrite were evaluated by the results of physico-chemical leaching parameters and Real-time Quantitative PCR (Q-PCR) community structure analysis.A mixed co-culture system composed of bacteria Acidithiobacillus caldus(At. caldus) and Leptospirillum ferriphilu (L. ferriphilum), and archaea Ferroplasma thermophilum (F thermophilum), involving transfer of organic and inorganic carbon and transformations of iron and sulfur, for the oxidative dissolution of chalcopyrite concentrate. According to the whole results of chalcopyrite bioleaching with the mixed co-culture, the following research of bioaugmentation was introduced at early (5th), mid-term (13th) and later (24th) three periods during the leaching process of the above-mentioned mixed culture.Chemomixotrophic archaea F. thermophilum was introduced into the bioleaching process of the above-mentioned mixed co-culture system at5th,13th and24th with different bioaugmented inoculum amounts. And effects of bioaugmented F. thermophilum on the chalcopyrite dissolution were determined by copper extraction and bacterial community monitoring. The results showed that bioleaching efficiencies of copper were increased dramatically when F. thermophilum was introduced at5th, and copper recovery was connected with the bioaugmented inoculum amount of F. thermophilum:the more inoculum, the more copper extracted. Yet, bioaugmentation of mid-term and later periods both had a negative effect on the copper extraction, and prohibitive degree of copper extraction is positively correlated with bioaugmented inoculum amount of F. thermophilum. Based on the Q-PCR analysis, the introduction of F. thermophilum promoted the growth of L. ferriphilum and At. caldus. However, the extensive growth of L. ferriphilum in turn inhibited the growth of F. thermophilum due to the competition for Fe2+The bioaugmentation strategy was applied to the above-mentioned mixed co-culture system by inoculating with enriched chemoautotrophic bacteria L. ferriphilum at the5th and13th bioleaching process with different augmented inoculum amount. Nonaugmented bioleaching system showed34.8%of copper recovery, while the co-culture system, augmented with L. ferriphilum at the early bioleaching period, showed significant enhancement of copper recovy efficiency, nearly approaching100%after10days of augmentation. However, with the increase of introduced inoculum at the mid-term bioaugmented system, promoting effects of L. ferriphilum bioaugmentation on copper recovery was converted to the inhibitory action on copper. Microbial diversity and dynamics of community structure demonstrated that augmentation of L. ferriphilum at early or mid-term bioleaching period promoted the growth of At. caldus, yet inhibited the extensive growth of F. thermophilum at both the early and mid-term bioaugmentated systems.Bioaugmentation of At. caldus introduced at early (5th) or mid-term (13th) period of the above-mentioned mixed co-culture system was assessed by copper extraction and bacterial community monitoring, too. Compared with nonaugmented bioleaching system, both early and mid-term bioaugmentation of At. caldus facilitated the copper extraction, and the bioleaching efficiency of copper in the early bioaugmentated system approached to100%at the end of bioleaching and12%higher than the one of nonaugmented bioleaching system. In addition, the amount of augmented inoculum amount had a direct effect on the copper recovery, which showed the more augmented inoculum, the more chalcopyrite dissolved. From the comparison of community structure between the bioaugmented system and nonaugmented, it was found that the growth of L. ferriphilum YSK was promoted by extra addition of At. caldus at early or mid-term period, while the growth of F. thermophilum was inhibited, although it was detected in the whole bioaugmented bioleaching system.In conclusion, it was feasible to carry out the biological monitoring of bioaugmentation for the treatment of promoting chalcopyrite dissolution. Moreover, it was the most effective augmented strategy that L. ferriphilum was introduced into the known mixed co-culture system at the early period. Besides, there were competitive, synergistic, mutualistic interactions or commensalisms between physiologically distinct moderately thermophilic acidophiles F. thermophilum L1、At. caldus s2and L. ferriphilum YSK.