Column Bioleaching Of Low-grade Copper Ore And Succession Of AMD Bacterial Communities Under High Fe³⁺ Concentration

As high-grade surface mineral deposits are worked out,the traditional pyrometallurgy-based metal recovery processes have become less economically viable in dealing with low-grade ores and mine waste. Bioleaching,an emerging technology for the recovery of metals from minerals,has attracted wide attention from the mining industry by offering a number of environmental and economical advantages over conventional approaches.Heap reactors are cheap to construct and operate and are therefore more suited to the treatment of lower grade ores. Leaching in columns simulates percolation leaching because the conditions are very similar to those in the heap.The aims of this investigation were(1) to test the feasibility of using pure culture of Acidithiobacillus ferrooxidans GF and a mixed culture with Acidiphilium sp.DX1-1 for the bioleaching of a low-grade copper ore and(2) to evaluate synergistic effect of autotrophic and heterotrophic acidophiles in column bioleaching.The leaching experiments were carried out at ambient temperature.Effects of temperature and other interacting parameters including pH,redox potential and the concentrations of total iron and ferrous ion in solution on column bioleaching were also described.Total DNA was extracted from solid samples taken from different depths of the column and corresponding microbial community structures were investigated by using Amplified Ribosomal DNA Restriction Analysis(ARDRA).Over a period of 102 days under the ambient temperature condition,bioleaching copper extractions by pure and mixed cultures achieved 14.87%and 20.11%, respectively.The ratios of autotrophic and heterotrophic bacteria at the top and bottom portion of the column were different.At the bottom and top of the column B,A.ferrooxidans accounted for 68.1%and 54.5%, while Adiciphilium sp.DX1-1 represented 31.9%and 45.5%, respectively. In acid mine drainage(AMD) environments,the bacteria rapidly oxidize ferrous ions to produce a large amount of ferric ions in its environment.However,less attention has been paid to the importance of ferric ions in the bacterial metabolism and succession of microbial community structure.Based on our previous results,the aim of the second investigation is to study the succession of bacterial communities under various Fe³⁺ concentrations by ARDRA method.Our result indicated that growth of acidophiles inhabited in AMD was remarkably influenced by concentration of Fe³⁺.A total of 8 OTUs were recovered in sample JX and FS when cultured in media with elevated concentration of ferric ion.These OTUs were affiliated toα-Proteobacteria(mainly Acidiphilium sp.),γ-Proteobacteria(mainly A. ferrooxidans),Nitrospira(mainly Leptospirillum species),and Actinobacteria(Ferrimicrobium acidophilum).The succession of bacterial community structure indicated the existence of a competitive relationship between A.ferrooxidans and Leptospirillum-like microorganisms.A.ferrooxidans grew first in media containing high ferrous ion concentrations and low ferric ion concentrations,but was significantly inhibited by high ferric ion concentration whilst Leptospirillum-like species were less sensitive to inhibition by ferric ion and their iron-oxidizing ability was much less affected.When sample FS was cultured in medium F with 12.5 g/L of ferric ion,a bacterium which had 99%phylogenetic similarity to Ferrimicrobium Acidiphilum became the most predominant specie.