Biogeochemical Process Of Pyrites Oxidation: A Laboratory-scale Study

The acid mine drainage (AMD), generated during the oxidation of sulfideminerals (Pyrite), represents a major environmental problem worldwide. Pyritesoxidation is the result of a complex set of processes dependent on rock type, mineralstructure and chemistry, microbial community and temperature, fluid abundance andchemistry. However, there are few models that link sulfide minerals oxidationprocesses and the changes of microbial communities based on the result of alaboratory study. Here, a simulated experiment of pyrites oxidation has beenconducted to develop a biogeochemical model for sulfide minerals oxidation andheavy metal release according to the pyrites physicochemical and mineralogicalcharacteristics, microbial community composition and the mobility of heavy metals.The geochemical and mineralogical analyses showed that soluble ions and theexchangeable of heavy metals correlated negatively with pH. Some sulfate minerals(i.e. jarosite and magnesiocopiapite) were formed at the late stage of the oxidation.16S rRNA pyrosequencing indicated that highly diverse microbial composition ofthe three stages of pyrites oxidation samples. In total, We got64,150reads with anaverage2,212sequences for each sample. At the early stage of pyrites oxidation (pH>5), sequences affiliated to Firmicutes (53%) phyla dominated the microbial community of pyrites. As the process of oxidation proceeded, the relative abundanceof Leptospirillum genus gradually increased and reached a peak at the late stage ofpyrites oxidation (pH <3). Acidithiobacillus, one genus with members having bothiron-and sulfur-oxidizing capacities, had the highest relative abundance at middlestage than at the other two stages. At the late stage, both microbial species richnessand pH significantly decreased, while Ferroplasma-related sequences were found todominate the associated microbial community, with the relative abundance of up to46%. Statistical analysis (Spearman) showed a positive relationship between therelative abundance of archaea and pH, but a negative relationship between therelative abundance of bacteria and pH, suggesting that archaea seemed to have astronger resistance to heavy metals than that of bacteria in the extreme acidenvironment.