Immobilization of arsenic by a thermoacidophilic mixed culture with pyrite as energy source

Arsenic is associated with a wide range of ores and therefore is a major contaminant in metallurgical wastewater. For long-term immobilization of arsenic, iron arsenate as the very stable mineral scorodite (FeAsO4·2H2O) is the preferred arsenic carrier. Scorodite can be formed with the aid of microorganisms of the natural iron cycle living at pH below 2 and high temperatures (>60˚C), which carry out the oxidation of ferrous iron with oxygen. As arsenic in metallurgical waste streams is often present as arsenite, oxidation to arsenate is needed for scorodite formation. Here, we have investigated the role of a thermoacidophilic mixed culture in the oxidation of As(III) and precipitation of As(V) in the form of scorodite from a synthetic wastewater containing 6.7mM of As(III) and 0.5%wt pyrite as main iron Fe(II) source. The results indicate that As(III) was completely oxidized from the synthetic wastewater in the presence of pyrite and scorodite was formed only in presence of the mixed culture at a Fe/As:1.3. This means a combination of biological oxidation with biocrystallisation accomplished by the presence of pyrite not only as the main energy source for the microorganisms but also as catalyst in the As(III) oxidation reaction