Treatment of acid mining waters

The objective of this work was to study the possibility of achieving a selective removal of iron from acid mine waters (AMW) by precipitation/biosorption producing an easily filterable pulp and a solution containing valuable metals such as copper, zinc etc. This treatment is an alternative to the traditional neutralization with Ca(OH)2, that produces a precipitate of ferric hydroxide (Fe(OH)3) and gypsum (CaSO4), which is extremely difficult to filter and is contaminated with heavy metals. The composition of the investigated solution was established in order to simulate a typical composition of AMW. To prevent the co-precipitation of the heavy metals in significant amounts, iron precipitation has to be carried out at low pH. The effect of the addition of a biomass (grape-stalks or cork powder) on the selective removal of iron and on the sedimentation and filtration operations was determined. The results showed that at pH 3 and for a solid–liquid ratio of 4 g/l it is possible to eliminate 65% of iron and only 5% of copper. Using 8 g/l of biomass the iron removal increased up to 85% of iron and 74% of copper, 90% of zinc and 99% of nickel remained in solution. The addition of the biomass to the pulp also allowed to improve the sedimentation and filtration operations.