Effects of the iron oxidation and precipitation processes on the arsenate sorption and coprecipitation

Abstract

The main aim of this study was to assess the effects of ferrous iron oxidation, hydrolysis and precipitation of the ferric iron on the mechanisms of arsenate removal from acid mine drainage. The study was realized at the pH range 2,0 – 6,5. H2O2 was the oxidant used in the chemical test. A mixed culture of mesophilic iron-oxidizing chemolithotrophic bacteria (Acidithiobacillus ferrooxidans, Leptospirillum ferroxidans) carried out the ferrous oxidation in the biological test. NaOH was used as an alkalizing agent which triggered the ferric iron hydrolysis and precipitation. The results showed that the total content of retained arsenic by ferric iron hydrous oxides and its speciation as geochemical fractions depended on the iron and phosphate concentrations in acid solution. The results showed that phosphate concentration lower than 6 mg/ L limited the ferrous iron oxidation rate. At the tested experimental conditions, arsenic sorption by formed ferric iron hydrous oxides was the main mechanism for its removal from acid mine drainage, as the ratio between iron and phosphate determined the proportions between the geochemical fractions of scavenged arsenic.