Bio-geochemical mechanisms influencing the stability of As-bearing iron oxides
Abstract
Hydrous Ferric Oxydes (HFO) often occurring in the organo-mineral matrix of soils and sediments act as a preferential substrate for the fixation of toxic metals and metalloids as arsenic. The chemical stability of these complexes strongly depends on the physico-chemical and biological conditions of the medium. In this context, the aim of this work was to study mobility factors of arsenic by analogy with bio-geochemical reactions involved in soils and sediments. We studied the conditions of arsenic release in solution upon the reaction of synthetic As-doped iron-oxide minerals with specific micro-organisms (Fe(III)-reducing bacteria or As(V)-reducing bacteria) under controlled laboratory conditions. Our results showed that As release in solution proceeds in two step. First, a rapid As release in solution is caused by competitive sorption processes with other oxy-anions present in the culture medium. In a second step, the microbial reduction of Fe(III) and/or As(V) become the main factor affecting the stability of the As-iron oxide complexes. These two mechanisms were regulated by the physico-chemical conditions of the medium (pH, Eh and phosphate concentration). These results should help in a better understanding of the arsenic mobility in polluted environment. They confirm the major influence of the biological factor on the stability of the As trapping by HFO. This latter chemical trapping mechanism being involved in numerous As water-treatment processes.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....1954G