BACKGROUND: The work described here concerns a laboratory-scale investigation into the remediation of sand artificially contaminated with a mixture of heavy metals using a two-step process: the first step involved solubilization of the sand contaminants with sulfur-oxidizing bacteria and the second step consisted of the precipitation of heavy metals from solution with sulfate-reducing bacteria. Initially it was necessary to study the immobilization of sulfur-oxidizing bacteria (Acidithiobacillus ferrooxidans and At. thiooxidans) on polyurethane foam. A support colonized by At. thiooxidans was selected and was added to a reactor for the continuous system. The acidic medium generated in this reactor was added to a column along with 50 g of artificially contaminated sand (85 mg Cr(III), 20 mg Ni(II) and 200 mg Zn(II)). The effluent from this step was collected in a reservoir tank and H2S, which was biologically generated by sulfate-reducing bacteria (Desulfovibrio sp.), was added in order to carry out the precipitation of metals. RESULTS: When 2.4 L of acid medium was passed through the column, it was observed that 14.6% of Cr(III), 26.7% of Ni(II) and 90.5% of Zn(II) were solubilized. The leachate (2.4 L) was treated with 2.2 L of reducing medium and 2.2% Cr(III), 54% Ni(II) and 28% Zn(II) of metals present in leachate were precipitated. CONCLUSION: The proposed process is therefore suitable for the extraction and deposition of heavy metals from contaminated media and several design changes are currently being made in order to improve and optimize this remediation system. (c) 2008 Society of Chemical Industry.