Metal-rich sludge from mine water treatment: from waste to effective arsenate adsorbent

摘要

Water contamination by arsenic is considered a global emergency due to both wide diffusion of this metalloid in the environment and its toxicity (10 mu g/L arsenic concentration guideline value in drinking water has been recommended by World Health Organisation). This issue is dramatic in developing countries suffering of inadequate water treatment infrastructures. Within this framework, a great effort towards the development of economically viable technology for arsenic removal has been undertaken. In particular, adsorption on mining industry wastes has drawn attention due to the great affinity of arsenic oxy-anions for iron oxy-hydroxide. Opportunity of turning iron-rich sludge from an Italian mine-water treatment facility (underground pyrite deposits in Colline Metallifere district, Tuscany) into effective arsenic adsorbent was verified through laboratory-scale tests carried out in batch regime. Specifically, adsorption was considered as a polishing step assuming about 100 mu g/L (i.e., 1.3 mu mol/L) initial arsenic concentration as arsenate. Arsenic concentration below guideline value was obtained contacting the model solutions with 0.5 g/L adsorbent for 10 min with no appreciable interferences from competing anions (i.e., borate, hydrogen carbonate, phosphate, silicate and sulphate).