To Örebro University

Abatement of ARD with passive treatment systems can quite often rely only on pH-control if the iron content is high enough and to allow for the formation of ferric hydrous oxides, which act as efficient adsorbents. The stability of ferric hydrous oxides is sensitive to lowering of pH as well as Eh why they must be controlled. Hence, it would be favourable to use a well ordered adsorbent that is stable over time and under the chemical conditions of ARD. Municipal waste water sludge is a growing problem in many countries and incineration under oxidative conditions can be used to oxidize anthropogenic organic molecules which pose a threat to the environment. Sludge ashes rendering from wastewater treatment in which iron is used as a flocculation agent have high concentrations of calcium/ magnesium and ferric oxides, and should therefore, in theory be a suitable candidate for treatment of ARD. This study has therefore focused on the ability for these ashes to act as a sorbent for the removal of metals from ARD. The stability and potential release of metals from the material were quantified in batch experiments by extraction at pH 2-10, resulting in equilibrium concentrations (at pH 8) of 11.9, 0.08 and 24.1 mg L-1 for Al, Fe and Mn respectively. However, after washing with water the corresponding values were 0.01, 0.03 and 0.09 mgL(-1). In fact, after washing the sludge ash is stable from pH 4 to 10, with only slightly higher concentrations found at pH 2. Batch experiments on metal adsorption from ARD showed more than 99% sorption of Cr, Cu, Pb and V, corresponding values for Co, Ni and Zn were 56, 86 and 34% respectively. The overall results from this study show that sludge ashes are a promising solution for treatment of ARD.