ATTENUATION OF TRACE ELEMENTS BY ALUMINUM PRECIPITATES IN ACID MINE DRAINAGE

Precipitation of Fe and Al hydroxides from waters contaminated by acid mine drainage (AMD) is known to attenuate trace element concentrations via co-precipitation and adsorption. Here, we investigate the ability of Al precipitates to attenuate trace elements from water contaminated by AMD at the Green Valley abandoned coal mine near Terre Haute, IN. We examined these processes in a laboratory simulant as well as in waters from the Green Valley site. In an effort to study the trace element attenuation properties of Al precipitates in the absence of Fe, an AMD simulant was created without dissolved Fe and titrated with a strong base to increase pH and cause precipitation of Al hydroxides. Resulting liquids were filtered through 5.0, 1.0, 0.4, 0.2, and 0.1 µm pore size filters, and the resulting filtrates were analyzed by inductively coupled mass spectrometry for Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Ag, Cd, Cs, Ba, Tl, Pb, and U. Samples of AMD-contaminated water were filtered and analyzed in the same manner. Under controlled laboratory conditions, Al colloids in the simulated AMD attenuated numerous dissolved elements. Concentrations of dissolved V, Cr, Cu, As, Se, Ag, Pb, and U in the simulated AMD water were reduced by at least 89% when filtered through 0.4 µm pore size filters. Attenuation of these elements was not observed in samples from the field site due to their low concentrations. Our results suggest that V, Cr, Cu, As, Se, Pb, and U are likely adsorbed by Al precipitates in actual AMD contaminated waters.