AVANCES EN EL TRATAMIENTO DE AGUAS ÁCIDAS DE MINAS.

Abstract

Aqueous effluents generated in mining activities (coal and metal sulfides), especially the acid mine drainage (AMD), cause great environmental problems due to its high contamination potential in surface or underground water resources. AMD is often characterized by low pH values and high concentrations of toxic inorganic ions. This work summarizes alternatives to remove sulfate and metal ions from mining effluents including neutralization, precipitation (or co-precipitation) and solid-liquid separation, at laboratory and pilot scale. In all cases, the solids (colloidal precipitates) generated are removed by dissolved air flotation (DAF). Among these ions, the removal of sulfate ions is one of the most difficult and costly process and for this reason the emphasis was posed in this element and the best alternative consisted in the removal of sulfate (> 1000 ppm), Fe and Mn ions, simultaneously, at pH 12. Under these conditions and in the presence of lime and aluminum salts (polyaluminum chloride-PAC) at a PAC:SO4 -2 =2:1 mass ratio, the sulfate ions are precipitated as Ettringite and the Fe and Mn ions are co-precipitated (hydroxides). The solids produced in all these precipitation treatments have been effectively separated be dissolved air flotation (DAF). DAF has been compared with settling and presented advantages regarding process kinetics and treated water quality. Best results were obtained at 13 m 3 m -2 h -1 (pilot 1 m 3 h -1 ) loading capacity yielding a residual turbidity of 0.5 NTU. Thus, it is believed that the techniques showed in this work have a great potential in the AMD treatment with water reuse.