Mina Esperanza DAS passive system treatment comprises a DAS-reactive pool (15m*8m*4m length-width-depth) and a decantation pond (10m*3m*2m), both connected by stepped concrete open channels.
At present the system has been working for a period of 12 months having treated a mean inflow rate of 0.5 l/s. Water analyses are available for the firsts 6 months of work and show encouraging results. The system eliminates a net acidity of 1500 mg/L as CaCO3 from the inflow water and removes 100% Al, Cu, Pb, Cd, V, 90-100% As, Cr, 75-90% Zn, 45% Fe and 20% SO42-.
Iron removal takes place along all the system although the greater precipitation happens at the surface of the DAS-reactive pool. This iron removal is controlled by the precipitation of schwertmannite, Fe8O8(OH)6(SO4). The precipitation of this mineral leads to the complete removal of As and Ti by processes of adsorption or coprecipitation.
The precipitation of hydrobasaluminite (Al4 (SO4)(OH)10 (12-36)H2O), at pH around 5, controls the removal of Al inside the reactive material and promotes the sorption or coprecipitation of Cu, Cd, V, Be and Cr.