Reclamation of metal-contaminated soils and groundwaters using sulfidization techniques

Sulfide can be used to effectively remediate heavy metal contaminated soils and groundwaters. Laboratory scale ex-situ separations using sulfide to precipitate and flocculate heavy metals prior to conventional froth flotation can remove approximately 80% of copper from soils contaminated with environmentally significant quantities of metal. Soils with relatively low exchange capacities will give superior recoveries when compared to soils with large exchange capacities. This is because in soils with high exchange capacities, the metal sulfide must first be desorbed from the soil, precipitate as a sulfide, flocculate, and compete with the soil for adsorption of collector. In low exchange soils, the soil desorption step and competitive collector adsorption phases are eliminated.; In-situ immobilization of heavy metals using chemical sulfide addition has proven to be very effective in the removal of heavy metals from aqueous solution and suspension resulting in solutions with metal concentrations below detection as measured by atomic adsorption spectrophotometry. These metals are precipitated, flocculated as large agglomerates due to increases in ionic strength, and removed from suspension by a clogging mechanism using soil as a filter medium.; These immobilized metals will remain immobile in the soil system until groundwater influent chemistry changes dramatically. Initial changes in ionic strength will mobilize many clays due to forced changes in surface chemistry. Metals which remain associated with these clays may become mobilized with them and be transported through the aquifer system. Other metals can be mobilized by dissolution as pH is decreased.