STABILIZATION OF LEAD IN ACIDIC MINE FILTERCAKE BY ADDITION OF ALKALINE TAILINGS

The potential for disposal of acidic Pb-bearing process waste in an al kaline tailings pond was assessed to ascertain if Pb would become stab ilized as opposed to diluted during mixing. This study demonstrated th at codisposal of the filtercake residue, consisting of ferrihydroxide, lead sulfate and lead oxide phases (pH = 6.2, Pb = 43 000 mg/kg), wit h tailings containing abundant calcium and strontium carbonate (pH = 9 .8, Pb = 2400 mg/kg) would result in Ph stabilization. The leachable P b was greater (p < 0.05%) for a sand-filtercake mixture compared with the tailings-filtercake at analogous ratios, demonstrating reactivity between filter cake and tailings. Stabilization occurs because abundan t remnant calcite in the tailings neutralizes the acidic filtercake, f acilitating sorption of Pb to ferrihydroxide at the pH of the filterca ke/tailings mix and a >98.5% decrease in Pb solubility. Sorption (Kd(P b) = 28 600 at pH 7.7) and possible precipitation of Ce-Pb and Ln-Pb o xides limit Pb solubility. These data suggest that disposal of acidic filtercake in an alkaline tailings pond would reduce Ph solubility to levels below relevant environmental standards.