P21

THE USE OF PHOSPHORUS IN SEQUESTRATION OF LEAD AND CADMIUM IN A SMELTER SLAG

Phosphate amendment of lead-contaminated soils is known to precipitate highly insoluble lead pyromorphite (Pb5(PO4)3Cl), effectively reducing its bioavailability to humans, animals, and plants. The situation with phosphate-amended, cadmium-contaminated soils and slags is less clear. In the present study, lead content of the amended slag decreased in the exchangable, carbonate, iron- and manganese-oxide, and organic fractions of the slag, and increased in the residual or recalcitrant fraction.

Cadmium content of the phosphate-amended slag decreased in the exchangable fraction of the slag, and increased in the carbonate and iron- and manganese-oxide fraction. At the same time, X-ray diffractometry shows that pyromorphite abundance increased in the phosphate-amended treatments. Lead in the phosphate-amended slag precipitated as highly insoluble pyromorphite, and cadmium may have precipitated as relatively insoluble octavite (CdCO3).

Of the two phosphate amendments, KH2PO4 was more effective in reducing soluble lead and cadmium, and increasing pyromorphite abundance. The effect of rate is more effective in remediating the slag than the effect of time.

Key words: lead pyromorphite, bioavailability, phosphate amendment