ACID-EXTRACTION AND SEQUENTIAL FRACTIONATION OF HEAVY-METALS IN WATER-TREATMENT SLUDGES

A sequential extraction procedure for the partitioning of Cu, Cr, Ni, Pb and Zn has been applied to urban sewage sludges of different origin treatment and cation content. The sludges were further treated with H Cl, HNO3 and H2SO4, (pH = 1.5). By relating the amount of each cation extracted by acids with its fractionation, an equation was obtained en abling the amount extracted with acids to be estimated as a function t hereof. Finally, the speciation of acid treatment residue compared to the initial one shows that although part of the cation content of all fractions including the residual one is mobilized, the reduction in th e two most labile is so great that it can be the said that the sludge' s polluting power is reduced to a greater degree of acid extraction th an could be deduced from the overall extraction efficiency.