Science of the total environment vol:118 pages:463-473
Boom clay is a reducing clay layer that contains 1. 5% pyrite, 1% CaCO3, 1.2% organic carbon and about 50% clay. Trace Cd conditional complexation constants were determined from Cd and organic matter distribution measurements at different solid/liquid ratios under in situ reducing conditions of solid- and liquid-phase composition. Cadmium forms 1:1 complexes with boom clay humic acids. The conditional complexation constant of trace Cd with boom clay humic acids under in situ solution conditions (pH 9, E(h) = -250 mV) is log K1 = 7.5. Conditional complexation constants decrease by about 0.15 log K1 units for each 10-fold increase in Cd loading in the range 10(-6) to 10(-10) eq. Cd/g organic matter. Cadmium-organic matter complexes were predicted to dominate the speciation of Cd in the in situ solution phase (pH 9, CO3 = 0.015 M, 100 ppm DOM).