LONG-TERM DIFFUSION OF ELEMENTS FROM MUNICIPAL SOLID-WASTE COMBUSTOR ASH BLOCKS IN THE MARINE-ENVIRONMENT

Municipal solid waste (MSW) combustor ash was combined with Portland c ement to form blocks which were placed in Conscience Bay, Long Island Sound, New York. During a 4.5-year period, ash blocks were returned to the laboratory to examine changes in the total elemental content of t he ash blocks following placement. A continuous loss of calcium, potas sium and zinc from the ash blocks was measured following submersion. C alculated effective diffusion coefficients ranged from 4.75 x 10(-8) s (-1) for potassium to 5.56 x 10(-8) cm(2) s(-1) for calcium. In contra st, lead and cadmium were effectively retained within the cementitious matrix of the submerged ash blocks. Following seawater submersion, th e substitution of magnesium for calcium in the ash block pore spaces, the alkaline ash block porewaters and the encapsulation of ash particl es within the Portland cement matrix contribute to reduce the leaching of contaminants from ash blocks in the marine environment.