CHLORINATED ETHENE REDUCTION BY CAST-IRON - SORPTION AND MASS-TRANSFER

Tetrachloroethylene (PCE) and trichlorethylene (TCE) exhibited signifi cant nonlinear sorption to nonreactive sites when exposed to four cast irons. Cast iron is a reactive material that promotes reductive dechl orination and has recently been used for in-situ remediation of chlori nated solvent contaminated ground water. Comparisons between PCE sorpt ion to cast iron, graphite, and iron-containing minerals indicate that nonreactive sorption is due to exposed graphite inclusions in the cas t iron. Sorption of the homologous series of chloroethenes to a cast i ron adheres to Traube's rule; thus, the extent of sorption is related primarily to compound hydrophobicity. An analytical model incorporatin g rate-limited sorption/desorption to nonreactive sites was used to as sess sorption nonequilibrium Effective sorption and desorption rate co efficients determined how significant mass transfer limitations to non reactive sorption sites exist for PCE and not for TCE. The nonreactive sorption observed indicates that how-through cast iron treatment syst ems will exhibit significant delayed attainment of steady-state condit ions for chlorinated ethenes, particularly PCE and TCE.