Leaching study of thermally treated cadmium-doped soils

Soils doped with cadmium were effectively immobilized by thermal treatment in a bench-scale fluidized- and fixed-bed incinerator. Toxicity characteristics leachability procedure (TCLP) was conducted to evaluate the effectiveness of Cd immobilization by thermal treatment of the doped soils. USEPA SW846 Methods 3050 and 3051 were performed to determine the presumptive total Cd content in the untreated and treated soils. Experimental parameters include thermal treatment temperature and time. Cd content in acidic and noncalcareous soils, sorbent type and amount added, soil particle diameter, and incinerator mode. Results illustrate that Cd in soils of smaller diameter is less effectively immobilized. At a temperature of 600{degrees}C, a treating time of 30 minutes, and a Cd content of 91.3 ppm in pre-treated sample, thermal treatment in fluidized-bed mode reduces Cd leaching percentage from 17% and 75% (untreated soil) to 12 and 22% for soils of particle size 16-20 mesh and 45-50 mesh, respectively. Data of treating 150-ppm Cd-doped soils in fluidized-bed mode at 600{degrees}C for 30 minutes show an increase of leaching percentage from 8.8 to 13% as Cd content in soils is increased from 75.0 to 175.0 ppm. The constancy of leaching percentage from soils treated in fluidized-bed mode is obviously due tomore » high degree of mixing. As the treating temperature increases (from 150{degrees}C to 750{degrees}C). Cd is better immobilized in mixtures. Excessive addition of sorbents will reduce their adsorption effectiveness of Cd for each unit mass of sorbent. Both the Langmuir and Freundlich isotherms fit the sorption data quite successfully with all correlation coefficients (r) greater than 0.984. 14 refs., 4 figs., 4 tabs.« less