EVALUATION OF MINERAL-BASED ADDITIVES AS SORBENTS FOR HAZARDOUS TRACE-METAL CAPTURE AND IMMOBILIZATION IN INCINERATION PROCESSES

Considerable interest exists in the use of mineral-based sorbents for capturing and retaining hazardous constituent trace metals in the inci neration process. The suitability of six minerals, silica, diatomaceou s earth, kaolin, bauxite, alumina and attapulgite clay, as potential s orbents for the capture and immobilization of trace metals was evaluat ed. The behavior of five trace metals, arsenic, cadmium, chromium, lea d and nickel was tested. The first five minerals constitute a spectrum of alumino-silicate compounds ranging from pure SiO2 (silica) to pure Al2O3 (alumina). The sixth mineral, attapulgite clay, is primarily a magnesium hydroxide-silicate compound with alumina as an impurity. II has frequently been used in trace metal related test programs at the I ncineration Research Facility (IRF) as a carrier of metals and organic s in blended synthetic waste streams. The objective of this test progr am was to evaluate the candidate sorbents with respect to: the degree to which they facilitate retention of the trace metals in the sorbent the degree to which they retain trace metals in the sorbent when subje cted to TCLP extraction Bench-scale tests were conducted in the IRF's thermal treatability unit (TTU). The test matrix was defined by varyin g: mineral (sorbent) type treatment temperature; treatment temperature s of 540 degrees, 700 degrees, and 870 degrees C were tested chlorine concentration in the feed; 0 and 4 percent by weight chlorine in the f eed were tested. Given the preliminary nature of the tests the results must be viewed qualitatively. Nevertheless, overall trends indicate t hat under specific conditions, varying for each mineral, all of the mi neral sorbents showed promise in limiting metal vaporization, and or T CLP leachability. Combining the dual criteria of limiting metal vapori zation and reducing leachability, kaolin and attapulgite clay appear t o have the greatest promise as potential sorbents.