Evaluation of Mineral-Based Additives as Sorbents for Hazardous Trace Metal Capture and Immobilization in Incineration Processes

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Considerable interest exists in the use of mineral-based sorbents for capturing and retaining hazardous constituent trace metals in the incineration process. The suitability of six minerals, silica, diatomaceous earth, kaolin, bauxite, alumina and attapulgite clay, as potential sorbents for the capture and immobilization of trace metals was evaluated. The behavior of five trace metals, arsenic, cadmium, chromium, lead and nickel was tested. The first five minerals constitute a spectrum of alumino-silicate compounds ranging from pure SiO 2 (silica) to pure Al 2 O 3 (alumina). The sixth mineral, attapulgite clay, is primarily a magnesium hydroxide-silicate compound with alumina as an impurity. It has frequently been used in trace metal related test programs at the Incineration Research Facility (IRF) as a carrier of metals and organics in blended synthetic waste streams. The objective of this test program 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 subjected to TCLP extraction Bench-scale tests were conducted in the IRF's thermal treatability unit (TTU). The test matrix was defined by varying: - mineral (sorbent) type - treatment temperature; treatment temperatures of 540°, 700°, and 870°C were tested - chlorine concentration in the feed; 0 and 4 percent by weight chlorine in the feed were tested Given the preliminary nature of the tests the results must be viewed qualitatively. Nevertheless, overall trends indicate that under specific conditions, varying for each mineral, all of the mineral sorbents showed promise in limiting metal vaporization, and or TCLP leachability. Combining the dual criteria of limiting metal vaporization and reducing leachability, kaolin and attapulgite clay appear to have the greatest promise as potential sorbents.