Mineralogical characteristics of MSWI fly ash stabilized by chemical reagents
LI Jian-tao1, ZENG Ming1, DU Bing2, SHANG Yi-xuan2, ZHANG Yu-xing1, LI Ying3, LIU Jian-guo2
1. School of Chemical & Environmental Engineering, China University of Mining Technology(Beijing), Beijing 100083, China;
2. School of Environment, Tsinghua University, Beijing 100084, China;
3. Environmental Convention Implementation Technical Center of Ministry of Environmental Protection of P. R., Beijing 100035, China
Several effective inorganic and organic chemicals were screened to stabilize MSWI fly ash from a MSWI plant of Jiangsu province. The aim is not only to investigate the stabilization effect of heavy metals, but characterize the mineralogy of MSWI fly ash under different chemical treatments to determine the heavy metal (Pb, Cr, Cd, et al.) fractions in mineral and non-mineral phases. The results indicated that phosphoric acid was the best inorganic chemical to reduce the lead leaching from 97.55mg/L to 2.16mg/L in this experiment, while such three single organic chemicals (polydithiocarbamate) with the addition of 2%~3% can markedly decrease the heavy metal leaching. In the original MSWI fly ash, the distribution of lead and cadmium were in the mineral phases, whereas the copper, chromium and zinc in non-mineral phases. The inorganic and organic chemicals resulted in matrix materials dissolution, soluble ions diffusion and secondary mineral transformation. After chelating treatment, the non-mineral fraction raised from 14.41% to 21.52%. Meanwhile the chromium in the non-mineral fraction was transformed to chromates. The cadmium in the mineral fraction increased due to the precipitate formation. The distributions of heavy metals in mineral phases were analogical behaviours that the chromium, zinc and lead were presented in calcite and chromium and copper in hematite.
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