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CHROMIUM SPECIATION IN MUNICIPAL SOLID WASTE: EFFECTS OF CLAY AMENDMENT AND COMPOSTING

The addition of clay in the form of bauxite refining residue (red mud) prior to composting has been suggested as a way to control heavy metal mobility in compost. Leachability and plant availability of metals in a mixture of grass clippings and sawdust spiked with metal solution was markedly reduced during the composting process. | Pergamon Wat. Sci. Tech. Vol. 38 No. 2 pp. 17-23 1998. _ IAWQ 1998 Published by Elsevier Science Ltd. Printed in Great Britain. All rights reserved __ 0273-1223 98 19-00 0 00 PII S0273-1223 98 00427-2 CHROMIUM SPECIATION IN MUNICIPAL SOLID WASTE EFFECTS OF CLAY AMENDMENT AND COMPOSTING Goen Ho and Liang Qiao Institute for Environmental Science Murdoch University Murdoch 6150 Western Australia ABSTRACT The addition of clay in the form of bauxite refining residue red mud prior to composting has been suggested as a way to conưol heavy metal mobility in compost. Leachability and plant availability of metals in a mixture of grass clippings and sawdust spiked with metal solution was markedly reduced during the composting process. The fate of metals in municipal solid waste compost applied to land was examined by using a sequential step extraction to investigate metal speciation into exchangeable and bound to carbonate forms to Mn Fe oxides to organic matter and in residue phase in red mud amended compost. The effects of red mud and the composting process on metal speciation in the compost for Cd Cr Cu Ni Pb and Zn were investigated and a comparison of some effects with biosolids compost was made. Addition of red mud reduced the metal mobility and the potential hazard of releasing metals from compost through promoted precipitation adsorption and complexation of free metal cations to red mud. Red mud however was not able to desorb metals bound to organic matter. Since most of the metals in the municipal solid waste were not usually bound to organic matter the addition of red mud prior to composting fixed the free metal ions before they bound to this fraction. Results for Cr speciation are reported in this paper. 1998 Published by Elsevier Science Ltd. All rights reserved KEYWORDS Bauxite refining residue red mud chromium composting metal mobility metal speciation municipal solid waste. INTRODUCTION Compost produced from mixed MSW can be .