Contaminant-immobilization Amendments: Immobilization Mechanisms and Environmental Considerations of Application

Pollutant discharge from agricultural systems as a result if agricultural activities is as one of the factors for soil and water quality. Various soil and water remediation techniques including the use of chemical amendments have been applied to reduce the risks associated with these contaminants. This paper reviews the use of chemical amendments for immobilizing chemical amendments، the chemistry of contaminant immobilization، and environmental concerns associated with the use of these products. The commonly used chemical amendments were grouped into aluminum-، calcium-، and iron-containing products. Other products of interest include phosphorus-containing compounds and silicate clays. Mechanisms of contaminant immobilization include one or a combination of the following: surface precipitation، adsorption to mineral surfaces (ion exchange and formation of stable complexes)، precipitation as salts، and co-precipitation. Reviews of environmental implications revealed that undesirable substances such as trace elements، fluoride، sulfate، total dissolved solids، as well as radioactive materials associated with some industrial wastes used as amendment could be leached to ground water or lost through runoff to receiving water bodies. The acidity or alkalinity associated with some of the industrial-waste amendments could also constitute a substantial environmental hazard. Chemical amendments have elements capable of affecting the activities of certain microbes that could influence geochemical processes such as mineral dissolution and formation، weathering، and organic matter mineralization.