Immobilization of heavy metals in soil by phosphate treatment: A review

Heavy metal contamination of soil is an environmental and public health issue of prime interest because metals are non-biodegradable and accumulate throughout the food chain. Conventional heavy metal remediation technologies include chemical precipitation, membrane filtration, ion exchange, electrochemical treatment, etc. Recently adsorption has become an alternative treatment method of contaminated media and a great effort has been devoted to develop new adsorbents. Phosphate treatment is widely considered an effective in situ treatment to reduce metal mobility and bioavailability in soils through the formation of highly insoluble phosphates which are stable in a wide range of environmental conditions. The mechanisms of metal retention are still debated and include: ion exchange, dissolution/precipitation and surface complexation. Various types of phosphate amendments, such as synthetic and natural apatites, phosphate rocks, bone meal and bone char have been tested. Phosphate treatment has been shown to be effective in stabilizing Pb, Cd, Cu, Zn, Co, Ni, Sb, Cr, V in contaminated soils. In soils phosphate stabilization has been applied mainly to remediate Pb contamination although the method can be used to reduce also the mobility and bioavailability of other metals. The main factors determining the removal capacity of phosphate treatment in contaminated soils include type of phosphate source due to their different solubilities, rate of phosphate application, heavy metals speciation, soil pH and Eh and grain size of the amendment. The adverse effects of phosphate stabilization resulting in enhanced leaching of phosphate and availability in the soil of contaminants, such as As, Se and W, have to be addressed for evaluating the environmental impact of phosphate treatment. © 2012 Nova Science Publishers, Inc. All rights reserved.