Remediation of contaminated land by formation of heavy metal phosphates

Phosphate compounds of Pb and Zn are highly insoluble and their formation in contaminated soils would aid immobilisation of heavy metals. In preliminary experiments to induce heavy metal phosphates in soils, two mine-waste contaminated soils were treated by the addition of soluble inorganic phosphate and the growth of Agrostis capillaris on soil amended with horticultural peat. After incubation for three months, EDX and XRD analysis were performed and the soil grains characterised using an automated SEM/EDX programme. The results showed the presence of Pb and Zn phosphates in the phosphate amended soils and in the rhizosphere of Agrostis. Therefore, both treatments have the potential to induce the formation of heavy metal phosphates. This study describes an additional benefit of vegetative remediation techniques which are more ecologically acceptable than the addition of soluble phosphate compounds.