Hidroxiapatita

Removal of toxic metals from water and soil by phosphate treatment
Dr Silvano Mignardi
Sapienza University, Rome, Italy
Archived topic page Published on 15 July 2010
The removal of toxic metalsfrom contaminated soils and wastewater is one of the most important issues of environmental remediation. Toxic metals such as Pb, Cd, Cu, Zn, Cr, Hg, and Ni are the main contaminants of surface water,groundwater, and soils which adversely affect water quality, soil ecology, and agricultural production [1-3]. The main sources of these contaminants are metal plating industries, abandoned disposalsites, and mining industries.
Conventional methods for toxic metal removal include oxidation, reduction, precipitation, membrane filtration, ion exchange, electrolytic recovery, biological treatment,and adsorption [4-6]. However, all these procedures vary in effectiveness and cost. Adsorption onto solid substrate materials has been used as one of the most suitable process for the removal of toxicmetals from water and soil. Among the mineral amendments, synthetic or natural apatite and phosphate rock have been proved to effectively remove toxic metals from contaminated water and soil [7-18].The aim is to remove metals through the formation of metal phosphates with a lower solubility and which are stable under a wide range of environmental conditions. The possible reaction mechanisms formetal immobilization include: (a) ion exchange processes; (b) surface complexation; (c) dissolution of phosphate amendments and precipitation of new metal phosphates, and (d) substitution of Ca byother metals during recrystallization (coprecipitation) [7,16].
Hydroxyapatite (HA) [Ca 10(PO 4) 6(OH) 2] is a unique inorganic compound because of its high removal capacity for divalent metals ions, andsynthetic HA has been used to remove heavy metals such as Pb, Zn, Cu, Cd, Co, and Sb from waters [7-18]. Although the removal capacity of natural phosphate rocks (PR) is relatively low compared to...