(47f) Activated and Deactivated Sintering of Hydroxyapatite Sorbent Using Metallic Additives

This work is part of a series of studies dealing with the evaluation of the effects of major elements of solid waste, especially metallic oxides, nitrates, sulfates and chlorides on the sintering and the densification of calcium hydroxyapatite , (Ca-HAP) adsorbent. Ca-HAP is a promising compound for adsorption and immobilisation of heavy metals from soils, incinerator fly ashes and hazardous industrial wastes. The immobilisation of heavy metals by Ca-HAP increases significantly by calcination at temperatures ranging from 650°C to 900°C. The effects of chloride salts of potassium (KCl) and zinc (ZnCl2) as well as lead oxide (PbO2) and lead nitrate [Pb(NO3)2] on sintering and densification of Ca-HAP were studied using specific surface area changes, and dynamics measurements methods such as Thermomechanical Analyser (for shrinkage studies) and Environmental Scanning Electron Microscopy (ESEM). The addition of KCl, PbO2 and Pb(NO3)2 (2% w/w) activated the sintering process by bringing a swift reduction in surface area, and lowering the densification temperature. However, a low final densification was achieved. Increasing the amount of those additive to 10% w/w further lowered the final densification and lowered the densification temperature of hydroxyapatite by 150°C. On the other hand, the addition of 2% of ZnCl2 deactivated the sintering process by slowing down the densification process and raising the densification temperature. However, the reduction of surface area was comparable to that of Ca-HAP. The densification rate contained two or more rate maxima indicating the additives (salts) bring multiple speeds in the densification process.

Key words: Densification, Activated and Deactivated sintering, Hydroxyapatite, Metallic additives

# Corresponding author: Tel., +33 5 63 49 32 22, fax : +33 5 63 49 30 99, E-mail: : ange.nzihou@enstimac.fr