4. Conclusions
This study investigated the effectiveness of different amount of nHA in immobilizing Pb, Cd in
contaminnated soils. The nHA treatment reduced Pb/Cd availability in this study, showing a significant
reduction of water soluble, bioaccessible and phytoavailable Pb/Cd by forming the Pb/Cd phosphate (e.g.,
hydroxypyromorphite-like mineral). The immobilization mechanism main involves both cation exchange
and partial dissolution of the nHA amendment and precipitation of heavy metal-containing phosphates.
Furthermore, treatment efficiency increased as the nHA dose (based on the molar ratio of P/(Pb+Cd))
increased, and it was observed that immobilization was the most effective when using the molar ratio of
P/(Pb+Cd) at 5:1. The results in this study showed that nHA can immobililize Pb and Cd in contaminated
soil effectively.