Laboratory assessment of rice husk ash (RHA) in the solidification/stabilization of heavy metal contaminated slurry

Abstract

This article presents a laboratory study investigating the effects of RHA on the immobilisation of lead and copper in a slurry treated with a binder content ranging from 100 to 300 kg/m³. Increased binder content was significant in the immobilisation of Pb, but less effective for Cu. A minimum binder content of 200 kg/m³ was required to stabilise Cu in the slurry. The incorporation of RHA significantly reduced the coefficient of diffusion of Pb and Cu spiked samples in comparison to samples treated with only cement. Sorption and precipitation reaction were important mechanisms that controlled the leaching of Cu and Pb. The increase of RHA content led to increase in sorption and precipitation reaction in the solidified/stabilised matrix. The results from mercury intrusion porosimetry (MIP) revealed that specimen spiked with Cu exhibited more macropores than those spiked with Pb. It is postulated that the cement hydration may be retarded due to the presence of Cu. The performance of the RHA stabilised samples is influenced significantly by the pH. The amount of binder content was crucial for Cu and Pb leachability. The presence of RHA offered little resistance under acidic conditions but minimised the leachability under neutral and alkaline conditions.

Keywords: Diffusion; Heavy metals; Leaching; Pozzolanic; Rice husk ash; Solidification/stabilization.