Heavy metal removal from aqueous solution by granular hydrated Portland cement

Granular hydrated Portland cement (HPC) was prepared as adsorbent to remove heavy metals in aqueous solution. Batch experiment results confirmed that heavy metals were removed through a combination of adsorption and precipitation. Adsorption played a more important role in the initial stage of the removal process or at lower concentrations of the heavy metals. After adsorption equilibrium was obtained in two days, the removal process continued for about three days due to the precipitation. Besides precipitation, the maximum Langmuir adsorption capacity reached 132.27, 87.14, 123.43 and 112.05 mg/g for Pb, Cu, Zn, and Cd, respectively. When various heavy metals coexisted, the removal capacity followed the order of Cu>Pb>Cd>Zn. The adsorption on the surfaces of HPC was mainly governed by surface precipitation and Ca2+ exchange, as suggested by XRD, SEM-EDS and released Ca2+ results. Most of the adsorbed heavy metals on the HPC and the precipitation formed in the liquid phase were stable under neutral and alkaline conditions. Overall, HPC particles exhibited a large potential for heavy metal removal. When cement-related materials containing HPC are employed for heavy metal removal, the dissolution of the precipitate at low pH might facilitate the migration of the heavy metals.