Immobilization of lead and copper in aqueous solution and soil using hydroxyapatite derived from flue gas desulphurization gypsum

Abstract

Flue gas desulphurization (FGD) gypsum is an abundant waste generated from coal-fired power plants. This study evaluated the potential application of hydroxyapatite (F-HAP) derived from FGD gypsum for immobilization of lead (Pb) and copper (Cu) in water and soil. MINTEQ software was employed to determine the species distribution of Pb(II) and Cu(II) at different solution pH conditions. The factors that affect sorption behavior such as pH effect, sorption kinetics, thermodynamics, and isotherms were investigated using batch tests. Various kinetics and isotherms models were used to fit the obtained data. The experimental results showed that the amount of Pb(II) and Cu(II) adsorbed on F-HAP increased as the pH increased from 2.0 to 6.0, and adsorption was enhanced with the rise in temperature. The predicted maximum adsorption capacities were found to be 1.376 and 0.460mmol/g for Pb(II) and Cu(II), respectively. The values of mean free energy (E) obtained from Dubinin-Radushkevich (D-R) model implied that the chemical reaction, which was stronger than ion exchange governed the process of Pb(II) adsorption, while the adsorption of Cu(II) was mainly ascribed to ion exchange. XRD analysis revealed that the final solid obtained after Pb(II) immobilization was mainly mixed of pyromorphite and F-HAP, while the final solid acquired after Cu(II) immobilization still consisted of a single phase of F-HAP. On the other hand, application of F-HAP in contaminated soil effectively reduced the leachable and exchangeable Pb and Cu, reflecting that F-HAP is a potential material for remediating environmental pollution with Pb and Cu. This study realized the potential of a modified geochemical waste material towards remediation of metal contaminated soils, providing very useful and valuable information for other similar solid wastes, such as paper sludge and phosphogypsum.