Arsenic removal using calcium hydroxyapatite synthesized from paper mill sludge

Abstract

Calcium hydroxyapatite (Ca-HAp) was synthesized from calcium carbonate (CaCO3) extracted from a paper mill sludge. The extraction of CaCO3 was carried out by chemical precipitation process and synthesized to HAp nanoparticle under appropriate stoichiometric condition through wet chemical precipitation process. The size of the HAp nanoparticle was 42.5 nm under an optimized aging period of 24 h. This work aims in the batch adsorption of arsenic, an anionic metal arsenic in the form of Arsenite: As(III) on the synthesized Ca-HAp in laboratory scale. Batch kinetics studies were conducted for varying operational parameters such as temperature, initial adsorbate concentration, dye solution pH and rotation speed (RPM). In comparison with the two suggested isotherm models, Langmuir isotherm was suited to this adsorption process with a correlation coefficient of 0.92 and isotherm constant as 1.18 (KL). Chemisorption was found to be the rate-limiting mechanism for the sorption of arsenite onto Ca-HAp and thus followed pseudo-second-order kinetics. A maximum monolayer adsorption of 0.43 mg/g of arsenic was obtained at an equilibrium time of 60 min with 93% to 94.2% removal efficiency.