The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH

Natural based composites of hydroxyapatite/Gum Arabic designed for removal of toxic metal arsenic (III) from waste water were synthesized and evaluated. Several composites with various compositions were prepared by the wet chemical method and analyzed using various spectroscopic and analytical methods such as: Fourier transform infrared spectroscopy, total organic carbon production, XRD analysis and scanning electron microscope. The rates of weight loss and water absorption of the HAp/GA composites as a function of time were evaluated in phosphate-buffered saline solution at 37 °C and a pH of 7.4. The effects of several variables on adsorption of arsenic (III) by HAp/GA composites were evaluated. The variables include arsenic (III) concentration, contact time (t) and complex surface nature of HAp/GA composite. Three surface complexation models were used to study the mechanisms controlled the adsorption. The models were Langmuir, Freundlich and Dubinin Radushkevich. The adsorption kinetic of arsenic (III) on the composite surface was described by three modes: pseudo first order, pseudo second order and the intra particle diffusion. The results revealed that, the rate of adsorption of arsenic (III) by HAp/GA composites was controlled by two main factors: the initial concentration of arsenic (III) and the contact time. The kinetic studies also showed that, the rate of adsorption is a second order. The results indicate that, composite offered in this study could be a valuable tool for removing toxic metals for contaminated water by adsorption.