[Removal of Pb from Aqueous Solution by Magnesium-Calcium Hydroxyapatite Adsorbent].

A novel magnesium-calcium hydroxyapatite adsorbent was prepared by the Sol-gel method with different proportions of Mg/(Ca+Mg) using Mg as doped ions, and the removal characteristics and process mechanism of Pb on the magnesium-calcium hydroxyapatite in an aqueous solutions were studied. The results show that the surface of the adsorbent is composed mainly of a hydroxyphosphonite compound[Pb(PO)(OH)], The morphological characteristics of the magnesium-calcium hydroxyapatite adsorbent surface was investigated as crystal structure changes from short rods to needle structures according to scanning electron microscopy (SEM). Testing at a temperature of 25℃ and pH of 5 showed that the adsorption of Pb by magnesium-calcium hydroxyapatite reached equilibrium within 720 min. The adsorption capacity was determined to be 813.17 mg·g at a dosage of 0.6 g·L. The thermodynamic test results of Δ<0, Δ>0, and Δ>0 indicated that the adsorption process of Pb by magnesium-calcium hydroxyapatite is a spontaneous process with endothermic reaction and entropy increments, and higher temperatures were considered be favorable for adsorption at a range of 25-45℃. The adsorption could be effectively described by a pseudo-second-order kinetic equation. The equilibrium data were found to follow the Langmuir adsorption model. Material characterization and adsorption tests showed that surface complexation and dissolution-precipitation were the main mechanisms for the removal of Pb by magnesium-calcium hydroxyapatite in an aqueous solution.