Aluminum adsorption using different models of hydroxyapatite via Molecular Dynamic simulations

The activities of the anodizing industry, mining, and the inadequate use of coagulants and flocculants for wastewater treatment are some of the causes of an alarming increase in aluminum levels in water bodies. Adsorbents, such as bone char, are used for the removal of metal ions from water due to their easy operation, regeneration, and low cost. Bone char is constituted mainly by hydroxyapatite and in order to understand the mechanism of aluminum adsorption onto hydroxyapatite an adequate analysis of the effect of the surface exposed to the aqueous solution is necessary. Different facets of hydroxyapatite, 001 and 010, were studied, which have been protonated to represent the acidic conditions of the wastewater from the anodizing industry. The results of Molecular Dynamic simulations show that the protonation of the 001 facet leads to an increase in the adsorption of aluminum. The coarse surface of the 010 facet at acidic pH conditions cause that the water molecules adsorb on the sub-layers of the surface. The adsorption of aluminum occurs preferentially on the phosphates of hydroxyapatite and is due to the formation of outer-sphere adsorption complexes.