Characteristic Features of Mg2+ Behavior and Mg2+ Effect on the Structure and Morphology of Nanohydroxyapatite in the Adsorption Method for the Fabrication of the HA-Mg Composite

Characteristic features of the sorption interaction of magnesium(II) ions in aqueous solutions with hydroxyapatite nanoparticles used as the sorbent were elucidated. The process kinetics was found to be adequately described by a pseudo-second order model. The sorption isotherm reflects consecutive changes in the mechanisms of sorbate and sorbent interaction with increasing sorbent concentration. Two main regions in the sorption isotherm were identified. Ion exchange is the major mechanism in the first region, while in the second region it is supplemented by physical adsorption. Formally, each region can separately be described by the Langmuir model with the following parameters: adsorption coefficient K = 33.7 and 32.1 L/mol and maximum adsorption Г∞ = 2.2 and 8.5 mol Mg/mol hydroxyapatite for the first and second regions, respectively. At high Mg2+ concentrations, morphological and structural changes of the sorbent were detected, which may be attributable to a chemical reaction between the components giving a new phase.