The study of the interactions of malonic acid ions with the hydroxyapatite surface in liquid

Abstract

• Adsorption is described by the multiexponantiate model. • The last stage of the adsorption kinetics indicates the process of precipitation of a new phase. • Adsorption of malonic acid is best described by the Redlich-Paterson isotherm model. • The presence of adsorbed malonate ions causes an increase in the concentration of acid groups on the hydroxyapatite surface. Adsorption of malonic acid at the hydroxyapatite/aqueous NaCl solution interface based on the measurements of adsorption / desorption kinetics and adsorption as a function of pH was presented. The adsorption of malonate ions was determined from the loss of ion concentration in the solution as measured by the radioisotope using 14C labeled malonic acid. The adsorption measurements were supplemented with electrophoretic zeta potential as well as and FTIR measurements. The kinetics of adsorption from a solution with an initial concentration of 1 mmol/dm3 of malonic acid proceeds in three stages, in the last stage there was observed a rapid increase in adsorption, which proves the precipitation of a new phase by the malonate ions. The presence of this phase was confirmed by examining the crystallinity of the hydroxyapatite sample conditioned in a malonic acid solution by the method of Landi et al. on the basis of XRD patterns and measurements of particle distribution using the light scattering method.