Comparison of Oxalate, Citrate and Tartrate Ions Adsorption in the Hydroxyapatite/Aqueous Electrolyte Solution System

Władysław Janusz,Ewa Skwarek

doi:10.3390/colloids4040045

Abstract

The kinetics of adsorption/desorption of oxalate, citrate and tartrate anions was investigated using hydroxyapatite from solutions at the initial concentrations of 0.000001 and 0.001 mol/dm3 anions. The adsorption process from a solution with a concentration of 0.001 mol/dm3 takes place in three stages and is well described by the multiexponential equation of adsorption kinetics. The process of tartrate and citrate ion desorption after increasing the pH to 10 is irreversible, while the oxalate ions undergo significant desorption with the increasing pH. The adsorption of oxalate ions decreases with the increasing pH. This effect is weaker in the adsorption of citrate and tartrate ions. Ion adsorption studies were supplemented with the measurements of zeta potential, FTIR and particle distribution of hydroxyapatite particles.

Highlights

Due to its properties, hydroxyapatite [Ca10(OH)2(PO4)6] (HAp) can be classified as a biocompatible and bioactive material, but due to its natural microporous structure, it is well known as a good adsorbent, for immobilization cations
As HAp is a mineral compound of human bones and teeth and, on the other hand, the organic acids naturally occur in our diet, the interactions of both compounds can lead in our organism to, e.g., subsequent processes of adsorption, dissolution, precipitation and aggregation
Studies of ion adsorption in the hydroxyapatite/aqueous electrolyte system due to the solubility of the hydroxyapatite are confined to the pH range of 6 to 11

Summary

Introduction

Hydroxyapatite [Ca10(OH)2(PO4)6] (HAp) can be classified as a biocompatible and bioactive material, but due to its natural microporous structure, it is well known as a good adsorbent, for immobilization cations. HAp is capable of reversible exchange of hydroxyl ions by anions like F, Cl or I ions [1]. HAp adsorbs/exchanges some larger ions like carbonate, oxalate, citrate or tartrate. As HAp is a mineral compound of human bones and teeth and, on the other hand, the organic acids naturally occur in our diet, the interactions of both compounds can lead in our organism to, e.g., subsequent processes of adsorption, dissolution, precipitation and aggregation. Citrate or tartrate salts can cause dissolution of hydroxyapatite but the mechanism of teeth surface etching by salts containing citrate ions is still not fully understood [2]. Studies of the heterogeneous nucleation of calcium oxalate monohydrate were carried out in supersaturated solutions of calcium and oxalate ions to ensure crystal nucleation and growth of calcium oxalate [3]

Methods

Findings

Discussion

Conclusion