Non-apatite Ca-Mg phosphate sorbent for removal of toxic metal ions from aqueous solutions

In this study, non-apatite Ca-Mg phosphate sorbent was synthesized by neutralization method using dolomite and phosphoric acid. The mixture of crystal hydrogen phosphates of calcium and magnesium with gross composition Ca_0.7Mg_0.3HPO₄∙2H₂O was observed in synthesized sorbent. Thermally activated dolomite was used for calcium-magnesium raw materials. The influence of sorbent dose, рН of solutions and contact time for the removal efficiency of synthesized sorbent for metal ions from aqueous solutions was studied. The maximum removal efficiency of metals was achieved at 10gL−1 sorbent dose and рН 2.5-3.5. The sorbent is characterized by high sorption capacity in relation to ions of Zn2+, Cu2+, Pb2+, Cd2+, Ni2+ and Co2+ (1.19-3.78mmolg−1) and a high rate of sorption (more than 90% uptake of metals ions was recorded within 3−5min). Adsorption isotherms were built for each tested metal ions and were found to fit to Freundlich and Redlich-Peterson models. It was determined that the possible mechanism for metal ion sorption includes the dissolution-precipitation and ion-exchange stages. The present study showed that synthesized non-apatite Ca-Mg phosphate sorbent can be successfully used for the treatment of Zn2+, Cu2+, Pb2+, Cd2+, Ni2+ and Co2+ containing wastewater and had a significantly higher sorption capacity towards toxic metal ions than phosphate and natural materials such as activated phosphare rock, hydroxyapatite, clay minerals, dolomite.