Mechanism of cadmium and lead ion exchange by α-zirconium bis-(monohydrogenorthophosphate) monohydrate

Abstract

An investigation of the ion-exchange processes between Cd²⁺ or Pb²⁺ and α-zirconium phosphate, Zr(HPO₄)₂·H₂O (α-ZrP), at 18, 50 ± 2, 75 ± 2, and 98 ± 1 °C has been carried out. The uptake of these ions was found to increase with increase in temperature. The fully ion-exchanged phases were obtained at the highest temperature. The exchanged samples have been characterised by X-ray diffraction and thermogravimetric analysis. The addition of small amounts of sodium chloride to the systems at room temperature increased the Cd²⁺–H⁺ exchange from 15% to 80% but the Pb²⁺–H⁺ exchange by only 30%. The effect of Na[NO₃] and Na[O₂CMe] on the Pb²⁺–H⁺ system was also studied. Ion-exchange isotherms and distribution coefficients have been calculated. A particularly high separation factor for Cd²⁺ and Pb²⁺ was observed in the experiment with added NaCl at room temperature.