Insights into Competitive Zn2+/Ni2+ Adsorption for Feasibility of Deep Purification and Selective Separation by Dolomite-derived Adsorbents

Abstract

This study presents insights into competitive Zn²⁺/Ni²⁺ adsorption for feasibility of deep purification and selective separation by dolomite-derived adsorbents. A comparative evaluation of carbonate and phosphate adsorbents, i.e., thermally activated dolomite (D-800), phosphatized dolomite (PD), and Zr-modified PD (PD-Zr), for the removal, separation, and immobilization of Ni²⁺ and Zn²⁺ ions from aqueous solutions. The adsorbents exhibited distinct adsorption capacities, with D-800 showing the highest performance: 364 mg·g⁻¹ for Ni²⁺ and 790 mg·g⁻¹ for Zn²⁺, followed by PD (185 and 269 mg·g⁻¹, respectively) and PD-Zr (50 and 189 mg·g⁻¹, respectively). Adsorption mechanisms were elucidated as chemisorption/precipitation for D-800 and PD, and a combined ion-exchange/precipitation process for PD-Zr. Desorption studies revealed excellent immobilization stability of adsorbed metals on D-800 and PD, with desorption below 0.15% across pH 3–8. Remarkably, D-800 achieved > 99.9% removal efficiency, reducing Ni²⁺ and Zn²⁺ concentrations to below drinking water standards (Ni²⁺ < 0.1 mg·L⁻¹, Zn²⁺ < 5 mg·L⁻¹) from high-concentration solutions (up to 700 and 1400 mg·L⁻¹, respectively). Competitive adsorption experiments further demonstrated the feasibility of selective Zn²⁺ removal using PD at low doses. This work highlights the tunable functionality of dolomite-derived adsorbents for targeted heavy metal remediation, offering insights into adsorbent design for purification, separation, and immobilization in wastewater treatment.