Adsorption of Zn²⁺ from solutions on manganese oxide obtained via ozone precipitation reaction

Synthesis via ozone precipitation reaction was used to obtain manganese dioxide (OMD) and it was probed as an adsorbent for zinc ions. Adsorption was followed along shaking time and increasing ratio [NO₃⁻] / [Zn²⁺], and isotherms were obtained at different pH values and in the presence of several anions (chloride, nitrate, sulphate, and acetate). It was found that adsorption equilibrium is fast and follows the pseudo-second order model (q_e = 34 ±1 mg/g and K = 0.07 ±0.01 g/mg h). Isotherms were fitted to Langmuir, Freundlich, and Langmuir-Freundlich models, and the best fitting was found with the last one. The process is dependent on pH and the efficiency increases from pH 1 to 4. The ratio [NO₃⁻] / [Zn²⁺] up to 3 does not seem to change the behaviour of the process. Regarding the anions, the efficiency of Zn(II) adsorption occurs according to: acetate > nitrate and sulphate > chloride. Manganese oxide obtained via ozonization is an excellent adsorbent for zinc ions.