Synthesis of zeolite A and zeolite X from electrolytic manganese residue, its characterization and performance for the removal of Cd2+ from wastewater

Abstract

Electrolytic manganese residue (EMR) can cause serious environmental and biological hazards. In order to solve the problem, zeolite A (EMRZA) and zeolite X (EMRZX) were synthesized by EMR. The pure phase zeolites were synthesized by alkaline melting and hydrothermal two-step process, which had high crystallinity and excellent crystal control. And the optimum conditions for synthesis of zeolite were investigated: NaOH-EMR mass ratio = 1.2, L/S = 10, hydrothermal temperature = 90 °C, and hydrothermal time = 6 h. Then, EMRZA and EMRZX showed excellent adsorption of Cd2+. When T = 25 °C, time = 120 min, pH = 6, C0 = 518 mg·L−1, and quantity of absorbent = 1.5 g·L−1, the adsorption capacities of EMRZA and EMRZX reached 314.2 and 289.5 mg·g−1, respectively. In addition, after three repeated adsorption–desorption cycles, EMRZA and EMRZX retained 80% and 74% of the initial zeolites removal rates, respectively. Moreover, adsorption results followed quasi-second-order kinetics and monolayer adsorption, which was regulated by a combination of chemisorption and intra-particle diffusion mechanisms. The adsorption mechanism was ions exchange between Cd2+ and Na+. In summary, it has been confirmed that EMRZA and EMRZX can be reused as highly efficient adsorbents to treat Cd2+-contaminated wastewater.