Recovery of zinc from wastewater for zinc oxide synthesis via adsorption-desorption-chemical precipitation pathway

Abstract

During the covid-19 pandemic large demand in gloves resulted in high consumption of zinc-oxide (ZnO) as an activator during the vulcanization process for glove production leading to the generation of zinc-containing wastewater requiring wastewater treatment to reduce zinc concentration below 2 mg/L. Zinc can be removed through adsorption, and this opens up an opportunity to recycle the removed zinc ions for ZnO synthesis. Therefore, the objective of this study is to evaluate the feasibility for ZnO synthesis via the adsorption-desorption-chemical precipitation pathway. Adsorption was conducted using palm shell activated carbon (PSAC), a low-cost adsorbent, and it exhibited a large surface area from BET analysis of 717 m2/g and showed excellent zinc adsorption possessing a Langmuir monolayer adsorption capacity of 3.6 mg/g. A Langmuir equilibrium (RL) of, 0 < RL < 1, was calculated for zinc adsorption showing favorable adsorption. PSAC exhibited endothermic adsorption attributed to the positive change in enthalpy of +ΔH = 63.356 kJ/mol. An initial adsorption characteristic of, Ri = 0.87 implies PSAC possesses fast initial adsorption properties, where most of the zinc removal happens within the first 30 min. HCl is an excellent desorption agent for zinc desorption achieving high average zinc desorption efficiency of 91.5 %. Chemical precipitation showed an average zinc conversion rate of 98 %. The resulting ZnO was characterized and it exhibited a high surface area of 97.4 m2/g after calcination (400 °C, 3 h), high purity and high crystallinity. The results confirmed the feasibility of zinc ion recovery for recycling to produce good quality ZnO.