Mercury adsorption from aqueous solution by regenerated activated carbon produced from depleted mercury-containing catalyst by microwave-assisted decontamination

Mercuric chloride supported on activated carbon was widely used as the catalyst for vinyl chloride monomer (VCM) production especially in Asia. The resultant depleted mercury-containing catalyst (DMC) was a hazardous solid waste due to the high mercury toxicity. Microwave heating (MWH) was used to decontaminate DMC. Effects of microwave power and treatment time on mercury removal efficiency were studied. Up to 99.98% of mercury could be recovered under the optimum treatment conditions of 700 W for 20 min with microwave energy consumption being 15.56 kWh kg(-1)(DMC); meanwhile the treated DMC was a clean regenerated activated carbon (RAC) without mercury leaching toxicity. The obtained RAC was a satisfactory mercury adsorbent with high specific surface area (632.9 m(2)/g) and abundant surface functional groups. Then the RAC was used to absorb mercury from HgCl2 solution. Effects of pH, adsorbent dose, agitation time and initial mercury concentration on mercury sorption were investigated. Reduction and ion exchange were mainly responsible for mercury sorption mechanisms. Adsorption process conforms to pseudo-second-order kinetic model and Langmuir adsorption isotherm model. The calculated adsorption capacity of RAC was 109.05 mg/g. The absorbed mercury was efficiently desorbed by MWH. High sorption capacity of RAC maintained after five times of cyclic sorption/desorption. This new process realized the recycling of secondary resource, providing a new idea for cleaner production of VCM in engineering applications. (C) 2018 Elsevier Ltd. All rights reserved.