Hexavalent Chromium Removal by an Ascorbic Acid Functionalized Polymer Hydrogel Adsorbent: the Effect of Physicochemical Factors

High-concentration Cr-contaminated wastewater can cause serious environmental and public health problems. Therefore, this study proposed a method that uses ascorbic acid, a cationic copolymer gel-supported reducing agent, to remove hexavalent chromium, Cr(VI), from wastewater. This gel adsorbed Cr(VI) via an ion exchange process that uses N -[3-(dimethylamino) propyl] acrylamide methyl chloride quaternary monomer (DMAPAAQ) (DQ) and trivalent chromium, Cr(III), reduced by l -ascorbic acid (VC) via chelation and insoluble hydroxide formation induced by N, N -dimethylamino propylacrylamide monomer (DMAPAA) (DA). Furthermore, the effects of solution pH, initial Cr(VI) concentration, co-existing anions, contact time, and temperature on the reduction and removal processes facilitated by the DA/DQ and DA/DQ/VC gels were investigated. Both gels maintained a high adsorption efficiency at pH 3–6; however, the DA/DQ gel had a lower efficiency than the DA/DQ/VC gel in acidic, neutral, and weak alkaline environments. Adsorption isotherms suggested that both gels had a structurally homogeneous surface. Kinetics indicated that Cr(VI) adsorption by both gels was dominated by different sorption at low- or high-concentrations of Cr-contaminated wastewater. Thermodynamic parameters calculated using equations and plotting results indicated that the adsorption by both gels was an endothermic, irreversible, and spontaneous process.