ARSENITE ADSORPTION UPON ACTIVATED CARBON AND ITS PVA-COMPOSITE
Sustainable process-product development & green chemistry
Environmental Engineering & Management (T1-3P)
Keywords: Arsenite adsorption, activated carbon-pva composite, thermodynamics, kinetics
Heavy metal ions introduced to the environment through industrial activities pose great threat upon environment and human health. Being one of the toxic trace elements, arsenic has been gaining public and scientific concern pertaining to its high toxicity and increased appearance in the biosphere. Of the two states of As existent in aquatic environment, arsenite, As(III) is more toxic than arsenate As(V). Chemical precipitation, membrane filtration, ion exchange, and adsorption are amongst the conventional methods applied for lowering the concentrations of arsenic in polluted waters below the maximum permissible level. Adsorption upon activated carbon is recognized as the most preferred and advantageous method mainly due to the high surface area, well developed porosity and structural features of the activated carbon, i.e. distribution and variety of heteroatoms and functional groups in its structure.
In this study, activated carbon and its pva composite were utilised in arsenite removal from wastewaters by adsorption. The effects of operation conditions, namely pH, adsorbent dosage, contact time and temperature on the extent removal were determined. Accordingly, the extent of removal was maximized after 16 hours of operation at pH of 4.5 and with 13 g/L adsorbent. Adsorption of arsenite was found to follow Langmuir isotherm with regression coefficient of 0.99. Kinetic analysis suggested that the rate adsorption was limited by both film and intraparticle diffusion. The adsorption process followed first order Lagergren equation. Mass transfer coefficients and rate constants of intraparticle diffusion were calculated. Thermodynamic analysis proved that the adsorption of arsenite was endothermic with ΔH of 18.51 kJ/mol. In above mentioned studies, synthetic solutions involving only arsenite were utilized. Operation conditions leading to maximum arsenite removal were tested using effluent from a galvanization facility involving other metals such as copper and nickel besides arsenite. In this case, the attained removal was significantly lower due to competition of ions.
In the second stage of experiments, activated carbon modified chemically by the production of carbon-polymer composites. The composite was prepared by sedimentation polymerization using polyvinylalcohol crosslinked with glutaraldehyde. With the modified adsorbent, the arsenite adsorption capacity of activated carbon was improved by 3.5% in the case of both synthetic wastewater and real effluent. Desorption studies were also conducted. The data showed that both activated carbon and its pva composite regained 95% of its original capacity in acidic media after 10 hours of regeneration. The capacity of modified material reduced by 67% after 5 successive cycles.
Presented Monday 17, 13:30 to 15:00, in session Environmental Engineering & Management (T1-3P).
