Adsorption of haloforms onto GACs: Effects of adsorbent properties and adsorption mechanisms

The adsorption of three haloforms (CHCl3, CHBr3 and CHI3) was studied using five different granular activated carbons (GACs), including acid washing carbon, coconut-shell carbon, briquetting carbon, coal and fibred carbon. The adsorption isotherms were fitted well using Freundlich model, and adsorption kinetics were fitted well using pseudo-second-order model. CHI3 was adsorbed most efficiently, followed by CHBr3 and CHCl3. Fibred carbon was the most efficient adsorbent for the studied haloforms. The adsorption capability of each GAC was calculated using the pseudo- second-order model which was then correlated to adsorbent properties. Generally, the surface area of GAC did not highly correlate to the amount of haloform adsorption. Highly positive correlations with methylene blue and iodine number were observed for CHBr3 and CHI3 adsorption capacity, but not for CHCl3. Micropores were correlated with CHCl3 adsorption capacity. Moreover, three models, including intraparticle diffusion, Byod kinetic and diffusion-chemisorption were used to illustrate the mechanisms of haloform adsorption mechanism. Film diffusion was determined to be the rate-limiting process and haloforms were adsorbed via chemical adsorption. The results of adsorption rate and capacity are crucial for practical application of haloform removal via GAC process.