Role of surface chemistry of activated carbon for anchoring iron particles by forced hydrolysis and evaluation of iron-loaded adsorbents for Cr (VI) adsorption

This research aimed to assess the role of granular activated carbon (GAC) functional groups for anchoring iron particles by forced hydrolysis and the effect of iron-loaded GAC for the adsorption of Cr (VI). First, to modify the surface chemistry of the GAC, the adsorbent was treated by oxidation, heating, and ammonia soaking. Next, the anchorage of iron on raw and modified GAC by forced hydrolysis was conducted. Subsequently, adsorbents were characterized, and adsorption tests were performed at pH 6 and 25 degrees C. Findings revealed that the incorporation of acid functional groups on the GAC surface by oxidation allowed an iron anchoring (1.5%) higher than the heat-treated GAC (0.2%). Besides, forced hydrolysis treatment significantly improved the Cr (VI) adsorption capacity at equilibrium concentrations lower than 150 mg/L. Heat-treated GAC with iron achieved the best Cr (VI) uptake capacity (57 mg/g) and the fastest adsorption kinetics of the studied adsorbents. Cr (VI) desorption (98%) from the best adsorbent (iron-loaded and heat-treated GAC) was attained with a 0.1 N NaOH-NaCl solution, suggesting an adsorption mechanism mainly by physical attraction. In conclusion, the surface chemistry of GAC plays a significant role in the anchorage of iron particles, and iron particles improve Cr (VI) adsorption.