Use of Caprolactam to Enhance Iron Ion Adsorption by an Anthracite-Based Carbon Sorbent

Abstract

This study investigates the potential to improve the adsorption capacity of a cost-effective domestic carbon sorbent toward iron (II) ions. The sorbent used was a carbon material based on anthracite, Purolat-Standard, along with its samples modified with caprolactam solutions. The impact of modification on the porous structure and surface properties of the material was examined. None of the applied modification methods (using sulfuric acid and/or caprolactam) caused significant changes in the porous structure. A comparison of micrographs of the carbon material before and after iron (II) adsorption suggests that iron ions may become fixed on surface fractures and defects during adsorption from aqueous solutions. Spectroscopic studies revealed that the modification process alters both the qualitative and quantitative composition of surface functional groups. Adsorption of iron ions onto the original and modified carbon sorbent samples was studied under static conditions. The Langmuir and Dubinin–Radushkevich isotherm models were employed to interpret the results and analyze the interactions between iron ions and the carbon materials. Key adsorption parameters were calculated. The findings suggest that iron ions can bind to the sorbent surface through both ion exchange and complexation with functional groups on the carbon surface. It was shown that the most promising sorbent for iron (II) removal from natural waters is the carbon material modified with caprolactam.