Removal of Co(II) Ions from Aqueous Solutions by Adsorption as Polyethylenimine Complexes

Heavy metals (HMs) form a distinct group within the vast range of organic and inorganic ecotoxicants. Because of their high solubility, heavy metals can exert mutagenic and toxic effects on all components of the biosphere. Among the most hazardous heavy metals is cobalt. In trace amounts, cobalt is an essential element for humans and animals; however, excessive cobalt intake can cause serious health disorders. Prolonged exposure to cobalt may lead to carcinogenic, teratogenic, or mutagenic effects in living organisms. Developing modern, efficient, and economically feasible methods for removing heavy metals, including cobalt, from contaminated water, therefore, remains a critical and urgent challenge. Adsorption using natural or synthetic, modified or unmodified adsorbents represents one of the most effective approaches for removing heavy metal ions from polluted water. This study examines the adsorptive removal of Co(II) ions from aqueous solutions using Filtrasorb 300 activated carbon premodified with Fe(III) oxide. This adsorbent shows high magnetic sensitivity, enabling a convenient and efficient separation from aqueous media. The study also demonstrates the potential of polymeric complexing agents—water-soluble polyethylenimines—to enhance the efficiency of Co(II) removal. The effects of several adsorption parameters, including pH, initial Co(II) concentration, polyethylenimine (PEI) concentration, and PEI molecular weight, on the adsorption capacity and removal efficiency of Co(II) were investigated. The results show that the extraction of Co(II) by the modified adsorbent depends on the stability and concentration of its complexes with PEI, which are influenced by both the molecular weight and the concentration of PEI in solution. Furthermore, the equilibrium adsorption data were analyzed using the Langmuir and Freundlich isotherm models.