Kinetics and mechanism of Pb(II), Cd(II) and Cu(II) adsorption on ferrochrome ash from aqueous solutions

There has been significant interest in the development of novel approaches and techniques that can effectively ensure the supply of safe and uncontaminated water to human communities. Among the several treatment strategies available, adsorption is particularly favourable due to its inherent versatility in terms of design and operation. Additionally, a diverse selection of cost-effective adsorbents has been successfully employed for the purpose of remediating heavy metal-contaminated wastewater. The current study employed an industrial waste ferrochrome ash (FCA), as a novel adsorbent to eliminate Pb(II) and Cd(II) ions from aqueous solutions. To accomplish this goal, the FCA underwent characterisation by XRF, XRD, and SEM-EDS analyses. Afterwards, batch adsorption experiments were carried out and the maximum adsorption capacities were obtained as 1519 and 84.5 for Pb(II) and Cd(II) mg/g, respectively which makes the FCA an applicable adsorbent for their removal from wastewater. Furthermore, it was found out that the adsorption of Pb(II) and Cd(II) on FCA fits the pseudo-second order (PSO) kinetics and Langmuir isotherm models. Based on the findings, it can be inferred that the adsorption mechanism of Pb(II) and Cd(II) followed a monolayer chemisorption process, characterised by the valency forces between the metal ions and the surface of the adsorbent. Furthermore, adsorption capacity of the WGFCA was examined at different temperatures and it was found out that the adsorption of Pb(II) and Cd(II) on WGFCA is an exothermic and spontaneous process. Additionally, an examination was conducted on the desorption characteristics and the structural integrity of the WGFCA, revealing that it may be successfully restored under acidic conditions for subsequent utilisation. Finally, competitive adsorption characteristics of Pb(II), Cd(II) and Cu(II) ions were investigated and the sequence of adsorption capacity in such multi-cationic systems was found to be Pb(II)>Cu(II)>Cd(II).