An integrated circular approach to chromium remediation via adsorption, adsorbent regeneration, and ceramic...

Hexavalent chromium (Cr(VI)) contamination in water bodies remains a major environmental concern due to its high toxicity, persistence, and carcinogenicity. Among available remediation strategies, adsorption using natural and modified clays has emerged as a cost-effective and sustainable alternative. In this study, a natural clay from Entre Ríos, Argentina, was modified with hexadecyltrimethylammonium bromide (HDTMA-Br) to produce an organoclay, which was evaluated for Cr(VI) removal. Material characterization by XRD, FTIR, and pHpzc analysis supported successful surfactant incorporation and the presence of both mineral and organic functional groups. Batch experiments showed that the organoclay achieved over 80% Cr(VI) removal under strongly acidic conditions. Kinetic analysis followed a pseudo-second-order model, indicating surface-controlled adsorption, while intraparticle diffusion contributed to the process but was not the rate-limiting step. Although the Langmuir model provided the best statistical fit, the contribution of heterogeneous surface domains cannot be excluded, as reflected by the reasonable agreement with the Freundlich model. Regeneration studies demonstrated that the organoclay retained considerable adsorption capacity over successive cycles, showing only a moderate decline in performance. The chromium-loaded material was subsequently incorporated into ceramic matrices, where leaching tests confirmed effective immobilization, with concentrations below regulatory limits. The resulting ceramic products also exhibited adequate mechanical strength, supporting their potential reuse. Overall, the integration of adsorption, regeneration, and ceramic stabilization represents a sustainable and scalable strategy for Cr(VI) remediation, enabling both efficient contaminant removal and safe valorization of chromium-laden residues.