Heavy metals adsorption using CDW adsorbents: A sustainable path for water purification

Effective removal of heavy metals from water is crucial for human health and environmental protection, and adsorbents provide a sustainable, cost-effective treatment solution. This study is the first to investigate Low-Density Concrete (LDC) for removing selected heavy metals (Pb²⁺, Co²⁺, and Mn²⁺) from water. The adsorbent was characterised using X-ray fluorescence (XRF), Fourier Transform Infrared spectrophotometry (FTIR), Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD) analysis, and Field Emission Scanning Electron Microscopy (FE-SEM). The One-Factor-at-A-Time (OFAT) method optimised the essential parameters affecting the metal removal. Eight different isotherm models were used to determine the adsorption parameters and elucidate the associated sorption mechanism. Then, its kinetic behavior and selectivity for decontamination were analyzed. The outcomes demonstrated that the adsorption capacities for Pb²⁺, Mn²⁺, and Co²⁺ were 43.1, 23.5, and 15.2 mg g⁻¹, respectively. Moreover, the second-order kinetic rate constants for Pb²⁺, Mn²⁺, and Co²⁺ were determined to be 1.99, 0.076, and 0.49 g mg⁻¹ min⁻¹, respectively. As a novel contribution, the regeneration process of heavy metal adsorption is modelled by Thales-based theorem. In this study, synthetic wastewater was used, while regeneration conditions simulated industrial effluents to enhance real-world relevance. Finally, the applied construction and demolition waste (CDW) adsorbent is evaluated by Sustainable Material Management, EPA models. The isothermal modelling illustrated that the adsorption of Pb²⁺, Co²⁺, and Mn²⁺ onto LDC wastes is done physically and on the heterogeneous surface as multilayer adsorption. The Thales-based model demonstrated that after nine cycles of adsorption and formal regeneration with acid, the LDC adsorbent consistently maintained lead concentrations below the World Health Organization (WHO) standard.