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<p>Chromium (Cr) contamination from Chromite Ore Processing Residue (COPR) dumps continues to impact the Rania-Khan Chandpur, Kanpur region of India, posing serious risks to soil-groundwater systems. This study quantifies the adsorption behaviour of Cr in locally collected silty loam soil and IS 650–1991 Grade-II sand as a control under simulated variable environmental conditions to elucidate the governing mechanisms. Batch adsorption experiments were performed under varying pH (4, 7, 11), temperature (25&#xa0;°C, 40&#xa0;°C), and water content (0.6, 0.8, 1.0) conditions. Kinetic models, including Pseudo-first order (PFO), Pseudo-second order (PSO), Intraparticle diffusion (IPD), and Liquid-film diffusion (LFD), as well as adsorption isotherm (Linear, Langmuir, Freundlich) models were applied, and thermodynamic (ΔH°, ΔG°, ΔS°) parameters were estimated to interpret the adsorption mechanisms. The silty loam soil (from Rania site) exhibited a significantly higher adsorption capacity (Qₑ = 13.507&#xa0;mg g⁻¹) compared to sand (1.407&#xa0;mg g⁻¹), mainly due to its higher organic matter content (2.01%) and porosity (56.17%). Adsorption followed PSO kinetics (R² = 0.96–0.99), indicating chemisorption, while the Freundlich model (1/<i>n</i> = 0.66–0.83) showed favourable heterogeneous adsorption. Thermodynamic parameters (ΔH° = 4.54&#xa0;kJ mol⁻¹; ΔG° = 9.25-9.72&#xa0;kJ mol⁻<sup>1</sup>) confirmed an endothermic and non-spontaneous process enhanced at higher temperature. These findings provide mechanistic insights into Cr retention in soils from COPR-affected regions, supporting future column and 3D tank-scale transport studies and contributing towards United Nations Sustainable Development Goals: SDG 6 (Clean Water) and SDG 15 (Life on Land).</p> Graphical Abstract <p></p> <p>This graphical abstract offers a concise overview of the methodologies and findings of the study. It shows the site soil collection from the COPR-affected region of Rania-Khan Chandpur. The left panel illustrates the batch experimental setup, while the right section depicts kinetic, isotherm, and thermodynamic analyses and results and conclusions. The experiment was designed under variable pH (4, 7, 11), water content (0.6, 0.8, 1.0), and temperature (25˚C and 40˚C) for adsorption kinetics, whereas the adsorption isotherm experiment was designed at variable pH (4, 7, 11) and Cr concentration (10 mgL<sup>− 1</sup>, 20 mgL<sup>− 1</sup>, 30 mgL<sup>− 1</sup>, 40 mgL<sup>− 1</sup> and 50 mgL<sup>− 1</sup>). PSO kinetics indicate chemisorption as the dominant mechanism, as well as the adsorption capacity of soil collected from Rania-Khan Chandpur, which is higher than the IS II grade sand, and Freundlich–Langmuir modelling confirms heterogeneous surface adsorption. The thermodynamic study shows an endothermic (ΔH° = 4.54&#xa0;kJ mol⁻¹) and non-spontaneous (ΔG° = 9.25-9.72&#xa0;kJ mol⁻¹) process enhanced by higher temperature. The study emphasizes the environmental relevance by linking improved Cr retention mechanisms to SDGs, promoting sustainable soil and groundwater protection in COPR-impacted areas.</p>

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Experimental Assessment of Chromium Adsorption under Variable Environmental Conditions in Soil from the COPR-affected Site at Rania–Khan Chandpur, India

  • 期刊论文

  • 发表日期：

    2026年6月26日

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  • Vaibhav Deoli,
  • Pankaj Kumar Gupta,
  • Anushree Malik,
  • Kamal Kishore Pant

摘要

Chromium (Cr) contamination from Chromite Ore Processing Residue (COPR) dumps continues to impact the Rania-Khan Chandpur, Kanpur region of India, posing serious risks to soil-groundwater systems. This study quantifies the adsorption behaviour of Cr in locally collected silty loam soil and IS 650–1991 Grade-II sand as a control under simulated variable environmental conditions to elucidate the governing mechanisms. Batch adsorption experiments were performed under varying pH (4, 7, 11), temperature (25 °C, 40 °C), and water content (0.6, 0.8, 1.0) conditions. Kinetic models, including Pseudo-first order (PFO), Pseudo-second order (PSO), Intraparticle diffusion (IPD), and Liquid-film diffusion (LFD), as well as adsorption isotherm (Linear, Langmuir, Freundlich) models were applied, and thermodynamic (ΔH°, ΔG°, ΔS°) parameters were estimated to interpret the adsorption mechanisms. The silty loam soil (from Rania site) exhibited a significantly higher adsorption capacity (Qₑ = 13.507 mg g⁻¹) compared to sand (1.407 mg g⁻¹), mainly due to its higher organic matter content (2.01%) and porosity (56.17%). Adsorption followed PSO kinetics (R² = 0.96–0.99), indicating chemisorption, while the Freundlich model (1/n = 0.66–0.83) showed favourable heterogeneous adsorption. Thermodynamic parameters (ΔH° = 4.54 kJ mol⁻¹; ΔG° = 9.25-9.72 kJ mol⁻1) confirmed an endothermic and non-spontaneous process enhanced at higher temperature. These findings provide mechanistic insights into Cr retention in soils from COPR-affected regions, supporting future column and 3D tank-scale transport studies and contributing towards United Nations Sustainable Development Goals: SDG 6 (Clean Water) and SDG 15 (Life on Land).

Graphical Abstract

This graphical abstract offers a concise overview of the methodologies and findings of the study. It shows the site soil collection from the COPR-affected region of Rania-Khan Chandpur. The left panel illustrates the batch experimental setup, while the right section depicts kinetic, isotherm, and thermodynamic analyses and results and conclusions. The experiment was designed under variable pH (4, 7, 11), water content (0.6, 0.8, 1.0), and temperature (25˚C and 40˚C) for adsorption kinetics, whereas the adsorption isotherm experiment was designed at variable pH (4, 7, 11) and Cr concentration (10 mgL− 1, 20 mgL− 1, 30 mgL− 1, 40 mgL− 1 and 50 mgL− 1). PSO kinetics indicate chemisorption as the dominant mechanism, as well as the adsorption capacity of soil collected from Rania-Khan Chandpur, which is higher than the IS II grade sand, and Freundlich–Langmuir modelling confirms heterogeneous surface adsorption. The thermodynamic study shows an endothermic (ΔH° = 4.54 kJ mol⁻¹) and non-spontaneous (ΔG° = 9.25-9.72 kJ mol⁻¹) process enhanced by higher temperature. The study emphasizes the environmental relevance by linking improved Cr retention mechanisms to SDGs, promoting sustainable soil and groundwater protection in COPR-impacted areas.