article · Chemical Physics Impact
This research examines the removal of methylene blue dye from water using natural and purified clay minerals, specifically smooth clay, rigorous clay, and bentonite clay. Mineralogical characterisation confirmed that bentonite clay is primarily swelling smectite, whereas the other clays contain smectite mixed with kaolinite, illite, and chlorite. Removing impurities raised both cation exchange capacity and specific surface area across all samples. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetic models. Purification substantially enhanced dye uptake, with purified bentonite achieving an adsorption capacity of 1383 mg/g compared to 681.85 mg/g in its natural form. Thermodynamic assessments demonstrated that the adsorption process is spontaneous, endothermic, and governed by chemisorption. The findings indicate that purified clays provide viable alternatives to expensive commercial adsorbents.
Industrial dyes such as methylene blue can pollute water systems, requiring effective and affordable treatment solutions. Commercial adsorbents are often costly, making water decontamination expensive. Demonstrating that readily available natural clays can be purified to dramatically improve their dye-capturing performance highlights an accessible and potentially economical approach for industrial wastewater purification.
This work represents early-stage laboratory research applicable to wastewater remediation and industrial dye removal. It could enable industrial operators and effluent treatment facilities to replace costly commercial adsorbents with cheaper purified clays. As the evidence is limited to bench-scale optimization of parameters such as contact time, temperature, and pH, further pilot-scale validation is needed before practical commercial adoption.
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The present work explores the optimization of experimental conditions for the adsorption of the organic cationic dye methylene blue (MB) by natural and purified clays. The adsorption capacities of samples were determinate to evaluate the efficiency of the purification process. At first, we performed mineralogical and textural analysis of the clay minerals, namely, smooth clay (SC), rigorous clay (RC) and bentonite clay (BC), using various techniques, particularly, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). The characterizations data showed that SC and RC are mainly composed of smectite associated with kaolinite, illite and chlorite. While BC is considered a mesoporous and swelling clay with smectite as the major component. The cation exchange capacity (CEC) was determinate as a 6.30 meq/100g, 10.69 meq/100g and 32.64 meq/100g for SC, RC and RC natural samples respectively. It was noticed that the CEC as well as the specific surface area increase once the impurities associated with the clay are removed. A preliminary study was carried out to elucidate the influence of different parameters; such as contact time, exchangeable cation, solute concentration, temperature and pH on MB adsorption in aqueous solution by clays. The adsorption equilibrium data were analyzed by the linear and nonlinear forms of the Langmuir and Freundlich isotherm models. The Langmuir isotherm fitted well with the experimental data, and the pseudo-second-order kinetic model represented appropriately the adsorption kinetics of MB dye. Moreover, purified clays showed improved adsorption capacity for MB compared to pristine ones: 147.64; 257.69 and 1383 mg/g versus 128.75; 193.4 and 681.85 mg/g for SC, RC and BC respectively. This is attributed to a suitable specific surface, ion exchange capacity and electrostatic interactions as result of a more adequate texture and composition of our treated clays. The thermodynamic studies reveled negative Gibbs free energy change (ΔG) values (from -6.293 to -18.608 KJ.mol−1), positive enthalpy change (ΔH) values, exceeding 40 kJ/mol and positive entropy change (ΔS) values confirming the spontaneous, endothermic and chemisorption nature of the MB adsorption process. The results show that the tested purified clays are efficient in MB removal and can be used as an alternative to the commercial adsorbents, which are often relatively expensive.
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DOI: 10.1016/j.chphi.2023.100405
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