Superior Competitive Adsorption Capacity of Natural Bentonite in the Efficient Removal of Basic Dyes from Aqueous Solutions

Innovative adsorbents based on bentonite mining waste for removal of cationic dyes from wastewater

Waste rock from bentonite mining (WRBM) was evaluated as potential adsorbents for removing crystal violet (CV) and methylene blue (MB) cationic dyes from contaminated water. The waste samples (AM01, AM02, and AM03) were collected from different locations of the bentonite mine and characterized through X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, N₂ adsorption/desorption, and cation exchange capacity. The adsorption efficiency of CV and MB dyes was investigated through the effect of initial concentration, contact time, pH, the dosage of adsorbent, and temperature. Sample AM02 showed the largest surface area (69.13 m²/g) and the best adsorptive performance for both dyes, with removal more significant than 90%. The adsorption of CV and MB in the waste followed the Langmuir isothermal model. Samples AM01 and AM02 followed the pseudo-second-order (PSO) kinetic model, while AM03 better fitted the Elovich kinetic model. The enthalpy (ΔH), entropy (ΔS), and Gibbs energy (ΔG) were evaluated as adsorption parameters. The process of adsorption of CV and MB dyes in the waste was predominantly endothermic and occurred spontaneously. WRBM samples proved to be a promising candidate for removing cationic dyes present in water.

Characterization of amphoteric bentonite-loaded magnetic biochar and its adsorption properties for Cu2+ and tetracycline

To realize simultaneous adsorption of heavy metal and antibiotic pollutants by a BC-based recyclable material, Fe₃O₄ magnetic biochar (MBC) was prepared by co-precipitation method. Then different ratios of dodecyl dimethyl betaine (BS-12)-modified bentonite (BS-B) were loaded on the surfaces of biochar (BC) and MBC to prepare BS-B-loaded BC and MBC composites, called BS-B/BC and BS-B/MBC, respectively. The physicochemical and structural properties of the composites were characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, specific surface area (S_BET) analysis, and vibrating sample magnetometry, and the adsorption efficiencies of BS-B/BC and BS-B/MBC to Cu²⁺ and tetracycline (TC) were studied. The following results were obtained. (1) Compared with BS-B/BC, BS-B/MBC had decreased pH and cation exchange capacity (CEC) and increased S_BET. The pH, CEC, and S_BET of BS-B/BC and BS-B/MBC decreased with the increase in the BS-12 proportion of BS-B. The surface of BS-B/MBC became rough after Fe₃O₄ loading. (2) The residual rate of BS-B/MBC was higher than that of BS-B/BC after high-temperature combustion, and the residual rate decreased with the increase in the BS-12 proportion of BS-B. The 2D infrared spectra showed that Fe₃O₄ and BS-12 were modified on the surface of BS-B/MBC. MBC and BS-B/MBC had splendid magnetism and could be separated by external magnetic field. (3) Compared with unmagnetized ones, the adsorption effects of Cu²⁺ and TC on different BS-B/MBCs improved, and the average adsorption rate reached the largest value of 91.92% and 97.76%, respectively. Cu²⁺ and TC adsorptions were spontaneous, endothermic, and entropy-increasing processes. The pH and S_BET of the material had a great influence on Cu²⁺ and TC adsorptions, respectively, than CEC.