Sorption Studies of Chromium(VI) onto Cerium/Ferroferric Oxide Composites

Fabrication, Characterization and Adsorption Investigation of Nano Zinc Oxide–Sodium Alginate Beads for Effective Removal of Chromium (VI) from Aqueous Solution

Alginate–zinc oxide (Alg–ZnO) biocomposite was synthesized and tested as a chromium ions Cr(VI) adsorbent for environmental applications. Alg–ZnO biocomposite was prepared by the interaction between sodium alginate biopolymer and zinc oxide nanoparticles (ZnO–NPs), prepared by modified wet chemical method. The solid adsorption characteristics of the synthesized Alg–ZnO biocomposite were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–Vis spectroscopy. Adsorption isotherms of chromium ions on the prepared Alg–ZnO biocomposite were investigated with varying the initial concentration of Cr(VI) under different application conditions such as pH, contact time, adsorbent dosage, and temperature. Adsorption of Cr(VI) was investigated by different isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. Maximum adsorption capacities (31.09 and 34.63 mg/g) were achieved by ZnO–NPs and Alg–ZnO, respectively at 25 °C. The results of isotherm models indicate the perfect applicability of Langmuir and Dubinin–Radushkevich models, revealing the dominance of monolayer and the physisorption of chromium ions onto the studied adsorbents.

Sorption of Palladium(II) from Aqueous Solution Using Diphenylthiocarbazone Immobilized onto Kieselguhr

Kieselguhr was immobilized with diphenylthiocarbazone (dithizone) and utilized as a new sorbent to extract palladium ions from an aqueous solution. The physicochemical features of the immobilized kieselguhr (K–Dz) were specified by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and thermogravimetric analysis–differential thermal analysis. The average crystal size of the prepared material was found to be 24.41 nm. The sorption potential of the immobilized kieselguhr for the extraction of Pd(II) and La(III) in a batch mode was studied. The effects of pH, shaking time as well as the initial concentration of metals have been examined. The results demonstrate that the optimum pH was found to be 4.5 and the equilibrium was attained within 15.0 min. The adsorption kinetics and equilibrium data were well described by the pseudo-second-order kinetic model and Sips isothermal model with a maximum sorption capacity of 20.3 (mg/g). Thermodynamic parameters of the studied metal ions show that the process is spontaneous and endothermic in nature. The desorption process of Pd(II) was highly managed using acidified thiourea giving a desorption percent of approximately 80.0%. The separation possibility of Pd(II) from some metal ions such as La(III) was achieved successfully. The developed (K–Dz) composite method was applied for the recovery and separation of Pd(II) and other metal ions from a simulated automotive catalyst leachate solution. The results indicated that the (K–Dz) composite has a good reusability potential.

Chromium(VI) Removal from Water by Lanthanum Hybrid Modified Activated Carbon Produced from Coconut Shells

Cr(VI) is considered to be the most hazardous and toxic oxidation state of chromium and hence the development of effective removal technologies, able to provide water with Cr(VI) below the drinking water limits (US EPA 100 μg/L, European Commission 50 μg/L, which will be reduced to 25 by 2036) is a very important issue in water treatment. This study aimed at examining the performance of activated carbon produced from coconut shells, modified by lanthanum chloride, for Cr(VI) removal from waters. The structure of the formed material (COC-AC-La) was characterized by the application of BET, FTIR and SEM techniques. The effect of the adsorbent's dosage, pH value, contact time, initial Cr(VI) concentration and water matrix was examined with respect to Cr(VI) removal. The results indicated that the maximum Cr(VI) removal was observed at pH 5; 4 h contact time and 0.2 g/L of adsorbent's dosage was adequate to reduce Cr(VI) from 100 μg/L to below 25 μg/L. Freundlich isotherm and pseudo-second order kinetic models fitted the experimental data sufficiently. The maximum adsorption capacity achieved was 6.3 μg/g at pH 5. At this pH value, the removal percentage of Cr(VI) reached 95% for an initial Cr(VI) concertation of 30 μg/L. At pH 7 the corresponding efficiency was roughly 60%, resulting in residual Cr(VI) concentrations below the anticipated drinking water limit of 25 μg/L of total chromium, when the initial Cr(VI) concentration was 50 μg/L. Consecutive adsorption and regeneration studies were conducted using 0.01 M of NaOH as an eluent to evaluate the reusability of the adsorbents, Results showed 20% decrease of adsorption capacity after 5 regeneration cycles of operation.

Adsorption Performance of Cd(II) by Chitosan-Fe3O4-Modified Fish Bone Char

In order to develop a low-cost, fast, and efficient adsorbent, the fish bone charcoal B₆₀₀ prepared at 600 °C was modified by chitosan (Cs) and Fe₃O₄ to produce the material Cs-Fe₃O₄-B₆₀₀. Results showed that Cs-Fe₃O₄-B₆₀₀ had magnetic responsiveness and can achieve solid–liquid separation, macropores disappeared, pore volume and specific surface area are increased, and amino functional groups appear on the surface. The adsorption process of Cd(II) by Cs-Fe₃O₄-B₆₀₀ conformed best to the pseudo-second order kinetics model and the Langmuir model, respectively. The behavior over a whole range of adsorption was consistent with chemical adsorption being the rate-controlling step, which is a very fast adsorption process, and the isothermal adsorption is mainly monolayer adsorption, which belongs to favorable adsorption. In addition, the saturated adsorption capacity obtained for the Cs-Fe₃O₄-B₆₀₀ to Cd(II) was 64.31 mg·g⁻¹, which was 1.7 times than B₆₀₀. The structure and morphology of Cs-Fe₃O₄-B₆₀₀ were characterized through SEM-EDS, TEM, FTIR, and XRD, indicating that the main mechanism of Cs-Fe₃O₄-B₆₀₀ and Cd(II) is mainly the complexation of amino groups, and it also includes part of the ion exchange between Cd(II) and Fe₃O₄. Therefore, Cs-Fe₃O₄-B₆₀₀ can be employed as an effective agent for remediation of Cd contaminated water.