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The adsorbed behavior of zeolite 13x was tested for the removal of chromium (Cr(VI)), nickel (Ni(II)), and cobalt (Co(II)) in single- and multi-solute (binary and ternary) systems, using a batch adsorption technique under different experimental conditions namely solution pH and initial metal-ion concentration. pH   6 was the optimum condition for the adsorption of Cr(VI), Ni(II), and Co(II). The removal rate decreased as the temperature and the initial concentration increased. Kinetics experiments indicated that the processes can be simulated by pseudo-second-order model. The Langmuir adsorption model fitted the experimental data reasonably well better than Freundlich, D–R, and Redlich–Peterson model for the three metal ions studied. The maximum monolayer adsorption capacity for Cr(VI), Ni(II), and Co(II) was 3.929, 6.195, and 10.389 mg/g, respectively. The main energy of adsorption (E), calculated as 8–16 kJ/mol, demonstrated chemical characteristics of adsorption process. Thermodynamic calculations showed that the adsorption of all metal ions onto zeolite 13x was feasible, endothermic in nature and the degrees of freedom increased at the solid–liquid interface during the adsorption. The sequential adsorption–desorption cycles showed that hydrochloric acid held good desorption on saturated zeolite. [ABSTRACT FROM PUBLISHER]

The adsorption of Cr(VI) and As(III) by amino-functionalized SBA-15 (NH-SBA-15) from single and binary systems were investigated in this work. The effects of pH and temperature on the adsorption of NH-SBA-15 were studied. Adsorption kinetics, isotherm model, and thermodynamics were studied to analyze the experimental data. pH 2 was the optimum condition for the adsorption of Cr(VI) and pH 4 for As(III) adsorption. Increasing temperature had a positive effect on the removal of both Cr(VI) and As(III). The Freundlich isotherm model can depict the adsorption process best. The pseudo-second-order kinetic model fitted well with the kinetic data of Cr(VI) and As(III) in the single-component system. In the binary system, the adsorption of As(III) by NH-SBA-15 was slightly enhanced with the presence of Cr(VI); however, As(III) had no obvious effect on the removal of Cr(VI). Regeneration experiments indicated that 0.1 mol/L NaHCO was an efficient desorbent for the recovery of Cr(VI) and As(III) from NH-SBA-15; the desorption rates for Cr(VI) and As(III) were 91.6 and 33.59 %, respectively. After five recycling cycles, the removal rates were 88 and 7 % for Cr(VI) and As(III) adsorption by NH-SBA-15, respectively. [ABSTRACT FROM AUTHOR]

The comparative and competitive adsorption of Cr(VI) and Ni(II) in single and binary systems using coconut shell activated carbon (CSAC) was investigated. The CSAC was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM). The effects of pH, initial metal concentration, and temperature on the adsorption of metal ions were studied. Cr(VI) removal was found to be maximum (94.5 %) at pH = 2.0. While, Ni(II) removal was found to be maximum at pH = 9.0 (58.92 %). The adsorption capacity of Cr(VI) was greater than that of Ni(II) in single component system. Parameters of adsorption isotherm model, kinetics, and thermodynamics were calculated. The single ion equilibrium adsorption data were fitted to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The Langmuir and Freundlich models represented the equilibrium data better than the D-R model. The result of the fitting of D-R isotherm model indicated a physical adsorption process. The adsorption kinetic data of Cr(VI) and Ni(II) were found fitting well in pseudo second-order equation both in single and binary system ( r > 0.99) and intraparticle diffusion was the rate controlling step. The negative Δ G° and the positive Δ H° indicated the spontaneous and endothermic nature of the adsorption process. The extended Langmuir isotherm model fitted well with the competitive adsorption data of Cr(VI) and Ni(II). For the desorption experiments, EDTA showed the maximum desorption efficiency of 69 % for Cr(VI) and 81 % for Ni(II). [ABSTRACT FROM AUTHOR]

This study evaluates the behavior of coconut charcoal (AC) to adsorb Cr(VI), As(III), and Ni(II) in mono- and multicomponent (binary and ternary) systems. Batch experiments were carried out for mono- and multicomponent systems with varying metal ion concentrations to investigate the competitive adsorption characteristics. The adsorption kinetics followed the mechanism of the pseudo-second-order equation in both single and binary systems, indicating chemical sorption as the rate-limiting step of adsorption mechanism. Equilibrium studies showed that the adsorption of Cr(VI), As(III), and Ni(II) followed the Langmuir model and maximum adsorption capacities were found to be 5.257, 0.042, and 1.748 mg/g, respectively. In multicomponent system, As(III) and Ni(II) adsorption competed intensely, while Cr(VI) adsorption was much less affected by competition than As(III) and Ni(II). With the presence of Cr(VI), the adsorption capacities of As(III) and Ni(II) on AC were higher than those in single system and the metal sorption followed the order of Ni(II) > As(III) > Cr(VI). The results from the sequential adsorption-desorption cycles showed that AC adsorbent held good desorption and reusability. [ABSTRACT FROM AUTHOR]