The preparation, characterization, and environmental application of crosslinked chitosancoated bentonite (CCB) beads for tartrazine adsorption have been investigated. CCB beads were characterized by using Fourier transform infrared spectrophotometer (FTIR), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution analyses were also determined. The values of pH of the aqueous slurry and pH of zero point charge (pH ZPC ) were almost equal. The adsorption at equilibrium of tartrazine was found to be a function of pH of the solution, stirring rate, contact time, and tartrazine concentration. The optimum conditions for tartrazine adsorption were pH 2.5, stirring rate of 400 rpm and contact time of 80 min. Pseudo-first-order and pseudo-second-order models were used to analyze the kinetics of adsorption with the latter found to agree well with the kinetics data, suggesting that the rate determining step may be chemisorption. The two most common isotherm models, Langmuir and Freundlich, were used to describe the adsorption equilibrium data. On the basis of Langmuir isotherm model, the maximum adsorption capacities were determined to be 250.0, 277.8, and 294.1 mg g −1 at 300, 310, and 320 K, respectively. Desorption studies were carried out at different concentrations of EDTA, H 2 SO 4 , and NaOH. All desorbing solutions showed poor recovery of tartrazine.

The removal of Malachite green (MG) from aqueous solutions by cross-linked chitosan coated bentonite (CCB) beads was investigated and the CCB beads were characterized by Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. Solubility and swelling tests were performed in order to determine the stability of the CCB beads in acidic solution, basic solution and distilled water. The amount of MG adsorbed was shown to be influenced by the initial pH of the solution, contact time and the initial MG concentration. A kinetic study indicated that a pseudo-second-order model agreed well with the experimental data. From the Langmuir isotherm model, the maximum adsorption capacity of MG was found to be 435.0 mg g -1 . Desorption tests were carried out at different concentrations of EDTA, H 2 SO 4 and NaOH. However, all desorbing solutions showed zero recovery of MG at all concentrations.

Monosodium glutamate functionalized chitosan (MSGC) beads were synthesized and used as an adsorbent for recovering precious cerium ion from aqueous solutions. Several parameters which can affect adsorption efficiency such as effect of pH and adsorbent dosage have been investigated. The optimum pH for Ce (III) adsorption was 4. The rate of Ce (III) uptake was fast as the time to reach equilibrium was less than 10 min. Based on the applied kinetic model, Ce (III) adsorption onto MSGC fitted well with pseudo-second-order model. The maximum adsorption capacity recorded from the Langmuir isotherm model was 369.0 mg g-1 at 300 K.

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Xanthated chitosan (XC) beads synthesized from the reaction between sulphur and hydroxyl groups were applied to adsorb rare earth metal ion, Nd (III). Adsorption of Nd (III) was found to be a function of pH of initial solution, adsorbent dosage and contact time. The optimum conditions for Nd (III) adsorption were at pH 3 and adsorbent dosage of 0.02 g. Rapid adsorption process was observed as it took only 10 min for reaching the equilibrium state. Chemisorption was identified as the rate limiting step and the kinetics data correlated well with the pseudo-second-order model.

In this study, cross-linked chitosan coated bentonite (CCB) beads were prepared as a potential adsorbent to adsorb Cu(II) from aqueous solution. As adsorption capacity was affected by several conditions such as initial Cu(II) concentrations, stirring period and temperature, these parameters were important to be investigated. Three different concentrations of Cu(II) were used in the kinetic study, which were 10, 25 and 50 mg/L. The experimental data was found fitted well with the pseudo-second-order model, an indication that chemisorption was the rate controlling mechanism. Isotherm study was done at different temperatures with concentration of Cu(II) was varied from 10 to 200 mg/L. The maximum monolayer adsorption of Cu(II) on CCB beads based on Langmuir isotherm model at 300, 310 and 320 K were 114.94, 119.05 and 77.52 mg/g, respectively. Therefore, adsorption of Cu(II) was preferred at lower temperatures. This work proved CCB beads as an effective adsorbent for fast removal of Cu(II) from wastewater solutions.