Synthesized chitosan-zeolite composite matrix for the adsorption of chromium (VI) ions

Abstract

Chitosan–zeolite 3A composite (CS/Z) adsorbent was prepared to investigate the removal of Cr(VI) from aqueous solution. The chitosan (CS) was prepared from shrimp waste (shell) using chemical processes. The percentage yield and degree of deacetylation were 13.64% and 87.07%, respectively. The matrix formulation was obtained with a response surface methodology using a central composite design. The best matrix ratio of chitosan to zeolite was 1:7. This ratio was used for adsorption studies. Batch adsorption studies were carried out to investigate the optimum condition for the removal of Cr(VI) using CS/Z and the adsorbent was characterized using X-ray diffraction and scanning electron microscopy. The influences of solution pH, adsorption dosage, initial Cr(VI) concentration, and temperature on the removal processes were investigated. Adsorbent dosage of 0.25 g using 20 mg/L as the initial solution concentration showed maximum metal uptake, at optimum pH 2. The result obtained from equilibrium isotherm adsorption studies of Cr(VI) ion was analyzed in three adsorption models namely: Langmuir, Freundlich, and Temkin. The equilibrium studies carried out followed Langmuir isotherm with the highest correlation coefficient (R2) value of 1. The kinetic parameters were evaluated utilizing the pseudo-first-order, pseudo-second-order, and Elovich-second-order. It was shown that the adsorption of Cr(VI) ions can be described by the Elovich kinetic model, with a correlation coefficient of 0.96. Thermodynamic parameters studies revealed that the adsorption process was spontaneous and endothermic in nature. In comparison between CS/Z, Z, and C, the percentage of removals were 97%, 68%, and 50%, respectively. Thus, it can be deduced that CS/Z composite adsorbent is effective and efficient for the removal of Cr(VI) ion.