Development of new adsorbent materials for the removal of arsenic(iii)and chromium (VI) from water & its mathematical modelling

Abstract

In current civilization, the aggressive development in industries and continuous innovation in technologies have changed our living surroundings bringing all kind of pollution. Heavy metal pollution in water is of major concern because of its detrimentaleffecton human health.
The present work was aimed to develop environment friendly hybrid materials and compositesasnovel adsorbents by three standard methods such as sol-gel, microwave assisted and co-precipitation techniques. Zirconium oxide ethanolamine (ZrO-EA), zirconium polyacrylamide (ZrPACM-43), lanthanum diethanolamine (La-DEA), cerium oxide hydroxylamine hydrochloride (Ce-HAHCl) and cerium oxide polyaniline composite (CeO2/PANI) were synthesized for the purpose of removal of arsenic (III) andchromium (VI)removal from water. The adsorbent materials were characterized by chemical analysis, specific surface area (BET), XRD, FTIR, TGA, DTA, Fe-SEM/SEM, EDX etc. Batch and column adsorption experiments were carried out for the removal of arsenic (III) and chromium (VI) from synthetic contaminated water. In batch experiments, influence of various important parameters such as, adsorbent dose, solution pH, contact time, temperature, competing ions and initial concentration were studied for the removal of arsenic (III) and chromium (VI). In column adsorption experiments, influence of bed depth, flow rate and initial concentration were varied and studied. Regeneration and reusability studies were carried out to understand the practical applicability of the adsorbent materials. The materials synthesized were excellent hybrid materials for removal of arsenic and chromium from water.
The removal of the arsenic (III) from water byusing hybrid material zirconium (IV) oxideethanolaminefor initial concentration 10mg/L was found to be 98% at pH 7. With specific surface area of 201.62 m2/g, and highest removal efficiency the hybrid material (ZrO-EA) represents excellent hybrid material for removal of arsenic (III) from water. Similarly the removal of arsenic (III) by using hybrid material zirconium polyacrylamide (ZrPACM-43) was98.22% under optimum conditions. The maximum adsorption capacity (qo) calculated from Langmuir isotherm was found to be 41.48mg/g. The adsorption data are best supported to Freundlich model and D–R model with maximum adsorption capacity of 0.20 and 0.80 mg/g. The reusability study signifies that the material can be easily reused up to eight cycles with maximum removal of 60%. Similar study was carried out for removal of hexavalent chromium by using lanthanum diethanolamine hybrid material (La-DEA), the maximum removal of Cr(VI) with initial concentration of 10 mg/L is found to be 99.31% at pH- 5.6, dose- 8 g/L and equilibrium time of 50 min. Adsorption kinetics studies reveal that the adsorption process followed first-order kinetics and intraparticle diffusion model with correlation coefficients (R2) of 0.96 and 0.97, respectively. The adsorption data were best fitted to linearly transformed Langmuir isotherm with correlation coefficient (R2) of 0.997. The maximum adsorption capacity of the material is 357.1 mg/g. Thermodynamic parameters were evaluated to study the effect of temperature on the removal process. The study shows that the adsorption process is feasible and endothermic in nature. The value of E (260.6 kJ/mol) indicates the chemisorption nature of the adsorption process. Column study and breakthrough analysis were also carried out to