Title of Thesis

Biosorption of direct dyes from aqueous solution using rice (Oryza sativa) husk

Author(s)

Yusra Safa

Abstract
In the present research study, the biosorption of Everdirect Orange-3GL, Direct Red-31, Direct Orange-26 and Direct Blue-67 onto free, CMC immobilized, PVA-alginate immobilized and modified rice (Oryza sativa) husk was investigated in a batch mode using = different process parameters like pH, particle size, biosorbent dose, initial dye concentration, contact time and temperature. Maximum biosorption capacity was observed at pH=1 for Everdirect Orange-3GL pH 3.0 for other three the dyes for free, immobilized and HCl treated biosorbent. The amount of dyes sorbed (mg/g) decreased with an increase in biosorbent dose and increased with increase in initial dyes concentration and temperature. Comparison of free, immobilized and HCl treatments showed that the HCl treated biosorbent exhibited the highest biosorption capacity 29.981mg/g (at 125 mg/l), 67.39 mg/g, 45.345 mg/g at 200 mg/l and 37.918 mg/g (at 200 mg/l) for Everdirect Orange-3GL, Direct Red-31, Direct Orange-26 and Direct Blue-67, respectively. The Langmuir Type 1 and 2 models were best fitted to experimental data for free, CMC, PVA-alginate immobilized andHCl treated biosorbent in case of Everdirect Orange-3GL dye, Direct Red-31, Direct Orange-26 and the correlation coefficient of Langmuir Type 2 was the highest for Direct Blue-67. The biosorption of all four dyes followed the pseudo-second-order and Elovich kinetic models suggesting a chemisorption mechanism.Negative values of (G°) for direct dyes at high temperatures showed that the process was spontaneous in nature at high temperature.The positive value of H° showed the endothermic nature of the process.The value of S° suggested that randomness increased after adsorption of dyes. Due to high uptake capacity rice husk could be used as an effective biosorbent for the removal of direct dyes from aqueous solution.FTIR, XRD, SEM studies and BET analysis were carried out to characterize the unloaded and dye loaded biosorbent. A 53 full factorial analysis experiment was also studied to determine the biosorption capacity of dyes onto rice husk biomass. Main and interaction effects were analyzed by ANOVA, F-test and p-values. The maximum biosorption was obtained at high initial dyes concentration, low biosorbent dose and low pH values for all dyes.In this research, the influence of electrolytes, heavy metals and surfactants on the removal of direct dyes (50 mg/L) was also examined. Industrial effluents were also removed by rice husk efficiently.Sorption/desorption studies showed that the rice husk biosorbent could be reused successfully and efficiently up to three cycles with four dyes.

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