Alkali modification of aluminium dross as an adsorbent for removal of Congo red in aqueous solution

Mohamad Zulfika Hazielim, Bin Zakaria (2019) Alkali modification of aluminium dross as an adsorbent for removal of Congo red in aqueous solution. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Textile industry usually pollutes water with dyes and chemicals. Adsorption using activated carbon was one of the successful ways to remove dyes from wastewater. Unfortunately, activated carbon become unfavourable due to the production of activated carbon was quite expensive. Therefore, researchers have discovered some of the adsorbents originated from waste. In this study, aluminium dross has been used as an adsorbent to removed Congo red in wastewater. Aluminium dross has been modified to enhance the efficiency in the removal of Congo red. Modification of aluminium dross was done by varying the NaOH concentration, stirring time and modification temperature from 5-20 wt%, 15-60 minutes, and 25-70 °C, respectively. The samples were calcined at 600 °C for 3 hours after the modification with NaOH. Before the modification, the surface area of raw aluminium dross was 10.05 m2/g. After the modification process, the surface area of aluminium dross after the modification was in the range of 6.1 to 79.8 m2/g. In this study, raw and modified aluminium dross with three different surface area known as modified aluminium dross with LSA, MSA and SSA with the surface area of 79.8, 43.4 and 6.1 m2/g, respectively were selected to remove Congo red in the synthetic wastewater. Parameters involved in the batch adsorption studies were pH, adsorbent dosage, initial concentration and time. The adsorption of Congo red increased as the time of the adsorption increased for raw and modified aluminium dross and the adsorbents reached the equilibrium state at 240 minutes. pH 6 was the most favourable pH for the Congo red adsorption onto raw and modified aluminium dross. From the results, the adsorption uptake increased when the initial concentration of Congo red increased and when the dosage of raw and modified aluminium dross increased. The results showed that the adsorption of Congo red onto raw and modified aluminium dross fitted well on the pseudo-first-order kinetic model with the small value of chi square, χ2 in the range of 1.40- iv 14 < χ2 < 2.686. The pseudo-first-order kinetic order indicated that the adsorption of Congo red onto raw and modified aluminium dross was controlled by the physisorption process. The intra-particle diffusion model showed that there were several mechanisms involved in the adsorption of Congo red onto raw and modified aluminium dross. The results revealed that Langmuir isotherm was the best isotherm to describe the adsorption of Congo red onto raw and modified aluminium dross due to the highest linear regression coefficient and had the smallest chi-square (χ2) value between the qe of experimental data and qe of predicted data. Moreover, the adsorption capacities of modified aluminium dross showed an increment compared to the raw aluminium dross where the maximum uptake of Congo red onto modified aluminium dross and raw aluminium dross was 67.57 and 23.75 mg/g, respectively. The results from this study showed that the modification of aluminium dross with alkali solution could increase the surface area and enhance the efficiency in the removal of Congo red. Converting aluminium dross as an adsorbent can create a new low-cost adsorbent that can be applied by the industry to remove Congo red.

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