A novel adsorbent for aniline blue removal from wastewater

Water is a very important natural source for human being. So, sources of groundwater and surface water should be protected. Today water pollution that is caused by wastewater contaminated with the products discharged from industries such as textile, paper, pharmaceutical, food is a huge concern. Therefore, the industrial wastewaters need to be refined before discharging. Dyes are commonly used in industry for various purposes. Many industries like textile, plastic, cosmetics, rubber, food and pharmaceutical use the dyes to colorify their industrial products. It is estimated that more than 10000 types of dyes are used in industry now. Because of this widespread usage dyes are found in wastewater discharged from industries with large amounts. The colored effluents from industries could mix with groundwaters and surface waters. This situation causes a pollution in drinking water, too. Therefore, it can be dangerous for human life because some dyes are in tha class of hazardous materials. These dyes can cause health problems in vital organs. Especially, kidney, liver, brain central nervous sytstem and reproductive system can be affected by these type of dyes. Also, dyes can give rise to some allergic dermatitis, skin irritation, eye irritation and cancer. Dyes bring about not only visual problems but also other important problems and effects on water bodies. Dyes absorb or reflect sunlight reaching water. So that, they block photosynthesis in aquatic life. It results in a decrease in the growth of some microorganisms and aquatic plants. In addition, dyes are very stable compounds because of their complex structures. They are stable to light and oxidizing agents. Also, dyes are non-biodegradable materials. All of these reasons bring about a need for water treatment and removal of contaminants from the wastewater. There are several methods for removal of dyes from aqueous phases such as precipitation, solvent extraction, membran filtration, biological oxidation, coagulation, flocculation, electro-floatation, reverse osmosis and electrodialysis. These methods can be used for decolorization of industrial effluents but these are not easily applicable and widely used. On the orher hand they have high costs and some disposal problems. Nowadays, adsorption has been the most popular treatment application to decolorize the aqueous solutions in terms of its easily-usage, lower costs, flexibility, easy recovery and reuse of adsorbents, insensitivity to hazardous and toxic materials, and high efficiency. Recently, there have been researches for producing and using economic, renewable adsorbents with high efficiency and large scale application. In last years, the usage of activated carbon, fly ash, agricultural wastes, biomasses, clay minerals, sand, polymer composites and other different types of adsorbents were reported for removal of dyes from wastewater. For another example, rice husk ash is a common adsorbent for dye removal. In this study, Fe3O4 modified rice husk ash (Fe3O4-RHA) was synthesized as a novel adsorbent for removal of aniline blue, which is a hazardous dye used in textile industry and medical laboratories, from aqueous solutions. FTIR spectroscopy was used for characterization of the adsorbent. For determination of adsorption amounts UV-Vis spectrophotometer was used. So, suitable wavelength for maximum absorbance was found firstly as 600 nm. The effects of pH, agitation rate, initial aniline blue concentration, adsorbent dosage and temperature were investigated. Maximum adsorption was obtained in original pH value, 5.5, of aniline blue and fastest agitation rate, 200 rpm. So, the other studies were carried out in 5,5 pH and 200 rpm. Then, the effects of initial aniline blue concentration (in 20-200 mg/L range), the adsorbent dosage (0.01 g, 0.025 g, 0.05 g, 0.1 g) and temperature (25 °C, 35 °C, 45 °C) on adsorption capacity (qt) were investigated. qt - t graphs were drawn by using experimental data obtained from these studies. The results showed that adsorption capacity increased by increase in aniline blue initial concentration. In contrast that, adsorption capacity decreased by increase in adsorbent dosage. Increase in temperature leads adsorbent capacity to increase. So, it was said that the adsorption process was endothermic. After determination of adsorption capacities, kinetic models were investigated and it was found that pseudo second order fitted to the experimental datas. Then second order rate consants (k2) were calculated. The data obtained from experiments at 25 °C, 35 °C and 45 °C was used for calculations of adsoption equilibrium consant (Kc), activation energy (Ea) and thermodynamic parameters such as Gibbs adsorption energy change ΔGº , adsorption enthalpie change ΔHº and adsorption entropy change ΔSº. Negative value of Gibbs adsorption energy showed that adsorption of aniline blue on Fe3O4 – RHA was spontaneous. Positive enthalpie value proved that the type of heat of adsorption was endothermic. Activation energy value was found below 40 kJ/mol. It showed that adsorption was a physical adsorption and no chemical reaction occured between adsorbate and adsorbent. Therefore, it was said that the bonds between adsorbate aniline blue and adsorbate Fe3O4 – RHA were weak bonds such as Van der Waals forces. The data obtained from different initial aniline blue concentration experiment were applied on the Langmuir and Freundlich adsorption isotherm models. It was found that both of the isotherms were suitable to describe the adsorption character because the data was fitted to the both of them. From Langmuir isotherm, maximum adsorption capacity was found as 232,56 mg/g. RL value was between 0 and 1. So it was said that the adsorption process was favorable. n value calculated from Freundlich equation was found nearly 1. So, it was found that adsorption was a physical process. As a result, it was proved that Fe3O4 – RHA was a novel, economic and suitable adsorbent for different conditions with high efficiency and easy usage.