Basic dyes removal from aqueous media by modified products of sugar beet pulp

Textile industry wastewaters, leading to water pollution are one of the major sources of pollution. Wastewaters containing dyes cause aesthetic problems, further, degradation intermediates of some dyes, which are formed in the water ecosystem are toxic, mutagenic and/or carcinogenic. Therefore, the removal of dyes from wastewaters is of great importance. To use adsorption methods in the treatment of textile wastewaters, intensive investigations onto the manufacture of cheap and effective adsorbents by using agricultural wastes have been done.In this study, firstly, saponification product has been obtained by treating the sugar beet pulp (ŞPK) with sodium hydroxide solution. Following, various modified products of SŞPK-F, SŞPK­EKH, SŞPK-SA ve SŞPK-FA have been prepared by reacting the saponified sugar beet pulp (SŞPK) with formaldehyde, epichlorohydrine, citric acid and phosphoric acid, respectively. After that, modified products have been characterized by determining some physical, physicochemical and chemical properties. Hydratation properties such as swelling capacity and water retention capacity of modified products have been found much lower than those of raw sugar beet pulp. Additionally, it has been found that the solubility in water and acid solution of modified products are both lower than those of precursor. But their cation exchange capacities are much higher compared to raw sugar beet pulp. By modifying, sugar beet pulp has become more stable against to aqueous solution and more efficient adsorbent with respect to cation binding.By taking into account the results of the preliminary studies dealing with the determination of pH, adsorbent dosage and adsorbent type, epichlorohydrine and citric acid modification products (SŞPK-EKH, SŞPK-SA) have been selected for systematic study. In order to determine the effect of removing characteristics of the Basic Red 46 (BR46) and Basic Violet 7 (BV7) dyestuffs, batch adsorption experiments have been carried out by using these modified products and the effects of initial dye concentration, contact time and temperature on dye removal have been investigated. The results obtained have been applied to the kinetic and isotherm equations that are widely used for adsorption models. In addition, basic dye removal characteristics have been identified by conducting the fixed-bed column experiments in the continuous system. On the other hand, dye desorption ability of pregnant adsorbents have been tested by using distilled water and various solutions in batch and continuous systems.In batch study, it has been found that dye removal attains within 360 min in almost neutral medium by using SŞPK­EKH and SŞPK­SA modified products under the conditions of adsorbent dosage= 2 g/L and temperature= 25°C. The results of applying the kinetic data to various models have revealed that the most appropriate model for the adsorption process is the pseudo second order kinetic model. Activation energies calculated from Arrhenius equation by using rate constants obtained from this model, have been found to be in the range of 10.82­17.27 kJ/mol. The experimental equilibrium data have been analyzed using various isotherm models and the Langmuir isotherm have been found to provide the best fit for the basic dye adsorption on selected modified products. For the temperatures in the range of 25-55°C, Langmuir adsorption capacities of the modified products of SŞPK­EKH ve SŞPK­SA have been estimated as in the range of 0.447 to 0.511 mmol/g. Thermodynamic parameters have been calculated using Langmuir energy constant and it has been found that the adsorption process is endothermic. For the removal of B46 by the modified products of SŞPK­EKH and SŞPK­SA, the ?Ho values have been calculated as 18.11 and 20.57 kJ/mol, respectively, while those are 17.15 and 22.86 kJ/mol for BV7 removal. The negative value of free energy change (?Go) indicates the process of dye removal to be spontaneous. Entropy changes (?So) have been found as about 0.15 kJ/mol.K. Based on the values of activation energy, enthalpy change and Dubinin-Radushkevich energy constant, it has been concluded that the predominant mechanisms took place in adsorption process are physical adsorption and ion exchange.Adsorption of BR46 and BV7 has been investigated in a continuous system by using columns packed with SŞPK-EKH and SŞPK-SA. It has been found that the treated dye solution volumes up to determined breaking point (C/Co= 0.1) for SŞPK-SA are bigger than those of SŞPK-EKH. On the other hand, treated dye solution volumes up to saturation point (C/Co= 0.9) for SŞPK-SA are lesser than those of SŞPK-EKH. Adsorption densities determined for both dyes in continuous system are lower than those of batch system. Adsorption densities for continuous column studies have been calculated to determine the column performance by using Bohart-Adams equation. These values calculated by Bohart-Adams equation for SŞPK-EKH and SŞPK-SA are 88.09 and 91.63 mmol/(L­bed volume) for BR46 and 86.59 and 78.91 mmol/(L-bed volume) for BV7, respectively.Some desorption tests have been carried out in batch and continuous systems by using distilled water and 0.001 N C6H8O7, HCl, NaOH solutions. It has been determined that the desorption efficiencies obtained by using HCl solution are higher than other reagents in both systems.As a result, it can be stated that effective adsorbents could be obtained from sugar beet pulp by some modification treatments by using simple chemical substances under mildly conditions.