Study Of Anionic Dyes Adsorption From The Aqueous Solutions By Ethylenediamine Modified Sawdust

With the rapid development of the printing and dyeing industry, a large number of dyeing wastewater emerged each year. Therefore, it’s important to find a simple and effective method to treat with the wastewater. Sawdust is a kind of natural cellulose materials; it is composed of water, hemicellulose, cellulose, lignin etc. There are a lot of hydroxyl and carboxyl groups in the natural sawdust (NSD) molecules, and NSD gains more amino groups after the ethylenediamine modified, which could improve the adsorption capacity of MSD for anionic dyes.The sawdust was characterized by FT-IR, SEM, elemental analysis, XRD and TGA. The potential feasibility of MSD as the adsorbent for removal of anionic dye Acid chrome blue K (ACBK), Light green SF yellowish (LG) and Congo red (CR) from aqueous solution was investigated. The competitive adsorption of the ACBK and LG was also presented.This study described adsorption of ACBK, LG and CR by MSD in batch and fixed-bed column mode. The effects of different experimental conditions, such as pH, adsorbent dosage, contact time, temperature, initial concentration and the salt concentration were performed in batch adsorption, and the competitive adsorption between ACBK and LG, the desorption and reuse for MSD was studied. The result showed that the adsorption capacity for anionic dyes on MSD was improved significantly, and the maximum adsorption capacity of ACBK, LG and CR were 68.0, 45.2 and 16.3 mg·g-1 at 298 K, respectively. The presence of salt inhibited the adsorption of ACBK and LG, while promoted the adsorption of CR onto it. In binary system, ACBK and LG exhibited competitive adsorption, the two dyes could be simultaneously adsorbed, and there was feeble competitive adsorption between them. Forthermore, the best desorption reagent for saturated sawdust with three dyes was NaOH (0.01 mol·L-1), and the desorption of ACBK and LG has a better reproducibility, while the reproducibility of CR desorption is worse.Through the analysis of the adsorption isotherm models, the equilibrium data for ACBK was fitted well by Langmuir, Temkin and Redlich-Peterson isotherm models, and the equilibrium data for LG was fitted well by Langmuir, Freundlich and Temkin isotherm models, while the equilibrium data of MSD to CR simultaneously were fitted well by Freundlich, Temkin and Redlich-Peterson isotherm models. The pseudo-second-order and Elovich models were the best choice to describe the adsorption behavior of MSD to three dyes. According to the thermodynamic analysis, the adsorption of the there dyes onto MSD was spontaneous, endothermic, and the entropy were increasing in the adsorption process. The nature of adsorption onto adsorbent was both physical adsorption and chemical adsorption.The effect of the initial dye concentration, bed height, flow rate, salt concentration and the solution pH were investigated in the fixed-bed column, and the competitive adsorption between ACBK and LG was also studied. The results showed that increasing influent concentration and bed heights, decreasing flow rate would increase the adsorption capacity of three dyes onto MSD. There was feeble competitive adsorption between ACBK and LG. ACBK and LG dyes were easily desorbed from the MSD column using 0.1 mol·L-1 NaOH solution and MSD could be reused in ACBK or LG removal from aqueous solution efficiently. The column data was fitted well by Yan model. The BDST equation can be used to predict adsorption performance in different initial concentrations or bed heights conditions. The research play an important role in developing suitable industrial adsorption system designs.