Removal of malachite green by mixture of textile sludge and sawdust chemically produced activated carbon

Abstract

The growing Malaysian textile industry has resulted in generation of large quantity of textile sludge and its disposal problem has become a critical environmental issue. Textile sludge based activated carbon (TSAC) derived using potassium hydroxide and potassium iodide chemical activation is a promising route for removal of dyes and it can also mitigate the sludge disposal complication. However, the optimum conditions of TSAC preparation and its applicability in the fixed bed adsorption process has yet to be examined. The purpose of this study is to investigate the potential of utilizing TSAC and its pellet (prepared using phosphoric acid impregnated sawdust as a binder) as adsorbents for malachite green (MG) removal in batch and continuous adsorption system. The impregnation ratio was varied (0-2) and the impregnated samples were activated at optimum temperature and time. The physicochemical properties of the TSACs were characterized using Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller (BET) surface area, Scanning Electron Microscope and CHNOS elemental analyzer. The BET surface area and microporosity of TSACs were in the range of 333-1037 m2/g and 27-64%, respectively. The TSACs were capable of removing 77-498 mg/g of MG. The Langmuir model gave the best conformity, suggesting a possible monolayer adsorption. The kinetics experimental data were best fitted to the pseudo-secondorder model. The intraparticle diffusion model shows that intraparticle diffusion is not the sole rate-limiting step, while the Boyd model reveals that film diffusion could be the rate controlling step. The adsorption of MG onto TSAC is endothermic and spontaneous by nature. Furthermore, H3PO4 -impregnated sawdust waste, a potential low-cost binder, yielded TSAC pellets with microporosity, surface area and compressive strength of 16-23%, 668-979 m2/g and 0.4-1.5 MPa, respectively. In addition, the fixed bed adsorption of MG showed that the breakthrough time increased with increasing bed height, and decreasing flow rate and influent dye concentration. The highest bed capacity of 565 mg/g was achieved at influent concentration of 50 mg/L, flow rate of 20 mL/min and bed height of 6 cm (0.954 g). Yoon-Nelson model was the most suitable in describing the dynamic adsorption behavior of the column. This study demonstrated the potential of H3PO4-impregnated sawdust waste as a low-cost binder and the applicability of TSAC in MG adsorption for batch and column operations.