Study On Preparation And Performance Of Activated Carbon From Cotton Straw Of South Xinjiang

Activated carbon (AC) was known as one of the most important industrialabsorbing materials because of its developed pore structure, prodigious surface area aswell as stable chemical properties, strong adsorption capacity and simple regenerationmethods. Due to its low cost and high commercial, AC was widely used for treatingorganic wastewater and heavy metals, purifying the gas and so on. With thedevelopment of industry and the enhancement of human consciousness, the demandof AC has increased year by year. Therefore，how to use the low-priced waste rawmaterial is a hotspot in the study. In this study, the development of the preparation andapplication of activated carbon in recent years were elaborated at home and abroad.The preparation and application of high specific surface area activated carbon ofagricultural straws for heavy metal wastewater of Cr(VI) treatment were investigated.AC was prepared by two-steps procedures from waste cotton straw of Yingjisha,Xinjiang with single KOH or complex KOH/NaOH as the activation agent. Theexperimental results show that it was feasible to choose KOH/NaOH as activatingagent for the preparation of high specific surface area activated carbons. The optimumpreparation conditions established by orthogonal experiment with iodine adsorptionvalue as the main evaluation indicator, and the effects on adsorption feature of thefactors are as follows: the ratio of alkali/char, carbonization temperature, activationtemperature and activation time. The optimum preparation conditions are obtained：the alkali/char ratio of3, carbonization temperature400℃, activation temperature700℃, activation time40min. The samples to be analyzed indicated that iodineadsorption value had reached1836mg/g.The characteristics were determined of the samples from the analysis ofinductively coupled plasma mass spectrometry, elemental analyzer, N2adsorptionisotherms. Element analysis results show that the samples of K, Na, Ca, Mg, Cr, Cdcontent were lower, that is to say the salinization degree of the samples was low. Cotton straw materials had abundant carbon element as high as42.84%. After KOH,KOH/NaOH activating, carbon content increased to55.15%,81.56%, respectively. H,N content decreased obviously. Results show that the prepared ACs have enormousspecific surface areas (SBET=1687,2417m2/g), pore distribution mainly concentratedon micropores with the average pore diameters of1.752,1.855nm. The morphology,functional group, microcrystalline structure of AC were observed by SEM and FT-IR,the composition of single KOH activation is similar with that of KOH/NaOHactivation, but AC by KOH/NaOH activation had more micropore and some measureof macropore.Under static condition, the effects of adsorption time, pH value，absorbent dosage，initial concentration solution and temperature on Cr (VI) adsorption were discussed.The optimum technological conditions was required to improve the efficiency of ACadsorption of Cr (Ⅵ) in the wastewater. In addition, Langmuir and Freundlichadsorption isotherms were applied to fit the adsorption equilibrium data. The pseudofirst-order equation, pseudo second-order equation and intra-particle diffusionequation were adopted to examine the kinetic data, respectively. The experimentalresults showed that the adsorption conditions of AC were the best when the adsorptiontime was180min, pH of Cr(VI) solution was3, initial concentration solution was150mg/L, AC dosage was0.05g, the temperature was25℃. The Langmuir adsorptionisotherms can agree with the adsorption behavior of Cr(VI) on AC, and the correlationcoefficient reached0.995. The adsorption type is surface chemical adsorption withsingle molecule. The adsorption kinetics was found to follow the pseudo second-orderkinetic model, and the correlation coefficient reached0.989.