Preparation Of Cassava Stalk Into Anion Adsorbent And Study Of Its Cr(?) Adsorption Properties

With along the rapid development of global economy and industry,huge material progress has been made,but environment crisis has been brought about at the same time.There have been a series of accidents on heavy metal pollution recently in China,which produce severe effect on people's physical and mental health and disturb our social stability.Heavy metal pollution has become a serious environmental problem,which has aroused high attention of many domestic experts and scholars.Therefore the use of low cost and biodegradable agricultural waste,which is a kind of biological adsorbent,for the treatment of heavy metal pollution has become a new hotspot.This paper,built on a number of domestic and foreign literatures,makes the research according to the local condition.The research takes the agricultural residual in Guangxi-cassava stalks as raw material to make an anion adsorbent.The paper studies the adsorption characteristics and mechanism of Cr(?)onto the anion adsorbent produced from cassava stalks.The main contents and results are as follows:1.Preparation of modified adsorbent.In this study,a cassava stalk anion adsorbent(CSAA)was prepared from cassava stalks by reaction with dimethyl dihydroxy ethylene urea resin((DMDHEU)and choline chloride after it was treated in sodium hydroxide solution.The preparation of CSAA adsorbent takes Cr(?)removal percentage as the evaluation criteria.Through a series of single factor experiments,the best conditions are produced for the preparation of CSAA with the best amount of 2D resin and choline chloride,the best proper reaction temperature and reaction time.The results showed that the best conditions for preparation of the CSAA are as follows:pH is 4 to 4.5;the reaction temperature is 180?;time for reaction is 4 h;the optimal reaction ratio was the preprocessed cassava stalks:DMDHEU:choline chloride=1g:1.152 g:0.8 g.2.Characterization of Adsorbents.A variety of characterization techniques will be used to find the differences of the cassava stalks before they are modified and after they have been modified,including the structure of appearance,the main elements and chemical groups,organizational structures of them.The scanning electron microscopy shows that the surface of pretreated cassava stalk was smoother.Cellulose became swelling and active after being soaked and moist by sodium hydroxide solution.The surface of CSAA powder became smoother and fibers of surface were in order.There are a number of hollow shapes in the internal cellulose in particular.The specific surface area increases.Infrared IR spectrum shows that the basic structure of the cassava stalks was slightly changed.In pretreated cassava stalk,the peak of at 1733 cm-1 around disappears which represents the lipids.The-NH amine peak and amide peak introduced in CSAA are masking by-OH peak,but Vc=o peak are obvious;peak at 1336 cm-1 is C-N peak.Elemental analysis showed that the nitrogen content of CSAA increased significantly.Zeta potential of the sorbent is positive;the electrical property of Anion Adsorbent changed.3?Study on adsorption of Cr(?)onto the CSAA.CSAA was used to deal with simulated wastewater containing Cr(?),and the adsorption results were analyzed.The CSAA produced a high capacity to absorb chromate ion.Adsorption of Cr(?)onto CSAA is strongly affected by the pH of the solution;when the pH is smaller and the removal of Cr(?)is higher;When pH=3,the initial concentration of Cr(?)is 20mmol/L,at room temperature,dosage is 30g/L,the removal rate of Cr(?)is above 93%.Pseudo-second-order kinetic equation can be a better way to reflect Cr(?)adsorption by CSAA.The rate of the entire adsorption process is controlled by intra-particle diffusion.Adsorption isotherm of Cr(?)onto CSAA can fit better for Langmuir and Freundlich,which shows that adsorption of Cr(?)onto CSAA is led by monolayer adsorption which is accompanied by multilayer adsorption.The value of enthalpy is greater than zero.It shows that the adsorbent process of CSAA to Cr(?)is an endothermic process and that the reaction of the CSAA with Cr(?)can happen spontaneously.The higher the temperature is,the greater the degree of spontaneous.