| Recently, many industrial wastewaters including cadmium-wastewater have become one of the most serious problems for surrounding environment and hunman health, thus cause widespread concern and research hotspot. Many heavy metal treatment technologies have been applied, but these are expensive because of higher operating costs. Adsorption, depending on various sources, low cost and excellent capacity, is a popular and effective process for the removal of heavy metals from wastewater.Corn stalk is an abundant agricultural waste in the world and usually has a high levels of cellulose, which can paly an important role in many fields. However, some corn stalks have been wasted and burnt without useful utilization. Base on the existing modification methods and treatment techniques, corn stalk can be modified into heavy metals adsorbent. These not only can solve pollution problems in aqueous, but also provide a new approach for corn stalk.In this study, acrylonitrile （AN） as chemical modification reagents, selecting two different methods to produce adsorbents. One was etherification, and another was grafting modification, then untreated corn stalks （named RCS-A and RCS-B） were modified completely in order to make the adsorbents （named AMCS and AGCS）. Meanwhile, the cellulose adsorbent （AGCS-Cell） was also produced through purification and grafting. These adrobents were analyzed by characterizated technologies, and their adsorption capacities, adsorption isotherm, kinetics, thermodynamics and models in the adsorption process were evaluated in batch experiments. The main results are as follow:1. In the characterization analysis of four adsorbents, the internal area of AMCS and AGCS were 2.74 and 3.43 times larger than RCS-A and RCS-B. After etherification and grafting modification, AMCS and AGCS structrues had been successfully introduced a new functional group, cyano （-CN）, which lead to N content increasing. The XRD patterns showed AGCS < AMCS < unmodified forms in X-ray crystallography exponential relationship, indicated that–OH groups in AGCS and AMCS were“liberated”from the hydrogen bonds and could be replaced easily by–CN groups, which were favor for Cd （II） ions adsorption. 13C-NMR explained the lower crystallinity and -CN location in AMCS and AGCS. In addition, TGA and DGC curves confirmed good thermal stability in AGCS.2. In the adsorption capacity experiments, adsorption kinetics and thermodynamics of four adsorbents, they were mainly affected by initial pH values and adsorbent dosage. When at high pH values and in small dosage, their adsorption capacities were better, and AGCS was best in all adsorbents. Their adsorption precesses fitted for Langmuir adsorption isotherm and the adsorption capacities of AMCS and AGCS were 12.73 and 22.17 mg g-1, obtained from linearization of Langmuir isotherm. AMCS and AGCS met the pseudo-second-order kinetics, describing that the adsorption rate was relation with square driving force. And film diffusion and particle diffusion rate controlled mainly the adsorption rate.3. The summary in the main mechanism of removal of Cd （II） ions by AMCS and AGCS was physical adsorption depengding on their larger surface are and pore structure, chemical adsorption such as coordination-complexation reaction because of–CN groups, their surface potential was useful for Cd （II） metal cations adsorption. AGCS also had spatial netting.4. The comparative analysis between AGCS and AGCS-Cell in their structure and adsorption capacities showed that AGCS-Cell is higher grafting. The graft copolymerization binary kinetic rate equation for corn stalk cellulose was deduced and proportion relationship with initiator and monimer concentration, confirmed to be reasonable under certain conditions by the validation results.5. The desorption studies showed that the desorption capacities of six reagents such as pure water, sodium hydroxide, citric acid, sodium chloride and EDTA, were relation with temperature and concentration. EDTA was a most excellent desorption reagent obviously. |
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