The Degradation Of Modified Corn Starch In Water

With the development of industry, the quantity of the heavy-metal wastewater produced by the manufacture world is increasing dramatically. New efficient measures to remove the heavy metal from the wastewater, as a result, have become the focus of the environment protection field. Many new heavy metal chelating reagents have been claimed to be successful while papers concerning the control of the secondary pollution are quite few.In this dissertation, a DTC-grafted starch (DTCS) has been synthesized via a series of processes and applied for the removal of heavy metals from aqueous solutions. The degradation of DTCS and DTCS heavy metal chelate (DYCS-M) is studied under strengthened physical and chemical conditions.The dissociation of heavy metal in 1mol/L HCl has been observed. The result shows the acid-resistant ability of DTCS as heavy metals have totally dissociated from DTCS-M (regard M as heavy metal), while the DTCS itself has no changes. In hydrogen peroxide, the degree of dissociation for different heavy metals is quite different, which consist with the chelate ability of DTCS for different metals.The stability of DTCS and DTCS-M has been tested under conditions involving oxidant, heating, and intense light. The best dosage of oxidant, temperature of degradation, time of degradation are finally determined after a series experiments as following: 25℃, 150mL 2%H₂O₂ /g(DTCS),10h; 25℃, 175mL 2%H₂O₂ /g(DTCS-M),48h. The degradation percent (calculated by the carbon content) is 5.48% and 47.5% respectively. DTCS and DTCS-M are quite stable as no apparent changes of TOC occur if only being heated. Oxidant and UV together can make the degradation more effective than oxidant only. FTIR, X-ray diffraction, SEM are used during the tests of degradation. The apparent changes observed on the surface of the DTCS and DTCS-M may prove the existence of reaction.The forms of C,N,S after degradation have been tested in the dissertation C is proved in forms of carboxylic acid and ester, N in forms of nitrate and nitrite, S in forms of sulfate and no sulfide.As the residues of DTCS are quite few in water, the concentration of degradation products will not be high. This means that our stable DTC-grafted starch will hardly have secondary pollution problem and has a bright future for both environmental and economic benefits.