Preparation And Heavy Metal Adsorption Studies Of Modified Starch

Heavy metals are serious threat to human health, so it is very critical to treat or process such metals. Many methods for the treatment of heavy metals have been reported but the treatment with modified starch is one of the most important and cheap methods.Starch as a natural polymer has abundant, inexpensive and biodegradable advantages. Modified starch is widely used in removing heavy metal ions from wastewater. Low efficiency for heavy metal removal makes this method a less useable.The purpose of our thesis is to develop a more valuable modified starch on the basis some important aspects which are given blow.① The efficiency of removal of heavy metals can be improved by increasing adsorption of target metals on modified starch and increasing the screening effect of crosslinking agents, monomers and initiators. The results show that crosslinking agent of epoxy chloropropane(ECH) is much better than that of sodium trimetaphosphate because of its active sites of epoxy and chlorine. The monomer methyl acrylate has more ability of chelating heavy metals than that of acrylic acid, acrylamide and methyl methacrylate. The triggered effect of initiator of potassium persufate(KPS) is much better than that of cyclohexanone with potassium bromated.②The removal and absorption of heavy metals can also be improved by providing the best reaction condition:1)Crosslinking degree of starch is 0.58%, starch to monomer mass ratio is 1:1. 2,keeping the concentration of initiator to 5 mmol/L, neutralization degree of monomer to 50%, the reaction temperature is 60°C;2)Rate of grafting reaction ratio and grafting reaction efficiency(utilization of monomers) was 94% and 78.3% respectively;3) By infrared spectrum, the modified starch is not only the characteristic absorption peaks of the starch, also appeared a ester group characteristic absorption peak, prove that starch was successfully modified. By SEM, the surface structure of the modified corn starch was severely damaged and aggregation degree increased, to a certain extent, starch is polymerization.③Main features and mechanism of adsorption of heavy metals can be explained as:1)At p H of heavy metals solution p H around 7, the removal rate of heavy metals was highest, exception for Zn2+ solution p H, which was a little higher; Reaction of modified starch with heavy metal solution takes 4h to reach adsorption equilibrium;2) Dynamic experiment proves that the reaction mechanism in conformity of secondary dynamic equation, the adsorption rate is mainly controlled by the chemical adsorption; adsorption isotherm experiments proves that the modified starch on the adsorption of Cu2+, Pb2+process accord with the Freundlich multilayer adsorption,while adsorption of Zn2+ more accord with Langmuir monolayer adsorption;Determination of temperature results show that the reaction is exothermic reaction thus low temperature can increase the rate of reaction;3)Results for six single ions adsorption show that the determination results for Cu2+ removal effect is best, second order for Cr3+、Hg2+、Pb2+、Zn2+、Cd2+, Adsorption of six ions mixed competition, found that the competitive adsorption order was in such order Cu2+>Cr3+ >Pb2+ > Cd2+≈Zn2+> Hg2+.