Synthesis Of Modified Starch Water-absorbent Resin And Study On Its Passivation Effect On Cu And Zn Polluted Soil

With the accelerating development of industrial production and urbanization,the problem of heavy metal pollution in soil has become increasingly prominent,which creates a great threat to the normal function of soil and human health.Therefore,It is one of the urgent problems to be solved by human that how to economically and efficiently deal with the heavy metal pollution in soil.After this process,the migration of the pollution in the soil environment or its absorbing possibility by plants should be quite reduced.Hence,based on the raw materials of soluble starch,acrylamide(AM)and hexadecyl dimethyl allyl ammonium chloride(C16DMAAC),Soluble starch-g-poly(AM-co-C16DMAAC),a high-molecular polymer,was synthesized by adopting aqueous solution graft copolymerization and performing the hydrolysis step under airtight and high temperature environment,which had a excellent performance of high water absorbency and heavy metal ions absorption capacity.Finally,the synthesized product was used as a heavy metal passivator to repair the polluted soil contaminated of Cu and Zn.The main research contents and results are as follows:(1)Under the synthesis of super absorbent resin(SAR),a hydrophobic monomer C16DMAAC was introduced to graft copolymerization of soluble starch and acrylamide onto the preparation of Soluble starch-g-poly(AM-co-C16DMAAC).The hydrolysis by adding sodium hydroxide(NaOH)under airtight and high temperature environment was also performed.Meanwhile,the best synthesis conditions were optimized by a series of single factor experiments.In this reaction,It is the hypothesis that the strength of the three-dimensional network structure of resin would be enhanced by the hydrophobic association of C16DMAAC,which would be confirmed by testing the rheological property of the polymers.On the other hand,after all monomers being polymerized,the hydrolysis step was performed to convert-CONH2 to-COONa,so that the resin would have more hydrophilic groups and the water absorbency would be increased.Finally,through the single factor synthesis optimization experiments,the most effective preparation conditions of Soluble starch-g-poly(AM-co-C16DMAAC)were determined,the weight of soluble starch was 40%of 10 g solid content in 50 g polymerization system,the molar ration of AM to C16DMAAC was 99.2/0.8,the volume of ammonium persulfate(APS,5000 mg/L)was 4 mL,the amount of N,N-methylene bisacrylamide(MBA)was 0.02 g,lastly the degree of hydrolysis(DH)was 80%.Under this experimental conditions,the maximum water absorbency of Soluble starch-g-poly(AM-co-C16DMAAC)was 1964.96 g/g in distilled water and 76.77 g/g in 0.9 wt.%NaCl solution,respectively.However,in the absence of C16DMAAC and under the same other experimental conditions,the maximum water absorbency of synthesized Soluble starch-g-poly(AM)was 1216.46 g/g in distilled water and 59.81 g/g in 0.9 wt.%NaCl solution,respectively.Comparing the results,the water absorbency of Soluble starch-g-poly(AM-co-C16DMAAC)was increased by 61.53%in distilled water and 28.35%in 0.9 wt.%NaCl solution,which confirmed the hypothesis that introducing C16DMAAC into the traditional polymerization system of soluble starch and AM could enhance the water absorbency and salt resistance of the resin.In addition,after immersed in distilled water or 0.9 wt.%NaCl solution,the swelling process of the resin showed good fitting of water absorbency data to Fickian diffusion model,and the main driving forces were water pressure difference and Na+ concentration difference.(2)Based on the synthesis of Soluble starch-g-poly(AM-co-C16DMAAC),its molecular chains contained lots of-COONa groups,which had the potential of absorbing heavy metal ions.So in this chapter,the heavy metal absorbing behaviour of the resin was investigated in configured CrCl3 and Ni(NO3)2 solutions.In details,some factors,including degree of hydrolysis(DH),pH,NaCl concentration,CaCl2 concentration,adding amount,absorbing time,and so on,were studied to evaluate the influence to the absorption capacity of the product.Furthermore,the adsorption equilibrium and kinetic of its absorption process were also fitted by the model.From the experimental results,the absorption capacity of the resin to absorb Cr3+and Ni2+ was increased linearly with the increase of DH.Specially,when the DH of gel was 100%,the heavy metal adsorption capacity was 106.53 mg/g of Cr3+ and 131.29 mg/g of Ni2+,respectively.From all absorption experiments,It can be concluded that the process of Soluble starch-g-poly(AM-co-C16DMAAC)absorbing heavy metal ions in solution belonged to ion exchange.Specially,the-COONa in polymer chains ionized and released Na+ into the solution,while the existence of electrostatic attraction between heavy metal ions in the solution and-COO-would promote the ions be absorbed.The heavy metal adsorption process of the resin conformed to the model particle internal diffusion.In the last,the experiment,performed to link Soluble starch-g-poly(AM-co-C16DMAAC)performance of water absorbency with heavy metal absorption,indicated that those two properties of the resin were a negative correlation,the heavy metal absorption capacity increased while the water absorbency decreased.(3)From the previous experiments,Soluble starch-g-poly(AM-co-C16DMAAC)has a double performance of water absorbency and heavy metal absorption,so it can be as a passivator to the remediation of heavy metal polluted soil.Referring to Solid waste.Extraction procedure for leaching toxicity.Horizontal vibration method(HJ 577-2010,China standard),the experiment was performed to evaluate the effects of the resin to heavy metal pollution in soil.The result showed that the removal efficiency of Cu and Zn were 50.02%and 83.41%,respectively,when the adding amount of resin was 0.5%to polluted soil.Meanwhile,that adding synthesized products into soil could enhance the water retention and increase the porosity of the soil.Lastly,planting swamp cabbage in Cu,Zn polluted soil with and without adding Soluble starch-g-poly(AM-co-C 16DMAAC)passivator,the results showed that it can promote the differentiation of root tissue by adding the resin,and the plants grew better than the black group.In addition,in the process of phytoremediation to heavy metal polluted soil,the heavy metal pollution was absorbed by swamp cabbage from the soil environment into plants.By means of the transport ability of plant ducts tissue,the heavy metal pollution were transported from roots to stems and leaves,leading to the heavy metal concentration:root>stem>leaf,and exhibiting the better absorption and enrichment effects of swamp cabbage.