Study On The Preparation And Performance Of Macromolecule Flocculant CSAX With The Function Of Trapping Heavy Metal

A novel macromolecule flocculant with the function of trapping heavy metal ions has been synthesized by using corn starch as matrices. Firstly, starch (St) was crosslinked by using epichlorohydrin (EPI) as cross-linking reagent under the basic conditions; then the crosslinked-starch-grafted-polyacrylamide of copolymer (CSA) was synthesized by using ceric ammonium nitrate (CAN) as initiator and acrylamide (AM) as monomer under the weak acid conditions; finally the new kind of flocculant called crosslinked starch-graft-polyacrylamide-co-sodium xanthate (CSAX) was synthesized by xanthation of the copolymer under the basic conditions. The structures of crosslinked starch (CSt),CSA,CSAX were characterized with fourier transform infrared spectroscopy (FTIR), elemental analysis, scanning electronic microscope (SEM), and Energy dispersive X-ray spectrometry (EDS). The effects of the preparation conditions, such as the dosage of EPI and CAN, the percentage by weight of NaOH and CS2, reaction temperature and reaction time etc, were investigated. Because of CSAX molecules containing both the PAM pendant chains and—(?)—S, the CSAX was endowed the double functions of removing turbidity and trapping heavy metal ions. It can be found that there were excellent flocculantion functions of CSAX through flocculantion test of laboratory water and factory effluent. It could offer a new method for the heavy metal wastewater treatment, set a new approach for one dosage multi-usage, decreased the treatment units and cost, and made the treatment of heavy metal ions simpler and easier.There were mainly six sections of experimental studies in the thesis:1. Synthesis of crosslinked starch and the effects of some factors, such as the dosage of reactant and initiator, reaction time, reaction temperature, crosslinking degree on the performance of CSAX, were investigated. The results showed that the optimal synthesis conditions are:corn starch of 50 g, NaCl of 75 mL (1%, w/v), NaOH of 20 mL (15%, w/v), EPI of 4 mL, at 30℃for 8 h, SV (sediment volume of CSt) of 45 mL. In order to form solid-liquid separation effectively in flocculation, the crosslinking degree can not be too high.2. Synthesis of crosslinked-starch-grafted-polyacrylamide of copolymer (CSA), and the effects of some factors, such as the concentration of monomer and initiator, reaction time, reaction temperature, grafting percentage, efficiency of grafting, molecular weight of grafted PAM pendant chains on the performance of CSAX, were investigated. The results showed that the optimal synthesis conditions are:the concentration of CSt, AM and CAN is 40 g/L, 0.939 mol/L and 6.67×10-4 mol/L, respectively, at 45℃for 3h. So the grafting percentage is 86.6%, the efficiency of grafting is 72.7%, and the molecular weight of grafted PAM pendant chains reaches 2.64×107. 3. Synthesis of crosslinked starch-graft-polyacrylamide-co-sodium xanthate (CSAX), and the effects of some factors, such as the material ratio, reaction time, reaction temperature on the performance of CSAX, was investigated. The results showed that the optimal synthesis conditions are:the concentration of CSA, NaOH and CS2 is 50 g/L,3.0 mol/L and 1.6 mol/L, respectively, at 30℃for 3 h. So the percent of S reaches 7.41%. As proven by FTIR, elemental analysis, and SEM, the CSAX can be successfully synthesized and can remove both turbidity-causing substances and heavy metal ions from aqueous solutions.4. The flocculation performance of CSAX was studied. It was treated in experiment by CSAX that the laboratory water containing Cu2+,Cr3+,Ni2+,Hg2+ or manifold heavy metal ions and actual electroplating wastewater of Lanzhou special electroplating. The results showed that CSAX exhibits the better removal capacity, either laboratory water containing one or manifold heavy metal ions. If actual electroplating wastewater of Lanzhou special electroplating is disposed by CSAX, Cu2+,Pb2+,Cd2+ are removed the better than that of Cr(Ⅵ),Ni2+,Zn2+5. The microscopic studies of CSAX flocs indicated that CSAX flocs' surface and interior presented highly irregularity. The research also indicated that CSAX flocs' structure and establishment possessed fractal characteristics. The waste water containing both Cu2+ and Kaolin was treated with CSAX in flocculation experiment; the relationships between flocs' characteristics and fractal dimension were studied. The fractional dimension of the floc was calculated to be 2.0 in the best flocculation. It was almost certain that we could control the flocculation process by meteraging of the flocs' fractal dimension.6. Stabilization of product and technical economical analysis were discussed. It can be seen that CSAX has better stabilization at the lower temperature and light-proof, and the treatment efficiency for heavy metal will be less affected. In addition, CSAX provided with low operating cost, simple treatment method, and higher efficiency. Therefore, it has a good social and economice benefit.