Preparation Of Macromolecule Heavy Metal Flocculant SSXA And Study On It's Performance

In this thesis, Macromolecule Heavy Metal Flocculant SSXA with double functions of both removing substance causing turbidity and heavy metal ions was synthesized by grafting some heavy metal ions ligand to starch-acrylamide graft copolymers (ST-g-PAM). Heavy metal ions and substance causing turbidity were removed simultaneously with macromolecule heavy metal flocculant SSXA and existing flocculantion equipments which made the treatment of heavy metal wastewater much easier.There were two sections of experiments study in the thesis. In the section one, ceric ammonium nitrate was used as initiator for the graft copolymerization of acrylamide(AM) onto starch(ST). The influences of different conditions including concentration of initiator and acrylamide, the molecular ratio of acrylamide to starch, polymerization temperature and time were investigated. The non-ionic starch-acrylamide graft copolymers have been tested for their properties of hydrolysis and corresponding anionic graft copolymers have been prepared by alkaline hydrolysis of the non-ionic graft copolymers. The flocculation performance of the anionic graft copolymers have been evaluated. In the section two, a novel water-soluble macromolecule heavy metal flocculant SSXA has been prepared by reacting starch-acrylamide graft copolymers with CS₂ in alkaline medium. Some influential factors(shch as concentration of reactant, proportionality of reactant, reacting time reacting temperature), characteristics productivity and sulphur percentage of SSXA were studied. Section two was the main study target of the thesis.In the study of section one, the main conclusions were as follows: 1) The optium conditions of preparation of starch-acrylamide graft copolymers were that: the concentration of initiator was 1.4×10^-3mol·L^-1, the concentration of acrylamide was 1.4mol·L^-1, the molecular ratio of AM to ST was 4.5:1, polymerization time was 3h and temperature was 50℃. 2) The properties of alkaline hydrolysis of the non-ionic starch-acrylamide graft copolymers were that: the weight ratio of NaOH: ST-g-PAM was 1:5, the best hydrolysis percentage of the graft copolymers was 20%～30%. 3) The flocculation performance of the anionic graft copolymers have been compared with that of anionic PAM which is approximately equal to the anionic graft copolymers in molecular weight. It has been shown that the flocculating effect of anionic starch-acrylamide graft copolymers was better than anionic PAM not only when they were used nonely but also when they were used together with Al₂(SO₄)₃.In the study of section two, the main conclusions were as follows: 1) The synthesization of the SSXA have been composed of two reactions. The graft copolymerization of acrylamide onto starch occured at first then the graft copolymers reacted with CS₂ in alkaline medium subsequently. 2) In general larger chain length of PAM branched chain of starch-acrylamide graft copolymers could increase the removal efficiency of turbidity, but the molecular weight and branching density of graft copolymers have some effect on the degree of xanthate reaction. Therefore, according to the experiments, the proportionality of AM: ST was 3:1(mole ratio). 3) The characteristics of macromolecule heavy metal flocculant SSXA were greatly affected by the input of sodiumhydroxide or carbon disulphide and improved with the increase of proportionality of these two chemicals. However If the input of sodiumhydroxide was too high, the pH value of treated wastewater was must higher(just for water supply). On the other hand, if the proportionality of carbon disulphide was higher, the volatilization loss of it was much more because of its volatility. So the proportionality of starch, sodiumhydroxide and carbon disulphide was 1:2:1.5(mole ratio). 4) According to the experiments, the graft polymerization time was 3h, and the xanthate reaction time was 2.5h. Much long time accelerated some by- reactions and increase the consumption level and production losts. 5) The macromolecule heavy metal flocculant SSXA could be prepared at moderate temperature. The graft polymerization temperature was 50℃and the xanthate reaction temperature was 30℃.Characteristics of macromolecule heavy metal flocculant SSXA, main factors influencing flocculant and the best experiment conditions were studied by using the target water sample with tap water or electroplating wastewater individually. Additionally, because both the SSXA and the SSX could be used for removal heavy metals. Therefore the flocculation performance of SSXA and SSX process for wastewater containing Cu²⁺ and turbidity-causing substance have been evaluated in section two of the thesis. The experiment results showed that: 1) SSXA has strong binding effect with Cu²⁺, but one of the major limitations was that the separation of the Cu-SSXA complex precipitate from the aqueous phase was difficult. This problem was solved by the addition of Al₂(SO₄)₃ solution followed by simple settling. The Al₂(SO₄)₃ acted as a co-precipitator. The removal rate of Cu²⁺ depends on the concentration of Cu²⁺, AL³⁺ and xanthate group of the macromolecule, and the optimum Al³⁺/Cu²⁺ concentration (mg.L^-1) ratio was 0.3. The SSX must be used together with polyethyleneimine(PEI) for the Cu²⁺ removal. The PEI acted as a co-precipitator in the system of SSX-PEI. However the settling property of the Cu-SSXA complex precipitate was better than Cu-SSX. 2) Treatment of wastewater containing heavy metal ions with macromolecule heavy metal flocculant SSXA had wilder range of the pH value. In this process turbidity was reduced while removing heavy metal ions. Moreover, the additional equipments and structures were not needed; a better removal result of heavy metal ions and turbidity could be attained by less input of SSXA; the forming of chelate spent less time, the dimension of chelate were nearly the same and big, it was easy to be separated form the mother solution; the sediment was less, the secondary pollution did not easily occur, it eas easier to operate and more convenient to manage. The eapalibilities of SSX-PEI for the heavy metal wae good, but this system could not removal the turbidity-causing substance of the wastewater. 3) Treatment of wastewater containing heavy metal ions and substance causing turbidity with macromolecule heavy metal flocculant SSXA heavy metal ions and substance causing turbidity promoted the removal of each other. SSXA was with double functions of both removing substance causing turbidity and heavy metal ions. 4) The treatment method of SSXA process for the wastewater containing a little heavy metal ions and turbidity- causing substance have been evaluated. It is showed that not only the flocculation-settling treatment method but also the micro- flocculation filtration treatment method were suitable for the wastewater as mentioned above. Both the treatment results were better. 5) The SSXA- Al₂(SO₄)₃ have been used to treatment the wastewater containing heavy metal ions and high turbidity. The result showed that the trapping and flocculating capalibilities of SSXA were strong and the substance causing turbidity and heavy metal ions were removed efficiently.