Development and application of modified starch flocculant

Molecular flocculant in wastewater treatment process, plays an indispensable role. In recent years, due to the natural polymer having a non-toxic, wide material, inexpensive and biodegradable, etc., are widely used for domestic and foreign researchers developed high-molecular flocculant, the flocculant of such a complex is suitable for water treatment waste water, in particular wastewater is complex, both for processed separately, can also be used in combination with other treatment methods, to reduce pollution of the waste water to the environment.

Among many natural modified polymer flocculants , the research and development of starch-modified flocculants is particularly striking. Starch molecules with a lot of hydroxyl groups, these hydroxyl group to react esterification, etherification, oxidation, crosslinking, etc., can change the nature of the starch, modified starch is the use of these chemical reactions produce industrially. Starch and synthetic polymer also monomers acrylonitrile, acrylic acid, acrylamide from graft copolymerization, chain connected with a synthetic polymer molecular chain, the copolymer having both of a natural polymer and synthetic polymer nature.

In recent years, studies of modified starch as flocculant has also made some progress, it will be the case in recent years in research, development and application of modified starch flocculants and other relevant domestic and brief comments.

1 non-ionic modified starch flocculant

1.1 dextrin

Dextrin has a relative molecular mass of 800 to 79,000 and can be used as a flocculant and inhibitor. When gold ore flotation, adding dextrin can reduce the flotation of minerals. When coal tar sands and other mineral mining, dextrin flocculant can be deposited sludge.

1.2 acrylamide grafted starch

The starch graft copolymer is due to the grafting of a polymer side chain having flocculation function on the starch , the side chain group is affinity with many substances, adsorbing to form a hydrogen bond ; or the side chain forms a physical interaction with the flocculated substance. linked state, so that flocculation is precipitated material, such as a dye wastewater, staple fibers and other paper mill waste water suspension, etc., it may also be used to treat mercury-containing waste water, electroplating waste oil and waste water. The key to polymer application is its molecular morphology, relative molecular mass, and ionicity. When a small molecule flocculant is used , when the flocculated substance is adsorbed around it , the flocculation effect is affected by the repulsion between the floc particles , and the graft type starch is a high-molecular flocculant , which overcomes this disadvantage.

Grafting vinyl monomers and copolymerization of the starch is an important way of making a biodegradable modified starch polymer materials, excited hydroxyl initiator screening agent is the key starch graft copolymerization reaction. The initiator systems currently used mainly include chemical methods and radiation methods.

Wu Gongsheng thiourea - hydrogen peroxide as a catalyst to prepare graft copolymers with acrylamide corn, can be used in the paper industry process waste water containing Hg2 + [1]; Lishu Hong et al ceric ammonium nitrate initiator by graft copolymerization the reaction, is introduced in the starch backbone polyacrylamide, starch was prepared - acrylamide graft by processing experiments of high salinity oil field waste water showed its high salinity oil field waste water turbidity and COD Removal shows excellent performance [ 2 ]. Chang Wenyue et al. initiated the free radical polymerization process with cerium ammonium nitrate / nitric acid , grafted acrylamide onto the starch matrix, and obtained grafted starch with a grafting efficiency of about 95% . For industrial wastewater such as papermaking, textile and electroplating, Good flocculation [ 3 ]. Wang Yuqin et al to Ce4 + -S2O82- composite initiator [4], Zhang Yifeng et al in CS2 / H2O2 as an initiator synthetic graft copolymer of starch and acrylic acid amide under basic conditions, for wastewater, waste paper and Other industrial wastewater removes heavy metal ions [ 5 ]. Wang Xin starch and polyacrylamide by using Hofmann rearrangement reaction product of the direct synthesis of the graft copolymer, and for dyeing wastewater treatment [6]. Jin Mangyi explored the effect of adsorption of heavy metal ions Cr(VI) by starch grafted acrylic acid and the adsorption conditions . This adsorbent has a large adsorption capacity and is of great application value to industrial and mining enterprises [ 7 ].

Radiation is also an effective method for forming the active initiation center of starch . The active initiation center can be a free radical, an anion, a cation or a radical - anion and a radical - cation. Yang Bo et al. studied the graft copolymerization reaction and reaction mechanism of starch and acrylamide under 60Co γ-ray initiation. The relationship between irradiation time and graft polymerization rate , and the effects of irradiation dose rate, monomer concentration, starch concentration and irradiation temperature on the graft copolymerization rate were obtained from the experimental results [ 8 ].

2 anionic modified starch flocculant

Starch phosphate 2.1

Starch phosphate can be used as flocculant for fish processing plant wastewater, slaughterhouse wastewater, fermentation plant wastewater, vegetable and fruit soaking water, pulp wastewater, mud , or as a settling agent for floating ore dressing , recovering aluminum from aluminum ore, and depositing coal. Coal powder in coal washing wastewater. The phosphate ester starch flocculant developed by Zhuang Yunlong et al . treated the waste paper deinking wastewater and the industrial wastewater of the fine chemical plant , and received obvious results . The amount of phosphate starch added, the pH of the wastewater and the flocculation time were discussed. effect of flocculation is determined optimum conditions of starch phosphate and black liquor fine chemical industrial wastewater [9].

2.2 starch xanthate

The use of native starch crosslinked acetylated, esterified or etherified crosslinked crosslinked, then xanthation, can be obtained insoluble crosslinked starch xanthates (ISX). This is the 1970s developed products, primarily for the treatment of metal waste, may generate insoluble salts with many valent metal ions, can be used to remove electroplating, mining, smelting and other industrial wastewater brass heavy metal ions [10] . Zhang Shuyuan et al. used ISX to treat nickel- containing electroplating wastewater with a removal rate of over 95% and a residual nickel concentration of <0.2 mg/L, which is lower than the national emission standards [ 11 ]. Zhang Shuyuan and others also used ISX to treat chromium- containing wastewater . Experiments show that ISX can be well removed for various valence chromium [ 12 ].

2.3 carboxymethyl starch

Carboxy starch crosslinked with two main varieties: called crosslinked carboxymethyl starch (C-CLS), which is a crosslinked starch in NaOH catalyzed reaction with sodium chloroacetate to obtain; the other is called carboxyl side chains are grafted crosslinked starch (GC-CLS), which is reacted with acrylonitrile is graft copolymerization initiator in the role of cross-linked starch cerium salts, iron salts or manganese salts, the copolymer prepared by the saponification.

After the Shanghai Institute of Organic Chemistry, sodium carbonate and sodium hydroxide in alcoholic solution with stirring, the starch slurry was added, was added a solution of chloroacetic acid dissolved in alcohol, and sodium carbonate, carboxymethylated reaction to obtain a degree of substitution It is 0.1 to 1 sodium carboxymethyl starch [ 13 ]. Quanyide et al Corn starch after the crosslinking reaction with epichlorohydrin and chloroacetic acid, to give the starch backbone containing - CH2COO- group crosslinked carboxymethyl starch (the CCMS), it has excellent ability to adsorb heavy metal ions [ 14 ]. Quanyide Ce4 + et al also used as the initiator, the grafting of acrylonitrile onto a crosslinked starch, carboxy starch graft copolymer is then obtained (ISC) by hydrolysis of the nitrile groups, it remove heavy metal ions in waste water (e.g. Cu2+, Pb2+) are also particularly effective [ 15 ]. Wang Yuting et al soluble starch as the matrix, the epichlorohydrin crosslinked, a crosslinked starch was prepared. The acrylonitrile monomer was grafted onto the crosslinked starch with Fe2+-H2O2 as an initiator , and then saponified to obtain a water-insoluble grafted carboxy starch polymer. It has excellent effect on removing Cd2+, Pb2+, Cu2+, Hg2+, Cr3+ plasma in water [ 16 ]. Ming-Hua Liu et al crosslinking and grafting process together, saving time, while salt contamination can be eliminated, the amount of adsorption of heavy metals in the resulting product is also improved [17]. Wang Zhonghua et al. studied the adsorption rate equation of carboxy starch graft copolymer for heavy metal ions . The study shows that the variation of adsorption amount with time follows the Langmuir equation [ 18 ].

3 cationic modified starch flocculant

3.1 cationic starch

Hydroxyl amine compound and the starch molecules produced etherification reaction ether derivatives having an amino group with a positive charge on the nitrogen atom, to obtain the ether derivative having many properties do not have native starch, has a negatively charged species attraction tends called cationic starch. Since most of the waste water treatment and the colloidal fine particles are negatively charged, therefore, cationically modified starch is an important research direction.

Cationic starch is an excellent polymer flocculant and anion exchanger in industrial wastewater treatment. It can adsorb negatively charged organic or inorganic suspended substances and effectively remove chromate, dichromate and ferrocyanide from wastewater. sodium molybdate, permanganate, anionic surface active agent. Gelatinized starch and a quaternary ammonium salt prepared by the reaction of the high degree of substitution derivatives thereof, may be organic or inorganic particles from flocculating the suspension, a cationic starch containing 15% to 25% of a quaternary ammonium group is a comprehensive and effective flocculant, The random propylene can be separated from the separation unit of regular polypropylene , and the flocculation effect is proportional to the relative molecular mass.

The quaternary ammonium type cationic starch is an ether derivative formed by reacting an amine compound having an epoxy group with a hydroxyl group in a starch molecule under a base catalysis. The preparation is generally carried out in two steps , first the synthesis of a quaternary ammonium etherifying agent , followed by the etherification of the starch. Yonghua et al quaternary ammonium salt as a phase transfer catalyst, at room temperature for the above synthesis of 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTMA), yield 97%. Koo et al implanted in the presence of a base catalyst, N- (2,3- epoxy-chloropropyl) trimethyl ammonium chloride (GTA) as cationizing agents, the cross-linked high degree of quaternary ammonium cationic substitution prepared Starch , this product has excellent decolorization effect on reactive dyes [ 19 ].

In addition to the quaternary ammonium type cationic starch , a series of cationically modified starch products such as tertiary ammonium type cationic starch, crosslinked cationic starch, and cationic dialdehyde starch are synthesized.

Cationic starch can also be of the anionic, amphoteric starch synthesis, using Zouxin Xi corn and sweet potato starch, crosslinked by epichlorohydrin, etherifying agent (acid and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride ) of anion and cation, to prepare amphoteric starch, amphoteric starch proved that the chelating agent is a highly efficient wastewater treatment agent, and has an excellent adsorption of heavy metals [20, 21].

3.2 grafted starch

Starch - polyacrylamide graft copolymers are compared with polyacrylamide, strong flocculation, increase the stability of the molecular chain, adapt to a wide range of cationization reaction easier characteristics, therefore, the cationic polyacrylamide grafted Starch is a new type of flocculant with good application prospects and low cost. Phan et al Hannesson cassava starch, cationic starch flocculant was synthesized [22] using the two-step process. The experimental results show that the grafted starch polyacrylamide has better flocculation settling velocity and light transmittance of the supernatant liquid than the homopolyacrylamide. Zhao Yansheng et al. carried out a one-step modification of the cationic flocculant CSGM with starch - acrylamide graft copolymer and studied the properties and obtained good results. When using this flocculant to treat printing and dyeing wastewater from Shanxi wool spinning mill , the optimum dosage is 1.5mg/L . As can be seen from Comparative Experiment different types of flocculant flocculation effect dyeing wastewater using CSGM dyeing wastewater treatment compared with a nonionic polyacrylamide, cationic polyacrylamide having better flocculation effect [23]. Maxi Chen et al starch as a substrate, a paraffin oil as oil phase, MT-1 (inorganic ammonium compound) - urea synthesis mixture as initiator and starch - dimethyl diallyl ammonium chloride (- DMDAAC) - acrylamide (AM) graft copolymer , the effect of copolymerization conditions on the grafting rate, grafting efficiency and cationization degree of the product was investigated . The grafting ratio was 126.67%, the grafting efficiency was 94.52%, and the solid mass fraction was 37.56% [ 24 ]. . Yin Hua et al . synthesized a cationic modified polymer flocculant FNQE with a starch - acrylamide graft copolymer as the precursor and a cationizing agent . The flocculant has good kaolin suspension, municipal wastewater and restaurant wastewater. The effect of treatment [ 25 ]. Yang Tong et al. used a 60Co gamma ray irradiation method to synthesize a graft copolymer of starch. On this basis, further by the reaction of methyl amine modified, the modified cationic flocculant, its structure is analyzed, and the properties have been studied [26].

4 Conclusion

In summary , in the past ten years , in the research of modified starch flocculants , China has made some progress . Through the chemical conversion and graft copolymerization of starch functional groups , a series of non-toxic, low-cost and good ones are synthesized. A flocculating effect of a polymer flocculant. However , there are still some shortcomings in practical applications , especially the research on water treatment process is less , and many products have not been converted into practical applications in time. It is recommended to strengthen the actual process research in the future , and fully consider the factors affecting the effect of flocculant on wastewater treatment , such as pH , temperature, the amount of water treatment agent and the method of use and the influence of ions in water , to develop a more effective flocculant.

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