| Flocculants are the important materials in water treatment. At present, flocculants based on aluminum and ferric salts are chiefly used abroad and in China. Because of low efficiency and environment problems by the aluminum salt, and the corrosion by ferric salt, in the world, the research and application of flocculants are required to develop to high efficiency, low consumption, safety, harmlessness and non-second pollution. The composite flocculants are one of important development trends in future. In this paper, ZnSO4·7H2O has been used as the materials to study the preparation and flocculation theory of composite flocculant based on zinc with higher flocculation efficiency, partly replacing the organic synthesis polymer flocculants, non-toxicity and environment-friendly. The main researches of this paper are: the study of inorganic polymer composite flocculant - poly silicate zinc sulfate (PZSS), inorganic-organic composite flocculant (Zn-CSM) based on zinc sulfate and cationic starch-modified, inorganic-organic hybrid flocculant (H-ZnPAM) on the basis of zinc hydroxide [Zn(OH)2] in nanometer size and polyacrylamide (PAM). They all include the investigations of preparation, flocculation mechanism, flocculation effect, wastewater treatment application and so on.(1)The studies of PZSS are summarized as following:The researches about PZSS showed that the percentge of SiO2 was between 1.3～2.2 %, the molar ratio of zinc to silicon was between 1.0～2.0, the pH value of PZSS was 1.5～2.0, the polymerization time of silicic acid was between 12 hours, the flocculant had excellent flocculation and better stability.The flocculation theory of PZSS was probed with micro-electrophoresis technology which revealed the advantageous configuration and provided the science basis for researching the flocculants. By studying the pH value change rules of PSA and PZSS, it was found that in the initial stages of preparation, their reaction was not in equilibrium but was in the process of interaction and adjust to aggregate by self, which was exhibited that there existed a changing process of pH value. The results of IR, XRD and TEM proved that the reaction was not the simplex physical blend, but the chemical reaction forming the inorganic polymer with special structure. The structure of PZSS are lied on the concentration of SiO2, molar ratio of Zn/Si, polymerization time, pH value and so on. There are some interactions between silicic acid, PSA, zinc hydroxide radicle and silicic hydroxide radicle. Zn2+ and hydrolyzed ion are chelated with polysilicic acid to produce the polymer of zinc-silicon. The chelation of Zn2+ with PSA, and the macromolecule PSA with stronger adsorption and bridge function can help to boost up the flocculation performance of flocculants.The researches about the species distribution and transformation of PZSS by Si-Mo timed complexation for colorimetric method displayed that the high aggregate species (Sic) was in PZSS at low pH value (0.8) after depositing for some days; the content of Sib in PZSS with higher pH value (1.5 and 2.0) was more than that in PZSS with lower pH value. It was proved from the flocculation experiments that the optimum species in PZSS for flocculation was Sib, and PZSS at pH 1.5 and 2.0 had better flocculation efficiency than at lower pH value of 0.8.Zeta (ζ) potential investigations showed that the charge characteristics of PZSS changed with pH value, concentration of SiO2, Zn/Si molar ratio of f1occulants, and so on. The flocculation mechanism of PZSS does not display the prominent charge neutralization ability, but reveals the obvious effects of absorption-bridging and net-sweeping.(2)The new type of inorganic-organic composite flocculant named cationic starch-modified with zinc radicel was prepared with ZnSO4·7H2O and cationic starch-modified.The optimal procedure was determined by orthogonal experiments and so on. The reaction conditions are as following:①The cationic polymer (CF) was prepared with ethylene diamine as the cross-linking agent at the molar ratio n(epichlorohydyin)/n(organic amine) 1.5:1 and 65～70℃for 3 h;②Starch was preliminary gelled with 4 % NaOH at 65℃for 2 h; the cationic starch-modified (CSM) was inarched at 50℃and the weight ratio (CF/starch) 1.8:1 for 2 h;③The inorganic-organic composite flocculant of cationic starch-modified with zinc radicel (Zn-CSM) was synthesized with ZnSO4·7H2O and CSM at the optimum conditions: pH value of CSM was adjusted to 5.0 with the weight ration of ZnSO4·7H2O/ CSM 1:1 at 45℃for polymerizing 3 h.It was known by flocculation experiments, microphotometric method and TEM for Zn-CSM that the optimum range of flocculation pH value was between 6.0～9.0 and the optimal flocculation species was the complex zinc hydrolysis polymer with positive charge after forming [Zn(OH)4]2-. The analysis results indicated that the excellent flocculation capabilities were determined by its special structure of molecule, which was the results of charge neutralization in cooperation with adsorption bridge and net-sweeping. (3)Based on the research of inorganic-organic composite flocculants, the inorganic-organic hybrid flocculant: ionic hybrid of Zn(OH)2–polyacrilamide (H-ZnPAM) was synthesized by in-situ polymerization.The hybrid flocculant was characterized with IR spectrum, viscosity, conductivity, TEM and TGA. The results showed that the flocculant H-ZnPAM could be the hybrid with ion bond between inorganic particles and polyacrylamide, i.e., PAM with negative chain end (-SO42-) bonding to the positive particle of Zn(OH)2 in H-ZnPAM. The influences of particle radius and dosage of Zn(OH)2, etc., were investigated systematically and it was found that dilute solution viscosity of H-ZnPAM increased at first and then declined with the increase of Zn(OH)2 particle radius and Zn(OH)2 dosage.Dilute solution viscosity behaviors of the hybrid flocculant were studied by viscosity method. The experiments proved that the viscosity behaviors of H-ZnPAM were deviated from Huggins equation in dilute solution, which was different from pure PAM. That is, the reduced viscosity (ηsp/C)～concentration (C) curve of the H-ZnPAM had a downturn at low concentration region. The effects of molecular weight, particle radius of inorganics and content on the deviation of dilute solution viscosity behaviours were researched. The results displayed that the concentration (Cη) correspond to the moment when the curve ofηsp/C～C started to downturn, increased with enhancing the inorganics particle radius and content, but reduced with increasing the hybrid molecular weight. This phenomenon is accounted for assuming ionization of the ionic hybrid PAM. Studies on ionization behavior of H-ZnPAM in dilute solution by conductivity method were illuminated that the curve of KC displayed non-linear behaviours. If CK was defined the concentration when the curve of KC began to downturn, the influence rules of molecular weight of H-ZnPAM, radius of inorganics particles and dosage on CK were analogous with that on Cη.The cluster theory of polymer solution was applied to explain the mechanism of polymer flocculation. The formation of polymer chain cluster in dilute solution is the necessary condition to cause the optimal flocculation. The structure of hybrid flocculant H-ZnPAM can be not only in favour of exerting charge neutralization and adsorption for inorganic flocculants as well as bridge for organic flocculants, but also can help to produce chain cluster for polymer. The investigation showed that the optimal dosage (Cod) of polymer flocculants was linearer to the dynamic contact concentration (CS) of polymer flocculants and the suspension solid concentration (CSS) in diatomite suspensions, i.e., Cod=5.8×10-2·(CS·CSS)0.5 - 4.1. The result illuminated the interrelation between the congregation state of polymer molecular chain in dilute solution and flocculation effect. Furthermore, it is important to form the polymer clusters in dilute solutions for reaching the optimal flocculation.(4)Zinc flocculants were applied in oily wastewater and oily sludge.The new type of zinc flocculants had better flocculation efficiency than conventional flocculants such as poly-aluminum chloride (PAC) and poly-ferric sulfate (PFS), and the hybrid flocculant showed the best flocculation performance, less shear sensitivity and more dense flocs than other flocculants. The results of oily sludge dewatering experiments indicated that the hybrid flocculant and PZSS had the best dewatering efficiency, the heat value was increased to 40 times of the primary after treated. The densed sludge was easy to mold and peel off, and could be incinerated with low cost and less pollution. Accordingly, the zinc flocculants are promising in wastewater treatment.
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