| Aluminum and iron salts are commonly used as coagulants in the treatment of water for public supply. In recent years, public concerns about the potential connection between the residual aluminum in drinking water and the suspected adverse health effects, e.g., Alzheimer's disease, have been brought to intense discussion. As a result, the use of iron-based coagulants has gradually gained in popularity. It is believed that better control of the chemistry of metal salts, the desirable highly charged cationic coagulant species can be obtained prior to their application. The objectives of this research are thus to prepare and characterize polyferric chloride (PFC) and to investigate the performance of PFCs in flocculation under varying conditions.By a series of experiments on raw material selection, preparation condition optimization and efficiency examination, it was found that oxidation method was favorable to prepare high quality and stable PFC when stabilizer existed. Moreover, this technique has been put into plant scale production with high economic and social profit.To prepare various polyferric solutions for characterization, ferric chloride solutions have been partially neutralized by adding NaHCO3 or NaOH solution at a range of hydrolysis ratio (0lmol/L) prepared by partially neutralization was prone to precipitate in short time, then deteriorated its coagulation behavior. Based on the researches of the past ten years, different phosphates were used to stabilize the PFC solution in this paper, which mainly focused on the stabilizer effect on the precipitation time, coagulation process and species distribution of Fe(III) hydrolysis. The results suggested that phosphate (AP) and (AH2P) could influence the Fe(III) hydrolysis way and were suitable as stabilizer. The experiments of streaming current indicated that the stabilizer,could benefit the coagulation process when the molar ratio of P to Fe is 0.07.On the condition of concentrated solution (>lmol) and stabilizer existence, the preparing technology of BPFC had been studied by species determination and jar test. The results showed that NaHCO3 was a little better than NaOH as the injection base, the appropriate speed of base injection could improve the stability of PFC, and the pre-addition of stabilizer was the best choice in BPFC preparation. Because BPFC solution had the min-precipitation time at the basicity of 0.4, this basicity should be avoided in preparation. It can be seen from FTIR (Fourier Transformation Infra-red) spectra that the stable action of PO43" is influenced by time point of stabilizer addition.To improve the relatively low stabilization and high cost of BPFC prepared bybasification, the pickle oxidation preparation method (OPFC) was put forward. Because few studies had addressed on the ferrous oxidation and hydrolysis in acid medium, ferrous oxidation was further investigated in this paper. The initial acid concentration, the oxidant adding way and the injection time of acid (aimed to adjust the basicity B) were all important factors, which affect the species distribution, stability and coagulation behavior of PFC. At last, the optimum oxidation conditions were obtained: (I) the initial acid concentration should be lower than 0.6mol/L; (2) the oxidant solution addition speed should be in the range of l-6.5mmol/min to 100ml Fe(II) solution; and (3) the acid injection to adjust the basicity B should be after the oxidant addition. The analysis of FTIR spectra indicated that complex forms of PO43" and Fe(III) species, which affected the stable action of PO43", were different under various preparation conditions.The PFCs efficiency prepared by both methods has been assessed by comparing them with conventional FeCl3 salts and polyferric sulfate in coagulation experiments. The results revealed tha...
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