Study On Phosphating At Middle-low Temperature And Flocculant

Phosphating, as a broad metal surface treatment, may alter the original characteristic of metal surface and provide new physical or chemical properties. Although phosphating in our country has made greatly progress, it still exists many shortcomings, such as high energy consume, low efficiency, serious pollution and unstable performance of phosphating solution etc. Therefore, it is necessary to develop a nice quality phosphating process.Through perpendicular experiment means, a new phosphating process at middle-low temperature is developed. The formula is as follows: zinc oxide is 7.5g/L, phosphate acid(85%)is 15.0mL/L, nickel nitrate is 1.0 g/L, sodium sulfate is 0.4 g/L, accelerator is 1.5 g/L, additive is 0.8g/L and complex is 0.5g/L. The feasible temperature range is 30~50癈, pH is 2.5~2.8 and the time for phosphating is 3 ~5 min.Chemical immersion, copper sulfate drop test, film weight measuring and electrochemical tests were investigated to analyze the phosphating film. The results indicated that the anodic dissolution performance of the carbon steel was improved after phosphating. According to the scanning electron microscope analysis, the phosphating film was crystal type, which appeared net and slices structure. Since this film was compact and uniform, it possessed good corrosion resistance. This phosphating process has low cost, fast film-forming rate and stable performance virtues. Thus it has application value in industry.Although there are many ways of water treatments in present, the wide application, low cost and classical method is coagulation. But the research on flocculants is in development stage. So it is necessary to develop new type, high efficient, secure and economical flocculants.In the experiments, a new style polyferric silicate sulfate was prepared in two steps. First, the polymerization of polysilicic acid was synthesized in solution containing 3%SiO2 at pH 5.0-5.5 for 25~30min. Then it was cured for 3h afteradding iron sulfate(the mol ratio of Fe3+/SiO2 is 0.8). This polyferric silicate sulfate presents the best coagulation efifect in the condition of 6-11 pH range, 30min coagulating time and 6mL/L concentration. After treatment, the photopermeability rate of waste water is 94.5% and Chemical Oxygen Consumption(COD) is 1.8 mg/L, respectively.Based on these experiments, the best compounding formula was chosen by perpendicular experiments. The formula is as follows: polyferric silicate sulfate is 5ml/L, polyacrylamide is 3mL/L and promoter is 3mL/Lo The flocculating time is 25min. After coagulation, the photopermeability rate of waste water is 97.6% and COD is 1.62mg/L, respectively.The effect of compounding flocculant is better than that of polyferric silicate sulfate. Because of its low cost and high efficiency, the compounding flocculant possesses good practical value.