Technological Optimization And Characterization Of Fe₃O₄ Magnetic Powders By Modified Co-precipitation Method

Combined with the merits and demerits of conventional co-precipitation method and precipitation-oxidation method,and the characteristics of waste pickling liquor.Without the protection of inert gas,a new type of modified Co-precipitation method is adopted to make Fe²⁺in waste pickling liquor partly oxidized to Fe³⁺?Using hydrogen peroxide as oxidant?by oxidation of waste pickling liquor.Using hydrogen peroxide as oxidant to partial oxidation of Fe²⁺of waste pickling liquor into Fe³⁺.The way of measuring the numerical value of Oxidation-reduction potential?ORP?is employed to monitor the molar ratio of Fe²⁺and Fe³⁺in the waste pickling liquor.Then,Fe₃O₄magnetic powders are obtained by adding the alkaline precipitation agent.Through the analysis of temperature,acid content and initial concentration of Fe²⁺by means of single factor experiment,the standard curve of Fe²⁺and Fe³⁺mole ratio in reaction system and Oxidation-reduction potential under different factors is plotted to make a preparation for latter experiments and the variation trend of the standard curve is analyzed.The result shows that Oxidation-reduction potential of reaction system is greatly affected by the temperature and the Oxidation-reduction potential is linearly increased with the increase of temperature.The acid content has a negative correlation with the Oxidation-reduction potential of waste pickling liquor.The higher of acid concentration,the lower of the Oxidation-reduction potential.And they have a good linear relationship under the common concentration range of waste pickling liquor.The initial concentration of iron salts in waste pickling liquor has little effect on the Oxidation-reduction potential.In this study,the orthogonal experiments of 3 factors 4 levels are designed to study the reactive temperature,organic sodium salt addition and aging temperature which affect the properties of Fe₃O₄.Thus we determine the optimum technological conditions for the preparation of Fe₃O₄ magnetic powders.The mechanism and influence of organic sodium salt addition,reactive temperature,inorganic sodium salt addition,aging time and drying temperature on the Fe₃O₄ magnetic powders are discussed by single factor experimental way.The best preparation conditions for the Fe₃O₄ magnetic powders are that reaction temperature is 50?,aging temperature is 90?,organic sodium salt addition is 0.2 g,PEG addition is 1 g,inorganic sodium salt addition is 2.5 g,drying temperature is80?.The Fe₃O₄ magnetic powders prepared under this condition are characterized,the saturation magnetization is 85.951 emu·g^-1,residual magnetization is 7.1772emu·g^-1,coercive force is 57.363 Oe,granularity is 0.28?m,oil absorption is 27.2mL/100 g.Its magnetic properties,Physical characteristics,chemical composition run up to the mature product level in the market.