| Owing to the fault of the basic research on the coprecipitation process and the problems of difficult control of ratio among components, size and their morphology, the basic research of coprecipitation process was systemly studied in this paper. The process of direct coprecipitation by the results of basic research was studied lastly, good coprecipitation powders and high-quality soft magnetic ferrite sample were prepared, some significant results were obtained too.After Gibbs free energy and thermodynamics data of all sediments were calculated, the components of coprecipitation powders were ascertained, namely MnCO3, FeCO3 and ZnCO3.2Zn(OH)2.H2O.The relationship between Me(OH)2 or MeCO3 and the value of pH where they began to be formed, was assayed. The results showed that the value of pH began to form Me(OH)2 was bigger than that began to form MeCO3, which testified the coprecipitation powders were composed of salts carbonate. Furthermore, which showed that the values of pH began to form FeCO3 and MnCO3 were very close, while the pH began to form ZnCO3.2Zn(OH)2H2O was the least, so Zn2+ was precipitated at first, Mn2+ and Fe2+ were following.The thermodynamics in the system of Me(Ⅱ)-NH3-CO32--SO42--H2O had been analyzed by the computerized accounting index method for constructing thermodynamic diagrams of the relationship between [Me2+]T and all of the conditions. The highest and the lowest solubility fields were revealed, while pH was the important demarcate sign. The three metal ions had the same field of precipitation where their carbonates have the lowest solubility, the up limit of pH was decided by the value of pH where Zn2+ precipitated completely, while the down limit of pH was decided by the value of pH where Fe2+ precipitated completely. The value of pH where three metal ions coprecipitated was 6.5 to 7.0 when the amount of the [CO32-] ([C]T) was 0.1mol.L-1 and the concentrate of ammonia and ammonium ([N]T) was 10 mol.L-1.The thermodynamics in the system of Mg(Ⅱ)-Ca(Ⅱ)-NH3-CO32--SO42-H20 had been analyzed by the same method for constructing the thermodynamic graphs of relationship between [Me2+]T and all of the conditions. The laws of solution of MgCO3 and CaCC>3 in the system had been revealed, the highest the lowest dissolution field of MgC03 and CaCO3 had been found too. While the higher dissolution field of MgCO3 was included in the best coprecipitation field. So magnesium could be removed in the coprecipitation process.Using mixture of NH4HCO3 and NH4OH or NH4HCO3 as precipitation agent, the procipitation process of Zn2\ Fe2+ and Mn2+ had been researched respectively in the system of salt sulfate. Technology parameters that affected components, size, morphology of coprecipitation and precipitating ratio had been confirmed, and sediments that was comprised of MnCO3, FeCO3 and ZnCCV2Zn(OH)2-H2C) respectively. But FeCC>3 was instable and would be disassembled a -FeO(OH) and Fe3O4 when it was drying. Under the optimum conditions, was complete sediment, could size be controlled and was size distribution narrow.By use of solutions of MeSC>4 that proportion of every metal concentrate was coincided with that in low power consumption materials as raw solutions, the laws that factors affected coprecipitation process were studied. Under the optimum conditions with the mixture of NH4HCO3 and NH4OH as precipitating agent that was co-dump, reaction temperature of 50°C, reaction time to be 50min, feeding time to be 50min, ambient maturation, maturation time being 12h, concentration of metal ions being 1.5mol\L"\ addition of NH4HCO3 to be theoretical 1.2 times, ph=7.0, was the size of coprecipitation powder 2.56 u m, was the precipitation ratio of Fe2+, Mn2+ and Zn2+ 99.962%, 99.870% and 99.328% respectively. When NH4HCO4 was used only as precipiting agent, all the conditions were the same as those except maturation time was 24h, the precipitation ratio of Fe2+, Mn2+ and Zn2+ was 99.965%, 100.00% and 99.302% respectively, the size of coprecipitation powder was 3.80 jum. Those circumstances showed that the two precipitation agents could control the ratio and the size of coprecipitation powders.On the basis of theories and experiments, large experiments of lOkg/tank and industry experiments of 500t/a had been carried out. Thelab experiments and industry experiments showed that the solution of MgCO3 was increased when the value of pH was brought down only, and the content of magnesium in the coprecipitation powders would be reduced directly. When the value of pH was controlled in the field of 6.5 to 7.0, the content of magnesium and calcium in the coprecipitation powders was 0.0084% and 0.006% respectively on lab experiments, while it was 0.0125% and 0.0445% respectively on industry experiments, they could be used to prepare high-quality soft magnetic ferrite. The quality of sample that was prepared by ferrite process could come up to PC30 and some met with that to PC40 of TDK in Japan furthermore.
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