| Pyrite cinder is the industry waste residue which is produced in the process of pyrite sulfuric acid manufacture. Every time along with production of 1 ton sulfuric acid is 0.8 ton of pyrite cinder,12,000,000 ton of pyrite cinder approximately have been discharged every year in China. As waste resources, such plentiful pyrite cinder emissions and stack, not only take land, but also work a series of environment problems. So, disposal of pyrite cinder has already become an important part of solid wastes in China. If we could use comprehensively beneficial ingredients in pyrite cinders, we not only might recycle national resources, enhancing the enterprises' benefits, but also could solve the environment problem, therefore it has vital practical significance. This thesis discusses how to use high-purityα-Fe2O3 for soft magnetic ferrite use, transparent iron oxide yellow, magnetic recording materialsγ-Fe2O3 have been prepared from pyrite cinder.Using sulfuric acid to leach pyrite cinder, scrap iron was used to reduce acid leaching solution. A purifying ferrous sulfate solution was obtained after when the new Fe(OH)3 sol was created by passing it through air, furthermore adsorbed the impurities such as colloidal silicic acid and by using NH4F to remove Ca. The ferrous carbonate was obtained when the ferrous sulfate solution was reacted with carbonate. The high-purityα-Fe2O3 for ferrite use is up to the standard of HG/T2574-94 after dried the ferrous carbonate product is calcined at 870℃for 1h. In the process of leaching pyrite cinder with sulfuric acid, reaction temperature has the greatest influence on the rate of iron recovery. Under the controlled conditions that sulfuric acid concentration is 50%, coefficient of the sulfuric acid dosage is 1.1, reaction at 118℃for 4h, the rate of iron recovery is up to 92.0%. In the process of reducing acid leaching solution with scrap iron, there are the faster reactive velocity and the high percent of reduction when Fe3+ is reduced to Fe2+ under the conditions of Fe3+ concentration of 1.6mol/L in acid leaching solution. In the process of removing Si with oxidation-flocculation by passing it through air and removing Ca by sedimentation with NH4F, under the controlled conditions that reaction temperature is 60℃, NH4F dosage is 4g, the ferrous sulfate solution pH adjustment 6.0 by ammonia, air flow rate is 0.2NM3/h, when solution pH is up to 5.0 for atmosphere oxidation, the dosage of flocculant polyacrylamide is 20～30ppm, settled and ageing 6～12h, the purified ferrous sulfate solution is obtained by filtrating. FeSO4-7H2O was crystallized from the ferrous sulfate solution by concentrating and cooling that is up to the chemical reagent standard of GB664-93. In the process of preparativeα-Fe2O3, under the controlled conditions that the concentration of the ferrous sulfate solution is 1.Omol/L, beginning pH of the solution is 2-3, reaction temperature is room temperature (less than 40℃), under moderate strength stirred, slowing addition ammonium carbonate proportioning by academic cost 1.1 double, after reacting 1h, the quality of a-Fe2O3 for soft magnetic ferrite use product is up to the standard of HG/T2574-94 after dried ferrous carbonate product by filtrating and sluicing is calcined at 870℃for 1 h. The content of Fe2O3 in the a-Fe2O3 product attains 99.4%, the apparent gravity is 0.95 g/cm3, the appearance color is purple-brown-red, the content of silicon dioxide and calcium oxide in the a-Fe2O3 product can be reduced to less than 0.01%.The nanometer crystalline forms a-FeOOH is obtained by air oxidizing, dropping ammonia and surfactant-modified method. The test results show that the eligible a-FeOOH crystal seed is obtained under the controlled conditions that ferrous sulfate concentration is 40%, alkaline ratio is 0.25, air flow rate 0.16-0.2m3/h, stirred rate 500-600r/min and reaction temperature at 30℃for 5h. In the process of secondary oxidation of a-FeOOH growth, the eligible a-FeOOH crystal is obtained under the controlled conditions that the content a-FeOOH crystal seed is 1.0%, beginning ferrous sulfate concentration is 0.40-0.50mol/L, air flow rate 0.6m3/h, stirred rate 800-900r/min and reaction temperature at 80℃for 50h. Finally, the goethite particle would be modification by dispersant tartaric acid and surfactant SDBS. The quality of a-FeOOH product is up to the standard of HG/T2574-94. The nanoparticles were characterized by X ray diffractometry (XRD), and transmission electron microscopy (TEM). The results showed that the homogenous acicular particles with good gloss and dispersion were a FeOOH. The average major axial diameter of the particles was 95-125 nm, and average minor axial diameter was 18-25 nm.Preparation process of magnetic recording materials y-Fe2O3 was investigated in detailed. Reaction process of preparation of the acicular a-FeOOH by air oxidation in the alkali condition was researched. The results show that the reaction order is zero for Fe(II), apparent activation energy is 6.84kJ/mol, and its rate equation is:The reaction mechanism is belong to the process of one solid ferrous hydroxide change from another solid goethite. The crystal shape of resultant have evident infection. The effect of process parameters such as reaction temperature, pH value, air rate, stirring rate, ferrous sulfate solution concentration and alkaline ratio on the crassitude and integrity of FeOOH particles was studied. The results showed that the ferrous sulfate solution concentration 0.3mol/L, reaction temperature 40℃, air rate 0.2 m3/h, stirring rate 420rpm, alkaline ratio 0.7 can be obtained acicular a-FeOOH of the average major axial diameter of the particles was 0.322μm, and average minor axial diameter was 0.028μm, and the aspect ratio was 11.5.In the process that the a-FeOOH is changed toα-Fe2O3 by dehydrating heat treatment, TG-DAT test shows that the reaction order is 0.81 forα-FeOOH, apparent activation energy is 147.65kJ/mol, The reaction mechanism is belong to Valens planar diffusing. The crystal type integrity acicularα-Fe2O3 is obtained when the a-FeOOH was heat treatment at 380℃for 60min.In the process that theα-Fe2O3 is changed to Fe3O4 by deoxidizing heat treatment with H2, thermodynamics analysis and XRD test shows that the deoxidizing process exists various phase change. The effect of process parameters such as deoxidizing reaction temperature, H2 flow, deoxidizing time on Fe304 particles was studied. The results showed that the deoxidizing reaction temperature 380℃, H2 flow 150ml/min, deoxidizing time 60min can be obtained the crystal type integrity acicular Fe3O4.In the process that the Fe3O4 is changed toγ-Fe2O3by oxidizing heat treatment with air, TG-DAT, XRD and technics test shows that the oxidizing process exists two phase change. The effect of process parameters such as oxidizing reaction temperature, oxidizing time onγ-Fe2O3 particles was studied. The crystal type integrity acicular Y-Fe2O3 is obtained when the Fe3O4 was heat treatment at 240℃for 45min.In the process of preparativeγ-Fe2O3 by sol-gel, the experimentation results showed that the complexing ferrite citrate sol was synthesized under the controlled conditions that ferrite citrate concentration is 0.8mol/L, the solution pH value was adjusted 7 by ammonia, reaction temperature at 40℃for concentrating 4/5. The Fe(III)-citrate complex gel powde was obtained that the Fe(III)-citrate complex was decompression dried in vacuum for 4h, dried in 80℃for 4h, dried in 110℃for 8h. The dry gel powder were analyzed by TG-DTA,XRD,FT-IR, The results show that theγ-Fe2O3 is obtained when dry gel powder was calcined at 450℃for 2.5h. The structure and crystal phase of the powders were characterized by XRDand TEM. Its primary crystal size calculated accurately by Deby-Scherrer equation was 32nm.
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