| The accumulation of chrysotile tailings are not only a waste of mineral resources, but also cause the pollution of the atmosphere, water, and soil. The chrysotile tailings also have great harmfulness to the ecological environment and human health. This paper takes Gansu province Aksay asbestos tailings as raw materials. The Gibbs free energy change of the direct baking asbestos tailings and adding roasting additive （including （NH4）2SO4, NH4HSO4, （NH4）2SO4-H2SO4, Na2CO3 and NaOH） mixed roasting asbestos tailings was calculated. The optimum roasting conditions of the technology of extracting magnesium from asbestos tailings by mixed （NH4）2SO4-H2SO4 and reaction mechanism of roasting process were studied. Non-isothermal kinetics of the roasting process was calculated in detail. The preparation of high purity silicon and magnesium compounds by using Magnesium Sulfate solution and water leaching residue was studied. The crystal growth kinetics of magnesium hydroxide and silica precipitation kinetics was calculated. Finally, comprehensive evaluation was done to sulfuric acid and ammonium sulfate roasting cycle process.The results show that reactivity of sulfuric acid and ammonium sulfate roasting method just below the ammonium hydrogen sulfate roasting method. Effect of reaction gas partial pressure to the six methods have same trend, but the magnitude of impact is different.Using ammonium sulfate as roasting additive, concentrated sulfuric acid as activator, the extraction rate of Magnesium Oxide can be reached at 86%. Leaching residue inherited physical characteristics of the tailings well. Reaction process of ammonium sulfate roasting method can be divided into three phases. Most probable mechanism function of the first and second phases are G（a）=-ln（1-a）, f（a）= 1 - a, the most probable mechanism function of the third phase are G（a）= [-ln（1-a）]2/3 and f（a）= 3/2（1-a）[-ln（1-a） The apparent activation energy Ea of the three steps are, successively, 93.21kJ·mol-1 162.34kJ·mol-1and 122.21kJ·mol-1. Pre-exponential factor 1gAk are 12.25S-1,20.36 S-1 and 14.17 S-1, successively.Refined magnesium sulfate solution as raw material, by simultaneous injection of precipitation at pH value for 10.5 conditions, the magnesium hydroxide sheet was of prepared, and the conversion rate Mg2+ was 94.8%. Kinetic analysis showed that the crystal quality ofMg（OH）2 and the average size of the crystal showed a trend of exponential increase with the prolonging of the reaction time. Use amagnesium hydroxide as raw materials to prepare Magnesium Oxide by roasting. The experimental results show that with the increase of the calcination temperature, the grain size of Magnesium Oxide increases gradually. Sodium silicate was prepared by alkaline leaching of water leaching residue, and then the superfine silica was prepared under the condition of system pH 8.5. Dynamic experiments show that this preparation process belongs to the two stage reaction, kinetic constants was 0.0019dm3/（mol·min）, and the reaction rate equation was r=0.0019（a-x）（b-x）.The results of sulfuric acid and ammonium sulfate roasting cycle processe show that ammonium sulfate and carbon dioxide can be recycled. Recovery of ammonium sulfate of calcination process reaches 88%, and in the process of preparation of magnesium hydroxide recovery of ammonium sulfate reaches 86%. Sulfuric acid and ammonium sulfate roasting cycle processe achieve target that a variety of compounds can be prepared in a process by researching the experim-ental conditions, including Mg（OH）2, magnesium carbonate, MgO and nano-SiO2 powder. The process can bring significant environmental benefits, and economic benefits. |
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