Preparation Of Layered Sodium Silicate From Nepheline Syenite: An Experimental Study

According to the supply and requirment report of nonmineral resources , sylvite and aluminosilicate are most scarce nonmineral resources in China,and the demands are still rising.Nepheline syenite is an important mineral resource rich in SiO2,Al₂O₃ and K₂O,the mass fraction of Al₂O₃ and K₂O are about 20% and 10%.So we can use nepheline syenite to preparation Al₂O₃ and K2SO4, as well as inorganic silica compound.Nepheline syenite from Gejiu of Yunnan province was used as real materials,with the composition of 53.67%SiO2,22.08%Al₂O₃ and 12.54%K₂O, which is mainly composed up of microcline and nepheline syenite.The whole technical processes for treating the nepheline syenite is as follows: sintering process, with Na2CO₃ as an additive, transferring the microcline into nepheline which can dissolve in sulfuric acid; dissolving process, making SiO2 changing into silica gel and Al₂O₃,K₂O entering the solution;preparation process,using the silica gel separated and solution contain Al3+,K+ prepared inorganic silica compound,alumina and potassium sulphate..Thermodynamic calculation shows that the temperature of the sintering reaction is around 800K,with sodium carbonate as the additive, and the products were mainly NaAlSiO4,KAlSiO4 and Na2SiO₃. The sintering experimental results show that the decomposition temperatures of the major aluminosilicate minerals in the nepheline syenite were ranging from 1073 to 1123K,and the products were those as expected. The mixtures of the nepheline syenite and Na2CO₃ were calcinated at 850℃for 90min, and sodium carbonate / nepheline syenite (in mass) was 0.75. The decomposition rate of minerals in the nepheline syenite is over 95%. Acidic Leaching experiments of the sintered products by acidic solution show that the separation of silica and alumina by the current procedure is superior, with extraction rates of SiO2, Al₂O₃, K₂O up to 91.4%, 92.2%, 92.5% respectively.The silica aerogel and layered sodium silicate were prepared by sol-gel and chemical precipitation methods.The silica aerogel BTH-1 and BTH-2 were prepared from silica gel through abstersion and sintering. The SiO2 content of the products is over 99.50%, and reaching the standard of the silica areogel TMS-100P, and specific surface area is up to 600m2/g.The layered sodium silicate is a new builder in detergents which may supersede sodium tripolyhosphate (STPP) in the future.In this thesis, the layered sodium silicate was preparedwith the separated silica gel and NaOH. The mixtures of the separated silica gel and NaOH were calcinated at 750℃for 25min, and SiO₂/ Na₂O(in mass) was about 1.8².3. The characteristic of the layered sodium silicate sample GJ-CG-4 accord with the enterprise standard of Clariant in Spanish. Its Ca²⁺ and Mg²⁺ binding capacity is 370mgCaCO3/g and 450mgMgCO3/g respectively, and pH=10.5.