Study On The Decomposition Of Potassium Feldspar By Mixed Sub-molten Salt And Molten-salt Method

Potassium feldspar is extensively distributed with large reserve in China.It is of high production value due to the enrichment of K₂O,SiO₂ and Al₂O₃ in ore.At present,it was focused on the topic of technique of decomposition and technology of processing and application of potassium feldspar.In this thesis,the potassium feldspar was decomposed by KOH-NaOH mixed sub-molten salt method at low temperature.Kalsilite and low silica X?LSX?zeolite were synthesized,respectively.Additionally,tobermorite was synthesized with KOH-CaO molten-salt method from potassium feldspar.At the same time,the extraction rate of K⁺was studied.Kalsilite was synthesized from the potassium feldspar by KOH-NaOH mixed sub-molten salt method.The effects of temperature,time,mass concentration of alkali,alkali-to-ore mass ratio and molar ratio of K/Na on the decomposition of potassium feldspar and the synthesis of product were investigated,respectively.Kalsilite can be synthesized with the optimal reaction conditions:temperature 190-220 ^oC,time 4.0-7.0 h,mass concentration of alkali 50-70%,alkali-to-ore mass ratio 4:1,molar ratio of K/Na1:1-2:1.The highest dissolving rate of K⁺from product is 94.69%.The transformation process from ore to kalsilite was investigated,which turned out to be dissolving-precipitation mechanism,that is,K⁺,[Al?OH?₄]^-and[H₂SiO₄]^2-in solution were precipitated to synthesize kalsilite and Na⁺is not involved in the process of precipitation.Additionally,the LSX zeolite was obtained using the decomposed filtrate from potassium feldspar as reactant.The mother liquor after preparing both kalsilite and zeolite can be recycled as reaction medium of the decomposition of potassium feldspar for the next cycle.LSX zeolite was successfully synthesized using the amorphous precursor from potassium feldspar with KOH-NaOH mixed sub-molten salt method.The effects of temperature,time,mass concentration of alkali,molar ratio of Na/K on the decomposition of potassium feldspar,and the effects of molar ratios of SiO₂/Al₂O₃,H₂O/?Na₂O+K₂O?and Na₂O/?Na₂O+K₂O?on the synthesis of LSX zeolite were investigated,respectively.The results indicated that the highly active amorphous precursor can be obtained in mixed sub-molten salt medium with 80%of mass concentration of alkali at 190 ^oC for 3.0 h.And the LSX zeolite can be synthesized in the system with the molar ratio of reaction materials?5.78-5.93?Na2O:1.65K2O:Al2O3:?2.1-2.3?SiO2:?113-125?H2O using the slurry obtained from the decomposition of potassium feldspar.The synthesized LSX zeolites present multi-faced spherulite morphology with the particle size ranging from 2 to 6?m.The dry product corresponded to a yield of 90.0%of theory based on the silica introduced from potassium feldspar.The mother liquor after preparing product can be recycled for avoiding environmental pollution and waste of resource.Additionally,4A zeolite was synthesized using the amorphous precursor from potassium feldspar by NaOH sub-molten salt method with 80%of mass concentration of alkali.And the molar ratio of reaction materials was3Na₂O:Al₂O₃:2SiO₂:185H₂O.Our results suggest that the amorphous precursor of the potassic rocks prepared after the activation of sub-molten salt method can be used for the zeolites synthesis and thus demonstrates itself a promising feedstock for the green synthesis of zeolites directly from natural aluminosilicates.The tobermorite was synthesized from potassium feldspar with the KOH-CaO molten-salt method.The effects of temperature,mass ratios of KOH/ore and CaO/ore on the synthesis of tobermorite were investigated,respectively.Tobermorite can be synthesized with the optimal reaction conditions:temperature 500 ^oC,time 2.0 h,mass ratio of KOH/ore 1:1,mass ratio of CaO/ore 0.5:1.The synthesized tobermorite was spherical agglomerate by short fibrous tobermorite crystals.And 96.00%of extraction rate of K⁺in this system can be achieved.