Decomposition Of Potassium Feldspar In NaOH-Na₂CO₃ Mixed Sub-molten Salt And Its Comprehensive Utilization

Potassium feldspar is insoluble potassium ore which is extensively distributed with large reserve in China.It is theoretically containing K2O 16.9%,SiO2 64.7%and Al2O318.4%.Therefore,it is very important to transform potassium,silicon and aluminum resources contained in potassium feldspar into high value-added products.NaOH-Na2CO3 mixed sub-molten salt was used to decompose potassium feldspar.The effects of the ratio of Na2CO3 to the total amount of alkali,NaOH-Na2CO3 concentration,liquid-to-solid mass ratio,reaction temperature and time on the decomposition of potassium feldspar were studied.The results indicated that the dissolution rate of K+ up to 95.33 wt%and cancrinite can be obtained when the ratio of Na2CO3 to the total amount of alkali was 1/2,concentration of NaOH-Na2CO3 was 50 wt%,liquid-solid mass ratio was 3:1,reaction temperature was 200 ? and the reaction time was 4 h.The aluminosilicate residues can be obtained when the pH of the decomposed mother liquor was adjusted to 9 by adding carbon dioxide.Then the acidified mother liquor by adding NaOH can be recycled for the decomposition of potassium feldspar.With the filtrate obtained from circulating the acidified mother liquor four times as the reactant,the industrial-grade potassium carbonate and sodium carbonate were produced by evaporating,cooling,crystallizing,separating and purifying.The industrial-grade potassium carbonate is met the criterion of GB/T1587-2000 and the sodium carbonate is met the criterion of GB 210.1-2004.At the same time,the aluminosilicate residues were used to synthesize molecular sieve after adjusting the ratio of component by adding the alkali source,the aluminum source and H2O.The results indicated that zeolite 4A was hydrothermally synthesized from aluminosilicate residues,NaOH,NaAlO2 and H2O with a formulation of Na2O/SiO2=2.10,Al2O3/SiO2=0.53,H2O/SiO2=52,followed by aging at 70 ? for 2 h,and crystallizing at 95 ? for 5 h.Under the optimal conditions,the zeolite 4A has a high Ca2+ exchange capacity(about 308 mgCaCO3/g),uniform particle sizes(between 1-2 pm)and good thermal stability.Also its other properties are met the criterion of QB/T 1768-2003.And the aluminosilicate residues were used to synthesize zeolite W after adjusting the ratio of component by adding KOH,Al(OH)3 and H2O.It was revealed that a batch of uniform,well crystallized and thermostable zeolite W was produced under the aging temperature of 30 ? for 2 h,and crystallizing temperature of 150 ? for 24 h with the ratio of K2O/SiO2 =1.0,Al2O3/SiO2=0.067,H2O/SiO2=45 in the reaction system.The K+exchange capacity of the product in the artificial simulated seawater is about 57 mg/g.