| Potash feldspar is a aluminum silicate mineral composed of mass silicon and aluminum.Only consider the recovery of potassium and other valuable components are not involved in,which are resource-wasting and not environmentally friendly.Therefore,it is necessary to develop a feasible method to treat potash feldspar responsibly and comprehensively by sintering in medium temperature with co solvent such as sodium carbonate.Theoretical and technical studies were carried out with the modern technology and some meaningful conclusions were obtained.The main contents and conclusions of this paper are as follows:1.Based on the results of thermodynamic analysis,the feasibility of extracting silica from potash feldspar by Na2CO3 roasting method is determined.The technology process for extracting silica from potash feldspar by Na2CO3 roasting method is studied.This technology mainly includes two parts:roasting by Na2CO3 and leaching by NaOH.The optimized reaction conditions in the roasting process are as below:molar ratio of Na2CO3 to potash feldspar 1.2:1,reaction temperature 875℃,reaction time 80 min,and granularity 74～89 μm at which the extraction rate of silica is 98.13%.The appropriate digestion conditions are concluded as follows:digestion temperature 95℃,digestion time 80 min,stirring intensity 400 r/min,clinker granularity 74～89 μm and NaOH concentration 0.2 mol/L.Under this conditions,the digestion rate of silica is reached up to 99%through single factor experiments and orthogonal experiments.2.The process of extracting silica from potash feldspar by Na2CO3 roasting is studied.According to Arrhenius expression,the activation energy is calculated to be 188.13 kJ/mol and the process can be expressed as:1-(1-α)1/3 = 3.12×105xexp[-188130/(R7)]t3.The digestion process of roasted clinker to dissolve silica is studied.The digestion process includes two stages.According to Arrhenius expression,the activation energy are calculated to be 15.24 kJ/mol and 29.94 kJ/mol,respectively.And the process can be expressed as:The first stage:1-(1-α)1/3 = 7.074×exp[-15239/(RT)]t The second stage:1-(1-α)1/3 2.18×10-2×exp[-29940/(RT)]t4.Taken the digestion solution of roasted clinker as raw material to prepare ultrafine silica by split-step carbonating.The precipitation rate of silica is 99.8%and granularity of silica is 200 um at a solution pH value of 9.0,a carbonating temperature of 50℃,a CO2 flow rate of 6 mL/min,a stirring intensity of 600 r/min,and a volume ratio of ethanol to water of 1:9.The quality of obtained ultrafine silica is accorded with the indexes of HG/T3065-1999.5.Taken the digestion solution of roasted clinker as raw material to prepare light calcium silicate by reacting with lime.The optimized reaction conditions are as below:reaction temperature 80℃,molar ratio of calcium oxide to silica 1:1,reaction time 40 min,and stirring intensity 500 r/min,at which the precipitation rate of silica is 99.28%.6.Aluminum hydroxide,aluminium oxide and iron oxide are preparation from the digestion residue of potash.feldspar(nepheline)by acidizing,water leaching,precipitating aluminum,alkali dissolving,and carbonating.It meets the target of extracting aluminum and iron.Potassium and sodium are enriched to achieve the separation.The extraction rate of aluminum is more than 94.36%in the process of acidizing when molar ratio of sulfuric acid to nepheline 2.4:1,mass fraction of sulfuric acid 90%for 5 min.The optimal conditions for the process of water leaching are water dissolving temperature 90℃,mass ratio of liquid to solid 5.5:1,and stirring intensity 400 r/min for 10 min.Under these conditions,the digestion rate of aluminum is more than 99.21%.The optimum conditions of precipitating aluminum,which could guarantee the precipitation rate of aluminum more than 99%is:keeping aluminum precipitating temperature as 50℃,fell the Na2CO3 solution which the mass concentration is 300 g/L into Al2(SO4)3 solution,controlling the pH value as 4.8 and the aging time as 40 min.The optimal conditions for the process of alkali dissolving are pH value of solution 14,alkali dissolving temperature 80℃,and alkali dissolving time 30 min.Under these conditions,the dissolving rate of aluminum is more than 99.42%and the removing rate of iron is more than 99.63%.The precipitation rate of aluminum is 98.69%at solution pH value of 9.0,carbonating temperature of 40℃,and CO2 flow rate of 6 mL/min in the process of carbonation.7.The potassium sulfate,sodium sulfate,and sodium sulfide are preparation using the purification solution as raw material.The potassium sulfate and sodium sulfate are synthesized by fractional crystallization.The optimal conditions are crystallization temperature 40℃,stirring intensity 400 r/min,and crystallization time 4 h.Under these conditions,the crystallization rate of potassium sulfate is more than 88.17%.The crystallization rate of sodium sulfate is more than 90.13%under the optimum conditions:crystallization temperature 10℃,stirring intensity 400 r/min,and crystallization time 8 h.The sodium sulfide is preparation by reducing using coal,CO,and H2,the sodium sulfate as raw material.The optimal conditions are the molar ratio of sodium sulfate to coal 1:8,reaction temperature 700℃,and reaction time 5 h.Under these conditions,the conversion rate of sodium sulfate is more than 82.13%by reducing using coal.The optimal conditions are reaction temperature 675℃,reaction time 120 min,and material thickness less than 4 cm.Under these conditions,the conversion rate of sodium sulfate is more than 93%by reducing using CO.The optimal conditions are reaction temperature 610℃,reaction time 90 min,and material thickness less than 2.5 cm.Under these conditions,the conversion rate of sodium sulfate is more than 94.25%by reducing using H2.A industrial application value technology was designed,as silicon,aluminum,potassium and sodium were extracted from potash feldspar to prepare ultrafine silicon dioxide,high purity aluminum hydroxide,shortage of potassium sulfate and sodium sulfide.The whole process without waste residue,waste gas and waste residue discharge,realize the high added value,green and comprehensive utilization of potashfeldspar. |
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