A hydrometallurgical process for the selective removal of silicon from titanium-vanadium slag by alkaline leaching was investigated. X-ray diffraction, scanning electron microscopy and electron dispersive spectroscopy...A hydrometallurgical process for the selective removal of silicon from titanium-vanadium slag by alkaline leaching was investigated. X-ray diffraction, scanning electron microscopy and electron dispersive spectroscopy were used to characterize the samples. The results show that anosovite, pyroxene and metallic iron are the major components of the titanium-vanadium slag. Anosovite is presented in granular and plate shapes, and pyroxene is distributed in the anosovite crystals. Metallic iron is spheroidal and wrapped in anosovite. Silicon is mainly in the pyroxene, and titanium and vanadium are mainly in the anosovite. The effects of agitation speed, leaching temperature, leaching time, sodium hydroxide concentration and liquid-solid （L/S） mass ratio on the leaching behavior of silica from titanium-vanadium slag were investigated. The leaching temperature and L/S mass ratio played considerable role in the desilication process. Under the optimal conditions, 88.2% silicon, 66.3% aluminum, 27.3% manganese, and only 1.2% vanadium were leached out. The desilication kinetics of the titanium-vanadium slag was described by the chemical control model. The apparent activation enerffv of the desilication orocess was found to be 46.3 kJ/mol.展开更多
The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, h...The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime in- creases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogamet. Desilication reactions during the digestion process promoted by lime result in the loss of A1203 entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethific A1203 entering the digested liquor. The alumina digestion rate at 245~C is higher than that at 145 C due to the more pronounced conversion of aluminogoethite to hema- tite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.展开更多
The liquor concentration, mineral proportion, crystal parameters and micro morphology of various desilication products（DSPs） precipitated in silica-supersaturated sodium aluminate solution at 95 ℃ under different r...The liquor concentration, mineral proportion, crystal parameters and micro morphology of various desilication products（DSPs） precipitated in silica-supersaturated sodium aluminate solution at 95 ℃ under different reaction conditions were systematically researched. The DSPs formed under atmospheric pressure comprise amorphous phase, zeolite A, zeolite and sodalite, and the DSPs concentration and crystallinity increase with the increase of initial silica concentration, initial molar ratio of caustic Na2O to Al2O3（αK） and desilication duration. Decreasing the initial silica concentration, initial αK and increasing the desilication duration can reduce the proportion of zeolite A. The zeolite and sodalite are the stable DSPs, while the precipitation of zeolite A occurs at a high silica-supersaturated state in sodium aluminate solution. The DSPs are precipitated in the form of agglomerates, but the morphologies of various DSPs are quite different. Both the molar ratios of Na2O to Al2O3 and SiO-2 to Al2O3 in DSPs increase with the increasing desilication duration, resulting in the increase of the cell volumes of various DSPs. The precipitation sequence of DSPs under atmospheric pressure is： amorphous phase→zeolite A→zeolite→sodalite.展开更多
Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction effic...Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction efficiency were studied. The results show that silicon extraction efficiency increases with increasing the reaction time and Na OH-to-CBM mass ratio. There are two stages for the desilication process of the calcined boron mud. The overall desilication process follows the shrinking-core model, and the first and second stages of the process were determined to obey the shrinking-core model for surface chemical reaction and the diffusion through the product layer, respectively. The activation energies of the first and second stages were calculated to be 44.78 k J/mol and 15.94 k J/mol, respectively.展开更多
To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication pro...To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al2O3·2 SiO2, SiO2, and Al2O3.展开更多
The structural changes of silicate anions in the desilication process with the addition of calcium hydrate alumino-carbonate were studied by measuring Raman spectra, infrared spectra and corresponding second derivativ...The structural changes of silicate anions in the desilication process with the addition of calcium hydrate alumino-carbonate were studied by measuring Raman spectra, infrared spectra and corresponding second derivative spectra. The results show that the desilication ratio in the solution prepared by the addition of sodium silicate(solution-SS) is much greater than that in the solution by the addition of green liquor(solution-GL), and low alumina concentration in the sodium aluminate solutions facilitates the desilication process. It is also shown that alumino-silicate anions in the solution-GL, and Q^3 polymeric silicate anions in solution-SS are predominant, respectively. In addition, increasing the concentration of silica favors respectively the formation of the alumino-silicate or the Q^3 silicate anions in the solution-GL or the solution-SS. Therefore, it can be inferred that the low desilication ratio in the silicate-bearing aluminate solution is mainly attributed to the existence of alumino-silicate anions.展开更多
The leaching desilication technology of roasted diasporic bauxite in atmosphere by caustic soda solution was investigated. The optimum parameters were: the grinding fineness of the roasted bauxite -0.076??mm and 80% ...The leaching desilication technology of roasted diasporic bauxite in atmosphere by caustic soda solution was investigated. The optimum parameters were: the grinding fineness of the roasted bauxite -0.076??mm and 80% ～ 85%, leaching time 2?h, Na 2O k 100 ～ 150?g/L, L/S 4～5, leaching temperature 90 ～ 95?℃. The desilication rate 55.20% and concentrate A/S (mass ratio of Al 2O 3 to SiO 2) 9.90, as good as those obtained at pressure, were obtained respectively. Investigation of two stage leaching shows that it can both improve desilication rate of roasted ore and reduce leaching time. When time of the first stage and the second stage is 30?min and 30?min respectively, desilication rate can reach 59.65%. X ray diffraction analysis of the concentrate has proved that desilication procedure is accompanied with the formation of sodium aluminosilicate hydrate. X ray spectra also show that silica removed during leaching is amorphous silica. SiO 2 occurring as quartz in raw ore or mullite formed during roasting can not dissolve in alkali solution.展开更多
The distribution behavior of the HZB collector (a kind of long chain fatty acid) in the desilication system of bauxite flotation was studied. The results show that the collector tends towards froth products in the ste...The distribution behavior of the HZB collector (a kind of long chain fatty acid) in the desilication system of bauxite flotation was studied. The results show that the collector tends towards froth products in the steps of the roughing, the first cleaning and the second cleaning, while towards the tailing product in the step of the scavenging, and in each job except scavenging the collector is mainly on the surface of solids. As for the froth product in the step of the scavenging, it is mainly in solution. To the tailing products of every step, it is mainly in the respective solutions. The collector added to the flotation system is mainly taken out by the last concentrate, by which the taken one occupies 65.2% of the whole, among which, 57.8% is by solid and 7.4% by solution, respectively. And the one by the last tail occupies 34.8% of the whole, among which, 8.8% is by solid and 26.0% by solution, respectively. The sum of the collector in the solution of the last concentrate and tailing is 33.4% of the amount of addition collector, and recycling the solutions will be in favor of decreasing the dosage of collector.展开更多
Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring sp...Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring speed on silica leaching rate were investigated and the kinetics of alkaline leaching process was studied. The results show that silica leaching rate reached 91.2% under the conditions of initial NaOH concentration of 20%, liquid-to-solid ratio of 4：1, leaching temperature of 180 ℃, leaching time of 4 h and stirring speed of 300 r/min. Shrinking-core model showed that the leaching process was controlled by the chemical surface reaction with activation energy Ea of 53.31 k J/mol. The fluidized roasting conditions for preparation of sodium manganate were optimized by the orthogonal experiments using the desiliconized residue. The conversion rate of sodium manganate was obtained to be 89.7% under the conditions of silica leaching rate of 91.2%, NaOH/MnO2 mass ratio of 3：1, roasting temperature of 500 ℃ and roasting time of 4 h, and it increased with the increase of silicon leaching rate.展开更多
Illite occurs widely in bauxite ores and results in low alumina grade of the ores. Differential thermal analysis （DTA）, thermal gravimetric analysis （TGA） and X-ray diffraction analysis （XRD） show the OH groups ...Illite occurs widely in bauxite ores and results in low alumina grade of the ores. Differential thermal analysis （DTA）, thermal gravimetric analysis （TGA） and X-ray diffraction analysis （XRD） show the OH groups split off from the structural framework of illite between 500 ℃ and 700 ℃. With the increase in temperature up to about 1 100 ℃, the layer structure of illite breaks up and Si in the layers is transformed into the amorphous state. Meanwhile, mullite comes out at 1 100 ℃. Quartz occurring in illite keeps unchanged in structure in the range of （500（1 200 ℃.）） A desilication process from illite by thermochemical activation followed by alkali leaching is therefore developed on the basis of the behavior that amorphous silica is alkali soluble. The investigation finds that the optimum parameters for desilication are activation temperature of 1 1001 150 ℃, activation time of 90120 min, leaching temperature of 95110 ℃, leaching time of 90120 min and concentration of caustic soda （Na2Ok） 120150 g/L. An overall desilication about 45% is attained under these conditions. XRD analysis confirms that the active amorphous SiO2 has been dissolved in the alkali solution and removed from the samples, while quartz and mullite have not. The investigation also shows that the formation of mullite during activation and formation of sodium hydroaluminosilicates (Na96Al96Si96O384 and 0.95Na2O·Al2O3·3.25SiO2·4.79H2O) during leaching lead to the relatively low desilication of illite.展开更多
By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was develop...By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process.Ca/(SiO2+TiO2)molar ratio,and NaO/Al2O3 molar ratio,sintering time,and temperature were the most significant parameters impacting on the aluminum extraction efficiency.The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2)molar ratio of 2.0,NaO/Al2O3 molar ratio of 0.98,and sintering at 1 200 ℃for 60 min.Astandard industrial dissolution method was used under conditions of caustic ratio(αk=n(NaO)/n(Al2O3)of 2.0,Al2O3 concentration of 50 g/L,sodium hydroxide concentration(Nk)of 60.78 g/L,Na2CO3 concentration of 10 g/L,temperature of 85℃, and dissolution duration of 10 min.The final aluminum extraction efficiency was 90%.展开更多
Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XR...Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XRF,XRD,FTIR,TEM,nitrogen adsorption/desorption,NH_3-TPD,^(29)Si and^(27)Al MAS NMR analytical techniques.Desilication was accompanied with the creation of super acid sites.There exists a limit(Si/Al molar ratio of9.67)for keeping high crystallinity and obtaining improved catalytic performance.Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers.The p-xylene approach to equilibrium improves by more than 7% at 400℃ and a WHSV of 2 h^(-1)for the optimum sample with respect to the parent zeolite.At the same conditions,the optimum sample exhibits the maximum ethylbenzene conversion of 89%,i.e.more than 40%w.r.t.of the parent zeolite.However,the xylene yield decreases only 3%.展开更多
It is important to depress diaspore effectively in order to remove silicates from diasporic bauxite. A new water soluble polymer hydroxamic acid starch (HA-starch) was prepared. The effects of the product on the diasp...It is important to depress diaspore effectively in order to remove silicates from diasporic bauxite. A new water soluble polymer hydroxamic acid starch (HA-starch) was prepared. The effects of the product on the diaspore and kaolinite flotation were investigated and its reactive mechanism was studied by zeta potential measurement and FTIR. The results show that HA-starch can depress diaspore while make positive effect on kaolinite flotation at low pH value(pH below 6). The flotation recovery of diaspore was sharply decreased with the increase of concentration of HA-starch. The chemical adsorption of HA-starch on the surface of diaspore was revealed.展开更多
基金Project(51090380)supported by the Major Program of the National Natural Science Foundation of ChinaProject(51125018)supported by the National Science Foundation for Distinguished Young Scholars of ChinaProjects(51374191,51104139,21006115)supported by the National Natural Science Foundation of China
文摘A hydrometallurgical process for the selective removal of silicon from titanium-vanadium slag by alkaline leaching was investigated. X-ray diffraction, scanning electron microscopy and electron dispersive spectroscopy were used to characterize the samples. The results show that anosovite, pyroxene and metallic iron are the major components of the titanium-vanadium slag. Anosovite is presented in granular and plate shapes, and pyroxene is distributed in the anosovite crystals. Metallic iron is spheroidal and wrapped in anosovite. Silicon is mainly in the pyroxene, and titanium and vanadium are mainly in the anosovite. The effects of agitation speed, leaching temperature, leaching time, sodium hydroxide concentration and liquid-solid （L/S） mass ratio on the leaching behavior of silica from titanium-vanadium slag were investigated. The leaching temperature and L/S mass ratio played considerable role in the desilication process. Under the optimal conditions, 88.2% silicon, 66.3% aluminum, 27.3% manganese, and only 1.2% vanadium were leached out. The desilication kinetics of the titanium-vanadium slag was described by the chemical control model. The apparent activation enerffv of the desilication orocess was found to be 46.3 kJ/mol.
基金the National Natural Science Foundation of China(Nos.51104041 and 51174054)
文摘The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime in- creases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogamet. Desilication reactions during the digestion process promoted by lime result in the loss of A1203 entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethific A1203 entering the digested liquor. The alumina digestion rate at 245~C is higher than that at 145 C due to the more pronounced conversion of aluminogoethite to hema- tite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.
基金Projects(51774079,51674075,51104041)supported by the National Natural Science Foundation of ChinaProject(N130402010)supported by the Fundamental Research Funds for the Central Universities,China
文摘The liquor concentration, mineral proportion, crystal parameters and micro morphology of various desilication products（DSPs） precipitated in silica-supersaturated sodium aluminate solution at 95 ℃ under different reaction conditions were systematically researched. The DSPs formed under atmospheric pressure comprise amorphous phase, zeolite A, zeolite and sodalite, and the DSPs concentration and crystallinity increase with the increase of initial silica concentration, initial molar ratio of caustic Na2O to Al2O3（αK） and desilication duration. Decreasing the initial silica concentration, initial αK and increasing the desilication duration can reduce the proportion of zeolite A. The zeolite and sodalite are the stable DSPs, while the precipitation of zeolite A occurs at a high silica-supersaturated state in sodium aluminate solution. The DSPs are precipitated in the form of agglomerates, but the morphologies of various DSPs are quite different. Both the molar ratios of Na2O to Al2O3 and SiO-2 to Al2O3 in DSPs increase with the increasing desilication duration, resulting in the increase of the cell volumes of various DSPs. The precipitation sequence of DSPs under atmospheric pressure is： amorphous phase→zeolite A→zeolite→sodalite.
基金Project(51204037)supported by the National Natural Science Foundation of ChinaProject(N140204016)supported by the Fundamental Research Funds for the Central Universities,China
文摘Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction efficiency were studied. The results show that silicon extraction efficiency increases with increasing the reaction time and Na OH-to-CBM mass ratio. There are two stages for the desilication process of the calcined boron mud. The overall desilication process follows the shrinking-core model, and the first and second stages of the process were determined to obey the shrinking-core model for surface chemical reaction and the diffusion through the product layer, respectively. The activation energies of the first and second stages were calculated to be 44.78 k J/mol and 15.94 k J/mol, respectively.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.U1812402,51664005,and 51774102)Talents of Guizhou Science and Technology Cooperation Platform(Talent Team Giant[2015]4005,Platform Talent[2017]5788,[2017]5626,and KY(2015)334).
文摘To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al2O3·2 SiO2, SiO2, and Al2O3.
基金Project(51274242)supported by the National Natural Science Foundation of ChinaProject(2015CX001)supported by the Innovation-driven Plan in Central South University,China
文摘The structural changes of silicate anions in the desilication process with the addition of calcium hydrate alumino-carbonate were studied by measuring Raman spectra, infrared spectra and corresponding second derivative spectra. The results show that the desilication ratio in the solution prepared by the addition of sodium silicate(solution-SS) is much greater than that in the solution by the addition of green liquor(solution-GL), and low alumina concentration in the sodium aluminate solutions facilitates the desilication process. It is also shown that alumino-silicate anions in the solution-GL, and Q^3 polymeric silicate anions in solution-SS are predominant, respectively. In addition, increasing the concentration of silica favors respectively the formation of the alumino-silicate or the Q^3 silicate anions in the solution-GL or the solution-SS. Therefore, it can be inferred that the low desilication ratio in the silicate-bearing aluminate solution is mainly attributed to the existence of alumino-silicate anions.
文摘The leaching desilication technology of roasted diasporic bauxite in atmosphere by caustic soda solution was investigated. The optimum parameters were: the grinding fineness of the roasted bauxite -0.076??mm and 80% ～ 85%, leaching time 2?h, Na 2O k 100 ～ 150?g/L, L/S 4～5, leaching temperature 90 ～ 95?℃. The desilication rate 55.20% and concentrate A/S (mass ratio of Al 2O 3 to SiO 2) 9.90, as good as those obtained at pressure, were obtained respectively. Investigation of two stage leaching shows that it can both improve desilication rate of roasted ore and reduce leaching time. When time of the first stage and the second stage is 30?min and 30?min respectively, desilication rate can reach 59.65%. X ray diffraction analysis of the concentrate has proved that desilication procedure is accompanied with the formation of sodium aluminosilicate hydrate. X ray spectra also show that silica removed during leaching is amorphous silica. SiO 2 occurring as quartz in raw ore or mullite formed during roasting can not dissolve in alkali solution.
文摘The distribution behavior of the HZB collector (a kind of long chain fatty acid) in the desilication system of bauxite flotation was studied. The results show that the collector tends towards froth products in the steps of the roughing, the first cleaning and the second cleaning, while towards the tailing product in the step of the scavenging, and in each job except scavenging the collector is mainly on the surface of solids. As for the froth product in the step of the scavenging, it is mainly in solution. To the tailing products of every step, it is mainly in the respective solutions. The collector added to the flotation system is mainly taken out by the last concentrate, by which the taken one occupies 65.2% of the whole, among which, 57.8% is by solid and 7.4% by solution, respectively. And the one by the last tail occupies 34.8% of the whole, among which, 8.8% is by solid and 26.0% by solution, respectively. The sum of the collector in the solution of the last concentrate and tailing is 33.4% of the amount of addition collector, and recycling the solutions will be in favor of decreasing the dosage of collector.
基金Project(2015ZX07205-003)supported by the Major Science and Technology Program for Water Pollution Control and Treatment,ChinaProject(DY125-15-T-08)supported by the China Ocean Mineral Resources Research&Development ProgramProjects(21176026,21176242)supported by the National Natural Science Foundation of China
文摘Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring speed on silica leaching rate were investigated and the kinetics of alkaline leaching process was studied. The results show that silica leaching rate reached 91.2% under the conditions of initial NaOH concentration of 20%, liquid-to-solid ratio of 4：1, leaching temperature of 180 ℃, leaching time of 4 h and stirring speed of 300 r/min. Shrinking-core model showed that the leaching process was controlled by the chemical surface reaction with activation energy Ea of 53.31 k J/mol. The fluidized roasting conditions for preparation of sodium manganate were optimized by the orthogonal experiments using the desiliconized residue. The conversion rate of sodium manganate was obtained to be 89.7% under the conditions of silica leaching rate of 91.2%, NaOH/MnO2 mass ratio of 3：1, roasting temperature of 500 ℃ and roasting time of 4 h, and it increased with the increase of silicon leaching rate.
文摘Illite occurs widely in bauxite ores and results in low alumina grade of the ores. Differential thermal analysis （DTA）, thermal gravimetric analysis （TGA） and X-ray diffraction analysis （XRD） show the OH groups split off from the structural framework of illite between 500 ℃ and 700 ℃. With the increase in temperature up to about 1 100 ℃, the layer structure of illite breaks up and Si in the layers is transformed into the amorphous state. Meanwhile, mullite comes out at 1 100 ℃. Quartz occurring in illite keeps unchanged in structure in the range of （500（1 200 ℃.）） A desilication process from illite by thermochemical activation followed by alkali leaching is therefore developed on the basis of the behavior that amorphous silica is alkali soluble. The investigation finds that the optimum parameters for desilication are activation temperature of 1 1001 150 ℃, activation time of 90120 min, leaching temperature of 95110 ℃, leaching time of 90120 min and concentration of caustic soda （Na2Ok） 120150 g/L. An overall desilication about 45% is attained under these conditions. XRD analysis confirms that the active amorphous SiO2 has been dissolved in the alkali solution and removed from the samples, while quartz and mullite have not. The investigation also shows that the formation of mullite during activation and formation of sodium hydroaluminosilicates (Na96Al96Si96O384 and 0.95Na2O·Al2O3·3.25SiO2·4.79H2O) during leaching lead to the relatively low desilication of illite.
基金Project(YFZX(0804))supported by Science Foundation of the Pingshuo Coal Industry Company,China
文摘By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process.Ca/(SiO2+TiO2)molar ratio,and NaO/Al2O3 molar ratio,sintering time,and temperature were the most significant parameters impacting on the aluminum extraction efficiency.The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2)molar ratio of 2.0,NaO/Al2O3 molar ratio of 0.98,and sintering at 1 200 ℃for 60 min.Astandard industrial dissolution method was used under conditions of caustic ratio(αk=n(NaO)/n(Al2O3)of 2.0,Al2O3 concentration of 50 g/L,sodium hydroxide concentration(Nk)of 60.78 g/L,Na2CO3 concentration of 10 g/L,temperature of 85℃, and dissolution duration of 10 min.The final aluminum extraction efficiency was 90%.
基金financed by BIPC,Mahshahr,Iran under the contract number 08-133/57665
文摘Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XRF,XRD,FTIR,TEM,nitrogen adsorption/desorption,NH_3-TPD,^(29)Si and^(27)Al MAS NMR analytical techniques.Desilication was accompanied with the creation of super acid sites.There exists a limit(Si/Al molar ratio of9.67)for keeping high crystallinity and obtaining improved catalytic performance.Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers.The p-xylene approach to equilibrium improves by more than 7% at 400℃ and a WHSV of 2 h^(-1)for the optimum sample with respect to the parent zeolite.At the same conditions,the optimum sample exhibits the maximum ethylbenzene conversion of 89%,i.e.more than 40%w.r.t.of the parent zeolite.However,the xylene yield decreases only 3%.
文摘It is important to depress diaspore effectively in order to remove silicates from diasporic bauxite. A new water soluble polymer hydroxamic acid starch (HA-starch) was prepared. The effects of the product on the diaspore and kaolinite flotation were investigated and its reactive mechanism was studied by zeta potential measurement and FTIR. The results show that HA-starch can depress diaspore while make positive effect on kaolinite flotation at low pH value(pH below 6). The flotation recovery of diaspore was sharply decreased with the increase of concentration of HA-starch. The chemical adsorption of HA-starch on the surface of diaspore was revealed.
