The equilibrium solubilities of 5(NH4)O·12WO3·5H2O (APT·5H2O) were determined at the terminal ammonia concentration of 2 mol/L at 87-95℃. Experimental data were regressed. The linear functional relatio...The equilibrium solubilities of 5(NH4)O·12WO3·5H2O (APT·5H2O) were determined at the terminal ammonia concentration of 2 mol/L at 87-95℃. Experimental data were regressed. The linear functional relation between the solubility of APT- 5H2O and the temperature (t /℃) is given as y = - 588.08 + 7.28t. The solubility of the species as a function of the terminal ammonia concentration (x / mol · L-1) is also achieved: y = 36.76 + 18.86x. The solubility of APT · 5H2O produced by ion-exchange method in China is much lower, which is due to much lower silica, much higher NH4Cl, and a small amount of APT · 7H2O with low solubility in the APT crystals. APT · 7H2O forms because of a large amount of NH4Cl and the low activity of water in the crystallization.展开更多
A new technology for the crystallization of ammonium paratungstate with coarse grain has beenstudied. The factors influencing the physi-chemical properties of ammonium paratungstate crystal, such astemperature, concen...A new technology for the crystallization of ammonium paratungstate with coarse grain has beenstudied. The factors influencing the physi-chemical properties of ammonium paratungstate crystal, such astemperature, concentration, seed crystal, agitation. etc. were examined. It is necessary to keep high temperature and low concentration in the process. and the addition of seed crystal and agitation with air is also in favor of the system. Ammonium paratungstate crystal with particle size of 36-42 μm and apparent density of2. 0-2. 2 g·cm- 3 were obtained by controlling suitable technological parameters.展开更多
The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising ...The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising temperature, prolonging duration, increasing ammonia concentration and decreasing ammonium carbonate concentration favor dissolving of ammonium paratungstate at temperature below 90 ℃, while the WO3 concentration decreases after a certain time at temperature above 100 ℃. Furthermore, the undissolved tungsten exists in the form of either APT·4 H2O below 90 ℃ or pyrochlore-type tungsten trioxide above 100℃. In dissolving process, the ammonium paratungstate dissolves into paratungstate ions followed by partially converting to tungstate ion, resulting in the coexistence of the both ions. This study may provide a new idea to exploit a novel technique for manufacturing ammonium paratungstate and pyrochlore-type tungsten trioxide.展开更多
The production of ammonium paratungstate(APT) is riddled with the generation of wastewater,which causes environmental problems.To solve the problem of wastewater generation at source,a membrane electrolysis-NH3·H...The production of ammonium paratungstate(APT) is riddled with the generation of wastewater,which causes environmental problems.To solve the problem of wastewater generation at source,a membrane electrolysis-NH3·H2O precipitation method,which prevents wastewater generation and recycles the reagents used in the process,was proposed and investigated in this study.The electrolysis process was investigated based on parameters such as initial cathodic and anodic NaOH concentrations,and current density.The results showed that an increase in current density and initial cathodic NaOH concentration and a decrease in the initial anodic NaOH concentration would enhance the separation of tungsten and sodium.The optimum condition was found at a current density of 666 A·m^(-2),initial anodic and cathodic NaOH concentrations of 69 g·L^(-1) and 40 g·L^(-1),with a current efficiency of 75.40%,and energy consumption for producing 1 ton of NaOH was 2184 kW·h.The precipitation process was investigated based on the acidic high W/Na molar ratio solution obtained by the electrolysis process with NH3·H2O as the precipitant.Parameters such as excessive coefficient,temperature,and W/Na molar ratio were studied.The result showed that the variation of excessive coefficient and solution temperature had an opposite effect on the purity of the APT,while an increase in the W/Na molar ratio would increase the product purity.The precipitation product obtained had a purity of 99.6% and was characterized using X-ray diffraction,inductively coupled plasma,and scanning electron microscopy.The methods proposed in this study could provide fundamental information for the design of a cleaner APT production process.展开更多
The heat of the thermal decomposition of monoclini c ammonium paratungstate, (NH4)10H2W12O42· 4H2O, was measured in a HT-1000 microcalorimeter using three-step calorimetry and suitable thermochemical cycle. The s...The heat of the thermal decomposition of monoclini c ammonium paratungstate, (NH4)10H2W12O42· 4H2O, was measured in a HT-1000 microcalorimeter using three-step calorimetry and suitable thermochemical cycle. The standard enthalpy of the thermal decomposition reaction at 298.15 K and the standard enthalpy of formation at 298.15 K for monoclinic ammonium paratung- state were obtained to be (430.1± 10.2) kJ· mol－ 1 and－ (13 423.7± 14.8) kJ· mol－ 1, respectively.展开更多
文摘The equilibrium solubilities of 5(NH4)O·12WO3·5H2O (APT·5H2O) were determined at the terminal ammonia concentration of 2 mol/L at 87-95℃. Experimental data were regressed. The linear functional relation between the solubility of APT- 5H2O and the temperature (t /℃) is given as y = - 588.08 + 7.28t. The solubility of the species as a function of the terminal ammonia concentration (x / mol · L-1) is also achieved: y = 36.76 + 18.86x. The solubility of APT · 5H2O produced by ion-exchange method in China is much lower, which is due to much lower silica, much higher NH4Cl, and a small amount of APT · 7H2O with low solubility in the APT crystals. APT · 7H2O forms because of a large amount of NH4Cl and the low activity of water in the crystallization.
文摘A new technology for the crystallization of ammonium paratungstate with coarse grain has beenstudied. The factors influencing the physi-chemical properties of ammonium paratungstate crystal, such astemperature, concentration, seed crystal, agitation. etc. were examined. It is necessary to keep high temperature and low concentration in the process. and the addition of seed crystal and agitation with air is also in favor of the system. Ammonium paratungstate crystal with particle size of 36-42 μm and apparent density of2. 0-2. 2 g·cm- 3 were obtained by controlling suitable technological parameters.
基金Project(51274243) supported by the National Natural Science Foundation of China
文摘The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising temperature, prolonging duration, increasing ammonia concentration and decreasing ammonium carbonate concentration favor dissolving of ammonium paratungstate at temperature below 90 ℃, while the WO3 concentration decreases after a certain time at temperature above 100 ℃. Furthermore, the undissolved tungsten exists in the form of either APT·4 H2O below 90 ℃ or pyrochlore-type tungsten trioxide above 100℃. In dissolving process, the ammonium paratungstate dissolves into paratungstate ions followed by partially converting to tungstate ion, resulting in the coexistence of the both ions. This study may provide a new idea to exploit a novel technique for manufacturing ammonium paratungstate and pyrochlore-type tungsten trioxide.
基金financially supported by National Key R&D Program of China (Nos.2020YFC1909703)the Natural Science Foundation of China (Nos.52104403)+1 种基金HBIS Group Co.,Ltd. Key R&D Program (No.20210036)Lv Liang Key R&D Program (No.2020GXZDYF7)。
文摘The production of ammonium paratungstate(APT) is riddled with the generation of wastewater,which causes environmental problems.To solve the problem of wastewater generation at source,a membrane electrolysis-NH3·H2O precipitation method,which prevents wastewater generation and recycles the reagents used in the process,was proposed and investigated in this study.The electrolysis process was investigated based on parameters such as initial cathodic and anodic NaOH concentrations,and current density.The results showed that an increase in current density and initial cathodic NaOH concentration and a decrease in the initial anodic NaOH concentration would enhance the separation of tungsten and sodium.The optimum condition was found at a current density of 666 A·m^(-2),initial anodic and cathodic NaOH concentrations of 69 g·L^(-1) and 40 g·L^(-1),with a current efficiency of 75.40%,and energy consumption for producing 1 ton of NaOH was 2184 kW·h.The precipitation process was investigated based on the acidic high W/Na molar ratio solution obtained by the electrolysis process with NH3·H2O as the precipitant.Parameters such as excessive coefficient,temperature,and W/Na molar ratio were studied.The result showed that the variation of excessive coefficient and solution temperature had an opposite effect on the purity of the APT,while an increase in the W/Na molar ratio would increase the product purity.The precipitation product obtained had a purity of 99.6% and was characterized using X-ray diffraction,inductively coupled plasma,and scanning electron microscopy.The methods proposed in this study could provide fundamental information for the design of a cleaner APT production process.
文摘The heat of the thermal decomposition of monoclini c ammonium paratungstate, (NH4)10H2W12O42· 4H2O, was measured in a HT-1000 microcalorimeter using three-step calorimetry and suitable thermochemical cycle. The standard enthalpy of the thermal decomposition reaction at 298.15 K and the standard enthalpy of formation at 298.15 K for monoclinic ammonium paratung- state were obtained to be (430.1± 10.2) kJ· mol－ 1 and－ (13 423.7± 14.8) kJ· mol－ 1, respectively.
