A technology of one-stage roughing and one-stage scavenging vanadium pre-concentration with shaking table was investigated for improving vanadium grade and decreasing acid consumption minerals content based on the qua...A technology of one-stage roughing and one-stage scavenging vanadium pre-concentration with shaking table was investigated for improving vanadium grade and decreasing acid consumption minerals content based on the quantitative evaluation of minerals by scanning electronic microscopy （QEMSCAN）. In order to visually illustrate how the vanadium-bearing minerals were separated from system, a loose-stratification model was established with Bagnold shear loose theory and Kelly stratification hypothesis. Through the model, it was inferred that fine fraction and coarse fraction of vanadium-bearing muscovite particles easily became the concentrate in roughing and scavenging stages, respectively. The type of the dominant effect on the loose-stratification was confirmed. In the roughing stage, gravity sedimentation played a leading role in the loose-stratification process. However, in the scavenging stage, shearing dispersion pressure caused by asymmetric motion of table deck took an important part in the loose-stratification process. Finally, the correction of the loose-stratification model was validated by the practical experiment.展开更多
A pilot-scale modified carbon source division anaerobic anoxic oxic(AAO) process with pre-concentration of returned activated sludge(RAS) was proposed in this study for the enhanced biological nutrient removal(BNR) of...A pilot-scale modified carbon source division anaerobic anoxic oxic(AAO) process with pre-concentration of returned activated sludge(RAS) was proposed in this study for the enhanced biological nutrient removal(BNR) of municipal wastewater with limited carbon source. The influent carbon source was fed in step while a novel RAS pre-concentration tank was adopted to improve BNR efficiency, and the effects of an influent carbon source distribution ratio and a RAS pre-concentration ratio were investigated. The results show that the removal efficiency of TN is mainly influenced by the carbon source distribution ratio while the TP removal relies on the RAS pre-concentration ratio. The optimum carbon source distribution ratio and RAS pre-concentration ratio are 60% and 50%, respectively, with an inner recycling ratio of 100% under the optimum steady operation of pilot test, reaching an average effluent TN concentration of 9.8 mg·L-1with a removal efficiency of 63% and an average TP removal efficiency of 94%. The mechanism of nutrient removal is discussed and the kinetics is analyzed. The results reveal that the optimal carbon source distribution ratio provides sufficient denitrifying carbon source to each anoxic phase, reducing nitrate accumulation while the RAS pre-concentration ratio improves the condition of anaerobic zone to ensure the phosphorus release due to less nitrate in the returned sludge. Therefore, nitrifying bacteria, denitrifying bacteria and phosphorus accumulation organisms play an important role under the optimum condition, enhancing the performance of nutrient removal in this test.展开更多
To achieve the utilization of the abandoned ultrafine ilmenite(-20 μm) produced in the titanium magnetite processing plant in Panzhihua,the superconducting high-gradient magnetic separation(SMS) technology was propos...To achieve the utilization of the abandoned ultrafine ilmenite(-20 μm) produced in the titanium magnetite processing plant in Panzhihua,the superconducting high-gradient magnetic separation(SMS) technology was proposed in this study.After optimizing the conditions of magnetic intensity,feeding and pulsation,an SMS concentrate with TiO_(2) grade of 16.03% and TiO_(2) recovery of 66.39% was obtained through one roughing-one cleaning pre-concentration flowsheet.The specific magnetic force and magnetic force were calculated and analysed to illustrate the pre-concentration mechanism,and the results revealed that the combination of high magnetic field and strong pulsating resulted in the effective preconcentration of the ultrafine ilmenite in the SMS process.In addition,the magnetic force analysis indicated that the high magnetic intensity and high magnetic gradient are the key factors of the SMS technology.Furthermore,the EDS-Mapping detection certified that the ultrafine ilmenite was concentrated from the gangue minerals using SMS technology.展开更多
A pilot-scale,pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater with limited carbon source.A novel return activated sludge(RAS) pre-concentration tank was adopted for improv-ing...A pilot-scale,pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater with limited carbon source.A novel return activated sludge(RAS) pre-concentration tank was adopted for improv-ing the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied.Under the opti-mal operational condition,the suspended total phosphorus(STP) and the total phosphorus(TP) removal efficiencies were around 58.9% and 63.9% respectively and the effluent-P was lower than 0.8 mg·L-1.The reason is that with the optimal RAS pre-concentration ratio,nitrate is completely removed with endogenous carbon source and the secondary phosphorus release is strictly restrained in the pre-anoxic tank.Therefore,the anaerobic phosphorus release and the carbon source uptake by phosphorus accumulation organisms(PAOs) in the sludge,which are ex-tremely important to the phosphorus removal process,can be fully satisfied.Furthermore,the oxidation-reduction potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and varied conditions.The novel modified system is also beneficial for PAO accumulation.展开更多
Macroporous amino-carboxvlic chelating resin of acrylic acid series may concentrate trace rare earth in the presence of 0.1 mol/l α-hydroxy-isobutyric acid at pH 4.5.With 0.10 mol/l HCl as eluant rare earth may be el...Macroporous amino-carboxvlic chelating resin of acrylic acid series may concentrate trace rare earth in the presence of 0.1 mol/l α-hydroxy-isobutyric acid at pH 4.5.With 0.10 mol/l HCl as eluant rare earth may be eluted quantitatively and separated from Ca,Mg,Fe and Cu.This method is used to determine trace amount of rare earth in human hair,stone (in kidney and bladder),peanut,grape,strawberry,cucumber,pig liver and other biological samples.展开更多
Rare earth elements(lanthanide and yttrium,abbreviated as REY) provide important support for national security,energy production,environmental protection and economic growth.In recent years,many studies have shown tha...Rare earth elements(lanthanide and yttrium,abbreviated as REY) provide important support for national security,energy production,environmental protection and economic growth.In recent years,many studies have shown that the content of REY in some coal or coal by-products is close to or even higher than that in traditional REY ore,which makes coal a potential source of REY.This study took the No.17 coal of Panzhou mining area in Liupanshui coal field as the research object,and the content and occurrence modes of REY in raw coal and 7 density fraction samples were studied.The results show that the content of REY in the raw coal reaches 220.67 μg/g,which is significantly higher than the average REY content in the world coal and Chinese coal as reported in the literature.Gravity separation has a certain pre-enrichment effect on REY and the fraction sample> 1.8 g/cm~3 has the highest REY of 426.27 μg/g(equal to rare earth oxide 0.1%).Study on correlation between REY and ash yields reveals that the organic affinity of the light rare earth is higher than that of the medium rare earth and the heavy rare earth.As shown by X-ray diffraction(XRD) and X-ray flouresence spectroscopy(XRF),the major minerals in coal are kaolinite,quartz and calcite,and the content of REY in coal is significantly related to Al,Si and kaolinite,which implies that REY occur mainly in kaolinite.Laser ablation inductively coupled plasma mass spectroscopy(LA-ICP-MS) was adopted to determine chemical composition of micro-zone in kaolinite in coal and the results show that there is no obvious correlation between REY and the contents of Al and Si.This indicates that the REY occur probably in the form of adsorption.The research results provide a scientific reference for the potential extraction of the associated REY in the coal.展开更多
In this work,the reflux classifier with closely spaced inclined channels is used as the pre-concentration facility to improve the separation efficiency before the shaking table separation.Three operating parameters of...In this work,the reflux classifier with closely spaced inclined channels is used as the pre-concentration facility to improve the separation efficiency before the shaking table separation.Three operating parameters of reflux classifier(RC)to pre-concentrate fine(0.023−0.15 mm)tailings of antimony oxide were optimized by response surface methodology(RSM)using a three-level Box-Behnken design(BBD).The parameters studied for the optimization were feeding speed,underflow,and ascending water speed.Second-order response functions were produced for the Sb grade and recovery rate of the concentrate.Taking advantage of the quadratic programming,when the factors of feeding,underflow and ascending water are respectively 225,30 and 133 cm^3/min,a better result can be achieved for the concentrate grade of 2.31% and recovery rate of 83.17%.At the same time,70.48% of the tailings with the grade of 0.20% were discarded out of the feeding.The results indicated that the reflux classifier has a good performance in dealing with fine tailings of antimony oxide.Moreover,second-order polynomial equations,ANOVA,and three-dimensional surface plots were developed to evaluate the effects of each parameter on Sb grade and recovery rate of the concentrate.展开更多
In this study,pre-concentrated bark,furfuryl alcohol and other biomass raw materials were used to prepare foaming materials by high-speed mechanical stirring without using a foaming agent.We investigated the effect of...In this study,pre-concentrated bark,furfuryl alcohol and other biomass raw materials were used to prepare foaming materials by high-speed mechanical stirring without using a foaming agent.We investigated the effect of the postadded water amount on the properties of foaming materials.In particular,we determined basic physical properties of these materials,including the limiting oxygen index(LOI),porosity,thermal conductivity,thermogravimetric analysis,pore size distribution,and microstructure.The results of scanning electron microscopy(SEM)indicated that the pore size distribution was uniform and the pore size increased with increasing water volume.Thermogravimetric analysis(TG/DTG)showed that when the temperature reached 410°C,the foam was easily decomposed,the final residual mass was only 2.8%,and water addition had little effect on it.Moreover,the amount of post-added water is 5–30 g,the density and compression strength of the foamed materials gradually decreased,while the degree of pulverization increased.LOI ranged from 26.1%to 30.79%,and porosity ranged from 81%to 83%.The change in water volume greatly affected the foam’s performance,the performance of foamed material deteriorated as the amount of added water increased,but the effect on thermal conductivity was not very obvious.The highest thermal conductivity was only 0.0179 W/(m·K),still providing excellent thermal insulation.展开更多
Pre-concentration of vanadium from low-grade stone coal by the method of desliming-flotation was investigated. The mineral composition and microstructure of stone coal were studied systematically by means of X-ray flu...Pre-concentration of vanadium from low-grade stone coal by the method of desliming-flotation was investigated. The mineral composition and microstructure of stone coal were studied systematically by means of X-ray fluorescence spectrometry （XRF）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that selective separation of vanadium-bearing minerals can be achieved by flotation in acidic solution using melamine （EA）. The final vanadium concentrate with V2O5 grade of 1.88% and recovery rate of 76.58% is obtained by desliming-flotation process and 72.51% of the raw ore is rejected as tailings. The pre-concentration of vanadium from low-grade stone coal can increase V2O5 grade and decrease the content of acid consuming minerals, which would enable economical utilization of metallurgical vanadium extraction technology.展开更多
Phosphogypsum(PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements(REEs). The current study focuses on the recovery of REE...Phosphogypsum(PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements(REEs). The current study focuses on the recovery of REEs content and the residual phosphate content existing in the PG with preserving on the CaSO_(4)skeleton to be used in other various applications. These attainments are carried out using citric acid leaching process via soaking technique. Several dissolution parameters for REEs using citric acid were studied, including soaking time, soaking temperature, citric acid concentration, solid-to-liquid ratio, and recycling of the citrate leaching solutions in the further REEs dissolution experiments. The best-operating conditions were 14 d of soaking time, 7.5% citric acid concentration, and the solid-toliquid ratio of 1/5 at ambient temperature. About 79.57% dissolution efficiency of REEs was achieved using the optimal conditions. Applying four soaking stages by mixing different fresh PG samples with the same citrate solution sequentially, cumulative dissolution efficiency for REEs was found to be 64.7% under optimal soaking conditions. REEs were recovered using Dowex 50X8 resin from citrate solutions with 96% extraction efficiency. Dissolution kinetics proved the pseudo-first-order nature, reversible reactions, and two activation energies for all REEs.展开更多
A bstract With the aim of elucidating the spatial and seasonal behaviors of rare earth elements(REEs), we investigated the dissolved REE concentrations of surface water collected during four seasons from middle, lower...A bstract With the aim of elucidating the spatial and seasonal behaviors of rare earth elements(REEs), we investigated the dissolved REE concentrations of surface water collected during four seasons from middle, lower reaches and estuary of the Minjiang River, southeastern China. The results display that the REE abundances in Minjiang River, ranging from 3.3–785.9 ng/L, were higher than those of many of the major global rivers. The total REE concentrations(∑REE) were seasonally variable, averaging in 5 937.30, 863.79, 825.65 and 1 065.75 ng/L during second highest flow(SHF), normal flow(NF), low flow(LF) and high flow(HF) season, respectively. The R_(( L/M)) and R_((H/M)) ratios reveal the spatial and temporal variations of REE patterns, and particularly vary apparently in the maximum turbidity zone and estuary. REE patterns of dissolved loads are characterized by progressing weaker LREEs-enrichment and stronger HREEsenrichment downstream from middle reaches to estuary during all four seasons. Comparing with NF and LF seasons, in which REE patterns are relatively flat, samples of SHF season have more LREE-enriched and HREE-depleted patterns that close to parent rocks, while samples of HF season are more LREEs-depleted and HREE-enriched. REE fractionations from the middle to lower reaches are stronger in the SHF and HF seasons than those in NF and LF seasons. Generally, spatial and seasonal variations in REE abundance and pattern are presumably due to several factors, such as chemical weathering, mixture with rainfall and groundwater, estuarine mixing, runoff, biological production and mountain river characters, such as strong hydrodynamic forces and steep slopes. The highest Gd/Gd* always occurs at north ports during all four seasons, where most of the large hospitals are located. This suggests Gd anomalies are depended on the density of modern medical facilities. Y/Ho ratios fl uctuate and positively correlate to salinity in estuary, probably because of the geochemical behavior differences between Y and Ho.展开更多
基金Projects(2011BAB05B01,2011BA05B04)supported by the National Key Technology R&D Program during the 12th Five-year Plan Period,ChinaProject(201271031380)supported by Twilight Plane of Wuhan Youth Science and Technology,China
文摘A technology of one-stage roughing and one-stage scavenging vanadium pre-concentration with shaking table was investigated for improving vanadium grade and decreasing acid consumption minerals content based on the quantitative evaluation of minerals by scanning electronic microscopy （QEMSCAN）. In order to visually illustrate how the vanadium-bearing minerals were separated from system, a loose-stratification model was established with Bagnold shear loose theory and Kelly stratification hypothesis. Through the model, it was inferred that fine fraction and coarse fraction of vanadium-bearing muscovite particles easily became the concentrate in roughing and scavenging stages, respectively. The type of the dominant effect on the loose-stratification was confirmed. In the roughing stage, gravity sedimentation played a leading role in the loose-stratification process. However, in the scavenging stage, shearing dispersion pressure caused by asymmetric motion of table deck took an important part in the loose-stratification process. Finally, the correction of the loose-stratification model was validated by the practical experiment.
基金Supported by the Major Science and Technology Program for Water Pollution Contro and Treatment-Crucial Technology Research and Engineering Sample Subject on Municipa Wastewater Treatment Process Updated to Higher Drainage Standard(2008ZX07317-02)Wuhan Water Pollution Control and the Water Environment Administer Technology and Synthetic Sample Project in Cities and Towns(2008ZX07317)
文摘A pilot-scale modified carbon source division anaerobic anoxic oxic(AAO) process with pre-concentration of returned activated sludge(RAS) was proposed in this study for the enhanced biological nutrient removal(BNR) of municipal wastewater with limited carbon source. The influent carbon source was fed in step while a novel RAS pre-concentration tank was adopted to improve BNR efficiency, and the effects of an influent carbon source distribution ratio and a RAS pre-concentration ratio were investigated. The results show that the removal efficiency of TN is mainly influenced by the carbon source distribution ratio while the TP removal relies on the RAS pre-concentration ratio. The optimum carbon source distribution ratio and RAS pre-concentration ratio are 60% and 50%, respectively, with an inner recycling ratio of 100% under the optimum steady operation of pilot test, reaching an average effluent TN concentration of 9.8 mg·L-1with a removal efficiency of 63% and an average TP removal efficiency of 94%. The mechanism of nutrient removal is discussed and the kinetics is analyzed. The results reveal that the optimal carbon source distribution ratio provides sufficient denitrifying carbon source to each anoxic phase, reducing nitrate accumulation while the RAS pre-concentration ratio improves the condition of anaerobic zone to ensure the phosphorus release due to less nitrate in the returned sludge. Therefore, nitrifying bacteria, denitrifying bacteria and phosphorus accumulation organisms play an important role under the optimum condition, enhancing the performance of nutrient removal in this test.
基金financial support from the Joint Fund (Key program U2067201) for Nuclear Technology Innovation Sponsored by the National Natural Science Foundation of China and the China National Nuclear CorporationNational key research and development program (2019YFC1907702) Sponsored by MOSTthe Fundamental Research Funds for the Central Universities (N2001013) for supporting this research。
文摘To achieve the utilization of the abandoned ultrafine ilmenite(-20 μm) produced in the titanium magnetite processing plant in Panzhihua,the superconducting high-gradient magnetic separation(SMS) technology was proposed in this study.After optimizing the conditions of magnetic intensity,feeding and pulsation,an SMS concentrate with TiO_(2) grade of 16.03% and TiO_(2) recovery of 66.39% was obtained through one roughing-one cleaning pre-concentration flowsheet.The specific magnetic force and magnetic force were calculated and analysed to illustrate the pre-concentration mechanism,and the results revealed that the combination of high magnetic field and strong pulsating resulted in the effective preconcentration of the ultrafine ilmenite in the SMS process.In addition,the magnetic force analysis indicated that the high magnetic intensity and high magnetic gradient are the key factors of the SMS technology.Furthermore,the EDS-Mapping detection certified that the ultrafine ilmenite was concentrated from the gangue minerals using SMS technology.
基金Supported by the Major Science and Technology Program for Water Pollution Control and Treatment (2008ZX07316)
文摘A pilot-scale,pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater with limited carbon source.A novel return activated sludge(RAS) pre-concentration tank was adopted for improv-ing the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied.Under the opti-mal operational condition,the suspended total phosphorus(STP) and the total phosphorus(TP) removal efficiencies were around 58.9% and 63.9% respectively and the effluent-P was lower than 0.8 mg·L-1.The reason is that with the optimal RAS pre-concentration ratio,nitrate is completely removed with endogenous carbon source and the secondary phosphorus release is strictly restrained in the pre-anoxic tank.Therefore,the anaerobic phosphorus release and the carbon source uptake by phosphorus accumulation organisms(PAOs) in the sludge,which are ex-tremely important to the phosphorus removal process,can be fully satisfied.Furthermore,the oxidation-reduction potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and varied conditions.The novel modified system is also beneficial for PAO accumulation.
文摘Macroporous amino-carboxvlic chelating resin of acrylic acid series may concentrate trace rare earth in the presence of 0.1 mol/l α-hydroxy-isobutyric acid at pH 4.5.With 0.10 mol/l HCl as eluant rare earth may be eluted quantitatively and separated from Ca,Mg,Fe and Cu.This method is used to determine trace amount of rare earth in human hair,stone (in kidney and bladder),peanut,grape,strawberry,cucumber,pig liver and other biological samples.
基金Project supported by National Natural Science Foundation of China (51964009,41802190)。
文摘Rare earth elements(lanthanide and yttrium,abbreviated as REY) provide important support for national security,energy production,environmental protection and economic growth.In recent years,many studies have shown that the content of REY in some coal or coal by-products is close to or even higher than that in traditional REY ore,which makes coal a potential source of REY.This study took the No.17 coal of Panzhou mining area in Liupanshui coal field as the research object,and the content and occurrence modes of REY in raw coal and 7 density fraction samples were studied.The results show that the content of REY in the raw coal reaches 220.67 μg/g,which is significantly higher than the average REY content in the world coal and Chinese coal as reported in the literature.Gravity separation has a certain pre-enrichment effect on REY and the fraction sample> 1.8 g/cm~3 has the highest REY of 426.27 μg/g(equal to rare earth oxide 0.1%).Study on correlation between REY and ash yields reveals that the organic affinity of the light rare earth is higher than that of the medium rare earth and the heavy rare earth.As shown by X-ray diffraction(XRD) and X-ray flouresence spectroscopy(XRF),the major minerals in coal are kaolinite,quartz and calcite,and the content of REY in coal is significantly related to Al,Si and kaolinite,which implies that REY occur mainly in kaolinite.Laser ablation inductively coupled plasma mass spectroscopy(LA-ICP-MS) was adopted to determine chemical composition of micro-zone in kaolinite in coal and the results show that there is no obvious correlation between REY and the contents of Al and Si.This indicates that the REY occur probably in the form of adsorption.The research results provide a scientific reference for the potential extraction of the associated REY in the coal.
基金Project(2015SK20792)supported by Key Province Key Technology Research and Development Program of the Ministry of Science and Technology of Hunan,ChinaProjects(2019zzts703,2020zzts740,2020zzts202)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(2020P4FZG03A)supported by State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization,China。
文摘In this work,the reflux classifier with closely spaced inclined channels is used as the pre-concentration facility to improve the separation efficiency before the shaking table separation.Three operating parameters of reflux classifier(RC)to pre-concentrate fine(0.023−0.15 mm)tailings of antimony oxide were optimized by response surface methodology(RSM)using a three-level Box-Behnken design(BBD).The parameters studied for the optimization were feeding speed,underflow,and ascending water speed.Second-order response functions were produced for the Sb grade and recovery rate of the concentrate.Taking advantage of the quadratic programming,when the factors of feeding,underflow and ascending water are respectively 225,30 and 133 cm^3/min,a better result can be achieved for the concentrate grade of 2.31% and recovery rate of 83.17%.At the same time,70.48% of the tailings with the grade of 0.20% were discarded out of the feeding.The results indicated that the reflux classifier has a good performance in dealing with fine tailings of antimony oxide.Moreover,second-order polynomial equations,ANOVA,and three-dimensional surface plots were developed to evaluate the effects of each parameter on Sb grade and recovery rate of the concentrate.
基金This work was supported by the National Natural Science Foundation of China(NSFC 31760187)Yunnan Provincial Reserve Talents for Middle&Young Academic and Technical Leaders(2019HB026)Yunnan Provincial“Ten thousand Talents Project”Youth Tip-Top Talents.
文摘In this study,pre-concentrated bark,furfuryl alcohol and other biomass raw materials were used to prepare foaming materials by high-speed mechanical stirring without using a foaming agent.We investigated the effect of the postadded water amount on the properties of foaming materials.In particular,we determined basic physical properties of these materials,including the limiting oxygen index(LOI),porosity,thermal conductivity,thermogravimetric analysis,pore size distribution,and microstructure.The results of scanning electron microscopy(SEM)indicated that the pore size distribution was uniform and the pore size increased with increasing water volume.Thermogravimetric analysis(TG/DTG)showed that when the temperature reached 410°C,the foam was easily decomposed,the final residual mass was only 2.8%,and water addition had little effect on it.Moreover,the amount of post-added water is 5–30 g,the density and compression strength of the foamed materials gradually decreased,while the degree of pulverization increased.LOI ranged from 26.1%to 30.79%,and porosity ranged from 81%to 83%.The change in water volume greatly affected the foam’s performance,the performance of foamed material deteriorated as the amount of added water increased,but the effect on thermal conductivity was not very obvious.The highest thermal conductivity was only 0.0179 W/(m·K),still providing excellent thermal insulation.
基金Project (2012BAB07B05) supported by the National Technology Support Project of ChinaProject (2013zzts066) supported by Independent Innovation Foundation of Central South University,China
文摘Pre-concentration of vanadium from low-grade stone coal by the method of desliming-flotation was investigated. The mineral composition and microstructure of stone coal were studied systematically by means of X-ray fluorescence spectrometry （XRF）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that selective separation of vanadium-bearing minerals can be achieved by flotation in acidic solution using melamine （EA）. The final vanadium concentrate with V2O5 grade of 1.88% and recovery rate of 76.58% is obtained by desliming-flotation process and 72.51% of the raw ore is rejected as tailings. The pre-concentration of vanadium from low-grade stone coal can increase V2O5 grade and decrease the content of acid consuming minerals, which would enable economical utilization of metallurgical vanadium extraction technology.
文摘Phosphogypsum(PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements(REEs). The current study focuses on the recovery of REEs content and the residual phosphate content existing in the PG with preserving on the CaSO_(4)skeleton to be used in other various applications. These attainments are carried out using citric acid leaching process via soaking technique. Several dissolution parameters for REEs using citric acid were studied, including soaking time, soaking temperature, citric acid concentration, solid-to-liquid ratio, and recycling of the citrate leaching solutions in the further REEs dissolution experiments. The best-operating conditions were 14 d of soaking time, 7.5% citric acid concentration, and the solid-toliquid ratio of 1/5 at ambient temperature. About 79.57% dissolution efficiency of REEs was achieved using the optimal conditions. Applying four soaking stages by mixing different fresh PG samples with the same citrate solution sequentially, cumulative dissolution efficiency for REEs was found to be 64.7% under optimal soaking conditions. REEs were recovered using Dowex 50X8 resin from citrate solutions with 96% extraction efficiency. Dissolution kinetics proved the pseudo-first-order nature, reversible reactions, and two activation energies for all REEs.
基金Supported by the National Natural Science Foundation of China(No.41376050)
文摘A bstract With the aim of elucidating the spatial and seasonal behaviors of rare earth elements(REEs), we investigated the dissolved REE concentrations of surface water collected during four seasons from middle, lower reaches and estuary of the Minjiang River, southeastern China. The results display that the REE abundances in Minjiang River, ranging from 3.3–785.9 ng/L, were higher than those of many of the major global rivers. The total REE concentrations(∑REE) were seasonally variable, averaging in 5 937.30, 863.79, 825.65 and 1 065.75 ng/L during second highest flow(SHF), normal flow(NF), low flow(LF) and high flow(HF) season, respectively. The R_(( L/M)) and R_((H/M)) ratios reveal the spatial and temporal variations of REE patterns, and particularly vary apparently in the maximum turbidity zone and estuary. REE patterns of dissolved loads are characterized by progressing weaker LREEs-enrichment and stronger HREEsenrichment downstream from middle reaches to estuary during all four seasons. Comparing with NF and LF seasons, in which REE patterns are relatively flat, samples of SHF season have more LREE-enriched and HREE-depleted patterns that close to parent rocks, while samples of HF season are more LREEs-depleted and HREE-enriched. REE fractionations from the middle to lower reaches are stronger in the SHF and HF seasons than those in NF and LF seasons. Generally, spatial and seasonal variations in REE abundance and pattern are presumably due to several factors, such as chemical weathering, mixture with rainfall and groundwater, estuarine mixing, runoff, biological production and mountain river characters, such as strong hydrodynamic forces and steep slopes. The highest Gd/Gd* always occurs at north ports during all four seasons, where most of the large hospitals are located. This suggests Gd anomalies are depended on the density of modern medical facilities. Y/Ho ratios fl uctuate and positively correlate to salinity in estuary, probably because of the geochemical behavior differences between Y and Ho.
