Ameliorating the problem of low leaching efficiency,long leaching period,and high agent consumption should be studied to efficiently exploit ion-absorbed rare earth ore resources.In this study,the surfactant sodium do...Ameliorating the problem of low leaching efficiency,long leaching period,and high agent consumption should be studied to efficiently exploit ion-absorbed rare earth ore resources.In this study,the surfactant sodium dodecyl sulfate(SDS) is used to enhance the leaching effect of an ion-absorbed rare earth ore by ameliorating the seepage effect for the first time.The effects of surfactant concentration,leaching agent dosage,solution flow velocity,and solution pH on the leaching rate were explored,and the mechanism of SDS was discussed.Under the optimum conditions,the addition of a small amount of SDS(mass fraction0.04%) can increase the leaching rate by about 5%,shorten the leaching period,and reduce the consumption of the leaching agent.SDS significantly ameliorates the seepage effect of the ore body by reducing the surface tension of the leaching agent and ameliorating the wettability of the mineral surface.This effect is the main factor that improves the leaching efficiency.DFT(density functional theory) calculation results show that SDS can react with rare earth ions,which reduces the adsorption strength on clay mineral surfaces.Hence,rare earth ions are easily exchanged by ammonium ions,and mass transfer is enhanced.展开更多
A heteropoly molybdoselenite complex （NH4）6[ Se2Mo8O31 ]·5H2O and its lanthanide salts Ln2 [Se2Mo8O31]-XH2O（Ln = La^3＋, Ce^3＋, Nd^3＋ Sm^3＋） were synthesized and characterized with elemental analysis, IR, ...A heteropoly molybdoselenite complex （NH4）6[ Se2Mo8O31 ]·5H2O and its lanthanide salts Ln2 [Se2Mo8O31]-XH2O（Ln = La^3＋, Ce^3＋, Nd^3＋ Sm^3＋） were synthesized and characterized with elemental analysis, IR, UV, XRD and TG-DTA. Their reactivity for hydroxylation of phenol was investigated. The results show that catalytic activity of （ NH4 ）6 [Se2Mo8O31 ]·5H2O is higher than that of its lanthanide salts. The reaction temperatures, the reaction time. the catalvst amount, the ratio of phenol and H2O2 have influence on the phenol conversation, H2O2 selectivity and product distribution. The optimum reaction condition was obtained with orthogonal method. At optimum reaction condition which the ratio of phenol and H2O2 = 1 ： 1, reaction time is 4 h, reaction temperatures is 70℃ and catalyst is 10 g·mol^-1, and the conversation of phenol reaches as high as 29.65 %, the product selectivity can reach 77.2 % for catalyst （NH4）6[ Se2Mo8O31 ]·5H2O.展开更多
Ionic clays,formed by the natural weathering of REE-bearing minerals and the adsorption of the resulting liberated REE ions onto the clay surface,are an important resource for critical rare earth elements(REEs).Here,a...Ionic clays,formed by the natural weathering of REE-bearing minerals and the adsorption of the resulting liberated REE ions onto the clay surface,are an important resource for critical rare earth elements(REEs).Here,a two-step desorption process using ammonium sulfate with active pH adjustment using sulfuric acid was developed to extract REEs from a South American clay.The desorption process was optimized using response surface methodology approach and the optimum operating conditions were determined to be 0.15 mol/L ammonium sulfate,pH 3,liquid to solid ratio of 3/1,and 25℃ with20 min residence time.It is shown that this ionic clay is significantly different from previously reported clays,e.g.,from southern China,as it consists of three modes of REEs,including ion-exchanged REEs physically adsorbed on the clay surface,hydrolyzed REEs chemically adsorbed on the clay surface,and mineralized(non-desorbable) REEs within the clay.Mechanistic investigations through progressive acidification during desorption and adsorption isotherms show that REE desorption/adsorption occurs due to the combined action of physical ion exchange adsorption and surface complexation chemical adsorption,with their relative importance depending on the pH of the system and the amount of sulfate anions present within the solution.This work supports overall efforts to utilize ionic clays as a relatively new resource for REEs to empower the development and adoption of modern green technologies such as wind turbines and electric vehicles.展开更多
The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewat...The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 51774153 and 92062110)。
文摘Ameliorating the problem of low leaching efficiency,long leaching period,and high agent consumption should be studied to efficiently exploit ion-absorbed rare earth ore resources.In this study,the surfactant sodium dodecyl sulfate(SDS) is used to enhance the leaching effect of an ion-absorbed rare earth ore by ameliorating the seepage effect for the first time.The effects of surfactant concentration,leaching agent dosage,solution flow velocity,and solution pH on the leaching rate were explored,and the mechanism of SDS was discussed.Under the optimum conditions,the addition of a small amount of SDS(mass fraction0.04%) can increase the leaching rate by about 5%,shorten the leaching period,and reduce the consumption of the leaching agent.SDS significantly ameliorates the seepage effect of the ore body by reducing the surface tension of the leaching agent and ameliorating the wettability of the mineral surface.This effect is the main factor that improves the leaching efficiency.DFT(density functional theory) calculation results show that SDS can react with rare earth ions,which reduces the adsorption strength on clay mineral surfaces.Hence,rare earth ions are easily exchanged by ammonium ions,and mass transfer is enhanced.
文摘A heteropoly molybdoselenite complex （NH4）6[ Se2Mo8O31 ]·5H2O and its lanthanide salts Ln2 [Se2Mo8O31]-XH2O（Ln = La^3＋, Ce^3＋, Nd^3＋ Sm^3＋） were synthesized and characterized with elemental analysis, IR, UV, XRD and TG-DTA. Their reactivity for hydroxylation of phenol was investigated. The results show that catalytic activity of （ NH4 ）6 [Se2Mo8O31 ]·5H2O is higher than that of its lanthanide salts. The reaction temperatures, the reaction time. the catalvst amount, the ratio of phenol and H2O2 have influence on the phenol conversation, H2O2 selectivity and product distribution. The optimum reaction condition was obtained with orthogonal method. At optimum reaction condition which the ratio of phenol and H2O2 = 1 ： 1, reaction time is 4 h, reaction temperatures is 70℃ and catalyst is 10 g·mol^-1, and the conversation of phenol reaches as high as 29.65 %, the product selectivity can reach 77.2 % for catalyst （NH4）6[ Se2Mo8O31 ]·5H2O.
基金Aclara Resources Inc.for providing financial support for this study。
文摘Ionic clays,formed by the natural weathering of REE-bearing minerals and the adsorption of the resulting liberated REE ions onto the clay surface,are an important resource for critical rare earth elements(REEs).Here,a two-step desorption process using ammonium sulfate with active pH adjustment using sulfuric acid was developed to extract REEs from a South American clay.The desorption process was optimized using response surface methodology approach and the optimum operating conditions were determined to be 0.15 mol/L ammonium sulfate,pH 3,liquid to solid ratio of 3/1,and 25℃ with20 min residence time.It is shown that this ionic clay is significantly different from previously reported clays,e.g.,from southern China,as it consists of three modes of REEs,including ion-exchanged REEs physically adsorbed on the clay surface,hydrolyzed REEs chemically adsorbed on the clay surface,and mineralized(non-desorbable) REEs within the clay.Mechanistic investigations through progressive acidification during desorption and adsorption isotherms show that REE desorption/adsorption occurs due to the combined action of physical ion exchange adsorption and surface complexation chemical adsorption,with their relative importance depending on the pH of the system and the amount of sulfate anions present within the solution.This work supports overall efforts to utilize ionic clays as a relatively new resource for REEs to empower the development and adoption of modern green technologies such as wind turbines and electric vehicles.
基金Project supported by the National Natural Science Foundation of China(51674037,51674036)Guangxi Science and Technology Major Project(Guike-AA18242022)。
文摘The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.
