Excess lithium in alumina is significantly bad for aluminum reduction.In this study,the concentration variation of lithium ion in sodium aluminate solution with addition of synthetic lithium aluminate was investigated...Excess lithium in alumina is significantly bad for aluminum reduction.In this study,the concentration variation of lithium ion in sodium aluminate solution with addition of synthetic lithium aluminate was investigated.Elevating temperature,increasing caustic soda concentration,reducing alumina concentration or raising molar ratioαk improved equilibrium concentration of lithium ion in sodium aluminate solution.Agitation speed had a minimal effect on lithium ion concentration.Over 0.65 g/L lithium ion equilibrium concentration was observed in digestion process,whereas 35 mg/L lithium ion concentration remained in solution after precipitation time of 9 h.Moreover,equilibrium concentration decreased sharply from digestion of boehmite or diaspore to seed precipitation,about 95%lithium was precipitated into red mud(bauxite residue)and aluminum hydroxide.This study provides a valuable perspective in removal or extraction of lithium from sodium aluminate solution in alumina refineries.展开更多
A safe,economical treatment of hazardous chromium-bearing vanadate residue(CVR)will significantly benefit the clean production of chromate-bearing salts.This study investigated recovery of sodium vanadate and sodium c...A safe,economical treatment of hazardous chromium-bearing vanadate residue(CVR)will significantly benefit the clean production of chromate-bearing salts.This study investigated recovery of sodium vanadate and sodium chromate from CVR in sodium bicarbonate solution.Results indicate that the stability of calcium vanadate and calcium chromate depends on pH and[HCO3?].CaV2O6?4H2O transforms into CaV2O6?4H2O,CaV2O6?2H2O,CaV2O6,Ca2V2O7?2H2O,and Ca5(VO4)3(OH)when pH increases from 7.51 to 12.32.Increasing pH and reducing CVR dosage improve the vanadate extraction rate,and high V2O5 and Na2Cr2O7?2H2O extraction rates are achieved in dilute NaHCO3 solution.Moreover,addition of NaOH positively contributes to the recovery of vanadate and chromate from CVR.Over 95%V2O5 and Na2Cr2O7?2H2O in CVR can be extracted from 60 g/L NaHCO3 and 30 g/L NaOH solutions at 90°C for 2 h.In order to reduce the hazardous residue containing chromate after recovery of CVR,calcium circulation is presented.Results show that more than 60%lime can be saved with fresh residue addition to remove vanadate from sodium chromate solution due to the active CaCO3.Moreover,no lime is required in removal of vanadate when the roasting residue is added.Therefore,a novel process is developed for utilization of CVR.展开更多
Fibrous activated alumina is widely applied in catalysts,adsorbents,and composite materials.This work presents a green approach in preparing the fibrous activated Al_(2)O_(3) with high purity and specific surface area...Fibrous activated alumina is widely applied in catalysts,adsorbents,and composite materials.This work presents a green approach in preparing the fibrous activated Al_(2)O_(3) with high purity and specific surface area through multistep phase transformation of aluminum-bearing substances using intermediate dawsonite as a template.Thermodynamic calculations and experimental results show that increasing the concentration of Na_(2)CO_(3) and(NH_(4))_(2)CO_(3) is remarkably beneficial to the formation of dawsonite and ammonium aluminum carbonate hydroxide,respectively.Based on determination of dissolution and precipitation mechanism,the ultrafine granular gibbsite is converted to the uniform fibrous dawsonite with a ratio of length to diameter over 50,and the fibrous dawsonite changes into the long fibrous ammonium aluminum carbonate hydroxide with a ratio of length to diameter is about 80 in above 70 g/L(NH_(4))_(2)CO_(3) solution.Furthermore,the activated alumina remains fibrous morphology after roasting ammonium aluminum carbonate hydroxide at a slow heating rate,plentiful open mesopore and weak aggregation of particles,which contributes to the high specific surface area of 159.37 m^(2)/g at 1273 K for the activated alumina.The complete transformation of dawsonite to ammonium aluminum carbonate hydroxide and high specific surface area contribute to the purity of the activated fibrous alumina above 99.9%with low Na and Fe content.展开更多
Gibbsite precipitation from sodium aluminate solution was intensified by adding mixed industrial and self-prepared active seeds,and its mechanism was researched preliminarily.The interfacial properties of seed/alumina...Gibbsite precipitation from sodium aluminate solution was intensified by adding mixed industrial and self-prepared active seeds,and its mechanism was researched preliminarily.The interfacial properties of seed/aluminate solution were determined for separate industrial and active seed.Contact angles of seed/aluminate solution and the specific surface area of seeds were respectively measured by sessile drop and BET method,and the morphology and particle size of precipitates were recorded by SEM and laser diffraction.The results show that,compared with the industrial seed,the active seed has a better wettability,lower interfacial tension,and larger specific surface area,being conducive to enhancing gibbsite precipitation from sodium aluminate solution.SEM analysis of the precipitates indicates that the embedment and accumulation/agglomeration of extremely fine particles on the surface of coarse industrial seed can effectively control the content of fine particles in the precipitation product.With extra 3.1–4.6 g/L active seed,the gibbsite precipitation ratio was increased by 3.23%–3.92%.Moreover,the mass percentage of particles<45μm in precipitation product has even a slight decrease compared with that for the traditional precipitation product or of the industrial seed itself.The result presented is favorable to developing an intensified gibbsite precipitation process for commercial alumina manufacture.展开更多
基金Project(2022JJ40616)supported by the Natural Science Foundation of Hunan Province,ChinaProject(2022YFC2904404)supported by the National Key Research and Development Program of China。
基金Project(2015BAB04B01)supported by the National Key Technology R&D Program of ChinaProject(FA2017029)supported by Science and Technology Program of Chongzuo,ChinaProject(CSUZC201811)supported by the Open-End Fund for the Valuable and Precision Instruments of Central South University,China
文摘Excess lithium in alumina is significantly bad for aluminum reduction.In this study,the concentration variation of lithium ion in sodium aluminate solution with addition of synthetic lithium aluminate was investigated.Elevating temperature,increasing caustic soda concentration,reducing alumina concentration or raising molar ratioαk improved equilibrium concentration of lithium ion in sodium aluminate solution.Agitation speed had a minimal effect on lithium ion concentration.Over 0.65 g/L lithium ion equilibrium concentration was observed in digestion process,whereas 35 mg/L lithium ion concentration remained in solution after precipitation time of 9 h.Moreover,equilibrium concentration decreased sharply from digestion of boehmite or diaspore to seed precipitation,about 95%lithium was precipitated into red mud(bauxite residue)and aluminum hydroxide.This study provides a valuable perspective in removal or extraction of lithium from sodium aluminate solution in alumina refineries.
基金Project(51274242)supported by the National Natural Science Foundation of ChinaProject(2015CX001)supported by the Innovation-driven Plan of Central South University,China
文摘A safe,economical treatment of hazardous chromium-bearing vanadate residue(CVR)will significantly benefit the clean production of chromate-bearing salts.This study investigated recovery of sodium vanadate and sodium chromate from CVR in sodium bicarbonate solution.Results indicate that the stability of calcium vanadate and calcium chromate depends on pH and[HCO3?].CaV2O6?4H2O transforms into CaV2O6?4H2O,CaV2O6?2H2O,CaV2O6,Ca2V2O7?2H2O,and Ca5(VO4)3(OH)when pH increases from 7.51 to 12.32.Increasing pH and reducing CVR dosage improve the vanadate extraction rate,and high V2O5 and Na2Cr2O7?2H2O extraction rates are achieved in dilute NaHCO3 solution.Moreover,addition of NaOH positively contributes to the recovery of vanadate and chromate from CVR.Over 95%V2O5 and Na2Cr2O7?2H2O in CVR can be extracted from 60 g/L NaHCO3 and 30 g/L NaOH solutions at 90°C for 2 h.In order to reduce the hazardous residue containing chromate after recovery of CVR,calcium circulation is presented.Results show that more than 60%lime can be saved with fresh residue addition to remove vanadate from sodium chromate solution due to the active CaCO3.Moreover,no lime is required in removal of vanadate when the roasting residue is added.Therefore,a novel process is developed for utilization of CVR.
基金Project(51874372)supported by the National Natural Science Foundation of China。
文摘Fibrous activated alumina is widely applied in catalysts,adsorbents,and composite materials.This work presents a green approach in preparing the fibrous activated Al_(2)O_(3) with high purity and specific surface area through multistep phase transformation of aluminum-bearing substances using intermediate dawsonite as a template.Thermodynamic calculations and experimental results show that increasing the concentration of Na_(2)CO_(3) and(NH_(4))_(2)CO_(3) is remarkably beneficial to the formation of dawsonite and ammonium aluminum carbonate hydroxide,respectively.Based on determination of dissolution and precipitation mechanism,the ultrafine granular gibbsite is converted to the uniform fibrous dawsonite with a ratio of length to diameter over 50,and the fibrous dawsonite changes into the long fibrous ammonium aluminum carbonate hydroxide with a ratio of length to diameter is about 80 in above 70 g/L(NH_(4))_(2)CO_(3) solution.Furthermore,the activated alumina remains fibrous morphology after roasting ammonium aluminum carbonate hydroxide at a slow heating rate,plentiful open mesopore and weak aggregation of particles,which contributes to the high specific surface area of 159.37 m^(2)/g at 1273 K for the activated alumina.The complete transformation of dawsonite to ammonium aluminum carbonate hydroxide and high specific surface area contribute to the purity of the activated fibrous alumina above 99.9%with low Na and Fe content.
基金Project(51604309)supported by the National Natural Science Foundation of ChinaProject(2015BAB04B01)supported by the National Key Technology R&D Program of China
文摘Gibbsite precipitation from sodium aluminate solution was intensified by adding mixed industrial and self-prepared active seeds,and its mechanism was researched preliminarily.The interfacial properties of seed/aluminate solution were determined for separate industrial and active seed.Contact angles of seed/aluminate solution and the specific surface area of seeds were respectively measured by sessile drop and BET method,and the morphology and particle size of precipitates were recorded by SEM and laser diffraction.The results show that,compared with the industrial seed,the active seed has a better wettability,lower interfacial tension,and larger specific surface area,being conducive to enhancing gibbsite precipitation from sodium aluminate solution.SEM analysis of the precipitates indicates that the embedment and accumulation/agglomeration of extremely fine particles on the surface of coarse industrial seed can effectively control the content of fine particles in the precipitation product.With extra 3.1–4.6 g/L active seed,the gibbsite precipitation ratio was increased by 3.23%–3.92%.Moreover,the mass percentage of particles<45μm in precipitation product has even a slight decrease compared with that for the traditional precipitation product or of the industrial seed itself.The result presented is favorable to developing an intensified gibbsite precipitation process for commercial alumina manufacture.
