CN109112293B - Method for selectively enriching scandium from Bayer process red mud - Google Patents
Method for selectively enriching scandium from Bayer process red mud Download PDFInfo
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- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
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Abstract
The invention discloses a method for selectively enriching scandium from Bayer process red mud, which is characterized in that Bayer process red mud is used as a raw material, a proper amount of water is added to fully wet the red mud, concentrated sulfuric acid is used for sulfating the red mud, roasting is carried out at high temperature, a solid roasting product is ground, mechanical activation is carried out, four-stage water leaching and water washing are carried out, and scandium-enriched leachate, scandium-enriched washing liquor and low-alkali iron-enriched slag are obtained. The method ensures that most of scandium is leached, the leaching rates of impurities of iron and aluminum are low, silicon and titanium are not basically leached, the formation of silicic acid colloid in the leaching solution is avoided, and the selective adsorption and extraction of scandium in the subsequent leaching solution are facilitated; the generated sulfur dioxide and sulfur trioxide can be reused for preparing sulfuric acid for recycling, so that a large amount of waste acid is avoided; the pH value of the low-alkali iron-rich slag is close to neutral, and the low-alkali iron-rich slag can be used in the industries of iron making, adsorbents, ceramics, buildings and the like, and provides a new way for scandium extraction and red mud comprehensive utilization.
Description
Technical Field
The invention belongs to the technical field of comprehensive utilization of solid wastes and mineral resource processing, and particularly relates to a method for selectively enriching scandium from Bayer process red mud.
Background
Scandium is an important strategic resource and is widely applied to high-tech fields such as optics, electronics, aviation, automobiles, superconduction and the like. Scandium belongs to associated rare-dispersion elements, has no independent deposit in nature, and is mainly recovered as a byproduct from low-alkali iron-rich slag, tailings and waste liquid for producing other metals such as rare earth, aluminum, titanium, tungsten, magnesium and the like.
The red mud is alkaline solid waste residue generated in the process of producing alumina from bauxite. It is estimated that 1-1.5 tons of red mud are produced per 1 ton of alumina produced. 1.5 million tons of red mud are generated in the world every year, and the accumulated stock of the red mud in China currently exceeds 5 million tons. The red mud is used as industrial waste residue, is accumulated on the land after being dehydrated, not only occupies a large amount of land area, but also causes serious harm to the surrounding environment due to high alkalinity and high dust content, so that the effective and large-scale reasonable utilization of the red mud becomes a difficult problem to be solved urgently in the global alumina industry. The red mud is rich in elements such as scandium, iron, titanium, rare earth and the like, is an available secondary resource, and has become one of the research hotspots of comprehensive utilization of red mud in recent years for extracting scandium from red mud.
Chinese patent CN1844421A discloses a method for extracting scandium from red mud, which takes red mud generated by alumina production from bauxite as raw material, and adopts the processes of hydrochloric acid leaching, P2O4 extraction, acid washing for impurity removal, sodium hydroxide back extraction, hydrochloric acid dissolution, hydrolysis by adding an ammonia water modifier for removing zirconium titanate, oxalic acid for scandium precipitation, moderate temperature calcination and the like, so as to obtain scandium oxide with the purity of 99.9%. Chinese patent CN105331837A discloses a method for enriching scandium from red mud, which takes red mud generated by alumina production from bauxite as raw material, and obtains scandium-containing filter residue after additive agglomeration, reduction roasting, magnetic separation for iron removal, phosphoric acid leaching for silicon removal and sodium hydroxide solution leaching for aluminum removal, wherein the total recovery rate of scandium is more than 90%. Chinese patent CN106086436A discloses a method for selectively leaching scandium and sodium from Bayer process red mud, which adopts concentrated sulfuric acid to mix uniformly, carries out low-temperature sulfation, then carries out medium-temperature roasting, and carries out water leaching to obtain scandium-sodium-rich low-iron washing liquor.
However, there are still some problems in the recovery of scandium in red mud: (1) at present, most of extraction methods adopt direct acid leaching to treat red mud, a large amount of silicon in the red mud is dissolved out in the direct acid leaching process to form silica gel, so that solid-liquid separation is difficult, the silicon content in the solution is too high, a large amount of emulsion is easy to generate during scandium extraction, organic phase separation is difficult, and the difficulty of subsequent processes is increased. (2) The iron content in the red mud is high, the recovery of scandium is influenced by the co-leaching of iron, and if the iron in the red mud is subjected to separation pretreatment, the existing process route is complex, the energy consumption is high, the acid and alkali consumption is high, and the treatment cost is increased. (3) After valuable metals are extracted from red mud by the existing treatment mode, a large amount of waste residues are still discharged because other components in the red mud are remained in the residues, the original alkaline waste residues are changed into acidic waste residues, the problem of large-amount storage of the waste residues is not fundamentally solved, and acid cannot be recycled to generate a large amount of waste acid, so that the pollution to underground water and the damage to the environment are caused.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for selectively enriching scandium from Bayer process red mud. The method can realize the selective separation of scandium from silicon, iron, aluminum and titanium, can efficiently enrich scandium in Bayer process red mud, improve the leaching rate of scandium and the concentration of scandium in the leaching solution, is beneficial to the selective adsorption and extraction of scandium in the subsequent leaching solution, further improves the total recovery rate of scandium by recycling scandium-rich washing liquor, recycles the generated sulfur dioxide and sulfur trioxide to prepare concentrated sulfuric acid for recycling, avoids the generation of a large amount of waste acid, is nearly neutral in low-alkali iron-rich slag, can be applied to industries such as iron making, adsorbents, ceramics, buildings and the like, realizes the zero emission of red mud, and meets the requirements of environmental protection and sustainable development.
The invention solves the technical problems and adopts the following technical scheme:
a method for selectively enriching scandium from Bayer process red mud is characterized in that Bayer process red mud is used as a raw material, a proper amount of water is added to fully wet the red mud, concentrated sulfuric acid is used for sulfating the red mud, roasting is carried out at high temperature, solid roasting products are ground, mechanically activated, and then subjected to four-stage water leaching and water washing to obtain scandium-enriched leachate, scandium-enriched washing liquor and low-alkali iron-enriched slag.
The method comprises the following steps:
s1, adding a proper amount of water into Bayer process red mud to fully wet the red mud;
s2, adding concentrated sulfuric acid with the mass fraction of 95% -98% into the slurry obtained in the step S1 for heating and curing to sulfate the red mud, wherein the curing temperature is 80-150 ℃, and the curing time is 20-60 min;
s3, roasting the red mud sulfation product obtained in the step S2 at a high temperature to obtain a solid roasting product and generate sulfur dioxide and sulfur trioxide; the roasting conditions are as follows: the roasting temperature is 800-850 ℃, and the roasting time is 20-75 min;
s4, fully grinding the solid roasted product obtained in the step S3 for mechanical activation, wherein the grinding time is 10-40 min;
s5, carrying out selective water leaching on the solid roasted product after mechanical activation in the step S4, wherein the leaching conditions are as follows: the reaction temperature is 25-95 ℃, the reaction time is 15-90 min, the stirring speed is 200-600 r/min, and the ratio of water to red mud is 4-12: 1 mL/g; carrying out solid-liquid separation on the obtained leaching slurry to obtain leaching residues and a first-stage scandium-rich leaching solution; adding water into the leached slag for washing, stirring and filtering to obtain a first-stage scandium-rich washing liquid and low-alkali iron-rich slag;
s6, leaching the solid roasting product mechanically activated in the step S4 by using the first-stage scandium-rich leaching solution obtained in the step S5, wherein the leaching conditions are the same as those of the step S5, the loss of water in the leaching process is supplemented by equal amount of water, and then washing the leaching slag by using the first-stage scandium-rich washing solution obtained in the step S5, and the loss of water in the washing process is supplemented by equal amount of water; the obtained secondary scandium-rich leachate and secondary scandium-rich washing liquor are repeatedly operated; repeatedly operating the obtained three-stage scandium-rich leachate and the three-stage scandium-rich washing liquor; obtaining a four-stage scandium-enriched leaching solution, a four-stage scandium-enriched washing liquid and low-alkali iron-enriched slag.
Preferably, the particle size of the bayer process red mud in the step S1 is less than 74 μm.
Preferably, the ratio of the water to the red mud in the step S1 is 0.4-0.8 mL/g.
Preferably, the adding amount of the concentrated sulfuric acid in the step S2 is 0.75-1.50 mL/g according to the ratio of the concentrated sulfuric acid to the red mud.
Preferably, the water washing in the step S5 is performed according to a ratio of water to red mud of 4-8 mL/g.
Preferably, the sulfur dioxide and sulfur trioxide produced in step S3 are reused for preparing the concentrated sulfuric acid used in step S2.
Preferably, the fourth-stage scandium-rich leachate and the fourth-stage scandium-rich washing liquid obtained in the step S6 are used as raw materials for selective scandium adsorption and extraction, and the low-alkali iron-rich slag obtained in the steps S5 and S6 is used as raw materials for iron making.
The technical principle of the invention is as follows:
when the red mud is directly leached by sulfuric acid, scandium, iron, aluminum and titanium in the red mud mineral react with the sulfuric acid, the obtained leachate has complex components, the difficulty of scandium adsorption or extraction in the subsequent leachate is increased, a large amount of waste acid is generated, the equipment is seriously corroded, and the waste acid cannot be recycled. More importantly, silicon element in the red mud in the direct acid leaching process is dissolved out in large quantity in cancrinite phase to generate silicic acid H4SiO4Under acidic conditions H4SiO4With H in solution+Ion binding to form H5SiO4 +，H4SiO4And H5SiO4 +The following polymerization reactions take place in the presence of water:
H3Am ++H2An→H3A+ m+n+2H2O
wherein A ismIs represented by [ Sim(OH)4m+2]2-，AnIs represented by [ Sin(OH)4n+2]2-
Silica gel formed by the reaction is suspended in the solution, so that solid-liquid separation is difficult after leaching, and the leaching of scandium is influenced by the fact that ore particles are wrapped by the silica gel. In addition, the presence of silicon also has a great influence on the adsorption and extraction of scandium in the leachate, so that leaching of silicon is avoided as much as possible in the scandium recovery process.
Before the 95-98% concentrated sulfuric acid is added, a proper amount of water is added to fully wet the red mud, so that the concentrated sulfuric acid and the red mud are mixed more uniformly, the sulfuric acid curing reaction is more complete, the scandium leaching rate in the water leaching process can be improved, and the use of sulfuric acid is reduced. The main elements in the red mud are converted into corresponding sulfates in the curing process, and the reaction equation is as follows:
Na8Al6Si6O24(OH)2(H2O)2+13H2SO4→4Na2SO4+3Al2(SO4)3+6H4SiO4+4H2O
Fe2O3+3H2SO4→Fe2(SO4)3+3H2O
AlO(OH)+3H2SO4→Al2(SO4)3+3H2O
CaTiO3+2H2SO4→CaSO4+TiOSO4+2H2O
CaCO3+H2SO4→CaSO4+CO2↑+H2O
TiO2+H2SO4→TiOSO4+H2O
Sc2O3+3H2SO4→Sc2(SO4)3+3H2O
in the high-temperature roasting process, as the roasting temperature increases, unstable sulfate is decomposed into corresponding oxides, and the following reactions occur in sequence at 800-850 ℃:
H4SiO4→SiO2+2H2O↑
TiOSO4→TiO2+SO3↑
Al2(SO4)3→Al2O3+3SO3↑
Fe2(SO4)3→Fe2O3+3SO3↑
scandium as Sc at a calcination temperature of less than 850 DEG C2(SO4)3When the roasting temperature is 800-850 ℃, the sulfate of silicon, iron, aluminum and titanium exists in the form of oxide after being decomposed, and calcium and sodium remain in the roasted sample in the form of sulfate.
The red mud sulfation product is fully ground after being roasted for mechanical activation, the grinding can reduce the particle size of minerals, increase the specific surface area of the minerals, and can perform more sufficient ion exchange with the surrounding leachate, thereby accelerating the leaching process.
Carrying out four-stage water leaching and water washing on the mechanically activated solid roasting product, wherein scandium and sodium enter a leaching solution, silicon, iron, aluminum and titanium mainly remain in leaching residues in the form of oxides, and most of calcium sulfate enters the leaching residues; the concentration of scandium in the first-stage washing liquid is too low to be used for next-step adsorption, so that the loss of scandium is caused, the recovery rate of scandium is reduced, soluble scandium adhered to leaching slag can be recovered by four-stage water leaching and water washing, the concentration of scandium in the leaching liquid and the washing liquid is improved, scandium is further enriched, subsequent selective adsorption and extraction of scandium are facilitated, the probability of combination of an adsorption site of an adsorbent and scandium ions is increased, and the adsorption effect is improved. If the leaching stage number is increased, although the concentration of scandium in the leachate is increased, the concentration of scandium in the leachate after the four stages is not obviously increased due to the change of the pH value of the leachate and the like, and the scandium loss is increased along with the increase of the concentration of scandium in the washing liquid, so that the total recovery rate is reduced. The four-stage water leaching and water washing meet the concentration requirement of selective adsorption of scandium in the subsequent leachate, the good adsorption effect is achieved, the scandium recovery rate is maintained to be high, and the four-stage water leaching and water washing are the best selection.
Because most of sodium enters the leaching solution, the alkalinity of the leaching slag is greatly weakened relative to the original red mud and is close to neutrality, so the leaching slag can be used as a raw material for ironmaking or applied to industries such as an adsorbent, ceramics, buildings and the like.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention adopts the processes of water wetting, sulfation, high-temperature roasting, mechanical activation, four-stage water leaching and water washing, scandium is dissolved out by controlling roasting and leaching conditions, and silicon, iron, titanium and aluminum are left in leaching slag. The formation of silica gel and the interference of iron, aluminum and titanium on the selective adsorption and extraction of scandium in the leaching solution in the leaching process can be avoided. Under the conditions of primary leaching and water washing, the leaching rate of scandium is as high as 85-92%, the leaching rate of iron is lower than 0.5%, the leaching rate of aluminum is lower than 10%, and titanium and silicon are not leached. The adsorption rate of scandium in the four-stage leaching solution and the four-stage washing liquid is more than 98%.
(2) Before adding 95-98% concentrated sulfuric acid, a proper amount of water is added to fully wet the red mud, so that the concentrated sulfuric acid and the red mud are mixed more uniformly, the sulfuric acid aging reaction is more complete, the scandium leaching rate in the water leaching process can be improved, and the use of sulfuric acid is reduced.
(3) The red mud sulfation product is fully ground after being roasted for mechanical activation, the grinding can reduce the particle size of the mineral, increase the specific surface area of the mineral, and perform more sufficient ion exchange with the surrounding leachate, thereby accelerating the leaching process and improving the leaching rate of scandium.
(4) Four-stage water leaching and washing are adopted, soluble scandium adhered to leaching slag can be recovered through the four-stage water leaching and washing, the concentration of scandium in leaching liquid and washing liquid is improved, scandium is further enriched, subsequent selective adsorption and extraction of scandium are facilitated, the probability of combination of an adsorption site of the adsorbent and scandium ions is increased, and the adsorption effect is improved. The concentration of scandium in the four-stage scandium-rich leachate reaches more than 18mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid reaches more than 12mg/L, and the total recovery rate reaches more than 73%. Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is more than 2.5 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
(5) The method has the advantages of short process flow, simple operation and capability of recovering SO generated in the process2And SO3The method can realize the recycling of the sulfuric acid, save the cost, avoid the generation of a large amount of waste acid and have no environmental pollution, and is expected to realize the large-scale resource utilization of the Bayer process red mud.
(6) The scandium-rich leachate and the scandium-rich washing liquid obtained by the method can be used as raw materials for subsequent selective scandium adsorption and extraction. Because most of sodium enters the leaching solution, the leaching residue is greatly weakened and nearly neutral relative to the original red mud, and can be used as a raw material for ironmaking or applied to industries such as an adsorbent, ceramics, buildings and the like.
Drawings
FIG. 1 is a process flow diagram of the present invention.
Detailed Description
Example 1
The raw material is Bayer process red mud, and the red mud contains Fe as the main component and mass percentage2O326.70％、Al2O323.46％、CaO 14.66％、SiO211.09％、TiO25.75％、Na2O 5.41％、Sc 0.008％。
Drying and grinding Bayer process red mud to a sample sieving sieve to obtain solid powder with the particle size less than 74 mu m; adding water according to the proportion of 0.5mL/g of water to the red mud to fully wet the red mud;
secondly, adding concentrated sulfuric acid into the slurry obtained in the first step according to the mass fraction of the concentrated sulfuric acid (95-98%) to the red mud of 1.0mL/g, and curing for 30min at 100 ℃ to sulfate the red mud;
thirdly, roasting the red mud sulfating product obtained in the second step at high temperature, wherein the roasting conditions are as follows: the roasting temperature is 850 ℃, and the roasting time is 60 min; obtaining a solid roasting product and generating sulfur dioxide and sulfur trioxide;
fourthly, fully grinding the solid roasted product obtained in the third step for mechanical activation, wherein the grinding time is 30 min;
fifthly, carrying out selective water leaching on the mechanically activated solid roasted product, wherein the leaching conditions are as follows: the reaction temperature is 60 ℃, the reaction time is 40min, the stirring speed is 400r/min, and the ratio of water to red mud is 8:1 mL/g; carrying out solid-liquid separation on the obtained leaching slurry to obtain leaching residues and a first-stage scandium-rich leaching solution; adding distilled water into the leaching residue according to the proportion of 5mL/g of water to the red mud for washing, stirring and filtering to obtain a first-stage scandium-rich washing liquid and low-alkali iron-rich residue.
Leaching the mechanically activated solid roasting product obtained in the step IV by using the first-stage scandium-rich leaching solution obtained in the step V, wherein the leaching condition is the same as that of the step V, and the loss of water in the leaching process is supplemented by equivalent water, so that the liquid-solid ratio in the leaching process is kept consistent; then, the leaching residue of the second leaching is washed by the first scandium-rich washing liquid obtained in the fifth step, and the loss of water in the washing process is supplemented by equivalent water, so that the liquid-solid ratio of the scandium-rich washing liquid to the red mud in the washing process is kept consistent; repeating the above operations on the obtained second-stage scandium-rich leachate and the second-stage scandium-rich washing liquid, and repeating the above operations on the obtained third-stage scandium-rich leachate and the third-stage scandium-rich washing liquid; obtaining a four-stage scandium-enriched leaching solution, a four-stage scandium-enriched washing liquid and low-alkali iron-enriched slag.
The sulfur dioxide or sulfur trioxide produced in the third step is reused for preparing the concentrated sulfuric acid used in the second step.
And sixthly, using the four-stage scandium-rich leaching solution and the four-stage scandium-rich washing liquid obtained in the step (c) as raw materials for selective scandium adsorption and extraction, and using the low-alkali iron-rich slag obtained in the step (c) and the step (c) as a raw material for iron making, wherein the low-alkali iron-rich slag is nearly neutral.
Under the conditions of primary water leaching and water washing, the leaching rate of scandium is 91.43%, the leaching rate of iron is 0.3%, the leaching rate of aluminum is 6.22%, titanium and silicon are not leached, the concentration of scandium in the primary scandium-rich leaching solution is 9.63mg/L, the concentration of scandium in the primary scandium-rich washing liquid is 2.54mg/L, and the total recovery rate is 74.20%.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 80.22%, the leaching rate of iron is 0.21%, the leaching rate of aluminum is 5.14%, titanium and silicon are not leached, the concentration of scandium in the four-stage scandium-rich leaching solution is 26.02mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid is 14.35mg/L, and the total recovery rate is 75.22%.
Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is 2.73 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
If the leaching stage number is increased, although the concentration of scandium in the leachate is increased, the concentration of scandium in the leachate after the four stages is not obviously increased due to the change of the pH value of the leachate and the like, and the scandium loss is increased along with the increase of the concentration of scandium in the washing liquid, so that the total recovery rate is reduced. The four-stage water leaching and water washing meet the concentration requirement of selective adsorption of scandium in the subsequent leachate, the good adsorption effect is achieved, the scandium recovery rate is maintained to be high, and the four-stage water leaching and water washing are the best selection.
Example 2
The raw material is Bayer process red mudThe main component and the mass percentage content of the red mud are Fe2O326.70％、Al2O323.46％、CaO 14.66％、SiO211.09％、TiO25.75％、Na2O 5.41％、Sc 0.008％。
Drying and grinding Bayer process red mud to a sample sieving sieve to obtain solid powder with the particle size less than 74 mu m; adding water according to the proportion of 0.4mL/g of water to the red mud to fully wet the red mud;
secondly, adding concentrated sulfuric acid into the slurry obtained in the first step according to the mass fraction of the concentrated sulfuric acid (95-98%) to the red mud of 1.5mL/g, and curing for 60min at 80 ℃ to sulfate the red mud;
thirdly, roasting the red mud sulfating product obtained in the second step at high temperature, wherein the roasting conditions are as follows: roasting at 825 deg.C for 20 min; obtaining a solid roasting product and generating sulfur dioxide and sulfur trioxide;
fourthly, fully grinding the solid roasted product obtained in the third step for mechanical activation, wherein the grinding time is 40 min;
fifthly, carrying out selective water leaching on the mechanically activated solid roasted product, wherein the leaching conditions are as follows: the reaction temperature is 25 ℃, the reaction time is 90min, the stirring speed is 200r/min, and the ratio of water to red mud is 4:1 mL/g; carrying out solid-liquid separation on the obtained leaching slurry to obtain leaching residues and a first-stage scandium-rich leaching solution; adding distilled water into the leaching residue according to the proportion of 8mL/g of water and red mud for washing, stirring and filtering to obtain a first-stage scandium-rich washing liquid and low-alkali iron-rich residue.
Leaching the mechanically activated solid roasting product obtained in the step IV by using the first-stage scandium-rich leaching solution obtained in the step V, wherein the leaching condition is the same as that of the step V, and the loss of water in the leaching process is supplemented by equivalent water, so that the liquid-solid ratio in the leaching process is kept consistent; then, the leaching residue of the second leaching is washed by the first scandium-rich washing liquid obtained in the fifth step, and the loss of water in the washing process is supplemented by equivalent water, so that the liquid-solid ratio of the scandium-rich washing liquid to the red mud in the washing process is kept consistent; repeating the above operations on the obtained second-stage scandium-rich leachate and the second-stage scandium-rich washing liquid, and repeating the above operations on the obtained third-stage scandium-rich leachate and the third-stage scandium-rich washing liquid; obtaining a four-stage scandium-enriched leaching solution, a four-stage scandium-enriched washing liquid and low-alkali iron-enriched slag.
The sulfur dioxide or sulfur trioxide produced in the third step is reused for preparing the concentrated sulfuric acid used in the second step.
And sixthly, using the four-stage scandium-rich leaching solution obtained in the step (v) as a raw material for selective scandium adsorption and extraction, wherein the low-alkali iron-rich slag obtained in the step (v) and the low-alkali iron-rich slag obtained in the step (v) are nearly neutral and can be used as a raw material for iron making.
Under the conditions of primary water leaching and water washing, the leaching rate of scandium is 90.03%, the leaching rate of iron is 0.47%, the leaching rate of aluminum is 7.62%, titanium and silicon are not leached, the concentration of scandium in the primary scandium-rich leaching solution is 17.89mg/L, the concentration of scandium in the primary scandium-rich washing liquid is 2.31mg/L, and the total recovery rate is 68.05%.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 78.32%, the leaching rate of iron is 0.35%, the leaching rate of aluminum is 5.94%, titanium and silicon are not leached, the concentration of scandium in the four-stage scandium-rich leaching solution is 45.22mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid is 12.08mg/L, and the total recovery rate is 73.31%.
Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is 2.52 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
If the leaching stage number is increased, although the concentration of scandium in the leachate is increased, the concentration of scandium in the leachate after the four stages is not obviously increased due to the change of the pH value of the leachate and the like, and the scandium loss is increased along with the increase of the concentration of scandium in the washing liquid, so that the total recovery rate is reduced. The four-stage water leaching and water washing meet the concentration requirement of selective adsorption of scandium in the subsequent leachate, the good adsorption effect is achieved, the scandium recovery rate is maintained to be high, and the four-stage water leaching and water washing are the best selection.
Example 3
The raw material is Bayer process red mud, and the red mud contains Fe as the main component and mass percentage2O326.70％、Al2O323.46％、CaO 14.66％、SiO211.09％、TiO25.75％、Na2O 5.41％、Sc 0.008％。
Drying and grinding Bayer process red mud to a sample sieving sieve to obtain solid powder with the particle size less than 74 mu m; adding water according to the proportion of 0.8mL/g of water to the red mud to fully wet the red mud;
secondly, adding concentrated sulfuric acid into the slurry obtained in the first step according to the mass fraction of 95-98% of the concentrated sulfuric acid to the red mud of 0.75mL/g, and curing for 20min at 150 ℃ to sulfate the red mud;
thirdly, roasting the red mud sulfating product obtained in the second step at high temperature, wherein the roasting conditions are as follows: the roasting temperature is 800 ℃, and the roasting time is 75 min; obtaining a solid roasting product and generating sulfur dioxide and sulfur trioxide;
fourthly, fully grinding the solid roasted product obtained in the third step for mechanical activation, wherein the grinding time is 10 min;
fifthly, carrying out selective water leaching on the mechanically activated solid roasted product, wherein the leaching conditions are as follows: the reaction temperature is 95 ℃, the reaction time is 15min, the stirring speed is 600r/min, and the ratio of water to red mud is 12:1 mL/g; carrying out solid-liquid separation on the obtained leaching slurry to obtain leaching residues and a first-stage scandium-rich leaching solution; adding distilled water into the leaching residue according to the proportion of 4mL/g of water and red mud for washing, stirring and filtering to obtain a first-stage scandium-rich washing liquid and low-alkali iron-rich residue.
Leaching the mechanically activated solid roasting product obtained in the step IV by using the first-stage scandium-rich leaching solution obtained in the step V, wherein the leaching condition is the same as that of the step V, and the loss of water in the leaching process is supplemented by equivalent water, so that the liquid-solid ratio in the leaching process is kept consistent; then, the leaching residue of the second leaching is washed by the first scandium-rich washing liquid obtained in the fifth step, and the loss of water in the washing process is supplemented by equivalent water, so that the liquid-solid ratio of the scandium-rich washing liquid to the red mud in the washing process is kept consistent; repeating the above operations on the obtained second-stage scandium-rich leachate and the second-stage scandium-rich washing liquid, and repeating the above operations on the obtained third-stage scandium-rich leachate and the third-stage scandium-rich washing liquid; obtaining a four-stage scandium-enriched leaching solution, a four-stage scandium-enriched washing liquid and low-alkali iron-enriched slag.
The sulfur dioxide or sulfur trioxide produced in the third step is reused for preparing the concentrated sulfuric acid used in the second step.
And sixthly, using the four-stage scandium-rich leaching solution obtained in the step (v) as a raw material for selective scandium adsorption and extraction, wherein the low-alkali iron-rich slag obtained in the step (v) and the low-alkali iron-rich slag obtained in the step (v) are nearly neutral and can be used as a raw material for iron making.
Under the conditions of primary water leaching and water washing, the leaching rate of scandium is 88.93%, the leaching rate of iron is 0.49%, the leaching rate of aluminum is 8.85%, titanium and silicon are not leached, the concentration of scandium in the primary scandium-rich leaching solution is 6.55mg/L, the concentration of scandium in the primary scandium-rich washing liquid is 2.67mg/L, and the total recovery rate is 75.18%.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 79.22%, the leaching rate of iron is 0.37%, the leaching rate of aluminum is 7.15%, titanium and silicon are not leached, the concentration of scandium in the four-stage scandium-rich leaching solution is 18.68mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid is 15.48mg/L, and the total recovery rate is 75.71%.
Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is 2.79 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
If the leaching stage number is increased, although the concentration of scandium in the leachate is increased, the concentration of scandium in the leachate after the four stages is not obviously increased due to the change of the pH value of the leachate and the like, and the scandium loss is increased along with the increase of the concentration of scandium in the washing liquid, so that the total recovery rate is reduced. The four-stage water leaching and water washing meet the concentration requirement of selective adsorption of scandium in the subsequent leachate, the good adsorption effect is achieved, the scandium recovery rate is maintained to be high, and the four-stage water leaching and water washing are the best selection.
Comparative example 1
Different from the embodiment 1, the roasting condition of the third step is as follows: the roasting temperature is 875 ℃, and the roasting time is 60 min. The results obtained with the same other process conditions were as follows:
under the conditions of primary water leaching and water washing, the leaching rate of scandium is 10.93%, the leaching rate of iron is 0.23%, the leaching rate of aluminum is 4.55%, titanium and silicon are not leached, the concentration of scandium in the primary leaching solution is 1.55mg/L, the concentration of scandium in the primary washing liquid is 0.46mg/L, and the concentrations of scandium in the leaching solution and the washing liquid are too low to be used for next-step adsorption.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 8.12%, the leaching rate of iron is 0.17%, the leaching rate of aluminum is 3.25%, titanium and silicon are not leached, the concentration of scandium in the four-stage leaching solution is 4.23mg/L, the concentration of scandium in the four-stage washing solution is 1.55mg/L, and the concentrations of scandium in the four-stage leaching solution and the four-stage washing solution are too low to be used for next-step adsorption.
Sc in the sample when the baking temperature is 875 DEG C2(SO4)3Conversion to Sc2O3，Sc2O3Is not easy to dissolve in water and can not be leached in the leaching link. Therefore, the roasting temperature should be controlled below 850 ℃ to control scandium and Sc2(SO4)3Is present in the calcined sample.
Comparative example 2
Different from the embodiment 1, the roasting condition of the third step is as follows: the roasting temperature is 750 ℃, and the roasting time is 60 min. The results obtained with the same other process conditions were as follows:
under the conditions of primary water leaching and water washing, the leaching rate of scandium is 91.73%, the leaching rate of iron is 26.74%, the leaching rate of aluminum is 39.26%, the leaching rate of titanium is 8.71%, the leaching rate of silicon is 2.3%, and the concentration of scandium in the primary scandium-rich leachate is 17.89 mg/L. The concentration of titanium in the first-stage scandium-rich washing liquid is 1660mg/L, selective separation cannot be realized, and impurity elements seriously influence the next step of scandium adsorption.
Al in the sample when the firing temperature is 750 DEG C2(SO4)3、Fe2(SO4)3Not yet completely converted to Al2O3、Fe2O3，Al2(SO4)3、Fe2(SO4)3Is easily dissolved in water. In the leaching process, scandium has higher leaching rate, but impurity metals of iron, aluminum and titanium enter the leaching solution along with scandium, and selective separation cannot be realized.
Comparative example 3
Unlike example 1, in step (i), water was not added to sufficiently wet the red mud. The results obtained with the same other process conditions were as follows:
under the conditions of primary water leaching and water washing, the leaching rate of scandium is 67.11%, the leaching rate of iron is 1.22%, the leaching rate of aluminum is 5.82%, titanium and silicon are not leached, the concentration of scandium in the primary scandium-rich leaching solution is 7.02mg/L, the concentration of scandium in the primary scandium-rich washing liquid is 1.89mg/L, and the total recovery rate is 52.5%.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 56.82%, the leaching rate of iron is 0.97%, the leaching rate of aluminum is 4.77%, titanium and silicon are not leached, the concentration of scandium in the four-stage scandium-rich leaching solution is 19.03mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid is 10.02mg/L, and the total recovery rate is 52.52%.
Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is 2.71 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
Because water is not added firstly to fully wet the red mud, the concentrated sulfuric acid and the red mud are not uniformly mixed, the agglomeration is serious, and the sulfuric acid aging reaction is incomplete, so that the leaching rate of scandium, the concentration of scandium in a leaching solution, the concentration of scandium in a washing solution and the total recovery rate of scandium are all reduced.
Comparative example 4
Unlike example 1, the "step (iv): fully grinding the solid roasted product obtained in the step (iii) for mechanical activation, wherein the grinding time is 30min, and directly carrying out selective water immersion on the solid roasted product obtained in the step (iii). The results obtained with the same other process conditions were as follows:
under the conditions of primary water leaching and water washing, the leaching rate of scandium is 69.21%, the leaching rate of iron is 0.23%, the leaching rate of aluminum is 5.77%, titanium and silicon are not leached, and the concentration of scandium in the primary scandium-rich leaching solution is 7.42 mg/L. The concentration of scandium in the first-stage scandium-rich washing liquid is 1.73mg/L, and the total recovery rate is 58.43%.
Under the conditions of four-stage water leaching and water washing, the leaching rate of scandium is 60.12%, the leaching rate of iron is 0.17%, the leaching rate of aluminum is 4.67%, titanium and silicon are not leached, the concentration of scandium in the four-stage scandium-rich leaching solution is 20.08mg/L, the concentration of scandium in the four-stage scandium-rich washing liquid is 11.92mg/L, and the total recovery rate is 57.72%.
Under the same condition, the same mass parts of adsorbents are used, the scandium adsorption amount in the four-stage scandium-rich leachate is 2.7 times that of the first-stage scandium-rich leachate, and the scandium adsorption rates in the four-stage scandium-rich leachate and the four-stage scandium-rich washing liquor are both more than 98%.
Since the solid roasted product is not ground, the particle size of the product is large and the product does not sufficiently contact with the surrounding leachate, resulting in a decrease in the leaching rate of scandium, the concentration of scandium in the leachate, the concentration of scandium in the washing liquid, and the total recovery rate of scandium.
Claims (4)
1. A method for selectively enriching scandium from Bayer process red mud is characterized in that Bayer process red mud is used as a raw material, a proper amount of water is added to fully wet the red mud, concentrated sulfuric acid is used for sulfating the red mud, then roasting is carried out at high temperature, a solid roasting product is ground, mechanically activated, and then four-stage water leaching and water washing are carried out to obtain scandium-enriched leachate, a scandium-enriched washing solution and low-alkali iron-enriched slag;
the method comprises the following steps:
s1, adding a proper amount of water into Bayer process red mud to fully wet the red mud;
s2, adding concentrated sulfuric acid with the mass fraction of 95% -98% into the slurry obtained in the step S1 for heating and curing to sulfate the red mud, wherein the curing temperature is 80-150 ℃, and the curing time is 20-60 min;
s3, roasting the red mud sulfation product obtained in the step S2 at a high temperature to obtain a solid roasting product and generate sulfur dioxide and sulfur trioxide; the roasting conditions are as follows: the roasting temperature is 800-850 ℃, and the roasting time is 20-75 min;
s4, fully grinding the solid roasted product obtained in the step S3 for mechanical activation, wherein the grinding time is 10-40 min;
s5, carrying out selective water leaching on the solid roasted product after mechanical activation in the step S4, wherein the leaching conditions are as follows: the reaction temperature is 25-95 ℃, the reaction time is 15-90 min, the stirring speed is 200-600 r/min, and the ratio of water to red mud is 4-12: 1 mL/g; carrying out solid-liquid separation on the obtained leaching slurry to obtain leaching residues and a first-stage scandium-rich leaching solution; adding water into the leached slag for washing, stirring and filtering to obtain a first-stage scandium-rich washing liquid and low-alkali iron-rich slag;
s6, leaching the solid roasting product mechanically activated in the step S4 by using the first-stage scandium-rich leaching solution obtained in the step S5, wherein the leaching conditions are the same as those of the step S5, the loss of water in the leaching process is supplemented by equal amount of water, and then washing the leaching slag by using the first-stage scandium-rich washing solution obtained in the step S5, and the loss of water in the washing process is supplemented by equal amount of water; the obtained secondary scandium-rich leachate and secondary scandium-rich washing liquor are repeatedly operated; repeatedly operating the obtained three-stage scandium-rich leachate and the three-stage scandium-rich washing liquor; obtaining a four-stage scandium-rich leaching solution, a four-stage scandium-rich washing liquid and low-alkali iron-rich slag;
the adding amount of the concentrated sulfuric acid in the step S2 is 0.75-1.50 mL/g according to the ratio of the concentrated sulfuric acid to the red mud;
the ratio of the water to the red mud in the step S1 is 0.4-0.8 mL/g;
and (4) washing with water in the step S5 according to the ratio of water to red mud of 4-8 mL/g.
2. The method as claimed in claim 1, wherein the particle size of the bayer process red mud of step S1 is less than 74 μm.
3. The method of claim 1, wherein the sulfur dioxide and sulfur trioxide produced in step S3 are recycled to the preparation of concentrated sulfuric acid used in step S2.
4. The method as claimed in claim 1, wherein the fourth-stage scandium-rich leachate and the fourth-stage scandium-rich washing liquid obtained in the step S6 are used as raw materials for selective scandium adsorption and extraction, and the low-alkali iron-rich slag obtained in the steps S5 and S6 is used as a raw material for iron making.
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| CN109750168A (en) * | 2019-03-20 | 2019-05-14 | 中国恩菲工程技术有限公司 | The method and device of Selectively leaching scandium, nickel and cobalt element from laterite metallurgical slag |
| CN109777973B (en) * | 2019-03-20 | 2023-09-29 | 中国恩菲工程技术有限公司 | Method and device for selectively leaching scandium from lateritic nickel ore smelting slag |
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| CN111137907A (en) * | 2020-01-10 | 2020-05-12 | 北京科技大学 | Comprehensive utilization method of Bayer red mud |
| CN112553480A (en) * | 2020-10-10 | 2021-03-26 | 吕梁学院 | Method for recovering zirconium from red mud |
| CN114480860B (en) * | 2022-01-11 | 2022-12-23 | 中国科学院地球化学研究所 | Method for selectively leaching rare earth elements from red mud |
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