CN113184889B - Comprehensive utilization method of crystallized sodium oxalate slag in alumina production - Google Patents
Comprehensive utilization method of crystallized sodium oxalate slag in alumina production Download PDFInfo
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Abstract
The invention particularly relates to a comprehensive utilization method of crystallized sodium oxalate slag in alumina production, belonging to the technical field of alumina production and comprising the following steps: obtaining sodium oxalate slag slurry; carrying out solid-liquid separation on the sodium oxalate slag slurry to obtain solid aluminum hydroxide and a high-concentration sodium oxalate solution; sending the solid aluminum hydroxide to a flat-disc aluminum hydroxide washing system for washing to obtain finished aluminum hydroxide and washing filtrate; roasting the finished product of aluminum hydroxide to obtain aluminum oxide; and (4) treating and separating out the washing filtrate to obtain crystalline sodium oxalate slag which is used as a raw material to prepare sodium oxalate slag slurry. The method has simple process flow, less equipment investment and good operating environment; no three wastes are generated in the process of producing oxalic acid from sodium oxalate; the obtained product has high quality, wider application of oxalic acid and remarkable economic and social benefits; the equipment is convenient to operate and easy to realize automation; has certain advantages in resources, technology and cost, and has good industrial application prospect.
Description
Technical Field
The invention belongs to the technical field of alumina production, and particularly relates to a comprehensive utilization method of crystalline sodium oxalate slag in alumina production.
Background
In view of the current situation of bauxite resources in China, the proportion of imported bauxite for enterprises producing alumina by the Bayer process in China is increased, the cost performance of part of ore resources is higher, the content of organic matters is also higher, the content of organic carbon in an alumina production system is generally increased, the content of sodium oxalate in the production system is increased, a series of hazards are generated to production when certain concentration is reached after cyclic accumulation, and the normal operation of production and the quality of alumina products are seriously influenced. With respect to the problem of sodium oxalate in industrial sodium aluminate solutions, researchers have proposed various methods for control and removal, mainly by seed washing, crystallization, precipitation, oxidation, and the like. However, for various reasons, the method applied in industry at present mainly removes sodium oxalate in sodium aluminate solution by crystallization, and is divided into crystallization to separate out sodium oxalate by strong filtrate to increase alkali concentration and crystallization to separate out sodium oxalate by taking measures in seed decomposition process, but in any way, aluminum hydroxide and sodium oxalate with a certain proportion are precipitated together to form crystallized sodium oxalate slag, which causes loss of aluminum hydroxide and pollution to environment, and sodium oxalate can not be fully utilized due to poor purity.
How to effectively recover the aluminum hydroxide and the sodium oxalate in the crystallized sodium oxalate slag is a problem to be solved urgently, which reduces the production cost and improves the product competitiveness. Current solutions include:
US patent application No. 4275043, which uses a calcination method to treat sodium oxalate in a sodium aluminate solution, concentrates the sodium aluminate solution to be treated to a solid, and then adds the solid to a combustion chamber for calcination. Although the method can treat sodium oxalate and recover alkali and sodium aluminate, the method has high energy consumption and discharges a large amount of carbon dioxide, thus being environment-friendly.
Chinese patent application CN101058433A proposes a new method for treating sodium oxalate crystallized from industrial sodium aluminate solution: aiming at the production characteristics of alumina in China, the crystallized sodium oxalate is returned to a proportioning system of the sintering method and then removed by calcination. This method is suitable for the alumina plant with sintering process, while the alumina plant adopting Bayer process has no sintering process, so the treatment of crystallized sodium oxalate requires additional calcination process, which increases the production cost and pollutes the environment.
The chinese patent application CN108002415A proposes a treatment method for removing sodium oxalate crystals in the production process of alumina: the crystallized sodium oxalate is dissolved and subjected to solid-liquid separation, and the solution is evaporated, cooled and crystallized to directly recover aluminum hydroxide and sodium oxalate. The sodium oxalate recovered by the method still contains about 1.0% of impurities, so that the use value of the sodium oxalate is limited, and the sodium oxalate serving as a chemical raw material is originally not wide in use range and is mainly used as an intermediate for producing oxalic acid. Oxalic acid is an important chemical raw material, has a wider application range than sodium oxalate, is mainly applied to industries such as drug production, polymer synthesis, rare earth element extraction, fabric bleaching and the like, and the demand is increasing day by day.
Liu hong Cao and the like are subjected to nontoxic treatment on crystallized sodium oxalate in the production of alumina, the nontoxic treatment is carried out by adopting a method of dissolving the crystallized sodium oxalate and causticizing the dissolved crystallized sodium oxalate with calcium hydroxide to generate calcium oxalate which is not easy to decompose, and the causticized product sodium hydroxide is recovered. The method only recovers the aluminum hydroxide and the sodium hydroxide contained in the crystallized sodium oxalate, and the oxalate in the crystallized sodium oxalate reacts with the lime to form calcium oxalate, so that the industrial application value of the method is not high, and the calcium oxalate is discharged as waste residue to cause the loss of useful substances.
Chinese patent application CN101462114A proposes a treatment method of sodium oxalate crystallization in heat exchanger in alumina production, which is to wash sodium oxalate crystallized in heat exchanger and pipeline with hot water, dissolve it in hot water, and then treat it by causticization. The basic principle of the method is the same as that of the non-toxic treatment of the crystallized sodium oxalate in the production of the alumina.
The Chinese patent application CN110498741A proposes a purification method of discharged sodium oxalate in alumina process, in the method, strong oxidant is added into sodium oxalate solution after the sodium oxalate and aluminium hydroxide coprecipitation particles are dissolved and filtered for purification, and the sodium oxalate purified liquid is evaporated and crystallized to obtain white sodium oxalate crystal. The method does not convert sodium oxalate into oxalic acid, so that the industrial application range of the method is limited.
The above different methods for treating sodium oxalate in alumina production have high energy consumption, large investment and environmental pollution, and the recovered product has limited use value. Therefore, a method which has low energy consumption and is environment-friendly and can comprehensively recycle useful substances in the crystallized sodium oxalate slag in the alumina production is needed.
Disclosure of Invention
In view of the above problems, the present invention has been made to provide a comprehensive utilization method of crystalline sodium oxalate slag in alumina production that overcomes or at least partially solves the above problems.
The embodiment of the invention provides a comprehensive utilization method of crystallized sodium oxalate slag in alumina production, which comprises the following steps:
obtaining sodium oxalate slag slurry;
carrying out solid-liquid separation on the sodium oxalate slag slurry to obtain solid aluminum hydroxide and a high-concentration sodium oxalate solution;
sending the solid aluminum hydroxide to a flat-disc aluminum hydroxide washing system for washing to obtain finished aluminum hydroxide and washing filtrate;
roasting the finished product of aluminum hydroxide to obtain aluminum oxide;
and treating and separating out the washing filtrate to obtain crystalline sodium oxalate slag which is used as a raw material for preparing the sodium oxalate slag slurry.
Optionally, the obtaining of the sodium oxalate slag slurry specifically includes:
and mixing and dissolving the crystallized sodium oxalate slag and a solvent to obtain sodium oxalate slag slurry, wherein the solvent is hot water at 100 ℃ or a low-concentration sodium oxalate solution.
Optionally, the crystallized sodium oxalate slag comprises the following components by weight: 40 to 65 percent of aluminum hydroxide, 34.5 to 60 percent of sodium oxalate and the balance of impurities.
Optionally, the crystallized sodium oxalate slag and the solvent are mixed and dissolved to obtain sodium oxalate slag slurry, wherein the solid-liquid mass volume ratio of the crystallized sodium oxalate slag to the solvent is 65g/L-115g/L.
Optionally, the crystalline sodium oxalate slag and the solvent are mixed and dissolved to obtain the sodium oxalate slag slurry, and the dissolving time is 25min-30min.
Optionally, the method further includes:
electrolyzing the high-concentration sodium oxalate solution in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, wherein the low-concentration sodium oxalate solution is used as a solvent for dissolving crystallized sodium oxalate slag; the sodium hydroxide is used for circularly producing alumina;
and carrying out evaporation concentration and cooling crystallization on the oxalic acid solution to obtain finished oxalic acid, steam condensate water and oxalic acid mother liquor, wherein the steam condensate water is used as a solvent for dissolving crystallized sodium oxalate slag, and the oxalic acid mother liquor is recycled to an acid making chamber of the electrolytic cell.
Optionally, the electrolytic cell is a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane.
Optionally, the high-concentration sodium oxalate solution is electrolyzed in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, wherein the temperature of the high-concentration sodium oxalate solution is 50-60 ℃.
Optionally, the high-concentration sodium oxalate solution is electrolyzed in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, wherein the temperature of the electrolytic cell is 45-55 ℃.
Optionally, the high-concentration sodium oxalate solution is electrolyzed in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, the high-concentration sodium oxalate solution is subjected to membrane electrolysis and repeated decomposition for desalination to obtain the oxalic acid solution, and the desalination rate is 40.4-58.8%.
One or more technical schemes in the invention at least have the following technical effects or advantages:
the invention provides a comprehensive utilization method of crystallized sodium oxalate slag in alumina production, which comprises the following steps: obtaining sodium oxalate slag slurry; carrying out solid-liquid separation on the sodium oxalate slag slurry to obtain solid aluminum hydroxide and a high-concentration sodium oxalate solution; sending the solid aluminum hydroxide to a flat-disc aluminum hydroxide washing system for washing to obtain finished aluminum hydroxide and washing filtrate; roasting the finished product of aluminum hydroxide to obtain aluminum oxide; treating and separating out the washing filtrate to obtain crystalline sodium oxalate slag which is used as a raw material to prepare the sodium oxalate slag slurry; the aluminum hydroxide obtained by dissolving the crystallized sodium oxalate slag by hot water can be independently washed without new water and sent to a flat disc filter, and is reversely washed together with the aluminum hydroxide obtained by separating decomposed discharged slurry to be used as finished aluminum hydroxide. When the part of aluminum hydroxide obtained after the crystallization of the sodium oxalate is dissolved in water is reversely washed, the concentration of the sodium oxalate in the primary washing filtrate of the flat-plate aluminum hydroxide is increased due to the sodium oxalate-containing auxiliary liquid, so that the washing liquid is favorably added with liquid alkali to promote the crystallization and the separation of the sodium oxalate, and hot water can be saved due to the fact that the washing liquid is not washed by new water alone, and the water balance of an aluminum oxide production system is not influenced. The method has simple process flow, less equipment investment and good operating environment; no three wastes are generated in the process of producing oxalic acid from sodium oxalate; the obtained product has high quality, wider application of oxalic acid and remarkable economic and social benefits; the equipment is convenient to operate and easy to realize automation. In conclusion, the invention has certain advantages in resources, technology and cost, and has better industrial application prospect.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method provided by an embodiment of the present invention;
fig. 2 is a block diagram of a method provided by an embodiment of the invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are illustrative of the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the general idea of the invention is as follows:
according to a typical embodiment of the invention, the comprehensive utilization method of the crystallized sodium oxalate slag in the alumina production is provided, and the method comprises the following steps:
s1, adding crystallized sodium oxalate slag separated out in the decomposition process of a sodium aluminate solution or crystallized sodium oxalate slag separated out after treating primary washing filtrate of a product aluminum hydroxide into a hot water tank with a stirrer according to a certain solid-liquid mass-volume ratio for dissolving;
as an alternative embodiment, the content of aluminum hydroxide in the crystallized sodium oxalate slag is 40.0-65.0% by weight, the content of sodium oxalate is 34.5-60.0% by weight, and the content of other impurities is 0-0.5% by weight.
The above limitation on the composition of the crystalline sodium oxalate slag is the composition of the sodium oxalate slag of the existing removal system currently mastered by the applicant, and is only used for proving that the method can be implemented, in other embodiments, because of different production systems, the proportion of aluminum hydroxide and sodium oxalate in the composition of the sodium oxalate slag may be different from that of the sodium oxalate slag, but according to the characteristics of aluminum oxide production, the difference in the composition ratio of aluminum hydroxide and sodium oxalate in the sodium oxalate slag does not change the solid-liquid mixture ratio during dissolution, and the substantial content of the invention is not affected, so that the method can be implemented in other embodiments with different compositions of the crystalline sodium oxalate slag.
As an optional embodiment, the crystallized sodium oxalate slag and a solvent are mixed and dissolved to obtain sodium oxalate slag slurry, and the solid-liquid mass volume ratio of the crystallized sodium oxalate slag to the solvent is 65g/L-115g/L.
For the sodium oxalate water solution, the solubility of the sodium oxalate is 65g/L at 100 ℃, the concentration of the sodium oxalate in the low-concentration sodium oxalate solution which returns to dissolve the sodium oxalate slag is 20-25g/L, and according to the composition of the sodium oxalate slag and the concentration limitation of the two aspects, the solid-liquid mass-volume ratio of the ingredients is controlled to be 65-115g/L so as to ensure that the sodium oxalate slag is completely dissolved as much as possible. When the ratio is too large, sodium oxalate in the sodium oxalate slag can not be completely dissolved, and the utilization rate of the sodium oxalate is low; when the ratio is too small, the concentration of the solution is too low, and the utilization rate of sodium oxalate is not influenced, but the production efficiency is low, so that the method is not preferable.
As an alternative embodiment, the dissolution of the crystalline sodium oxalate slag is carried out in a hot water tank with a stirring device, using hot water of 100 ℃ or a low-concentration sodium oxalate solution as a solvent.
The reason why the dissolution temperature is controlled to 100 c is that the solubility of sodium oxalate increases with the increase of temperature, and in order to obtain a high-concentration sodium oxalate solution as high as possible, the higher the dissolution temperature is, the better the dissolution of sodium oxalate slag is, and thus a high-concentration sodium oxalate solution can be obtained at the maximum by controlling to 100 c.
S2, conveying the slurry obtained after dissolving for a certain time to a settling tank by using a pump for solid-liquid separation to obtain solid aluminum hydroxide and a high-concentration sodium oxalate solution;
as an alternative embodiment, the dissolving time of the crystallized sodium oxalate slag is 30min, and slurry obtained by dissolving is conveyed to a settling tank by a pump for solid-liquid separation to obtain solid aluminum hydroxide and a sodium oxalate solution with the concentration of 45-65 g/L.
S3, conveying the solid aluminum hydroxide obtained by solid-liquid separation to a flat disc aluminum hydroxide washing system of an aluminum oxide production process, and roasting to obtain aluminum oxide after washing;
by adopting the design, the aluminum hydroxide obtained by dissolving the crystallized sodium oxalate slag by hot water can be independently washed without new water and sent to a flat disc filter, and is reversely washed together with the aluminum hydroxide obtained by separating decomposed discharged slurry to be used as finished aluminum hydroxide. When the part of aluminum hydroxide obtained after the crystallization of the sodium oxalate is dissolved in water is reversely washed, the concentration of the sodium oxalate in the primary washing filtrate of the flat-plate aluminum hydroxide is increased due to the fact that the part of the aluminum hydroxide contains the sodium oxalate auxiliary solution, which is beneficial to adding liquid alkali into the washing solution to promote the crystallization and the separation of the sodium oxalate, and hot water can be saved due to the fact that the washing solution is not separately washed by new water, and the water balance of an aluminum oxide production system is not influenced.
S4, slowly cooling the high-concentration sodium oxalate solution obtained by solid-liquid separation in a standing state;
as an optional embodiment, the cooling of the high-concentration sodium oxalate solution is performed slowly in a standing state, it should be noted that the production scale of an alumina enterprise generally produces more than 100 million tons every year, but the sodium oxalate discharge amount is 10 tons daily to meet the requirement of stable production, so that the treatment of sodium oxalate does not need to be performed continuously, the cooling of the high-concentration sodium oxalate solution can be performed in a natural cooling manner, and the cooling speed is different according to different environmental temperatures and different treated solution amounts, and no specific requirement is made here; of course, when the sodium oxalate needs to be continuously treated, the cooling speed can be required according to the production condition. Specifically, the temperature eventually dropped to 55 ℃.
The reason for controlling the temperature to be finally reduced to 55 ℃ is to consider the requirement of 50 ℃ on the electrolysis temperature of the next electrolysis bath, and to consider that a natural cooling process exists in the process of conveying the solution from the liquid storage tank to the electrolysis bath, the adverse effect of excessively large temperature value is not beneficial to reaching the electrolysis temperature, and the adverse effect of excessively small temperature value is that on one hand, the solution is not easy to realize when being cooled from 100 ℃ to lower temperature, and on the other hand, the dissolved sodium oxalate is crystallized and separated out again, scars are formed on the wall of the electrolysis bath, the conveying of the solution is influenced, and further the next electrolysis process is influenced.
S5, conveying the high-concentration sodium oxalate solution with the temperature reduced to the set temperature to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane for electrolysis, wherein C in the sodium oxalate solution 2 O 4 2- And Na + under the action of electric field making directional movement, selectively passing through anion-cation exchange membrane and making it react with electrode to obtain OH - And H + Respectively combining to obtain oxalic acid solution and aluminum hydroxide, and desalting the high-concentration sodium oxalate solution to obtain low-concentration sodium oxalate solution;
as an alternative embodiment, the cooled high-concentration sodium oxalate solution is delivered to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane, and the temperature of the electrolytic cell is 50 ℃.
The reason for controlling the cell temperature to 50 ℃ is to obtain a higher current efficiency and an oxalic acid solution with as high a concentration as possible. During electrolysis, the electrolysis temperature is high, the electrolyte equilibrium concentration is high, and the current efficiency is not favorably improved, so that the electrolysis temperature is not easy to be excessively high; in addition, because the solubility of the oxalic acid dihydrate in the oxalic acid aqueous solution decreases with the decrease of the temperature, when the electrolysis temperature is too low, the oxalic acid is crystallized and precipitated due to the decrease of the solubility, the electrolysis is affected, and the oxalic acid solution cannot be conveyed to an evaporation crystallization system.
As an optional implementation mode, after the sodium oxalate is desalted by electrolysis, an oxalic acid solution is generated in the acid making chamber, and after the high-concentration sodium oxalate solution is desalted, a low-concentration sodium oxalate solution is obtained, wherein the desalting rate is 40.4-58.8%.
S6, carrying out evaporation concentration, cooling crystallization and separation on an oxalic acid solution obtained by carrying out electrolytic desalination on sodium oxalate to obtain a finished product oxalic acid, obtaining a crystallized oxalic acid mother liquor, and feeding the crystallized oxalic acid mother liquor back to an acid making chamber of the three-membrane four-chamber electrolytic cell;
s7, returning the steam condensate water generated in the evaporation of the oxalic acid solution and the desalted low-concentration sodium oxalate solution to a hot water tank together to dissolve the next batch of crystallized sodium oxalate slag;
s8, conveying sodium hydroxide generated after the sodium oxalate is subjected to the electrolysis and double decomposition reaction by the anion-cation exchange membrane to an evaporation system of a main process of alumina production, mixing the sodium hydroxide with Bayer process mother liquor, and taking the mixture as circulating mother liquor to dissolve out the next batch of bauxite after the mixture is qualified.
By adopting the design, sodium oxalate is converted into oxalic acid and sodium hydroxide through electrolysis and double decomposition by an anion-cation exchange membrane method, and the oxalic acid is used as an important chemical raw material and is mainly applied to the industries of medicine production, polymer synthesis, rare earth element extraction, fabric bleaching and the like, the application range of the oxalic acid is wider than that of the sodium oxalate, and the demand is increasingly increased; the sodium hydroxide obtained after electrolysis is an indispensable important substance for dissolving bauxite in alumina produced by a Bayer process, and the alkali consumption in alumina production can be obviously reduced through recovery.
With the increase of the proportion of imported ores used by Bayer process alumina enterprises, the amount of the crystalline sodium oxalate slag discharged through various ways is larger and larger, so that the raw material resource implemented by the method has obvious advantages, various component substances in the crystalline sodium oxalate slag can be utilized, the utilization value is improved, the comprehensive utilization of solid waste is realized, and the method is particularly suitable for enterprises which have higher system sodium oxalate content in the process of producing alumina by the Bayer process and can adopt measures to promote the crystallization separation and discharge of sodium oxalate. .
The method for comprehensively utilizing the crystalline sodium oxalate slag in the production of alumina according to the present invention will be described in detail below with reference to examples, comparative examples, and experimental data.
Example 1
Adding the crystalline sodium oxalate slag containing 65.0 percent of aluminum hydroxide, 34.5 percent of sodium oxalate and 0.5 percent of impurities discharged from Bayer process production into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 65.0g/L of the ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain high-concentration sodium oxalate aqueous solution with the concentration of solid aluminum hydroxide and sodium oxalate being 45.2 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying the solid aluminum hydroxide to a roasting furnace to obtain a product aluminum oxide; standing and cooling the high-concentration sodium oxalate aqueous solution to 55 ℃, conveying the cooled high-concentration sodium oxalate aqueous solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 40.4%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 97.5 percent, and the content of the obtained oxalic acid is 99.40 percent calculated by oxalic acid dihydrate.
Example 2
Adding crystalline sodium oxalate slag which is discharged from Bayer process production and contains 65.0 percent of aluminum hydroxide, 34.5 percent of sodium oxalate and 0.5 percent of impurities into a hot water tank with a stirrer according to the mass-to-volume ratio of the solid to the liquid of the mixture of 115g/L and dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain high-concentration sodium oxalate aqueous solution with the concentration of solid aluminum hydroxide and sodium oxalate being 61.2 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying the solid aluminum hydroxide to a roasting furnace to obtain a product aluminum oxide; standing a high-concentration sodium oxalate aqueous solution, cooling to 55 ℃, conveying the solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 56.2%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor returns to an acid making chamber of the ion membrane electrolytic cell to be used for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 95.5 percent, and the content of the obtained oxalic acid is 99.42 percent calculated by oxalic acid dihydrate.
Example 3
Adding crystalline sodium oxalate slag which is discharged from Bayer process production and contains 40.0 percent of aluminum hydroxide and 60.0 percent of sodium oxalate into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 65g/L of the ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain solid aluminum hydroxide and a high-concentration sodium oxalate aqueous solution with the concentration of 60.1 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying the solid aluminum hydroxide to a roasting furnace to obtain a product aluminum oxide; standing and cooling the high-concentration sodium oxalate aqueous solution to 55 ℃, conveying the cooled high-concentration sodium oxalate aqueous solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 55.4%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 96.5 percent, and the content of the obtained oxalic acid is 99.42 percent calculated by oxalic acid dihydrate.
Example 4
Adding crystalline sodium oxalate slag which is discharged from Bayer process production and contains 40.0% of aluminum hydroxide and 60.0% of sodium oxalate into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 115g/L of ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain high-concentration sodium oxalate aqueous solution with the concentration of solid aluminum hydroxide and sodium oxalate being 65.0 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying to a roasting furnace to obtain a product aluminum oxide; standing a high-concentration sodium oxalate aqueous solution, cooling to 55 ℃, conveying the solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 58.8%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 64.4 percent, and the content of the obtained oxalic acid is 99.42 percent calculated by oxalic acid dihydrate.
Example 5
Adding 50.0 percent of aluminum hydroxide, 49.8 percent of sodium oxalate and 0.2 percent of other impurities discharged from Bayer process production into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 90g/L of the ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain high-concentration sodium oxalate aqueous solution with the concentration of solid aluminum hydroxide and sodium oxalate being 65.0 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying to a roasting furnace to obtain a product aluminum oxide; standing and cooling the high-concentration sodium oxalate aqueous solution to 55 ℃, conveying the cooled high-concentration sodium oxalate aqueous solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 58.8%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 98.5 percent, and the content of the obtained oxalic acid is 99.47 percent calculated by oxalic acid dihydrate.
Comparative example 1
Adding 50.0 percent of aluminum hydroxide, 49.8 percent of sodium oxalate and 0.2 percent of other impurities discharged from Bayer process production into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 50g/L of the ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain high-concentration sodium oxalate aqueous solution with the concentration of solid aluminum hydroxide and sodium oxalate being 47.4 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying to a roasting furnace to obtain a product aluminum oxide; standing and cooling the high-concentration sodium oxalate aqueous solution to 55 ℃, conveying the cooled high-concentration sodium oxalate aqueous solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 43.5%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate finishing liquid after sodium oxalate desalination are conveyed to a hot water tank together for dissolving next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 96.8 percent, and the content of the obtained oxalic acid is 99.45 percent calculated by oxalic acid dihydrate.
Comparative example 2
Adding 50.0 percent of aluminum hydroxide, 49.8 percent of sodium oxalate and 0.2 percent of other impurities discharged from Bayer process production into a hot water tank with a stirrer according to the solid-liquid mass volume ratio of 130g/L of the ingredients for dissolving at 100 ℃; conveying the slurry obtained after dissolving for 30min to a settling tank by a pump for solid-liquid separation to obtain solid aluminum hydroxide and a high-concentration sodium oxalate aqueous solution with the concentration of 65 g/L; conveying the solid aluminum hydroxide to a flat disc filter for washing, and then conveying the solid aluminum hydroxide to a roasting furnace to obtain a product aluminum oxide; standing and cooling the high-concentration sodium oxalate aqueous solution to 55 ℃, conveying the cooled high-concentration sodium oxalate aqueous solution to a desalting chamber of a three-membrane four-chamber electrolytic cell with an anion-cation exchange membrane by using a pump to perform electrolytic double decomposition reaction, wherein the electrolytic temperature is 50 ℃, and the sodium oxalate is subjected to membrane electrolytic double decomposition and desalting to obtain an oxalic acid solution, and the desalting rate is 58.8%; the oxalic acid solution is evaporated, concentrated, cooled and crystallized to separate out finished oxalic acid; the crystallized oxalic acid mother liquor is returned to an acid making chamber of the ion membrane electrolytic cell to be used as a raw material for electrolyzing oxalic acid; when the oxalic acid solution is evaporated, steam condensate water and the low-concentration sodium oxalate completion solution after sodium oxalate desalination are conveyed to a hot water tank together for dissolving the next batch of crystallized sodium oxalate slag; and continuously taking out sodium hydroxide from the cathode chamber in the electrolysis process, conveying the sodium hydroxide to an evaporation system of the main flow of the alumina production, mixing the sodium hydroxide with the mother liquor, adjusting the sodium hydroxide to be qualified, and taking the sodium hydroxide as circulating mother liquor to dissolve out the next batch of bauxite. After the crystallized sodium oxalate slag is treated, the utilization rate of sodium oxalate is 64.9 percent, and the content of the obtained oxalic acid is 99.41 percent calculated by oxalic acid dihydrate.
The method provided by the invention is adopted to comprehensively utilize the crystallized sodium oxalate slag in the production of alumina, and the utilization rate of sodium oxalate and the content of oxalic acid are both high through reasonable control of the mass-to-volume ratio of solid and liquid of the ingredients during the dissolution of sodium oxalate. The appropriate solid-liquid mass-volume ratio is related to the content of sodium oxalate in the sodium oxalate slag, and during the batching, not only the high-concentration sodium oxalate solution is considered to be obtained, and the production efficiency is improved, but also the sodium oxalate in the slag is considered to be completely dissolved out as much as possible, and the utilization rate of the sodium oxalate is improved. Therefore, the mass-to-volume ratio of solid to liquid of the ingredients is determined according to the actually processed materials. For the sodium oxalate composition and the batching conditions given by the comparative example, when the batching solid-liquid mass-volume ratio of the crystallized sodium oxalate slag dissolved in the low-concentration sodium oxalate solution is not in the range provided by the embodiment, the comparative example 1 has low production efficiency because the obtained sodium oxalate concentration is low due to the small amount of the sodium oxalate slag; in comparative example 2, the amount of the added sodium oxalate slag is large, so that the solubility of sodium oxalate is exceeded under the condition, the material is not completely dissolved, the utilization rate of sodium oxalate is low, and part of undissolved sodium oxalate and aluminum hydroxide are separated together and enter an aluminum oxide production system, so that the product quality is influenced.
One or more technical schemes in the invention at least have the following technical effects or advantages:
(1) According to the method provided by the invention, along with the increase of the proportion of the inlet ore used by Bayer process alumina enterprises, the amount of the crystalline sodium oxalate slag discharged through various ways is increased, so that the raw material resource implemented by the method has remarkable advantages;
(2) The aluminum hydroxide obtained by dissolving the crystallized sodium oxalate slag by hot water can be independently washed without new water and sent to a flat disc filter, and is reversely washed with the aluminum hydroxide separated from the decomposed discharged slurry to obtain the finished product aluminum hydroxide. When the part of aluminum hydroxide obtained after the crystallization of the sodium oxalate is dissolved in water is reversely washed, the concentration of the sodium oxalate in the primary washing filtrate of the flat-plate aluminum hydroxide is increased due to the contained sodium oxalate auxiliary liquid, which is beneficial to adding liquid alkali into the washing liquid to promote the crystallization and precipitation of the sodium oxalate, and hot water can be saved due to no need of separate washing of new water, so that the water balance of an aluminum oxide production system is not influenced;
(3) The method provided by the invention converts sodium oxalate into oxalic acid and caustic soda through electrolysis and double decomposition by an anion-cation exchange membrane method, and the oxalic acid is used as an important chemical raw material and is mainly applied to the industries of medicine production, polymer synthesis, rare earth element extraction, fabric bleaching and the like, the application range of the method is wider than that of the sodium oxalate, and the demand is increasingly increased; the caustic soda sodium hydroxide obtained after electrolysis is an indispensable important substance for dissolving bauxite in the alumina production by the Bayer process, and the alkali consumption in the alumina production can be obviously reduced through recovery. Therefore, the technology provided by the method can utilize all component substances in the crystallized sodium oxalate slag, improve the utilization value and realize the comprehensive utilization of solid wastes;
(4) The method provided by the invention is particularly suitable for enterprises which have high sodium oxalate content in the system in the process of producing alumina by a Bayer process and can adopt measures to promote the sodium oxalate to be crystallized and separated out and discharged;
(5) The method provided by the invention has the advantages of simple process flow, less equipment investment and good operating environment; no three wastes are generated in the process of producing oxalic acid from sodium oxalate; the obtained product has high quality, wider application of oxalic acid and remarkable economic and social benefits; the equipment is convenient to operate and easy to realize automation. In conclusion, the invention has certain advantages in resources, technology and cost, and has better industrial application prospect.
Finally, it should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (2)
1. A comprehensive utilization method of crystalline sodium oxalate slag in alumina production is characterized by comprising the following steps:
obtaining sodium oxalate slag slurry;
carrying out solid-liquid separation on the sodium oxalate slag slurry to obtain solid aluminum hydroxide and a high-concentration sodium oxalate solution;
sending the solid aluminum hydroxide to a flat-disc aluminum hydroxide washing system for washing to obtain finished aluminum hydroxide and washing filtrate;
roasting the finished product of aluminum hydroxide to obtain aluminum oxide;
treating and separating out the washing filtrate to obtain crystalline sodium oxalate slag which is used as a raw material to prepare the sodium oxalate slag slurry;
the method for obtaining the sodium oxalate slag slurry specifically comprises the following steps:
mixing and dissolving crystallized sodium oxalate slag and a solvent to obtain sodium oxalate slag slurry, wherein the solvent is hot water at 100 ℃ or a low-concentration sodium oxalate solution;
the sodium oxalate crystallization slag comprises the following components in parts by weight: 40 to 65 percent of aluminum hydroxide and 34.5 to 60 percent of sodium oxalate, and the balance of impurities;
mixing and dissolving the crystallized sodium oxalate slag and a solvent to obtain sodium oxalate slag slurry, wherein the solid-liquid mass volume ratio of the crystallized sodium oxalate slag to the solvent is 65g/L-115g/L;
mixing and dissolving the crystallized sodium oxalate slag and a solvent to obtain sodium oxalate slag slurry, wherein the dissolving time is 25-30 min;
the method further comprises the following steps:
electrolyzing the high-concentration sodium oxalate solution in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, wherein the low-concentration sodium oxalate solution is used as a solvent for dissolving crystallized sodium oxalate slag; the sodium hydroxide is used for circularly producing alumina;
evaporating, concentrating, cooling and crystallizing the oxalic acid solution to obtain finished oxalic acid, steam condensate water and oxalic acid mother liquor, wherein the steam condensate water is used as a solvent for dissolving crystallized sodium oxalate slag, and the oxalic acid mother liquor is recycled to an acid making chamber of the electrolytic cell;
the electrolytic bath is a three-membrane four-chamber electrolytic bath with an anion-cation exchange membrane;
electrolyzing the high-concentration sodium oxalate solution in an electrolytic cell to obtain oxalic acid solution, sodium hydroxide and low-concentration sodium oxalate solution, wherein the temperature of the high-concentration sodium oxalate solution is 50-60 ℃;
electrolyzing the high-concentration sodium oxalate solution in an electrolytic cell to obtain an oxalic acid solution, sodium hydroxide and a low-concentration sodium oxalate solution, and carrying out repeated decomposition and desalination on the high-concentration sodium oxalate solution by membrane electrolysis to obtain the oxalic acid solution, wherein the desalination rate is 40.4-58.8%.
2. The method for comprehensively utilizing crystallized sodium oxalate slag in aluminum oxide production according to claim 1, characterized in that the high-concentration sodium oxalate solution is electrolyzed in an electrolytic cell to obtain oxalic acid solution, sodium hydroxide and low-concentration sodium oxalate solution, and the temperature of the electrolytic cell is 45-55 ℃.
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| CN102515223A (en) * | 2011-12-09 | 2012-06-27 | 沈阳工业大学 | Method for efficient and comprehensive utilization of high-iron bauxite |
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| CN108002415B (en) * | 2017-12-06 | 2019-11-15 | 中国铝业股份有限公司 | The processing method of the crystal of sodium oxalate is removed in aluminum oxide production process |
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