Method for producing aluminum oxide and byproduct potassium carbonate by comprehensive utilization of bauxite resources

Abstract

The invention relates to a method for producing aluminum oxide and byproduct potassium carbonate by comprehensive utilization of bauxite, and belongs to the field of comprehensive utilization of resources. According to the method, the mother liquor for producing the aluminum oxide by the Bayer process passes through a potassium adsorbent, so that potassium ions in the mother liquor are adsorbed on the potassium adsorbent, and the mother liquor subjected to adsorption continues to enter the next process of aluminum oxide production; and desorbing potassium ions adsorbed in the potassium adsorbent into a sodium carbonate desorption solution by using a sodium carbonate solution as a desorption solution to obtain a potassium-enriched qualified desorption solution. And the desorbed potassium adsorbent can be recycled after being cleaned. And carrying out decoloration and impurity removal, evaporation and concentration, carbonization and purification, drying and calcination on the qualified desorption solution rich in potassium to obtain a potassium carbonate product. According to the method, sodium carbonate discharged in the aluminum oxide production process is used as a main component of the desorption solution, potassium ions of bauxite dissolved into the Bayer process aluminum oxide mother liquor are effectively extracted, production of aluminum oxide is not affected, the byproduct potassium carbonate is low in production cost, and the process is simple and efficient.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive utilization of bauxite resources, and relates to a method for comprehensively utilizing bauxite resources to produce potassium carbonate as a by-product of alumina production. Background Art

[0002] China is the largest consumer of potassium salts, but China's external dependence on potassium resources exceeds 50%. In the past three years in China, the annual domestic import volume of potassium salts has been more than 5 million tons, and the external dependence has remained above 50%. Compared with the world's major potassium resource countries, China does not have an advantage in the resource volume of water-soluble potassium ore, while insoluble potassium salt ore is a potential potassium resource pool. The identified reserves of bauxite in China have exceeded 5 billion tons, and the basic reserves exceed 1 billion tons. The reserves of associated potassium resources are quite considerable, which will ultimately bring huge economic benefits and alleviate the shortage of water-soluble potassium resources to a certain extent.

[0003] The production of alumina by the Bayer process is a cyclic process. When bauxite is digested, more than 80% of potassium dissolves into the Bayer solution and accumulates continuously. The potassium content in the mother liquor of some Bayer solutions can reach 75 g / L. Such a high concentration of potassium will not only increase the potassium content in the produced alumina, deteriorate the quality of alumina, but also make the electrolyte system in the downstream electrolytic aluminum process complex, reduce the conductivity, increase the electrolysis energy consumption, and reduce the service life of the electrolytic cell, seriously affecting the normal production of electrolytic aluminum enterprises. When the potassium in the mother liquor reaches a certain concentration, most of it is discharged with red mud in the form of potassium aluminosilicate, and the potassium resources are completely wasted.

[0004] During the alumina production process, about 95% of the organic matter enters with the ore, and the remaining 5% comes from the addition of chemicals such as flocculants, crystallization aids, and defoamers during the process. Humus-like organic matter is easily reacted with the alkali solution and enters the sodium aluminate solution, and degrades into sodium carbonate during the digestion process. If it cannot be discharged in time, it will accumulate and enrich in the system, affecting the normal production of alumina. Therefore, most alumina plants discharge a large amount of sodium carbonate during the evaporation stage of the circulating mother liquor. Since this part of sodium carbonate contains many impurities and cannot be sold as industrial products, new ways to utilize this part of the miscellaneous salts with value need to be developed.

[0005] Currently, the main method for extracting potassium from alumina mother liquor is to add sodium sulfate and sodium nitrate, and then obtain the corresponding high-value potassium salts through multiple evaporation and cooling crystallization using solubility differences. However, since the solubility of potassium carbonate is much greater than that of sodium carbonate, the method of adding sodium carbonate to the alumina mother liquor to crystallize and precipitate potassium carbonate is not feasible.

[0006] Potassium carbonate is an important chemical reagent and is currently mainly used in high-grade potassium glass, pesticides, food additives, etc. With the rapid development of China's automotive industry and the rapid growth of high-grade potassium glass for vehicles, the consumption of potassium carbonate in potassium glass has increased rapidly. Potassium carbonate is the raw material for the herbicide dicamba, which clears the obstacles in the transgenic demand side for the promotion of dicamba and drives the demand for potassium carbonate in pesticides.

[0007] Currently, there are two commercial production processes for potassium bicarbonate: the ion exchange method and the ion-exchange membrane electrolysis carbonization method.

[0008] In the ion exchange method, ammonium bicarbonate is used as the eluent to elute potassium ions from the cation exchange resin. The potassium ions combine with bicarbonate ions to form potassium bicarbonate. However, in the exchange process, excessive ammonium bicarbonate also comes down with the potassium bicarbonate solution. Although most of the ammonium bicarbonate can be decomposed by subsequent evaporation, concentration and drying, it is difficult for the conventional process to meet the requirement that the ammonium content in the potassium bicarbonate product is less than 10 ppm. Since the ammonium bicarbonate used in the production of potassium bicarbonate by the ion exchange method contains an anti-caking agent, the potassium bicarbonate product also contains residues of the ammonium bicarbonate anti-caking agent, so it is difficult to meet the requirement of product clarity. During the production process, due to the need to treat low-concentration ammonium-containing wastewater, the production cost is relatively high.

[0009] In the process of producing potassium bicarbonate by the ion-exchange membrane electrolysis carbonization method, the raw material potassium chloride undergoes refining, electrolysis, evaporation, concentration, carbonation and drying processes. Since the raw material potassium chloride contains ammonium chloride and organic amines (suspending agents and anti-caking agents), it is very difficult to completely remove chlorine and ammonium even through refining treatment, so the chlorine and ammonium contents in potassium bicarbonate will exceed the standard. The electrolysis process requires a large amount of energy consumption, and the treatment of hydrochloric acid also requires the support of the surrounding industrial supply chain.

[0010] Patent CN1283552C "Method for preparing electronic-grade potassium carbonate from potassium-rich rock" mixes potassium-rich rock powder with sodium carbonate after crushing and ore dressing to obtain a powder with potassium feldspar as the main phase. After calcining at 750 °C - 850 °C, an appropriate amount of water is added to the calcined clinker powder and stirred thoroughly to form a potassium-containing solution. By introducing CO2 into the potassium-containing solution for acidification and neutralization reaction, silicon, aluminum and other impurity components form precipitates, which are filtered and used to prepare a new type of inorganic non-metallic material mineral polymer material. The clarified potassium-containing solution obtained by filtration is evaporated, crystallized and separated to obtain the by-product high-quality pure sodium carbonate. The remaining small amount of sodium carbonate forms a potassium-sodium double salt, which can be used as a calcination ingredient for recycling. The remaining high-concentration potassium carbonate solution is further purified and then subjected to secondary acidification, crystallization and calcination to obtain the finished product of electronic-grade potassium carbonate. This process has complex operation steps, requires ore grinding, calcination and acid leaching, and the production cost is too high, making it difficult to operate industrially.

[0011] Therefore, it is necessary to develop a production method for comprehensively utilizing bauxite resources to produce potassium carbonate as a by-product of alumina, effectively utilizing the potassium resources in bauxite and the miscellaneous salts discharged during the alumina production process, and converting them into high-value potassium carbonate. Summary of the Invention

[0012] The purpose of the present invention is to provide a production method for comprehensively utilizing bauxite resources to produce potassium carbonate as a by-product of alumina, which can effectively extract the potassium resources in bauxite, utilize the miscellaneous salts discharged during the alumina production process, and produce high-value potassium carbonate. The production process of potassium carbonate does not affect the production of alumina, and the process is simple, efficient, and low-cost.

[0013] The purpose of the present invention can be achieved through the following technical solutions: A production method for comprehensively utilizing bauxite resources to produce potassium carbonate as a by-product of alumina, characterized by including the following steps: S1. Potassium ion adsorption: The mother liquor produced by the Bayer process for alumina production is introduced into an adsorption device loaded with an alkali-resistant potassium adsorbent. The adsorption time is 45 - 120 minutes, and the temperature of the mother liquor during adsorption is 25 - 50 °C. The adsorbent is an alkali-resistant ion sieve type adsorbent, which selectively adsorbs potassium ions. Through the ion exchange of potassium and sodium, the potassium ions in the mother liquor are adsorbed.

[0014] S2. Flushing: Deionized water is used as the flushing liquid and introduced into the adsorption device after adsorption to flush the potassium adsorbent, washing away the mother liquor and organic impurities attached to the surface of the potassium adsorbent. To reduce the amount of flushing water, three rounds of flushing are adopted. The first round of flushing uses the flushing liquid of the second round of the previous batch, and the flushing liquid after the first round of flushing is discharged into the alumina production process as the washing water for red mud. The second round of flushing uses the flushing liquid of the third round of the previous batch, and the flushing liquid after the second round of flushing is used as the flushing liquid for the first round of the next batch. The third round of flushing liquid uses deionized water, and the flushing liquid after flushing is used as the flushing liquid for the second round of the next batch.

[0015] S3. Desorbing liquid preparation: The miscellaneous salts discharged from the evaporation, concentration, and crystallization of the mother liquor during the alumina production process are dissolved in deionized water and a leaching solution, where the mass fraction of sodium carbonate is 10 - 25%. After the sodium carbonate solution is filtered, a desorbing liquid is obtained.

[0016] S4. Adsorbent desorption and regeneration: The prepared sodium carbonate desorbing liquid is introduced into the adsorption device to desorb the loaded potassium adsorbent, so that the potassium ions adsorbed in the potassium adsorbent are desorbed into the desorbing liquid, obtaining a desorbing qualified liquid enriched with potassium. The sodium ions in the desorbing liquid are exchanged onto the adsorbent, enabling the adsorbent to be regenerated; S5. Elution: The potassium adsorbent after desorption and regeneration is eluted with a sodium hydroxide solution with a mass fraction of 0.2 - 1%. After elution, the adsorbent enters the next batch of adsorption process stage for recycling; the eluent after elution is used to prepare the desorbing solution.

[0017] S6. Decolorization and impurity removal: Activated carbon is used to decolorize the qualified desorbing solution and adsorb organic substances. Then, filtration is carried out by means of pressure filtration or suction filtration to obtain filter residue and refined qualified solution respectively.

[0018] S7. Evaporation and concentration: The potassium-rich refined qualified solution is subjected to evaporation and concentration and heat preservation sedimentation crystallization. The sodium carbonate precipitated first is used to prepare the desorbing solution. Then, evaporation and concentration are continued to precipitate the sodium carbonate-potassium carbonate double salt. The double salt is washed with deionized water. The main component of the washed filter cake is sodium carbonate for preparing the desorbing solution. The washing solution of the double salt is added to the evaporation system and evaporated to 52°Bé to obtain a saturated potassium carbonate solution with a potassium ion concentration of 12.5 mol / L, a sodium ion molar concentration of 0.5 mol / L, and a potassium-sodium ratio of 25.

[0019] S8. Carbonization and purification: The saturated potassium carbonate solution obtained in step S7 is pumped into a carbonization tower, and a carbonization reaction is carried out at a temperature of 45 - 60°C and a pressure of 0.2 - 2 Mpa. Carbon dioxide is continuously introduced during the carbonization reaction until the pH of the reaction slurry reaches 8.0 - 8.5 to end the above carbonization reaction. The carbonized slurry is pumped into a cooling crystallizer and cooled to 20 - 35°C for crystallization. The crystallized slurry is centrifuged for solid-liquid separation, and deionized water is used for elution during centrifugation to obtain high-purity potassium bicarbonate. The liquid after centrifugation is added to the refined qualified solution and sent to the evaporation system.

[0020] S9. Calcination: The obtained high-purity potassium bicarbonate is calcined to obtain high-quality potassium carbonate products and carbon dioxide gas. The carbon dioxide is recycled to the carbonization and purification process section S8.

[0021] As a preferred technical solution of the present invention, in step S1, the mother liquor is one of the seed mother liquor, carbon mother liquor, circulating mother liquor, evaporation mother liquor, and gallium extraction residue liquor after gallium extraction in the production process of Bayer process alumina, and the potassium ion concentration therein is 15 - 90 g / L.

[0022] As a preferred technical solution of the present invention, in step S3, the miscellaneous salts discharged from the evaporation and concentration of the mother liquor can be washed first to wash away most of the organic substances and the attached aluminum hydroxide. The washing solution is discharged into the main process of alumina production for dilution and washing of red mud. The washed filter cake is dissolved in deionized water and the eluent to obtain the desorbing solution. The mass fraction of the desorbing solution is 10 - 25%, preferably 15 - 20%. As a preferred technical solution of the present invention, in step S4, the temperature of the desorption and regeneration process is 60-95 °C. Preferably, the temperature of the desorption and regeneration process is 85-95 °C As a preferred technical solution of the present invention, in step S6, the activated carbon is powdered activated carbon, and ≥5 grams of activated carbon is added to each liter of desorbed qualified liquid; the light transmittance of the refined qualified liquid should be ensured to be greater than 99.8%, otherwise step S6 needs to be repeated As a preferred technical solution of the present invention, in step S8, the carbonation reaction is carried out at a temperature of 45-60 °C and a pressure of 0.2-2 Mpa. Preferably, the carbonation reaction is carried out at a temperature of 55-60 °C and a pressure of 0.5-1 Mpa As a preferred technical solution of the present invention, in step S9, the calcination temperature is 200-600 °C, and the calcination time is 30-200 minutes. Preferably, the calcination temperature is 250-300 °C, and the calcination time is 90-120 minutes, and the mass purity of the potassium carbonate product obtained is greater than 99%.

[0023] Advantages of the present invention: (1) In the present invention, for the comprehensive utilization of potassium resources in potassium-containing bauxite, only during the production of alumina, by adsorbing potassium from the alumina mother liquor, after potassium adsorption, the next production link of alumina can be continued without changing the process flow of the Bayer process for producing alumina, having no impact on subsequent production conditions, and the equipment process is simple and effective.

[0024] (2) In the present invention, using the miscellaneous salts mainly composed of sodium carbonate discharged during the alumina production process as the main raw material to produce potassium carbonate with higher value. Effectively supplementing sodium salts in the Bayer alumina production, the miscellaneous salts are effectively utilized, saving production raw materials, greatly reducing the cost of the product potassium carbonate, and significantly improving economic and social benefits.

[0025] (3) The traditional method for producing potassium carbonate, the ion exchange method, uses potassium chloride and ammonium bicarbonate as the main raw materials, and the ion membrane electrolysis carbonization method uses potassium chloride (the raw material potassium chloride contains ammonium chloride and organic amine suspending agents and anti-caking agents). Even through refined filtration, it is difficult to completely remove ammonium and chlorine elements. Therefore, it is easy to cause the content of ammonium and chlorine in the product potassium carbonate to exceed the standard. In the present invention, during the whole process of producing potassium carbonate, no impurities such as ammonium ions and chloride ions are introduced. Therefore, it is relatively easy to produce first-class potassium carbonate products without ammonium.

[0026] (4)The production method of comprehensively utilizing bauxite to produce alumina with by - product potassium carbonate of the present invention has the advantages of low production cost, no new three - wastes, good quality and high purity of potassium carbonate product (ammonium content is less than 10 ppm, chlorine content is less than 50 ppm), and uses the miscellaneous salts discharged in the alumina production process as raw materials, etc., meeting the production requirements of circular economy and green chemistry. Brief Description of the Drawings

[0027] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings.

[0028] Figure 1 It is the process flow diagram of comprehensively utilizing potassium resources in bauxite by the Bayer process to produce alumina with by - product potassium carbonate. Detailed Embodiments

[0029] To further elaborate the present invention, the technical means and effects taken to achieve the predetermined invention purpose are described in detail below with reference to the accompanying drawings and preferred embodiments, regarding the specific embodiments, processes, features and their effects of the present invention. Embodiment

[0030] S1. Potassium ion adsorption: The mother liquor from the Bayer process for producing alumina is introduced into an adsorption device loaded with an alkali - resistant potassium adsorbent. The adsorption time is 45 minutes, and the temperature of the mother liquor during adsorption is 25 °C. The adsorbent is an alkali - resistant ion - sieve type adsorbent, which selectively adsorbs potassium ions. Through the ion exchange of potassium and sodium, the potassium ions in the mother liquor are adsorbed. The potassium concentration of the seeded mother liquor before adsorption is 25 g / L, and the potassium concentration of the seeded mother liquor after adsorption is 10 g / L.

[0031] S2. Flushing: Deionized water is used as the flushing liquid and introduced into the adsorption device after adsorption to flush the potassium adsorbent, washing away the mother liquor and organic impurities attached to the surface of the potassium adsorbent. The flushing water volume is 0.5 BV.

[0032] S3. Desorbing liquid preparation: The miscellaneous salts discharged from the evaporation, concentration and crystallization of the mother liquor in the alumina production process are dissolved in deionized water and eluent. The mass fraction of sodium carbonate is 15%. After the sodium carbonate solution is filtered through a filter press, the desorbing liquid is obtained.

[0033] S4. Adsorbent desorption and regeneration: The prepared sodium carbonate desorbing liquid is heated to 80 °C and then introduced into the adsorption device to desorb the loaded potassium adsorbent. The desorption time is 45 minutes, so that the potassium ions adsorbed in the potassium adsorbent are desorbed into the desorbing liquid, obtaining a desorbing qualified liquid enriched with potassium. The sodium ions in the desorbing liquid are exchanged onto the adsorbent, enabling the regeneration of the adsorbent. The potassium ion concentration in the desorbing qualified liquid is 22 g / L.

[0034] S5. Elution: The potassium adsorbent after desorption and regeneration is eluted with a sodium hydroxide solution with a mass fraction of 0.2%. After elution, the adsorbent enters the next batch of adsorption process stage for recycling; the eluent after elution is used to prepare the next batch of desorbing solution.

[0035] S6. Decolorization and impurity removal: 6 g / L of activated carbon is added to the qualified desorbing solution for decolorization and adsorption of organic substances. Then, filtration is carried out by means of pressure filtration to obtain filter residue and refined qualified solution respectively. The refined qualified solution is colorless and transparent.

[0036] S7. Evaporation and concentration: The potassium-rich refined qualified solution is evaporated and concentrated. Sodium carbonate is precipitated by heat preservation at 80 °C for crystallization. The precipitated sodium carbonate is used to prepare the next batch of desorbing solution. Then, evaporation and concentration are continued to precipitate the double salt of sodium carbonate and potassium carbonate. The double salt is washed with deionized water. The potassium carbonate content in the filter cake after washing is 2%, and the remaining part is sodium carbonate and crystal water for preparing the next batch of desorbing solution. The washing solution of the double salt is added to the evaporation system and continued to be evaporated to 52 °Bé to obtain a saturated potassium carbonate solution with a potassium ion concentration of 12.5 mol / L, a sodium ion molar concentration of 0.5 mol / L, and a potassium-sodium ratio of 25.

[0037] S8. Carbonization and purification: The saturated potassium carbonate solution obtained in step S7 is pumped into a carbonization tower, and a carbonization reaction is carried out at a temperature of 45 °C and a pressure of 0.3 Mpa. Carbon dioxide is continuously introduced during the carbonization reaction until the pH of the reaction slurry reaches 8.1 to end the above carbonization reaction. The carbonized slurry is pumped into a cooling crystallizer and cooled to 20 °C for crystallization. The crystallized slurry is centrifuged for solid-liquid separation, and deionized water is used for washing during centrifugation to obtain high-purity potassium bicarbonate. The liquid after centrifugation is added to the refined qualified solution and sent to the evaporation system.

[0038] S9. Calcination: The obtained high-purity potassium bicarbonate is calcined for 60 minutes at a calcination temperature of 300 °C to obtain first-class potassium carbonate products and carbon dioxide gas. The carbon dioxide is recycled to the carbonization and purification process section S8.

[0039] After testing, the component content in the potassium carbonate prepared in this example is as follows: the potassium carbonate content is 99.5%, and the chloride (calculated as KCl) is 0.003%, meeting the requirements of first-class industrial potassium carbonate. Example

[0040] S1. Potassium ion adsorption: The mother liquor from the production of alumina by the Bayer process is introduced into an adsorption device loaded with an alkali-resistant potassium adsorbent. The adsorption time is 90 minutes, and the temperature of the mother liquor during adsorption is 35 °C; the adsorbent is an alkali-resistant ion sieve type adsorbent, which selectively adsorbs potassium ions. Through the ion exchange of potassium and sodium, potassium ions in the mother liquor are adsorbed. The potassium concentration in the mother liquor of the seed before adsorption is 50 / L. The potassium concentration in the mother liquor of the seed after adsorption is 15 g / L.

[0041] S2. Flushing: Deionized water is used as the flushing liquid and introduced into the adsorption device after adsorption to flush the potassium adsorbent, washing away the mother liquor and organic impurities attached to the surface of the potassium adsorbent; the flushing water volume is 0.5 BV.

[0042] S3. Desorbing liquid preparation: The miscellaneous salts discharged from the evaporation, concentration and crystallization of the mother liquor in alumina production are dissolved in deionized water and the eluent. The mass fraction of sodium carbonate is 20%. After the sodium carbonate solution is filtered through a filter press, the desorbing liquid is obtained.

[0043] S4. Adsorbent desorption and regeneration: The prepared sodium carbonate desorbing liquid is heated to 85 °C and then introduced into the adsorption device to desorb the loaded potassium adsorbent. The desorption time is 90 minutes, so that the potassium ions adsorbed in the potassium adsorbent are desorbed into the desorbing liquid, and a qualified desorbing liquid enriched with potassium is obtained. The sodium ions in the desorbing liquid are exchanged onto the adsorbent, enabling the adsorbent to be regenerated; the potassium ion concentration in the qualified desorbing liquid is 28 g / L.

[0044] S5. Elution: The potassium adsorbent after desorption and regeneration is eluted with a sodium hydroxide solution with a mass fraction of 0.2%. After elution, the adsorbent enters the next batch of adsorption process for recycling; the eluent after elution is used to prepare the next batch of desorbing liquid.

[0045] S6. Decolorization and impurity removal: 8 g / L of activated carbon is added to the qualified desorbing liquid for decolorization and adsorption of organic substances. Then, filtration is carried out by the method of pressure filtration to obtain filter residue and refined qualified liquid respectively. The refined qualified liquid is colorless and transparent.

[0046] S7. Evaporation and concentration: The potassium-rich refined qualified liquid is evaporated and concentrated. Sodium carbonate is precipitated by heat preservation and crystallization at 80 °C. The precipitated sodium carbonate is used for the preparation of the next batch of desorbing liquid. Then, evaporation and concentration continue to precipitate the double salt of sodium carbonate and potassium carbonate. The double salt is washed with deionized water. The potassium carbonate content in the filter cake after washing is 2%, and the remaining part is sodium carbonate and crystal water for the preparation of the next batch of desorbing liquid. The washing solution of the double salt is added to the evaporation system and evaporated to 52 °Bé to obtain a saturated potassium carbonate solution with a potassium ion concentration of 12.5 mol / L, a sodium ion molar concentration of 0.5 mol / L, and a potassium-sodium ratio of 25.

[0047] S8. Carbonization and purification: Pump the saturated potassium carbonate solution obtained in step S7 into a carbonation tower, and carry out a carbonation reaction at a temperature of 55 °C and a pressure of 0.5 Mpa. Continuously introduce carbon dioxide during the carbonation reaction until the pH of the reaction slurry reaches 8.3, at which point the above carbonation reaction ends. The carbonated slurry is pumped into a cooling crystallizer and cooled to 30 °C for crystallization. The crystallized slurry is centrifuged for solid-liquid separation, and deionized water is used for rinsing during centrifugation to obtain high-purity potassium bicarbonate. The liquid after centrifugation is added to the refined qualified liquid and sent to an evaporation system.

[0048] S9. Calcination: Calcinate the obtained high-purity potassium bicarbonate for 90 minutes at a calcination temperature of 280 °C to obtain a first-class potassium carbonate product and carbon dioxide gas. The carbon dioxide is recycled and used in the carbonization and purification process of S8.

[0049] After testing, the component content in the potassium carbonate prepared in this example is as follows: the potassium carbonate content is 99.6%, and the chloride (calculated as KCl) is 0.004%, meeting the requirements of first-class industrial potassium carbonate. Example

[0050] S1. Potassium ion adsorption: Feed the mother liquor from alumina production by the Bayer process into an adsorption device loaded with an alkali-resistant potassium adsorbent. The adsorption time is 120 minutes, and the temperature of the mother liquor during adsorption is 45 °C. The adsorbent is an alkali-resistant ion sieve type adsorbent, which selectively adsorbs potassium ions. Through the ion exchange of potassium and sodium, potassium ions in the mother liquor are adsorbed. The potassium concentration in the mother liquor before adsorption is 70 g / L, and the potassium concentration in the mother liquor after adsorption is 25 g / L.

[0051] S2. Flushing: Use deionized water as the flushing liquid to feed it into the adsorption device after adsorption to flush the potassium adsorbent and wash away the mother liquor and organic impurities attached to the surface of the potassium adsorbent. The flushing water volume is 0.5 BV.

[0052] S3. Desorbing liquid preparation: Dissolve the miscellaneous salts discharged from the evaporation, concentration, and crystallization of the mother liquor during alumina production into deionized water and the rinsing liquid, where the mass fraction of sodium carbonate is 25%. The sodium carbonate solution is filtered through a filter press to obtain the desorbing liquid.

[0053] S4. Adsorbent desorption and regeneration: Heat the prepared sodium carbonate desorbing liquid to 95 °C, and then feed it into the adsorption device to desorb the loaded potassium adsorbent. The desorption time is 120 minutes, so that the potassium ions adsorbed in the potassium adsorbent are desorbed into the desorbing liquid to obtain a desorbing qualified liquid enriched with potassium. The sodium ions in the desorbing liquid are exchanged onto the adsorbent, enabling the adsorbent to be regenerated. The potassium ion concentration in the desorbing qualified liquid is 45 g / L.

[0054] S5. Elution: The potassium adsorbent after desorption and regeneration is eluted with a sodium hydroxide solution with a mass fraction of 0.2%. After elution, the adsorbent enters the next batch of adsorption process stage for recycling; the eluent after elution is used to prepare the next batch of desorbing solution.

[0055] S6. Decolorization and impurity removal: 10 g / L of activated carbon is added to the qualified desorbing solution for decolorization and adsorption of organic substances. Then, filtration is carried out by means of pressure filtration to obtain filter residue and refined qualified solution respectively. The refined qualified solution is colorless and transparent.

[0056] S7. Evaporation and concentration: The potassium-rich refined qualified solution is evaporated and concentrated. Sodium carbonate is precipitated by heat preservation at 80 °C for crystallization. The precipitated sodium carbonate is used to prepare the next batch of desorbing solution. Then, evaporation and concentration continue to precipitate the double salt of sodium carbonate and potassium carbonate. The double salt is washed with deionized water. The potassium carbonate content in the filter cake after washing is 2%, and the remaining part is sodium carbonate and crystal water for preparing the next batch of desorbing solution. The washing solution of the double salt is added to the evaporation system and continues to be evaporated to 52 °Bé to obtain a saturated potassium carbonate solution with a potassium ion concentration of 12.5 mol / L, a sodium ion molar concentration of 0.5 mol / L, and a potassium-sodium ratio of 25.

[0057] S8. Carbonization and purification: The saturated potassium carbonate solution obtained in step S7 is pumped into a carbonization tower, and a carbonization reaction is carried out at a temperature of 60 °C and a pressure of 1.8 Mpa. Carbon dioxide is continuously introduced during the carbonization reaction until the pH of the reaction slurry reaches 8.4 to end the above carbonization reaction. The carbonized slurry is pumped into a cooling crystallizer and cooled to 30 °C for crystallization. The crystallized slurry is centrifuged for solid-liquid separation, and deionized water is used for washing during centrifugation to obtain high-purity potassium bicarbonate. The liquid after centrifugation is added to the refined qualified solution and sent to the evaporation system.

[0058] S9. Calcination: The obtained high-purity potassium bicarbonate is calcined for 120 minutes at a calcination temperature of 250 °C to obtain a first-class potassium carbonate product and carbon dioxide gas. The carbon dioxide is recycled to the carbonization and purification process section S8.

[0059] After testing, the component content in the potassium carbonate prepared in this example: the potassium carbonate content is 99.7%, and the chloride (calculated as KCl) is 0.004%, meeting the requirements of first-class industrial potassium carbonate.

[0060] The above are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above in the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for producing alumina and potassium carbonate as a by-product by comprehensive utilization of bauxite resources, characterized in that: The following steps are involved: S1. Potassium ion adsorption: The mother liquor produced by the Bayer process for producing alumina is passed into an adsorption device loaded with an alkali-resistant potassium adsorbent. The adsorption time is 45 to 120 minutes, and the temperature of the mother liquor during adsorption is 25 to 50 °C. The adsorbent is an alkali-resistant ion sieve type adsorbent, which selectively adsorbs potassium ions and adsorbs potassium ions in the mother liquor through ion exchange of potassium and sodium.

2. S2, flushing: Use deionized water as the flushing liquid to pass into the adsorption device after the adsorption is completed to flush the potassium adsorbent, and wash away the mother liquor and organic impurities attached to the surface of the potassium adsorbent; in order to reduce the amount of flushing water, three rounds of flushing are used. The first round of flushing uses the flushing liquid of the second round of the previous batch, and the flushing liquid after the first round of flushing is discharged into the alumina production process as red mud washing water. The second round of flushing uses the flushing liquid of the third round of the previous batch, and the flushing liquid after the second round of flushing is used as the flushing liquid of the first round of the next batch. The third round of flushing uses deionized water, and the flushing liquid after flushing is used as the flushing liquid of the second round of the next batch.

3. S3, desorption liquid configuration: the impurities discharged from the mother liquor during the alumina production process by evaporation, concentration and crystallization Dissolve in deionized water and eluent, wherein the mass fraction of sodium carbonate is 10-25%, and filter the sodium carbonate solution to obtain a desorption solution.

4. S4, adsorbent desorption and regeneration: the prepared sodium carbonate desorption solution is passed into the adsorption device to desorb the loaded potassium adsorbent, so that the potassium ions adsorbed in the potassium adsorbent are desorbed into the desorption solution to obtain a potassium-enriched desorption qualified solution, and the sodium ions in the desorption solution are exchanged with the adsorbent, so that the adsorbent can be regenerated; S5. Elution: Use a sodium hydroxide solution with a mass fraction of 0.2~1% to elute the potassium adsorbent after desorption and regeneration. After elution, the adsorbent enters the next batch of adsorption process stage for recycling; the eluent after elution is used to prepare the desorption solution.

5. S6, decolorization and impurity removal: Use activated carbon to decolorize the desorbed qualified liquid and adsorb organic matter. Then use the pressure filtration or suction filtration method to filter and obtain the filter residue and refined qualified liquid respectively. 6.S7, evaporation and concentration: The potassium-rich refined qualified liquid is evaporated and concentrated and heat-insulated and crystallized. The sodium carbonate precipitated first is used for the configuration of the desorption liquid, and then the sodium carbonate and potassium carbonate double salt are precipitated by evaporation and concentration. The double salt is washed with deionized water. The main component of the filter cake after washing is sodium carbonate for the configuration of the desorption liquid. The double salt washing solution is added to the evaporation system and continued to evaporate to 52°Bé to obtain a saturated potassium carbonate solution with a potassium ion concentration of 12.5mol / L, a sodium ion molar concentration of 0.5mol / L, and a potassium-sodium ratio of 25. 7.S8, carbonization purification: The saturated potassium carbonate solution obtained in step S7 is pumped into a carbonation tower, and a carbonation reaction is carried out at a temperature of 45-60°C and a pressure of 0.2~2Mpa. Carbon dioxide is continuously introduced during the carbonation reaction until the pH of the reacted slurry reaches 8.0~8.5, and the carbonization reaction is terminated. The carbonized slurry is pumped into a cooling crystallizer and cooled to 20-35°C for crystallization. The crystallized slurry is centrifuged for solid-liquid separation, and deionized water is used for elution during the centrifugation process to obtain high-purity potassium bicarbonate. The liquid after centrifugation is added to the refined qualified liquid deevaporation system.

8. S9, drying and calcining: calcine the obtained high-purity potassium bicarbonate to obtain high-quality potassium carbonate products and carbon dioxide gas. The carbon dioxide is recycled to the carbonization and purification S8 process section.

9. As a preferred technical solution of the present invention, in step S1, the mother liquor is one of the seed mother liquor, carbon mother liquor, circulating mother liquor, evaporated mother liquor and gallium extraction residual liquor in the Bayer process alumina production process, and contains potassium ion concentration of 15~90 g / L.

10. As a preferred technical solution of the present invention, in step S3, the impurities discharged from the mother liquor by evaporation and concentration can be washed first to wash away most of the organic matter and attached aluminum hydroxide. The washing liquid is discharged into the main process of alumina production to dilute and wash the red mud. The washed filter cake is dissolved in deionized water and eluent to obtain a desorption liquid. The mass fraction of the desorption liquid is 10-25%, preferably, the mass fraction of the desorption liquid is 15-20% As a preferred technical solution of the present invention, in step S4, the temperature of the desorption and regeneration process is 60-95°C. Preferably, the temperature of the desorption and regeneration process is 85-95°C. As a preferred technical solution of the present invention, in step S6, the activated carbon is powdered activated carbon, and ≥50 g of activated carbon is added to each 1 liter of desorption qualified liquid; the obtained refined qualified liquid should ensure that the transmittance is greater than 99.8%, otherwise step S6 needs to be repeated As a preferred technical solution of the present invention, in step S8, the carbonation reaction is carried out at a temperature of 45-60°C and a pressure of 0.2-2Mpa. Preferably, the carbonation reaction is carried out at a temperature of 55-60°C and a pressure of 0.5-1Mpa. As a preferred technical solution of the present invention, in step S9, the calcination temperature is 200-600°C, and the calcination time is 30-200 minutes. Preferably, the calcination temperature is 250-300°C, and the calcination time is 90-120 minutes, wherein the mass purity of potassium carbonate is greater than 99%.

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