WO2007082447A1

WO2007082447A1 - Method for improving cycle efficiency of bayer process alumina production

Info

Publication number: WO2007082447A1
Application number: PCT/CN2006/003313
Authority: WO
Inventors: Songqing Gu; Nianyi Chen; Xiangmin Liu; Zhonglin Yin; Wencong Lu; Wei Liu; Liangmiao Zhang; Lijuan Qi; Wanquan Bai; Guobing Li; Wancheng Liu; Dongzhan Han
Original assignee: Aluminum Corporation Of China Limited
Priority date: 2006-01-16
Filing date: 2006-12-06
Publication date: 2007-07-26
Also published as: AU2006336147B2; CN100418884C; CN1792799A; AU2006336147A1

Abstract

Disclosed is a method for extracting sodium hydroxide from a concentrated Bayer process circulating liquor through a liquid-liquid extraction process to decrease caustic ratio of evaporation mother liquor or decomposition mother liquor and thus to enhance seed decomposition and to improve Bayer process system cycle efficiency. Extractants such as C6-C20 aliphatic alcohols (eg., n-octyl alcohol) and mixture thereof, alkyl phenols with carbon chain length of C13-C18, fluorinated alcohols, etc. are used to extract sodium hydroxide from a Bayer process circulating liquor, and then the extraction phase is back-extracted with water to give concentrated sodium hydroxide solution free of aluminum, which is then directly used to digest bauxites or to recover aluminum oxide and caustic alkali from red muds. Back-extracted extractants may be regenerated and recycled, the raffinate is continuely used as seeds to produce aluminum hydroxide via decomposition.

Description

Method for improving cycle efficiency of alumina production by Bayer process

A method for improving the cycle efficiency of alumina production by Bayer process, relating to extracting sodium hydroxide (caustic alkali such as potassium hydroxide) from a concentrated Bayer process liquid by liquid-liquid extraction method to reduce evaporation mother liquid or decomposition The caustic ratio of the mother liquor, thereby enhancing the decomposition of the seed and improving the cycle efficiency and alumina yield of the Bayer process. technical background

The Bayer process is the primary method of alumina production. The method uses a bauxite and a Bayer process circulating solution containing sodium hydroxide to dissolve the reaction under high temperature and high pressure conditions, so that the alumina in the bauxite enters the solution to form a sodium aluminate solution, and then the sodium aluminate solution is diluted and red. Mud separation, in the case of seeding, the sodium aluminate solution is decomposed to produce aluminum hydroxide, which is calcined into an alumina product. After the decomposition, the seed decomposition mother liquid containing sodium hydroxide and residual sodium aluminate is evaporated and used as a circulating mother liquor for re-dissolving the bauxite. The alumina production of this process constitutes the first half of the aluminum metallurgical industry.

However, Bayer's method itself has obvious weaknesses: (1) Because the hydrolysis reaction is incomplete in the process of seed decomposition, generally only about 50% of sodium aluminate produces aluminum hydroxide, so that the circulating fluid still contains a large amount of sodium aluminate circulating in the process. , causing a large amount of solution circulation, and the total alkali amount of the circulating liquid still contains a large amount of sodium aluminate, and only a part of it is a free sodium hydroxide which can actually act as a dissolution. Therefore, the dissolution efficiency is limited; (2) China's bauxite contains high silicon, and a large amount of alumina and sodium oxide enter the red mud loss when Bayer process is dissolved. It has been envisaged to use a high pressure hydration technique that can recover alumina from red mud in series with the Bayer process to increase the yield of alumina. However, the concentration of sodium aluminate in the Bayer process circulating liquid is too high to be used for the dissolution of red mud by high pressure hydration. This difficulty has become a bottleneck that hinders the series connection of Bayer process and high pressure hydration method. (3) China's bauxite is mainly The diaspore type ore is harsh in the Bayer process, and it is difficult to prepare a caustic ratio low dissolution solution, which also makes it difficult to decompose the seed to produce sand-like alumina. There is little potential for using a enhanced dissolution technique to reduce the caustic ratio of the eluate. (4) Bayer process dissolution has a low yield ratio due to the low molecular ratio of the mother liquor.

The partial separation of sodium hydroxide in the sodium aluminate solution is effectively separated, so that the caustic ratio of the Bayer seed decomposition mother liquor is greatly reduced, so that the seed decomposition can be continued, and the seed decomposition production process can be strengthened or shortened, and the Bayer cycle can be improved. Efficiency and alumina yield. At the same time, the sodium hydroxide is separated to obtain a concentrated solution of sodium hydroxide containing no aluminum, instead of the original The Bayer process circulating solution dissolves the bauxite, which may greatly reduce the circulation of the Bayer process circulating fluid and enhance the Bayer process. Furthermore, the red mud can be treated in series for the Bayer process and the high pressure hydration method, and a new way for the treatment of the bauxite containing higher silicon by the Bayer process is opened up. The Bayer process has undergone major changes, greatly improving the efficiency of the Bayer process for dissolution and seed decomposition, increasing the alumina yield per production cycle, and expanding the range of ores suitable for Bayer process. Therefore, it is necessary to find a liquid-liquid extraction of the Bayer process circulating liquid with a cheap extractant to reduce the caustic ratio, and to obtain a concentrated solution of sodium hydroxide by stripping, and to improve and design the alumina production technology. Alumina plants with efficient and low-cost new technologies are of great significance.

For the separation of sodium hydroxide technology, in recent years, the US Atomic Energy Commission Oak Ridge Laboratory has conducted a series of research work to recover sodium hydroxide from sodium hydroxide-containing nuclear fuel waste. In their patents and published papers, it is recommended to use fluoroalcohol and several macrocyclic crown ethers as extractants. They also try to use alkylphenols as extractants. They use these extractants to achieve hydration of kerosene or alcohol solutions. Sodium extraction. Moreover, they also found that sodium hydroxide solution can be obtained by back-extracting with water. Although the above patented technology in the United States can achieve extraction and stripping, the purpose of recovering sodium hydroxide from waste liquid is achieved. The process of strengthening the Bayer process differs from that of the US atomic energy industry in recovering sodium hydroxide from wastewater because sodium hydroxide is originally recycled in the Bayer process. At present, production has reached zero discharge of wastewater, and there is no requirement to recover sodium hydroxide from wastewater. The technical solutions recommended by US patents are not applicable to us. The specific reasons are as follows: (1) U.S. Patent No. 6,322,702 recommends a higher fluoroalcoholic cost (this patent document has indicated that the preparation of fluoroalcohol may be costly) and that macrocyclic crown ethers are also valuable chemical products. For the production of large-scale, inexpensive products such as alumina, it is economically uneconomical to use too expensive extractants; (2) US technology is suitable for treating dilute sodium hydroxide solutions with a lower concentration of stripping solution. However, we need to prepare a high concentration of sodium hydroxide solution to achieve the requirements of enhanced Bayer process production; (3) The alkylphenol extractant recommended by the US literature is suitable for the extraction of radioactive cesium from nuclear waste, in USP 3598547, USP 3598548 states: The number of carbon atoms in a single side chain of an alkylphenol molecule shall not exceed 12, due to the small number of side chain carbon atoms, the greater the water solubility, and because the Bayer process's seed decomposition is extremely sensitive to organic impurities, the extractant Not applicable. Summary of the invention

The object of the present invention is to address the deficiencies of the prior art described above, and to provide an To extract caustic alkali such as sodium hydroxide from the Bayer process to reduce the caustic ratio of the evaporation mother liquor or the decomposition mother liquor (the molar ratio of alumina to caustic alkali in sodium aluminate solution), and greatly improve the Bayer process. Cycle efficiency method.

The object of the present invention is achieved by the following technical solutions.

A method for improving the cycle efficiency of producing alumina by the Bayer process, characterized in that liquid-liquid extraction is used to extract sodium hydroxide from the Bayer process liquor, thereby reducing the caustic ratio, thereby enhancing seed decomposition and improving cycle efficiency of the Bayer process system. A method of alumina yield.

A method for improving the cycle efficiency of producing alumina by the Bayer process, characterized in that the steps of the method are as follows:

a. The caustic concentration in sodium oxide is 100 - 500g / L, the caustic ratio is 2.0

- 4.2 Bayer process circulating solution, adding extractant, mechanically stirring in the extraction tank at 60 - ΙΟΟ temperature for 2-20 minutes;

b. After the extraction reaction is completed, the oil and water are separated;

c pumping the separated oil phase into the stripping tank, using water as a stripping agent, stirring and stripping at 60-100 °C for 2-20 minutes;

d. After the stripping reaction is completed, the oil and water are separated; the separated oil phase is pumped again into the extraction tank mentioned in step a, and extracted again;

e. cycle several times in the order of steps a - d;

f. The caustic ratio of the Bayer process in final step a is reduced to 1.4, and direct dilution is used for seed decomposition to produce sand-like alumina.

The method of the present invention is characterized in that, in the step d, the concentration of caustic alkali in the stripping water is from 200 to 300 g/L, which is directly used for dissolving bauxite or for dissolving red mud by high pressure hydration.

The method of the present invention is characterized in that the Bayer process circulating liquid refers to a sodium aluminate solution in the production process of alumina, and the solution contains alkali metal ions such as lithium, sodium and potassium.

The method of the present invention is characterized in that the extracting agent used in the extraction process is a fatty alcohol having a carbon chain length of 6 to 20 or a mixture thereof.

The method of the present invention is characterized in that the extracting agent used in the extraction process is n-octanol.

The method of the present invention is characterized in that the extracting agent used in the extraction process is an alkylphenol, characterized in that the position on the alkyl-substituted benzene ring can be ortho, meta and para, preferably in the para position, a single The alkyl branch length is 13 - 18 carbons. The alkylphenol extractant, the diluent thereof may be an alkane having a carbon chain length of 6 to 18 carbons or a mixture of kerosene and a fatty alcohol. The method of the present invention is characterized in that the stripping agent used in the extraction process is pure water, or a low alkali washing waste liquid having a concentration of less than 7 mol/L of a NaOH diluted solution or an alumina industrial washing aluminum hydroxide product.

Experiments on the present invention show that: (1) By properly evaporating and concentrating the Bayer seed seed mother liquor, it is possible to extract sodium hydroxide with high efficiency, inexpensive, industrially mass-produced fatty alcohol (for example, n-octanol), and water. Stripping can obtain 300-400g/L concentrated sodium hydroxide solution; (2) In order to reduce the water solubility of alkylphenol, use kerosene with small water-soluble, octadecylphenol with 18 carbon atoms in the side chain - positive The octanol solution extraction can also get good results. Using the extraction scheme of the present invention, liquid-liquid extraction is carried out by using a fatty alcohol (for example, n-octanol), an alkylphenol, or a fluoroalcohol extractant, and caustic alkali such as sodium hydroxide is extracted from the concentrated Bayer process liquor to reduce evaporation. The caustic ratio of the mother liquor or the decomposition mother liquor, the caustic ratio of 2.0 to 4.2 seed decomposed mother liquor after concentration and extraction, the caustic ratio can be reduced to about 1.4 - 1,5, and further seed decomposition can be repeated. In order to greatly improve the cycle efficiency of Bayer process and the output of alumina plant, and to use Bayer method to efficiently process the medium and low grade bauxite resources with higher silicon content, a new way is opened.

After our research, we found C ₆ - C ₂ . An aliphatic alcohol (for example, n-octanol) or a mixture thereof, an extracting agent having a carbon chain length of C ₁₃ - 0 ₁₈ alkylphenol, fluoroalcohol or the like can be used to extract sodium hydroxide from a suitably concentrated Bayer process circulating liquid, in particular (1) When the Bayer process seed decomposition mother liquor is properly concentrated to bring Na ₂ to a concentration of 360 g/L or more, extract with an inexpensive 8 - 10 carbon fatty alcohol as an extractant, and back-extract with water to obtain an aluminum-free hydrogen. The concentrated solution of sodium oxide is used as a circulating liquid, and the circulating liquid can be directly used for dissolution of bauxite or high pressure hydration of red mud. After stripping, the extractant is regenerated and can be recycled. The raffinate is continuously used as a seed to decompose and prepare aluminum hydroxide; (2) Bayer seed decomposing mother liquid is appropriately concentrated, extracted with octadecylphenol n-octanol solution or n-octanol-kerosene solution, and stripped with water , can obtain aluminum-free sodium hydroxide solution, which can be used for dissolution of bauxite or high-pressure hydration of red mud. After stripping, the extractant is regenerated and can be recycled. The raffinate can be used for seed decomposition to produce aluminum hydroxide.

Originally, Bayer's seed decomposition mother liquor was condensed by evaporation and then recycled for high pressure dissolution. According to the present invention, it can be extracted to obtain a sodium aluminate solution having a caustic ratio of about ^1.5 , and the seed can be further decomposed to recover more aluminum hydroxide. At the same time, a sodium hydroxide solution containing no sodium aluminate is obtained by back-extraction, and the cycle is used for dissolution of bauxite. Because it does not contain alumina, the dissolution efficiency and the utilization rate of the dissolution equipment may be significantly improved, and the circulation amount of the solution may be significantly reduced, which is advantageous for greatly improving the cycle efficiency of the Bayer process. Therefore, it is possible that the amount of circulation is large. Reduced amplitude and reduced energy consumption. It is also possible to use the obtained concentrated sodium hydroxide solution to dissolve and recover the alumina and caustic in the red mud by high-pressure hydration method, and obtain a caustic ratio of 9 - 10 solution, and then use it for dissolution of bauxite, thereby using Bayer method. - High-pressure hydration process to treat high-silica bauxite to achieve high dissolution rate of alumina. Expand the range of bauxite grades that Bayer can handle. Specific implementation

Place the Bayer system sodium aluminate circulating solution in the extraction tank, the sodium oxide concentration is 100 - 500g / L, the caustic ratio is 2.0 - 4.2, using C ₆ - C _2Q fatty alcohol (such as n-octanol) or their mixture, carbon The chain length is C ₁₃ - (: ₁₈ alkyl phenol, fluoroalcohol and other extractants mechanically extracted, the temperature is controlled at 60 - 100 Ό, the extraction time is controlled at 2 - 20 minutes, after the reaction is completed, the oil and water are separated. The separated oil The phase is pumped into another stripping tank with water or a caustic alkali low alkali solution as a stripping agent, and the mixture is stirred and stripped at a temperature of 60 - 100 Torr, and the stripping time is controlled at 2 - 20 minutes. The oil and water are separated. The extracted sodium hydroxide has entered the stripping water phase, and the regenerated oil phase can be recycled. At this point, the regenerated oil phase is pumped back into the extraction tank, and the extractant is recycled. The phase can be replaced with new stripping water according to the concentration requirements. After several times, the caustic ratio of the extracting liquid can be lowered.

The following description will be made in conjunction with specific embodiments. Embodiment 1:

Take < ₈ and. a mixture of fatty alcohols (weight percent C _{8 :} C ₁₀ =51 : 49 ) as extractant, extracting 1 volume of concentrated Bayer evaporation mother liquor, caustic ratio 2.70, caustic concentration 482 _g / L, extractant volume It is 4 times the volume. The extraction was carried out under conditions of 95 Torr, and the stirring time was controlled for 10 minutes. After the completion of the reaction, the oil and water were separated. The separated oil phase was pumped into the stripping tank and stirred and stripped with 1 volume of water. The temperature was controlled at 95 Torr and the stripping time was also controlled at 10 minutes. After the reaction is completed, the oil and water are separated. The regenerated extractant is recycled. This cycle. When the caustic concentration of the raffinate is less than 300 g/L, the mixture is heated and concentrated, and the extraction is continued, and the cycle is repeated. Concentrated twice in the middle process, 15 extraction-back extraction, and finally, the raffinate caustic ratio is 1.40, which can be used for seed decomposition. The concentration of caustic in the stripping solution can reach more than 300g/L. It was determined that the stripping water could not detect aluminum, indicating that the extracting agent used did not extract aluminum. Using n-octanol as extractant, extract 1 volume of concentrated Bayer evaporation mother liquor with a caustic ratio of 3.28, caustic concentration of 49 ⁹ g/L, and 4 volumes of extractant. The mixture was extracted under 90 Torr conditions, and the stirring time was controlled for 10 minutes. After the reaction was completed, the oil and water were separated. The separated oil phase was placed in a stripping tank and stirred back with 1 volume of water. The temperature was controlled at 90 ° C and the stripping time was also controlled at 10 minutes. After the reaction is completed, the oil and water are separated. The regenerated extractant is recycled. This cycle. When the caustic concentration of the raffinate is less than 10 mol/L, the mixture is heated and concentrated, and the extraction is continued, and the cycle is repeated. The intermediate process is concentrated 3 times, 11 times extraction-back extraction, and finally, the caustic ratio of the raffinate is ^1.68 , which can be decomposed by seeds. The concentration of caustic in the stripping solution can reach more than 300g/L. It was determined that the stripping water could not detect aluminum, indicating that the extractant used did not extract aluminum. Embodiment 3:

Using 0.5 mol/L octadecylphenol as extractant and n-octanol-kerosene as diluent, extract 1 volume of Bayer evaporation mother liquor with a caustic ratio of 3.18, caustic concentration of 232 g/L, 5 times volume Extractant. The mixture was extracted at 80 ° C, and the stirring time was controlled for 10 minutes. After the reaction was completed, the oil and water were separated. The separated oil phase was placed in a stripping tank and stirred back with 1 volume of water. The temperature was controlled at 80 ° C and the stripping time was also controlled at 10 minutes. After the reaction is completed, the oil and water are separated. The regenerated extractant is recycled. This cycle 4 times, and finally, the raffinate caustic ratio is 1.88, which can be used for seed decomposition. The concentration of caustic alkali in the stripping water was 115 _g / L. After analysis, the stripping water could not detect aluminum, indicating that the extracting agent used did not extract aluminum. If the Bayer seed decomposing mother liquor is pre-concentrated to Na ₂ O _k 360 _g /L, and the caustic ratio of the raffinate is up to 1.5, the concentration of the stripping solution can reach 300 g/L or more. Embodiment 4:

Using 0.5 mol/L octadecylphenol as extractant and n-octanol-kerosene as diluent, extract 1 time volume of Bayer evaporation mother liquor with caustic ratio of 3.06, caustic concentration of 109g/L, 5 times volume Extractant. The mixture was extracted under conditions of 85 Torr, and the stirring time was controlled for 10 minutes. After the reaction was completed, the oil and water were separated. The separated oil phase was placed in a stripping tank and stirred back with 1 volume of water. The temperature was controlled at 80 Torr and the stripping time was also controlled at 10 minutes. After the reaction is completed, the oil and water are separated. The regenerated extractant is recycled. This cycle is 7 times, and finally, the raffinate caustic ratio is 1.79, which can be used for seed decomposition. The concentration of the stripping caustic alkali was lllg/L. After analysis, the stripping water could not detect aluminum, indicating that the extracting agent used did not extract aluminum.

Claims

Rights request

1. A method for improving the cycle efficiency of alumina production by the Bayer process, characterized in that liquid-liquid extraction is used to extract sodium hydroxide from the Bayer process liquor, thereby reducing the caustic ratio, thereby enhancing seed decomposition and improving the Bayer process cycle. Method of efficiency and alumina yield.

2. A method of improving the cycle efficiency of producing alumina by the Bayer process according to claim 1, wherein the steps of the method are:

a. In the Bayer process circulating solution with a caustic alkali concentration of 100 - 500 _g / L and a caustic ratio of 2.0 - 4.2, add the extractant at a temperature of ⁶⁰ - 100 ° C in the extraction tank. Mechanically agitated extraction for 2-20 minutes;

b. After the extraction reaction is completed, the oil and water are separated;

e. cycle several times in the order of steps a - d;

3. A method for improving the cycle efficiency of alumina production by the Bayer process according to claim 2, wherein the caustic concentration of the sodium oxide in the stripping water in step d is 200.

- 300g / L, used directly to dissolve bauxite or used for high pressure hydration to dissolve red mud.

4. A method for improving the cycle efficiency of producing alumina by the Bayer process according to claim 2, wherein the Bayer process liquor refers to a sodium aluminate solution in the production process of alumina, the solution containing lithium, sodium, An alkali metal ion such as potassium.

A method for improving the cycle efficiency of producing alumina by the Bayer process according to claim 2, characterized in that the extracting agent used in the extraction process is an aliphatic alcohol having a carbon chain length of 6 - 20 or a mixture thereof.

6. A method of increasing the cycle efficiency of producing alumina by the Bayer process according to claim 2, characterized in that the extracting agent used in the extraction process is n-octanol.

7. A method for improving the cycle efficiency of producing alumina by the Bayer process according to claim 2, wherein the extracting agent used in the extraction process is an alkylphenol, characterized in that the position on the alkyl substituted benzene ring is For ortho, meta and para, preferably in alignment, single The alkyl branch length is from 1 ^{3 to} 18 carbons. The alkyl hydrazine extracting agent may be a diluent of a terpene hydrocarbon having a carbon chain length of 6 to 18 carbons or a mixture of kerosene and a fatty alcohol.

8. A method of increasing the cycle efficiency of producing alumina by the Bayer process according to claim 2, characterized in that the stripping agent used in the extraction process is pure water.

9. A method for improving the cycle efficiency of producing alumina by the Bayer process according to claim 2, wherein the stripping agent used in the extraction process is a NaOH diluted solution having a concentration of less than 7 mol/L or an alumina industrial washed aluminum hydroxide. Low alkali washing waste liquid for the product.