CN102398914B - Modifying Bayer process for processing low-grade diaspore bauxite and producing alumina - Google Patents

Abstract

The invention relates to a method for improving the Bayer process to process low-grade diaspore-type bauxite to produce alumina. The method comprises the following steps: 1) chemical pre-desilication: the low-grade bauxite is immersed in aluminum containing stabilizer 2) Desilication of high sodium aluminosilicate solution: filter the resulting slurry, add desilication seed crystals for desilication; 3) Seed classification of sodium aluminate solution: Add the desiliconized sodium aluminate solution to aluminum hydroxide seed crystals to decompose the seeds; 4) roast the obtained aluminum hydroxide finished product to obtain alumina products; 5) high-pressure dissolution: the obtained seed separation mother liquor is evaporated to supplement alkali It is used in the high-pressure stripping of the concentrate obtained in step 2) to obtain a sodium aluminate solution and add a stabilizer to process the next batch of bauxite, and repeat steps 1) to 4). The invention is suitable for processing low-grade diaspore type bauxite, effectively solves the problem of silicon scaling in the alumina industry, and can obviously reduce energy consumption and improve the quality of the final product alumina.

Description

A method of improving Bayer process to process low-grade diaspore bauxite to produce alumina

technical field

The invention relates to the field of bauxite treatment, in particular, the invention relates to an improved Bayer method for processing low-grade diaspore bauxite to produce alumina.

Background technique

At present, in the production of alumina, there are mainly Bayer method, sintering method and hybrid method to realize industrial production. Among them, the Bayer method has the advantages of low energy consumption, simple process, and low production cost. However, the production of alumina by the Bayer method has strict requirements on raw materials. Generally, the aluminum-silicon ratio is required to be greater than 8, and it is especially suitable for Sanshui with a high aluminum-silicon ratio. Alumina production from bauxite raw materials. However, more than 80% of China's bauxite is a medium-low-grade diaspore type with an aluminum-silicon ratio (the mass ratio of Al ₂ O ₃ and SiO ₂ in bauxite) of 4 to 8. The content of silica is high, so it cannot be directly applied to the pure Bayer process with low production cost, but has to adopt the sintering process or hybrid process with long process, high energy consumption and large construction investment. According to this situation, how to develop a new alumina production process with simple process, low energy consumption and effective cost reduction is a strategic issue that my country's alumina enterprises must solve.

With the increasing reduction of monohydrate bauxite with an aluminum-silicon ratio greater than 8 and the need to reduce energy consumption and production costs, low-grade diaspore bauxite is used as raw material for alumina production, and the Bayer process is used to produce alumina Aluminum is an important topic for the alumina industry. For this reason, people have carried out a lot of researches, one of which is to improve the traditional pure Bayer method.

The essence of the traditional Bayer method is that the following reactions are carried out alternately under different conditions:

That is, the bauxite is subjected to pressure cooking and dissolution treatment in an alkaline solution, so that the alumina in it enters the liquid phase. In this process, some impurity components in minerals are harmful to the reaction, among which the silicon component has the greatest influence on the reaction. The silicon component in the pulp in the conventional Bayer method leaching process reacts with lye to form hydrous sodium aluminosilicate, and its molecular formula is roughly equivalent to Na ₂ O·Al ₂ O ₃ ·1.7SiO ₂ ·nH ₂ O, in which Al ₂ O ₃ and SiO The weight of ₂ is equal, that is, A/S is 1, if all SiO ₂ in the ore is converted into this hydrous sodium aluminosilicate, every 1kg SiO ₂ will cause 1kg Al ₂ O ₃ and 0.608kg Na ₂ O loss. Under pressure cooking conditions, _SiO2 in the ore reacts with alkali to form hydrous sodium aluminosilicate, which is discharged out of the process together with the residue red mud, resulting in chemical loss of alkali and has to be recycled by sintering, increasing production capacity Consumption increases production costs. It is generally believed that bauxite with a low aluminum-silicon ratio will cause quite high alkali consumption in Bayer process production, which will make the production cost too high. At present, it is generally believed that A/S below 7-8 is not suitable for production by conventional Bayer process.

In order to reduce alkali consumption, energy consumption and more effective use of my country's bauxite resources, many improvements have been made to the traditional Bayer process, such as beneficiation Bayer process, lime Bayer process, series process, Bayer hydration process, hydrothermal process, etc. Production Process. There are still some problems in the above-mentioned production process, such as the use of chemical agents in the Bayer process of beneficiation, which causes a large amount of tailings to be unusable, which is not conducive to the effective utilization of bauxite in China; although the lime Bayer process reduces the alkali consumption, there is alumina Low recovery rate, serious silicon scaling and other problems; although the series method can improve the utilization rate of resources, there is still a sintering method, which still consumes a lot of energy; Bayer hydration method and hydrothermal method can improve the recovery rate of alumina, It can also reduce alkali consumption and energy consumption, and has great advantages in processing low- and medium-grade bauxite, but it is difficult to obtain high caustic ratio solutions, and it is difficult to decompose high caustic ratio solutions. Many, can not effectively recycle and other problems, so it is difficult to realize industrialization.

In addition, the patent application 20041004691 proposed the "symmetrical Bayer method" for the effective treatment of high-silicon bauxite. Unlike the traditional Bayer method, which uses a low-concentration caustic soda solution, it uses a high-concentration solution to dissolve bauxite. After the dissolution is completed, the concentration of caustic soda in the solution is greater than that of alumina hydrate (bauxite) at the dissolution temperature. The concentration of caustic soda at the common thermodynamic equilibrium of sodium aluminate (or sodium aluminate hydrate). In this way, the equilibrium of the dissolution system is transformed from the equilibrium between the bauxite and the sodium aluminate solution in the traditional Bayer process to the dissolution-crystallization equilibrium between the sodium aluminate solution and the sodium aluminate crystal. Therefore, neither gibbsite, boehmite nor diaspore will exist stably. However, this method requires a higher alkali concentration, is difficult to achieve filtration separation, and has stricter requirements on equipment, and the process needs to evaporate a large amount of water, and it is also difficult to recover alkali from the dissolution residue. Chinese patent CN1807251A discloses a "method for extracting alumina from high-silicon bauxite". Aluminum oxide, and then use high-pressure hydrochemical method to treat red mud, and recover Al ₂ O ₃ bound by SiO ₂ . The obtained solution does not need to be processed again, and is directly sent to the symmetrical Bayer process system to dissolve the next batch of ore, and the resulting hydrated silicon Sodium calcium acid is hydrolyzed to recover the alkali in it. However, the alkali concentration used in the high-pressure hydrochemical part of the method is relatively high, the liquid-solid separation is relatively difficult, and the process is relatively complicated and difficult to operate.

When dealing with low-grade diaspore bauxite ore in the prior art, either the energy consumption is high, the process is complicated, the cost is high, and the product quality is unstable, or the recovery rate of alumina is low due to the addition of chemical reagents. And cause a large amount of tailings to be unusable, or the alkali concentration used is higher, making liquid-solid separation more difficult, the process is relatively complicated, unfavorable operation and so on. For the alumina industry currently using low-grade diaspore type as the main raw material, the development of a new production process with simple process, low energy consumption and effective cost reduction will greatly promote the production of alumina in my country .

Contents of the invention

The object of the present invention is to provide an improved Bayer method for processing low-grade diaspore bauxite to produce alumina, which successfully solves the above problems.

The improved Bayer process provided by the invention processes the method for producing alumina from low-grade diaspore type bauxite comprising the following steps:

1) Chemical pre-desilication: immerse the low-grade diaspore bauxite with a particle size of less than 0.098 mm in a sodium aluminate solution containing a stabilizer, and contact it to make the diaspore bauxite in the Active silica is dissolved and stabilized in the slurry to obtain a slurry with silica dissolved;

2) Desiliconization of high-aluminosilicate sodium solution: filter the slurry obtained in step 1) to obtain sodium aluminate solution with high silicon content and high-aluminum-silicon ratio concentrate, dilute the sodium aluminate solution and add desiliconization seeds to carry out Desiliconization to obtain a sodium aluminate solution, washing the high-aluminum-silicon ratio concentrate, and washing water as a diluent for high-aluminosilicate sodium;

3) Seed separation of sodium aluminate solution: add the desiliconized sodium aluminate solution obtained in step 2) to aluminum hydroxide seed crystals for seed decomposition, obtain aluminum hydroxide coarse crystals and seed separation mother liquor after separation, and fully crystallize hydrogen Alumina, after washing, recovering the aluminum oxide and sodium oxide attached to the aluminum hydroxide, the finished product of aluminum hydroxide is obtained, and the washing liquid is returned to the seed separation mother liquor;

4) Aluminum hydroxide roasting: roasting the aluminum hydroxide finished product obtained in step 3) to obtain an alumina product;

5) High-pressure stripping: the seed separation mother liquor obtained in step 3) is evaporated and supplemented with alkali for high-pressure stripping of the concentrate obtained in step 2), and the stripping solution is filtered and separated to obtain sodium aluminate solution and red mud. The sodium solution is used to process the next batch of bauxite after adding a stabilizer, and steps 1) to 4) are repeated. The red mud is washed and enters the red mud yard, and the washing liquid is returned to step 2) for high aluminosilicate Sodium dilution.

According to the improved Bayer method of the present invention for processing low-grade diaspore-type bauxite to produce alumina, the contact temperature between the low-grade diaspore-type bauxite and the sodium aluminate solution containing stabilizer It is 70-130°C, preferably 80-105°C, and the contact time is 2-10h, preferably 4-8h.

According to the improved Bayer method of the present invention to process low-grade diaspore type bauxite to produce alumina, the stabilizer in the described step 1) is dipotassium hydrogen phosphate, aminotrimethylene phosphonic acid, ethylenediamine One of sodium tetramethylene phosphonate and polyol phosphate, the concentration is not higher than 0.1g/L; the amount of bauxite added is 100-400g/L, preferably 200-300g/L, sodium aluminate solution The concentration of sodium hydroxide (calculated as NaOH) in the medium is 200g/L～500g/L, preferably higher than _300g /L, and the concentration of alumina (calculated as _Al2O3 ) is 200g/L～400g/L, preferably higher than 250g/L; After chemical pre-desilication treatment, the amount of dissolved and stable silica is 6-25g/L, preferably higher than 8g/L, while the digested alumina from raw materials is less than 20%, preferably low at 8%.

According to the improved Bayer method of the present invention for processing low-grade diaspore bauxite to produce alumina, the desilication in the step 2) is to desilicate the diluted filtrate at 150-170° C. 10h, the seed crystal is red mud or sodium silicate slag or kaolinite; or add red mud or sodium silicate slag or kaolinite at 90~120℃ for 4~8h, add 5~20g/L Calcium oxide, calcium sulfate dihydrate, calcium aluminate, calcium aluminum carbonate, preferably one of hydrotalcites (such as Friedel salt and Kuzel salt), and then desiliconized for 0.5-4 hours; the high-alumina-silicon ratio concentrate obtained by desiliconization The aluminum-silicon ratio is 7-20, preferably 9 or more.

According to the improved Bayer method of the present invention for processing low-grade diaspore bauxite to produce alumina, the seed decomposition conditions in step 3) are decomposition initial temperature of 60-75°C and final decomposition temperature of 40-50°C. °C, the decomposition time is 40-70 hours, preferably 50 hours or more, and the amount of seed crystals added is 50-300 g/L, preferably 150 g/L or more.

According to the improved Bayer method of the present invention for processing low-grade diaspore bauxite to produce alumina, the roasting in step 4) is at 1000-1200° C. for 30 seconds to 30 minutes, preferably more than 10 minutes.

According to the improved Bayer method of the present invention for processing low-grade diaspore bauxite to produce alumina, the temperature of the high-pressure dissolution section in step 5) is 220-280°C, preferably 260-280°C , the pressure is 3-6MPa, the dissolution time is 30-120min, preferably more than 45min, and the amount of concentrate added is 200-400g/L, preferably 250-300g/L or more.

The present invention is different from the prior art. In the prior art, after the bauxite and the leaching solution are in contact for a short time, the desilication product (DSP) precipitates quickly, and the stability of silicon dioxide in the solution is very poor. Not enough time for solid/liquid separation. The technology of the present invention is to contact the low-grade bauxite with a high-concentration sodium aluminate solution containing a stabilizer, so that most of the active silica in the low-grade bauxite can enter the slurry and reach a high concentration, typically 10g /L. In addition, the method of the present invention can stabilize the dissolved silica in the slurry for a period of time, such as more than 2 hours, while avoiding the precipitation and adsorption of DSP on the surface of the bauxite. This allows sufficient time to dissolve the silica and separate the silica-rich sodium aluminate solution and high alumina-silicon ratio (A/S) concentrate from the pulp.

In silica dissolution, the minimization of alumina dissolution is caused by sodium aluminate solutions with high alumina content and low stabilizer content. In the process of dissolving active silica, use the sodium aluminate solution that contains high alumina or close to alumina saturation, this solution limits its ability to dissolve alumina at the leaching temperature proposed by the present invention, thus Ensure that as little alumina as possible is dissolved from bauxite, so as to achieve the purpose of increasing the aluminum-silicon ratio (A/S) of bauxite.

In the traditional Bayer process technology, the solution after high-pressure dissolution is diluted and desiliconized and then enters the crystallization section. The mother liquor after crystallization is evaporated to make up alkali and then used to process the next batch of bauxite, thereby realizing the cycle of the Bayer process. However, in the present invention, the sodium aluminosilicate solution after chemical pre-desilication is diluted and desiliconized and then sent to the crystallization section, and the crystallized mother liquor is evaporated and supplemented with alkali to treat the concentrate obtained after chemical pre-desilication. The leachate enters the chemical pre-desilication section to process the next batch of bauxite. The purpose of this is to use the leachate with high aluminum content for chemical pre-desilication, which meets the conditions of chemical pre-desilication and also realizes Cycle through the entire process.

The key of the method of the present invention lies in the chemical pre-desilication section. In the desiliconization process, a high-concentration sodium aluminate solution containing a small amount of stabilizer is used, which can make low-grade bauxite The active silica (mainly derived from kaolinite in bauxite) dissolves quickly, and the dissolved silica can maintain stability in the slurry for a long time and have enough time for solid/liquid separation to avoid solid/liquid Precipitation of DSP before separation to obtain a bauxite concentrate with a high aluminum-silicon ratio (A/S).

By using high-concentration sodium aluminate solution containing a stabilizer in the present invention to chemically pre-desilicate the bauxite, the dissolved silicon dioxide can be stably present and not precipitate on the surface of the bauxite. After adding the desiliconization seed Afterwards, most of the silicon dioxide in the low-grade bauxite can be successfully removed, and a concentrate with a high aluminum-silicon ratio is obtained, which realizes the application in the low-grade bauxite of the Bayer process; in addition, using the crystallization method of the present invention The final mother liquor is evaporated to supplement alkali and used to treat the concentrate obtained after chemical pre-desilication, and the high-pressure dissolved sodium aluminate solution is returned to the chemical pre-desilication section for the treatment of the next batch of aluminum ore, realizing the perfection of the whole process cycle.

Compared with the prior art method, the technical characteristics of the inventive method are embodied in the following aspects:

1) The method of the present invention adopts the high-concentration sodium aluminate solution to make most of the active silicon dioxide in the low-grade bauxite enter the solution, and 50-85% of the silicon dioxide in the low-grade bauxite is removed.

2) The inventive method has enhanced the stability of silicon dioxide in the slurry by adding a small amount of stabilizing agent in sodium hydroxide solution or sodium aluminate solution, and the silicon dioxide that avoids dissolving changes into desilication product (DSP) and Re-entering the solid phase, solutions with high silica content (6-12 SiO ₂ g/L) are stable for a long enough time, such as more than 2 hours, to ensure solid/liquid separation of the pulp.

3) The method of the present invention can convert low-grade diaspore bauxite (A/S≤5) into high-grade concentrate (A/S≥9), thereby realizing the comprehensive utilization of low-grade bauxite in my country .

4) The present invention can reduce alkali consumption, reduce silicon scaling, and improve the efficiency of reactors, especially pressure cookers.

5) Compared with the existing sintering method, the present invention can significantly reduce energy consumption and improve the quality of the final product alumina.

6) The present invention can also accurately control the desiliconization of the high sodium aluminosilicate solution to obtain a pure siliceous product with a consistent feed composition, which can be further processed for recovery of caustic soda or for other purposes or sales.

Description of drawings

Fig. 1 is the improved Bayer process flow chart of the present invention.

Detailed ways

Example 1

A low-grade diaspore-type bauxite (produced in Jinjiang, see Table 1 for ingredients) was ground and sieved to obtain mineral powder, in which mineral powder with a particle size of less than 0.074mm accounted for 80%, and dissolved in silica Add 100 g of mineral powder obtained after grinding and sieving into the container, and make low-grade diaspore bauxite and sodium aluminate solution containing stabilizer (by NaOH and Al(OH) _Add water to prepare sodium aluminate solution ) 500ml for mixing, wherein, the concentration of the stabilizer in the sodium aluminate solution containing the stabilizer (dipotassium hydrogen phosphate) is 0.1g/L, the concentration of NaOH is 400g/L, and the concentration of Al ₂ O ₃ is 300g/L; Take the temperature as 130°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore bauxite for 6 to 8 hours, and the sodium aluminate solution dissolves 65wt% of the silicon dioxide in the diaspore bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Table 1: Unit wt%

Al ₂ O ₃ SiO _{2 Fe2O3 _} TiO ₂ H ₂ O A/S 60.5 11.9 6.3 2.8 - 5.1

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and obtain a solid concentrate with an aluminum-silicon ratio (A/S) of 9.9 after separation, and the silica content in the resulting filtrate It is 10.12g/L. Take 375ml of filtrate, add 225ml of water, add 20g of CaO to desilicate at 160°C for 3 hours, then separate solid and liquid, and the silicon content index in the filtrate reaches 264.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 60h, and a seed crystal addition amount of 300g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 43.8%. The aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 10 minutes to obtain alumina products.

Evaporate the resulting mother liquor to 300ml and place it in a high-pressure reactor, add 21.37g of NaOH to obtain 78g of concentrate and 5g of CaO, stir and react at 260°C for 2h and then filter. The filter residue was discarded, and the filtrate was sodium aluminate solution. After testing, the concentration of NaOH was 375g/L, the concentration of _Al2O3 was 304g/L, _SiO2 was 0.84g/L, the content of iron _was 12mg/L, and the dissolution rate of aluminum was 89.3 %.

Take 500ml of the above-mentioned high-pressure eluate and mix it with the ground Jinjiang bauxite, and add 0.05g of stabilizer aminotrimethylene phosphonic acid; the leaching temperature is 130°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore type bauxite for 6 to 8 hours, and the sodium aluminate solution dissolves 70wt% of the silicon dioxide in the diaspore type bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into the solid/liquid separator, and obtain a solid concentrate with an aluminum-silicon ratio (A/S) of 11.88 after separation, and the silica content in the resulting filtrate It is 13.05g/L. Take 375ml of filtrate, add 225ml of water, add 20g of Friedel's salt (3CaO·Al ₂ O ₃ ·CaCl ₂ ·10H ₂ O) and desilicate at 120°C for 3 hours. After solid-liquid separation, the silicon content index in the filtrate reaches 228.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 45 hours, and a seed crystal addition amount of 300g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, decomposition rate 42.8.%. Aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 20 minutes to obtain alumina products.

Evaporate the obtained seed separation mother liquor to 300ml, put it in a high-pressure reactor, add 25.82g of NaOH, obtain 78g of concentrate, 5g of CaO, stir and react at 260°C for 2h, and then filter. The filter residue was discarded, and the filtrate was a sodium aluminate solution. After testing, the concentration of NaOH was 342g/L, the concentration of Al ₂ O ₃ was 318g/L, the concentration of SiO ₂ was 0.88g/L, the content of iron was 23mg/L, and the dissolution rate of aluminum was 90.4 %.

Example 2

A low-grade diaspore-type bauxite (sourced from Sanmenxia Cayman Aluminum Co., Ltd., whose composition is shown in Table 2) was ground and sieved to obtain mineral powder, of which the mineral powder with a particle size of less than 0.074mm accounted for 80%. Add 100 g of ore powder obtained after grinding and sieving into the silica dissolution container, and make the low-grade diaspore type bauxite and the sodium aluminate solution containing stabilizer (by NaOH and Al(OH) ₃ add water preparation Obtain sodium aluminate solution) 500ml and mix, wherein, the concentration of stabilizer in the sodium aluminate solution containing stabilizer (aminotrimethylene phosphonic acid) is 0.1g/L, the concentration of NaOH is _400g /L, and the concentration of _Al2O3 It is 300g/L; the leaching temperature is 90°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore type bauxite for 6-8 hours, and the sodium aluminate solution dissolves 72wt% of the silicon dioxide in the diaspore type bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Table 2: Unit wt%

Al ₂ O ₃ SiO _{2 Fe2O3 _} TiO ₂ H ₂ O A/S 62.3 11.47 6.29 2.8 - 5.43

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and obtain a solid concentrate with a aluminum-silicon ratio (A/S) of 11.56 after separation, and the silica content in the resulting filtrate It is 12.12g/L. Take 375ml of filtrate, add 225ml of water, add 20g of CaO and desilicate at 160°C for 3 hours, then separate the solid from the liquid, and the silicon content index in the filtrate reaches 285.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 45h, and a seed crystal addition amount of 400g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 46.5%. Aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 20 minutes to obtain alumina products.

Evaporate the resulting mother liquor to 300ml and place it in a high-pressure reactor, add 18.75g of NaOH to obtain 78g of concentrate and 5g of CaO, stir and react at 260°C for 2h, and then filter. The filter residue was discarded, and the filtrate was a sodium aluminate solution. After testing, _the concentration of NaOH was 382g/L, the concentration of _Al2O3 was 315g/L, the concentration of _SiO2 was 0.92g/L, the content of iron was 18mg/L, and the dissolution rate of aluminum was 91.2 %.

Take 500ml of the above-mentioned high-pressure eluate and mix it with the ground Cayman bauxite, and add 0.05g of stabilizer aminotrimethylene phosphonic acid; the leaching temperature is 90°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore bauxite for 6 to 8 hours, and the sodium aluminate solution dissolves 78wt% of the silicon dioxide in the diaspore bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and obtain a solid concentrate with a aluminum-silicon ratio (A/S) of 12.03 after separation, and the silica content in the resulting filtrate It is 12.78g/L. Take 375ml of the filtrate, add 225ml of water, add 20g of Friedel's salt (3CaO·Al ₂ O ₃ ·CaCl ₂ ·10H ₂ O) and desilicate at 120°C for 3 hours. After solid-liquid separation, the silicon content index in the filtrate reaches 245.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 45h, and a seed crystal addition amount of 350g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 44.5%. Aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 20 minutes to obtain alumina products.

Evaporate the resulting mother liquor to 300ml and place it in a high-pressure reactor, add 22.75g of NaOH to obtain 78g of concentrate and 5g of CaO, stir and react at 260°C for 2.5h, and then filter. The filter residue was discarded, and the filtrate was sodium aluminate solution. After testing, the concentration of NaOH was 375g/L, the concentration of _Al2O3 was 321g/L, _SiO2 was 0.88g/L, the content of iron _was 21mg/L, and the dissolution rate of aluminum was 92.4 %.

Example 3

Grind and sieve low-grade diaspore-type bauxite in a certain place in Guizhou (see Table 3 for composition) to obtain mineral powder, wherein the mineral powder with a particle size of less than 0.074mm accounts for 80%, and put it into the silica dissolution container Add 100g of ore powder obtained after grinding and sieving to make low-grade diaspore bauxite and sodium aluminate solution containing stabilizer (sodium aluminate solution is prepared by adding water to NaOH and Al(OH) ₃ ) 500ml was mixed, wherein, _the concentration of the stabilizer in the sodium aluminate solution containing the stabilizer (sodium ethylenediamine tetramethylene phosphonate) was 0.1g/L, the concentration of NaOH was 400g/L, and the concentration of _Al2O3 was 300g /L; The leaching temperature is 90°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore bauxite for 6 to 8 hours, and the sodium aluminate solution dissolves 78wt% of the silicon dioxide in the diaspore bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Table 3: Unit wt%

Al ₂ O ₃ SiO _{2 Fe2O3 _} TiO ₂ H ₂ O A/S 62.65 13 2.58 2.95 - 4.82

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and obtain a solid concentrate with a aluminum-silicon ratio (A/S) of 10.38 after separation, and the silica content in the resulting filtrate It is 10.24g/L. Take 375ml of the filtrate, add 225ml of water, add 20g of calcium aluminate, desilicate at 160°C for 3 hours, and then separate the solid from the liquid. The silicon content index in the filtrate reaches 235.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 65°C, a decomposition time of 45 hours, and a seed crystal addition amount of 300g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 44.68%. Aluminum hydroxide crystals are washed, dried, and calcined at 1000°C for 30 minutes to obtain alumina products.

Evaporate the obtained seed separation mother liquor to 300ml, put it in a high-pressure reactor, add 24.5g of NaOH, obtain 90g of concentrate, 5g of CaO, stir and react at 240°C for 2h, and then filter. The filter residue was discarded, and the filtrate was sodium aluminate solution. After testing, the concentration of NaOH was 362g/L, the concentration of Al ₂ O ₃ was 298g/L, the concentration of SiO ₂ was 1.14g/L, the content of iron was 17mg/L, and the dissolution rate of aluminum was 88.5 %.

Take 500ml of the above-mentioned high-pressure eluate and mix it with the ground Guizhou bauxite, and add 0.05g of sodium ethylenediamine tetramethylene phosphonate as a stabilizer; the leaching temperature is 90°C. In the silica dissolving container, the sodium aluminate solution soaked the diaspore type bauxite for 8 hours, and the sodium aluminate solution dissolved and stabilized 82wt% of the silicon dioxide in the diaspore type bauxite In the slurry, there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite to obtain a slurry with dissolved silicon dioxide.

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and obtain a solid concentrate with a aluminum-silicon ratio (A/S) of 11.58 after separation, and the silica content in the resulting filtrate It is 12.15g/L. Take 375ml of the filtrate, add 225ml of water, add 20g of calcium aluminate, desilicate at 170°C for 3 hours, and then separate the solid from the liquid. The silicon content index in the filtrate reaches 245.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 45 hours, and a seed crystal addition amount of 320g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 45.2%. Aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 20 minutes to obtain alumina products.

Evaporate the obtained seed separation mother liquor to 300ml, put it in a high-pressure reactor, add 24.82g of NaOH, obtain 78g of concentrate, 5g of CaO, stir and react at 280°C for 2h, and then filter. The filter residue was discarded, and the filtrate was a sodium aluminate solution. After testing, the concentration of NaOH was 372g/L, the concentration of Al ₂ O ₃ was 338g/L, the concentration of SiO ₂ was 0.74g/L, the content of iron was 18mg/L, and the dissolution rate of aluminum was 93.1 %.

Example 4

Grind and sieve the low-grade diaspore-type bauxite in Yangquan, Shanxi (see Table 4 for the composition) to obtain mineral powder, wherein the mineral powder with a particle size of less than 0.074mm accounts for 80%, and put it into the silica dissolution container Add 100g of mineral powder obtained after grinding and sieving, and make 500ml of low-grade diaspore bauxite and sodium aluminate solution containing stabilizer (prepared by adding water to NaOH and Al(OH) ₃ ) Mixing, wherein, the concentration of the stabilizer in the sodium aluminate solution containing the stabilizer (polyol phosphate) is 0.1g/L, the concentration of NaOH is 400g/L, and the concentration of _Al2O3 is 300g/L; the leaching _temperature is 100°C. In the silica dissolving container, the sodium aluminate solution soaks the diaspore bauxite for 6 to 8 hours, and the sodium aluminate solution dissolves 68wt% of the silicon dioxide in the diaspore bauxite And it is stable in the slurry, and there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite, and a slurry with silicon dioxide dissolved is obtained.

Table 4: Unit wt%

Al ₂ O ₃ SiO _{2 Fe2O3 _} TiO ₂ H ₂ O A/S 60.34 17.16 5.61 2.15 - 3.5

Pass the silica-dissolved slurry discharged from the silica dissolving vessel into a solid/liquid separator, and after separation, obtain a solid concentrate with an aluminum-silicon ratio (A/S) of 9.12, and the silica content in the resulting filtrate It is 10.04g/L. Take 375ml of filtrate, add 225ml of water, add 20g of CaO to desilicate at 170°C for 3 hours, then separate solid and liquid, and the silicon content index in the filtrate reaches 218.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 65°C, a decomposition time of 50h, and a seed crystal addition amount of 300g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 47.68%. The aluminum hydroxide crystals are washed, dried, and calcined at 1100°C for 10 minutes to obtain alumina products.

Evaporate the resulting mother liquor to 300ml and place it in a high-pressure reactor, add 27.5g of NaOH, 90g of the obtained concentrate, 5g of CaO, stir and react at 250°C for 2h, and then filter. The filter residue was discarded, and the filtrate was sodium aluminate solution. After testing, the concentration of NaOH was 382g/L, the concentration of _Al2O3 was 302g/L, the concentration of _SiO2 was 1.02g/L, the content of iron _was 21mg/L, and the dissolution rate of aluminum was 91.2 %.

Take 500ml of the above-mentioned high-pressure eluate and mix it with the ground Shanxi Yangquan bauxite, and add 0.05g of stabilizer polyol phosphate; the leaching temperature is 100°C. In the silica dissolving container, soak the diaspore type bauxite in sodium aluminate solution for 7 hours, and the sodium aluminate solution dissolves and stabilizes 65wt% of the silicon dioxide in the diaspore type bauxite In the slurry, there is no obvious precipitation and adsorption of sodium aluminum silicate (DSP) on the surface of the raw material diaspore-type bauxite to obtain a slurry with dissolved silicon dioxide.

Pass the silica-dissolved slurry discharged from the silica dissolving container into a solid/liquid separator, and obtain a solid concentrate with a aluminum-silicon ratio (A/S) of 9.95 after separation, and the silica content in the resulting filtrate It is 10.72g/L. Take 375ml of the filtrate, add 225ml of water, add 20g of calcium aluminate, desilicate at 160°C for 3 hours, and then separate the solid from the liquid. The silicon content index in the filtrate reaches 224.

Take 500ml of the desiliconized sodium aluminate solution and add aluminum hydroxide seed crystals, decompose the seeds at a decomposition temperature of 60°C, a decomposition time of 45h, and a seed crystal addition amount of 350g/L to obtain white aluminum hydroxide crystals and seed separation mother liquor About 450ml, the decomposition rate is 46.8%. The aluminum hydroxide crystals are washed, dried, and calcined at 1050°C for 30 minutes to obtain alumina products.

Evaporate the obtained seed separation mother liquor to 300ml, put it in a high-pressure reactor, add 28.16g of NaOH, obtain 78g of concentrate, 5g of CaO, stir and react at 260°C for 2h, and then filter. The filter residue was discarded, and the filtrate was sodium aluminate solution. After testing, the concentration of NaOH was 366g/L, the concentration of _Al2O3 was 313g/L, _SiO2 was 0.94g/L, the content of iron _was 23mg/L, and the dissolution rate of aluminum was 90.8 %.

Claims (11)

1. A method for improving the Bayer process to process low-grade diaspore type bauxite to produce alumina, characterized in that the method may further comprise the steps: 1) Chemical pre-desilication: immerse the low-grade diaspore bauxite with a particle size of less than 0.098 mm in a sodium aluminate solution containing a stabilizer, and contact it to make the diaspore bauxite in the Active silica is dissolved and stabilized in the slurry to obtain a slurry with silica dissolved; 2) Desiliconization of high-aluminosilicate sodium solution: filter the slurry obtained in step 1) to obtain sodium aluminate solution with high silicon content and high-aluminum-silicon ratio concentrate, dilute the sodium aluminate solution and add desiliconization seeds to carry out Desiliconization to obtain a sodium aluminate solution, washing the high-aluminum-silicon ratio concentrate, and washing water as a diluent for high-aluminosilicate sodium; 3) Seed separation of sodium aluminate solution: add the desiliconized sodium aluminate solution obtained in step 2) to aluminum hydroxide seed crystals for seed decomposition, obtain aluminum hydroxide coarse crystals and seed separation mother liquor after separation, and fully crystallize hydrogen Alumina, after washing, recovering the aluminum oxide and sodium oxide attached to the aluminum hydroxide, the finished product of aluminum hydroxide is obtained, and the washing liquid is returned to the seed separation mother liquor; 4) Aluminum hydroxide roasting: roasting the aluminum hydroxide finished product obtained in step 3) to obtain an alumina product; 5) High-pressure stripping: the seed separation mother liquor obtained in step 3) is evaporated and supplemented with alkali for high-pressure stripping of the concentrate obtained in step 2), and the stripping solution is filtered and separated to obtain sodium aluminate solution and red mud. The sodium solution is used to process the next batch of bauxite after adding a stabilizer, and steps 1) to 4) are repeated. The red mud is washed and enters the red mud yard, and the washing liquid is returned to step 2) for high aluminosilicate sodium dilution; The stabilizer in the step 1) is one of dipotassium hydrogen phosphate, aminotrimethylene phosphonic acid, sodium ethylenediamine tetramethylene phosphonate and polyol phosphate, and the concentration is less than or equal to 0.1 g/L. 2. the improved Bayer process according to claim 1 processes low-grade diaspore type bauxite to produce the method for alumina, it is characterized in that, described step 1) low-grade diaspore type aluminum The contact temperature between soil ore and sodium aluminate solution containing stabilizer is 70-130°C, and the contact time is 2-10 hours. 3. the improved Bayer process according to claim 2 processes the method for low-grade diaspore type bauxite to produce alumina, is characterized in that, described step 1) middle and low grade diaspore type aluminum The contact temperature between soil ore and sodium aluminate solution containing stabilizer is 80-105°C, and the contact time is 4-8h. 4. the improved Bayer method according to claim 1 processes the method for producing alumina from low-grade diaspore type bauxite, it is characterized in that, the addition of bauxite in described step 1) is 100～ 400g/L, the concentration of sodium hydroxide in the sodium aluminate solution is 200g/L-500g/L, and the concentration of alumina is 200g/L-400g/L. 5. the improved Bayer process according to claim 4 processes low-grade diaspore type bauxite and produces the method for alumina, it is characterized in that, described step 1) in the addition of bauxite is 200～ 300g/L, the concentration of sodium hydroxide in the sodium aluminate solution is greater than 300g/L, and the concentration of alumina is greater than 250g/L. 6. the improved Bayer method according to claim 1 processes the method for producing alumina from low-grade diaspore type bauxite, it is characterized in that, the desilication in described step 2) is to dilute filtrate in Desiliconization at 150-170°C for 4-10 hours, with red mud, sodium silicate slag or kaolinite as the seed crystal; Add 5 to 20 g/L of calcium oxide, calcium sulfate dihydrate, calcium aluminate, calcium carbonoaluminate or hydrotalcite at low temperature and desilicate for 0.5 to 4 hours. 7. the improved Bayer process according to claim 1 processes low-grade diaspore type bauxite and produces the method for alumina, it is characterized in that, described step 3) in seed decomposition condition is decomposition initial temperature 60～ 75°C, the final decomposition temperature is 40-50°C, the decomposition time is 40-70h, and the amount of seed crystals added is 50-300g/L. 8. the improved Bayer process according to claim 7 processes the method for producing alumina from low-grade diaspore type bauxite, it is characterized in that, in described step 3), the seed decomposition condition is greater than 50h, and seed crystals are added The amount is greater than 150g/L. 9. The improved Bayer method according to claim 1 for processing low-grade diaspore bauxite to produce alumina, characterized in that the roasting in step 4) is roasting at 1000-1200°C 30s～30min. 10. The improved Bayer method according to claim 1 for processing low-grade diaspore bauxite to produce alumina, characterized in that the temperature of the high-pressure dissolution section in step 5) is 220 to 280 ℃, pressure 3-6MPa, dissolution time 30-120min, concentrate addition 200-400g/L. 11. The improved Bayer method according to claim 10 for processing low-grade diaspore bauxite to produce alumina, characterized in that the temperature of the high-pressure dissolution section in step 5) is 260-280 ℃, the pressure is 5-6MPa, the dissolution time is more than 45min, and the amount of concentrate added is 250-300g/L.

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