RU2774385C1 - Method for processing boxite to obtain alumina - Google Patents

Abstract

FIELD: non-ferrous metallurgy.

SUBSTANCE: invention relates to non-ferrous metallurgy, namely to the processing of bauxite to obtain alumina. The method includes filtration of alumina production slurry formed after bauxite leaching. The pulp after leaching, dilution or thickening is filtered at a temperature of at least 95°C to obtain a filtrate - an aluminate solution after filtration, and a solid phase of red mud, after which the solid phase of red mud is washed on filtering equipment. Washing is carried out with hot water, preferably at a temperature not exceeding 98°C. To achieve the specified concentrations of the aluminate solution and the liquid phase of the red mud, the said filtrate is sent for control filtration and/or decomposition. Water after red mud washing is supplied to dilute the pulp after bauxite leaching and/or dilute the said filtrate until a predetermined concentration of aluminate solution is reached, while the resulting cake is a final product.

EFFECT: method allows to increase productivity at the decomposition stage and reduce the loss of soda products with an increase in the output of commercial metallurgical alumina.

8 cl, 3 dwg, 6 ex

Description

Technical field

The invention relates to non-ferrous metallurgy, in particular, to the production of alumina by the Bayer or Bayer sintering method, and in particular, to methods for increasing the productivity of aluminate solutions due to the effective separation and washing of slurry suspensions.

State of the art

The high productivity of the solution during decomposition makes it possible to withstand low specific flows of the aluminate solution, which ensures a low level of consumption of the main fuel and energy resources (FER) for the production of alumina. The productivity of the solution achieved today is due to the accepted classical technology for thickening and washing red mud in volumetric devices. This technology does not allow to increase the concentration of the aluminate solution, and, accordingly, its productivity, without increasing the loss of alkali with the liquid phase of the waste red mud. In addition, significant volumes of solutions are required for settling and washing red mud, which leads to prolonged contact of the solid and liquid phases and the hydrolysis process (losses of alumina with red mud).

The problem of efficient separation and washing of slurry suspensions and increasing the productivity of aluminate solutions has been solved in a number of technical solutions.

A known method for filtering slurry slurries in the "tail" of alumina production (Abhijeet Bandi, Kausikisaran Misra, N. Nagesh, Uttam Kumar Giri and Rama Chandra Nahak Improvement of Mud Circuit Efficiency while Processing East Coast Bauxite of India, Proceedings of the 38th International ICSOBA Conference, November 16-18, 2020), which consists in filtering the suspension of waste sludge for the purpose of its dry storage on the sludge floor.

The disadvantages of this method include:

- the impossibility of exclusion from the technological chain of red mud thickening and washing;

- no effect on the productivity of aluminate solutions;

- the absence of significant savings in resources and energy consumption in the production of alumina.

A known method for filtering slurry suspensions in the "tail" of alumina production (Sedat Arslan, Gökhan Kürsat Demir, Bekir Çelikel and Meral Baygül Implementation and Optimization of Filter Press in Red Mud Washing Process at Eti Aluminium, Proceedings of the 36th International ICSOBA Conference, Belem, Brazil , 29 October - 1 November 2018), which consists in filtering the suspension of waste sludge for the purpose of its dry storage on the sludge sludge.

The disadvantages of this method include the same problems as in the first example.

A known method for increasing the productivity of aluminate solutions (Lu Zijian, Zhaoqun, Xie yanli, Bi shiwen, Yang Yihong, USE OF ADDITIVES IN THE DECOMPOSITION OF ALKALINE ALUMINATE SOLUTIONS IN THE BAYER PROCESS, Light Metals, TMS The Minerals, Metals & Materials Society, 2004). Options for increasing the efficiency of the decomposition process by introducing various additives into the process are proposed. Additives affect not only productivity, but also the fineness and quality of the resulting aluminum hydroxide.

The disadvantages of this method include:

- the impossibility with this method of exclusion from the technological chain of red mud thickening and washing;

- the use of additives leads to additional contamination of solutions with organic or inorganic impurities, requiring a decision on their removal;

- lack of economy of soda products and flocculant;

- the need to use expensive reagents.

Closest to the claimed method is a method of processing low-quality bauxite into alumina (patent KZ No. 13802, publ. 15.12.2003). In the method, the filtration of red mud is carried out immediately after thickening in several stages. The filtered sludge of each stage is repulped with the filtrate of the subsequent stages of filtration, the repulped sludge is heated to a temperature not exceeding 95°C, and hot water is supplied to the last stage in an amount that ensures, at the first stage, the concentration of the red mud pulp in terms of caustic alkali (Na ₂ O _ky ) is not higher than 135 g/l, and the filtration is carried out at a caustic modulus not lower than the caustic modulus corresponding to the equilibrium aluminate solution. The number of filtration stages is determined by the residual alkali content in the liquid phase of the filtered red mud of the last stage. The method allows to reduce the specific consumption of hot water for red mud washing, to reduce the loss of aluminum hydroxide, alkali and flocculant consumption. Production areas are also freed up at the red mud separation stage.

The disadvantages of this method are that:

- the scheme contains several stages of filtration, which increases by several times the amount of equipment required for the implementation of the process;

- low degree of sludge washing with filtrates of subsequent stages, which reduces the efficiency of the process and increases the loss of alkalis;

- in the technological chain there is a redistribution of thickening, which does not allow to completely eliminate the loss of alumina with the solid phase due to the hydrolysis process, as well as completely abandon the consumption of flocculants;

- the possibility of achieving a solution concentration not higher than 135 g/l Na ₂ O _to that is not the optimal parameter to achieve maximum productivity of the solution;

- relatively low filtration temperature not higher than 95°C, leading to additional losses of alumina from the solution due to the hydrolysis process and low fabric durability.

Disclosure of the essence of the invention

The proposed invention is based on the task of developing a cost-effective method for increasing the productivity of aluminate solutions in the production of alumina from bauxite, which makes it possible to increase the productivity of aluminate solution by increasing its concentration and reducing the caustic modulus. Increasing the concentration and reducing the caustic modulus is achieved by replacing the operations of thickening and washing of red mud with filtration and washing on filtering equipment, while reducing the specific consumption of hot water for washing the sludge. The aluminate solution obtained in this way with an increased concentration and a reduced caustic modulus is processed according to the existing scheme for the production of alumina. Also, with this method, there is a significant reduction in soluble losses of alumina and alkali with the liquid phase of the sludge.

The technical result is to solve the problem and increase productivity at the stage of decomposition and reduce losses of soda products and, as a result, increase the efficiency of alumina production by saving soda products, heat and energy resources, as well as increasing the output of commercial metallurgical alumina.

The achievement of the above technical result is achieved by the fact that the method of processing bauxite to obtain alumina includes filtration of sludge suspensions (pulp after bauxite leaching, diluted, thickened), which is performed on filtering equipment for the fastest separation of solid and liquid phases. The filtrate - aluminate solution is then fed to the control filtration unit to remove solid phase residues, while part of the filtrate, upon reaching the specified quality in terms of solid particles content, can be sent directly to decomposition. After control filtration, the solution is sent to the decomposition stage to extract aluminum hydroxide from it. After the filtration operation, the resulting cake is washed in the clamped layer on the filter with hot water at a temperature preferably not more than 98°C to wash the solid phase of the sludge from the solution. Rinse water from the sludge washing is supplied to dilute the pulp after bauxite leaching to achieve the specified concentration of aluminate solution. Filter cake is a dump product suitable for storage in a sludge field in a dry, semi-dry or wet way.

The proposed method of the so-called "direct filtration" of sludge suspensions will reduce the loss of alumina by eliminating the hydrolysis of the aluminate solution in the thickening-flushing system, reduce the consumption of hot water for washing, which, with a high coefficient of sludge washing, will increase the concentration of the aluminate solution, reduce the caustic modulus and increase it productivity. Increasing fluid productivity will reduce the specific fluid fluxes per tonne of alumina produced, which will increase the throughput of alumina production and reduce the cost of basic technical and economic indicators (TEI).

The introduction of technology will provide a number of advantages:

- replace two operations: thickening and washing of red mud in the existing capacitive equipment with one - filtration and washing in filtering equipment, which will reduce the loss of alumina due to hydrolysis;

- to reduce the soluble losses of alkali and alumina with the liquid phase of the waste sludge from the current level by 60-75% by reducing the amount of moisture in the waste sludge and returning filtrates obtained in the process of cake washing to the alumina production;

- reduce heat consumption for mother liquor evaporation by increasing the concentration of aluminate solution, reduce fuel consumption at the sintering stage by increasing the proportion of the Bayer branch, and reduce or completely eliminate the consumption of flocculants by eliminating their supply to the thickening and washing stages;

- to reduce the consumption of electricity and compressed air by reducing the specific flows of the solution in decomposition and evaporation, reducing the share of the sintering process (as a special case in the production of alumina by the Bayer-sintering method) and replacing capacitive and pumping equipment in the thickening-washing stages with press filters.

The method is complemented by special cases of its execution.

So, as a pulp for filtration, a pulp obtained after leaching of bauxite is used. The filtrate is sent to collection mixers for mixing with the wash water from the sludge washing, the mixed solution is then sent to the control filtration of the solution, while part of the strong filtrate, upon reaching the specified quality in terms of solids content, can be sent directly to decomposition after dilution with water. The filter cake is washed with hot water in a pinched bed. After washing the cake, the industrial water is sent to the mixers to dilute the filtrate. The washed cake is repulped with water and pumped out to the sludge field, or stored in the form of a cake in a dry or semi-dry way.

Thus, thickened pulp obtained after thickening the dilute pulp is used as a pulp for filtration. The drain of the thickeners is directed to the control filtration of the solution. The filtrate is sent to the collection mixers and then to the control filtration of the solution, while part of the filtrate, upon reaching the specified quality in terms of the content of solid particles, can be sent directly to the decomposition. The filter cake is washed with hot water in a pinched bed. After washing the cake, the industrial water is sent to agitators (dilution mixers) to obtain a diluted pulp. The washed cake is repulped with water and pumped out to the sludge field, or stored in the form of a cake in a dry or semi-dry way.

Brief description of the drawings

In FIG. Figures 1, 2, 3 show options for the process flow diagrams for obtaining alumina during bauxite processing.

The differences between the variants of the schemes are in the nature of the filtered pulp.

The hardware-technological scheme of filtration and washing of the diluted pulp is shown in Fig. one.

Source for filtration - dilute pulp, obtained by leaching raw pulp. Obtained in the process of raw pulp leaching - the pulp after bauxite leaching is diluted with industrial waters formed during cake washing with water. The pulp is fed to filtration to separate and wash the solid phase. The temperature of the initial diluted pulp entering the pressure filters is preferably up to 110°C, the content of solid particles in the pulp is about 40-110.0 kg/m ³ .

The filtrate (aluminate solution) is sent to the control solution filtration unit to remove solid particles. With the appropriate quality (the content of Fe ₂ O ₃ is not more than 0.016 g/dm ³ ), part of the filtrate can be transferred directly to the decomposition, bypassing the control filtration.

The red mud cake obtained during the filtration process is washed with water from the aluminate solution (specific water consumption is not less than 2.0 m ³ /t of dry mud). The hot water temperature is preferably not more than 98°C. Rinse water (prom water) obtained at the cake washing stage is used to dilute the pulp after bauxite leaching. The washed red mud with a moisture content of W 25-30% is supplied for repulpation with water returned from the sludge field and is then pumped out in the form of a pulp, or in the form of a cake, and is also sent to the sludge field.

The hardware-technological scheme of pulp filtration and washing after bauxite leaching is shown in Fig. 2.

The initial pulp for filtration is obtained by leaching raw pulp. The pulp obtained in the process of leaching the raw pulp after leaching is fed to filtration to separate and wash the solid phase. The temperature of the initial pulp after leaching of bauxite entering the press filters is up to 120°C, the content of solid particles in the pulp is about 50-180.0 kg/m ³ . The filtrate (strong aluminate solution) is sent for dilution with washing water to obtain a given concentration of the solution. The resulting aluminate solution is fed to the control filtration unit of the solution for purification from solid particles. With the appropriate quality (Fe ₂ O ₃ content is not more than 0.016 g/dm ³ ), a part of the filtrate can be transferred for dilution to obtain a given concentration and then sent to decomposition, bypassing control filtration.

The red mud cake obtained in the process of filtration is washed with water from the aluminate solution (specific water consumption of the order of at least 2.0 m ³ /t of dry mud). The hot water temperature is preferably not more than 98°C. Wash water obtained at the cake washing stage is directed to dilute the strong aluminate solution. Washed red mud with moisture W 25-30% is repulped with water returned from the sludge field, and then pumped out in the form of a pulp, or in the form of a cake, and is also sent to the sludge field.

The hardware-technological scheme for filtering and washing the thickened pulp is shown in Fig. 3.

The thickened pulp initial for filtration is obtained by leaching raw pulp. The pulp obtained after leaching of the raw pulp after leaching is diluted with industrial waters formed during the washing of the cake with water. The diluted pulp thickens. The thickening process produces two products: a clarified solution and a thickened pulp. The clarified solution is sent to the control filtration unit of the solution for cleaning from solid particles. The thickened slurry is fed to filtration to separate and wash the solid phase. The temperature of the initial thickened pulp entering the press filters is about 100-105°C, the content of solid particles in the pulp is 400-800 kg/m ³ .

The filtrate (aluminate solution) is sent to the control solution filtration unit to remove solid particles.

The red mud cake obtained in the process of filtration is washed with water from the aluminate solution (specific water consumption of the order of at least 2.0 m ³ /t of dry mud). The hot water temperature is preferably not more than 98°C. Rinse water obtained at the cake washing stage is used to dilute the pulp after leaching. The washed red mud with moisture (moisture content) W 25-30% is supplied for repulping with water returned from the sludge field and then pumped out in the form of a pulp or in the form of a cake is also sent to the sludge field.

Implementation of the invention

The method is designed to produce alumina during bauxite processing by high-speed separation and washing of alumina production sludge suspensions formed after bauxite leaching. Filtration of sludge suspensions (pulp after bauxite leaching, diluted, thickened) is carried out on filtering equipment at a temperature of at least 95°C, preferably 95-120°C. Washing of the resulting cake is carried out on the filter at a water temperature of not more than 98°C at a specific hot water consumption of at least 2.0 m ³ /t of sludge.

Particular cases in hardware design are the use of the following filtering equipment: centrifuges, press filters, hyperbaric filters, belt press filters.

The filtrate obtained at the pulp filtration stage is sent to an additional purification operation - control filtration, or immediately to decomposition. Rinsing water from the washing operation is used either to dilute the feed pulp or to dilute the filtrate to achieve the desired concentration of aluminate solution. The filter cake after the washing stage is either repulped and pumped to the sludge field, or transported in dry form to the sludge field for dry storage.

Thus, the proposed method for producing alumina from bauxite provides a high rate of separation and washing of suspensions, which makes it possible to increase the concentration of the aluminate solution, reduce the soluble losses of alumina and alkali, which increases the efficiency of alumina production.

The proposed method is illustrated by the following examples.

Example 1

The pulp after bauxite leaching was diluted with washing water after washing the sludge on the filter. The pulp was diluted with washing water to a concentration of the liquid phase in terms of caustic alkali of 160 g/l, while the caustic modulus of the solution was 1.73 (unchanged relative to the base case). The resulting diluted pulp was filtered at a pressure of 8 atm. and a temperature of 105°C, while receiving the filtrate and cake. The cake was washed with hot water at a temperature of 80°C. The amount of hot water for washing was supplied based on obtaining a filtrate concentration of 160 g/l Na ₂ O _ku . The reduction in the loss of soluble alumina and alkali amounted to 64 wt. %. The filtrate (aluminate solution) was subjected to decomposition, while the productivity of the solution increased by 5.0 kg/m ³ .

Example 2

The pulp after bauxite leaching was filtered at a pressure of 8 atm. and a temperature of 120°C, while receiving the filtrate and cake. The cake was washed with hot water at a temperature of 98°C. The amount of hot water for washing was supplied based on obtaining the concentration of the mixture of the pulp filtrate after leaching and washing water from washing the cake 160 g/l in caustic alkali, while the caustic modulus of the solution was 1.68 (with a decrease of 0.05 units relative to the base option). The reduction in the loss of soluble alumina and alkali amounted to 69 wt. %. The mixture of filtrate and washing water (aluminate solution) was subjected to decomposition, while the productivity of the solution increased by 15.0 kg/m ³ .

Example 3

The pulp after leaching of bauxite was diluted with washing water after washing the sludge on the filter in the clamped layer. The pulp was diluted with washing water to a concentration of the liquid phase in terms of caustic alkali of 160 g/l, while the caustic modulus of the liquid phase was 1.68 (with a decrease of 0.05 units relative to the base case). The resulting dilute pulp was thickened. The clarified part was separated from the thickened part. The resulting thickened pulp was filtered at a pressure of 8 atm. and a temperature of 95°C, while receiving the filtrate and cake. The cake was washed with hot water at a temperature of 95°C. The amount of hot water for washing was supplied based on obtaining a dilute pulp concentration of 160 g/l Na ₂ O _ku . In this case, the caustic modulus of the solution was - 1.68, which indicates the absence of losses of alumina with hydrolysis. The reduction in the loss of soluble alumina and alkali amounted to 61 wt. %. The filtrate and the clarified part after thickening the diluted pulp were combined and subjected to decomposition, while the productivity of the solution increased by 12.4 kg/m ³ .

Example 4

The pulp after leaching of bauxite was diluted with washing water after washing the sludge on the filter. The pulp was diluted with washing water to a concentration of the liquid phase in terms of caustic alkali of 160 g/l, while the caustic modulus of the solution was 1.65. The resulting diluted pulp was filtered at a pressure of 6 atm. and a temperature of 105°C, while receiving the filtrate and cake. The cake was washed with hot water at a temperature of 90°C. The amount of hot water for washing was supplied based on obtaining the concentration of the filter filtrate 160 g/l Na ₂ O _ku . The reduction in the loss of soluble alumina and alkali amounted to 59 wt. %. The filtrate (aluminate solution) was subjected to decomposition, while the productivity of the solution increased by 12.0 kg/m ³ .

Example 5

The pulp after bauxite leaching was diluted with washing water after washing the sludge in a centrifuge. The pulp was diluted to a concentration of the liquid phase in terms of caustic alkali of 160 g/l, while the caustic modulus of the liquid phase was 1.65. The resulting dilute pulp was thickened in thickeners, where the clarified part was separated from the thickened part. The resulting thickened pulp was centrifuged at a temperature of 95°C, while receiving centrate and cake. The cake was washed with hot water at a temperature of 95°C. The amount of hot water for washing was supplied based on obtaining a dilute pulp concentration of 160 g/l Na ₂ O _ku . In this case, the caustic modulus of the solution was - 1.65, which indicates the absence of losses of alumina with hydrolysis. The reduction in the loss of soluble alumina and alkali amounted to 60 wt. %. The centrifuge centrifuge and the clarified part after thickening the diluted pulp were combined, filtered on the control filtration and then subjected to decomposition, while the productivity of the solution increased by 13.5 kg/m ³ .

Example 6

The pulp after leaching of bauxite was diluted with washing water after washing the sludge on the filter in the clamped layer. The pulp was diluted with washing water to a concentration of the liquid phase in terms of caustic alkali of 160 g/l, while the caustic modulus of the liquid phase was 1.64 (with a decrease of 0.09 units relative to the base case). The resulting dilute pulp was thickened. The clarified part was separated from the thickened part. The resulting thickened pulp was filtered at a pressure of 3 atm. and a temperature of 95°C, while receiving the filtrate and cake. The cake was washed with hot water at a temperature of 98°C. The amount of hot water for washing was supplied based on obtaining a dilute pulp concentration of 160 g/l Na ₂ O _ku . In this case, the caustic modulus of the solution was - 1.64, which indicates the absence of losses of alumina with hydrolysis. The reduction in the loss of soluble alumina and alkali amounted to 57 wt. %. The filtrate and the clarified part after thickening the diluted pulp were combined, filtered on the control filtration and subjected to decomposition, while the productivity of the solution increased by 14.4 kg/m ³ .

Thus, the proposed method for increasing the productivity of aluminate solutions using filtration and washing technology provides not only effective cleaning of sludge from soluble alkali and alumina, but also increases the productivity of aluminate solutions by increasing their concentration and reducing the caustic modulus. Thus, the achieved productivity of the aluminate solution is 5-15 kg/m ³ higher than from the solution obtained in the standard way.

As a general example, the method includes milling bauxite on a recycled solution, leaching it, diluting the pulp after bauxite leaching, desiliconizing the aluminate solution, thickening and/or filtering and washing the red mud suspension, separating aluminum hydroxide from the aluminate solution, followed by its separation from the mother liquor, washing and calcination, sintering red mud and/or bauxite with soda and limestone, leaching the resulting sinter, thickening and/or filtering and washing the leached sinter pulp to obtain an aluminate solution and its subsequent desiliconization and decomposition, while filtering the red mud and leached sinter pulp carried out immediately before or after thickening. The filtered sludge is washed with hot water directly on the filtering equipment in an amount that provides the necessary concentrations of the aluminate solution and the liquid phase of the cake, which is the final product, and the filtration is carried out at a caustic modulus not lower than the caustic modulus corresponding to the equilibrium aluminate solution. The method allows to increase the productivity of the aluminate solution, reduce the heat consumption for evaporation of solutions, the loss of aluminum hydroxide and alkali with red mud, and also reduce the consumption of flocculant, compressed air and electricity. The proposed method provides for the simultaneous implementation of two technological processes - pulp filtration and washing on the same equipment. In the production of alumina, several pulps are successively obtained: the first of them is the pulp after bauxite leaching, from this pulp, diluted pulp is obtained by dilution with industrial water. Thickened pulp is obtained from the diluted pulp by thickening. Depending on the type of pulp, the proposed schemes for obtaining alumina are used. For each plant, the concentration of aluminate solution is different and depends on the maximum level of productivity achieved at the stage of decomposition. For example, for UAZ solutions this range is in the range of 160-170 g/l for Na ₂ Ok.

Claims (8)

1. A method for processing bauxite to produce alumina, including filtering the alumina production pulp formed after bauxite leaching, in which the pulp after leaching, dilution or thickening is filtered at a temperature of at least 95 ° C to obtain a filtrate - an aluminate solution after filtration, and a red solid phase sludge, after which the solid phase of the red mud is washed on filtering equipment, while washing is carried out with hot water, preferably at a temperature of not more than 98 ° C, to achieve the specified concentrations of the aluminate solution and the liquid phase of the red mud, the said filtrate is sent for control filtration and / or for decomposition, and water after washing the red mud is fed to dilute the pulp after bauxite leaching and/or dilute the said filtrate until the specified concentration of the aluminate solution is reached, while the resulting cake is a final product. 2. The method according to p. 1, characterized in that the pulp is filtered after bauxite leaching, and the resulting cake is washed with hot water. 3. The method according to p. 1, characterized in that the pulp is filtered after dilution of the pulp from the leaching of bauxite, and the resulting cake is washed with hot water. 4. The method according to p. 1, characterized in that the thickened pulp is filtered after the thickening of the diluted pulp, and the resulting cake is washed with hot water. 5. The method according to p. 1, characterized in that the filtration is carried out preferably at a temperature of 95-120°C. 6. The method according to p. 1, characterized in that the washing of red mud is carried out at a specific consumption of hot water of at least 2.0 m ³ / t of mud. 7. The method according to claim 1, characterized in that press filters, centrifuges, belt press filters, hyperbaric filters are alternatively used to filter and wash the sludge. 8. The method according to p. 1, characterized in that the said filtrate is sent directly to the decomposition, bypassing the control filtration.

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