Preparation and adding method of sodium aluminate solution fine filter aid

Abstract

The application belongs to the technical field of alumina production and specifically relates to a preparation method of a sodium aluminate solution fine filtration filter aid, which uses lime or lime milk, a sodium aluminate solution and ethanol or methanol as raw materials, and the ratio of the raw materials is as follows: 1 part of lime or lime milk, 2-20 parts of the sodium aluminate solution, 0.02-0.2 parts of ethanol or 0.01-0.1 parts of methanol, the concentration of the sodium aluminate solution is 100-300 g / L of Na2O and 50-220 g / L of Al2O3, the sodium aluminate solution fine filtration filter aid is prepared under the conditions of a reaction temperature of 25-105 DEG C and a reaction time of 5-240 minutes. The application has the following effects: the use amount of the lime milk for filtration can be greatly reduced, and the loss of alumina, steam consumption, water consumption and power consumption caused by the large use amount of the lime milk can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of alumina production technology and relates to a method for preparing and adding a sodium aluminate solution fine filtration aid. Background Technology

[0002] Fine filtration of sodium aluminate solution is one of the main processes in the alumina industrial production. Its function is to further remove suspended solids from the overflow of the red mud separation settling tank (i.e., crude sodium aluminate solution) through filtration, so that the suspended solids content in the purified solution obtained after filtration is controlled below 15 mg / L (suspended solids content before filtration: 150-300 mg / L), ensuring that the impurity content in the final product, alumina, is lower than the standard requirements. To improve filtration efficiency, a filter aid needs to be added during the filtration of crude sodium aluminate solution. The filter aid helps to quickly form a filter layer on the filter cloth surface, effectively preventing suspended solids from passing through, while slowing down the rate of increase in liquid resistance. Currently, the filter aid mainly used in alumina plants is lime slurry, requiring the addition of 20 kg of lime per ton of alumina product.

[0003] While existing domestic filter aid addition processes can meet filtration requirements and the suspended solids in the filtrate can also meet the specifications, they have the following four main problems:

[0004] (1) The consumption of lime milk is large. During the filtration operation, lime milk is added to the crude sodium aluminate solution as a filter aid. However, the filter aid only plays a major role during the filter cloth circulation period. After entering the normal filtration and purification period, the filter aid and floating matter attached to the filter cloth in the early stage can meet the needs of blocking the floating matter from passing through the filter medium. Continuing to add lime milk will have a limited effect on the filter aid and will instead increase the unnecessary consumption of lime.

[0005] (2) Alumina loss: The lime slurry added to the process reacts with alumina, causing alumina loss, which can be direct or indirect. Direct reaction loss refers to the lime entering the alumina production process reacting with alumina to form hydrated garnet, which is then discharged from the production system along with the red mud. Therefore, the more lime slurry added, the more alumina is lost.

[0006] Al2O3+3Ca(OH)2+3H2O→3CaO·Al2O3·6H2O

[0007] The filter residue produced by leaf filtration will promote hydrolysis of the solution and cause loss of alumina during the process of returning it to the preceding red mud washing process to recover the attached loss.

[0008] (3) Increasing the amount of filter cake leads to increased losses of alkali and alumina. During leaf filtration, the amount of lime slurry added increases, resulting in a larger amount of filter cake. When the amount of lime slurry added is 5‰ of the crude sodium aluminate solution and the concentration of suspended solids in the crude sodium aluminate solution is 0.5 g / L, the solids formed by lime slurry in the filter cake account for more than 60% of the total filter cake. Returning the filter cake to the preceding red mud washing process increases the amount of red mud, thus increasing the loss of discarded red mud.

[0009] (4) Increased evaporation water consumption and electricity consumption, etc. Most domestic alumina plants use the hydration lime process to prepare lime slurry. The large amount of lime slurry used results in a large amount of water entering the system with the lime slurry, increasing the load on the evaporation process and increasing steam and electricity consumption. The large amount of lime slurry used will increase the water and electricity consumption in lime slurry preparation and transportation. Summary of the Invention

[0010] Purpose of the invention

[0011] To address the problems of high lime consumption and significant alumina loss during sodium aluminate solution filtration in existing alumina production processes, a method for preparing and adding a sodium aluminate solution filtration aid is provided. This method reduces lime consumption during filtration and decreases alumina loss during filtration.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for preparing a sodium aluminate solution filtration aid, using lime or lime milk, sodium aluminate solution, and ethanol or methanol as raw materials, with the following ratio: 1 part lime or lime milk, 2-20 parts sodium aluminate solution, 0.02-0.2 parts ethanol or 0.01-0.1 parts methanol, wherein the concentration of the sodium aluminate solution is 100-300 g / L Na2O and 50-220 g / L Al2O3; the sodium aluminate solution filtration aid is prepared under the conditions of a reaction temperature of 25-105℃ and a reaction time of 5-240 minutes.

[0014] As a further description of the above scheme, the concentration of the lime slurry is 50-300 g / L CaO.

[0015] As a further description of the above scheme, the sodium aluminate solution in the raw materials is one of crude sodium aluminate solution, refined sodium aluminate solution, and mother liquor, and the crude sodium aluminate solution is 2-10 parts, the refined sodium aluminate solution is 2-10 parts, or the mother liquor is 4-20 parts.

[0016] As a further description of the above scheme, the concentration of ethanol or methanol is 10-99%.

[0017] A method for adding a filter aid for the fine filtration of sodium aluminate solution includes the following steps:

[0018] Step 1: Mix the sodium aluminate solution fine filtration aid described in claim 1 with the crude sodium aluminate solution at a mass ratio of 0.001-0.02:1 and feed the mixture into a leaf filter for fine filtration. Stop adding the filter aid after 2-30 minutes.

[0019] Step 2: After adding the crude sodium aluminate solution for 10-120 minutes, stop adding the crude sodium aluminate solution.

[0020] Step 3: Unloading the filter cake from the leaf filter;

[0021] Step 4: After unloading the filter cake, repeat Step 1 to start a new cycle.

[0022] Advantages and effects of the present invention:

[0023] This invention addresses the problem of high lime consumption and significant alumina loss in existing alumina production processes involving sodium aluminate solution filtration. This patented technology can significantly reduce the amount of lime slurry used for filtration, and also reduce alumina loss, steam consumption, water consumption, and electricity consumption caused by the large amount of lime slurry used. Attached Figure Description

[0024] Figure 1 Scanning electron microscope image 1 of the filter aid prepared for this invention;

[0025] Figure 2 Scanning electron microscope image 2 of the filter aid prepared in this invention. Detailed Implementation

[0026] It is understood that the specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. It is impossible to exhaustively describe all the implementation methods here. Those skilled in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

[0027] A method for preparing a sodium aluminate solution filtration aid, using lime or lime milk, sodium aluminate solution, and ethanol or methanol as raw materials, with the following ratio: 1 part lime or lime milk, 2-20 parts sodium aluminate solution, 0.02-0.2 parts ethanol or 0.01-0.1 parts methanol, wherein the concentration of the sodium aluminate solution is 100-300 g / L Na2O and 50-220 g / L Al2O3; the sodium aluminate solution filtration aid is prepared under the conditions of a reaction temperature of 25-105℃ and a reaction time of 5-240 minutes. The filter aid prepared by this method has a mesh and bridge structure, which can better filter fine particles. At the same time, in the existing alumina production, the high consumption of lime for fine filtration of sodium aluminate solution leads to high alumina loss. Implementing this patented technology can reduce lime consumption for fine filtration by 60-90%, reduce alumina loss by 60-90%, and also reduce steam, water and electricity consumption. In addition, the design of sodium aluminate solution concentration is combined with the on-site process and production conditions, making it suitable for all alumina plants.

[0028] The lime slurry concentration of the present invention is 50-300 g / L CaO.

[0029] The sodium aluminate solution in the raw materials of this invention is one of crude sodium aluminate solution, refined sodium aluminate solution, seed mother liquor, or circulating mother liquor, wherein the crude sodium aluminate solution comprises 2-10 parts, the refined sodium aluminate solution comprises 2-10 parts, or the mother liquor comprises 4-20 parts. This design allows for selection of the optimal solution based on the on-site process and configuration, and has a wide range of applicable raw materials.

[0030] The concentration of ethanol or methanol in this invention is 10-99%. The addition of ethanol or methanol in this invention provides hydroxyl groups, forming a bridged structure.

[0031] The present invention provides a method for preparing and adding a sodium aluminate solution fine filtration aid, comprising the following steps:

[0032] Step 1: Mix the above-mentioned crude sodium aluminate solution with the crude sodium aluminate solution at a ratio of 0.001-0.02:1 and put it into a leaf filter for fine filtration. Stop adding filter aid after 2-30 minutes.

[0033] Step 2: After adding the crude sodium aluminate solution for 10-120 minutes, stop adding the crude sodium aluminate solution.

[0034] Step 3: Unloading the filter cake from the leaf filter;

[0035] Step 4: After unloading the filter cake, repeat Step 1 to start a new cycle. The preparation and addition method of this invention for a sodium aluminate solution fine filtration aid achieves good filtration effect and reduces the amount of filter aid used.

[0036] Example 1

[0037] In this embodiment, the preparation and addition method of sodium aluminate solution filtration aid uses lime or lime milk, sodium aluminate solution and methanol as raw materials, with a ratio of 1 part lime milk, 2 parts crude sodium aluminate solution and 0.01 parts methanol. The sodium aluminate solution filtration aid is prepared under the conditions of reaction temperature of 25°C and reaction time of 240 minutes.

[0038] The above method for preparing and adding the sodium aluminate solution filtration aid includes the following steps:

[0039] Step 1: Mix the filter aid and crude sodium aluminate solution at a ratio of 0.001:1 and feed them into the leaf filter for fine filtration. Stop adding the filter aid after 2 minutes.

[0040] Step 2: After adding the crude sodium aluminate solution for another 10 minutes, stop adding the crude sodium aluminate solution.

[0041] Step 3: Unloading the filter cake from the leaf filter;

[0042] Step 4: After unloading the filter cake, repeat Step 1 to start a new cycle.

[0043] In this embodiment, the lime slurry concentration is 50 g / L CaO.

[0044] The methanol concentration in this embodiment is 99%.

[0045] In this embodiment, the concentration of crude sodium aluminate solution is 300 g / L Na2O and 220 g / L Al2O3.

[0046] The sodium aluminate solution filtration aid obtained in the example was used in the production of alumina in the prior art. The amount of lime added per ton of alumina product was 7 kg, and the corresponding alumina loss was 4.1 kg.

[0047] Example 2

[0048] In this embodiment, the preparation and addition method of sodium aluminate solution fine filtration aid uses lime or lime milk, sodium aluminate solution and methanol as raw materials, with a ratio of 1 part lime milk, 10 parts crude sodium aluminate solution and 0.1 part methanol. The sodium aluminate solution fine filtration aid is prepared under the conditions of reaction temperature of 105℃ and reaction time of 5 minutes.

[0049] The above method for preparing and adding the sodium aluminate solution filtration aid includes the following steps:

[0050] Step 1: Mix the filter aid and crude sodium aluminate solution at a ratio of 0.02:1 and feed them into a leaf filter for fine filtration. Stop adding the filter aid after 30 minutes.

[0051] Step 2: After adding the crude sodium aluminate solution for another 120 minutes, stop adding the crude sodium aluminate solution.

[0052] Step 3: Unloading the filter cake from the leaf filter;

[0053] Step 4: After unloading the filter cake, repeat Step 1 to start a new cycle.

[0054] In this embodiment, the lime slurry concentration is 300 g / L;

[0055] In this embodiment, the methanol concentration is 10%;

[0056] In this embodiment, the concentration of the crude sodium aluminate solution is 100 g / L for Na2O and 50 g / L for Al2O3.

[0057] The sodium aluminate solution filtration aid obtained in the example was used in the production of alumina in the prior art. The amount of lime added per ton of alumina product was 2 kg, and the corresponding alumina loss was 1.7 kg.

[0058] Compared to Comparative Example 1

[0059] In existing alumina production technology, the amount of lime added as a filter aid is 20 kg per ton of alumina product, resulting in a loss of 12.6 kg of alumina.

[0060] Compared with Comparative Example 1, which did not use the technology of the present invention, Examples 1 and 2 showed that lime consumption was reduced by 70% and 90%, respectively, and alumina loss was reduced by 70% and 90%, respectively.

[0061] Depend on Figure 1 and Figure 2 It can be seen that the filter aid prepared by the present invention has a particle size of 0.5-1 micrometer, complete crystallization, and a tetrahedral microstructure. This morphology has a large specific surface area and can form a bridging structure when the particles aggregate.

[0062] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a filter aid for fine filtration of sodium aluminate solution, characterized in that: A sodium aluminate solution filtration aid is prepared using lime or lime slurry, sodium aluminate solution, and ethanol or methanol as raw materials, in the following proportions: 1 part lime or lime slurry, 2-20 parts sodium aluminate solution, and 0.02-0.2 parts ethanol or 0.01-0.1 parts methanol. The concentration of the sodium aluminate solution is 100-300 g / L Na₂O and 50-220 g / L Al₂O₃. The reaction is carried out at a temperature of 25-105℃ for 5-240 minutes. The lime slurry concentration is 50-300 g / L CaO; the sodium aluminate solution in the raw materials is one of crude sodium aluminate solution, refined sodium aluminate solution, and mother liquor, and the crude sodium aluminate solution is 2-10 parts, the refined sodium aluminate solution is 2-10 parts, or the mother liquor is 4-20 parts; the ethanol or methanol concentration is 10-99%; the sodium aluminate solution fine filtration aid has a particle size of 0.5-1 micrometer, complete crystallization, and a tetrahedral microstructure, which can form a bridging structure when the particles aggregate.

2. A method for adding a filter aid for the fine filtration of sodium aluminate solution, characterized in that: Includes the following steps: Step 1: Mix the sodium aluminate solution fine filtration aid described in claim 1 with the crude sodium aluminate solution at a mass ratio of 0.001-0.02:1 and feed the mixture into a leaf filter for fine filtration. Stop adding the filter aid after 2-30 minutes. Step 2: After adding the crude sodium aluminate solution for 10-120 minutes, stop adding the crude sodium aluminate solution. Step 3: Unloading the filter cake from the leaf filter; Step 4: After unloading the filter cake, repeat Step 1 to start a new cycle.

Images