Method for removing organic matters in sodium aluminate solution

Abstract

The invention discloses a method for removing organic matters in a sodium aluminate solution. The method comprises the following steps: mixing the sodium aluminate solution produced in an aluminum oxide production process with a qualified particle size material with an adsorption function, and conveying the mixture to a settling tank for settling; the settled solid underflow is conveyed to a mixing tank to be mixed and filtered with red mud slurry output by the red mud settling, separating and washing procedure; grinding the filtered filter cake and other materials and solutions required for sintering, and conveying the ground materials to a blending tank; and spraying into a sintering kiln through a spray gun for sintering, so that organic matters in the material are converted into carbon dioxide. The method utilizes pulverized coal or fly ash to adsorb organic matters and sodium oxalate in the solution, and is high in removal efficiency and simple and convenient to operate; and a filter for filtering red mud in a conventional series-connection method aluminum oxide production process is replaced by a filter press, a tilting-pan filter or a centrifugal filter with higher applicability, and a filter cake is low in moisture and stable, so that more solutions rich in organic matters can be digested, and the removal efficiency of the organic matters is improved.

Description

Technical Field

[0001] The invention relates to the technical field of alumina production, in particular to a method for removing organic matter in a sodium aluminate solution. Background Art

[0002] In the Bayer process of alumina production, due to the use of organic additives in the ore production process, the organic matter content in the process will gradually accumulate. At the same time, the organic matter will also undergo degradation reactions, and long-chain organic matter will degrade into short-chain organic matter, of which sodium oxalate is a major degradation product.

[0003] Sodium oxalate will have an adverse effect on the decomposition process, causing the particle size of the alumina product to become finer and the impurity content in the product to exceed the standard. Long-chain organic matter does not have a fixed solubility in the solution. In addition to some of it being carried away from the production system with the red mud, it will continue to accumulate in the production system, causing the solution viscosity to increase, reducing the operating efficiency of processes such as sedimentation, and increasing the energy consumption of material transportation.

[0004] Liquid combustion is a major method for removing organic matter in alumina production. The conventional process is that the seed liquor containing organic matter is concentrated and then mixed with aluminum ore, red mud or aluminum hydroxide dust to make a raw slurry, which is then calcined at high temperature in a calcining kiln. The organic matter generates carbon dioxide under high temperature conditions and is discharged into the atmosphere.

[0005] Problems existing in the current method include: if the evaporated mother liquor is mixed with aluminum hydroxide powder, due to the moisture requirement of the raw material slurry entering the calcining kiln, in order to process a sufficient amount of seed liquor, it is necessary to add a specified proportion of aluminum hydroxide powder, and the repeated dissolution of aluminum hydroxide causes a decrease in production efficiency; if a series red mud calcining kiln is used to treat materials containing organic matter, the filtration effect of the vertical disc vacuum filter commonly used to filter red mud is significantly affected by changes in material properties, and the filter cake has a high moisture content, which also limits the processing capacity of organic carbon-containing materials. Summary of the invention

[0006] In view of the above shortcomings and deficiencies, the present invention provides a method for removing organic matter in a sodium aluminate solution to solve the problem of low efficiency in organic matter treatment.

[0007] In order to achieve the above object, the main technical solution adopted by the present invention includes the following steps S1. Mixing the sodium aluminate solution produced in the alumina production process with qualified particle size materials with adsorption function and transporting them to a sedimentation tank for sedimentation; S2, the solid underflow after sedimentation in step S1 is transported to a mixing tank, mixed with the red mud slurry output from the red mud sedimentation, separation and washing process, and then the solid underflow is transported to a filter for filtration; S3, conveying the filter cake filtered in step S2 to a grinder, adding other materials and solutions required for sintering for grinding, and conveying the ground materials to a blending tank; S4. Add solution into the mixing tank again for mixing, so that the material in the mixing tank meets the transportation requirements of entering the sintering kiln, and spray it into the sintering kiln through the spray gun for sintering, so that the organic matter in the material is converted into carbon dioxide.

[0008] In step S1, the sodium aluminate solution produced in the alumina production process includes the product evaporation mother liquor of the mother liquor evaporation process or the product dissolution liquid of the dissolution process.

[0009] In step S1, the qualified particle size material with adsorption function is coal powder or fly ash, and the proportion of coal powder particles with a particle size greater than 88um is less than or equal to 10% of the total. The coal powder or fly ash adsorbs the organic matter carried in the sodium aluminate solution to the surface of the material and discharges it from the bottom of the sedimentation tank to the filter.

[0010] The overflow produced in step S1 and the filtrate produced in step S2 are returned to the original production process of the sodium aluminate solution.

[0011] The moisture content of the filter cake after filtration in step S2 is 28-35%.

[0012] The other materials required for sintering in step S3 include limestone, soda ash, and coal powder for sintering; the solution includes the flat plate strong filtrate produced by the aluminum hydroxide filtration process, the seed washing liquid produced by the seed filtration and washing process, and the evaporated mother liquor produced by the mother liquor evaporation process.

[0013] In step S4, the material in the mixing tank meets the transportation requirement of entering the sintering kiln, that is, the moisture content of the mixed slurry in the mixing tank meets 38-42%. After the mixed slurry enters the sintering kiln, the organic matter in the material is converted into carbon dioxide at a sintering temperature of 1000-1200°C.

[0014] The filter described in step S2 includes a filter press, a tilting plate vacuum filter, and a centrifuge.

[0015] The mill in step S3 includes a tube mill, a ball mill, and a rod mill.

[0016] The present invention has the following beneficial effects and advantages: The present invention grafts a method for removing organic matter in sodium aluminate solutions such as evaporation mother liquor or post-dissolution liquor onto the existing alumina production process, and utilizes coal powder or fly ash to adsorb organic matter and sodium oxalate in the solution, thereby achieving high removal efficiency and simple operation. The vertical disc vacuum filter for filtering red mud in the conventional series-connected alumina production process is replaced with a more applicable filter press, flip disc filter or centrifugal filter, and the equipment has high reliability, and the filter cake has low and stable moisture content. The raw slurry prepared can absorb more organic-rich solutions, thereby improving the organic matter removal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart of the method for removing organic matter from sodium aluminate solution. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings of the specification. A method for removing organic matter in a sodium aluminate solution comprises the following steps: S1. The sodium aluminate solution produced in the alumina production process is mixed with qualified particle size materials with adsorption function and transported to the sedimentation tank. The sedimentation tank is equipped with a mechanical stirring paddle (also called a rake) to accelerate the mixing of materials. In addition, the sedimentation tank can also provide sufficient residence time for the materials and realize gravity separation of the materials.

[0019] Specifically, the sodium aluminate solution produced in the alumina production process includes the product of the mother liquor evaporation process, the evaporation mother liquor, and the Na2O concentration of the evaporation mother liquor is 200g / L~300g / L, or the product of the dissolution process, the post-dissolution liquid, and the Na2O concentration is 200g / L~250g / L; the qualified particle size material with adsorption function is coal powder or fly ash, and the proportion of coal powder particles with a particle size greater than 88um is less than or equal to 10% of the total. The coal powder or fly ash adsorbs the organic matter carried in the sodium aluminate solution to the surface of the material and discharges it from the bottom of the sedimentation tank to the filter. The mixed material stays in the sedimentation tank for 2 to 3 hours, and the organic matter carried in the liquid is adsorbed and fixed to the surface of the solid material. Under the action of gravity, the solids are enriched to the bottom flow and discharged from the bottom of the sedimentation tank, which is called the bottom flow. The upper clear liquid containing less solids flows out from the overflow port of the sedimentation tank, which is called the overflow.

[0020] The solid content in the overflow of the sedimentation tank is 1-2 g / L. If the processed material is evaporation mother liquor, the overflow is sent to the evaporation mother liquor tank. If the processed material is dissolution post-liquid, the overflow is sent to the dissolution dilution tank. The solid content of the sedimentation tank bottom flow is 100-200g / L, which is discharged from the bottom flow outlet of the sedimentation tank into the mixing tank.

[0021] S2. The solid underflow after sedimentation in step S1 is transported to a mixing tank, and red mud slurry is added to the mixing tank. The red mud slurry comes from the last washing tank of the red mud sedimentation separation and washing process. The solid content of the red mud slurry is 400-500 g / L. The red mud slurry is mixed with the underflow of the sedimentation tank and then sent to a filter press or a tilting disc vacuum filter or a centrifuge or other filter for filtration. The filtrate after filtration has a solid content of 1-2 g / L. If the treated material is an evaporation mother liquor, the overflow is sent to the evaporation mother liquor tank. If the treated material is a post-dissolution liquid, the overflow is sent to the dissolution dilution tank. The filter cake attachment rate of the filter is 25-30%.

[0022] S3, conveying the filter cake filtered in step S2 to a tube mill, a ball mill, a rod mill or other mills, and adding limestone, soda ash, and sintering coal powder at the same time; and adding a solution rich in organic matter, including the product flat plate strong filtrate of the aluminum hydroxide filtration process, the product seed washing liquid of the seed filtration and washing process, and the product evaporation mother liquor of the mother liquor evaporation process, the amount of solution added is to meet the solid content of the material in the mill within the range of 800-1000g / L, at this time the mill working efficiency is higher.

[0023] S4. The ground material enters the blending tank, and a certain amount of solution will be added to the blending tank again to make the solid content of the material in the blending tank reach 38-42%. This solid content can meet the transportation requirements of entering the sintering kiln. For the sintering process, the higher the solid content of the material, the better, which can save sintering energy. However, since the material entering the sintering kiln needs to be sprayed with a spray gun, if the solid content is too high, on the one hand, there will be problems with transportation, and on the other hand, the material cannot be sprayed in this way, so a part of the solution is added to the mill discharge for blending. The prepared solution enters the sintering kiln, and the temperature of the sintering kiln is about 1100℃. Under this high temperature condition, the organic matter in the material is converted into carbon dioxide, realizing the elimination of organic matter.

[0024] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for removing organic matter from a sodium aluminate solution, characterized in that: The following steps are involved: S1. Mixing the sodium aluminate solution produced in the alumina production process with qualified particle size materials with adsorption function and transporting them to a sedimentation tank for sedimentation; S2, the solid underflow after sedimentation in step S1 is transported to a mixing tank, mixed with the red mud slurry output from the red mud sedimentation, separation and washing process, and then the solid underflow is transported to a filter for filtration; S3, conveying the filter cake filtered in step S2 to a grinder, adding other materials and solutions required for sintering for grinding, and conveying the ground materials to a blending tank; S4. Add solution into the mixing tank again for mixing, so that the material in the mixing tank meets the transportation requirements of entering the sintering kiln, and spray it into the sintering kiln through the spray gun for sintering, so that the organic matter in the material is converted into carbon dioxide.

2. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: In step S1, the sodium aluminate solution produced in the alumina production process includes the product evaporation mother liquor of the mother liquor evaporation process or the product dissolution liquid of the dissolution process.

3. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: In step S1, the qualified particle size material with adsorption function is coal powder or fly ash, and the proportion of coal powder particles with a particle size greater than 88um is less than or equal to 10% of the total. The coal powder or fly ash adsorbs the organic matter carried in the sodium aluminate solution to the surface of the material and discharges it from the bottom of the sedimentation tank to the filter.

4. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: The overflow produced in step S1 and the filtrate produced in step S2 are returned to the original production process of the sodium aluminate solution.

5. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: The moisture content of the filter cake after filtration in step S2 is 28-35%.

6. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: The other materials required for sintering in step S3 include limestone, soda ash, and coal powder for sintering; the solution includes the flat plate strong filtrate produced by the aluminum hydroxide filtration process, the seed washing liquid produced by the seed filtration and washing process, and the evaporated mother liquor produced by the mother liquor evaporation process.

7. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: In step S4, the material in the mixing tank meets the transportation requirement of entering the sintering kiln, that is, the moisture content of the mixed slurry in the mixing tank meets 38-42%. After the mixed slurry enters the sintering kiln, the organic matter in the material is converted into carbon dioxide at a sintering temperature of 1000-1200°C.

8. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: The filter described in step S2 includes a filter press, a tilting plate vacuum filter, and a centrifuge.

9. A method for removing organic matter in a sodium aluminate solution according to claim 1, characterized in that: The mill in step S3 includes a tube mill, a ball mill, and a rod mill.

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