A process for treating impurities in alumina evaporation mother liquor

Abstract

This invention discloses a process for treating impurities in alumina evaporation mother liquor, belonging to the field of alumina mother liquor purification technology. The process includes: sending coal powder with adsorbed impurities into a drying device for drying, then into an electrolytic cracking furnace for anaerobic cracking at above 450℃, decomposing organic matter and converting sodium oxalate into carbonate; sending the cracked coal powder into a coal powder washing device, washing it with pure water until it can be discharged for incineration; sending the washing water into a neutralization and alumina precipitation device for acid neutralization and alumina precipitation, and recovering alumina through a filter press; filtering the filtrate and sending it into a resin tower for removing metal ions using aluminum removal resin or chelating resin; sending the effluent into a pH adjustment device to adjust the pH to 2.5 to remove carbonate ions; concentrating it in a salt concentration system and then sending it into an acid and alkali production system to produce acid and alkali; recycling the acid back to the pH adjustment device, returning the alkali to the mother liquor system, circulating the brine, and reusing the pure water. This invention can efficiently remove organic matter and sodium oxalate, recover aluminum resources, achieve acid and alkali self-sufficiency and closed-loop water circulation, with no external wastewater discharge, significantly improve the stability of alumina production and product quality, and is suitable for the purification treatment of industrial alumina evaporation mother liquor.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and mother liquor purification technology in alumina production, specifically involving a closed-loop recycling process for treating impurities such as organic matter and sodium oxalate in alkaline evaporation mother liquor, which includes coal powder pyrolysis, water washing for aluminum removal, ion exchange membrane, and bipolar membrane. Background Technology

[0002] In the Bayer process of alumina production, the evaporation mother liquor accumulates impurities such as organic matter, sodium oxalate, and carbonates over a long period of time, easily leading to increased mother liquor viscosity, reduced decomposition efficiency, equipment scaling and clogging, and a decline in alumina product quality. Existing technologies generally suffer from incomplete impurity removal, low resource recovery rates, high acid and alkali consumption, wastewater discharge, and difficulties in the harmless treatment of coal powder after adsorption, making it difficult to meet the long-term stable operation requirements of industrial production. Therefore, developing a treatment process that can deeply purify the mother liquor, recover aluminum resources, generate its own acids and alkalis, and achieve a closed-loop circulation throughout the entire process is of great significance for improving the quality and efficiency of the alumina industry and promoting green production. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention discloses a process for treating impurities in alumina evaporation mother liquor. Through anaerobic pyrolysis of pulverized coal, pure water washing, neutralization and aluminum precipitation, removal of metal ions with resin, decarbonate removal, ion-exchange membrane concentration, and bipolar membrane acid and alkali production, the process achieves efficient removal of impurities, aluminum recovery, acid and alkali self-sufficiency, and water recycling, thereby achieving the goals of mother liquor purification and stable production operation.

[0004] This invention is achieved through the following technical solution: a process for treating impurities in alumina evaporation mother liquor, characterized by comprising the following steps: (1) The coal powder adsorbed with impurities of alkaline evaporation mother liquor is sent to a drying device and dried to a moisture content of about 20%; then it is sent to an electric pyrolysis furnace, where it is pyrolyzed and kept warm under oxygen-free conditions above 450°C, so that the organic matter is decomposed and discharged with the flue gas, and sodium oxalate is converted into carbonate. (2) The pyrolysis coal powder is sent to the coal powder washing device and washed with pure water multiple times until the coal powder meets the requirements for discharge and incineration. (3) The washing water is sent to the neutralization and aluminum precipitation device, acid is added to neutralize and it is allowed to stand to precipitate aluminum oxide precipitate; then it is sent to the filter press to recover the precipitate, and the filtrate is then filtered to intercept the residual precipitate. (4) The filtered water is sent to the resin tower to remove metal ions by aluminum removal resin or chelating resin. The resin regenerated water is returned to the neutralization and aluminum precipitation device in step (3). (5) The resin effluent is sent to a pH adjustment device, and acid is added to adjust the pH to about 2.5 to remove carbonate ions from the water; (6) The water after pH adjustment is sent to the salt concentration system (ion membrane concentration device), the produced pure water is sent to the pure water production system for reuse, and the high concentration brine is sent to the acid and alkali production system (bipolar membrane electrodialysis device). (7) The bipolar membrane produces acid solution with a concentration of 9-12%, alkali solution with a concentration of about 8% and low-concentration brine solution; the acid solution is recycled to the pH adjustment device, the alkali solution is returned to the alumina evaporation mother liquor system, and the low-concentration brine solution is returned to the salt concentration system for recycling.

[0005] The apparatus system of the present invention includes: a drying device, an electropyrolysis furnace, a coal powder washing device, a neutralization and alumina precipitation device, a filter press, a filtration device, a resin tower, a pH adjustment device, a salt concentration system, an acid and alkali production system, and a pure water production system. Each device is connected in sequence through pipelines to achieve a closed-loop circulation throughout the entire process.

[0006] The electrocracking furnace is an oxygen-free tubular furnace or rotary furnace, capable of decomposing organic matter in pulverized coal and converting sodium oxalate at 450℃~600℃; the filter press is a plate and frame filter press used to recover alumina precipitate generated from neutralization and precipitation; the resin tower is filled with aluminum-removing chelating resin to deeply remove residual metal ions from the water; the salt concentration system uses an ion-exchange membrane device to achieve brine concentration and pure water separation; the acid and alkali production system uses a bipolar membrane electrodialysis device to convert concentrated brine into acid, alkali, and low-concentration brine, achieving self-sufficient acid and alkali reuse; the pure water production system refines the pure water produced by the salt concentration system for use in the pulverized coal cleaning device and system makeup water. Attached Figure Description Figure 1 This is a flowchart of the process flow of the present invention. Detailed Implementation

[0007] Example: A process for treating impurities in alumina evaporation mother liquor, comprising the following steps: (1) The coal powder with adsorbed impurities is sent to the drying device and dried to a moisture content of about 20%; then it enters the electro-pyrolysis furnace and is pyrolyzed under anaerobic conditions of 450℃~600℃. The organic matter is decomposed and discharged, and sodium oxalate is converted into carbonate. (2) The pyrolysis coal powder is fed into the coal powder cleaning device and cleaned multiple times with pure water until the coal powder meets the requirements for external discharge and incineration; (3) The washing water is sent to the neutralization and aluminum precipitation device, acid is added for neutralization, and the mixture is allowed to stand to precipitate aluminum oxide. The aluminum oxide is then recovered by a filter press, and the filtrate is filtered again to remove suspended solids. (4) The filtered water is sent to the resin tower, where aluminum removal resin or chelating resin is filled to remove metal ions, and the regenerated water is circulated to the neutralization and aluminum precipitation device. (5) The resin effluent is sent to a pH adjustment device, and acid is added to adjust the pH to 2.4-2.6 to remove carbonate ions; (6) The water after pH adjustment is sent to the salt concentration system to obtain recycled pure water and high-concentration brine; (7) High-concentration brine is sent to the acid-alkali production system, producing 9-12% acid, about 8% alkali, and low-concentration brine; acid is returned to the pH adjustment device, alkali is returned to the mother liquor system, and low-concentration brine is returned to the salt concentration system for circulation; the pure water produced by the pure water production system is returned to the coal powder cleaning device.

[0008] This process significantly reduces organic matter and sodium oxalate in the evaporation mother liquor, effectively recovers aluminum resources, achieves acid and alkali self-sufficiency, establishes a closed-loop water circulation system, eliminates wastewater discharge, stabilizes the alumina production process, and improves product quality. Beneficial effects

[0009] 1) Thorough removal of impurities: High-temperature anaerobic pyrolysis decomposes organic matter, and sodium oxalate is converted into carbonate, resulting in significant purification of the mother liquor; 2) Aluminum resource recycling: Neutralization and aluminum precipitation + pressure filtration recovery improves resource utilization; 3) Acid and alkali self-sufficiency: Bipolar membrane produces acid and alkali which can be directly reused, significantly reducing operating costs; 4) Closed-loop circulation: Pure water, reclaimed water, and brine are all circulated, with no wastewater discharge; 5) Pulverized coal is rendered harmless: after cleaning, it can be discharged and incinerated, which is environmentally compliant; 6) Improved production stability: Reduced impurities in mother liquor, reduced equipment scaling, and improved alumina product quality.

Claims

1. A process for treating impurities in alumina evaporation mother liquor, characterized in that, Includes the following steps: (1) The coal powder adsorbed with impurities of alkaline evaporation mother liquor is sent to a drying device and dried to a moisture content of about 20%. Then it is sent to an electric pyrolysis furnace for pyrolysis and heat preservation under oxygen-free conditions above 450°C, so that the organic matter in the coal powder is decomposed and discharged with the flue gas, and sodium oxalate is converted into carbonate. (2) The pyrolysis coal powder is sent to the coal powder washing device and washed with pure water multiple times until the coal powder meets the requirements for discharge and incineration. (3) The washing water is sent to the neutralization and aluminum precipitation device, acid is added for neutralization and the mixture is allowed to stand to precipitate aluminum oxide. The precipitate is recovered by a filter press, and the filtrate is filtered to remove the remaining precipitate. (4) The filtered water is sent into the resin tower, where metal ions are removed by aluminum removal resin or chelating resin. The resin regenerated water is returned to the neutralization and aluminum precipitation device in step (3). (5) The resin effluent is sent to a pH adjustment device, and acid is added to adjust the pH value to about 2.5 to remove carbonate ions from the water; (6) The water after pH adjustment is sent to the salt concentration system, the produced pure water is sent to the pure water production system for reuse, and the high-concentration brine is sent to the acid and alkali production system. (7) The bipolar membrane produces acid solution with a concentration of 9-12%, alkali solution with a concentration of about 8%, and low-concentration brine. The acid solution is recycled to the pH adjustment device, the alkali solution is returned to the alumina evaporation mother liquor system, and the low-concentration brine is returned to the salt concentration system for recycling. According to the process described in claim 1, the characteristic is that the electrocracking furnace in step (1) is an oxygen-free tube furnace or a rotary furnace, and the pyrolysis temperature is 450℃~600℃.

2. The process according to claim 1, characterized in that: The electrocracking furnace mentioned in step (1) is an oxygen-free tube furnace or a rotary furnace, and the pyrolysis temperature is 450℃~600℃.

3. The process according to claim 1, characterized in that: The electrocracking furnace mentioned in step (1) is an oxygen-free tube furnace or a rotary furnace, and the pyrolysis temperature is 450℃~600℃.

4. The process according to claim 1, characterized in that: The pH control range of the pH adjustment device in step (5) is 2.4 to 2.

6.

5. The process according to claim 1, characterized in that: In step (4), the resin tower is filled with aluminum-removing resin or chelating resin to deeply remove metal ions from the water.

6. The process according to claim 1, characterized in that: The system's drying unit, electrocracking furnace, coal powder cleaning unit, neutralization and alumina precipitation unit, filter press, filtration unit, resin tower, pH adjustment unit, salt concentration system, acid and alkali production system, and pure water production system are connected in the process sequence through pipelines to achieve closed-loop reuse of pure water, reclaimed water, low-concentration brine, acid, and alkali, with no wastewater discharge.

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