Red mud sedimentation process for aluminum oxide production

Abstract

The invention relates to the technical field of aluminum oxide production, and provides a red mud settling process for aluminum oxide production, which comprises the following steps of: 1, taking evaporation wastewater with the temperature of 55-62 DEG C generated by an aluminum oxide evaporation system as a main washing hot water source of a red mud settling tank to replace traditional dam return water and production circulating water; when evaporation water is insufficient, supplementing evaporation disqualified condensate water with the temperature of 85-90 DEG C, mixing the evaporation disqualified condensate water and the evaporation disqualified condensate water to form mixed washing water, and controlling the temperature of the mixed washing water to be 60-75 DEG C; secondly, primary washing underflow generated in aluminum oxide production is conveyed to a slag removal box through an underflow pump, scab blocks and impurities are filtered and removed, and follow-up equipment is prevented from being blocked; according to the process, heating energy consumption is reduced through evaporation, and natural gas consumption is reduced; grading and sedimentation are optimized, the sedimentation speed is increased, and the hydrolysis loss is reduced; accurate temperature control and high-pressure washing alkali extraction recovery rate are achieved, and the water utilization rate is increased through washing liquor recycling; and multiple processes are also adapted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alumina production, in particular to a red mud settling process for alumina production. BACKGROUND

[0002] In the production of alumina, red mud settling is a key link, the main task of which is to remove residual alkali liquor in the red mud, recover usable alkali and solution, and provide qualified raw materials for subsequent processes, while realizing the harmless storage of red mud. The effect of red mud settling directly affects the dissolution rate of alumina, alkali consumption and production cost, and the temperature and amount of washing hot water are one of the core factors determining the settling efficiency.

[0003] In the existing production of alumina, the washing hot water for red mud settling is mostly dam backwater, production circulating water or a mixture of the two, supplemented by a small amount of high-temperature condensed water; the red mud treatment process is usually "one-washing bottom flow directly into multi-stage settling tank washing-plate and frame filter press filtration", and some processes will add a hydrocyclone classifier before settling. These processes can achieve the basic function of red mud settling, but form a fixed mode in hot water utilization and process optimization.

[0004] The existing technology has significant defects: the dam backwater and production circulating water in the traditional hot water source are low in temperature, and a large amount of natural gas or steam needs to be consumed to heat them to the required temperature, which is high in energy consumption and high in operating cost; the multi-stage settling tank design process is complex, the number of equipment is large, and flocculants need to be continuously added, which not only increases investment and operating cost, but also causes alumina hydrolysis loss due to long slurry residence time; the connection of the hydrocyclone and the settling tank is unreasonable, and additional power is needed to transport the slurry, which increases energy consumption; the washing water does not fully contact with the red mud, the residual alkali liquor is not completely washed, which affects the efficiency of the subsequent dissolution process, and the recycling rate of the washing liquor is low, which causes waste of water resources, and it is difficult to balance the comprehensive needs of settling effect, energy consumption control and cost optimization. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a red mud settling process for alumina production, which solves the problems of the traditional red mud settling process using low-temperature dam backwater and circulating water, the need for a large amount of energy consumption for heating, the complex process of multi-stage settling tank, high consumption of flocculants, long slurry residence time causing alumina hydrolysis loss, the need for additional power for the connection of the hydrocyclone and the settling tank, insufficient contact of the washing water, low alkali recovery, poor utilization rate of the washing liquor, and the difficulty in balancing the effect, energy consumption and cost.

[0006] To achieve the above purpose, the present application is implemented by the following technical scheme: a red mud settling process for alumina production, comprising:

[0007] Step one: the evaporation underflow produced by the alumina evaporation system at a temperature of 55-62℃ is used as the main washing hot water source for the red mud settling tank, replacing the traditional dam backwater and production circulating water; when the evaporation underflow is insufficient, the evaporation unqualified condensate water at a temperature of 85-90℃ is supplemented, and after mixing, the mixed washing water is formed, and the temperature of the mixed washing water is controlled at 60-75℃;

[0008] Step two: the first washing underflow of the alumina production is transported to the deslag tank by the underflow pump, and the scab blocks and sundries are filtered to avoid the subsequent equipment from being blocked;

[0009] Step three: the first washing underflow after the pretreatment is sent to the hydrocyclone for classification, and the hydrocyclone is arranged above the separation settling tank, the overflow of the hydrocyclone flows into the separation settling tank, and the underflow is temporarily stored in the underflow tank;

[0010] Step four: the flocculating agent is added to the overflow in the separation settling tank, the residence time of the slurry in the settling tank is controlled at 2-3h, the solid-liquid separation of the red mud and the solution is realized, the overflow of the settling tank is sent to the desiliconization process, and the underflow is discharged into the underflow tank and combined with the underflow of the hydrocyclone;

[0011] Step five: the mixed washing water is transported to the separation settling tank by the washing water pump, the washing water penetrates the red mud filter cake, the residual alkali liquor of the filter cake is washed, and the washing pressure is controlled at 8-10bar to ensure that the washing water and the red mud are fully contacted;

[0012] Step six: the combined underflow and the second washing liquor of the red mud are mixed, transported to the washing plate-and-frame filter by the underflow pump, and filtered, the filtration pressure of the feeding is 6-8bar, the filtrate after the filtration is mixed with the overflow of the first washing and then sent to the leaching process;

[0013] Step seven: the filter cake of the red mud is pressed by the power wind provided by the air compressor, the pressing time is 4-6min, and then the filter cake is blown dry for 1-2min to blow off the residual liquid, and the filter cake after the blowing is transported to the red mud storage yard for storage;

[0014] Step eight: the washing liquor produced by the washing plate-and-frame filter is collected in the red mud washing liquor tank and transported back to the separation settling tank by the washing liquor pump, so that the washing liquor is recycled;

[0015] Step nine: the temperature of the mixed washing water is monitored in real time, the amount of the mixed washing water is adjusted according to the NK concentration of the pregnant liquor, the amount of the washing water is reduced when the NK concentration of the pregnant liquor needs to be increased, and the amount of the washing water is increased when the NK concentration of the pregnant liquor needs to be reduced, and meanwhile, the evaporation system is adjusted to adjust the production of the evaporation underflow, so as to ensure the balance between the supply and demand of the hot water.

[0016] Preferably, the evaporation underflow in step one is the water body after the negative pressure steam produced by the last two-effect vacuum evaporation of the alumina evaporation system is absorbed by cold water, and the water quality meets the red mud washing requirements and does not contain impurities affecting the alumina leaching.

[0017] Preferably, the classification efficiency of the hydrocyclone in step three is greater than or equal to 70%, and the overflow particle size is less than or equal to 0.1 mm, so that the slurry entering the separation settling tank has uniform solid content.

[0018] Preferably, in step four, the flocculating agent is polyacrylamide flocculating agent, and the adding method is multi-point uniform spraying to avoid uneven settling caused by excessive local flocculating agent concentration.

[0019] Preferably, in step five, the liquid-solid ratio of the washing water to the red mud is controlled to be 4-6:1, and the flow rate of the washing water is monitored in real time by a flow meter to ensure that each batch of red mud is washed sufficiently and hot water is not wasted.

[0020] Preferably, in step six, the pressure filtration cycle of the washing plate and frame filter is 23-36 min, which is divided into:

[0021] 35 min of feeding, 0.5-1.5 min of pre-pressing, 6-10 min of washing, 4-6 min of pressing, 1-2 min of blowing, and 8-12 min of cake unloading;

[0022] The pressure and time parameters of each stage are automatically controlled by a PLC system.

[0023] Preferably, in step seven, the blowing direction of the power wind is at an angle of 30-45° with the surface of the filter cake, so that the airflow uniformly penetrates the filter cake and the moisture content of the filter cake is reduced to below 25%.

[0024] Preferably, in step eight, a liquid level sensor is arranged in the red mud washing liquid tank, and when the liquid level is higher than 80%, a standby washing liquid pump is started to send part of the washing liquid to an adjusting liquid tank as the adjusting liquid of the ball mill, so that the washing liquid is recycled in the whole process.

[0025] Preferably, in step nine, a platinum resistance thermometer is used for temperature monitoring, which is installed at the outlet of the mixed washing water pipeline and transmits data to the control system in real time.

[0026] Preferably, in step nine, when the temperature is lower than 60℃, the amount of dam backwater supplement is reduced and the proportion of unqualified condensate water from evaporation is increased; when the temperature is higher than 75℃, the amount of normal temperature production circulating water is appropriately supplemented to maintain the stability of the washing water temperature.

[0027] The present application provides a red mud settling process for alumina production, which has the following beneficial effects:

[0028] 1. The present application uses evaporated water as the main heat source, uses its own waste heat to replace low-temperature water sources, reduces natural gas heating energy consumption, reduces the natural gas consumption per unit of red mud settling, and reduces water resource waste through the recycling of evaporated water and unqualified condensate water, thereby significantly reducing the operating cost compared with the traditional process.

[0029] 2. The present application adopts the optimized layout of hydrocyclone and settling tank to realize overflow self-flow and save conveying power; the staged pretreatment reduces the solid content of the settling tank feed, cooperates with precise flocculant addition, improves the settling speed, shortens the slurry residence time, and reduces the hydrolysis loss of alumina.

[0030] 3. The present application precisely controls the temperature of mixed washing water and designs high-pressure washing to ensure that the residual alkali liquor of red mud is fully removed and the alkali recovery rate is improved; the washing liquor is recycled throughout the process, and the water resource utilization rate is improved.

[0031] 4. In the process of the present application, the linkage regulation and control of hot water source and evaporation system, settling system, and filter pressing system can adapt to different requirements of fine liquor NK concentration, and can flexibly adjust the parameters of each link according to the fluctuation of alumina production capacity; in addition, the process can be migrated to different alumina production processes such as series connection method and Bayer method, breaking through the adaptation limitation of traditional process. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The flowchart of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Embodiment:

[0035] Please refer to the drawings Figure 1 The embodiment of the present application provides a red mud settling process for alumina production, which comprises:

[0036] Step one: the evaporation underflow with a temperature of 55-62 DEG C generated by the alumina evaporation system is used as the main washing hot water source of the red mud settling tank, replacing the traditional dam backwater and production circulating water; when the evaporation underflow is insufficient, the evaporation unqualified condensate with a temperature of 85-90 DEG C is supplemented, and the mixed washing water is formed after mixing, the temperature of the mixed washing water is controlled to be 60-75 DEG C, the evaporation underflow is the water body after the negative pressure steam generated by the last two effects of the alumina evaporation system is absorbed by cold water, and the water quality meets the red mud washing requirements and does not contain impurities affecting the dissolution of alumina;

[0037] Step two: the one washing bottom flow of alumina production is transported to the deslag box by the bottom flow pump, and the scab block and sundries are filtered and removed to avoid the blockage of subsequent equipment;

[0038] Step three: the pre-processed first washing overflow is sent to a hydrocyclone for classification, the hydrocyclone is arranged above the separation and sedimentation tank, the overflow of the hydrocyclone flows into the separation and sedimentation tank by itself, the underflow is temporarily stored in the underflow tank, the classification efficiency of the hydrocyclone is greater than or equal to 70%, the particle size of the overflow is less than or equal to 0.1 mm, and the slurry solid content entering the separation and sedimentation tank is uniform;

[0039] Step four: a polyacrylamide flocculating agent is added to the overflow in the separation and sedimentation tank in a multi-point uniform spraying manner, so that uneven settling caused by excessively high local flocculating agent concentration is avoided, the residence time of the slurry in the settling tank is controlled to be 2-3 h, the solid-liquid separation of the red mud and the solution is realized, the overflow of the settling tank is sent to a desiliconization process, and the underflow is discharged into the underflow tank and combined with the underflow of the hydrocyclone;

[0040] Step five: the mixed washing water is sent to the separation and sedimentation tank through a washing water pump, the washing water penetrates the red mud filter cake, and the residual alkali liquor of the filter cake is washed, the washing pressure is controlled to be 8-10 bar, the washing water and the red mud are ensured to be fully contacted, the liquid-solid ratio of the washing water and the red mud is controlled to be 4-6:1, the washing water flow is monitored in real time through a flowmeter, and it is ensured that each batch of red mud is fully washed and hot water is not wasted;

[0041] Step six: the combined underflow and the secondary washing liquid of the red mud are mixed and sent to a water washing plate-and-frame filter press through an underflow pump for pressure filtration, the pressure filtration feeding pressure is 6-8 bar, the filter liquid after pressure filtration is mixed with the first washing overflow and then sent to a leaching process, the pressure filtration cycle of the water washing plate-and-frame filter press is 23-36 min, which is divided into:

[0042] 35 min of feeding, 0.5-1.5 min of pre-pressing, 6-10 min of washing, 4-6 min of pressing, 1-2 min of blowing and 8-12 min of cake unloading, and the pressure and time parameters of each stage are automatically controlled through a PLC system;

[0043] Step seven: the red mud filter cake is pressed by using the power wind provided by an air compressor, the pressing time is 4-6 min, then the filter cake is blown dry for 1-2 min to blow off residual liquid, and the filter cake after blowing dry is sent to a red mud storage yard for storage, the blowing direction of the power wind is at an angle of 30-45° with the surface of the filter cake, so that the airflow uniformly penetrates the filter cake, and the moisture content of the filter cake is reduced to below 25%;

[0044] Step eight: the washing liquid generated by the water washing plate-and-frame filter press is collected in a red mud washing liquid tank and then sent back to the separation and sedimentation tank through a washing liquid pump, so that the washing liquid is recycled, and the red mud washing liquid tank is provided with a liquid level sensor, when the liquid level is higher than 80%, a standby washing liquid pump is started to send part of the washing liquid to an adjusting liquid tank as a ball mill adjusting liquid, and the washing liquid is fully recovered in the whole process;

[0045] Step nine: real-time monitoring of mixed washing water temperature, when the temperature is lower than 60℃, reduce the dam backwater supplement, increase the proportion of evaporative unqualified condensate water; when the temperature is higher than 75℃, appropriately supplement the normal temperature production circulating water, maintain the washing water temperature stable, adjust the mixed washing water consumption according to the NK concentration of the semen, reduce the washing water consumption when the NK of the semen needs to be increased, increase the washing water consumption when the NK of the semen needs to be reduced, at the same time, link the evaporation system to adjust the evaporation water yield, ensure the balance of hot water supply and demand, the temperature monitoring adopts platinum resistance thermometer, is installed at the outlet of the mixed washing water pipeline, and data is transmitted to the control system in real time.

[0046] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences, modifications, replacements and variations of the embodiments of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A red mud settling process for alumina production, characterised in that, The application relates to a method for washing red mud in an alumina production process. Step one: evaporated water with a temperature of 55-62 DEG C generated by an alumina evaporation system is used as the main washing hot water source of a red mud settling tank, replacing traditional dam backwater and production circulating water; when the evaporated water is insufficient, evaporated unqualified condensate water with a temperature of 85-90 DEG C is supplemented, and after the two are mixed, mixed washing water is formed, and the temperature of the mixed washing water is controlled to be 60-75 DEG C; Step two: the one-washing bottom stream of the alumina production is transported to a deslagging tank through a bottom stream pump, and scab blocks and sundries are filtered and removed to avoid the subsequent equipment from being blocked; Step three: the one-washing bottom stream after the pretreatment is sent into a hydrocyclone for grading, the hydrocyclone is arranged above a separation settling tank, the overflow of the hydrocyclone flows into the separation settling tank, and the bottom stream is temporarily stored in a bottom stream tank; Step four: a flocculating agent is added into the overflow in the separation settling tank, the residence time of the slurry in the settling tank is controlled to be 2-3 h, the solid-liquid separation of the red mud and the solution is realized, the overflow of the settling tank is sent to a desilication process, and the bottom stream is discharged into the bottom stream tank and combined with the bottom stream of the hydrocyclone; Step five: the mixed washing water is transported to the separation settling tank through a washing water pump, the washing water penetrates the red mud filter cake, and the residual alkali liquor of the filter cake is washed, the washing pressure is controlled to be 8-10 bar, and the washing water and the red mud are ensured to be fully contacted; Step six: the combined bottom stream and the secondary washing liquor of the red mud are mixed, transported to a washing plate-and-frame filter through a bottom stream pump, and filtered, the filtering feeding pressure of the plate-and-frame filter is 6-8 bar, the filtered liquor is mixed with the one-washing overflow and then sent to a leaching process; Step seven: the red mud filter cake is pressed by power wind provided by an air compressor, the pressing time is 4-6 min, then the filter cake is blown dry for 1-2 min to blow off residual liquid, and the filter cake after the blowing is transported to a red mud storage yard for storage; Step eight: the washing liquor generated by the plate-and-frame filter is collected into a red mud washing liquor tank and then transported back to the separation settling tank through a washing liquor pump, so that the washing liquor is recycled; Step nine: the temperature of the mixed washing water is monitored in real time, the amount of the mixed washing water is adjusted according to the concentration of the fine liquor, the amount of the washing water is reduced when the fine liquor needs to be increased, the amount of the washing water is increased when the fine liquor needs to be reduced, and meanwhile, the evaporation system is adjusted to adjust the yield of the evaporated water, so that the balance between the supply and the demand of the hot water is ensured.

2. The red mud settling process for alumina production according to claim 1, characterized in that, The evaporated water in step one is water absorbed by negative pressure steam generated by the last two-effect vacuum evaporation of the alumina evaporation system through cold water, and the water quality meets the washing requirement of the red mud and does not contain impurities affecting the dissolution of the alumina.

3. The red mud settling process for alumina production according to claim 1, characterized in that, The grading efficiency of the hydrocyclone in step three is greater than or equal to 70%, the particle size of the overflow is less than or equal to 0.1 mm, and the uniformity of the solid content of the slurry entering the separation settling tank is realized.

4. The red mud settling process for alumina production according to claim 1, characterized in that, The flocculating agent in step four is a polyacrylamide flocculating agent, and the adding mode is multi-point uniform spraying, so that the uneven settlement caused by the excessively high local flocculating agent concentration is avoided.

5. The red mud settling process for alumina production according to claim 1, characterized in that, The liquid-solid ratio of the washing water and the red mud in step five is controlled to be 4-6:1, the washing water flow is monitored in real time through a flowmeter, and the washing of each batch of red mud is ensured to be sufficient and the hot water is not wasted.

6. The red mud settling process for alumina production according to claim 1, characterized in that, The filtering period of the plate-and-frame filter in step six is 23-36 min, and the filtering period is divided into six stages, namely, 35 min of feeding, 0.5-1.5 min of pre-pressing, 6-10 min of washing, 4-6 min of pressing, 1-2 min of blowing and 8-12 min of cake discharging. ​ The pressure and time parameters of each stage are automatically controlled by the PLC system.

7. The red mud settling process for alumina production according to claim 1, characterized in that, In step seven, the blowing direction of the power wind forms an angle of 30-45° with the surface of the filter cake, so as to realize uniform airflow penetration through the filter cake and reduce the moisture content of the filter cake to below 25%.

8. The red mud settling process for alumina production according to claim 1, characterized in that, In step eight, a liquid level sensor is arranged in the red mud washing liquid tank, and when the liquid level is higher than 80%, a standby washing liquid pump is started to send part of the washing liquid to the adjusting liquid tank as the ball mill adjusting liquid, so as to realize the full-process recovery of the washing liquid.

9. The red mud settling process for alumina production according to claim 1, characterized in that, In step nine, a platinum resistance thermometer is used for temperature monitoring, which is installed at the outlet of the mixed washing water pipeline and transmits data to the control system in real time.

10. The red mud settling process for alumina production according to claim 1, characterized in that, In step nine, when the temperature is lower than 60℃, the amount of backwater supplement of the dam is reduced, and the proportion of evaporated unqualified condensed water is increased; when the temperature is higher than 75℃, the production circulating water at normal temperature is appropriately supplemented to maintain the stability of the washing water temperature.

Images