Method and equipment for resource recovery and utilization of alumina red mud

Abstract

A method and equipment for recycling alumina red mud. First, the alumina red mud is added to a mixed acid of hydrochloric acid and sulfuric acid for reaction to dissolve metals such as iron, aluminum, calcium, sodium, and a small amount of zinc, copper, magnesium, etc., and the solid silicon dioxide is left to be separated as building materials or glass raw materials; after the solution is collected, ammonium bicarbonate is added to obtain aluminum, calcium, and some metal precipitates and separated. Iron and sodium remain in the solution and continue to react with sodium hydroxide to obtain iron hydroxide precipitate and separate out sodium salts. After evaporation of the concentrated solution, iron oxide is obtained as a raw material for steel production; the aluminum, calcium, and other metal precipitates are added to sulfuric acid with a concentration of 90-98% for reaction. After all are dissolved, the solution is subjected to membrane separation and then carbonates are added to obtain calcium carbonate precipitate as a raw material for cement production; after evaporation of the concentrated solution, high-purity alumina is obtained and sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products; the separated sodium salt solution is evaporated to be used as industrial and agricultural salt; the acid mist and harmful gases in the reactor process are treated by an absorption tower and then discharged. The present invention can make full use of the iron oxide, alumina, and effective components of alumina red mud, solves the problem of environmental pollution caused by the large amount of piled-up alumina red mud at present, has a low cost, and is suitable for the current alumina production plants.

Description

Technical Field

[0001] The present invention relates to a method for comprehensive utilization of industrial waste residues and solving environmental pollution, in particular to a method and equipment for resource recovery and utilization of alumina red mud. Background Art

[0002] The solid waste - red mud generated during alumina production is accumulating in increasing amounts. Generally, in the Bayer process, for every 1 ton of alumina produced on average, 1.0 - 2.0 tons of red mud are generated as a by - product. The resulting ecological impacts and potential environmental risks are becoming increasingly severe. Red mud contains a large amount of strongly alkaline chemical substances. After being diluted 10 times, its pH value is still 11.25 - 11.50. Such a high pH value determines the strong corrosiveness of red mud to organisms, metals, and siliceous materials. The highly alkaline sewage seeps into the ground or enters surface water, increasing the pH value of the water body. Mostly at home and abroad, red mud is transported to storage yards for stacking. The large - scale stacking of red mud not only occupies land but also wastes resources. Moreover, red mud contains various trace elements, and many resources have not been fully utilized. According to analysis, the data of various chemical components detected in the waste red mud of a certain aluminum company in Guangxi in recent years are as follows:

[0003] As a typical bulk solid waste in the alumina industry, the current comprehensive utilization rate of red mud does not exceed 6%, and the annual utilization amount is less than 7 million tons. To achieve the goal of increasing the comprehensive utilization rate of newly - generated bulk solid waste to 60% and orderly reducing the stock of bulk solid waste by 2025, the annual comprehensive utilization amount of red mud needs to reach more than 60 million tons. There is still a large gap between the current red mud utilization scale and utilization rate and the target value.

[0004] Although the iron grade in red mud is relatively low, considering the huge discharge amount of red mud, high - iron red mud is considered as one of the substitute raw materials for low - grade iron ore. Iron in red mud mainly exists in the form of composite mineral phases such as hematite (Fe2O3), goethite (α - FeOOH), aluminogoethite, and aluminomagnetite. Recovering iron is one of the important ways to reduce the amount of red mud. Scholars at home and abroad have carried out a large amount of research work on iron separation from red mud. The main iron - separation routes include physical separation, pyrometallurgy, and hydrometallurgy.

[0005] It can be seen that a large amount of alumina, iron oxide, etc. exist in red mud, which is a useful resource. If not utilized, it will be a great waste. Therefore, many different methods for the resource recovery and utilization of red mud have been proposed at home and abroad. For example, KASLIWAL et al. abroad proposed to leach components such as Fe, Al, Ca, Na, etc. in red mud in a hydrochloric acid solution at 60-90 °C and 1.0-1.5 mol / L, and then calcine with sodium carbonate at a temperature of 850-1150 °C, and then remove the soluble part by washing with water; some literature uses silica and calcium carbonate in red mud for the production of crystallized glass or cement production materials, such as the production of composite cement and alkali slag cement; due to the ultra-fine slurry particles of red mud, the cement produced from red mud has a higher consistency than ordinary cement. It is found through experiments that the cement produced by adding an appropriate proportion of red mud has good physical and mechanical properties and environmental safety; there is also literature introducing that according to the characteristics of highly alkaline red mud, its pH can be used to modify acidic soil (most of the red land in Guangxi is acidic soil). The mineral components containing iron and aluminum in red mud can also improve the phosphorus fixation ability of the soil, which is beneficial to the survival and reproduction of plants and microorganisms in the soil and also has a positive impact on preventing water eutrophication. In addition, red mud can also be used to repair heavy metal-polluted soil, reduce the content of heavy metal elements in the soil, and inhibit the adsorption of heavy metals by organisms and microorganisms. LOMBI et al. found that adding 2% of red mud to the soil can inhibit the adsorption of 2+ Cu 2+ Ni 2+ Zn 2+ Cd

[0006] After retrieval, we found the following public literatures:

[0007] 1. Discussion on the Comprehensive Utilization and Recovery Process of Alumina Red Mud, "China Mining Magazine", April 2001, authors Tan Hongqi and Liu Yuping. This article proposed that red mud should recover valuable elements, and recover elements such as iron, zinc, titanium, and rare earth through methods such as washing, heating, calcining, and magnetic separation.

[0008] 2. Chinese Patent, Application No.: 201110275267.8, a method for comprehensive utilization of alumina red mud treatment, comprising the following steps: First, pulp the alumina red mud and feed the slurry into a de-alkalization reaction tank; Second, de-alkalization treatment, add a de-alkalizing agent to the red mud slurry and stir evenly, where the de-alkalizing agent reacts rapidly in the reaction tank, and after the reaction, solid-liquid separation is carried out; Third, roasting reduction, subject the de-alkalized red mud to reduction treatment using a roasting reduction iron oxide process; Fourth, magnetic separation, use a mortar pump to send it into a magnetic separator to divide the red mud into two parts, magnetic and non-magnetic. The magnetic part is sent to a ball mill for fine grinding. The non-magnetic parts separated by the two magnetic separations are further filtered and dried and reserved as medium-fine sand for dry mortar, and alkaline materials such as carbide slag or limestone powder are added to activate the SiO2 and Al2O3 components therein.

[0009] 3. Chinese Patent, a method for comprehensive utilization of alumina red mud, Application No.: 2017102914171. Aiming at the problem that alumina red mud is difficult to treat and effectively recycle, this method uses vacuum thermal reduction to treat red mud, with carbon or aluminum as the reducing agent, to reduce iron oxide in the red mud to metallic iron under vacuum conditions, and then separates the iron in the reduced slag by magnetic separation for the production of reduced iron powder, reduces the combined sodium oxide to metallic sodium and distills it out, so as to achieve the purpose of removing alkali from red mud and recovering alkali. At the same time, other valuable substances in the red mud (such as scandium, niobium, cesium, etc.) are reduced to the metallic state and form alloys with aluminum, thus separating from the slag mainly composed of silicon oxide and aluminum oxide, realizing the harmless treatment of alumina red mud and the comprehensive recovery and utilization of valuable elements.

[0010] 4. Chinese Patent, a comprehensive utilization method for all-wet red mud, Application No. CN202011514868.5, Publication No. CN112981100A, Zhongxing Environmental Protection Technology (Guangxi) Co., Ltd., Inventors: Wu Chengshun; Yan Guiqing; Zhu Jiawen; Tang Wenhui; Chen Jian, Abstract. The present invention discloses a comprehensive utilization method for all-wet red mud. The inventors comprehensively recover calcium, aluminum, titanium, scandium, and iron in the red mud through reasonable process interspersion, with low cost, and produce six mid- to high-end chemical products in the market, such as calcium sulfate whiskers, alumina, titanium dioxide, scandium oxide, ferrous sulfate, and battery-grade iron phosphate. In addition, the present invention is completely wet-process, and the main equipment is only reaction tanks and filter presses, without special equipment, and the investment is relatively small. At present, the domestic red mud stockpile has reached one billion tons, and each alumina plant produces several million tons of red mud every year. The wet-process treatment is relatively flexible and can infinitely expand the production scale, while the fire-process treatment equipment is relatively special, the treatment scale is limited, and the energy consumption is also high. If the present invention can be widely promoted and applied, it can not only realize the reuse of waste, but also reduce the environmental pressure of the aluminum industry and can also achieve certain economic benefits.

[0011] 5. Chinese Patent: An Efficient and Low-Consumption Method for Comprehensive Utilization of Red Mud, Application No.: 2019104024474, Publication No.: CN110093471B, Inventors: Li Fangzheng; Peng Yu; Li Jiayi; Applicant: Shenzhen Qianhai Zhongneng Renewable Resources Co., Ltd., Abstract: The present invention discloses an efficient and low-consumption method for comprehensive utilization of red mud. The method involves stirring and slurrying red mud with water and then pressure filtering to obtain pre-alkali-removed red mud; mixing the pre-alkali-removed red mud with a reducing agent and a calcium-containing additive and pressing into pellets, and the pellet material is preheated and then melted at high temperature. The molten product is crushed and separated by magnetic separation to obtain reduced iron and slag that can be used as raw materials for compound fertilizers. This method can achieve the comprehensive utilization of red mud to obtain reduced iron and compound fertilizer raw materials with higher added value. Moreover, the red mud treatment process is simple, the raw materials are easily available, the operability is strong, the energy utilization rate is high, and the cost is low, which can generate good economic and social benefits.

[0012] 6. A new process for recovering alumina and iron oxide from low-temperature leached red mud, Application No.: CN202111429962.5, Publication (Announcement) No.: CN114212809A, Inventor (Designer): Feng Shengsheng; Liu Jiankang; Applicant: Feng Shengsheng, Abstract. The present invention relates to a new process for recovering alumina and iron oxide from low-temperature leached red mud, which includes the following steps: 1) batching; 2) high-temperature leaching; 3) cooling of the slurry; 4) liquid-solid separation; 5) washing of the red mud; 6) solid content adjustment; 7) rough selection; 8) tailings thickening; 9) thickening and de-sludging of the rough selection concentrate; 10) fine selection; 11) concentrate thickening; 12) concentrate pressure filtration; 13) thickening and de-sludging of the fine selection tailings; 14) scavenging; 15) middlings thickening; 16) middlings pressure filtration. Adopting this technical solution to treat low-temperature leached red mud has obvious advantages of high alumina recovery rate, high iron oxide recovery rate, good red mud sedimentation performance, and large red mud emission reduction.

[0013] 7. A method for comprehensively recovering aluminum oxide, sodium oxide and iron oxide from red mud, application number: CN201610700591.2, publication (announcement) number: CN106319226A, inventor: Li Xinhua; Gu Songqing; Yin Zhonglin, applicant: Aluminum Corporation of China Limited; Abstract: A method for comprehensively recovering aluminum oxide, sodium oxide and iron oxide from red mud, which relates to a method for comprehensively recovering aluminum oxide, sodium oxide and iron oxide from high-iron red mud, the waste of alumina production by the Bayer process. Its characteristic lies in that when the comprehensive recovery process uses alkaline solution to wet-treat Bayer red mud, an organic additive glycerol is added. The method of the present invention uses high molecular ratio alkaline solution and adds lime, and at the same time adds an organic additive, and carries out autoclave treatment on high-iron Bayer red mud at high temperature, so that most of the sodium oxide and aluminum oxide in the red mud enter the solution, and the iron minerals in the red mud have magnetism, so that while recovering aluminum oxide and sodium oxide, iron oxide can also be recovered by magnetic separation. The aluminum-silicon ratio A / S of the discarded red mud is 0.3 - 0.8, and the sodium-silicon ratio N / S is 0.01 - 0.1. The Na2O content is below 1%. After magnetic separation of the discarded red mud, the iron concentrate yield is 10 - 40%, and the iron grade is above 50%.

[0014] 8. A method for recovering aluminum oxide and sodium oxide from Bayer red mud, application number: CN201210532609.4, publication (announcement) number: CN103030160A, inventor: Cao Shaotao; Guo Tao; Zhang Yifei, applicant: Institute of Process Engineering, Chinese Academy of Sciences, Abstract: The present invention relates to a method for recovering aluminum oxide and sodium oxide from Bayer red mud. This method uses a high molecular ratio and high alkali concentration sodium aluminate solution, and can quickly carry out the aluminum extraction reaction under mild operating conditions. The recovery rate of aluminum oxide in the red mud is as high as over 85%, and it can effectively prevent and even eliminate problems such as equipment scaling; by realizing the efficient crystallization process of the intermediate product sodium aluminate hydrate, the circulation efficiency of the dissolution medium can be greatly improved; the complete transformation of the phases in the aluminum extraction reaction enables the reaction process of recovering sodium oxide to be carried out at low temperature and normal pressure. After the secondary sodium removal reaction, the sodium oxide content in the final red mud is not higher than 1%, which is much lower than the sodium oxide content of 6 - 8% in Bayer red mud. Thus, a large proportion of red mud can be doped and used for preparing cement, bricks, roadbed materials, concrete admixtures, environmental remediation materials and other fillers, etc., and is expected to solve problems such as the resource utilization of red mud and potential environmental hazards.

[0015] The above-mentioned disclosed methods for treating red mud only propose to recover some useful elements, and cannot fully recover all the effective elements in the red mud. Some processes and equipment are also very complex, require harsh conditions, and the recovery rates of iron and aluminum are relatively low. Therefore, how to recover all useful elements at low cost as much as possible is still a scientific research problem worthy of study. Summary of the Invention

[0016] The purpose of the present invention is to provide a method and equipment for recycling alumina red mud, which solves the problem of environmental pollution caused by the large-scale stacking of current alumina red mud, and can also recover a large amount of resources, with low cost and good economic benefits.

[0017] The present invention dissolves alumina red mud, adds certain chemical agents and undergoes a series of chemical reactions to convert components such as iron, aluminum, calcium, sodium, and silicon dioxide in the red mud into by-products such as recoverable iron oxide, aluminum oxide, silicon dioxide, calcium carbonate, sodium sulfate, and sodium chloride, effectively disposing of the red mud and generating considerable economic benefits with a high recovery rate, thereby realizing the harmless treatment of red mud.

[0018] The present invention is realized in the following manner:

[0019] A method for resource recycling of alumina red mud, characterized in that: First, after metering the alumina red mud, add mixed acid and place it in the first reactor to form a slurry, stir and react for 2 - 3 hours, with the reaction temperature of 40 - 50 °C. Chlorides, sulfates of iron, aluminum, calcium, and sodium and solid silicon dioxide are obtained in the solution, and the pH of the reaction is 1 - 2. More than 95% of iron, aluminum, calcium, and sodium can be dissolved. After the solution is collected, place it in the second reactor, add ammonium bicarbonate, and adjust the pH of the reaction to 8 - 9.5 to obtain precipitated aluminum oxide and calcium carbonate. The remaining ferric chloride and ferrous sulfate solutions are stored in the No. 1 collection tank and pumped to the third reactor for reaction by a liquid pump. According to the content of iron oxide in the solution, add a sodium hydroxide solution with a weight content of 10 - 15%, react for 1 - 2 hours to obtain iron hydroxide precipitate and separate it in the No. 1 membrane separator to separate out dilute liquid and iron hydroxide concentrate. The iron hydroxide concentrate is evaporated in an evaporator to obtain solid iron oxide; the dilute liquid is returned to the first reactor for reuse or concentrated to obtain sodium salts when the concentration reaches a certain level;

[0020] The mixed acid described is an aqueous solution of 25 - 30% hydrochloric acid and 5 - 15% dilute sulfuric acid, with a weight ratio of 5:1;

[0021] The precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor and reacts with 90 - 98% sulfuric acid. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, dissolve aluminum, calcium, magnesium, zinc, and other metal salts. The reaction temperature is 70 - 90 °C, and the reaction time is 1.5 - 2.5 hours. More than 99% of metal salts can be dissolved. After the reaction is complete, solid silicon dioxide is separated by centrifugation. The silicon dioxide can be used as a raw material for glass or quartz sand in the building materials industry;

[0022] The solution separated by the fourth reactor enters the No. 2 collection tank, and is pumped to the No. 2 membrane separation device by a liquid pump. Dilute liquid and concentrated liquid are separated. The dilute liquid can be returned to the first reactor for reuse or, when the concentration reaches a certain level, sodium salt is obtained through evaporation and concentration; the concentrated liquid is alumina and calcium salt. After passing through a storage tank, it enters the fifth reactor and reacts with a carbonate, namely sodium carbonate or sodium bicarbonate. The reaction temperature is 20 - 40°C, the reaction time is 1 - 2 hours, and the pH of the reaction is 10 - 12. Calcium carbonate precipitate and alumina are formed, and then it enters the No. 2 centrifugal separation tank. The calcium carbonate precipitate is separated, and the alumina in the concentrated liquid finally obtains high-purity alumina through evaporation. The total recovery rate of Al2O3 reaches 93%, and the weight content of alumina is ≥95%. It is sent to an aluminum processing factory to produce pure aluminum or aluminum alloy products.

[0023] The No. 1 membrane separator described is a microfiltration membrane, and its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm; it can permeate sodium salt and intercept the iron hydroxide concentrated liquid; the No. 2 membrane separation device described is an ultrafiltration membrane, and its filter membrane is made of a material that can permeate sodium nanomaterials, and its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm; it can permeate sodium salt; it intercepts alumina and calcium carbonate.

[0024] The first reactor, the second reactor and the fourth reactor are closed reactors. An air outlet pipe is provided above the closed reactor to lead the acid mist and harmful gases after the reaction to an exhaust gas processor for absorption with alkali liquid and clean water to purify them, and then they are discharged by a induced draft fan; the alkali liquid described can be the solution filtered by the No. 1 membrane separator or the No. 2 membrane separator, or an alkaline solution prepared separately.

[0025] The residence time of the acid mist and harmful gases in the exhaust gas processor is generally 10 - 30 minutes (the power of the induced draft fan is designed according to the gas discharge volume).

[0026] The evaporators used for the iron hydroxide concentrated liquid and the alumina concentrated liquid are steam evaporators or high-temperature hot oil evaporators.

[0027] The main chemical reactions occurring in the reactors of the present invention are as follows:

[0028] Chemical equation for the reaction of alumina with hydrochloric acid: Al2O3 + 6HCl = 2AlCl3 + 3H2O

[0029] Chemical equation for the reaction of alumina with sulfuric acid: Al2O3 + 3H2SO4 = 3H2O + Al2(SO4)3

[0030] Chemical equation for the reaction of iron oxide with hydrochloric acid: Fe2O3 + 6HCl = 2FeCl3 + 3H2O

[0031] Chemical equation for the reaction of iron oxide with sulfuric acid: Fe2O3 + 3H2SO4 = Fe2(SO4)3 + 3H2O

[0032] Reaction equation of calcium carbonate with hydrochloric acid: CaCO3 + 2HCl = CaCl2 + CO2↑ + H2O

[0033] Reaction equation of ammonium bicarbonate with iron is 3(NH4) + + 2Fe(OH)3 = Fe2(CO3)3 + 6NH3↑ + 6H2O

[0034] Reaction equation of sodium hydroxide solution with ferric chloride: FeCl3 + 3NaOH = Fe(OH)3↓ + 3NaCl

[0035] Reaction equation of calcium carbonate with sulfuric acid: CaCO3 + 2H2SO4 = CaSO4 + CO2↑ + H2O

[0036] Reaction equation of ferrous sulfate with sodium hydroxide: FeSO4 + 2NaOH = Fe(OH)3↓ + Na2SO4

[0037] Because the red mud reaction system is relatively complex and there are some side reactions, the reaction equations are not listed here.

[0038] When the red mud contains other minor metals such as zinc, copper, silver, manganese, lead, nickel, titanium, chromium, cobalt, and cadmium, they are almost dissolved by concentrated sulfuric acid in the second reactor, and other reagents need to be added for further recovery or removal according to specific circumstances.

[0039] The equipment for the resource recovery and utilization of alumina red mud according to the present invention is characterized in that: it includes a first reactor, a second reactor, a third reactor, a fourth reactor, a fifth reactor, and liquid pumps, collection tanks and separation tanks connected to each reactor. The first reactor is equipped with a red mud feeder and a mixed acid meter; the second reactor is equipped with a red mud feeder and a mixed acid meter; the third reactor has an ammonium bicarbonate meter; the fourth reactor is equipped with a sulfuric acid meter; the fifth reactor is equipped with a carbonate meter. The outlet pipe of the second reactor is connected to a No. 1 collection tank, then through a liquid pump and then connected to the third reactor, and then connected to a No. 1 membrane separation device to separate dilute liquid and iron oxide concentrate, and the concentrate is connected to an iron oxide evaporator; the second reactor is provided with a centrifugal device to send the solid to the fourth reactor, the fourth reactor is connected to a No. 1 centrifugal separation tank to separate silicon dioxide, and the liquid from the No. 1 centrifugal tank enters a No. 2 collection tank, and after passing through a liquid pump, it is connected to a No. 2 membrane separator to separate dilute liquid. The dilute solution can be returned to the first reactor for reuse or evaporated to obtain sodium salts; the concentrate enters the fifth reactor through a storage tank, reacts with carbonate to obtain calcium carbonate solid and alumina solution, and then enters a No. 2 centrifugal tank, where the calcium carbonate solid and alumina solution are separated. The alumina solution enters an alumina evaporator to obtain alumina solid.

[0040] The first reactor, the second reactor and the fourth reactor are closed reactors. There is an exhaust gas outlet pipe above the reactor, which leads to an exhaust gas processor to absorb and treat acid mist and harmful gases. Inside the exhaust gas processor is an absorption tower with three sections: upper, middle and lower. The top is a packing layer, which is composed of several layers of circular cross partition ring packings stacked together. Ceramic rings or acid-resistant plastic rings can be used. Inside the middle part of the exhaust gas processor is a cyclone plate absorber, and a funnel and a perforated plate are provided in the middle and lower parts. The funnel and the perforated plate are both provided with small holes to evenly drop the liquid droplets; a clear water spray head is provided below the packing layer, and an alkali liquid spray head is provided below the cyclone plate absorber; there is an exhaust gas inlet pipe and a liquid outlet pipe after absorbing the gas at the lower part of the absorption tower; the acid mist and harmful gases enter the exhaust gas processor from the exhaust gas inlet pipe, pass through the liquid layer and upward through the perforated plate and the funnel, react with the alkali liquid sprayed by the alkali liquid spray head, then go up through the cyclone plate absorber to reduce the acid mist again, and finally go up through the packing layer, become harmless gas and are taken out by the induced draft fan at the top of the absorption tower. The waste water is sent to the sewage treatment pool through the outlet pipe and the valve for unified treatment.

[0041] The above-described cyclone plate absorber is a device for cyclone plate demisting, with a structure that consists of a central shaft and bearings supporting a double-layer cyclone plate. The inner layer has a smaller diameter and is located above, while the outer layer has a larger diameter and is located below. It is a device that utilizes the function of the cyclone plate to transform axial flow into swirling flow and the centrifugal force generated by the swirling flow for demisting. After the liquid is sprayed down from above and falls onto the cyclone plate, at this time, the flue gas flows upward from the bottom of the tower. Due to tangential entry into the tower, especially the guiding effect of the tower plate blades, the flue gas rotates upward, causing the liquid flowing down plate by plate on the tower plate to be sprayed into droplets, resulting in a large contact area between the gas and the liquid. The droplets are driven by the airflow to rotate, and the centrifugal force generated strengthens the contact between the gas and the liquid. Finally, they are thrown onto the tower wall and flow down along the wall, passing through the overflow device to the next tower plate, where they are atomized again by the airflow for gas-liquid contact. After the liquid comes into full contact with the gas, it can be effectively separated - avoiding entrainment of mist droplets. Its gas-liquid load ratio is more than twice that of common tower plates. Compared with the packing layer, it can reduce acid mist and harmful gases by dozens of times. Therefore, in the middle of the waste gas processor of the present invention, the waste gas can be purified without secondary treatment of the waste gas.

[0042] Before the solution containing sodium salt separated by the No. 1 membrane separator and the No. 2 membrane separator and returned to the first reactor enters the evaporator, there is a valve that can be controlled. When the concentration is relatively dilute, evaporation is not required. When the concentration reaches a certain level, it must be adjusted through the valve to enter the evaporator to avoid affecting the balance of the chemical reaction.

[0043] The membrane separator in the production process is a device for separating iron oxide, aluminum oxide, sodium chloride, sodium sulfate, and calcium carbonate according to different needs. Currently, in laboratory or industrial-scale production, the membrane is made into a component of a certain form as the separation unit of the membrane separation device. The membrane components applied and commercialized in industry mainly include flat plate type, round tube type, spiral wound type, and hollow fiber type. The corresponding geometric shapes of the membrane are divided into flat plate type, tube type, and hollow fiber type. The capillary membrane has a diameter between 0.5 and 10 mm; the hollow fiber membrane has a diameter less than 0.5 mm. The smaller the diameter of the tubular membrane, the larger the membrane area per unit volume. Under the action of a static pressure difference as the driving force, the solvent and small solute particles in the feed liquid pass through the membrane from the high-pressure feed liquid side to the low-pressure side, which is generally called the filtrate or permeate, while the large particle components are blocked by the membrane, increasing their concentration in the retentate. According to such a separation mechanism, the main factor for the ultrafiltration membrane to have a selective surface layer is to form pores of a certain size and shape, and the chemical properties of the polymer have little influence on the separation characteristics of the membrane. That is, the retention of solutes in the ultrafiltration process has three ways: mechanical retention (screening) on the surface of the membrane, removal by staying in the membrane pores (blocking), and adsorption on the surface and inside the pores of the membrane (primary adsorption). The industrial applications of ultrafiltration membranes can be divided into three types: (1) concentration; (2) separation of small molecule solutes; (3) fractionation of large molecule solutes. The vast majority of industrial applications belong to the concentration aspect. Small molecule solutes can be separated by methods of binding or compounding with macromolecules. Another finer separation is the application of microfiltration membranes. Microfiltration is the most widely used and largest-selling technology among all membrane processes, mainly used in occasions where particles larger than 0.1 mm are separated from the solution, such as the separation, concentration, fractionation, and purification of iron oxide, aluminum oxide, sodium chloride, and sodium sulfate in the present invention. Its advantages are: improved production efficiency and product quality; simplified process flow.

[0044] The first reactor described above is provided with a heater; the first reactor, the third reactor, and the fourth reactor are provided with bubblers; the fourth reactor is provided with a water cooling jacket.

[0045] The several reactors and auxiliary equipment described above can be provided with temperature, pressure, and liquid level sensors inside. Transmitted to the central computer through the sensors, automated operation control can be achieved.

[0046] The evaporators used for the iron hydroxide concentrate and the aluminum oxide concentrate described above are steam evaporators or high-temperature hot oil evaporators.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] 1. By using the method of dissolving red mud twice with mixed acid and concentrated sulfuric acid, iron oxide, aluminum oxide, calcium oxide and some metal oxides are dissolved in the solution, and then iron oxide, aluminum oxide, calcium carbonate, sodium salt and silicon dioxide are extracted and separated respectively. The process method is reasonable, simple and low-cost, and can realize continuous operation. It can effectively dispose of red mud and generate considerable economic benefits, thus realizing the harmless treatment of red mud. A treatment plan has been found for the nearly 1 billion tons of red mud stored in the country, and the economic benefits and social benefits brought to alumina enterprises are very considerable, with a very broad prospect.

[0049] 2. More than 90% of iron oxide and 95% of aluminum oxide can be recovered, and resources are fully utilized, enabling alumina production enterprises to fully recover iron and aluminum. The recovery rate of iron oxide is greater than 90%, the content reaches more than 95%, the aluminum oxide reaches more than 90%, and it contains no sulfur. The removal rates of calcium and silicon reach more than 98%, meeting the conditions for producing high-purity aluminum.

[0050] 3. All red mud can be utilized, which not only brings very considerable economic benefits to enterprises, but also greatly reduces red mud emissions. The cost of resource recovery and utilization of alumina red mud is lower than the cost of harmless disposal, and it does not occupy land resources. It avoids harm to the environment and can achieve a double harvest of economic benefits and social benefits.

[0051] 4. In the present invention, mixed acid is added to the first reactor, which can increase the reaction temperature, time and speed. The reactions of aluminum, iron and other metals are relatively complete, and it is not necessary to heat the red mud slurry because the mixed acid contains some sulfuric acid and the heater does not need to be turned on. When hydrochloric acid is added alone, the reaction time is prolonged.

[0052] In the present invention, since mixed acid is added to the first reactor, iron oxide reacts with sulfuric acid and hydrochloric acid to form ferrous sulfate and ferric chloride. When ammonium bicarbonate is added, it is not easy to form iron oxide precipitation, so that ferrous sulfate and ferric chloride can be separated from aluminum oxide.

[0053] 5. The silicon dioxide content reaches 98%, which is suitable for producing high-performance glass. If further purified, silicon wafers can be prepared as raw materials for semiconductor production.

[0054] 6. The by-product calcium carbonate can be used as a raw material for cement production. It has fine particles, can reduce the sintering temperature of clinker, improve the compressive strength of cement, make the crystal grains and liquid phase microstructure in the clinker more uniform, reduce the sintering temperature, and the 28d compressive strength reaches 48.9MPa, meeting the strength of 525R cement.

[0055] 7. The present invention can also extract non-ferrous metals Mn, Mg, Ti, Zn, Cu and some rare metals from red mud, comprehensively improving the recovery ability.

[0056] 8. There is no waste gas emission during the production process of the present invention. The first reactor, the second reactor, and the fourth reactor are closed reactors. There is an exhaust gas outlet pipe above the reactors, which leads to an exhaust gas processor to absorb and treat acid mist and harmful gases. Inside the exhaust gas processor is an absorption tower with three sections: upper, middle, and lower. The acid mist and harmful gases enter the exhaust gas processor from the waste gas pipe inlet, pass through the liquid layer upwards, pass through the perforated plate and the funnel, react with the alkali solution sprayed by the alkali solution nozzle, then pass upwards through the cyclone plate absorber to reduce the acid mist again, and finally pass upwards through the packing layer, becoming harmless gases and being taken out by the induced draft fan at the top of the absorption tower. The wastewater passes through the outlet pipe and the valve to the sewage treatment pond for unified treatment, realizing that all the reaction outlet gases of the red mud treatment with acid, alkali, and ammonium salt are completely absorbed by the exhaust gas processor, and the production process is safe and controllable without waste gas and waste residue emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is the process flow chart of the method for resource recovery and utilization of alumina red mud in the present invention.

[0058] Figure 2 is the schematic diagram of the internal structure of the exhaust gas processor.

[0059] Figure 3 is Figure 2 the enlarged view of A-A (the device for removing mist by the cyclone plate absorber)

[0060] The equipment and process principle for the resource recovery and utilization of alumina red mud in the present invention will be described below with reference to the drawings first:

[0061] As Figure 1 shown, the present invention includes a first reactor, a second reactor, a third reactor, a fourth reactor, a fifth reactor, and liquid pumps, collection tanks, and separation tanks connected to each reactor. The first reactor is equipped with a red mud feeder and a mixed acid meter, the second reactor is equipped with a red mud feeder and a mixed acid meter, the third reactor has an ammonium bicarbonate meter, the fourth reactor is equipped with a sulfuric acid meter, and the fifth reactor is equipped with a carbonate meter. The outlet pipe of the second reactor is connected to the No. 1 collection tank, then through a liquid pump and then connected to the third reactor, and then connected to the No. 1 membrane separation device to separate the dilute liquid and the iron oxide concentrate. The concentrate is connected to the iron oxide evaporator; the second reactor is provided with a centrifugal device to send the solid to the fourth reactor. The fourth reactor is connected to the No. 1 centrifugal separation tank to separate silicon dioxide. The liquid from the No. 1 centrifugal tank enters the No. 2 collection tank, and through a liquid pump is connected to the No. 2 membrane separator to separate the dilute liquid. The dilute solution can be returned to the first reactor for reuse or evaporated to obtain sodium salts; the concentrate enters the fifth reactor through a storage tank, reacts with carbonate to obtain calcium carbonate solid and alumina solution, and then enters the No. 2 centrifugal tank, where the calcium carbonate solid and alumina solution are separated. The alumina solution enters the alumina evaporator to obtain alumina solid.

[0062] The first reactor, the second reactor and the fourth reactor are closed reactors. There is an exhaust gas outlet pipe above the reactor, which leads to the exhaust gas processor to absorb and treat the acid mist and harmful gases. The exhaust gas processor is an absorption tower with three sections, upper, middle and lower. The top is a packing layer, which is composed of a number of stacked circular cross partition ring packings. Ceramic rings or acid-resistant plastic rings can be used. There is a cyclone plate absorber in the middle of the exhaust gas processor, and a funnel and a flower plate are provided in the middle and lower parts. The funnel and the flower plate are both provided with small holes to allow the droplets to flow evenly. Fall; a clean water nozzle is provided below the packing layer, and an alkali solution nozzle is provided below the cyclone plate absorber; a waste gas inlet pipe and a liquid outlet pipe after the absorbed gas are provided at the lower part of the absorption tower; acid mist and harmful gases enter the waste gas processor from the waste gas pipe inlet, pass through the flower plate and funnel upward through the liquid layer, react with the alkali solution sprayed by the alkali solution nozzle, and then go up through the cyclone plate absorber to reduce the acid mist again, and finally go up through the packing layer, become harmless gas to the top of the absorption tower and be taken out by the induced draft fan, and the wastewater is led to the sewage treatment pool for unified treatment through the outlet pipe and valve.

[0063] The sodium salt solution separated by membrane separator No. 1 and membrane separator No. 2 and returned to the first reactor is provided with a valve before entering the evaporator for control. When the concentration is relatively thin, evaporation is not required. When the concentration reaches a certain level, it must be regulated by the valve to enter the evaporator.

[0064] Figure 2 The waste gas processor provided is a wet processor. The internal structure of the waste gas processor is an absorption tower with three sections, upper, middle and lower. The top is a packing layer, which is composed of several stacked cylindrical ceramic rings or acid-resistant polymer rings. The middle is a cyclone plate absorber, and the lower part is a funnel and a flower plate. The funnel and the flower plate are both provided with small holes to allow the droplets to fall evenly. Acid mist and harmful gases enter the absorber from the lower part of the waste gas processor through valves and pipes, pass through the liquid layer, and are first absorbed once, then go upward, pass through the flower plate and funnel, and come into contact with the alkali solution sprayed by the nozzle, continue upward, pass through the double-layer cyclone plate supported by the central axis and bearings, remove acid mist and harmful gases, and come into contact with the clean water sprayed by the nozzle, and finally pass through the packing layer, and the water foam is removed by several stacked cylindrical ceramic rings or acid-resistant polymer ring packing layers, and becomes harmless gas and is taken out by the induced draft fan. After the liquid at the bottom of the waste gas processor reaches a certain concentration, it is discharged to the sewage treatment pool through the valve for treatment.

[0065] The present invention can effectively recover the residual iron and aluminum in the alumina red mud, and can also obtain silicon dioxide suitable for glass production, calcium carbonate suitable as a cement raw material, and sodium chloride and sodium sulfate (as chemical raw materials).

[0066] from Figure 3It is understood that the cyclone plate absorber is a device that relies on the cyclone plate to remove fog. It has a structure that supports a double-layer cyclone plate by a central shaft and bearings. The inner layer has a smaller diameter and is located above, while the outer layer has a larger diameter and is located below. It is a device that uses the function of the cyclone plate to change the axial flow into a cyclone flow and the centrifugal force generated by the cyclone to remove fog.

[0067] Inside several reactors, waste gas processors and auxiliary equipment described in the present invention, temperature, pressure, liquid level, and pH sensors can be provided. Transmitted to the central computer through the sensors, automatic operation control can be achieved. Detailed implementation mode

[0068] Example 1

[0069] Method for resource recovery and utilization of alumina red mud. The specific process is as follows: First, measure the alumina red mud and add it to a mixed acid. The mixed acid is 25% hydrochloric acid and 8% dilute sulfuric acid aqueous solution, with a weight ratio of 5:1. Put the mixed acid into the first reactor, adjust it into a slurry, and stir and react with the red mud for 3 hours. The reaction temperature is 40 - 45 °C, and the pH of the reaction is 1 - 2. In the solution, chloride salts, sulfate salts of iron, aluminum, calcium, and sodium, as well as solid silicon dioxide are obtained. More than 95% of iron, aluminum, calcium, and sodium can be dissolved. After collecting the solution, put it into the second reactor, add ammonium bicarbonate, and adjust the pH of the reaction to 7 - 9. The reaction time is 2 hours to obtain precipitated alumina and calcium carbonate. The remaining ferric chloride and aluminum sulfate solutions are stored in the No. 1 collection tank and pumped to the third reactor for reaction. According to the content of iron oxide in the solution, add a 10% sodium hydroxide solution by weight and react for 1 hour to obtain ferric hydroxide precipitate, which is separated in the No. 1 membrane separator to separate out the dilute solution and ferric hydroxide concentrate. The ferric hydroxide concentrate is evaporated in an evaporator to obtain solid iron oxide. The dilute solution is returned to the first reactor for reuse or concentrated to obtain sodium salts when the concentration reaches a certain level. The precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor and reacts with 92% sulfuric acid. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, dissolve aluminum, calcium, magnesium, zinc, and other metal salts. The reaction temperature is 80 °C, and the reaction time is 1.5 hours. More than 99% of the metal salts can be dissolved. After the reaction is complete, solid silicon dioxide is separated by centrifugation. The silicon dioxide can be used as a raw material for glass or quartz sand in the building materials industry. The solution separated from the fourth reactor enters the No. 2 collection tank and is pumped to the No. 2 membrane separation device to separate out the dilute solution and concentrate. The dilute solution can be returned to the first reactor for reuse or concentrated by evaporation to obtain sodium salts when the concentration reaches a certain level. The concentrate is alumina and calcium salts. After passing through a storage tank, it enters the fifth reactor and reacts with a carbonate, namely sodium carbonate or sodium bicarbonate. The reaction temperature is 25 °C, and the reaction time is 1 hour. The pH of the reaction is 10 - 12 to generate calcium carbonate precipitate and alumina. Then it enters the No. 2 centrifugal separation tank to precipitate calcium carbonate and separate out calcium carbonate. The alumina in the concentrate is finally evaporated to obtain high-purity alumina. The total recovery rate of Al2O3 reaches 93%, and the weight content of alumina is ≥95%. It is sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products.

[0070] The No. 1 membrane separator mentioned above is a microfiltration membrane, and its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm. It can permeate sodium salts and retain the ferric hydroxide concentrate. The No. 2 membrane separation device is an ultrafiltration membrane, and its filter membrane is made of a material that can permeate sodium nanomaterials. Its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm. It can permeate sodium salts and retain alumina and calcium carbonate.

[0071] The first reactor, the second reactor, and the fourth reactor are enclosed reactors. An exhaust pipe is provided above the enclosed reactor to lead the acid mist and harmful gases after the reaction to an exhaust gas processor for absorption by alkali solution and clean water, so as to purify them, and then they are extracted and discharged through a induced draft fan; the alkali solution can be the solution filtered by the No. 1 membrane separator or the No. 2 membrane separator, or an alkaline solution prepared separately. The evaporators used for the iron hydroxide concentrate and the aluminum oxide concentrate are steam evaporators or high-temperature hot oil evaporators.

[0072] The equipment for resource recovery and utilization of bauxite residue in the present invention includes a first reactor, a second reactor, a third reactor, a fourth reactor, a fifth reactor, and the liquid pumps, collection tanks, and separation tanks connected to each reactor. The first reactor is equipped with a bauxite residue feeder and a mixed acid meter, the second reactor is equipped with a bauxite residue feeder and a mixed acid meter, the third reactor has an ammonium bicarbonate meter, the fourth reactor is equipped with a sulfuric acid meter, the fifth reactor is equipped with a carbonate meter. The outlet pipe of the second reactor is connected to the No. 1 collection tank, then through a liquid pump and then connected to the third reactor, and then connected to the No. 1 membrane separation device to separate the dilute solution and the iron oxide concentrate, and the concentrate is connected to the iron oxide evaporator; the second reactor is provided with a centrifugal device to send the solid to the fourth reactor, the fourth reactor is connected to the No. 1 centrifugal separation tank to separate silicon dioxide, the liquid from the No. 1 centrifugal tank enters the No. 2 collection tank, and after passing through a liquid pump, it is connected to the No. 2 membrane separator to separate the dilute solution. The dilute solution can be returned to the first reactor for reuse or evaporated to obtain sodium salts; the concentrate enters the fifth reactor through a storage tank, reacts with carbonate to obtain calcium carbonate solid and aluminum oxide solution, and then enters the No. 2 centrifugal tank, and the calcium carbonate solid and the aluminum oxide solution are separated. The aluminum oxide solution enters the aluminum oxide evaporator to obtain aluminum oxide solid.

[0073] The first reactor, the second reactor, and the fourth reactor are enclosed reactors. There is an exhaust gas outlet pipe above the reactor, which is connected to an exhaust gas processor to absorb and process the acid mist and harmful gases. Inside the exhaust gas processor is an absorption tower with three sections: upper, middle, and lower. The top is a packing layer, which is composed of several layers of circular cross partition ring packings stacked together. Ceramic rings or acid-resistant plastic rings can be used. Inside the middle part of the exhaust gas processor, there is a cyclone plate absorber. The middle and lower parts are provided with a funnel and a perforated plate. The funnel and the perforated plate are both provided with small holes to make the liquid droplets fall evenly; a clean water spray head is provided below the packing layer, and an alkali solution spray head is provided below the cyclone plate absorber; there is an exhaust gas inlet pipe and a liquid outlet pipe after absorbing the gas at the lower part of the absorption tower; the acid mist and harmful gases enter the exhaust gas processor from the exhaust gas pipe inlet, pass through the liquid layer, pass upward through the perforated plate and the funnel, react with the alkali solution sprayed by the alkali solution spray head, then pass upward through the cyclone plate absorber to reduce the acid mist again, and finally pass upward through the packing layer to become harmless gases and are taken out by the induced draft fan at the top of the absorption tower. The wastewater passes through the outlet pipe and the valve to the sewage treatment pool for unified treatment.

[0074] The above-mentioned cyclone plate absorber is a device for cyclone plate demisting, with a structure that supports a double-layer cyclone plate by a central shaft and bearings. The inner layer has a smaller diameter and is located above, while the outer layer has a larger diameter and is located below. It is a device that uses the function of the cyclone plate to change the axial flow into a cyclone flow and the centrifugal force generated by the cyclone to remove mist. After the liquid is sprayed down from above and falls onto the cyclone plate, at this time, the flue gas flows upward from the bottom of the tower. Due to the tangential inlet into the tower, especially the guiding effect of the tower plate blades, the flue gas rotates upward, causing the liquid flowing down plate by plate on the tower plate to be sprayed into droplets, resulting in a large contact area between the gas and the liquid. The droplets are driven by the gas flow to rotate, and the generated centrifugal force strengthens the contact between the gas and the liquid. Finally, they are thrown onto the tower wall and flow down along the wall, passing through the overflow device to the next layer of the tower plate, where they are atomized again by the gas flow and gas-liquid contact occurs. After the liquid is in full contact with the gas, it can be effectively separated - avoiding entrainment of mist droplets. Its gas-liquid load ratio is more than twice that of common tower plates. Compared with the packing layer, it can reduce acid mist and harmful gases by dozens of times. Therefore, the present invention can achieve the purpose of purifying gas without secondary treatment of the waste gas when used in the middle of the waste gas processor. The solution containing sodium salt separated by the No. 1 membrane separator and the No. 2 membrane separator and returned to the first reactor is provided with a valve before entering the evaporator, which can be controlled. When the concentration is relatively dilute, evaporation is not required. When the concentration reaches a certain level, it must enter the evaporator through the valve to avoid affecting the balance of the chemical reaction.

[0075] The above-mentioned first reactor is provided with a heater; the first reactor, the third reactor, and the fourth reactor are provided with bubblers; the fourth reactor is provided with a water cooling jacket.

[0076] Temperature, pressure, and liquid level sensors can be provided inside the several reactors and their auxiliary equipment, and transmitted to the central computer through the sensors, enabling automated operation control.

[0077] The evaporators used for the above-mentioned ferric hydroxide concentrate and alumina concentrate are steam evaporators or high-temperature hot oil evaporators.

[0078] Example 2

[0079] Method for recycling and utilization of alumina red mud, and specific process is as follows: First, after metering alumina red mud, add mixed acid. The mixed acid is 26 - 30% hydrochloric acid and 10% dilute sulfuric acid aqueous solution, with a weight ratio of 5:1. Put the mixed acid into the first reactor, adjust it into a slurry state, stir and react with red mud for 2.5 hours, with a reaction temperature of 45 - 48°C and a reaction pH of 1 - 2. Obtain chloride salts, sulfate salts of iron, aluminum, calcium, and sodium, as well as solid silicon dioxide in the solution. More than 95% of iron, aluminum, calcium, and sodium can be dissolved. After collecting the solution, put it into the second reactor, add ammonium bicarbonate, adjust the reaction pH to 7 - 9, and react for 1.5 hours to precipitate alumina and calcium carbonate. The remaining ferric chloride and aluminum sulfate solutions are stored in the No. 1 collection tank, pumped to the third reactor through a liquid pump for reaction. According to the content of iron oxide in the solution, add 10% sodium hydroxide solution by weight, react for 1 - 2 hours to obtain ferric hydroxide precipitate and separate it in the No. 1 membrane separator to separate out dilute liquid and ferric hydroxide concentrate. The ferric hydroxide concentrate is evaporated in an evaporator to obtain solid iron oxide; the dilute liquid is returned to the first reactor for reuse or concentrated to obtain sodium salts when the concentration reaches a certain level; the precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor, add 96% sulfuric acid for reaction. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, dissolve aluminum, calcium, magnesium, zinc, and other metal salts. The reaction temperature is 85°C and the reaction time is 1.5 hours. More than 99% of metal salts can be dissolved. After the reaction is complete, centrifuge to separate out solid silicon dioxide, and the silicon dioxide can be used as raw material for glass or quartz sand in the building materials industry; the solution separated from the fourth reactor enters the No. 2 collection tank, is pumped to the No. 2 membrane separation device through a liquid pump to separate out dilute liquid and concentrate. The dilute liquid can be returned to the first reactor for reuse or concentrated by evaporation to obtain sodium salts when the concentration reaches a certain level; the concentrate is alumina and calcium salts, enters the fifth reactor after passing through a storage tank, add carbonate, namely sodium carbonate or sodium bicarbonate for reaction. The reaction temperature is 30°C and the reaction time is 1 hour, with a reaction pH of 10 - 11, to generate calcium carbonate precipitate and alumina, and then enter the No. 2 centrifugal separation tank to precipitate calcium carbonate, separate out calcium carbonate, and the alumina in the concentrate is finally evaporated to obtain high-purity alumina. The total recovery rate of Al2O3 reaches 95%, and the weight content of alumina is ≥95%, which is sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products.

[0080] The structure of the equipment described is the same as that in Example 1.

[0081] Example 3

[0082] Method for recycling and utilization of alumina red mud resources. The specific process is as follows: First, measure the alumina red mud and add it to a mixed acid. The mixed acid is an aqueous solution of 30 - 32% hydrochloric acid and 12 - 15% dilute sulfuric acid, with a weight ratio of 5:1. Put the mixed acid into the first reactor, adjust it into a slurry, and stir and react with the red mud for 2 hours. The pH of the reaction is 1 - 2, and the reaction temperature is 50°C. In the solution, chloride salts, sulfate salts of iron, aluminum, calcium, and sodium, as well as solid silicon dioxide are obtained. More than 95% of iron, aluminum, calcium, and sodium can be dissolved. After collecting the solution, put it into the second reactor, add ammonium bicarbonate, and adjust the pH of the reaction to 8 - 9.5. The reaction time is 1.5 - 2 hours to obtain precipitated alumina and calcium carbonate. The remaining ferric chloride and aluminum sulfate solutions are stored in a No. 1 collection tank and pumped to the third reactor for reaction. According to the content of iron oxide in the solution, add a sodium hydroxide solution with a weight content of 10% and react for 1.5 hours to obtain ferric hydroxide precipitate, which is separated by a No. 1 membrane separator to separate out dilute liquid and ferric hydroxide concentrated liquid. The ferric hydroxide concentrated liquid is evaporated in an evaporator to obtain solid iron oxide; the dilute liquid is returned to the first reactor for reuse or concentrated to obtain sodium salts when the concentration reaches a certain level; the precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor and reacts with 98% sulfuric acid. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, dissolve aluminum, calcium, magnesium, zinc, and other metal salts. The reaction temperature is 75°C, and the reaction time is 1.5 hours. More than 99% of the metal salts can be dissolved. After the reaction is complete, solid silicon dioxide is separated by centrifugation. The silicon dioxide can be used as a raw material for glass or quartz sand in the building materials industry; the solution separated from the fourth reactor enters a No. 2 collection tank and is pumped to a No. 2 membrane separation device to separate out dilute liquid and concentrated liquid. The dilute liquid can be returned to the first reactor for reuse or concentrated by evaporation to obtain sodium salts when the concentration reaches a certain level; the concentrated liquid is alumina and calcium salts. After passing through a storage tank, it enters the fifth reactor and reacts with a carbonate, namely sodium carbonate or sodium bicarbonate. The reaction temperature is 30°C, the reaction time is 1 - 1.5 hours, and the pH of the reaction is 10.0 - 10.9 to generate calcium carbonate precipitate and alumina. Then it enters a No. 2 centrifugal separation tank to precipitate calcium carbonate and separate out calcium carbonate. The alumina in the concentrated liquid is finally evaporated to obtain high-purity alumina. The total recovery rate of Al2O3 reaches 96%, and the weight content of alumina is ≥95%, which is sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products.

[0083] The structure of the equipment described is the same as that in Example 1.

[0084] Example 4 (Comparative Example)

[0085] Method for resource recovery and utilization of alumina red mud. The specific process is as follows: First, measure the alumina red mud and add hydrochloric acid, which is an aqueous hydrochloric acid solution with a concentration of 25 - 32%, into the first reactor, make it into a slurry, heat it to 20 - 35°C, and stir and react with the red mud for 3 - 4 hours. In the solution, chlorides of iron, aluminum, calcium, and sodium, as well as solid silicon dioxide, are obtained. The pH of the reaction is 2 - 3, and more than 90% of iron, aluminum, calcium, and sodium can be dissolved. After collecting the solution, put it into the second reactor, add sodium bicarbonate, adjust the pH of the reaction to 8 - 10, and react for 3 - 4 hours to obtain precipitated alumina and calcium carbonate (note that we found the existence of a small amount of brown iron oxide precipitate here). The remaining ferric chloride and aluminum sulfate solution are stored in the No. 1 collection tank, pumped to the third reactor by a liquid pump for reaction. According to the content of iron oxide in the solution, add a sodium hydroxide solution with a weight content of 10%, react for 1 - 2 hours, the reaction temperature is 30 - 40°C, and the pH of the reaction is 1 - 3 to obtain precipitated iron hydroxide and separate it in the No. 1 membrane separator to obtain dilute liquid and concentrated iron hydroxide solution. The concentrated iron hydroxide solution is evaporated in an evaporator to obtain solid iron oxide; the dilute liquid is returned to the first reactor for reuse or concentrated to obtain sodium salts when the concentration reaches a certain level; the precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor and reacts with 90 - 98% sulfuric acid. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, dissolve aluminum, calcium, magnesium, zinc, and other metal salts. The reaction temperature is 70 - 90°C, and the reaction time is 1.5 - 2 hours. More than 99% of the metal salts can be dissolved. After the reaction is complete, solid silicon dioxide is separated by centrifugation. The silicon dioxide can be used as a raw material for glass or quartz sand for the building materials industry; the solution separated from the fourth reactor enters the No. 2 collection tank, is pumped to the No. 2 membrane separation device by a liquid pump to separate dilute liquid and concentrated liquid. The dilute liquid can be returned to the first reactor for reuse or concentrated by evaporation to obtain sodium salts when the concentration reaches a certain level; the concentrated liquid is alumina and calcium salts. After passing through a storage tank, it enters the fifth reactor and reacts with a carbonate, namely sodium carbonate or sodium bicarbonate. The reaction temperature is 20 - 40°C, the reaction time is 1 - 3 hours, and the pH of the reaction is 10.0 - 10.9 to generate precipitated calcium carbonate and alumina, and then enter the No. 2 centrifugal separation tank to precipitate calcium carbonate and separate calcium carbonate. The alumina in the concentrated liquid is finally evaporated to obtain high-purity alumina. The total recovery rate of Al2O3 is 85%, and the weight content of alumina is ≥90%, which is sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products.

[0086] The five reactors and the attached separation equipment described are the same as those in Example 1, but the waste gas processor does not have a swirl plate tower. Acid mist and harmful gases pass through the bottom alkaline liquid absorption after the inlet pipe of the waste gas processor, then go up through the middle perforated plate and then through the packing layer, and then are discharged from the outlet of the induced draft fan. As a result, the gas discharged into the environment contains 1 - 3% of acid mist and harmful gases, which does not meet the emission standards.

[0087] Summary of data for four embodiments: The data of the above-described Embodiments 1-4 (Embodiment 4 is a comparative embodiment, with the same equipment but different process conditions. The hydrochloric acid added to the first reactor is a 25-30% hydrochloric acid aqueous solution, and sodium carbonate is added to the second reactor instead of ammonium bicarbonate, and there is a very small amount of brown iron oxide precipitate in the solution) are shown in Table 1 below.

[0088]

Claims

1. A method for resource recovery and utilization of alumina red mud, characterized in that: First, measure the alumina red mud and add it to the mixed acid, then place it in the first reactor to form a slurry, and stir and react for 2 - 3 hours at a reaction temperature of 40 - 50°C. In the solution, chloride salts, sulfate salts of iron, aluminum, calcium, and sodium, as well as solid silicon dioxide are obtained. The pH of the reaction is 1 - 2. After collecting the solution, place it in the second reactor, add ammonium bicarbonate, and adjust the pH of the reaction to 8 - 9.

5. React for 1 - 2 hours to obtain precipitated alumina and calcium carbonate. The remaining ferric chloride and ferrous sulfate solutions are stored in the No. 1 collection tank and pumped to the third reactor by a liquid pump for reaction. According to the content of iron oxide in the solution, add a sodium hydroxide solution with a weight content of 10 - 15% and react for 1 - 2 hours to obtain ferric hydroxide precipitate, which is separated in the No. 1 membrane separator to separate dilute liquid and ferric hydroxide concentrated liquid. The ferric hydroxide concentrated liquid is evaporated in an evaporator to obtain solid iron oxide; the dilute liquid is returned to the first reactor for reuse or concentrated to obtain sodium salts; The mixed acid described above is an aqueous solution of 25 - 30% hydrochloric acid and 5 - 15% dilute sulfuric acid, with a weight ratio of 5:1; The precipitate containing aluminum chloride, calcium carbonate, and silicon dioxide separated from the second reactor enters the fourth reactor and reacts with 90 - 98% sulfuric acid. According to the content of aluminum chloride, calcium carbonate, and other impurity metals, all aluminum, calcium, magnesium, zinc, and other metal salts are dissolved. The reaction temperature is 70 - 90°C, and the reaction time is 1.5 - 2.5 hours. After the reaction is complete, solid silicon dioxide is separated by centrifugation. The silicon dioxide can be used as a raw material for glass or quartz sand in the building materials industry; The solution separated from the fourth reactor enters the No. 2 collection tank and is pumped to the No. 2 membrane separation device by a liquid pump to separate dilute liquid and concentrated liquid. The dilute liquid can be returned to the first reactor for reuse or concentrated by evaporation to obtain sodium salts; the concentrated liquid is alumina and calcium salts. After passing through a storage tank, it enters the fifth reactor and reacts with a carbonate, namely sodium carbonate or sodium bicarbonate. The reaction temperature is 20 - 40°C, and the reaction time is 1 - 2 hours. The reaction pH value range is 10 - 12, generating calcium carbonate precipitate and alumina. Then it enters the No. 2 centrifugal separation tank to precipitate calcium carbonate and separate calcium carbonate. The alumina in the concentrated liquid is finally evaporated to obtain high-purity alumina. The total recovery rate of Al2O3 reaches 93%, and the weight content of alumina is ≥95%, which is sent to an aluminum processing plant to produce pure aluminum or aluminum alloy products; The No. 1 membrane separator described above is a microfiltration membrane, and its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm; it can permeate sodium salts and retain ferric hydroxide concentrated liquid; the No. 2 membrane separation device is an ultrafiltration membrane, and its filter membrane is made of a material that can permeate sodium nanomaterials, and its filter membrane is made of molecular sieve membrane material, with a thickness of 0.02 - 0.05 mm; it can permeate sodium salts; it retains alumina and calcium carbonate; The first reactor, the second reactor, and the fourth reactor are closed reactors. An air outlet pipe is provided above the closed reactor to lead the acid mist and harmful gases after the reaction to an exhaust gas processor for absorption with alkali solution and clean water to purify it, and then it is discharged by an induced draft fan; the alkali solution can be the solution filtered by the No. 1 membrane separator or the No. 2 membrane separator, or a separately prepared alkaline solution.

2. The method for resource recovery and utilization of alumina red mud according to claim 1, characterized in that: The evaporator used for the ferric hydroxide concentrated solution and the aluminum oxide concentrated solution is a steam evaporator or a high-temperature hot oil evaporator.

3. An apparatus for the resource recovery and utilization of alumina red mud, characterized in that: The invention comprises a first reactor, a second reactor, a third reactor, a fourth reactor, a fifth reactor and a liquid pump, a collecting tank and a separating tank connected to each reactor. The first reactor is equipped with a red mud feeder and a mixed acid meter, the second reactor is equipped with a red mud feeder and a mixed acid meter, the third reactor is equipped with an ammonium bicarbonate meter, the fourth reactor is equipped with a sulfuric acid meter, the fifth reactor is equipped with a carbonate meter, the outlet pipe of the second reactor is connected to the No. 1 collecting tank and then to the third reactor through a liquid pump, and then to the No. 1 membrane separation device to separate the dilute liquid and the iron oxide concentrated liquid, and the concentrated liquid is The liquid is connected to the iron oxide evaporator; the second reactor is provided with a centrifugal device to pass the solid to the fourth reactor, the fourth reactor is connected to the No. 1 centrifugal separation tank to separate the silicon dioxide, the liquid from the No. 1 centrifugal tank enters the No. 2 collection tank, and is connected to the No. 2 membrane separator through a liquid pump to separate the dilute liquid, which can be returned to the first reactor for reuse, or evaporated to obtain sodium salt; the concentrated liquid enters the fifth reactor through the storage tank, is added with carbonate to react to obtain calcium carbonate solid and aluminum oxide solution, and then enters the No. 2 centrifugal tank to separate the calcium carbonate solid and the aluminum oxide solution, and the aluminum oxide solution enters the aluminum oxide evaporator to obtain aluminum oxide solid.

4. The equipment for resource recovery and utilization of alumina red mud according to claim 3, characterized in that: The first reactor, the second reactor and the fourth reactor are closed reactors. There is a waste gas outlet pipe above the reactor, which leads to the waste gas processor to absorb and treat the acid mist and harmful gases. The waste gas processor is an absorption tower with three sections, upper, middle and lower. The top is a packing layer, which is composed of a number of circular cross partition ring packings stacked together. There is a cyclone plate absorber in the middle of the waste gas processor, and a funnel and a flower plate are provided in the middle and lower parts. The funnel and the flower plate are both provided with small holes to allow the droplets to fall evenly; a clean water nozzle is provided below the packing layer, and an alkali solution nozzle is provided below the cyclone plate absorber; a waste gas inlet pipe and a liquid outlet pipe after absorbing the gas are provided at the bottom of the absorption tower; the acid mist and harmful gases enter the waste gas processor from the waste gas pipe inlet, pass through the flower plate and the funnel upward through the liquid layer, react with the alkali solution sprayed by the alkali solution nozzle, and then go up through the cyclone plate absorber to reduce the acid mist again, and finally go up through the packing layer to become harmless gas to the top of the absorption tower and be taken out by the induced draft fan, and the wastewater is passed to the sewage treatment pool through the outlet pipe and the valve for unified treatment.

5. The equipment for resource recovery and utilization of alumina red mud according to claim 3, characterized in that: The first reactor is provided with a heater; the first reactor, the third reactor and the fourth reactor are provided with bubblers; and the fourth reactor is provided with a water cooling jacket.

6. The equipment for resource recovery and utilization of alumina red mud according to claim 3, characterized in that: The first to fifth reactors and the auxiliary equipment may be provided with temperature, pressure and liquid level sensors, which can be transmitted to the central computer through the sensors to realize automatic operation control.

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