Metal oxide preparation method for NH3-CO2-HCl-H2O circulation and waste heat recycling

Abstract

The invention belongs to the technical field of hydrometallurgy, and discloses a metal oxide preparation method for NH3-CO2-HCl-H2O circulation and waste heat recycling, which comprises the steps of metal oxide preparation, bipolar membrane electrodialysis treatment and material recycling. The disadvantage of low concentration of ammonia water and hydrochloric acid prepared by electrolyzing the NH4Cl solution through the bipolar membrane is cooperated with a low-concentration metal oxide precipitation technology, so that the problems of corrosion, high equipment requirements, high cost and the like in the concentration process of dilute ammonia water and diluted hydrochloric acid are solved, and low-cost circulation of NH3-CO2-HCl-H2O and waste heat recycling in the metal oxide preparation process are realized; and the method has both technical advancement and industrial feasibility.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology and relates to a method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery. Background Technology

[0002] In the smelting and separation process, the NH4HCO3 precipitation method is commonly used to prepare metal carbonates from chloride solutions of various metals. This process generates a large amount of NH4Cl wastewater, especially low-concentration NH4Cl wastewater produced through washing processes. Direct discharge of NH4Cl wastewater causes serious water pollution. Furthermore, the production capacity of hydrochloric acid, ammonia, and ammonium bicarbonate byproducts from the petrochemical, coking, and agricultural fertilizer / pesticide industries in some cities is insufficient to support the capacity expansion of non-ferrous and rare earth industries, leading to price increases for hydrochloric acid and ammonia, and even intermittent production shutdowns in these industries. Therefore, achieving low-cost decomposition and conversion of NH4Cl wastewater into hydrochloric acid and ammonia for reuse in metal oxide smelting, and reducing the dependence of non-ferrous and rare earth industries on purchased hydrochloric acid and ammonia, is of great significance for cost reduction, efficiency improvement, and enhanced market competitiveness in these industries.

[0003] In addition, the current main method for preparing oxides is to use internal heating equipment such as tunnel kilns, roller kilns or pusher kilns to heat metal carbonates. The CO2 produced by burning natural gas in the internal heating method has a complex composition, high temperature and low CO2 concentration, which increases the difficulty and cost of CO2 recovery and utilization. This not only causes carbon emission problems in the smelting process, but also wastes a lot of carbon resources.

[0004] Based on the above problems, there is an urgent need to develop a method for preparing metal oxides using NH3-CO2-HCl recycling for the non-ferrous and rare earth industries. This method would enable the synergistic treatment of NH4Cl wastewater and CO2 in tail gas, solving the problem of emission treatment while reducing raw material costs for enterprises, improving resource utilization, and eliminating the limitations imposed by raw materials on enterprise capacity expansion.

[0005] Currently, decomposition and stripping of alkaline substances such as CaO, MgO, and NaOH or hot air stripping are common methods for treating NH4Cl wastewater. Ammonia water is recovered through alkaline / pyrolysis separation and distillation concentration. However, the production process cannot fully utilize the recovered ammonia water, resulting in a backlog of recycled resources and a low utilization rate of ammonia resources.

[0006] Chinese patent application CN106517621B discloses a process for recycling ammonium chloride-containing wastewater. The process includes: adding alkaline substances such as CaO and NaOH to the wastewater containing NH4Cl formed by rare earth extraction and precipitation to form a slurry; heating and decomposing NH4Cl to obtain recovered ammonia; concentrating and crystallizing to obtain byproducts such as CaCl2 and NaCl; and passing the recovered ammonia, along with CO2 generated from the pyrolysis of rare earth carbonates and the combustion of natural gas, into a rare earth chloride solution to undergo a gas-liquid precipitation reaction, yielding rare earth carbonates and NH4Cl wastewater, thus achieving the recovery and utilization of ammonia and carbon. This technology uses CO2 generated from the pyrolysis of rare earth carbonates mixed with the combustion of natural gas as a carbon source. However, the CO2 composition is complex, the temperature is high, the CO2 concentration is low, and the flow rate is unstable. Using it for rare earth chloride carbon precipitation would cause instability in the precipitation process, affecting product quality. Furthermore, CO2 is easily released during the reaction, resulting in low recovery and utilization rates. In addition, because the system uses alkaline substances such as CaO and NaOH, scaling and other problems are prone to occur during the treatment process, affecting treatment efficiency. Although the related processes have achieved the recovery of ammonia and carbon resources, the recovery efficiency is not high, and the chlorine resources have not been recovered and utilized.

[0007] Chinese patent application CN112850775A discloses a method for carbon-ammonia recycling in the rare earth oxide production process. This method involves mixing CO2 generated during rare earth precipitation and calcination with ammonia nitrogen wastewater obtained from ammonia stripping to produce ammonia water, which is then carbonized to yield an NH4HCO3 solution. This NH4HCO3 solution is returned to the precipitation process as a precipitant. While this method uses recovered CO2 and ammonia water to prepare an NH4HCO3 solution for rare earth precipitation, ensuring the stability of the precipitation process, CO2 is still released during precipitation. This CO2 is difficult to recover and capture, reducing the utilization rate of carbon and ammonia resources. Similarly, this method does not achieve chlorine resource recovery and utilization, resulting in a low water reuse rate.

[0008] Chinese patent application CN110606610B discloses a method for the cyclical treatment of metal chloride wastewater using an ammonia process. This method involves precipitating the metal chloride wastewater with ammonia to obtain metal hydroxides and an NH4Cl solution. Magnesium oxide is added to the NH4Cl solution, and the mixture is heated to evaporate ammonia and recover the ammonia water. After cooling and crystallization, solid MgCl2·6H2O is obtained. The solid MgCl2·6H2O is then pyrolyzed to yield MgO and hydrochloric acid. The ammonia water and MgO are recycled for wastewater and NH4Cl solution treatment, while hydrochloric acid is used as a byproduct. This method offers high resource recovery rates, but the pyrolysis temperature of MgCl2·6H2O is between 400 and 650°C. This high temperature places high demands on the corrosion resistance of the equipment, and dynamic ignition is required to ensure chlorine release rates. This results in high investment in process equipment and high overall wastewater treatment costs.

[0009] Chinese patent application CN106007110A discloses a method for the resource recovery and treatment of low-salinity wastewater. This method involves concentrating low-concentration inorganic salt wastewater (such as NH4Cl) through membrane distillation, followed by bipolar membrane electrodialysis to obtain low-concentration ammonia and hydrochloric acid solutions (<8 wt%). These solutions are then concentrated to 15-30 wt% through membrane distillation for use in smelting processes. While this method can efficiently achieve the synergistic recovery of ammonia and chlorine resources, the recovery of dilute ammonia and hydrochloric acid requires concentration through multi-effect evaporation and electrodialysis, placing high demands on the concentration equipment and significantly increasing operation and maintenance costs. Furthermore, bipolar membrane treatment of low-concentration wastewater still requires electrodialysis-reverse osmosis to produce clean freshwater before it can be returned to the system, resulting in low water recycling rates and failing to achieve closed-loop resource utilization.

[0010] While the above method achieves resource utilization of NH4Cl wastewater and partially couples with the metal oxide production process to realize the recovery and utilization of NH3-CO2-HCl, the following technical bottlenecks exist:

[0011] ① The resource recycling efficiency is low. The recovered ammonia and hydrochloric acid need to be concentrated twice before they can be reused. The treatment of highly corrosive media leads to an increase in equipment investment and operation and maintenance costs.

[0012] ② The CO2 capture rate is insufficient and a systematic cycle has not been formed;

[0013] ③ The low-salt wastewater produced by the process cannot be directly reused, the water reuse rate is low and the waste heat resources are not effectively utilized.

[0014] Therefore, it is urgent to construct a quaternary synergistic recycling system of "decomposition-capture-reuse-recovery" and to develop a green preparation method for metal oxides that integrates "NH3-CO2-HCl-H2O" full-element recycling and waste heat utilization, in order to achieve the following objectives:

[0015] ① Achieve direct recycling of low-concentration hydrochloric acid and ammonia water;

[0016] ② Achieve efficient CO2 capture and deep coupling with the metal oxide production system;

[0017] ③ Establish a graded water reuse system, especially for the reuse of low-salinity treated water, to achieve closed-loop utilization of process water;

[0018] ④ Achieve waste heat recovery and improve energy utilization efficiency. Summary of the Invention

[0019] This invention provides a method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery to solve the aforementioned problems.

[0020] To achieve the above objectives, the technical solution used in this invention is as follows:

[0021] Methods for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery include:

[0022] A metal chloride solution is reacted with a low-carbon precipitant to produce a metal oxide precursor and a low-concentration NH4Cl solution. The metal oxide precursor is then continuously and dynamically pyrolyzed to prepare the metal oxide, stably releasing CO2.

[0023] Low-concentration NH4Cl solution is electrolyzed by bipolar membrane electrodialysis into dilute hydrochloric acid, dilute ammonia water, and dilute saline solution;

[0024] Dilute ammonia absorbs CO2 from pyrolysis to prepare a low-carbon precipitant, dilute hydrochloric acid is used to prepare a metal chloride solution, and dilute brine is used as the base solution for the precipitation reaction.

[0025] Furthermore, a low-carbon precipitant is prepared, and the low-carbon precipitant is reacted with a metal chloride solution to produce a precipitation reaction. After solid-liquid separation and washing, a metal oxide precursor, a precipitated NH4Cl solution, and a washing solution are obtained. The metal oxide precursor is then continuously and dynamically pyrolyzed to prepare metal oxides, stably releasing CO2.

[0026] Furthermore, after precipitating and purifying the NH4Cl solution, a low-concentration NH4Cl solution is prepared. This solution is then processed through coagulation sedimentation, ultrafiltration, oil removal resin system, activated carbon adsorption system, chelating resin system, bipolar membrane electrodialysis system, electrodialysis system, and reverse osmosis system to obtain dilute hydrochloric acid with a concentration of 1.5-3 mol / L, dilute ammonia water with a concentration of 1.5-3 mol / L, and dilute saline solution.

[0027] Furthermore, the recovered dilute ammonia water captures the released CO2, and the reaction temperature is controlled at 10-80℃ to prepare a low-carbon precipitant; the dilute brine is used to wash the precipitation reaction substrate or metal oxide precursor; the washing liquid is used to prepare low-concentration NH4Cl solution and to wash the precipitation reaction substrate or carbon-containing metal oxide precursor.

[0028] Furthermore, the alkalinity of the low-carbon precipitant is 1.5–3 mol / L, and the CO3 content is [missing information]. 2- The concentration is 0.2-1.5 mol / L.

[0029] Furthermore, the metal element in the metal chloride solution is selected from one or more of Co, Ni, Cu, Zn, Nb, rare earth elements, etc., and its chloride ion concentration is 1.5-6 mol / L.

[0030] Furthermore, the precipitation reaction is carried out at a temperature of 10–100°C, and the final pH value is 6–8; the metal oxide precursor is one or a combination of two of the carbonates, basic carbonates, and hydroxides of the corresponding metal element.

[0031] Furthermore, the concentration of the low-concentration NH4Cl solution is <3mol / L, and the temperature is 5-60℃. The low-concentration NH4Cl solution is prepared by mixing the precipitated NH4Cl solution with the washing solution, or by mixing the precipitated NH4Cl solution with the condensed water recovered from the dilute hydrochloric acid and metal chloride solution.

[0032] Furthermore, the recovered dilute ammonia and released CO2 are mixed with the prepared metal chloride solution to precipitate and prepare metal oxide precursors; the concentrated condensate is used for organic washing, or for washing or precipitating the metal oxide precursor, or for preparing low-concentration NH4Cl solution.

[0033] Furthermore, it also includes the utilization of waste heat from the pyrolysis preparation of metal oxides. The pyrolysis CO2 is heated by a heat exchanger to produce brine, which is then used as the base liquid for precipitation reaction or for washing the carbon-containing precursors of the produced metal oxides, thus reducing the heating supply. After the pyrolysis CO2 is cooled, it is absorbed by dilute ammonia water to obtain a room temperature low-carbon precipitant for the precipitation of metal precursors. The brine produced absorbs dilute hydrochloric acid and dilute metal chloride solution to concentrate water vapor, and the resulting hot brine is used for washing the metal oxide precursors.

[0034] The technical effects of this invention include:

[0035] This invention combines the disadvantages of low concentration in the bipolar membrane electrolysis of NH4Cl solution to produce ammonia and hydrochloric acid with low-concentration metal oxide precipitation technology, solving the problems of corrosion, high equipment requirements, and high costs in the concentration process of dilute ammonia and dilute hydrochloric acid. It realizes low-cost recycling of NH3-CO2-HCl-H2O and waste heat recovery in the metal oxide preparation process, and has both technological advancement and industrial feasibility.

[0036] 1. This invention couples bipolar membrane electrodialysis, CO2 absorption, and metal oxide preparation technologies to achieve four benefits: wastewater treatment, ammonia recovery, chlorine reuse, and carbon capture. It forms a closed-loop cycle from NH4Cl wastewater → hydrochloric acid / ammonia water → metal oxide precursor production → NH4Cl wastewater, creating a complete resource recycling chain and realizing the recycling of NH3-CO2-HCl-H2O with no external discharge.

[0037] 2. This invention uses bipolar membrane electrodialysis to produce dilute NH3·H2O solution to directly prepare low-carbon precipitant, reducing the ammonia concentration operation; in addition, the low-concentration NH4Cl solution produced by bipolar membrane electrodialysis is returned to the purified freshwater system without electrodialysis-reverse osmosis, and can be directly used for washing metal oxide precursors or precipitating the bottom solution, significantly reducing treatment energy consumption and cost.

[0038] 3. This invention utilizes externally heated continuous dynamic pyrolysis, eliminating the need for natural gas combustion to produce CO2. The resulting CO2 is produced at stable and pure concentrations and flow rates, facilitating the capture of dilute ammonia and the control of the carbon content in the low-carbon precipitant. The hot CO2 gas generated during pyrolysis exchanges heat with the dilute brine produced during bipolar membrane electrodialysis to prepare hot water for washing metal salts, achieving comprehensive energy utilization.

[0039] 4. This invention uses a low-concentration, low-carbon precipitant to precipitate metal chlorides to prepare metal oxide precursors. The low concentration of the precipitant helps reduce impurity accumulation during the precipitation process and makes it easier to precisely control the precipitation process, achieving controllable preparation of materials with specific morphologies, particle size distributions, and specific surface areas. Furthermore, using a low-carbon precipitant avoids CO2 generation during the precipitation process, concentrating carbon emissions in the calcination step of the metal oxide precursor, improving resource recovery efficiency, and reducing overall carbon emissions.

[0040] 5. This invention uses treated NH4Cl brine or washing solution as the base liquid to increase the ionic strength of the precipitation environment, which can significantly improve the precipitation effect and enhance the filtration performance of metal oxide precursors.

[0041] 6. This invention utilizes the heat and water vapor generated during the process of absorbing CO2 pyrolysis with process-produced water or ammonia solution, and the concentration process of dilute hydrochloric acid or metal chloride solution, without adding other materials to achieve heat recovery and use for the precipitation of metal oxide precursors, thus realizing the reuse of waste heat. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery in this invention;

[0043] Figure 2 This is a flowchart of the ammonium chloride wastewater treatment process in this invention. Detailed Implementation

[0044] The following description fully illustrates specific embodiments of the invention to enable those skilled in the art to practice and reproduce them.

[0045] A method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery includes the following steps:

[0046] Step 1: Preparation of metal oxides;

[0047] A low-carbon precipitant was prepared and reacted with a metal chloride solution to induce a precipitation reaction. After solid-liquid separation and washing, a metal oxide precursor, a precipitated NH4Cl solution, and a washing liquid were obtained. The metal oxide precursor was then continuously and dynamically pyrolyzed to prepare metal oxides, stably releasing CO2.

[0048] In this embodiment, the low-carbon precipitant has an alkalinity of 1.5-3 mol / L and a CO3 content of [missing information]. 2- The concentration is 0.2-1.5 mol / L. Using low-carbon precipitants can reduce or even eliminate CO2 release during the carbon precipitation process of metal chlorides, thereby reducing carbon emissions during precursor preparation.

[0049] In addition, the use of low-alkalinity precipitants can effectively suppress problems such as explosive nucleation and co-precipitation of impurities caused by excessively high concentrations, making the precipitation process more precisely controlled and the product quality more stable.

[0050] In this embodiment, the metal chloride solution has a metal element selected from, but not limited to, one or more of Co, Ni, Cu, Zn, Nb, rare earth elements, etc., and its chloride ion concentration is 1.5-6 mol / L.

[0051] In this embodiment, the precipitation reaction is carried out at a temperature of 10-100℃, and the final pH value is 6-8.

[0052] In this embodiment, the metal oxide precursor is one or a combination of two of the following: carbonates, basic carbonates, and hydroxides of the corresponding metal element. With the metal oxide precursor CO3... 2- As the content decreases, the resulting metal hydroxides contain varying amounts of basic metal salts, with a Cl content ranging from 1% to 10%.

[0053] In this embodiment, continuous dynamic pyrolysis is used to form CO2 with stable concentration and flow rate, facilitating the capture of dilute ammonia and the control of the carbon content of the low-carbon precipitant. To ensure the purity of the CO2 atmosphere released during continuous dynamic pyrolysis, an externally heated continuous dynamic pyrolysis device is preferred. Using externally heated pyrolysis avoids impurities introduced by natural gas combustion and the impact of high-heat CO2 production on recovery efficiency.

[0054] In this embodiment, the metal oxide is accompanied by the metal oxide precursor CO3. 2- When the content decreases, it can form a mixture of metal chloride oxides and metal oxides with a Cl content of 1.5-25% or a pure metal chloride oxide.

[0055] like Figure 2 The diagram shown is a flow chart of ammonium chloride wastewater treatment in this invention.

[0056] Step 2: Bipolar membrane electrodialysis (BMED) treatment;

[0057] After precipitating and purifying the NH4Cl solution, a low-concentration NH4Cl solution was prepared. This solution was then separated using a bipolar membrane electrodialysis system to obtain 1.5-3 mol / L dilute hydrochloric acid, 1.5-3 mol / L dilute ammonia, and dilute saline solution.

[0058] In this embodiment, the purification method for the low-concentration NH4Cl solution is one or a combination of neutralization purification, ion exchange column purification, and chelating resin / activated carbon adsorption purification. After purification, the total content of divalent and higher cations such as Ca, Mg, Fe, and Zn in the NH4Cl solution is <1.0 g / L, and the SiO2 content is <0.1 g / L. Preferably, the total content of divalent and higher cations such as Ca, Mg, Fe, and Zn is <0.5 g / L, and the SiO2 content is <0.05 g / L.

[0059] In this embodiment, the NH4Cl concentration in the low-concentration NH4Cl solution is <3 mol / L, and the temperature of the bipolar membrane electrodialysis treatment is 5-60℃; preferably, the NH4Cl concentration is <2 mol / L, and the temperature of the bipolar membrane electrodialysis treatment is 5-40℃. The low-concentration NH4Cl solution is prepared by mixing a precipitated NH4Cl solution with a washing solution, or by mixing a precipitated NH4Cl solution with dilute hydrochloric acid produced in step 2: bipolar membrane electrodialysis treatment and a metal chloride solution produced in step 3: material recycling, followed by the concentration and recovery of condensate.

[0060] In this embodiment, the operating conditions for bipolar membrane electrodialysis are: current density 0.02-0.10 A / cm². 2 Voltage 50-120V.

[0061] Step 3: Material recycling.

[0062] 1. The dilute hydrochloric acid recovered in step 2 is used to prepare a metal chloride solution.

[0063] 2. Methods for preparing metal chloride solutions: Back-extraction of the loaded organic material with metal ions using dilute hydrochloric acid. If the concentration of the prepared metal chloride solution is low, the dilute hydrochloric acid solution can be directly concentrated before preparing the metal chloride solution; alternatively, energy-saving technologies such as membrane technology and multi-effect evaporation can be used to concentrate low-concentration metal chloride solutions.

[0064] The equipment, technology, and cost of concentrating metal chloride solutions are far lower than those for concentrating dilute hydrochloric acid. The condensate produced by concentration can be used for organic washing, washing of metal oxide precursors in step 1, precipitation of the bottom solution, and preparation of low-concentration NH4Cl solution in step 2.

[0065] 3. The dilute ammonia water recovered in step 2 is used to capture the CO2 released in step 1. The reaction temperature is controlled at 10-80℃ to prepare a low-carbon precipitant for recycling. The brine is used to wash the bottom liquid of the precipitation reaction or the metal oxide precursor.

[0066] The dilute ammonia water recovered in step 2, the CO2 released in step 1, and the metal chloride solution prepared in step 2 can be mixed and precipitated to prepare a metal oxide precursor.

[0067] 4. The washing solution obtained in step 1 is used for the preparation of low-concentration NH4Cl solution, the precipitation reaction substrate, or the washing of metal oxide precursors.

[0068] 5. The dilute brine obtained in step 2 can be used directly as the precipitation reaction substrate, or partially as a washing solution for metal oxide precursors. Using dilute brine containing a small amount of NH4Cl and washing water as the precipitation reaction substrate can increase the ionic strength of the reaction system, significantly improve the precipitation effect, and enhance the filtration performance of metal oxide precursors.

[0069] 6. Waste heat utilization methods include, but are not limited to, the following processes: ① The waste heat from the pyrolysis of CO2 in step 1 is recovered using a heat exchanger and applied to the dilute brine produced in step 2. After heating, the dilute brine is used as the base liquid for the precipitation reaction, reducing the heating supply. ② The waste heat from the pyrolysis of CO2 in step 1 is absorbed by the dilute ammonia water in step 2 to obtain a hot low-carbon precipitant for the precipitation of metal precursors, reducing the heating supply. ③ The dilute brine produced in step 2 absorbs dilute hydrochloric acid and dilute metal chloride solution to concentrate water vapor, obtaining hot dilute brine for washing metal oxide precursors.

[0070] 7. Prepare a metal chloride solution by recovering dilute hydrochloric acid. The preparation method involves back-extracting the loaded organic material containing metal ions with dilute hydrochloric acid. If the concentration of the prepared metal chloride solution is low, the dilute hydrochloric acid solution can be directly concentrated before preparing the metal chloride solution; alternatively, energy-saving technologies such as membrane technology and multi-effect evaporation can be used to concentrate the low-concentration metal chloride solution. The equipment, technology, and cost for concentrating the metal chloride solution are far lower than those for concentrating with dilute hydrochloric acid. The condensate produced from the concentration process can be used for washing the loaded organic material, washing the metal oxide precursor in step 1, or as the precipitate solution, and can also be used to prepare the low-concentration NH4Cl solution in step 2.

[0071] Example 1: Preparation and Integration Process of Nickel-Copper Mixed Oxide

[0072] (1) Preparation of metal oxides

[0073] Low-carbon precipitant: ammonia-ammonium bicarbonate system, alkalinity 1.8 mol / L, CO3 2- Concentration 0.3 mol / L.

[0074] Precipitation reaction: A mixed solution of NiCl2 and CuCl2 (Cl...) - The total concentration of 3.5 mol / L was reacted with the precipitant at 80℃, and the final pH was 6.5, producing a Ni(OH)2-Cu2(OH)3Cl composite precursor (Cl content 8%).

[0075] Pyrolysis: The mixture of NiO-CuO-CuCl2 (Cl content 18%) was obtained by external heating pyrolysis furnace (500℃). CO2 was directly absorbed by dilute ammonia water to form a precipitant.

[0076] (2) BMED processing

[0077] Feed solution: The precipitate mother liquor is mixed with the membrane concentration condensate, and the NH4Cl concentration is 1.2 mol / L.

[0078] BMED operation: current density 0.03 A / cm² 2 Voltage 1.2V / film pair, output:

[0079] Dilute hydrochloric acid (1.6 mol / L) → evaporated and concentrated to a Cl- concentration of 4 mol / L to dissolve metal waste;

[0080] Dilute ammonia (1.8 mol / L) → mixes with pyrolysis CO2 gas and liquid to precipitate, simultaneously generating a metal precursor as a precipitant;

[0081] Dilute saline solution (TDS≤3g / L) → can be used directly as a precursor washing solution.

[0082] (3) Material circulation

[0083] The residual heat from CO2 pyrolysis is used to preheat the brine feed solution;

[0084] Dilute hydrochloric acid is used to extract concentrated water vapor, which is then condensed and reused in the preparation of washing solution.

[0085] The brine absorbs the vapors of metal chlorides, which are then heated and used as a washing solution.

[0086] The terminology used in this invention is descriptive and exemplary, not restrictive. Since this invention can be embodied in many forms without departing from the spirit or essence of the technical solution, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery, characterized in that, include: A metal chloride solution is reacted with a low-carbon precipitant to produce a metal oxide precursor and a low-concentration NH4Cl solution. The metal oxide precursor is then continuously and dynamically pyrolyzed to prepare the metal oxide, stably releasing CO2. Low-concentration NH4Cl solution is electrolyzed by bipolar membrane electrodialysis into dilute hydrochloric acid, dilute ammonia, and dilute saline solution. Dilute ammonia absorbs CO2 from pyrolysis to prepare a low-carbon precipitant, dilute hydrochloric acid is used to prepare a metal chloride solution, and dilute brine is used as the base solution for the precipitation reaction.

2. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, A low-carbon precipitant was prepared, and the low-carbon precipitant was reacted with a metal chloride solution to produce a precipitation reaction. After solid-liquid separation and washing, a metal oxide precursor, a precipitated NH4Cl solution, and a washing solution were obtained. Metal oxide precursors are prepared by continuous dynamic pyrolysis, which stably releases CO2.

3. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, After precipitating and purifying the NH4Cl solution, a low-concentration NH4Cl solution is prepared. This solution is then processed through coagulation and sedimentation, ultrafiltration, oil removal resin system, activated carbon adsorption system, chelating resin system, bipolar membrane electrodialysis system, electrodialysis system, and reverse osmosis system to obtain dilute hydrochloric acid with a concentration of 1.5-3 mol / L, dilute ammonia water with a concentration of 1.5-3 mol / L, and dilute brine.

4. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The recovered dilute ammonia water captures the released CO2, and the reaction temperature is controlled at 10-80℃ to prepare a low-carbon precipitant; the brine is used to wash the precipitation reaction solution or metal oxide precursor. The washing solution is used for preparing low-concentration NH4Cl solutions, precipitating reaction substrates, or washing carbon-containing precursors of metal oxides.

5. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The alkalinity of the low-carbon precipitant is 1.5–3 mol / L, and the CO3 content is [missing information]. 2- The concentration is 0.2-1.5 mol / L.

6. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The metal chloride solution uses one or more of the following metal elements: Co, Ni, Cu, Zn, Nb, rare earth elements, etc., and its chloride ion concentration is 1.5-6 mol / L.

7. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The precipitation reaction is carried out at a temperature of 10-100℃, and the final pH value is 6-8. The metal oxide precursor is one or a combination of two of the carbonates, basic carbonates, and hydroxides of the corresponding metal element.

8. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The concentration of low-concentration NH4Cl solution is <3mol / L, and the temperature is 5-60℃. The low-concentration NH4Cl solution is prepared by mixing precipitated NH4Cl solution with washing solution, or by mixing precipitated NH4Cl solution with condensed water recovered from dilute hydrochloric acid and metal chloride solution.

9. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, The recovered dilute ammonia and released CO2 are mixed with the prepared metal chloride solution to precipitate and prepare metal oxide precursors. The concentrated condensate is used for organic washing, or for washing or precipitating the metal oxide precursor, or for preparing low-concentration NH4Cl solution.

10. The method for preparing metal oxides using NH3-CO2-HCl-H2O recycling and waste heat recovery as described in claim 1, characterized in that, It also includes the utilization of waste heat from the pyrolysis preparation of metal oxides. The pyrolysis CO2 is heated by a heat exchanger to produce brine, which is then used as the base liquid for precipitation reaction or for washing the carbon-containing precursors of the produced metal oxides, thus reducing the heating supply. After the pyrolysis CO2 is cooled, it is absorbed by dilute ammonia water to obtain a low-carbon precipitant at room temperature for the precipitation of metal precursors. The brine produced absorbs dilute hydrochloric acid and dilute metal chloride solution to concentrate water vapor, and the resulting hot brine is used for washing the metal oxide precursors.

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