Method for resource utilization of stainless steel pickling solution

Abstract

The present application relates to the technical field of stainless steel pickling solution treatment process, and particularly relates to a method for resource utilization of stainless steel pickling solution, comprising: S1, mixing the stainless steel pickling solution with magnesite, and then performing a temperature rising oxygen reaction to obtain a leaching solution and iron residue; S2, adding magnesium oxide to the leaching solution to obtain a chromium precipitation residue and a chromium precipitation mother liquor; S3, continuously adding magnesium oxide to the chromium precipitation mother liquor to perform a reaction, and then filtering to obtain a nickel-cobalt hydroxide and a nickel-cobalt precipitation mother liquor; S4, adding hydrogen peroxide and magnesium oxide to the nickel-cobalt precipitation mother liquor to perform a reaction, and then filtering to obtain a manganese residue and a manganese precipitation mother liquor; and S5, adding calcium oxide to the manganese precipitation mother liquor to perform a reaction, and then filtering to obtain a fluorine precipitation residue and a magnesium nitrate solution. The free acid, iron, chromium, nickel, cobalt, manganese and fluorine elements in the stainless steel pickling solution are again subjected to segmented and stepped resource utilization, no secondary pollution is generated, no waste residue and waste gas are discharged, and the method has the advantages of green, low carbon, environmental protection and the like and good social and economic value.

Description

Technical Field

[0001] This invention relates to the field of stainless steel pickling solution treatment technology, and in particular to a method for the resource utilization of stainless steel pickling solution. Background Technology

[0002] Improving the utilization rate of waste acid resources has become an urgent need for the sustainable development of the acid industry. Since magnesium nitrate solution has a wide range of applications in industry and agriculture, the generated magnesium nitrate solution can be used directly or after concentration, especially as a dehydrating agent in the production of nitric acid. Therefore, reproducing magnesium nitrate from waste acid can save costs and produce a variety of products. The recycled waste acid has a smaller impact on the environment, achieving the harmless treatment of waste acid.

[0003] However, existing stainless steel pickling solution recovery processes have the following problems: Most stainless steel pickling solutions utilize two main methods for acid regeneration: free acid regeneration and total acid regeneration. Free acid regeneration has two methods: resin adsorption and diffusion dialysis. Free acid regeneration has the disadvantage of unstable metal separation, requiring increased waste acid treatment volume to control the metal content in the pickling solution. The latter has a slightly lower recovery rate than resin adsorption. Total acid regeneration is currently the most advanced acid regeneration process in the world, but the technology is not particularly mature, is expensive, and difficult to maintain. Summary of the Invention

[0004] This invention provides a method for the resource utilization of stainless steel pickling solution. This method uses a stepwise precipitation method, which is beneficial for the separation of valuable metals. The amount of magnesite (containing a suitable low content of magnesium oxide) added is easy to control. The precipitate obtained by stepwise precipitation has less residual valuable metals in the mother liquor after solid-liquid separation, resulting in low recovery costs. The auxiliary materials can be recycled, and high-purity magnesium nitrate is obtained. This method can effectively reduce sewage discharge costs and recover multiple metal elements. This process has the advantages of high efficiency, simplicity, green and low-carbon environmental protection, and great social and economic value.

[0005] Specifically, the present invention provides the following technical solution:

[0006] A method for the resource utilization of stainless steel pickling solution includes the following steps:

[0007] S1. After mixing the stainless steel pickling solution with magnesite, the mixture is heated and oxygenated for 1-3 hours. The solution is filtered to obtain leaching solution and iron slag. After washing, the iron slag is iron concentrate with an iron content of more than 60%.

[0008] S2. Add magnesium oxide to the leachate and react, then filter to obtain chromium precipitate slag and chromium precipitate mother liquor;

[0009] S3. Add magnesium oxide to the chromium precipitation mother liquor and filter to obtain nickel cobalt hydroxide and nickel cobalt precipitation mother liquor;

[0010] S4. Add hydrogen peroxide and magnesium oxide to the nickel-cobalt precipitate mother liquor and react, then filter to obtain manganese slag and manganese precipitate mother liquor.

[0011] S5. Add calcium oxide to the manganese precipitation mother liquor and react, then filter to obtain fluorine precipitation residue and magnesium nitrate solution;

[0012] S6. The magnesium nitrate solution is concentrated and crystallized under negative pressure to obtain magnesium nitrate crystals;

[0013] S7. Some magnesium nitrate crystals are heated and melted into liquid, then sprayed into a decomposition furnace to come into contact with the hot circulating gas for thermal decomposition. After passing through a high-temperature membrane dust collector, the resulting gas is cooled and pressurized for absorption to obtain new nitric acid.

[0014] In S1 of this invention, the amount of magnesite used is 1.3 to 1.8 times, preferably 1.5 to 1.8 times, the molar amount of iron in the stainless steel pickling solution. This invention uses a combined treatment of magnesite and stainless steel pickling solution, which can precipitate most of the iron and excess residual acid in the stainless steel pickling solution, thus improving the quality of the subsequent precipitate product. Furthermore, by using an appropriate ratio of ingredients, iron can be effectively precipitated without precipitating other elements, further improving the quality of the precipitate product. However, if the ratio of ingredients is inappropriate, such as excessive magnesite leading to the precipitation of other valuable metals, or insufficient magnesite resulting in incomplete iron precipitation, the quality of the subsequent precipitate product will be affected.

[0015] In S1 of this invention, the oxygen pressure is controlled at 0.1-0.6 MPa, preferably 0.2-0.6 MPa, and the reaction temperature is 100-150°C. Combined with an appropriate reaction time, this can maximize the conversion of ferrous iron in the stainless steel pickling solution into ferric iron, which is conducive to the rapid precipitation of iron, reduces the iron content in the solution, and indirectly improves the influence of iron on the quality of subsequent precipitation products.

[0016] Preferably, the magnesite comprises: Co 0-0.0020wt%, Ni 0.01-0.029wt%, Fe 0.005-0.011wt%, Mn 0.005-0.011wt%, Ca 2.0-4.0wt%, Mg 22-24wt%, Na 0.01-0.03wt%, and Si 0.03-0.05wt%. This preferred embodiment uses magnesite with a suitable composition, which is not only inexpensive but also effectively consumes excess residual acid in the stainless steel pickling solution. Furthermore, the addition of an appropriate amount of magnesium ions reduces the impact on subsequent precipitation, thus facilitating production cost control.

[0017] Optionally, the stainless steel pickling solution comprises: Co 0.3-0.6 g / L, Ni 0.5-0.8 g / L, Fe 55-60 g / L, Mn 5-7 g / L, Ca 0.005-0.01 g / L, Cr 7-9.5 g / L, NO3- 120-135 g / L, Si 0.4-0.6 g / L. This invention is particularly suitable for treating stainless steel pickling solutions with this specific composition. Through stepwise precipitation, it can maximize the comprehensive recovery of valuable metals in the solution, enabling harmless and resource-based treatment, and maximizing the economic benefits of stainless steel pickling solution recycling.

[0018] Optionally, the reaction conditions in S2 include: a temperature of 50–80°C, a reaction time of 1–3 h, and a magnesium oxide dosage of 1.2–1.8 times, preferably 1.45–1.8 times, the total molar amount of iron and chromium in the leachate. This preferred scheme provides suitable reaction conditions. By adding an appropriate amount of magnesium oxide, trace amounts of iron and chromium are precipitated. Furthermore, since the amount of magnesium oxide added is only slightly different from the molar amount of iron and chromium compared to the theoretical reaction amount, it is insufficient to precipitate nickel and cobalt. This not only ensures more thorough precipitation of iron and chromium but also allows nickel and cobalt to remain in the solution as much as possible.

[0019] Optionally, the reaction conditions in S3 include: a temperature of 50–80°C, a reaction time of 1–3 h, followed by aging for 0.5–2 h, and the amount of magnesium oxide used being 1–1.1 times the total molar amount of nickel and cobalt in the chromium precipitation mother liquor. This preferred scheme has suitable reaction conditions, which are more conducive to the precipitation of nickel and cobalt, resulting in a higher nickel and cobalt content and better quality in the nickel and cobalt precipitate.

[0020] Optionally, the reaction conditions in S4 include: a temperature of 50–80°C, a reaction time of 1–3 h, followed by aging for 0.5–2 h; the amount of magnesium oxide used is 1–1.1 times the total molar amount of nickel and manganese in the nickel-cobalt precipitate mother liquor; and the amount of hydrogen peroxide used is 1–1.15 times the molar amount of manganese in the nickel-cobalt precipitate mother liquor. This preferred scheme provides suitable reaction conditions, which is more conducive to the precipitation of small amounts of nickel and manganese, and reduces the manganese content in the solution, resulting in higher quality of the subsequent precipitated product.

[0021] Optionally, the reaction conditions in S5 include: a temperature of 50–80°C, a reaction time of 1–3 h, followed by aging for 0.5–2 h, and the amount of calcium oxide used being 1–1.1 times the molar amount of fluorine in the manganese precipitation mother liquor. This preferred scheme provides suitable reaction conditions, which are more conducive to the precipitation of fluorine. Within this range, fluorine can be completely precipitated, resulting in a higher magnesium nitrate content and fewer impurities after the subsequent magnesium nitrate concentration.

[0022] Optionally, the conditions for evaporation, concentration, and crystallization in S6 include: an evaporation and concentration temperature of 80-90℃, and evaporation to a solution specific gravity of 1.35-1.42, where the solution specific gravity is the ratio of the solution density to the density of water. This preferred scheme provides suitable reaction conditions, which is more conducive to increasing the concentration of magnesium nitrate, laying the foundation for subsequent thermal spraying to obtain high-concentration magnesium nitrate.

[0023] Optionally, the temperature at which thermal decomposition occurs in S7 is 500–700°C.

[0024] Optionally, the high-temperature membrane in S7 is made of highly reactive magnesium oxide, which is recyclable. Highly reactive magnesium oxide means that it can react rapidly with nitrates within a pH range of 2.5-8.

[0025] The beneficial effects of the technical solution provided by this invention include at least the following:

[0026] This invention uses waste acid-stainless steel pickling solution as raw material, specifically employing a mixture of magnesite and the stainless steel pickling solution. This process consumes residual acid in the waste acid and precipitates most of the iron in the stainless steel pickling solution. Combined with other steps, this stepwise precipitation facilitates the separation and purification of the precipitate. Without magnesite, the resulting precipitate is not singular but rather a mixture containing numerous impurities, hindering the resource utilization of valuable metals in the pickling solution. This invention uses high pressure and high temperature under specific conditions to leach and separate iron slag, i.e., ferric hydroxide precipitate. Subsequent multi-step precipitation processes remove nickel, cobalt, chromium, manganese, and fluorine elements to obtain the desired crude magnesium nitrate, ultimately yielding high-purity magnesium nitrate crystals with high purity and high recovery rate. This technical solution is fast-responding and efficient, and the materials used are common industrial products, readily available and inexpensive. The entire process is low-cost, has a wide range of raw material sources, is easily scaled up, and is readily industrialized. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram of a method for resource utilization of stainless steel pickling solution according to Embodiment 1 of the present invention. Detailed Implementation

[0029] This invention utilizes the free acid, iron, chromium, nickel, cobalt, manganese, fluorine and other elements in stainless steel pickling solution in a segmented and tiered manner, without generating secondary pollution or discharging waste residue or exhaust gas. It has the advantages of being green, low-carbon and environmentally friendly, and has good socio-economic value.

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The component analysis results of the stainless steel pickling solution raw materials used in the following examples are shown in Table 1.

[0032] Table 1. Analysis results of main components of waste acid feedstock

[0033]

[0034] Partial composition of magnesite: Co 0.001wt%, Ni 0.015wt%, Fe 0.009wt%, Mn 0.009wt%, Ca 2.3wt%, Mg 22wt%, Na 0.01wt%, Si 0.05wt%.

[0035] Example 1

[0036] like Figure 1 As shown, a method for the resource utilization of stainless steel pickling solution specifically includes the following steps:

[0037] S1: The waste acid from stainless steel pickling solution is mixed with magnesite and then added to a pressure vessel for reaction. The amount of magnesite is 1.6 times the molar amount of iron in the stainless steel pickling solution. The reaction is carried out in the pressure vessel for 3 hours, with an oxygen pressure of 0.6 MPa and a reaction temperature of 150℃. The leachate and iron slag are obtained by filtration. After washing, the iron slag is iron concentrate with an iron content of more than 60%.

[0038] S2: Add magnesium oxide to the above leachate, the reaction temperature is 80℃, the reaction time is 3h, and the amount of magnesium oxide is 1.5 times the molar amount of iron and chromium in the solution; filter to obtain chromium precipitate slag and chromium precipitate mother liquor;

[0039] S3: Add magnesium oxide to the above chromium removal mother liquor to remove nickel and cobalt. The reaction temperature is 80℃, the reaction time is 3h, the aging time is 2h, and the amount of magnesium oxide is 1.01 times the molar amount of nickel and cobalt in the solution. Filter to obtain nickel and cobalt hydroxide and nickel and cobalt precipitation mother liquor (or nickel and cobalt precipitation post-liquid).

[0040] S4: Add hydrogen peroxide and magnesium oxide to the above nickel-cobalt precipitate mother liquor to remove manganese. The reaction temperature is 80℃, the reaction time is 3 hours, the aging time is 2 hours, and the amount of magnesium oxide is 1.1 times the molar amount of nickel and manganese in the solution. The amount of hydrogen peroxide is 1.15 times the molar amount of manganese. Filter to obtain manganese slag and manganese precipitate mother liquor.

[0041] S5: Add calcium oxide to the above manganese precipitation mother liquor to remove fluoride, filter to obtain fluoride precipitate residue and crude magnesium nitrate solution, the temperature is 80℃, the reaction time is 3h, the aging time is 2h, and the amount of calcium oxide is 1.1 times the molar amount of fluoride in the solution;

[0042] S6: Crude magnesium nitrate solution is concentrated and crystallized under negative pressure to obtain magnesium nitrate crystals. The evaporation and concentration temperature is 90℃, and the solution specific gravity is reduced to 1.38.

[0043] S7: Some magnesium nitrate crystals are heated and melted into a liquid state, then injected into the decomposition furnace to decompose upon contact with the circulating hot gas. After passing through a high-temperature membrane dust collector, the resulting gas is cooled and pressurized for absorption, yielding new nitric acid. The heating temperature of the gas injected into the decomposition furnace is 700℃.

[0044] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 1.1 and 1.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 98.35%. The nickel content in the nickel-cobalt hydroxide was 14.89 wt%, and the cobalt content was 11.46 wt%. The magnesium recovery rate was 98.56%.

[0045] Table 1.1 Analysis results of major components of magnesium nitrate hexahydrate

[0046]

[0047] Table 1.2 Analysis results of main components of nickel-cobalt hydroxide

[0048]

[0049] Example 2

[0050] The method is the same as in Example 1, except that the process parameters are different, as follows:

[0051] S1: Magnesite is added to a pressure vessel at a rate of 1.6 times the molar amount of iron in the waste acid, and reacted for 2 hours at an oxygen pressure of 0.2 MPa and a reaction temperature of 100℃.

[0052] S2: The reaction temperature is 70℃ and the reaction time is 2h;

[0053] S3: The reaction temperature is 70℃, the reaction time is 2h, the aging time is 1h, and the amount of magnesium oxide is 1.05 times the molar amount of nickel and cobalt in the solution;

[0054] S4: The reaction temperature is 70℃, the reaction time is 2 hours, the aging time is 1 hour, and the amount of magnesium oxide used is 1.05 times the molar amount of nickel and manganese in the solution. The amount of hydrogen peroxide used is 1.1 times the molar amount of manganese.

[0055] S5: Temperature is 70℃, reaction time is 2h, aging time is 1h, and the amount of calcium oxide is 1.05 times the molar amount of fluorine in the solution;

[0056] S6: Evaporation and concentration temperature is 80℃, and the solution specific gravity is evaporated to 1.40.

[0057] S7: The temperature of the gas injected into the decomposition furnace and the heating temperature of the hot circulating gas is 500℃.

[0058] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 2.1 and 2.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 97.28%. The nickel content in the nickel-cobalt hydroxide was 14.32 wt%, and the cobalt content was 10.31 wt%. The magnesium recovery rate was 96.47%.

[0059] It can be seen that, compared with Example 1, the reaction temperature and reaction time of Example 2 were reduced and the aging time was shortened, resulting in insufficient reaction, lower magnesium nitrate content, and higher impurities. Iron could not be completely precipitated in S1, which led to incomplete precipitation in the subsequent process and affected the purity of the product.

[0060] Table 2.1 Analysis results of major components of magnesium nitrate hexahydrate

[0061]

[0062] Table 2.2 Analysis results of main components of nickel-cobalt hydroxide

[0063]

[0064] Example 3

[0065] The method is the same as in Example 1, except that the process parameters are different, as follows:

[0066] S1: Magnesite is added in an autoclave at a rate of 1.3 times the molar amount of iron in the solution and reacted for 1.5 hours.

[0067] S2: The reaction time is 1.5 hours;

[0068] S3: The reaction time is 1.5 h, and the amount of magnesium oxide used is 0.8 times the molar amount of nickel and cobalt in the solution;

[0069] S4: The reaction time is 1.5h, the amount of magnesium oxide is 1.0 times the molar amount of nickel and manganese in the solution, and the amount of hydrogen peroxide is 1.05 times the molar amount of manganese;

[0070] S5: The reaction time is 1.5 h, and the amount of calcium oxide used is 1.0 times the molar amount of fluorine in the solution;

[0071] S6: Evaporate until the solution specific gravity is 1.42.

[0072] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 3.1 and 3.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 92.37%. The nickel content in the nickel-cobalt hydroxide was 14.96 wt%, and the cobalt content was 10.12 wt%. The magnesium recovery rate was 95.33%.

[0073] Table 3.1 Analysis results of major components of magnesium nitrate hexahydrate

[0074]

[0075] Table 3.2 Analysis results of major components of nickel-cobalt hydroxide

[0076]

[0077] Example 4

[0078] The method was carried out in accordance with Example 1, except that the amount of magnesite used in S1 was 1.3 times the molar amount of iron in the stainless steel pickling solution, and the oxygen pressure was controlled at 0.1 MPa.

[0079] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 4.1 and 4.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 88.21%. The nickel content in the nickel-cobalt hydroxide was 14.65 wt%, and the cobalt content was 10.08 wt%. The recovery rate was 93.86%.

[0080] Table 4.1 Analysis results of major components of magnesium nitrate hexahydrate

[0081]

[0082]

[0083] Table 4.2 Analysis results of main components of nickel-cobalt hydroxide

[0084]

[0085] Example 5

[0086] The procedure was carried out in accordance with the method of Example 1, except that the oxygen pressure in S1 was 0.1 MPa.

[0087] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 5.1 and 5.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 96.87%. Magnesium recovery rate: 98.34%.

[0088] Table 5.1 Analysis results of major components of magnesium nitrate hexahydrate

[0089]

[0090] Table 5.2 Analysis results of major components of nickel-cobalt hydroxide

[0091]

[0092] Example 6

[0093] The procedure was carried out in accordance with the method of Example 1, except that the amount of magnesium oxide used in S2 was 1.2 times the molar amount of iron and chromium in the solution.

[0094] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables 6.1 and 6.2. In this example, the magnesium nitrate content in the magnesium nitrate hexahydrate crystals was 91.78%. The nickel content in the nickel-cobalt hydroxide was 14.07 wt%, and the cobalt content was 10.56 wt%. The magnesium recovery rate was 94.82%.

[0095] Table 6.1 Analysis results of major components of magnesium nitrate hexahydrate

[0096]

[0097]

[0098] Table 6.2 Analysis results of major components of nickel-cobalt hydroxide

[0099]

[0100] Comparative Example 1

[0101] The procedure was carried out according to Example 1, except that magnesite was not added in S1. Instead, a conventional iron removal agent, a 1 mol / L phosphoric acid solution, was used in an amount 1.05 times the molar amount of iron. The use of phosphoric acid introduces new anions, resulting in low purity of the magnesium nitrate solution.

[0102] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables D1.1 and D1.2. The magnesium nitrate content in the obtained magnesium nitrate hexahydrate crystals was 88.73%. The nickel content in the nickel-cobalt hydroxide was 14.13 wt%, and the cobalt content was 9.96 wt%. The magnesium recovery rate was 93.86%.

[0103] Table D1.1 Analysis results of major components of magnesium nitrate hexahydrate

[0104]

[0105] Table D1.2 Analysis Results of Major Components of Nickel-Cobalt Hydroxide

[0106]

[0107] Comparative Example 2

[0108] The method was carried out in accordance with Example 1, except that the amount of magnesite used in S1 was 1.2 times the molar amount of iron in the stainless steel pickling solution.

[0109] The compositional analysis of the obtained magnesium nitrate crystals and nickel-cobalt hydroxide is shown in Tables D2.1 and D2.2. The magnesium nitrate content in the obtained magnesium nitrate hexahydrate crystals was 87.04%. The nickel content in the nickel-cobalt hydroxide was 14.11 wt%, and the cobalt content was 9.86 wt%. The magnesium recovery rate was 92.46%.

[0110] Table D2.1 Analysis results of major components of magnesium nitrate hexahydrate

[0111]

[0112]

[0113] Table D2.2 Analysis Results of Major Components of Nickel-Cobalt Hydroxide

[0114]

[0115] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for the resource utilization of stainless steel pickling solution, characterized in that, Includes the following steps: S1. After mixing the stainless steel pickling solution with magnesite, the amount of magnesite is 1.3 to 1.8 times the molar amount of iron in the stainless steel pickling solution; then, the temperature is raised and oxygen is introduced for 1 to 3 hours, during which the oxygen pressure is controlled at 0.1 to 0.6 MPa and the reaction temperature is 100 to 150℃; the leachate and iron slag are obtained by filtration, and the iron slag is washed to obtain iron concentrate with an iron content of more than 60%; In S1, the stainless steel pickling solution comprises: Co 0.3-0.6 g / L, Ni 0.5-0.8 g / L, Fe 55-60 g / L, Mn 5-7 g / L, Ca 0.005-0.01 g / L, Cr 7-9.5 g / L, and NO3. - 120-135 g / L, Si 0.4-0.6 g / L; the composition of the magnesite includes: Co 0-0.0020 wt%, Ni 0.01-0.029 wt%, Fe 0.005-0.011 wt%, Mn 0.005-0.011 wt%, Ca 2.0-4.0 wt%, Mg 22-24 wt%, Na 0.01-0.03 wt%, Si 0.03-0.05 wt%. S2. Add magnesium oxide to the leachate and react, then filter to obtain chromium precipitate slag and chromium precipitate mother liquor; The reaction conditions in S2 include: a temperature of 50–80℃, a reaction time of 1–3 h, and a magnesium oxide dosage of 1.2–1.8 times the total molar amount of iron and chromium in the leachate; S3. Add magnesium oxide to the chromium precipitation mother liquor and filter to obtain nickel cobalt hydroxide and nickel cobalt precipitation mother liquor; The reaction conditions in S3 include: a temperature of 50-80℃, a reaction time of 1-3h, followed by aging for 0.5-2h, and the amount of magnesium oxide used is 1-1.1 times the total molar amount of nickel and cobalt in the chromium precipitation mother liquor; S4. Add hydrogen peroxide and magnesium oxide to the nickel-cobalt precipitate mother liquor and react, then filter to obtain manganese slag and manganese precipitate mother liquor. The reaction conditions in S4 include: a temperature of 50-80℃, a reaction time of 1-3h, followed by aging for 0.5-2h, with magnesium oxide dosage being 1-1.1 times the total molar amount of nickel and manganese in the nickel-cobalt precipitate mother liquor, and hydrogen peroxide dosage being 1-1.15 times the molar amount of manganese in the nickel-cobalt precipitate mother liquor. S5. Add calcium oxide to the manganese precipitation mother liquor and react, then filter to obtain fluorine precipitation residue and magnesium nitrate solution; The reaction conditions in S5 include: a temperature of 50-80℃, a reaction time of 1-3h, followed by aging for 0.5-2h, and the amount of calcium oxide used is 1-1.1 times the molar amount of fluorine in the manganese precipitation mother liquor. S6. The magnesium nitrate solution is concentrated and crystallized under negative pressure to obtain magnesium nitrate crystals; S7. Some magnesium nitrate crystals are heated and melted into liquid, then sprayed into a decomposition furnace to come into contact with the hot circulating gas for thermal decomposition. The gas obtained after high-temperature membrane dust collection is cooled and pressurized for absorption to obtain new nitric acid. The temperature at which S7 decomposes under heat is 500–700°C, and the high-temperature film is made of highly active magnesium oxide.

2. The method according to claim 1, characterized in that, The conditions for evaporation, concentration, and crystallization in S6 include: an evaporation and concentration temperature of 80-90℃, and evaporation until the solution specific gravity is 1.35-1.42, where the solution specific gravity is the ratio of the solution density to the density of water.

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