A method for preparing metallic nickel by electrowinning in a green and sustainable nitric acid system

Abstract

A green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system belongs to the field of electrochemical metallurgy. This method addresses the shortcomings of existing acid leaching processes where nickel nitrate solutions cannot be directly used for electrolysis and must undergo sulfate / chloride conversion. Furthermore, the nickel nitrate-aqueous solution system suffers from severe equipment corrosion and NO generation at the cathode. x Bottlenecks such as pollution have hindered the actual production of nickel nitrate systems. This method uses nickel ore as raw material, and obtains low-hydrate nickel nitrate through acid leaching, solid-liquid separation, extraction, evaporation crystallization, and drying. After being mixed with liquid ammonia and a small amount of additives to form an electrolyte, bright electrowinning nickel is obtained through electrodeposition. Simultaneously, the ammonia can be recycled, and there is no acid mist or NO emission. x This invention reduces chlorine emissions, and its tail gas treatment method is simple and low-cost. It achieves a short process for the nitric acid system: "nickel ore → acid leaching → liquid ammonia electrowinning → high-purity nickel". This invention also eliminates acid mist and NO emissions. x Alternatively, chlorine gas can be used, which offers advantages such as high safety, low cost, and the ability to achieve green, zero-pollution recycling of liquid ammonia.

Description

Technical Field

[0001] This invention relates to the field of electrochemical metallurgy, and in particular to a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system. Background Technology

[0002] Nickel and nickel-based alloys occupy a key strategic position in new energy batteries, aerospace, and high-end equipment manufacturing. Currently, industrial hydrometallurgical processes still primarily rely on sulfuric acid or hydrochloric acid leaching followed by electrolytic refining of nickel sulfate / nickel chloride aqueous solutions. While emerging nitric acid leaching can directly yield nickel hydroxide or nickel nitrate, existing electrolytic devices are only compatible with sulfate or chloride systems, requiring the leachate to undergo sulfation or chlorination conversion, resulting in a lengthy process, high energy consumption, and significant acid and alkali consumption. If nickel nitrate-aqueous solution electrolysis is used, it faces challenges such as severe equipment corrosion and the reduction of nitrate ions at the cathode to NO. x Technical bottlenecks such as by-products hinder industrialization.

[0003] liquid ammonia Boiling point at normal pressure The system can be recycled and reused through evaporation and condensation, and the exhaust gas can be recovered with water, making the method simple and low-cost. Its dielectric constant and viscosity are close to water, and it has good solubility for nickel nitrate, meeting the requirements for electrolysis. Furthermore, the liquid ammonia system has fewer free protons, and anodic oxidation only generates N2, with no acid mist or NO. x The process may release chlorine gas, making it safer for the electrolytic preparation of metallic nickel compared to nickel sulfate-aqueous solution or nickel chloride-aqueous solution systems. Therefore, constructing a direct electrowinning process using nickel nitrate and liquid ammonia can eliminate the sulfate / chloride conversion step, directly obtaining high-purity nickel from nickel nitrate; it also avoids problems such as severe equipment corrosion and numerous cathode side reactions, achieving a short-process, low-cost, safe, and green metallurgical process of "nickel ore → acid leaching → liquid ammonia electrowinning → high-purity nickel" in the nitric acid system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system. This method eliminates the sulfate / chloride conversion step, directly obtaining high-purity nickel from nickel nitrate; it does not generate acid mist or NO. x Alternatively, chlorine gas can be used, requiring only water to absorb the exhaust gas. This method offers advantages such as high safety, low cost, and the ability to achieve green, zero-pollution recycling of liquid ammonia.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention discloses a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system, comprising the following steps:

[0007] Step 1: After acid leaching of nickel ore, solid-liquid separation is performed. The nickel-containing liquid is then purified, extracted, evaporated, concentrated and crystallized, and further dried to obtain dried nickel nitrate.

[0008] Step 2: Mix liquid ammonia, dried nickel nitrate, and additives evenly to obtain a nickel nitrate-liquid ammonia electrolyte solution.

[0009] Step 3: Immerse the polished cathode and anode in a nickel nitrate-liquid ammonia electrolyte solution. At a certain temperature and current density, nickel is deposited onto the cathode by electrodeposition. After the cathode is cleaned, a cobalt deposition layer with a smooth surface and metallic luster is obtained. After peeling, it becomes metallic nickel.

[0010] The acid in step one can be one or more of sulfuric acid, hydrochloric acid, or nitric acid.

[0011] The nickel nitrate dried in step one refers to nickel nitrate in a low hydration state, with a hydration number of less than 4 (i.e., Ni(NO3)2·nH2O, where n < 4).

[0012] The additive in step two is one or more of the following: calcium oxide, potassium nitrate, sodium nitrate, ammonium nitrate, ammonium iodide, and potassium iodide.

[0013] In step two, the amounts of liquid ammonia, nickel nitrate, and additives added are such that the solid-liquid ratio of nickel nitrate to liquid ammonia after drying is > 3 g / L; and the solid-liquid ratio of additives to liquid ammonia is 0.1~30 g / L.

[0014] In step three, the cathode substrate material is one of titanium, stainless steel, copper, or nickel. The anode substrate material is one of platinum, nickel, graphite carbon, nickel alloy, titanium-coated lead dioxide, or titanium-coated iridium dioxide. The anode-cathode spacing is 0.5 to 5 cm, and the anode-cathode area ratio is 1:0.25 to 4.

[0015] In step three, the temperature is -70 ~ 15 °C, and the current density is 10 ~ 200 A / m. 2 Electrowinning is performed under certain conditions.

[0016] In step three, the solvent of the cleaning solution is one or more of deionized water, acetone, and anhydrous ethanol, and the solute is one or more of oxalic acid, sulfuric acid, hydrochloric acid, citric acid, and carbonic acid. The solid-liquid ratio of the solute to the solvent is 0.5 to 50 g / L.

[0017] Beneficial effects:

[0018] 1. The present invention provides a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system, which can directly use nickel nitrate as a solute to prepare metallic nickel by electrowinning.

[0019] 2. The present invention provides a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system. The method uses nickel nitrate as a solute and liquid ammonia as a solvent for electrowinning, which avoids the strong corrosiveness of nitric acid and the pollution problems of cathode byproducts present in the nickel nitrate-aqueous solution system.

[0020] 3. The present invention provides a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system. Electrowinning is performed using a nickel nitrate-liquid ammonia system. No chloride ions are introduced into the system, no chlorine gas is generated, and the tail gas can be treated with water. The method is safe and low in cost.

[0021] 4. The present invention provides a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system. The medium operating temperature is -70 ~ 0 °C, which can be carried out in an extreme low temperature environment, while avoiding the problem of acid mist generation at higher operating temperatures.

[0022] 5. The present invention provides a green and sustainable method for preparing metallic nickel by electrowinning in a nitric acid system. The ammonia medium can be almost completely recovered and recycled. The solute-solvent separation operation is simple, the post-processing is simple, and the pollution emissions are low. Attached Figure Description

[0023] Figure 1 This is a flowchart of a green and sustainable method for preparing metallic nickel by electrowinning using a nitric acid system, according to the present invention.

[0024] Figure 2 The image shows the actual nickel electrolytic product from Case 1.

[0025] Figure 3 The XRD pattern of the nickel electrolytic product in Case 1.

[0026] Figure 4 The cell pressure-time curve for the electrolysis process in Case 1 is shown.

[0027] Figure 5 This is a photograph of the electrolytic nickel product from Comparative Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, see [link to relevant documentation]. Figure 1 The present invention will be further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0029] Example 1:

[0030] Step (1) involves leaching the nickel ore with nitric acid. The leaching solution is then neutralized with lime to remove iron and further dealuminized by hydrolysis. Subsequently, high-purity nickel-containing back-extraction solution is obtained by extraction and back-extraction using Cynex 272 and Versatic 10. The back-extraction solution is then evaporated, concentrated, crystallized, and dried at 100 °C and -0.1 MPa for 36 hours to obtain dried nickel nitrate (Ni(NO3)2·H2O).

[0031] Step (2): Cool the electrolytic cell to a constant temperature of -34 °C, seal the electrolytic cell and remove air, then fill the electrolytic cell with argon gas to 1.6 MPa to check for leaks, then exhaust the gas to a vacuum and adjust the pressure to -0.1 MPa; introduce ammonia gas to liquefy and obtain 50 mL of liquid ammonia, add 0.5 g of dried nickel nitrate and 3 g of calcium oxide to the electrolytic cell and mix them evenly to obtain a nickel nitrate-liquid ammonia electrolyte solution.

[0032] Step (3): The copper and nickel sheets are polished to a bright finish using sandpaper of different grits (100-10000 grit), then treated with anhydrous ethanol and dried to serve as the cathode and anode, respectively. A dual-electrode system is used with an electrode spacing of 1 cm and an anode-to-cathode area ratio of 1:2. The temperature is -34°C and the current density is 100 A / m. 2 Under the given conditions, an electrodeposition of 90 min was performed to obtain a cathode deposit. The cooling of the electrolytic cell was stopped to allow it to warm up, and the ammonia storage tank was cooled to recover ammonia. After recovery, the cathode sample was removed and washed sequentially with 5 g / L oxalic acid-anhydrous ethanol solution and deionized water. After drying, it was peeled off to obtain metallic nickel.

[0033] Example 2:

[0034] Step (1) involves leaching nickel ore with sulfuric acid. The leaching solution is then neutralized with lime and NaOH to remove iron, and aluminum is removed by hydrolysis. Subsequently, nitric acid is added, and high-purity nickel nitrate back-extraction solution is obtained by extraction and back-extraction with P204 and P507. The back-extraction solution is evaporated, concentrated and crystallized, and then dried at 80 °C and -0.1 MPa for 24 hours to obtain dried nickel nitrate (Ni(NO3)2·2H2O).

[0035] Step (2): Mix 100 mL of liquid ammonia, 1.5 g of dried nickel nitrate and 1 g of calcium oxide evenly to obtain a nickel nitrate-liquid ammonia electrolyte solution.

[0036] Step (3): The copper sheet and graphite carbon sheet are polished to a bright finish with sandpaper of different grits (100-10000 grit), then treated with anhydrous ethanol and dried to serve as the cathode and anode respectively. A dual-electrode system is adopted with an electrode spacing of 1.2 cm and an anode-to-cathode area ratio of 1:1. The temperature is 0°C and the current density is 50 A / m. 2Under the given conditions, a cathode deposit was obtained by electrowinning for 180 min. After recovering the liquid ammonia, the cathode sample was removed and washed sequentially with 5 g / L oxalic acid-deionized water. After drying, it was peeled off to obtain metallic nickel.

[0037] Example 3:

[0038] Step (1): The nickel ore is leached with hydrochloric acid. The leaching solution is neutralized by adding lime and NaOH to remove iron and aluminum is removed by hydrolysis. Then, nitric acid is added and high-purity nickel nitrate back-extraction solution is obtained by extraction and back-extraction with P204 and P507. The back-extraction solution is evaporated, concentrated and crystallized and then dried at 100 °C and atmospheric pressure for 36 hours to obtain dried nickel nitrate (Ni(NO3)2·H2O).

[0039] Step (2): Mix 80 mL of liquid ammonia and 1 g of dried nickel nitrate evenly to obtain a nickel nitrate-liquid ammonia electrolyte solution.

[0040] Step (3): The copper and nickel sheets are polished to a bright shine with sandpaper of different grits (100-10000 grit), then treated with anhydrous ethanol and dried to serve as the cathode and anode respectively. A dual-electrode system is adopted with an electrode spacing of 0.5 cm and an anode-to-cathode area ratio of 1:2. The temperature is -34°C and the current density is 75 A / m. 2 Under the given conditions, electrodeposition for 60 min yielded a cathode deposit. After recovering the liquid ammonia, the cathode sample was removed and washed sequentially with a 10 g / L citric acid-anhydrous ethanol solution and deionized water. After drying, it was peeled off to obtain metallic nickel.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0042] Comparative Example

[0043] Comparative Example 1:

[0044] Unlike Example 1, the nickel nitrate after drying in step (1) has the composition Ni(NO3)2·4H2O, while all other conditions are the same.

[0045] Unlike Example 1, the electrolyte prepared with nickel nitrate dried at this temperature produces a black electrodeposition product.

[0046] Comparative Example 2:

[0047] Unlike Example 1, the ratio of anode to cathode area in step (1) is 1:5, while all other conditions are the same.

[0048] Unlike Example 1, when electrowinning is performed using this anode-cathode area ratio, the electrowinning product is black.

[0049] Comparative Example 3:

[0050] Unlike Example 1, the current density in step (2) is 250 A / m. 2 All other conditions are the same.

[0051] Unlike Example 1, when using this current density for electrodeposition, the electrodeposition products are prone to detachment, and some products are black.

[0052] Comparative Example 4:

[0053] Unlike Example 2, the temperature before electrowinning in step (2) is 15 °C, while all other conditions are the same.

[0054] Unlike Example 2, at this temperature, the electrolyte is colorless and transparent, meaning the dried cobalt nitrate solution is undissolved and cannot be used for electrodeposition.

[0055] Comparative Example 5:

[0056] Unlike Example 2, the interpole spacing in step (1) is 6.0 cm, while all other conditions are the same.

[0057] Unlike Example 2, the electrodeposition operation using this electrode spacing produces a black electrodeposition product.

[0058] Comparative Example 6:

[0059] Unlike Example 3, in step (3), the cathode sample was washed directly with deionized water after being taken out, while all other conditions were the same.

[0060] Unlike Example 3, the cathode surface after being washed directly with deionized water will have hydroxide, additives or salt residues.

[0061] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing metallic nickel by electrowinning using a green and sustainable nitric acid system, characterized in that: Includes the following steps: Step 1: After acid leaching of nickel ore, solid-liquid separation is performed. The nickel-containing liquid is then purified, extracted, evaporated, concentrated and crystallized, and further dried to obtain dried nickel nitrate. Step 2: After uniformly mixing liquid ammonia, dried nickel nitrate, and additives, a nickel nitrate-liquid ammonia electrolyte solution is obtained. Step 3: Immerse the polished cathode and anode in a nickel nitrate-liquid ammonia electrolyte solution. At a certain temperature and current density, nickel is deposited onto the cathode by electrodeposition. After the cathode is cleaned, a cobalt deposition layer with a smooth surface and metallic luster is obtained. After peeling, it becomes metallic nickel.

2. The method as described in claim 1, characterized in that: The acid is one or more of sulfuric acid, hydrochloric acid, and nitric acid.

3. The method as described in claim 1, characterized in that: Dry nickel nitrate refers to nickel nitrate in a low-hydration state, with a hydration number of less than 4, namely Ni(NO3)2·nH2O, where n < 4.

4. The method as described in claim 1, characterized in that: The additive is one or more of the following: calcium oxide, potassium nitrate, ammonium nitrate, sodium nitrate, ammonium iodide, and potassium iodide.

5. The method as described in claim 1, characterized in that: The amounts of liquid ammonia, nickel nitrate, and additives added are such that, after drying, the solid-liquid ratio of nickel nitrate to liquid ammonia is > 3 g / L; and the solid-liquid ratio of additives to liquid ammonia is 0.1~30 g / L.

6. The method as described in claim 1, characterized in that: The cathode substrate material is one of titanium, stainless steel, copper, or nickel.

7. The method as described in claim 6, characterized in that: The anode substrate material is one of the following: platinum sheet, nickel sheet, graphite carbon sheet, nickel alloy sheet, titanium-coated lead dioxide plate, or titanium-coated iridium dioxide plate.

8. The method as described in claim 7, characterized in that: The distance between the anode and cathode is 0.5 ~ 5 cm, and the ratio of the anode and cathode areas is 1:0.25~4.

9. The method as described in claim 1, characterized in that: Temperature range: -70 ~ 15 °C; Current density range: 10 ~ 200 A / m 2 Electrowinning is performed under certain conditions.

10. The method as described in claim 1, characterized in that: The solvent for the cleaning solution is one or more of deionized water, acetone, and anhydrous ethanol, and the solute is one or more of oxalic acid, hydrochloric acid, citric acid, and carbonic acid. The solid-liquid ratio of the solute to the solvent is 0.5 ~ 50 g / L.

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