Method and apparatus for removing chromium from ferronickel leachate

Abstract

A method and an apparatus for removing chromium from a ferronickel leachate. Iron phosphate seed crystals are used as an inducer to treat a ferronickel leachate, so that formation of chromium phosphate dihydrate precipitate can be rapidly induced in the form of nucleation, and chromium can be removed from the ferronickel leachate more thoroughly at a specific reaction temperature, significantly enhancing the chromium removal rate.

Description

Method for removing chromium from ferronickel leaching solution and device for removing chromium from ferronickel leaching solution Technical Field

[0001] The present disclosure belongs to the technical field of valuable metal recovery, and in particular relates to a method for removing chromium from a nickel-iron leachate and a device for removing chromium from the nickel-iron leachate. Background Art

[0002] Lithium-ion batteries have been widely used due to their advantages of high voltage, high energy density, and long cycle life. Cathode materials are a key technology for lithium-ion batteries. Currently, the main cathode materials include lithium iron phosphate (LFP) and ternary materials (NCM / NCA). Iron phosphate and nickel sulfate are important raw materials for preparing cathode materials.

[0003] Ferrophosphate and nickel sulfate can be produced using nickel-iron alloy extracted from laterite nickel ore as raw material. The nickel-iron alloy produced through pyrometallurgical smelting of laterite nickel ore has a nickel content exceeding 15%, an iron content exceeding 60%, and a chromium content of 0.1%. Industrially, hydrometallurgy is primarily used to remove chromium from the nickel-iron alloy, thereby reducing its impact on the performance of ferrophosphate and nickel sulfate products. The industrial process for separating chromium is as follows: acid is added to the raw material to form a leachate. Na2CO3 is then added to the leachate to precipitate NiCO3, which is then precipitated to produce NiO or other nickel materials. To ensure the high purity and excellent performance of the NiO or other nickel materials, impurity removal from the nickel-iron leachate is particularly important.

[0004] Currently, the impurity removal methods for nickel-iron leaching solutions mainly have the following problems: the chromium removal rate is not ideal, and impurities (such as sodium ions) are easily introduced.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure includes providing a method for removing chromium from nickel-iron leaching solution and a device for removing chromium from nickel-iron leaching solution, aiming to efficiently separate chromium metal and improve the chromium removal rate.

[0008] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0009] In a first aspect, the solution provided by the present disclosure includes a method for removing chromium from a nickel-iron leachate, comprising: mixing the nickel-iron leachate containing chromium with ferric phosphate, and reacting them under conditions of a pH value of 1.8-2.5 and a temperature of 70°C-95°C.

[0010] In some embodiments of the present disclosure, after adjusting the pH value of the nickel-iron leachate to 1.8-2.5, seed ferric phosphate is added to the nickel-iron leachate for crystallization co-precipitation, and the reaction temperature is controlled at 80° C.-90° C. and the reaction time is 1 h-6 h.

[0011] In some embodiments of the present disclosure, the seed ferric phosphate is selected from at least one of dihydrate ferric phosphate (FePO4·2H2O) and anhydrous ferric phosphate (FePO4), and the amount of seed ferric phosphate added is calculated based on the content of nickel-iron-phosphorus-chromium in the nickel-iron leachate, and the mass ratio of the content of nickel-iron-phosphorus-chromium to the amount of seed ferric phosphate added is controlled to be 100:(5-50).

[0012] In some embodiments of the present disclosure, the mass ratio of the nickel iron phosphorus chromium content to the added amount of seed ferric phosphate is controlled to be 100:(15-20), and the added seed ferric phosphate is ferric phosphate or ferric phosphate slurry.

[0013] In some embodiments of the present disclosure, the pH value of the nickel-iron leaching solution is adjusted using NiCO3, NiCO3 slurry and nickel hydroxide.

[0014] In some embodiments of the present disclosure, during the reaction with ferric phosphate, the stirring rate is controlled to be 60 r / min-90 r / min.

[0015] In some embodiments of the present disclosure, during the reaction with ferric phosphate, the stirring rate is controlled to be 75 r / min-85 r / min.

[0016] In some embodiments of the present disclosure, seed ferric phosphate is first added to the chromium-nickel-iron leachate with a pH value of 2.0-2.5 for 1-2 hours, and then nickel hydroxide is added to gradually increase the pH value to 5.8-6.2 for reaction.

[0017] In some embodiments of the present disclosure, after the reaction is completed at a pH value of 2.0-2.5, the reaction is carried out at pH values ​​of 2.9-3.1, 3.9-4.1, 4.9-5.1, and 5.8-6.2 for 1-2 hours, respectively, and the reaction temperature is controlled at 70°C-95°C.

[0018] In some embodiments of the present disclosure, after the reaction is completed at a pH of 2.0-2.5, the reaction is continued at 3.9-4.1 and 5.8-6.2 for 1-2 hours, respectively, and the reaction temperature is controlled at 70° C.-95° C.

[0019] In some embodiments of the present disclosure, the nickel-iron leaching solution is sequentially passed through a plurality of leaching solution chromium removal reaction tanks for continuous reaction, and the number of the leaching solution chromium removal reaction tanks is 2-5.

[0020] In some embodiments of the present disclosure, each leachate chromium removal reaction tank is connected to a steam pipeline for introducing heat source steam, and a feeding port is also provided on the top of each leachate chromium removal reaction tank to add iron phosphate and materials for adjusting the pH value through the feeding port.

[0021] In some embodiments of the present disclosure, a driving pump is installed on the top of each leaching liquid chromium removal reaction tank, and a stirring device is also provided in each leaching liquid chromium removal reaction tank. The driving pump is connected to the stirring device to drive the stirring device to rotate.

[0022] In some embodiments of the present disclosure, the stirring device includes a stirring rod and a plurality of stirring blades arranged from top to bottom, and the plurality of stirring blades are all connected to the stirring rod and are evenly distributed in the circumferential direction of the stirring rod.

[0023] In some embodiments of the present disclosure, the number of stirring blades is 3-8.

[0024] In some embodiments of the present disclosure, the height-to-diameter ratio of each leaching solution chromium removal reaction tank is (1-3):1.

[0025] In some embodiments of the present disclosure, a feed pipe is provided between two adjacent leaching liquid chromium removal reaction tanks, the inlet end of each feed pipe is connected to one leaching liquid chromium removal reaction tank, and the outlet end of each feed pipe is connected to the next leaching liquid chromium removal reaction tank, and each feed pipe is installed with a delivery pump to provide delivery power.

[0026] In some embodiments of the present disclosure, there are three leachate chromium removal reaction tanks. The pH value of the first leachate chromium removal reaction tank is adjusted to 2.0-2.5 before the reaction. The pH value of the second leachate chromium removal reaction tank is adjusted to about 3.9-4.1 before the reaction. The pH value of the third leachate chromium removal reaction tank is adjusted to about 5.8-6.2.

[0027] In some embodiments of the present disclosure, the nickel-iron leaching solution is a sulfuric acid leaching solution with an initial pH value of 0.5-1.

[0028] In some embodiments of the present disclosure, the metal element composition of the nickel-iron leachate is as follows, measured by mass volume concentration: nickel 10-60 g / L, iron 40-80 g / L, chromium 0.01-0.1 g / L, and phosphorus 0.2-5 g / L.

[0029] In some embodiments of the present disclosure, the process further includes: after the reaction with ferric phosphate is completed, solid-liquid separation is performed to obtain a chromium-removed filtrate and a first chromium slag, and then fine filtration and separation of the chromium-removed filtrate is performed to obtain a chromium-removed fine filtrate and a second chromium slag.

[0030] In some embodiments of the present disclosure, the further step includes testing the obtained chromium-removed filtrate. If the chromium content is less than 10 ppm, the filtrate enters the next step; if the chromium content is greater than or equal to 10 ppm, the filtrate returns to the chromium removal unit.

[0031] In a second aspect, the present disclosure also provides a nickel-iron leachate chromium removal device for implementing the method in any of the above embodiments, comprising a plurality of leachate chromium removal reaction tanks, wherein a feed pipe is provided between two adjacent leachate chromium removal reaction tanks, the inlet end of each feed pipe is connected to one leachate chromium removal reaction tank, and the outlet end of each feed pipe is connected to the next leachate chromium removal reaction tank.

[0032] In some embodiments of the present disclosure, a leachate storage tank is further included. A feed pipeline is provided between the leachate storage tank and the first leachate chromium removal reaction tank. The inlet end of the feed pipeline is connected to the leachate storage tank, and the outlet end of the feed pipeline is connected to the first leachate chromium removal reaction tank. A feed pump is installed on the feed pipeline to provide conveying power.

[0033] In some embodiments of the present disclosure, a filter press device and a fine filtration device are further included, and the last leaching liquid chromium removal reaction tank is connected to the inlet of the filter press device, and the outlet of the filter press device is connected to the inlet of the fine filtration device.

[0034] In some embodiments of the present disclosure, the method further includes: a chromium removal filtrate storage tank and a chromium removal fine filtrate storage tank, wherein the inlet of the chromium removal filtrate storage tank is connected to the outlet of the filter press device, the outlet of the chromium removal filtrate storage tank is connected to the inlet of the fine filtration device, and the inlet of the chromium removal fine filtrate storage tank is connected to the outlet of the fine filtration device.

[0035] The present invention uses ferric phosphate as an inducer to treat nickel-iron leachate. Ferric phosphate does not precipitate and adsorb divalent cations such as Zn, Cd, Co and Ni, but can make Cr 3+ Ion precipitation: Ferric phosphate is less affected by temperature, while chromium phosphate is strongly affected by temperature. By utilizing the mechanism that chromium phosphate is more easily precipitated than ferric phosphate, the dihydrate chromium phosphate precipitation can be quickly induced in the form of crystal nucleus growth. This can more fully remove chromium from the nickel-iron leachate at a specific reaction temperature, significantly improving the chromium removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0037] FIG1 is a process flow chart provided by the present disclosure;

[0038] FIG2 is a schematic structural diagram of a chromium removal device for ferronickel leaching solution provided by the present disclosure;

[0039] FIG3 is a process flow chart provided in a specific embodiment of the present disclosure.

[0040] Icons: 100 - leachate storage tank; 101 - feed pipeline; 102 - feed pump; 110 - first leachate chromium removal reaction tank; 111 - first steam pipeline; 112 - first drive pump; 113 - first feeding port; 114 - first stirring device; 1141 - first stirring rod; 1142 - first stirring blade; 121 - first delivery pipe; 122 - first delivery pump; 130 - second leachate chromium removal reaction tank; 131-second steam pipeline; 132-second driving pump; 133-second feeding port; 134-second stirring device; 1341-second stirring rod; 1342-second stirring blade; 141-second feeding pipe; 142-second delivery pump; 150-filter press device; 155-chromium removal filtrate storage tank; 156-third feeding pipe; 157-third delivery pump; 160-fine filtration device; 161-chromium removal fine filtrate storage tank. DETAILED DESCRIPTION

[0041] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0042] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0043] The present disclosure provides a method for removing chromium from nickel-iron leachate, referring to FIG1 , comprising the following steps:

[0044] S1 precipitated chromium

[0045] The nickel-iron leachate is mixed with ferric phosphate as a seed crystal in a chromium removal reaction tank and reacted at a pH of 1.8-2.5 and a temperature of 70°C-95°C. Under these temperature conditions, the ferric phosphate seed crystals act as an inducer and can quickly induce the formation of dihydrate chromium phosphate precipitation in the form of crystal nucleus growth. The chromium is then continuously removed through multi-stage pH adjustment to fully remove the chromium in the nickel-iron leachate. The reaction formula is as follows: 2H2O+Cr 3+ +PO4 3- =CrPO4·2H2O↓;

[0046] In some embodiments, after adjusting the pH value of the nickel-iron leachate to 1.8-2.5, seed ferric phosphate is added to the nickel-iron leachate for crystallization co-precipitation, and the reaction temperature is controlled to 80°C-90°C and the reaction time is 3h-6h. By further optimizing the reaction temperature and time, the chromium deposition rate can be further increased and the chromium can be more fully removed.

[0047] Specifically, the reaction temperature of the nickel-iron leachate and ferric phosphate can be 70°C, 75°C, 80°C, 85°C, 90°C, etc., the reaction time can be 3h, 4h, 5h, 6h, etc., and the reaction pH value can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.

[0048] In some embodiments, the ferronickel leachate can be a sulfuric acid leachate, and the initial pH value can be 0.5-1, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc. The metal element composition of the ferronickel leachate, measured by mass volume concentration, is as follows: 10-60 g / L nickel, 40-80 g / L iron, 0.01-0.1 g / L chromium, and 0.2-5 g / L phosphorus. The composition of each metal element within the above range is suitable for the chromium removal method provided in the embodiments of the present disclosure.

[0049] Furthermore, the seed ferric phosphate is selected from at least one of dihydrate ferric phosphate (FePO4·2H2O) and anhydrous ferric phosphate (FePO4), and may be any one or two of the above, but is not limited thereto. The amount of seed ferric phosphate added is calculated based on the content of nickel-iron-phosphorus-chromium in the nickel-iron leachate, and the mass ratio of the nickel-iron-phosphorus-chromium content to the amount of seed ferric phosphate added is controlled to be 100:(5-50), preferably 100:(15-20), such as 100:5, 100:10, 100:15, 100:20, 100:30, 100:40, 100:50, etc., that is, the ferric phosphate seed crystals can be added according to 5%-20% of the total content of nickel-iron-phosphorus-chromium in the nickel-iron leachate. Nickel, iron, phosphorus, and chromium are the primary elements in a ferronickel leachate. For example, if the concentration of nickel, iron, phosphorus, and chromium in a ferronickel leachate is 100g / L and the volume is 100L, and ferric phosphate is added at a rate of 20%, the amount of ferric phosphate added is 100g / L * 100L * 20% = 2000g. Ferric phosphate can be added in several batches, with the seed crystal dosage adjusted based on the chromium removal effect. The seed ferric phosphate can be either ferric phosphate or ferric phosphate slurry.

[0050] In some embodiments, the pH value of the nickel-iron leachate is adjusted using NiCO3, NiCO3 slurry, Ni(OH)2 or Ni(OH)2 slurry. When the pH adjustment effect of NiCO3 or NiCO3 slurry is not good, the pH value is adjusted by adding Ni(OH)2 or Ni(OH)2 slurry. Since nickel carbonate (NiCO3) is a weak alkaline salt, it can accurately control the pH value. The principle of pH adjustment is that the carbonate radical of nickel carbonate reacts with the hydrogen ions of the solution to generate non-toxic and harmless carbon dioxide and water, thereby playing a role in pH adjustment; and nickel hydroxide Ni(OH)2 is a strong base, and the principle of pH adjustment is that the hydroxide ions of nickel hydroxide react with the hydrogen ions of the solution to generate non-toxic and harmless water, thereby playing a role in pH adjustment. It is worth noting that the addition of nickel carbonate or nickel hydroxide will not introduce other impurities, thereby avoiding bringing other impurities (such as sodium ions) into subsequent products and affecting product purity.

[0051] In some embodiments, during the reaction with ferric phosphate, the stirring rate is controlled to be 60r / min-90r / min, preferably 75r / min-85r / min. Too high a stirring rate is not conducive to the stability of the precipitation, and too low a stirring rate is not conducive to the formation of the precipitation. It is advisable to control the stirring rate within the above range. Specifically, during the reaction process, the stirring rate can be controlled to be 60r / min, 65r / min, 70r / min, 75r / min, 80r / min, 85r / min, 90r / min, etc.

[0052] In some embodiments, seed ferric phosphate can be added to a chromium-nickel-iron leachate at a pH of 2.0-2.5 and allowed to react for 1-2 hours. Then, nickel hydroxide can be added to gradually raise the pH to 5.8-6.2. Chromium metal begins to precipitate effectively at a pH of 2.0-2.5, achieving a good chromium removal rate. When the pH is gradually raised to 5.8-6.2, chromium precipitation is more complete within this pH range.

[0053] In some embodiments, after the reaction is completed at a pH of 2.0-2.5, the reaction is carried out at pH values ​​of 2.9-3.1, 3.9-4.1, 4.9-5.1, and 5.8-6.2 for 1-2 hours, respectively, and the reaction temperature is controlled at 70° C.-95° C. That is, after the reaction is completed at a pH of 2.0-2.5, the pH value can be increased to 2.9-3.1 for 1-2 hours, then increased to 3.9-4.1 for 1-2 hours, then increased to 4.9-5.1 for 1-2 hours, and then increased to 5.8-6.2 for 1-2 hours. By optimizing the reaction process, the chromium removal effect can be further improved.

[0054] In another embodiment, after the reaction is completed at a pH of 2.0-2.5, the reaction is carried out at pH 3.9-4.1 and at pH 5.8-6.2 for 1-2 hours, respectively, with the reaction temperature controlled at 70° C.-95° C. That is, after the reaction is completed at a pH of 2.0-2.5, the pH can be increased to 3.9-4.1 for 1-2 hours, and then increased to 5.8-6.2 for 1-2 hours. By simplifying the process stages, the reaction cycle can be shortened while ensuring the chromium removal effect.

[0055] It should be noted that ferrous hydroxide in the solution begins to precipitate at a pH of 6.5-7.5, while nickel hydroxide begins to precipitate at a pH of 7.11. Experiments have shown that a higher pH value leads to better chromium ion precipitation, while also ensuring that nickel and ferrous ions do not form precipitates. Therefore, initially reacting at a pH of 1.8-2.5 and then continuing at a pH of 5.0-6.5 can more effectively remove chromium.

[0056] In some embodiments, in order to fully carry out the reaction and improve production efficiency, the nickel-iron leachate can be sequentially passed through multiple leachate chromium removal reaction tanks for continuous reaction. The number of leachate chromium removal reaction tanks can be 2-5, such as 2, 3, 4, 5, etc.

[0057] In some embodiments, as shown in FIG2 , the number of chromium removal reaction tanks for the leachate can be three. The pH value of the first chromium removal reaction tank is adjusted to 2.0-2.5 (e.g., 2.0) before the reaction, the pH value of the second chromium removal reaction tank is adjusted to 3.9-4.1 (e.g., 4.0) before the reaction, and the pH value of the third chromium removal reaction tank is adjusted to 5.8-6.2 (e.g., 6.0). By controlling the pH value within the pH range before the precipitation of divalent iron and nickel ions, the use of two chromium removal reaction tanks can fully precipitate the chromium and improve the operation efficiency.

[0058] When two leachate chromium removal reaction tanks are used, the device diagram is shown in Figure 3. The nickel-iron leachate chromium removal device provided in the embodiment of the present disclosure includes a leachate storage tank 100, a first leachate chromium removal reaction tank 110, and a second leachate chromium removal reaction tank 130. The leachate output from the leachate storage tank 100 first enters the first leachate chromium removal reaction tank 110 and then enters the second leachate chromium removal reaction tank 130, and the chromium removal reaction is carried out in two steps.

[0059] A feed pipeline 101 is provided between the leachate storage tank 100 and the first leachate chromium removal reaction tank 110. The inlet end of the feed pipeline 101 is connected to the leachate storage tank 100, and the outlet end of the feed pipeline 101 is connected to the first leachate chromium removal reaction tank 110 (i.e., the first leachate chromium removal reaction tank). A feed pump 102 is installed on the feed pipeline 101. The feed pump 102 provides power, and the feed pipeline 101 is used as a medium to pump the nickel-iron leachate from the leachate storage tank 100 into the first leachate chromium removal reaction tank 110 for reaction.

[0060] A first delivery pipe 121 is provided between the first leachate chromium removal reaction tank 110 and the second leachate chromium removal reaction tank 130. A first delivery pump 122 is provided on the first delivery pipe 121. The first delivery pump 122 provides power, and the first delivery pipe 121 is used as a medium to deliver the material output from the first leachate chromium removal reaction tank 110 to the second leachate chromium removal reaction tank 130.

[0061] The first leaching solution chromium removal reaction tank 110 is connected to a first steam pipeline 111 for introducing heat source steam. The first steam pipeline 111 can be used to introduce heating steam, which can be water vapor, into the first leaching solution chromium removal reaction tank 110. A first feeding port 113 is also provided at the top of the first leaching solution chromium removal reaction tank 110, so that iron phosphate and materials for adjusting the pH value can be added through the first feeding port 113. NiCO3 or NiCO3 slurry is first added to adjust the pH value of the nickel-iron leachate, and then the iron phosphate is added for reaction. Specifically, the first feeding port 113 can be located at the top edge of the first leaching solution chromium removal reaction tank 110 for adding nickel carbonate and seed crystals FePO4·2H2O; the first steam pipeline 111 can be located at the top of the first leaching solution chromium removal reaction tank 110. During operation, steam is introduced through the first steam pipeline 111 to raise the temperature to about 85° C., and nickel carbonate is added and mixed under stirring to adjust the pH value to about 2.0. Then, FePO4·2H2O seed crystals with a mass volume concentration of 5% to 20% of the leachate are added, and the chromium removal is continuously stirred for 3 to 6 hours. At this time, a large amount of precipitation begins to appear in the leachate.

[0062] It should be noted that the method provided by the present disclosure has good separation characteristics of chromium and iron under the conditions of temperature 85°C and pH value equal to 2.0-6.5. Using seed ferric phosphate dihydrate as an inducer can quickly induce the precipitation of chromium phosphate dihydrate in the form of crystal nucleus growth, and the chromium removal rate can reach more than 98%, with good chromium removal effect.

[0063] Furthermore, a first driving pump 112 (which can be a centrifugal pump) is installed on the top of the first leachate chromium removal reaction tank 110. A first stirring device 114 is also provided in the first leachate chromium removal reaction tank 110. The first driving pump 112 is connected to the first stirring device 114 to drive the first stirring device 114 to rotate. The first stirring device 114 includes a first stirring rod 1141 and a plurality of first stirring blades 1142 arranged from top to bottom. The first stirring rod 1141 can be multi-stage connected. The plurality of first stirring blades 1142 are all connected to the first stirring rod 1141 and are evenly distributed 360° around the circumference of the first stirring rod 1141, that is, the first stirring blades 1142 are evenly distributed 360° on the first stirring rod 1141 in a spatial three-dimensional manner. The first driving pump 112 provides power to drive the first stirring rod 1141 to rotate, driving the first stirring blades 1142 to rotate around the first stirring rod 1141, and driving the leachate to undergo a sufficient mixing reaction.

[0064] The second leaching solution chromium removal reaction tank 130 has a similar structure to the first leaching solution chromium removal reaction tank 110:

[0065] A second steam line 131 for introducing heat source steam is connected to the second chromium removal reaction tank 130. Heating steam can be introduced into the second chromium removal reaction tank 130 through the second steam line 131. A second feed port 133 is also provided at the top of the second chromium removal reaction tank 130, through which ferric phosphate and materials for adjusting the pH value are added. NiCO3, NiCO3 slurry, Ni(OH)2, and Ni(OH)2 slurry are first added to adjust the pH of the nickel-iron leachate, and then the ferric phosphate is added for reaction.

[0066] Furthermore, a second driving pump 132 (which may be a centrifugal pump) is installed at the top of the second leachate chromium removal reaction tank 130. A second stirring device 134 is also provided in the second leachate chromium removal reaction tank 130. The second driving pump 132 is connected to the second stirring device 134 to drive the second stirring device 134 to rotate. The second stirring device 134 includes a second stirring rod 1341 and a plurality of second stirring blades 1342 arranged from top to bottom. The plurality of second stirring blades 1342 are all connected to the second stirring rod 1341 and are evenly distributed 360° around the circumference of the second stirring rod 1341.

[0067] It is understood that when there are multiple leaching solution chromium removal reaction tanks, a feed pipe is provided between two adjacent leaching solution chromium removal reaction tanks, the inlet end of each feed pipe is connected to one leaching solution chromium removal reaction tank, and the outlet end of each feed pipe is connected to the next leaching solution chromium removal reaction tank, so as to transport materials from the previous leaching solution chromium removal reaction tank to the next leaching solution chromium removal reaction tank. Each feed pipe is installed with a delivery pump to provide delivery power.

[0068] In some embodiments, the number of stirring blades in each leaching liquid chromium removal reaction tank can be 3-8, preferably 6, the connection between the stirring blades and the stirring rod can be a snap-on connection, and the angular velocity of the stirring paddle can be adjusted as needed and can be controlled between 60 r / min and 90 r / min, preferably 80 r / min.

[0069] In some embodiments, the height-to-diameter ratio of each leaching solution chromium removal reaction tank is (1-3):1, preferably 2:1, which can reduce the floor space and achieve the best stirring effect when combined with a stirring device.

[0070] S2 post-processing

[0071] As shown in Figure 1, after the reaction with ferric phosphate is complete, solid-liquid separation is performed to obtain a chromium-removed filtrate and a first chromium residue. The chromium-removed filtrate is then finely filtered to obtain a chromium-removed fine filtrate and a second chromium residue. This two-step separation allows for better separation of the chromium residue.

[0072] In some embodiments, the obtained chromium-removed filtrate can be tested. If the chromium content is less than 10 ppm, it will enter the next process. If the chromium content is greater than or equal to 10 ppm, it will return to the chromium removal unit, that is, return to the chromium removal reaction tank of the leachate to continue the reaction.

[0073] As shown in FIG3 , the chromium removal device for ferronickel leachate provided in the embodiment of the present disclosure further includes a filter press 150 and a fine filter 160. The last leachate chromium removal reaction tank is connected to the inlet of the filter press 150, and the outlet of the filter press 150 is connected to the inlet of the fine filter 160. The filter press 150 can be a general device for solid-liquid separation by filter press, and the specific model is not limited; the fine filter 160 can be a general device with high filtration accuracy, such as a filter screen with an aperture of 70-100 mesh.

[0074] In some embodiments, the chromium removal apparatus for ferronickel leachate further includes a chromium removal filtrate storage tank 155 and a chromium removal fine filtrate storage tank 161. The inlet of chromium removal filtrate storage tank 155 is connected to the outlet of filter press 150, the outlet of chromium removal filtrate storage tank 155 is connected to the inlet of fine filtration device 160, and the inlet of chromium removal fine filtrate storage tank 161 is connected to the outlet of fine filtration device 160. The filtrate output from filter press 150 first enters chromium removal filtrate storage tank 155, then enters fine filtration device 160 for further filtration, and is then transferred to chromium removal fine filtrate storage tank 161.

[0075] Specifically, the material output from the last leaching liquid chromium removal reaction tank (such as the second leaching liquid chromium removal reaction tank 130) passes through the second delivery pipe 141 and then enters the filter press device 150. This process is powered by the second delivery pump 142 and uses the second delivery pipe 141 as a medium to allow the material to enter the filter press device 150 from the second leaching liquid chromium removal reaction tank 130.

[0076] Specifically, the material output from the chromium removal filtrate storage tank 155 enters the fine filtration device 160 through the third delivery pipe 156 . This process is powered by the third delivery pump 157 and uses the third delivery pipe 156 as a medium to allow the material to enter the fine filtration device 160 from the chromium removal filtrate storage tank 155 .

[0077] The implementation device is not limited to multiple chromium removal devices connected by pumps, and continuous chromium removal reaction can also be achieved by pipeline overflow.

[0078] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0079] Example 1

[0080] The present disclosure provides a method for removing chromium from a nickel-iron leachate. The apparatus used in this embodiment is based on FIG3 and further includes a leachate chromium removal reaction tank, comprising the following steps:

[0081] (1) Providing nickel-iron leaching solution to be treated

[0082] In the nickel-iron leaching solution, the Ni ion concentration is 53.39 g / L, the Fe ion concentration is 49.87 g / L, the P ion concentration is 2.49 g / L, and the Cr ion concentration is 0.0923 g / L.

[0083] (2) Precipitated chromium

[0084] The nickel-iron leachate is pumped from the leachate storage tank 100 into the first leachate chromium removal reaction tank 110. Steam is introduced to raise the leachate temperature to 90°C. NiCO3 is added through the first feeding port 113 to adjust the pH to 2.0-2.5. Then, FePO4·2H2O is added at a ratio of 50% of the mass volume concentration of the leachate (i.e., 50g of ferric phosphate is used for 1L of 100g / L nickel-iron leachate). After reacting for 2 hours at a stirring rate of 80 r / min, the reaction is pumped into the second leachate chromium removal reaction tank 130. Similarly, in the second leachate chromium removal reaction tank 130, the temperature is raised to 70°C, and an appropriate amount of Ni(OH)2 is added to maintain the pH at approximately 4.0. Then, FePO4·2H2O seed crystals are added for reaction precipitation (so that the concentration of the seed ferric phosphate dihydrate is maintained at 50% of the mass volume concentration of the leachate), and the reaction is stirred for 2 hours. Similarly, the temperature of the third leaching solution chromium removal reaction tank was raised to 90° C., an appropriate amount of Ni(OH)2 was added to maintain the pH value at about 6.0, and then seed crystals FePO4·2H2O were added for reaction precipitation (so that the concentration of seed crystals of ferric phosphate dihydrate was maintained at a ratio of 50% of the mass volume concentration of the leaching solution), and the reaction was stirred for 2 hours.

[0085] (3) Post-processing

[0086] After chromium removal, the solution is pumped into the filter press 150 for solid-liquid separation to obtain a chromium-removed filtrate and a first chromium residue. The chromium-removed filtrate is pumped into the fine filtration device 160 for secondary solid-liquid separation to obtain a chromium-removed fine filtrate and a second chromium residue.

[0087] The test showed that the chromium ion concentration of the chromium removal filtrate was 0.0048 g / L, and the chromium removal rate was (0.0923-0.0048) / 0.0923=94.8%.

[0088] Example 2

[0089] The present disclosure provides a method for removing chromium from nickel-iron leachate, which is processed using the apparatus shown in FIG3 . The process flow is shown in FIG2 , and includes the following steps:

[0090] (1) Providing nickel-iron leaching solution to be treated

[0091] In the nickel-iron leaching solution, the Ni ion concentration is 48.88 g / L, the Fe ion concentration is 47.81 g / L, the P ion concentration is 3.38 g / L, and the Cr ion concentration is 0.0884 g / L.

[0092] (2) Precipitated chromium

[0093] The nickel-iron leachate is transferred from the leachate storage tank 100 to the first leachate chromium removal reaction tank 110 via a pump. Steam is introduced to raise the leachate temperature to 85° C. NiCO3 is added through the first feeding port 113 to adjust the pH to 2.0-2.5. Then, FePO4·2H2O is added at a ratio of 20% of the leachate mass volume concentration (i.e., 20 g of ferric phosphate is used for every 1 L of 100 g / L nickel-iron leachate). After reacting for 2 hours at a stirring rate of 80 r / min, the solution overflows through a pipeline to the second leachate chromium removal reaction tank 130. Similarly, the second leachate chromium removal reaction tank 130 is heated to 85° C., an appropriate amount of NiCO3 is added to maintain the pH value at approximately 2.0-2.5, and then FePO4·2H2O seed crystals are added for reaction precipitation (i.e., maintaining the ferric phosphate concentration of 1 L of 100 g / L nickel-iron leachate at 20 g / L). The solution is stirred and reacted for 2 hours.

[0094] (3) Post-processing

[0095] After chromium removal, the solution is pumped into the filter press 150 for solid-liquid separation to obtain a chromium-removed filtrate and a first chromium residue. The chromium-removed filtrate is pumped into the fine filtration device 160 for secondary solid-liquid separation to obtain a chromium-removed fine filtrate and a second chromium residue.

[0096] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0126 g / L, and the chromium removal rate = (0.0884-0.0126) / 0.0884 = 85.7%.

[0097] Example 3

[0098] The present disclosure provides a method for removing chromium from a nickel-iron leachate, which is processed using the apparatus shown in FIG3 , and includes the following steps:

[0099] (1) Providing nickel-iron leaching solution to be treated

[0100] The composition of the nickel-iron leaching solution is the same as that of Example 2.

[0101] (2) Precipitated chromium

[0102] The nickel-iron leachate is transferred from the leachate storage tank 100 to the first leachate chromium removal reaction tank 110 via a pump. Steam is introduced to raise the leachate temperature to 70°C. NiCO3 is added through the first feeding port 113 to adjust the pH to 2.0-2.5. Then, FePO4·2H2O is added at a ratio of 10% of the leachate mass volume concentration (i.e., 10g of ferric phosphate is added to 1L of 100g / L nickel-iron leachate). After reacting for 3 hours at a stirring rate of 90r / min, the reaction is pumped into the second leachate chromium removal reaction tank 130. Similarly, the second leachate chromium removal reaction tank 130 is heated to 70°C, and an appropriate amount of NiCO3 is added to maintain the pH at approximately 2.5. Then, seed crystals of FePO4·2H2O are added to the second leachate chromium removal reaction tank for reaction precipitation (i.e., maintaining the ferric phosphate concentration of 10g / L for 1L of 100g / L nickel-iron leachate). The reaction is stirred for 3 hours.

[0103] (3) Post-processing

[0104] After chromium removal, the solution is pumped into the filter press 150 for solid-liquid separation to obtain a chromium-removed filtrate and a first chromium residue. The chromium-removed filtrate is pumped into the fine filtration device 160 for secondary solid-liquid separation to obtain a chromium-removed fine filtrate and a second chromium residue.

[0105] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0168 g / L, and the chromium removal rate = (0.0884-0.0168) / 0.0884 = 80.9%.

[0106] Example 4

[0107] The present disclosure provides a method for removing chromium from a nickel-iron leachate, which is processed using the apparatus shown in FIG3 , and includes the following steps:

[0108] (1) Providing nickel-iron leaching solution to be treated

[0109] The composition of the nickel-iron leaching solution is the same as that of Example 2.

[0110] (2) Precipitated chromium

[0111] The nickel-iron leachate is transferred from the leachate storage tank 100 to the first leachate chromium removal reaction tank 110 via a pump. Steam is introduced to raise the leachate temperature to above 90° C. NiCO3 is added through the first feeding port 113 to adjust the pH to 2.5. Then, FePO4·2H2O is added at a ratio of 50% of the leachate mass volume concentration (i.e., 50 g of ferric phosphate is added to 1 L of 100 g / L nickel-iron leachate). After reacting for 3 hours at a stirring rate of 90 r / min, the leachate is pumped into the second leachate chromium removal reaction tank 130. Similarly, in the second leachate chromium removal reaction tank 130, the temperature is raised to above 90° C., an appropriate amount of NiCO3 is added to maintain the pH at approximately 2.5, and then seed crystals of FePO4·2H2O are added for reaction precipitation (i.e., maintaining the ferric phosphate concentration of 1 L of 100 g / L nickel-iron leachate at 50 g / L), and the reaction is stirred for 3 hours.

[0112] (3) Post-processing

[0113] After chromium removal, the solution is pumped into the filter press 150 for solid-liquid separation to obtain a chromium-removed filtrate and a first chromium residue. The chromium-removed filtrate is pumped into the fine filtration device 160 for secondary solid-liquid separation to obtain a chromium-removed fine filtrate and a second chromium residue.

[0114] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0106 g / L, and the chromium removal rate = (0.0884-0.0106) / 0.0884 = 88%.

[0115] Example 5

[0116] The only difference from Example 2 is that the reaction temperature in step (2) is 80°C.

[0117] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0136 g / L.

[0118] Example 6

[0119] The only difference from Example 2 is that the reaction temperature in step (2) is 70°C.

[0120] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0139 g / L.

[0121] Example 7

[0122] The only difference from Example 2 is that the reaction temperature in step (2) is 60°C.

[0123] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0145 g / L.

[0124] Example 8

[0125] The only difference from Example 2 is that the reaction temperature in step (2) is 50°C.

[0126] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0152 g / L.

[0127] Example 9

[0128] The only difference from Example 2 is that the reaction temperature in step (2) is 90°C.

[0129] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0114 g / L.

[0130] Example 10

[0131] The only difference from Example 2 is that step (2) uses three leaching solution chromium removal reaction tanks for treatment, the pH values ​​of the three leaching solution chromium removal reaction tanks are 2.0-2.5, 3.9-4.1, and 5.8-6.2, respectively, and the parameters such as the amount of seed crystal addition, temperature, and rotation speed are referred to Example 2.

[0132] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0074g / L.

[0133] Example 11

[0134] The only difference from Example 2 is that FePO4·2H2O is added at a concentration of 5% by volume of the leachate (i.e., 5 g of ferric phosphate is added to 1 L of 100 g / L nickel-iron leachate). The chromium ion concentration of the chromium-removed filtrate is 0.0219 g / L.

[0135] Example 12

[0136] The only difference from Example 2 is that FePO4·2H2O is added at a ratio of 10% of the mass volume concentration of the leachate (i.e., 10 g of ferric phosphate is added to 1 L of 100 g / L nickel-iron leachate). After testing, the chromium ion concentration of the chromium-removed filtrate is 0.0189 g / L.

[0137] Example 13

[0138] The only difference from Example 2 is that FePO4·2H2O is added at a concentration of 15% by volume of the leachate (i.e., 15 g of ferric phosphate is added to 1 L of 100 g / L nickel-iron leachate). The chromium ion concentration of the chromium-removed filtrate is 0.0156 g / L.

[0139] Example 14

[0140] The only difference from Example 2 is that FePO4·2H2O is added at a ratio of 30% of the mass volume concentration of the leachate (ie, 30 g of ferric phosphate is added to 1 L of 100 g / L nickel-iron leachate).

[0141] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0122 g / L.

[0142] Example 15

[0143] The only difference from Example 2 is that FePO4·2H2O is added at a ratio of 40% of the mass volume concentration of the leachate (ie, 40 g of iron phosphate is added to 1 L of 100 g / L nickel-iron leachate).

[0144] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0120 g / L.

[0145] Example 16

[0146] FePO4·2H2O was added at a ratio of 50% of the mass volume concentration of the leaching solution (ie, 50 g of iron phosphate was added to 1 L of 100 g / L nickel-iron leaching solution).

[0147] After testing, the chromium ion concentration of the chromium removal filtrate was 0.0116 g / L.

[0148] From Example 1 and Examples 11-16, it can be seen that the amount of FePO4·2H2O added has an impact on the chromium removal effect, and it is best to control it at around 15%-20%. If it exceeds 20%, the removal effect will not be significantly improved.

[0149] Comparative Example 1

[0150] The only difference from Example 2 is that nickel carbonate is replaced with sodium hydroxide for pH adjustment. Since sodium hydroxide is a strong base, it is difficult to accurately control the pH value of the solution, and the introduction of sodium ions increases the difficulty of the sodium removal process.

[0151] Comparative Example 2

[0152] This comparative example provides a method for removing chromium from a conventional nickel-iron leachate. The composition of the nickel-iron leachate is the same as that of Example 2, and the specific chromium removal process is as follows: (1) adjusting the pH value of the nickel leachate to 1.0-2.5; (2) adding a precipitant to generate a chromium precipitate; and (3) separating the chromium precipitate to obtain a nickel leachate chromium removal solution. The precipitant is a chromium pyrophosphate, sodium monohydrogen phosphate, or sodium polyphosphate, and the addition of the precipitant in step (2) further includes precipitation conversion. This method removes chromium impurities while introducing impurities such as sodium ions and pyrophosphate, which increases the difficulty of impurity removal. The chromium removal rate is approximately 90%, while the chromium removal rate of the present embodiment is greater than 95%. Industrial Applicability

[0153] The present invention utilizes ferric phosphate seeds as an inducer to treat a nickel-iron leachate, rapidly inducing the formation of chromium phosphate dihydrate precipitates through crystal nucleation. This one-step precipitation reaction allows for more complete removal of chromium from the nickel-iron leachate at a specific reaction temperature. The method provided by the present invention is easy to operate, simple to control, and possesses excellent industrial applicability.

Claims

1. A method for removing chromium from nickel-iron leaching solution, characterized in that, Including: Mix the chromium-containing nickel-iron leaching solution with iron phosphate and react under the conditions of a pH value of 1.8 - 2.5 and a temperature of 70°C - 95°C.

2. The method according to claim 1, wherein After adjusting the pH value of the nickel-iron leaching solution to 1.8 - 2.5, add seed iron phosphate to the nickel-iron leaching solution for crystallization coprecipitation, control the reaction temperature at 80°C - 90°C, and the reaction time at 1 h - 6 h.

3. The method according to claim 1 or 2, characterized in that, The seed iron phosphate is selected from at least one of iron phosphate dihydrate and anhydrous iron phosphate. Calculate the addition amount of the seed iron phosphate according to the contents of nickel, iron, phosphorus, and chromium in the nickel-iron leaching solution, and control the mass ratio of the contents of nickel, iron, phosphorus, and chromium to the addition amount of the seed iron phosphate to be 100:(5 - 50).

4. The method according to claim 3, wherein Control the mass ratio of the contents of nickel, iron, phosphorus, and chromium to the addition amount of the seed iron phosphate to be 100:(15 - 20), and the added seed iron phosphate is iron phosphate or an iron phosphate slurry.

5. The method according to claim 4, wherein Use NiCO3, a NiCO3 slurry, Ni(OH)2, or a Ni(OH)2 slurry to adjust the pH value of the nickel-iron leaching solution.

6. The method according to any one of claims 1-5, characterized in that, During the reaction with the iron phosphate, control the stirring rate at 60 r / min - 90 r / min.

7. The method according to claim 6, characterized in that, During the reaction with the iron phosphate, control the stirring rate at 75 r / min - 85 r / min.

8. The method according to any one of claims 1-7, characterized in that, First, add seed iron phosphate to the chromium-containing nickel-iron leaching solution with a pH value of 2.0 - 2.5 and react for 1 h - 2 h, then gradually increase the pH value to 5.8 - 6.2 by adding nickel hydroxide for reaction.

9. The method according to claim 8, wherein After the reaction is completed under the condition of a pH value of 2.0 - 2.5, react for 1 h - 2 h respectively under the conditions of a pH value of 2.9 - 3.1, 3.9 - 4.1, 4.9 - 5.1, and 5.8 - 6.2, and control the reaction temperature at 70°C - 95°C.

10. The method according to claim 8, wherein After the reaction is completed under the condition of a pH value of 2.0 - 2.5, react for 1 h - 2 h respectively under the conditions of 3.9 - 4.1 and 5.8 - 6.2, and control the reaction temperature at 70°C - 95°C.

11. The method according to any one of claims 1-10, characterized in that, Pass the nickel-iron leaching solution through multiple leaching solution chromium removal reaction tanks in sequence for continuous reaction, and the number of the leaching solution chromium removal reaction tanks is 2 - 5.

12. The method according to claim 11, wherein A steam pipeline for introducing heat source steam is connected to each of the leaching solution chromium removal reaction tanks, and a feeding port is further provided at the top of each of the leaching solution chromium removal reaction tanks to add iron phosphate and the material for adjusting the pH value through the feeding port.

13. The method according to claim 12, characterized in that A driving pump is installed at the top of each of the leaching solution chromium removal reaction tanks, and a stirring device is further provided in each of the leaching solution chromium removal reaction tanks. The driving pump is connected to the stirring device to drive the stirring device to rotate.

14. The method according to claim 13, wherein The stirring device includes a stirring rod and a plurality of stirring blades arranged from top to bottom. The plurality of stirring blades are all connected to the stirring rod and are evenly distributed in the circumferential direction of the stirring rod.

15. The method according to claim 14, characterized in that, The number of the stirring blades is 3 - 8.

16. The method according to any one of claims 11-15, characterized in that, The height-diameter ratio of each of the leaching solution chromium removal reaction tanks is (1 - 3):

1.

17. The method according to any one of claims 11-16, characterized in that, A feed pipe is provided between every two adjacent chromium removal reaction tanks for leaching solution. The inlet end of each feed pipe is connected to one chromium removal reaction tank for leaching solution, and the outlet end of each feed pipe is connected to the next chromium removal reaction tank for leaching solution. A delivery pump is installed on each feed pipe to provide the delivery power.

18. The method according to any one of claims 11 - 17, characterized in that, There are three chromium removal reaction tanks for leaching solution. The pH value of the first chromium removal reaction tank for leaching solution is adjusted to 2.0 - 2.5 before the reaction, the pH value of the second chromium removal reaction tank for leaching solution is adjusted to 3.9 - 4.1 before the reaction, and the pH value of the third chromium removal reaction tank for leaching solution is adjusted to 5.8 - 6.

2.

19. The method according to any one of claims 1-18, characterized in that, The nickel-iron leaching solution is a sulfuric acid leaching solution with an initial pH value of 0.5 - 1.

20. The method according to any one of claims 1-19, characterized in that, By mass-volume concentration, the metal element composition in the nickel-iron leaching solution is as follows: nickel 10 - 60 g / L, iron 40 - 80 g / L, chromium 0.01 - 0.1 g / L, phosphorus 0.2 - 5 g / L.

21. The method according to any one of claims 1-20, characterized in that, It also includes: After the reaction with the iron phosphate is completed, solid-liquid separation is carried out to obtain a chromium-removed filtrate and a first chromium slag, and then the chromium-removed filtrate is subjected to fine filtration separation to obtain a chromium-removed fine filtrate and a second chromium slag.

22. The method according to claim 21, wherein It also includes: detecting the obtained chromium-removed fine filtrate. If the chromium content is less than the chromium removal requirement, it enters the next process; if the chromium content is greater than or equal to the chromium removal requirement, it returns to the chromium removal unit.

23. A nickel-iron leaching solution chromium removal device for implementing the method according to any one of claims 1-22, characterized in that, It includes multiple chromium removal reaction tanks for leaching solution. A feed pipe is provided between every two adjacent chromium removal reaction tanks for leaching solution. The inlet end of each feed pipe is connected to one chromium removal reaction tank for leaching solution, and the outlet end of each feed pipe is connected to the next chromium removal reaction tank for leaching solution.

24. The chromium removal device for nickel-iron leaching solution according to claim 23, wherein, It also includes a leaching solution storage tank. A feed pipeline is provided between the leaching solution storage tank and the first chromium removal reaction tank for leaching solution. The inlet end of the feed pipeline is connected to the leaching solution storage tank, and the outlet end of the feed pipeline is connected to the first chromium removal reaction tank for leaching solution. A feed pump is installed on the feed pipeline to provide the delivery power.

25. The chromium removal device for nickel-iron leaching solution according to claim 23 or 24, characterized in that, It also includes a pressure filtration device and a fine filtration device. The outlet of the last chromium removal reaction tank for leaching solution is communicated with the inlet of the pressure filtration device, and the outlet of the pressure filtration device is communicated with the inlet of the fine filtration device.

26. The chromium removal device for nickel-iron leaching solution according to claim 25, characterized in that, It also includes: A chromium-removed filtrate storage tank and a chromium-removed fine filtrate storage tank. The inlet of the chromium-removed filtrate storage tank is communicated with the outlet of the pressure filtration device, the outlet of the chromium-removed filtrate storage tank is communicated with the inlet of the fine filtration device, and the inlet of the chromium-removed fine filtrate storage tank is communicated with the outlet of the fine filtration device.

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