Method for recycling iron, chromium and nickel in waste acid solution

Abstract

The invention relates to a method for recycling iron, chromium and nickel in a waste acid solution, which comprises the following steps: (1) taking the waste acid solution containing + 3-valent iron ions, + 3-valent chromium ions and + 2-valent nickel ions as a reduction end solution, taking a chromium-containing iron acid solution containing + 2-valent iron as an oxidation end solution, carrying out diaphragm electrolysis treatment to obtain a ferrous iron acid solution at the reduction end, oxidizing the end to obtain an iron-chromium solution containing ferric iron; (2) carrying out nickel removal treatment on the ferrous-iron-containing acid liquor through hydrogen sulfide to obtain a nickel sulfide product and nickel-removed liquor; the nickel-removed solution is sequentially subjected to iron-chromium separation and acid dissolution to obtain a chromium-containing iron acid solution containing + 2-valent iron, and the chromium-containing iron acid solution is circulated to the step (1) to be used as an oxidation end solution; and (3) the iron-chromium solution is sequentially subjected to iron removal and chromium precipitation, and a chromium hydroxide product is obtained. Divalent iron and trivalent chromium are separated by utilizing valence change of iron and property difference between divalent iron and trivalent iron; nickel is removed by hydrogen sulfide, so that iron, chromium and nickel in the waste acid solution are completely separated, and no byproduct waste is produced.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of industrial waste liquid, and in particular to a resource utilization method for iron, chromium and nickel in waste acid liquid. Background Art

[0002] The waste liquid from hydrochloric acid washing of stainless steel contains iron ions, chromium ions and nickel ions. Currently, when separating and recovering iron, chromium and nickel in the waste liquid, most of them are directly neutralized with alkaline solution and treated harmlessly; a small part of them is to wash the metal mud and reuse it in stainless steel smelting; there are few metal separations, and those that are separated only carry out preliminary separation and use the metal mud as an intermediate product for resource utilization, without conducting in-depth separation and optimization exploration.

[0003] CN107324303A discloses a method for separating and refining iron and chromium from multi-metallic hazardous waste, the method comprising the following steps: (1) acid leaching: preparing a comprehensive sludge containing metal elements, adding water to the sludge to make a slurry, slowly adding 98% H2SO4 while stirring, and stopping the addition of acid when the pH is adjusted to be stable at 0.5, and continuing to dissolve the sludge to allow the metal elements in the sludge to enter the solution; (2) filter pressing: filter pressing the solution after acid leaching, washing the filter residue, returning the washing water to be used as slurry water, purifying the washed residue, and the filter filtrate entering the next process for further processing; (3) crude ferrochrome alum: placing the collected filtrate in a container and stirring, slowly adding CaCO3 slurry under normal pressure to adjust the pH to 4.0, continuing the reaction, slowly adding H2O2, and controlling the pH to 3.8-4.1 with CaCO3 slurry at the same time, until H2O2 removes Fe 2+ Completely oxidized to Fe 3+ , then filter press, the filter cake obtained is crude ferrochrome alum, and the filtrate enters the copper, zinc, nickel, cobalt, and manganese separation process; (4) dissolving crude ferrochrome alum: the crude ferrochrome alum filter cake is slurried with water, 98% H2SO4 is added thereto to adjust the pH to 0.5 so that iron and chromium enter the solution, and then filter press, the filter cake is crude gypsum, which is purified and washed to obtain a gypsum product, and the filtrate enters the next process; (5) reduction: iron filings are added to the filtrate, and 98% H2SO4 is added to maintain the pH to 1.0-1.5, and Fe 3+ Reduction to Fe 2+ (6) Chromium precipitation: add 10% CaCO3 slurry to the filtrate and adjust the pH to 5.5 to precipitate Cr 3+ , the filter cake after filtration is Cr(OH)3; (7) Iron precipitation: the Fe 2+The filtrate is returned to the crude ferrochrome alum process, and iron is added thereto or further alkali solution is added for precipitation, and then oxidized in the air to obtain Fe(OH)3. This invention can only process solutions with a divalent iron ion content of less than 5000ppm. If the iron content is greater than 100,000ppm, when chromium is converted into chromium hydroxide precipitation, the chromium mud contains a large amount of iron, including the precipitated iron and the ferrous chloride entrained in the precipitation. During the subsequent cleaning of the chromium mud, the entrained ferrous chloride will also be oxidized by air to ferric hydroxide precipitation, reducing the purity of the chromium mud and the product value.

[0004] CN109850928A discloses a method for recovering sulfate and metals from sulfuric acid containing pickling residue, comprising the following steps: a) mixing the sulfuric acid containing the pickling residue with at least one magnesium compound selected from magnesium oxide, magnesium hydroxide, and magnesium carbonate to obtain a modified pickling residue having a pH value in the range of 7-10; b) heating the modified pickling residue to a temperature of 70-90°C and adjusting the pH value with sulfuric acid, thereby bringing magnesium from the modified pickling residue into solution in the form of magnesium sulfate at a stable pH of 6-6.5; c) recovering the magnesium sulfate in the form of a magnesium sulfate solution by filtration, and obtaining a FeNiCr residue as a precipitate. During the separation of iron and chromium, ferric phosphate and chromium phosphate products are produced separately; however, when the ferric phosphate is precipitated, the chromium phosphate is also partially precipitated. To obtain a higher-purity ferric phosphate, an excess of iron is required, which results in the subsequent chromium phosphate being mixed with some iron. In other words, the invention only achieves a preliminary separation of the metals and does not produce a high-purity industrial-grade product.

[0005] Therefore, it is necessary to develop a resource utilization method to separate and purify iron, chromium and nickel, obtain high-purity iron-, chromium- or nickel-containing separated products, and improve the quality and value of the products. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a method for resource recovery of iron, chromium and nickel in waste acid liquid. By electrolyzing the waste acid liquid, nickel is first removed, and the valence change of iron and the difference in properties between divalent iron and trivalent iron are utilized to control the precipitation of trivalent chromium while divalent iron does not precipitate to recover divalent iron (ferrous salt solution), and the precipitation of trivalent iron while trivalent chromium does not precipitate to recover trivalent chromium (chromium hydroxide product). Iron, chromium and nickel are fully recovered as resources without any by-product waste.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for recycling iron, chromium and nickel in waste acid solution, the method comprising:

[0009] (1) a waste acid solution containing +3-valent iron ions, +3-valent chromium ions and +2-valent nickel ions is used as a reducing end solution, and a chromium-containing ferric acid solution containing +2-valent iron is used as an oxidizing end solution, wherein the reducing end solution and the oxidizing end solution are separated by a diaphragm and subjected to diaphragm electrolysis treatment together, thereby obtaining a ferrous acid solution at the reducing end and a ferrochromium solution containing trivalent iron at the oxidizing end;

[0010] (2) the ferrous acid solution in step (1) is subjected to a nickel removal treatment and a first solid-liquid separation in sequence with hydrogen sulfide to obtain a nickel sulfide product and a nickel-removed liquid;

[0011] The nickel-removed liquid is subjected to iron-chromium separation to obtain a ferrous salt solution and chromium mud; the chromium mud is dissolved in acid to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution;

[0012] (3) the iron-chromium solution in step (1) is subjected to iron removal and chromium precipitation in sequence to obtain a chromium hydroxide product;

[0013] There is no order between steps (2) and (3).

[0014] It should be noted that the technical solutions disclosed in the prior art have the following problems when separating and recovering iron, chromium and nickel in waste liquid: (1) When iron powder is used to reduce pickling waste liquid, the iron powder will react with hydrogen ions in the solution to produce a large amount of hydrogen, which poses certain safety risks; (2) When removing chromium and nickel, a large amount of iron will be mixed in the chromium mud and nickel mud, resulting in a low purity of the chromium mud and nickel mud, which limits the high value of the product; (3) The iron recovery rate is relatively low.

[0015] The present invention uses diaphragm electrolysis to perform electrolysis, reduces trivalent iron at the reducing end, and oxidizes divalent iron at the oxidizing end, thereby avoiding the use of redox agents and reducing agent costs. The present invention first removes nickel, and utilizes the valence change of iron and the difference in properties between divalent iron and trivalent iron to control the precipitation of trivalent chromium while divalent iron does not precipitate to recycle divalent iron (ferrous salt solution), and the precipitation of trivalent iron while trivalent chromium does not precipitate to recycle trivalent chromium (chromium hydroxide product). Moreover, iron, chromium and nickel are fully recycled without by-product waste. At the same time, the present invention uses hydrogen sulfide to remove nickel, which, on the one hand, avoids the introduction of sodium. If sodium sulfide is directly used, the sodium ion content in the ferrous salt solution increases. On the other hand, the acidity of the solution can be increased, thereby avoiding the precipitation of ferrous sulfide, improving the recovery rate of iron, and improving the purity and value of nickel sulfide.

[0016] The ferrous acid solution contains not only +2-valent iron but also +3-valent chromium ions and +2-valent nickel ions.

[0017] The anions in the waste acid solution and the chromium-containing ferric acid solution each independently include chloride ions.

[0018] As a preferred technical solution of the present invention, the waste acid solution also contains +2-valent iron ions.

[0019] Preferably, the concentration of +3 valent iron ions in the waste acid solution is 1×10 5 ~2×10 5 ppm, for example, 1×10 5 ppm, 1.2×10 5 ppm, 1.4×10 5 ppm, 1.6×10 5 ppm, 1.8×10 5 ppm or 2×10 5 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0020] Preferably, the concentration of +2-valent iron ions in the waste acid solution is 1×10 4 ~3×10 4 ppm, for example, 1×10 4 ppm, 1.5×10 4 ppm, 2×10 4 ppm, 2.5×10 4 ppm or 3×10 4 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0021] Preferably, the concentration of +3 chromium ions in the waste acid solution is 7×10 3 ~2×10 4 ppm, for example, it could be 7×10 3 ppm, 1×10 4 ppm, 1.3×10 4 ppm, 1.6×10 4 ppm or 2×10 4 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0022] Preferably, the concentration of +2-valent nickel ions in the waste acid solution is 2×10 3 ~1×10 4 ppm, for example, 2×10 3 ppm, 4×10 3 ppm, 6×10 3 ppm, 8×10 3 ppm or 1×10 4 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0023] As a preferred technical solution of the present invention, the voltage of the diaphragm electrolysis treatment is 1.2 to 2.8 V, for example, it can be 1.2 V, 1.5 V, 1.8 V, 2.0 V, 2.2 V, 2.5 V or 2.8 V, but it is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0024] The present invention controls the voltage of the diaphragm electrolysis treatment to be 1.2-2.8V, so that only the reaction of divalent iron to trivalent iron occurs at the oxidation end, and only the reaction of trivalent iron to divalent iron occurs at the reduction end. If the voltage of the diaphragm electrolysis treatment is less than 1.2V, the potentials of both the oxidation end and the reduction end are insufficient, so that divalent iron still exists at the oxidation end and trivalent iron still exists at the reduction end, which increases the difficulty of subsequent separation. If the voltage of the diaphragm electrolysis treatment is greater than 2.8V, a reaction of hydrogen atoms being reduced to hydrogen will occur at the reduction end, and side reactions of chloride ions being oxidized to chlorine, water being oxidized to oxygen, and trivalent chromium being oxidized to hexavalent chromium will occur at the oxidation end.

[0025] Preferably, the current of the diaphragm electrolysis treatment is 50 to 200 A, for example, 50 A, 100 A, 150 A or 200 A, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0026] Preferably, the time of the diaphragm electrolysis treatment is 2 to 12 hours, for example, it can be 2 hours, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, but it is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0027] As a preferred technical solution of the present invention, the iron-chromium separation in step (2) includes: the nickel-removed liquid is subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and chromium-containing ferrous salt solution respectively.

[0028] Preferably, the chromium-containing ferrous salt solution is neutralized to remove chromium to obtain the chromium mud and the ferrous salt solution.

[0029] Preferably, the pH value of the chromium-containing ferrous salt solution is 0.2-1, for example, 0.2, 0.4, 0.6, 0.8 or 1, but is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0030] Preferably, the ferrous salt solution is ferrous chloride water purifier.

[0031] Preferably, the chromium mud comprises chromium hydroxide and ferrous hydroxide.

[0032] Preferably, the mass ratio of the chromium hydroxide to the ferrous hydroxide is (1.5-2):1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0033] Preferably, the reagent used in the neutralization and chromium removal process includes an alkaline substance.

[0034] Preferably, the alkaline substance comprises any one or a combination of at least two of calcium oxide, calcium carbonate or calcium hydroxide, wherein typical but non-limiting combinations include: a combination of calcium oxide and calcium carbonate, a combination of calcium oxide and calcium hydroxide, a combination of calcium carbonate and calcium hydroxide, and a combination of calcium oxide, calcium carbonate and calcium hydroxide.

[0035] Preferably, during the neutralization and chromium removal process, the pH value of the solution is adjusted to 4.8 to 5.5, for example, 4.8, 5.0, 5.2, 5.4 or 5.5, but is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0036] In the present invention, the pH value of the solution during the neutralization and chromium removal process is controlled to be 4.8-5.5, so that chromium hydroxide and ferrous salt solution are obtained after the neutralization and chromium removal treatment, so as to separate chromium and iron. If the pH value of the solution during the neutralization and chromium removal process is less than 4.8, incomplete precipitation of chromium ions will occur, thereby increasing the content of chromium ions in the ferrous salt solution and reducing the separation efficiency. If the pH value of the solution during the neutralization and chromium removal process is greater than 5.5, the iron loss rate is high, which increases the subsequent treatment load.

[0037] As a preferred technical solution of the present invention, the iron content of the chromium-containing ferric acid solution is 5×10 3 ~3×10 4 ppm, for example, 5×10 3 ppm, 1×10 4 ppm, 1.5×10 4 ppm, 2×10 4 ppm, 2.5×10 4 ppm or 3×10 4 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0038] Preferably, the chromium content of the chromium-containing ferric acid solution is 1×10 4 ~5×10 4 ppm, for example, 1×10 4 ppm, 2×10 4 ppm, 3×10 4 ppm, 4×104 ppm or 5×10 4 ppm, but is not limited to the listed values, and other values ​​not listed within the above value range are also applicable.

[0039] Preferably, the pH value of the chromium-containing ferric acid solution is 0.8-1.2, for example, it can be 0.8, 0.9, 1.0, 1.1 or 1.2, but it is not limited to the listed values. Other values ​​not listed within the above range are also applicable.

[0040] As a preferred technical solution of the present invention, the molar ratio of the hydrogen sulfide and the nickel in the ferrous acid solution in step (2) is (1.5-2):1, for example, it can be 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0041] Preferably, the acid-soluble acidic reagent is hydrochloric acid obtained by evaporation and concentration.

[0042] It should be noted that the hydrochloric acid used in the present invention is completely carried by the material itself and generated during the reaction process, and no additional acid or alkali is required, thereby reducing the dosage and cost of the reagents.

[0043] Preferably, the pH value of the ferrochromium solution is 0.8-1.2, for example, it can be 0.8, 0.9, 1.0, 1.1 or 1.2, but it is not limited to the listed values. Other values ​​not listed within the above range are also applicable.

[0044] As a preferred technical solution of the present invention, the reagent used in the iron removal process in step (3) includes an alkaline solution.

[0045] Preferably, the alkaline solution comprises sodium hydroxide and / or potassium hydroxide.

[0046] Preferably, the mass fraction of the alkaline solution is 32-50%, for example, 32%, 35%, 40%, 45% or 50%, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0047] Preferably, the pH value of the solution during the iron removal process is adjusted to 3.5-4.0, for example, 3.5, 3.6, 3.7, 3.8, 3.9 or 4.0, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0048] In the present invention, the pH value of the solution during the iron removal process is controlled to be 3.5-4.0, so that the iron ions in the iron-chromium solution are converted into iron hydroxide, and the chromium ions in the iron-chromium solution continue to remain in the solution. If the pH value of the solution during the iron removal process is less than 3.5, the iron ions will not be completely precipitated, so that the iron ions still exist in the solution, reducing the separation efficiency. If the pH value of the solution during the iron removal process is greater than 4.0, the chromium loss rate increases.

[0049] As a preferred technical solution of the present invention, the reagent used in the chromium precipitation process includes the alkaline solution.

[0050] Preferably, the pH value of the solution during the chromium precipitation process is adjusted to 7-10, for example, 7, 8, 9 or 10, but is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0051] Preferably, the resource recovery method further comprises adding the ferric hydroxide obtained after the iron removal to the waste acid solution in step (1).

[0052] As a preferred technical solution of the present invention, the resource recovery method further includes: first mixing the hydrogen sulfide gas in step (2) with liquid alkali to obtain an alkaline sodium sulfide solution; second mixing the hydrochloric acid obtained by evaporation and concentration with the alkaline sodium sulfide solution to obtain a hydrogen sulfide-containing solution, performing a second aeration treatment on the hydrogen sulfide-containing solution to obtain hydrogen sulfide gas; and circulating the hydrogen sulfide gas to step (2) for nickel removal treatment.

[0053] Preferably, the mass fraction of the liquid caustic soda is 8-10%, for example, 8%, 8.5%, 9%, 9.5% or 10%, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0054] Preferably, the pH value of the solution during the first mixing process is greater than 11, for example, it can be 11.5, 12, 12.5, 13, 13.5 or 14, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0055] In the present invention, the separation and recovery process of hydrogen sulfide is carried out by utilizing the property that hydrogen sulfide is soluble in alkali but insoluble in acid, thereby maximizing the utilization of negative divalent sulfur ions in sodium sulfide and having extremely high economic efficiency at the chemical atomic (ionic) level. Specifically, hydrogen sulfide gas can react with liquid alkali to generate sodium sulfide; and sodium sulfide can react with hydrochloric acid to generate hydrogen sulfide. Therefore, under acidic conditions, the equipment needs to be pressurized and maintained in a hydrogen sulfide environment to improve the recovery rate of nickel, while the solution needs to be kept at a relatively strong acidity to avoid the formation of ferrous sulfide and improve the recovery rate of iron.

[0056] Preferably, the pH value of the solution in the second mixing process is adjusted to 0.2-0.5, for example, 0.2, 0.3, 0.4 or 0.5, but is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0057] Preferably, the first solid-liquid separation treatment comprises filter pressing.

[0058] As a preferred technical solution of the present invention, the resource utilization method includes:

[0059] (1) Contains 1×10+3-valent iron ions 5 ~2×10 5 ppm, +3 valent chromium ion 7×10 3 ~2×10 4 ppm and +2-valent nickel ions 2×10 3 ~1×10 4 ppm of waste acid as the reducing end solution, with an iron content of 5×10 3 ~3×10 4 ppm and chromium content of 1×10 4 ~5×10 4 ppm chromium-containing ferric acid solution is used as the oxidation end solution, the reducing end solution and the oxidation end solution are separated by a diaphragm, and are both subjected to diaphragm electrolysis treatment at a voltage of 1.2 to 2.8 V and a current of 50 to 200 A for 2 to 12 hours, thereby obtaining a ferrous acid solution at the reducing end and a ferric iron solution at the oxidation end;

[0060] (2) the ferrous acid solution in step (1) is subjected to a nickel removal treatment and a first solid-liquid separation in sequence with hydrogen sulfide to obtain a nickel sulfide product and a nickel-removed liquid;

[0061] The nickel-removed liquid is sequentially subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution; the chromium-containing ferrous salt solution is neutralized to remove chromium, and the pH value of the solution is adjusted to 4.8-5.5 to obtain chromium mud and a ferrous salt solution; the hydrochloric acid obtained by the evaporation and concentration is used to acid-dissolve the chromium mud to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution;

[0062] The hydrogen sulfide gas is first mixed with liquid alkali to obtain an alkaline sodium sulfide solution; the hydrochloric acid obtained by evaporation and concentration is secondly mixed with the alkaline sodium sulfide solution to obtain a hydrogen sulfide-containing solution; the hydrogen sulfide-containing solution is secondly aerated to obtain hydrogen sulfide gas; the hydrogen sulfide gas is circulated to the nickel removal process;

[0063] (3) the iron-chromium solution in step (1) is subjected to iron removal and chromium precipitation in sequence to obtain a chromium hydroxide product;

[0064] There is no order between steps (2) and (3).

[0065] Compared with the prior art, the present invention has at least the following beneficial effects:

[0066] (1) The resource utilization method provided by the present invention realizes the separation of iron, chromium and nickel, and obtains ferrous chloride product, chromium hydroxide product and nickel sulfide product, without by-product waste. At the same time, the recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.9%, 99.3% and 99.5%, respectively, and the purity of the ferrous chloride product, chromium hydroxide product and nickel sulfide product can reach 99.93%, 99.91% and 99.83%, respectively. Furthermore, the chromium content in the ferrous chloride product is less than 30ppm and the nickel content is less than 10ppm; the iron content in the chromium hydroxide product is less than 0.005% and the nickel content is less than 0.001%; ​​the iron content in the nickel sulfide product is less than 0.01% and the chromium content is less than 0.002%;

[0067] (2) The present invention uses diaphragm electrolysis to regulate the valence of iron ions in the waste acid solution, reduces trivalent iron at the reducing end, and oxidizes divalent iron at the oxidizing end, thereby avoiding the use of redox agents, reducing the safety risks and agent costs of the disposal process, and having greater economy and advancement. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a flow chart of the process for separating iron, chromium and nickel from waste acid solution provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0069] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0070] The volumes of the reducing end solution and the oxidizing end solution in the following examples and comparative examples are each independently 2 L.

[0071] Example 1

[0072] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. Figure 1 , the resource utilization method includes:

[0073] (1) Contains 1.5×10+3-valent iron ions 5 ppm, +2-valent iron ion 3×10 4 ppm, +3 valent chromium ion 1.2×10 4 ppm and +2-valent nickel ions 6×10 3ppm of waste acid as the reducing end solution, with an iron content of 2×10 4 ppm, chromium content is 3×10 4 ppm, pH value of 1, chromium-containing ferric acid solution as the oxidation end solution, wherein the anions in the waste acid solution and the chromium-containing ferric acid solution are both chloride ions, the reducing end solution and the oxidation end solution are separated by an anion exchange membrane, and are both subjected to diaphragm electrolysis treatment at a voltage of 2V and a current of 100A for 8h, to obtain a ferrous acid solution containing ferrous iron at the reducing end and a ferrochromium solution containing ferric iron at the oxidation end;

[0074] (2) reacting hydrogen sulfide with nickel in the ferrous acid solution of step (1) at a molar ratio of 1.8:1 to remove nickel, and then filtering and washing the mixture to obtain a nickel sulfide product and a nickel-removed solution;

[0075] The nickel-removed liquid is sequentially subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution; the pH value of the chromium-containing ferrous salt solution is 0.6, and the chromium-containing ferrous salt solution is neutralized and chromium removed using calcium oxide to adjust the pH value of the solution to 5.1, thereby obtaining chromium mud and a ferrous salt solution; the ferrous salt solution is a ferrous chloride water purifier;

[0076] The chromium mud comprises chromium hydroxide and ferrous hydroxide in a mass ratio of 1.7:1, and the chromium mud is acid-dissolved using hydrochloric acid obtained by evaporation and concentration to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution;

[0077] The hydrogen sulfide gas is first mixed with liquid caustic soda having a mass fraction of 9%, and the pH value of the solution is adjusted to 12 to obtain an alkaline sodium sulfide solution; the hydrochloric acid obtained by evaporation and concentration is secondly mixed with the alkaline sodium sulfide solution, and the pH value of the solution is adjusted to 0.4 to obtain a hydrogen sulfide-containing solution; the hydrogen sulfide-containing solution is secondly aerated to obtain hydrogen sulfide gas; and the hydrogen sulfide gas is circulated to the nickel removal process;

[0078] (3) The pH value of the ferrochromium solution in step (1) is 0.9, and the ferrochromium solution is subjected to iron removal treatment using a 40% by mass sodium hydroxide solution to adjust the pH value of the solution to 3.8, thereby obtaining ferric hydroxide and a de-ironified solution, and the ferric hydroxide is recycled to the waste acid solution in step (1);

[0079] Using a 40% by mass sodium hydroxide solution to precipitate chromium on the deironing solution, adjusting the pH value of the solution to 8, to obtain a chromium hydroxide product;

[0080] There is no order between steps (2) and (3).

[0081] Example 2

[0082] This embodiment provides a method for recycling iron, chromium, and nickel in waste acid solution, the method comprising:

[0083] (1) Contains 1×10+3-valent iron ions 5 ppm, +2-valent iron ion 2×10 4 ppm, +3 valent chromium ion 2×10 4 ppm and +2-valent nickel ions 1×10 4 ppm of waste acid as the reducing end solution, with an iron content of 3×10 4 ppm, chromium content is 5×10 4 ppm, a chromium-containing ferric acid solution with a pH value of 1.2 as an oxidation end solution, wherein the anions in the waste acid solution and the chromium-containing ferric acid solution are both chloride ions, the reducing end solution and the oxidation end solution are separated by an anion exchange membrane, and are both subjected to diaphragm electrolysis treatment at a voltage of 1.2 V and a current of 50 A for 12 hours, to obtain a ferrous acid solution containing ferric iron at the reducing end and a ferrochromium solution containing ferric iron at the oxidation end;

[0084] (2) reacting hydrogen sulfide with nickel in the ferrous acid solution of step (1) at a molar ratio of 1.5:1 to remove nickel, and then filtering and washing the mixture to obtain a nickel sulfide product and a nickel-removed solution;

[0085] The nickel-removed liquid is sequentially subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution; the pH value of the chromium-containing ferrous salt solution is 0.2, and the chromium-containing ferrous salt solution is neutralized and chromium removed using calcium carbonate to adjust the pH value of the solution to 5.5, thereby obtaining chromium mud and a ferrous salt solution; the ferrous salt solution is a ferrous chloride water purifier;

[0086] The chromium mud comprises chromium hydroxide and ferrous hydroxide in a mass ratio of 2:1, and the chromium mud is acid-dissolved using hydrochloric acid obtained by evaporation and concentration to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution;

[0087] The hydrogen sulfide gas is first mixed with 10% by mass of liquid caustic soda, and the pH value of the solution is adjusted to 11.5 to obtain an alkaline sodium sulfide solution; the hydrochloric acid obtained by evaporation and concentration is secondly mixed with the alkaline sodium sulfide solution, and the pH value of the solution is adjusted to 0.2 to obtain a hydrogen sulfide-containing solution; the hydrogen sulfide-containing solution is secondly aerated to obtain hydrogen sulfide gas; the hydrogen sulfide gas is circulated to the nickel removal process;

[0088] (3) The pH value of the ferrochromium solution in step (1) is 1, and the ferrochromium solution is subjected to iron removal treatment using a potassium hydroxide solution having a mass fraction of 32%, and the pH value of the solution is adjusted to 4.0 to obtain ferric hydroxide and a de-ironified solution, and the ferric hydroxide is recycled to the waste acid solution in step (1);

[0089] Using a potassium hydroxide solution with a mass fraction of 32% to precipitate chromium on the deironing solution, adjusting the pH value of the solution to 7, to obtain a chromium hydroxide product;

[0090] There is no order between steps (2) and (3).

[0091] Example 3

[0092] This embodiment provides a method for recycling iron, chromium, and nickel in waste acid solution, the method comprising:

[0093] (1) Contains 2×10+3-valent iron ions 5 ppm, +2-valent iron ion 1×10 4 ppm, +3 valent chromium ion 7×10 3 ppm and +2-valent nickel ions 2×10 3 ppm of waste acid as the reducing end solution, with an iron content of 5×10 3 ppm, chromium content is 1×10 4 ppm, a chromium-containing ferric acid solution with a pH value of 0.8 as an oxidizing end solution, wherein the anions in the waste acid solution and the chromium-containing ferric acid solution are both chloride ions, the reducing end solution and the oxidizing end solution are separated by an anion exchange membrane, and are both subjected to diaphragm electrolysis treatment at a voltage of 2.8 V and a current of 200 A for 2 hours, to obtain a ferrous acid solution containing ferric iron at the reducing end and a ferrochromium solution containing ferric iron at the oxidizing end;

[0094] (2) reacting hydrogen sulfide with nickel in the ferrous acid solution of step (1) at a molar ratio of 2:1 to remove nickel, and then filtering and washing the mixture to obtain a nickel sulfide product and a nickel-removed solution;

[0095] The nickel-removed liquid is sequentially subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution; the pH value of the chromium-containing ferrous salt solution is 1, and the chromium-containing ferrous salt solution is neutralized and chromium removed using calcium hydroxide to adjust the pH value of the solution to 4.8, thereby obtaining chromium mud and a ferrous salt solution; the ferrous salt solution is a ferrous chloride water purifier;

[0096] The chromium mud comprises chromium hydroxide and ferrous hydroxide in a mass ratio of 1.5:1, and the chromium mud is acid-dissolved using hydrochloric acid obtained by evaporation and concentration to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution;

[0097] The hydrogen sulfide gas is first mixed with 8% by mass of liquid caustic soda, and the pH value of the solution is adjusted to 14 to obtain an alkaline sodium sulfide solution; the hydrochloric acid obtained by evaporation and concentration is secondly mixed with the alkaline sodium sulfide solution, and the pH value of the solution is adjusted to 0.5 to obtain a hydrogen sulfide-containing solution; the hydrogen sulfide-containing solution is secondly aerated to obtain hydrogen sulfide gas; the hydrogen sulfide gas is circulated to the nickel removal process;

[0098] (3) The pH value of the ferrochromium solution in step (1) is 0.8, and the ferrochromium solution is subjected to iron removal treatment using a 50% by mass sodium hydroxide solution to adjust the pH value of the solution to 3.5 to obtain ferric hydroxide and a de-ironified solution, and the ferric hydroxide is circulated to the waste acid solution in step (1);

[0099] Using a 50% by mass sodium hydroxide solution to precipitate chromium on the deironing solution, adjusting the pH value of the solution to 10, to obtain a chromium hydroxide product;

[0100] There is no order between steps (2) and (3).

[0101] Example 4

[0102] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. The only difference from Example 1 is that, except for adjusting the voltage of the diaphragm electrolysis treatment in step (1) from 2V to 0.5V, the rest is the same as Example 1.

[0103] Example 5

[0104] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. The only difference from Example 1 is that, except for adjusting the voltage of the diaphragm electrolysis treatment in step (1) from 2V to 5V, the rest is the same as Example 1.

[0105] Example 6

[0106] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. The only difference from Example 1 is that, except for adjusting the pH value of the solution from 5.1 to 4 in step (2) and during the chromium removal process, the rest is the same as Example 1.

[0107] Example 7

[0108] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. The only difference from Example 1 is that, except for adjusting the pH value of the solution from 3.8 to 3 during the iron removal treatment in step (3), the rest is the same as Example 1.

[0109] Example 8

[0110] This embodiment provides a method for recycling iron, chromium and nickel in waste acid solution. The only difference from Example 1 is that, except for adjusting the pH value of the solution from 3.8 to 5 during the iron removal treatment in step (3), the rest is the same as Example 1.

[0111] Comparative Example 1

[0112] This comparative example provides a method for recycling iron, chromium and nickel in waste acid solution. The difference from Example 1 is that the resource recycling method includes:

[0113] (1) removing iron from waste acid solution by extraction to obtain an iron-containing extract and a nickel-chromium-containing solution; wherein the extractant is di(2-ethylhexyl)phosphoric acid (D2EHPA), wherein the pH value of the waste acid solution is adjusted to 1.5, the volume ratio of the extractant to the waste acid solution during the extraction process is 1:1, the extraction temperature is 25°C, and the extraction time is 10 minutes, the iron-containing extract is stripped with a sulfuric acid solution having a mass concentration of 10% to obtain a solution containing +3 valent iron, wherein the volume ratio of the iron-containing extract to the sulfuric acid solution is 2:1, the stripping temperature is 25°C, and the stripping time is 15 minutes, and the ferrous salt solution is obtained after reduction with excess reduced iron powder;

[0114] (2) reacting hydrogen sulfide with the nickel in the nickel-chromium solution of step (1) at a molar ratio of 1.8:1 to remove nickel, and obtaining a nickel sulfide product and a nickel-removed liquid after filter pressing;

[0115] (3) using 40% by mass of sodium hydroxide to precipitate chromium on the nickel-removed solution, adjusting the pH value of the solution to 8, and obtaining a chromium hydroxide product;

[0116] The rest are the same as in Example 1.

[0117] The chromium hydroxide products separated in Examples 1 to 8 and Comparative Example 1 were washed with water, and the contents of iron, chromium, and nickel were determined using an ICP spectrometer (inductively coupled plasma spectrometer) to calculate the purity and recovery of the three products.

[0118] The formula for calculating purity is: Purity (%) = target metal content in the product / (the sum of the iron, chromium and nickel metal contents in the product) × 100%;

[0119] The recovery rate is calculated as follows: Recovery rate (%) = mass of metal in target product / mass of metal in initial waste acid solution × 100%. The calculation results are shown in Table 1.

[0120] Table 1

[0121]

[0122] The test results show that:

[0123] (1) It can be seen from Examples 1 to 3 that the present invention uses diaphragm electrolysis to regulate the valence of iron ions in the waste acid solution, reduces trivalent iron at the reducing end, and oxidizes divalent iron at the oxidizing end, utilizing the change in the valence of iron and the difference in properties between divalent iron and trivalent iron to separate divalent iron and trivalent chromium; and utilizes hydrogen sulfide to remove nickel, so that the iron, chromium and nickel in the waste acid solution are completely separated without any by-product waste. The recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.9%, 99.3% and 99.5%, respectively, and the purities of the ferrous chloride product, chromium hydroxide product and nickel sulfide product can reach 99.93%, 99.91% and 99.83%, respectively.

[0124] (2) It can be seen from Examples 1 and 4-5 that the voltage of the diaphragm electrolysis treatment in Example 1 of the present invention is 2V, and the recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.96%, 99.58% and 99.83%, respectively, and the purity of the ferrous chloride product, chromium hydroxide product and nickel sulfide product can reach 99.95%, 99.92% and 99.85%, respectively; while the voltage of the diaphragm electrolysis treatment in Example 4 is 0.5V, and the recovery rates of iron, chromium and nickel in the waste acid solution are 26.68%, 34.82% and 0%, respectively, and the purity of the ferrous chloride product and chromium hydroxide product can reach 99.95%, 99.92% and 99.85%, respectively. The purities of the chromium hydroxide products are 82.14% and 51.43%, respectively. In Example 5, the voltage of the diaphragm electrolysis treatment is 5V, and the recoveries of iron, chromium and nickel in the waste acid solution are 99.97%, 0% and 99.87%, respectively. The purities of the ferrous chloride product and the nickel sulfide product are 99.95% and 99.86%, respectively. This shows that the present invention controls the voltage of the diaphragm electrolysis treatment to 1.2-2.8V, so that only the reaction of divalent iron to ferric iron occurs at the oxidation end, and only the reaction of ferric iron to divalent iron occurs at the reduction end, so as to efficiently separate iron, chromium and nickel from the waste acid solution.

[0125] (3) It can be seen from Examples 1 and 6 that the pH value of the solution in the neutralization and chromium removal process in step (2) of Example 1 of the present invention is 5.1, and the recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.96%, 99.58% and 99.83%, respectively, and the purities of the ferrous chloride product, chromium hydroxide product and nickel sulfide product can reach 99.95%, 99.92% and 99.85%, respectively; while the pH value of the solution in the neutralization and chromium removal process in step (2) of Example 6 is 4, and the recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.96%, 99.58% and 99.83%, respectively. .95%, 58.54% and 99.83%, and the purity of the ferrous chloride product, chromium hydroxide product and nickel sulfide product are 97.72%, 99.92% and 99.85% respectively; thus, it is shown that the present invention controls the pH value of the solution in the neutralization and chromium removal process to be 4.8-5.5, so that chromium hydroxide and ferrous salt solution are obtained after neutralization and chromium removal, so as to separate chromium and iron; if the pH value of the solution in the neutralization and chromium removal process is less than 4.8, it will lead to incomplete precipitation of chromium ions, so that the content of chromium ions in the ferrous salt solution increases, and the separation efficiency is reduced.

[0126] (4) It can be seen from Example 1 and Examples 7-8 that the pH value of the solution during the iron removal treatment in step (3) of Example 1 of the present invention is 3.8, and the recovery rates of iron, chromium and nickel in the waste acid solution can reach 99.96%, 99.58% and 99.83%, respectively, and the purities of the ferrous chloride product, chromium hydroxide product and nickel sulfide product can reach 99.95%, 99.92% and 99.85%, respectively; while the pH value of the solution during the iron removal treatment in step (3) of Example 7 is 3, and the recovery rates of iron, chromium and nickel in the waste acid solution are 99.74%, 99.58% and 99.83%, respectively, and the purities of the ferrous chloride product, chromium hydroxide product and nickel sulfide product are 99.95%, 98.87% and 99.85%, respectively; In Example 8, the pH value of the solution during the iron removal treatment in step (3) is 5, and the recoveries of iron, chromium and nickel in the waste acid solution are 99.96%, 0.41% and 99.83%, respectively. The purities of the ferrous chloride product, chromium hydroxide product and nickel sulfide product are 99.95%, 99.92% and 99.85%, respectively. This shows that the present invention controls the pH value of the solution during the iron removal process to 3.5-4.0 so that the iron ions in the ferrochromium solution generate ferric hydroxide and the chromium ions in the ferrochromium solution continue to remain in the solution. If the pH value of the solution during the iron removal process is less than 3.5, incomplete precipitation of the iron ions will result, so that iron ions still exist in the solution, reducing the separation efficiency. If the pH value of the solution during the iron removal process is greater than 4.0, the chromium loss rate increases.

[0127] (5) It can be seen from Example 1 and Comparative Example 1 that the present invention regulates the valence of iron ions in the waste acid solution through diaphragm electrolysis treatment, reduces trivalent iron at the reducing end, and oxidizes divalent iron at the oxidizing end, thereby avoiding the use of redox agents, reducing the safety risks and agent costs of the disposal process, and improving the recovery rate of iron, chromium and nickel in the waste acid solution and the purity of the corresponding products.

[0128] In summary, the present invention regulates the valence state of iron ions in the waste acid solution through diaphragm electrolysis treatment, reduces trivalent iron at the reducing end, and oxidizes divalent iron at the oxidizing end, thereby avoiding the use of redox agents, reducing the safety risks and agent costs of the disposal process, and ultimately obtaining a ferrous chloride product with a purity of 99.93%, a chromium hydroxide product with a purity of 99.91%, and a nickel sulfide product with a purity of 99.83%, without any by-product waste. At the same time, the recovery rates of iron, chromium, and nickel in the waste acid solution can reach 99.9%, 99.3%, and 99.5%, respectively.

[0129] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for recycling iron, chromium and nickel in waste acid solution, characterized in that: The resource utilization method includes: (1) a waste acid solution containing +3-valent iron ions, +3-valent chromium ions and +2-valent nickel ions is used as a reducing end solution, and a chromium-containing ferric acid solution containing +2-valent iron is used as an oxidizing end solution, wherein the reducing end solution and the oxidizing end solution are separated by a diaphragm and subjected to diaphragm electrolysis treatment together, thereby obtaining a ferrous acid solution at the reducing end and a ferrochromium solution containing trivalent iron at the oxidizing end; (2) the ferrous acid solution in step (1) is subjected to a nickel removal treatment and a first solid-liquid separation in sequence with hydrogen sulfide to obtain a nickel sulfide product and a nickel-removed liquid; The nickel-removed liquid is subjected to iron-chromium separation to obtain a ferrous salt solution and chromium mud; the chromium mud is dissolved in acid to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution; (3) the iron-chromium solution in step (1) is subjected to iron removal and chromium precipitation in sequence to obtain a chromium hydroxide product; There is no order between steps (2) and (3).

2. The resource utilization method according to claim 1, characterized in that: The waste acid solution also contains +2-valent iron ions; Preferably, the concentration of +3 valent iron ions in the waste acid solution is 1×10 5 ~2×10 5 ppm; Preferably, the concentration of +2-valent iron ions in the waste acid solution is 1×10 4 ~3×10 4 ppm; Preferably, the concentration of +3 chromium ions in the waste acid solution is 7×10 3 ~2×10 4 ppm; Preferably, the concentration of +2-valent nickel ions in the waste acid solution is 2×10 3 ~1×10 4 ppm.

3. The resource utilization method according to claim 1 or 2, characterized in that: The voltage of the diaphragm electrolysis treatment is 1.2 to 2.8 V; Preferably, the current of the diaphragm electrolysis treatment is 50 to 200 A; Preferably, the diaphragm electrolysis treatment time is 2 to 12 hours.

4. The resource utilization method according to any one of claims 1 to 3, characterized in that: The iron-chromium separation in step (2) comprises: the nickel-removed liquid is subjected to a first aeration treatment in sequence to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution respectively; Preferably, the chromium-containing ferrous salt solution is neutralized to remove chromium to obtain the chromium mud and the ferrous salt solution; Preferably, the pH value of the chromium-containing ferrous salt solution is 0.2 to 1; Preferably, the ferrous salt solution is ferrous chloride water purifier; Preferably, the chromium mud comprises chromium hydroxide and ferrous hydroxide; Preferably, the mass ratio of the chromium hydroxide to the ferrous hydroxide is (1.5-2):1; Preferably, the reagent used in the neutralization and chromium removal process includes an alkaline substance; Preferably, the alkaline substance includes any one of calcium oxide, calcium carbonate or calcium hydroxide, or a combination of at least two thereof; Preferably, the pH value of the solution is adjusted to 4.8-5.5 during the neutralization and chromium removal process.

5. The resource utilization method according to any one of claims 1 to 4, characterized in that: The iron content of the chromium-containing ferric acid solution is 5×10 3 ~3×10 4 ppm; Preferably, the chromium content of the chromium-containing ferric acid solution is 1×10 4 ~5×10 4 ppm; Preferably, the pH value of the chromium-containing ferric acid solution is 0.8-1.

2.

6. The resource utilization method according to claim 4, characterized in that: The molar ratio of hydrogen sulfide to nickel in the ferrous acid solution in step (2) is (1.5-2):1; Preferably, the acid-soluble acidic reagent is the hydrochloric acid obtained by evaporation and concentration; Preferably, the pH value of the iron-chromium solution is 0.8-1.

2.

7. The resource utilization method according to any one of claims 1 to 6, characterized in that: The reagent used in the iron removal process of step (3) includes an alkaline solution; Preferably, the alkaline solution comprises sodium hydroxide and / or potassium hydroxide; Preferably, the mass fraction of the alkaline solution is 32-50%; Preferably, the pH value of the solution is adjusted to 3.5-4.0 during the iron removal process.

8. The resource utilization method according to claim 7, characterized in that: The reagents used in the chromium precipitation process include the alkaline solution; Preferably, the pH value of the solution during the chromium precipitation process is adjusted to 7 to 10; Preferably, the resource recovery method further comprises adding the ferric hydroxide obtained after the iron removal to the waste acid solution in step (1).

9. The resource utilization method according to claim 4, characterized in that: The resource recovery method further comprises: first mixing the hydrogen sulfide gas in step (2) with liquid alkali to obtain an alkaline sodium sulfide solution; second mixing the hydrochloric acid obtained by evaporation and concentration with the alkaline sodium sulfide solution to obtain a hydrogen sulfide-containing solution; performing a second aeration treatment on the hydrogen sulfide-containing solution to obtain hydrogen sulfide gas; and circulating the hydrogen sulfide gas to step (2) for nickel removal treatment. Preferably, the mass fraction of the liquid caustic soda is 8 to 10%; Preferably, the pH value of the solution during the first mixing process is >11; Preferably, the pH value of the solution is adjusted to 0.2-0.5 during the second mixing process.

10. The resource utilization method according to any one of claims 1 to 9, characterized in that: The resource utilization method includes: (1) Contains 1×10+3-valent iron ions 5 ~2×10 5 ppm, +2-valent iron ion 1×10 4 ~3×10 4 ppm, +3 valent chromium ion 7×10 3 ~2×10 4 ppm and +2-valent nickel ions 2×10 3 ~1×10 4 ppm of waste acid as the reducing end solution, with an iron content of 5×10 3 ~3×10 4 ppm and chromium content of 1×10 4 ~5×10 4 ppm chromium-containing ferric acid solution is used as the oxidation end solution, the reducing end solution and the oxidation end solution are separated by a diaphragm, and are both subjected to diaphragm electrolysis treatment at a voltage of 1.2 to 2.8 V and a current of 50 to 200 A for 2 to 12 hours, thereby obtaining a ferrous acid solution at the reducing end and a ferric iron solution at the oxidation end; (2) the ferrous acid solution in step (1) is subjected to a nickel removal treatment and a first solid-liquid separation in sequence with hydrogen sulfide to obtain a nickel sulfide product and a nickel-removed liquid; The nickel-removed liquid is sequentially subjected to a first aeration treatment to generate hydrogen sulfide gas, and evaporated and concentrated to obtain hydrochloric acid and a chromium-containing ferrous salt solution; the chromium-containing ferrous salt solution is neutralized to remove chromium, and the pH value of the solution is adjusted to 4.8-5.5 to obtain chromium mud and a ferrous salt solution; the hydrochloric acid obtained by the evaporation and concentration is used to acid-dissolve the chromium mud to obtain a chromium-containing ferric acid solution containing +2-valent iron, and the chromium-containing ferric acid solution is circulated to step (1) as an oxidation end solution; The hydrogen sulfide gas is first mixed with liquid alkali to obtain an alkaline sodium sulfide solution; the hydrochloric acid obtained by evaporation and concentration is secondly mixed with the alkaline sodium sulfide solution to obtain a hydrogen sulfide-containing solution; the hydrogen sulfide-containing solution is secondly aerated to obtain hydrogen sulfide gas; the hydrogen sulfide gas is circulated to the nickel removal process; (3) the iron-chromium solution in step (1) is subjected to iron removal and chromium precipitation in sequence to obtain a chromium hydroxide product; There is no order between steps (2) and (3).

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