Method for comprehensively recovering valuable elements from waste acid

Abstract

The invention discloses a method for comprehensively recovering valuable elements from waste acid, the waste acid contains copper, nickel and arsenic, the concentration of copper in the waste acid is 25g / l-70g / l, the concentration of arsenic in the waste acid is 5g / l-50g / l, the concentration of nickel in the waste acid is 2g / l-25g / l, and the concentration of acid in the waste acid is 70g / l-220g / l, and the method comprises the steps of evaporative crystallization, membrane dialysis, primary neutralization and secondary neutralization. According to the method, the copper recovery rate is not lower than 98%, the nickel recovery rate is not lower than 90%, and the arsenic recovery rate is not lower than 80%. According to the invention, neutralization is carried out after evaporative crystallization and membrane dialysis, so that the alkali consumption can be reduced by 40-60%, and the treatment cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy and industrial wastewater treatment technology, and more specifically, to a method for comprehensively recovering valuable elements from waste acid, and even more specifically, to a method for comprehensively recovering valuable elements from waste acid with high copper and low arsenic and nickel content. Background Technology

[0002] The waste acid from copper smelting has a complex composition, containing not only a high concentration of copper ions, but also a certain concentration of arsenic, nickel and other ions. Because it is rich in valuable elements such as copper, arsenic and nickel, it has comprehensive recycling value.

[0003] Currently, steel mills, chemical plants, dye factories, electroplating plants, and smelters mostly use chemical methods to recover metallic copper and nickel from waste acid. The most common existing technology is the stepwise neutralization method, but the traditional direct stepwise neutralization method has the following main problems:

[0004] 1. Low separation efficiency: Due to the similar physicochemical properties of copper and nickel, the existing technology uses a neutralization method, resulting in nickel hydroxide containing more than 5% copper and copper slag containing more than 5% nickel.

[0005] 2. Arsenic dispersion risk: Arsenic disperses into copper slag and nickel hydroxide, affecting subsequent purification, increasing the difficulty of treatment, and also increasing the difficulty of arsenic resource recovery;

[0006] 3. High processing cost: Direct neutralization of high acidity requires a large amount of alkali, resulting in high processing cost per ton of acid.

[0007] Therefore, there is an urgent need to provide a method for the comprehensive recovery of valuable elements from waste acid in order to solve the problems of 1. low separation rate, 2. risk of arsenic dispersion, and 3. high processing cost. Summary of the Invention

[0008] In view of this, the present invention provides a method for the comprehensive recovery of valuable elements from waste acid, in order to solve the problems of 1. low separation rate, 2. risk of arsenic dispersion, and 3. high processing cost.

[0009] This invention provides a method for comprehensively recovering valuable elements from waste acid, wherein the waste acid contains copper at a concentration of 25 g / L to 70 g / L, arsenic at a concentration of 5 g / L to 50 g / L, nickel at a concentration of 2 g / L to 25 g / L, and acid at a concentration of 70 g / L to 220 g / L. The method includes:

[0010] The waste acid is subjected to evaporation crystallization, which includes evaporation concentration and crystallization separation. After crystallization separation, copper sulfate crystals and a post-crystallization liquid are obtained.

[0011] The evaporation and concentration process includes: evaporating at a temperature of 80℃ to 110℃ to increase the concentration of the waste acid solution to a specific gravity of 1.38 to 1.5, while controlling the arsenic concentration at the concentration endpoint so that the ratio of copper to arsenic ions in the crystallized solution is controlled at (0.4 to 1.5):1.

[0012] The crystallization separation includes: cooling to less than or equal to 50°C, copper sulfate crystals precipitate, followed by solid-liquid separation to obtain copper sulfate crystals and a post-crystallization liquid;

[0013] Membrane dialysis involves feeding the crystallized liquid into a membrane dialysis device, controlling the volume ratio of the crystallized liquid to the incoming water to be 1:(0.5-2), to obtain recovered acid and residual liquid, with an acid recovery rate of not less than 65%, and the dialysis membrane used in the membrane dialysis device is an anion exchange membrane.

[0014] A first neutralization process involves adding liquid sodium hydroxide to neutralize the residual liquid, controlling the final pH value to be 2.5–5, yielding copper-arsenic slag and a first-neutralized solution. The copper-arsenic slag produced in the first neutralization process includes copper arsenate, and the chemical reaction equation is as follows:

[0015] 3Cu 2+ +2H3A S O₄ + 6NaOH = Cu₃(A) S O4)2+6H2O+6Na + ;

[0016] Cu 2+ +H3A S O₄⁻ + 2NaOH = CuHA S O4 + 2H2O + 2Na + ;

[0017] Cu 2+ +2H3A S O₄ + 2NaOH = Cu(H₂A) S O4)2+2H2O+2Na + ;

[0018] A second neutralization process is performed by adding liquid sodium hydroxide to the primary neutralized solution, controlling the final pH value to be 8-11, yielding nickel hydroxide and a secondary neutralized solution. The nickel hydroxide produced by the secondary neutralization contains less than 1% copper and arsenic and not less than 30% nickel. The chemical reaction equation is as follows:

[0019] Ni 2+ (aq) + 2NaOH = Ni(OH)₂↓ + 2Na + (aq);

[0020] Using the above methods, the copper recovery rate is greater than or equal to 98%, the nickel recovery rate is greater than or equal to 90%, and the arsenic recovery rate is greater than or equal to 80%.

[0021] Optionally, the evaporation and crystallization are carried out in an evaporation crystallizer, which is equipped with an online specific gravity monitor, a copper ion concentration monitor, and an arsenic ion concentration monitor to monitor the specific gravity of the waste acid solution and the copper ion concentration and arsenic ion concentration in real time during the evaporation and concentration process.

[0022] Compared with existing technologies, the method for comprehensively recovering valuable elements from waste acid provided by this invention achieves at least the following beneficial effects:

[0023] 1. The method for comprehensive recovery of valuable elements from waste acid provided by this invention has a high recovery rate and high product purity. The copper recovery rate is greater than or equal to 98%, the purity of the copper sulfate product is greater than or equal to 98%, the nickel recovery rate is greater than or equal to 90%, the nickel hydroxide product contains more than or equal to 30% nickel and less than or equal to 1% copper and arsenic, the arsenic recovery rate is greater than or equal to 80%, and the arsenic content in the copper and arsenic slag is greater than or equal to 25%, which solves the problem of low separation rate in the prior art.

[0024] 2. In this invention, copper-arsenic slag can be used as a raw material for arsenic smelting, with a hazardous waste conversion rate of 100%.

[0025] 3. Compared with direct neutralization, the present invention performs neutralization after evaporation crystallization and membrane dialysis, which can reduce alkali consumption by 40-60% and reduce treatment costs.

[0026] 4. The present invention first evaporates and crystallizes the waste acid, which has the following beneficial effects:

[0027] (1) Evaporation crystallization can recover copper sulfate in advance, reducing the load on subsequent treatment. High copper and low arsenic nickel waste acid has a high copper content, and directly entering the membrane dialysis and neutralization system will increase the load on the membrane system: firstly, high copper ion content may lead to membrane fouling or blockage; secondly, more NaOH is needed to precipitate copper during neutralization, increasing alkali consumption. Through evaporation crystallization, most of the copper can be recovered in the form of copper sulfate crystals (CuSO4·5H2O), obtaining a first-grade smelting by-product, thus achieving preliminary resource utilization.

[0028] (2) Evaporation crystallization can adjust the copper-arsenic ratio and optimize the precipitation conditions of copper arsenate. The copper-arsenic concentration ratio in the crystallization solution is controlled at (0.4–1.5):1. This is to ensure preferential formation of copper arsenate precipitate during the subsequent neutralization (pH 2.5–5). If the copper-arsenic ratio is too high, some copper will precipitate as copper hydroxide, competing for nickel precipitation sites, leading to nickel entering the copper-arsenic slag. If the copper-arsenic ratio is too low, excess arsenic will co-precipitate with nickel during the secondary neutralization process, resulting in high arsenic content in nickel hydroxide. Removing excess copper through evaporation crystallization brings the copper-arsenic ratio closer to the stoichiometric ratio, which is beneficial for the preferential precipitation of copper arsenate and improves the separation efficiency of copper, arsenic, and nickel.

[0029] (3) Evaporation crystallization can also improve the purity of nickel products. By preferentially precipitating copper arsenate, the amount of copper entering the nickel precipitate is reduced, and the copper and arsenic content in the nickel hydroxide precipitate is ultimately less than 1%, thereby increasing the added value of the product.

[0030] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0031] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0033] Figure 1 This is a flowchart of a method for comprehensively recovering valuable elements from waste acid, provided by the present invention. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0035] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0036] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0037] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0038] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0039] Combination Figure 1This invention provides a method for comprehensively recovering valuable elements from waste acid, which is a high-copper, low-arsenic, and low-nickel waste acid, containing copper at a concentration of 25 g / L to 70 g / L, arsenic at a concentration of 5 g / L to 50 g / L, nickel at a concentration of 2 g / L to 25 g / L, and acid at a concentration of 70 g / L to 220 g / L. Specifically, in this invention, copper mainly exists in the form of copper sulfate, arsenic mainly exists in the form of arsenic acid, and nickel mainly exists in the form of nickel sulfate. The method of this invention includes the following steps:

[0040] S101, Evaporation and Crystallization: The waste acid is subjected to evaporation and crystallization, including evaporation concentration and crystallization separation. After crystallization separation, copper sulfate crystals and a post-crystallization liquid are obtained.

[0041] The evaporation and concentration process includes: evaporating at a temperature of 80℃ to 110℃ to increase the concentration of the waste acid solution to a specific gravity of 1.38 to 1.5, while controlling the arsenic concentration at the concentration endpoint so that the ratio of copper to arsenic in the crystallized solution is controlled at (0.4 to 1.5):1.

[0042] The crystallization separation includes: cooling to less than or equal to 50°C, copper sulfate crystals precipitate, followed by solid-liquid separation to obtain copper sulfate crystals and a post-crystallization liquid;

[0043] S102, membrane dialysis, the crystallized liquid is fed into a membrane dialysis device, the ratio of crystallized liquid to clean water is controlled to be 1:(0.5~2), and recovered acid and residual liquid are obtained. The acid recovery rate is not less than 65%. The dialysis membrane used in the membrane dialysis device is an anion exchange membrane.

[0044] S103, primary neutralization: add liquid sodium hydroxide to perform primary neutralization treatment on the residual liquid, control the final pH value to 2.5-5, and obtain copper arsenic slag and primary neutralization liquid;

[0045] S104, secondary neutralization, continue to add liquid sodium hydroxide to perform secondary neutralization treatment on the primary neutralized solution, control the final pH value to 8-11, and obtain nickel hydroxide and secondary neutralized solution;

[0046] Using the above method, the copper recovery rate is greater than or equal to 98%, the nickel recovery rate is greater than or equal to 90%, and the arsenic recovery rate is greater than or equal to 80%. See Table 1 below, which shows the recovery rates and product purity after processing according to this invention.

[0047] Table 1. Recovery rate and product purity after treatment according to the present invention.

[0048] element Recovery rate Product purity copper ≥98％ <![CDATA[Copper sulfate CuSO4 ≥ 98%]]> nickel ≥90％ Nickel hydroxide: Ni ≥ 30%, Cu, As ≤ 1% arsenic ≥80％ Copper-arsenic slag: As ≥ 25%, Ni ≤ 1%

[0049] In the recycling and treatment of waste acid, this invention first involves evaporation and crystallization, which is a continuous process comprising the following two stages:

[0050] a. Evaporation and concentration stage. Evaporation is carried out by heating (80℃~110℃) to increase the solution concentration to a specific gravity between 1.38 and 1.5; at the same time, the concentration of copper ions in the waste acid at 50℃ is combined with the concentration of arsenic ions at the concentration endpoint to control the concentration ratio of copper to arsenic ions in the crystallized solution to be controlled at (0.4~1.5):1.

[0051] b. Crystallization and separation stage. Cool to below 50℃ to induce copper sulfate crystallization, followed by solid-liquid separation (such as centrifugation or filtration) to obtain copper sulfate crystals and the crystallized liquid.

[0052] Optionally, the evaporation and concentration temperature can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, or 110℃, or any value between 80℃ and 110℃, or any range between any two of the above points; no specific limitation is made here. This temperature range is chosen based on the boiling point and thermal stability of the solution, as well as considerations of evaporation efficiency. Temperatures between 80℃ and 110℃ can accelerate the evaporation rate; temperatures above 110℃ may lead to the decomposition or volatilization of certain components in the waste acid.

[0053] During the evaporation process, by monitoring the specific gravity of the solution, the heating temperature and evaporation time can be adjusted in a timely manner to ensure that the solution concentration reaches the predetermined range. Optionally, the specific gravity can be 1.38, 1.4, 1.42, 1.45, 1.47, 1.49, or 1.5, or any value between 1.38 and 1.5, or any range between any two of the above points.

[0054] By monitoring the copper ion concentration, the ratio of copper to arsenic ions in the crystallized solution can be predicted, allowing for adjustments to the evaporation and concentration conditions to control this ratio. Based on the copper ion concentration and the desired copper-to-arsenic ion ratio, the arsenic concentration at the concentration endpoint can be determined. Controlling the copper-to-arsenic ion concentration ratio can improve product purity and reduce impurity content.

[0055] The purpose of evaporation and crystallization is:

[0056] a. Pre-recover copper sulfate to reduce the load on subsequent treatment. High-copper, low-arsenic, and low-nickel waste acid has a high copper content; directly entering the membrane dialysis and neutralization system will increase the load on the membrane system: firstly, high copper ion levels may lead to membrane fouling or blockage; secondly, neutralization requires more NaOH to precipitate copper, increasing alkali consumption. Through evaporation and crystallization, most of the copper can be recovered firstly as copper sulfate crystals (CuSO4·5H2O), obtaining a first-grade smelting by-product and achieving preliminary resource utilization.

[0057] b. Adjust the copper-arsenic ratio to optimize copper arsenate precipitation conditions. The Cu:As concentration ratio in the post-crystallization solution is controlled at (0.4–1.5):1. This ensures preferential formation of copper arsenate precipitate during the subsequent neutralization (pH 2.5–5). If the copper-arsenic ratio is too high, some copper will precipitate as copper hydroxide, competing for nickel precipitation sites, leading to nickel entering the copper-arsenic slag. If the copper-arsenic ratio is too low, excess arsenic will co-precipitate with nickel during the secondary neutralization process, resulting in high arsenic content in nickel hydroxide. Removing excess copper through evaporation and crystallization brings the copper-arsenic ratio closer to the stoichiometric ratio, facilitating preferential precipitation of copper arsenate and improving the separation efficiency of copper, arsenic, and nickel.

[0058] c. Improve the purity of nickel products. By preferentially precipitating copper arsenate, the amount of copper entering the nickel precipitate is reduced, ultimately ensuring that the copper and arsenic content in the nickel hydroxide precipitate is both below 1%, thereby increasing the added value of the product.

[0059] The evaporation and crystallization process requires an online specific gravity monitor, a copper ion concentration monitor, and an arsenic ion concentration monitor to dynamically control the evaporation intensity and separate the solid and liquid to obtain copper sulfate (a first-grade by-product of smelting) and the crystallized liquid.

[0060] An online specific gravity monitor, copper ion concentration monitor, and arsenic ion concentration monitor are installed inside the evaporator crystallizer to monitor the changes in solution specific gravity and the concentrations of copper and arsenic ions in real time during evaporation. These signals are transmitted to the central control unit (DCS / PLC). If the specific gravity is below the lower limit (e.g., below 1.38), the steam supply is increased or the evaporation time is extended. If the specific gravity reaches (1.38–1.5), the current evaporation intensity is maintained. If the specific gravity is above the upper limit (1.5), the steam is shut off, evaporation is stopped, or water is added for dilution to prevent excessive evaporation leading to impurity eutectic. Simultaneous monitoring of copper and arsenic ion concentrations: The instrument can be set to automatically sample and analyze every 5–30 minutes to obtain the Cu concentration in the solution. 2+ The central control unit calculates the Cu:As ion concentration ratio in real time, in conjunction with the As (total arsenic) concentration. If the Cu:As ion concentration ratio is greater than 1.5, it is determined that "copper is excessive," and evaporation continues to precipitate more copper sulfate crystals, reducing the copper concentration. If the Cu:As ion concentration ratio is within the range of (0.4–1.5):1, it is determined that "the ratio is appropriate," and the current evaporation intensity is maintained. If the Cu:As ion concentration ratio is less than 0.4, it is determined that "arsenic is excessive," and an early warning is issued, allowing for the addition of copper-containing solution. This process requires coordinated control; only when the specific gravity meets the standard and the Cu:As ion concentration ratio both meet the requirements will the crystallization separation process begin.

[0061] Optionally, the ratio of copper ion concentration to arsenic ion concentration in the crystallization solution can be controlled to (0.4–1.5):1 to ensure the stoichiometric ratio of copper arsenate. Matching the copper-arsenic concentration ratio allows copper arsenate to be generated at a lower pH during the subsequent neutralization process, achieving more complete preferential co-precipitation of copper and arsenic, avoiding excessive copper competing for nickel precipitation, effectively reducing the amount of nickel entering the copper-arsenic slag, and achieving efficient separation of copper, arsenic, and nickel.

[0062] The online specific gravity monitor, copper ion concentration monitor, and arsenic ion concentration monitor in this invention all adopt the structure of the prior art, and no improvement is made to the structure of the online specific gravity monitor, copper ion concentration monitor, and arsenic ion concentration monitor.

[0063] Online specific gravity monitors can continuously monitor the specific gravity of solutions online and provide real-time feedback of measurement data, facilitating the control and adjustment of the production process. Examples of suitable online specific gravity meters include JT-1000, SG-2110RS, KBD-ONLINE, LDX-YT01, and system monitors for flux specific gravity meter concentration testing.

[0064] Optionally, the copper ion concentration monitor can determine the copper ion concentration based on the redox reaction of metal ions in the electrolyte. The sample is injected into an electrolyte containing a special oxidizing agent and a reducing agent. The copper ions undergo a redox reaction in the electrolyte, forming an instantaneous current. The magnitude of the current is the same as the number of copper ions oxidized. By calculating the ratio between the current and the copper ion concentration, the concentration of copper ions in the sample can be determined.

[0065] Optionally, the arsenic ion concentration monitor can quantify the heavy metal by atomizing it and measuring its characteristic spectral absorbance. Arsenic is reduced to HAs in a hydride flame and forms arsenic vapor within a spectral range. The arsenic vapor absorbs light of a specific wavelength in an absorber, thus obtaining the measurement result.

[0066] Step S102, membrane dialysis: the crystallized liquid is sent into the membrane dialysis device, and the volume ratio of the crystallized liquid to the clean water inlet is controlled at 1:(0.5~2). The temperature is at room temperature to obtain recovered acid and low-acid residue. The acid recovery rate is not less than 65%. The dialysis membrane is an anion exchange membrane.

[0067] The membrane dialysis process utilizes the selective permeability of the membrane to reduce the acidity in the crystallized solution, thereby reducing the alkali consumption required for acid neutralization. The dialysis membrane is an anion exchange membrane.

[0068] For step S103, the copper-arsenic slag produced in the primary neutralization process is mainly copper arsenate, and the chemical reaction equation is:

[0069] 3Cu 2+ +2H3A S O₄ + 6NaOH = Cu₃(A) SO4)2+6H2O+6Na + ;

[0070] Cu 2+ +H3A S O₄⁻ + 2NaOH = CuHA S O4 + 2H2O + 2Na + ;

[0071] Cu 2+ +2H3A S O₄ + 2NaOH = Cu(H₂A) S O4)2+2H2O+2Na + .

[0072] Arsenate (ASO4) 3- ) and Cu 2+ Arsenic acid is converted to the sparingly soluble salt Cu3(ASO4)2 via a metathesis reaction. The reaction requires alkaline conditions (pH > 8) to promote the stable existence of the arsenate ion. Under weakly alkaline conditions, arsenic acid may partially dissociate into H2ASO4. - or HASO4 2- , with Cu 2+ It forms acid salts such as CuHASO4, but these compounds are usually unstable and easily converted into neutral arsenates or dissolved.

[0073] In this invention, only alkali is added; no other substances are required.

[0074] For step S104, the nickel hydroxide produced by the secondary neutralization contains less than 1% copper and arsenic, and not less than 30% nickel, indicating high quality. The chemical reaction equation is as follows:

[0075] Ni 2+ (aq) + 2NaOH = Ni(OH)₂↓ + 2Na + (aq).

[0076] In the secondary neutralization, NaOH, as a strong base, provides OH-. - Ions and Ni 2+ They combine to form Ni(OH)2 precipitate.

[0077] Example 1

[0078] Raw materials: Waste acid containing Cu 45g / L, As 18g / L, Ni 12g / L, and H2SO4 120g / L.

[0079] A certain amount of waste acid was evaporated to a specific gravity of 1.41, then cooled and crystallized at 45℃. After crystallization, the Cu / As ratio in the liquid was 1.2:1, yielding 98.3 kg / m³ of copper sulfate. 3Waste acid and crystallization liquid; the crystallization liquid is sent to a membrane dialysis unit, controlling the volume ratio of crystallization liquid to water at 1:0.6, with an acid recovery rate of 66% and a residual liquid acidity of 35 g / L; the residual liquid undergoes a first neutralization treatment, with 32% alkali added to adjust the pH to 3.1, producing copper-arsenic slag containing 32.5% Cu, 26.1% As, and 0.42% Ni; the resulting first neutralized liquid is further adjusted to pH 8.9 with 32% alkali added, producing nickel hydroxide containing 34.7% Ni and 0.51% Cu.

[0080] Recovery rates in this embodiment: Cu 98.6%, Ni 91.2%, As 83.5%.

[0081] Copper recovery rate = (Copper metal content in (copper sulfate + copper arsenic slag) / Copper metal content in waste acid) × 100%;

[0082] Nickel recovery rate = (Nickel metal content in nickel hydroxide / Nickel metal content in waste acid) × 100%;

[0083] Arsenic recovery rate = Arsenic metal content in copper arsenic slag / Arsenic metal content in waste acid × 100%.

[0084] Example 2

[0085] Raw materials: Waste acid containing 68 g / L Cu, 48 g / L As, 23 g / L Ni, and 180 g / L H2SO4.

[0086] A certain amount of waste acid was evaporated to a specific gravity of 1.47, then cooled and crystallized at 47℃. After crystallization, the Cu / As ratio in the liquid was 0.5:1, yielding 179.6 kg / m³ of copper sulfate. 3 Waste acid and crystallized liquid were collected. The crystallized liquid was fed into a membrane dialysis unit, with the volume ratio of crystallized liquid to purified water controlled at 1:1.8. The acid recovery rate was 71%, and the residual liquid acidity was 28 g / L. The residual liquid underwent a first neutralization treatment, with 32% alkali added to adjust the pH to 4.2, producing copper-arsenic slag containing 28.9% Cu, 31.3% As, and 0.76% Ni. The resulting first neutralized liquid was further adjusted to pH 10.3 with 32% alkali, producing nickel hydroxide containing 36.6% Ni and 0.85% Cu.

[0087] Recovery rates in this example: Cu 99.1%, Ni 92.6%, As 86.4%.

[0088] Example 3

[0089] Raw materials: Waste acid containing Cu 32g / L, As 9g / L, Ni 4g / L, and H2SO4 80g / L.

[0090] A certain amount of waste acid was evaporated to a specific gravity of 1.40, then cooled and crystallized at 40℃. After crystallization, the Cu / As ratio in the liquid was 1:1, yielding 76.7 kg / m³ of copper sulfate. 3 Waste acid and crystallized liquid were collected. The crystallized liquid was fed into a membrane dialysis unit, with the volume ratio of crystallized liquid to purified water controlled at 1:1. The acid recovery rate was 68%, and the residual liquid acidity was 33 g / L. The residual liquid underwent a first neutralization treatment, with 32% alkali added to adjust the pH to 3.6, producing copper-arsenic slag containing 30.4% Cu, 29.6% As, and 0.29% Ni. The resulting first neutralized liquid was further adjusted to pH 9.6 with 32% alkali, producing nickel hydroxide containing 31.7% Ni and 0.62% Cu.

[0091] Recovery rates in this example: Cu 98.3%, Ni 90.4%, As 82.8%.

[0092] Example 4

[0093] Raw materials: Waste acid containing Cu 53g / L, As 26g / L, Ni 16g / L, and H2SO4 150 g / L.

[0094] A certain amount of waste acid was evaporated to a specific gravity of 1.45, then cooled and crystallized at 44℃. After crystallization, the Cu / As ratio in the liquid was 0.8:1, yielding 126.3 kg / m³ of copper sulfate. 3 Waste acid and crystallized liquid were collected. The crystallized liquid was fed into a membrane dialysis unit, with the volume ratio of crystallized liquid to purified water controlled at 1:1.2. The acid recovery rate was 67%, and the residual liquid acidity was 36 g / L. The residual liquid underwent a first neutralization treatment, with 32% alkali added to adjust the pH to 3.7, producing copper-arsenic slag containing 30.4% Cu, 33.1% As, and 0.62% Ni. The resulting first neutralized liquid was further adjusted to pH 10.8 with 32% alkali added, producing nickel hydroxide containing 32.5% Ni and 0.69% Cu.

[0095] Recovery rates in this example: Cu 98.9%, Ni 91.8%, As 83.1%.

[0096] Example 5

[0097] Raw materials: Waste acid containing Cu 31g / L, As 11g / L, Ni 9g / L, and H2SO4 200g / L.

[0098] A certain amount of waste acid was evaporated to a specific gravity of 1.44, then cooled and crystallized at 46℃. After crystallization, the Cu / As ratio in the solution was 1.3:1, yielding 65.9 kg / m³ of copper sulfate. 3Waste acid and crystallized liquid; the crystallized liquid is sent to a membrane dialysis unit, controlling the volume ratio of crystallized liquid to water at 1:0.9, with an acid recovery rate of 70% and a residual liquid acidity of 39 g / L; the residual liquid undergoes a first neutralization treatment, with 32% liquid alkali added to adjust the pH to 4.1, producing copper-arsenic slag containing 35.2% Cu, 28.7% As, and 0.46% Ni; the resulting first neutralized liquid is further adjusted to pH 9.9 with 32% liquid alkali, producing nickel hydroxide containing 32.6% Ni and 0.77% Cu.

[0099] Recovery rates in this embodiment: Cu 98.8%, Ni 90.9%, As 81.5%.

[0100] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. A method for comprehensively recovering valuable elements from waste acid, characterized in that, The waste acid contains copper at a concentration of 25 g / L to 70 g / L, arsenic at a concentration of 5 g / L to 50 g / L, nickel at a concentration of 2 g / L to 25 g / L, and acid at a concentration of 70 g / L to 220 g / L. The method includes: The waste acid is subjected to evaporation crystallization, which includes evaporation concentration and crystallization separation. After crystallization separation, copper sulfate crystals and a post-crystallization liquid are obtained. The evaporation and concentration process includes: evaporating at a temperature of 80℃ to 110℃ to increase the concentration of the waste acid solution to a specific gravity of 1.38 to 1.5, while controlling the arsenic concentration at the concentration endpoint so that the ratio of copper to arsenic ions in the crystallized solution is controlled at (0.4 to 1.5):

1. The crystallization separation includes: cooling to less than or equal to 50°C, copper sulfate crystals precipitate, followed by solid-liquid separation to obtain copper sulfate crystals and a post-crystallization liquid; Membrane dialysis involves feeding the crystallized liquid into a membrane dialysis device, controlling the volume ratio of the crystallized liquid to the incoming water to be 1:(0.5-2), to obtain recovered acid and residual liquid, with an acid recovery rate of not less than 65%, and the dialysis membrane used in the membrane dialysis device is an anion exchange membrane. A first neutralization process involves adding liquid sodium hydroxide to neutralize the residual liquid, controlling the final pH value to be 2.5–5, yielding copper-arsenic slag and a first-neutralized solution. The copper-arsenic slag produced in the first neutralization process includes copper arsenate, and the chemical reaction equation is as follows: 3Cu 2+ +2H3A S O4 + 6NaOH=Cu3(A S O4)2 + 6H2O + 6Na + ; Cu 2+ +H3A S O4 + 2NaOH=CuHA S O4 + 2H2O + 2Na + ; Cu 2+ +2H3A S O4 + 2NaOH=Cu(H2A) S O4)2 + 2H2O + 2Na + ; A second neutralization process is performed by adding liquid sodium hydroxide to the primary neutralized solution, controlling the final pH value to be 8-11, yielding nickel hydroxide and a secondary neutralized solution. The nickel hydroxide produced by the secondary neutralization contains less than 1% copper and arsenic and not less than 30% nickel. The chemical reaction equation is as follows: Nor 2+ (aq)+2NaOH=Ni(OH)2↓+2Na + (pork); Using the above methods, the copper recovery rate is greater than or equal to 98%, the nickel recovery rate is greater than or equal to 90%, and the arsenic recovery rate is greater than or equal to 80%.

2. The method for comprehensively recovering valuable elements from waste acid according to claim 1, characterized in that, The evaporation and crystallization are carried out in an evaporator crystallizer, which is equipped with an online specific gravity monitor, a copper ion concentration monitor, and an arsenic ion concentration monitor to monitor the specific gravity of the waste acid solution, and the copper ion concentration and arsenic ion concentration in real time during the evaporation and concentration process.

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