Method and System for Microwave Co-treatment of Electroplating Wastewater and Recovery of Valuable Metals

Abstract

This invention relates to the field of wastewater treatment technology, specifically a method and system for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals. The method includes pretreatment based on specific characteristics, advanced treatment, and resource recovery. Pretreatment is used for acidic cleaning, cyanide-containing, chromium-containing, and copper-nickel-containing wastewater, employing microwave-Fenton, microwave, microwave-assisted, and microwave gas-liquid membrane processes respectively. Advanced treatment utilizes a multi-layer coupled reaction tower to achieve microwave radiation, catalytic ammonia nitrogen decomposition, and ZIF-8@cellulose adsorption. Resource recovery employs segmented acid washing desorption-electrowinning to recover copper and nickel, chromium alum crystallization, and calcination to produce ZnO. The system includes corresponding pretreatment, advanced treatment, and resource recovery units. This invention achieves high pollutant removal rates, copper and nickel recovery rates exceeding 98%, energy consumption per ton of water of 4.8 kW·h, and metal recovery revenue covering over 130% of treatment costs.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method and system for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals. Background Technology

[0002] The electroplating industry generates various types of wastewater with high concentrations and complex compositions, including cyanide, chromium, copper, nickel, and acid cleaning agents. If this wastewater is not treated properly, it will not only seriously pollute water and soil environments, but also waste valuable metal resources such as copper, nickel, and chromium.

[0003] Current electroplating wastewater treatment technologies have the following problems:

[0004] Existing technologies lack targeted designs for the recovery of valuable metals from electroplating wastewater. Copper and nickel recovery rates are usually below 90%, and the purity of the recovered products is low (e.g., copper purity is less than 95%), making it difficult to achieve resource utilization. Chromium is mostly disposed of in the form of sludge and has not been converted into high-value chromium alum products.

[0005] In terms of energy consumption, traditional electrochemical methods consume up to 14.2 kWh per ton of wastewater, and sludge disposal requires an additional 2-3 kWh, resulting in high treatment costs. Furthermore, existing technologies do not effectively recover cyanide-containing wastewater breakdown products, further reducing the process's economic viability. Metal recovery revenue often fails to cover treatment costs, limiting the large-scale engineering application of the technology. Summary of the Invention

[0006] The purpose of this invention is to provide a method for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals, in order to solve the problems mentioned in the background art.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for microwave co-treatment of electroplating wastewater and recovery of valuable metals includes the following steps:

[0009] S1: Separate pretreatment;

[0010] Separate pretreatment is used for acidic cleaning wastewater, cyanide-containing wastewater, chromium-containing wastewater and copper-nickel wastewater, respectively, employing microwave synergistic processes for treatment;

[0011] S2: Deep processing;

[0012] This is achieved by combining catalytic ammonia nitrogen decomposition and MOF adsorption through a coupled reaction tower.

[0013] S3: Resource recycling;

[0014] Valuable metals or products are recovered from the copper-nickel, chromium, and cyanide conversion products using corresponding processes.

[0015] Furthermore, the treatment process for the acidic cleaning wastewater is as follows:

[0016] First, adjust the pH, then use the microwave-Fenton method to remove COD, while simultaneously recovering the surfactant.

[0017] Furthermore, the treatment process for the cyanide-containing wastewater is as follows:

[0018] microwave Oxidation breaks down cyanide, generating recyclable cyanide conversion products in the process;

[0019] The treatment process for the chromium wastewater is as follows:

[0020] Microwave-assisted reduction with reducing agent, followed by crystallization to recover chromium from the reduction product.

[0021] Furthermore, the treatment process for the copper-nickel wastewater is as follows:

[0022] microwave Selective precipitation via gas-liquid membrane reaction; after precipitation, copper and nickel are recovered through adsorption, acid washing and desorption, and electrodeposition.

[0023] Furthermore, the coupled reaction tower has a multi-layer structure and integrates microwave radiation, catalytic reaction and adsorption functions, and the catalytic decomposition of ammonia nitrogen is carried out under non-biochemical conditions.

[0024] Another object of the present invention is to provide a system for microwave co-treatment of electroplating wastewater and recovery of valuable metals, comprising:

[0025] The pretreatment unit for different types of electroplating wastewater includes a microwave co-treatment device for the corresponding type of electroplating wastewater.

[0026] A deep processing unit, wherein the deep processing unit includes a coupled reaction tower and a MOF adsorption device;

[0027] And a resource recycling unit, which includes a metal desorption and recovery, crystallization and conversion product processing device.

[0028] Furthermore, in the fractional pretreatment unit, the copper-nickel wastewater treatment device is a microwave oven. Gas-liquid membrane reactor, the microwave The gas-liquid membrane reactor contains a hydrophobic hollow fiber membrane; the cyanide-containing wastewater treatment device integrates microwave and UV radiation components.

[0029] Furthermore, the coupled reaction tower of the deep processing unit is provided with a microwave radiation layer, a catalytic layer and a MOF adsorption rotating bed from bottom to top.

[0030] The resource recovery unit includes an acid washing and desorption device, an electrowinning device, a crystallizer, and a calcination device.

[0031] The beneficial effects of this invention are:

[0032] 1. In this invention, the separate pretreatment adopts a microwave-assisted proprietary process, achieving a cyanide removal rate >99.9% (total cyanide ND in effluent) for cyanide-containing wastewater and a chromium removal rate >99.9% for chromium-containing wastewater. 6 ⁺ 100% conversion rate (effluent) The COD removal rate is 99.1% and the ammonia nitrogen removal rate is 97.5%, which are far superior to existing technologies. No microorganisms are involved in the entire process. Through microwave enhancement and catalytic reaction, it can withstand cyanide ion shock concentrations of up to 500 mg / L, significantly improving the stability of the treatment process and avoiding system paralysis caused by water quality fluctuations.

[0033] 2. In this invention, the copper recovery rate is >99.5%, the nickel recovery rate is >98.7%, the chromium alum purity is >99%, and the ZnO purity is 92%, which is 10% to 15% higher than the existing technology. Moreover, the recovered products are high-value industrial raw materials. The net energy consumption for treating each ton of wastewater is only 4.8 kW·h, which is 66.2% more energy-efficient than the traditional electrochemical method (14.2 kW·h). The energy-saving mechanism comes from microwave selective heating (reducing ineffective energy consumption) and the offsetting effect of metal recovery revenue (energy consumption converted to -0.8 kW·h). The metal recovery revenue covers more than 130% of the treatment cost (calculated at 50 yuan / kg for Cu and 120 yuan / kg for Ni). At the same time, the resource utilization of cyanide conversion products is realized, which greatly enhances the engineering application value of the process. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 It is the XRD pattern of chromium alum crystals;

[0036] Figure 2 It is microwave Schematic diagram of a gas-liquid membrane reactor;

[0037] Figure 3 This is a schematic diagram of the coupled reaction tower. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1:

[0040] Please see Figures 1-3 In this embodiment of the invention, a method for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals is described below:

[0041] (I) Separate pretreatment steps

[0042] A proprietary microwave-assisted process is used to treat acidic cleaning wastewater, cyanide-containing wastewater, chromium-containing wastewater, and copper-nickel wastewater, taking into account their different characteristics.

[0043] 1. Treatment of acidic cleaning wastewater

[0044] First, the pH of the wastewater was adjusted to 3.0-4.0 using an alkali addition device. Then, the wastewater was fed into a microwave-Fenton reaction system. The microwave parameters were set to a frequency of 2.45 GHz and pulse mode (10s on / 5s off). Fenton's reagent was added... and The molar ratio was 1:10, and the reaction time was 30 minutes. The wastewater after the reaction entered a manganese dioxide adsorption column, where residual organic matter was adsorbed and removed while surfactants were recovered, ultimately achieving a COD removal rate of 90%.

[0045] 2. Treatment of cyanide-containing wastewater

[0046] Microwave The cyanide oxidation process integrates a microwave (parameters as above), a UV lamp (wavelength 254nm), and... The dosing module controls the reaction process via an online ORP monitor, ensuring ORP ≥ 800mV. The dosage is calculated based on "2 mg / L per 1 mg / L of total cyanide treated", and the reaction time is 15 min. This process achieves a cyanide removal rate >99.9%, while simultaneously generating... The precipitate is collected using a precipitation separation device.

[0047] 3. Chromium-containing wastewater treatment

[0048] Microwave strengthening The reduction process involves sending wastewater into a microwave reaction tank with temperature control. The microwave parameters are the same as above, and the reaction temperature is controlled at 60°C.

[0049] Dosage based on The calculated reaction time is 5 minutes. This process can achieve... ⁺ 100% conversion rate, reducing the amount of reducing agent by 40% compared to traditional processes.

[0050] 4. Copper-nickel wastewater treatment

[0051] Using microwave Selective precipitation is carried out in a gas-liquid membrane reactor, which is equipped with a hydrophobic PTFE hollow fiber membrane (pore size 0.1μm, membrane area 2.5m²). Gas enters from the bottom inlet of the reactor and is dispersed through the membrane module; wastewater flows in tangentially from the side, and is deposited on the membrane surface based on the difference in solubility product between CuS (pKsp=36.1) and NiS (pKsp=24). CuS nanocrystals are preferentially generated. The microwave parameters are 2.45 GHz frequency, 800 W power, pulse mode (10 s on / 5 s off). Microwave induces the CuS crystal phase to transform from amorphous to crystalline, and the sedimentation rate is increased to >5 m / h. The CuS precipitate falls into the collection tank at the bottom.

[0052] (II) Deep Processing Steps

[0053] After being pretreated separately, the wastewater is collected and enters a coupled reaction tower. This tower has a multi-layer integrated structure and realizes microwave radiation, catalytic ammonia nitrogen decomposition and MOF adsorption functions from bottom to top.

[0054] 1. Microwave radiation layer treatment

[0055] The bottom of the coupling reaction tower is equipped with a microwave radiation layer with a microwave frequency of 2.45 GHz and a pulse mode (10s on / 5s off), which enhances the reactivity of residual pollutants in wastewater through selective heating.

[0056] 2. MnO2-catalyzed ammonia nitrogen decomposition

[0057] Wastewater enters the middle section The catalyst layer reacts under non-biochemical conditions:

[0058] .

[0059] This layer The catalyst performance parameters are as follows:

[0060] The ammonia nitrogen degradation rate constant at 50℃ is 0.42 min⁻¹. Dissolution rate < 0.05%, microwave enhancement factor 3.8.

[0061] 3. MOF adsorption treatment

[0062] The wastewater ultimately enters the top ZIF-8@cellulose adsorption rotating bed, which rotates at 5 rpm. Through the highly selective adsorption of the MOF material, residual trace heavy metal ions are removed. , ) and organic matter.

[0063] (III) Resource recycling steps

[0064] 1. Copper and nickel recycling

[0065] The adsorbent material desorbed from the ZIF-8@cellulose adsorption bed was subjected to a staged acid washing desorption process: the first stage used... Desorption The desorption time was 30 min, and the recovery rate was 98.2%.

[0066] The last section Desorption The desorption time was 40 min, and the recovery rate was 99.1%. The desorbed solutions were fed into an electrodeposition unit, and the current density was controlled at 200 A / m². The final copper recovery rate was >99.5%, and the nickel recovery rate was >98.7%.

[0067] 2. Chromium recovery

[0068] A reducing solution containing Cr³⁺ is fed into a chromium alum crystallizer, the pH is adjusted to 3.5, and the crystallization temperature is controlled at 25°C to produce potassium chromium alum. .

[0069] XRD pattern analysis confirmed that the main peak (200) was located at 18.4°, with a deviation of <0.2° from the standard card JCPDS01-1013. Impurities (not detected at 20.5°), half-maximum width 0.15°, crystal purity > 99%.

[0070] 3. Recovery of cyanide conversion products

[0071] Collected The precipitate is fed into a calcining furnace and calcined at 450°C, where the reaction is as follows:

[0072]

[0073] Generates ZnO industrial raw material (92% purity). It is discharged after exhaust gas treatment.

[0074] (iv) Key performance testing and data

[0075] 1. Influent water quality (before branch treatment)

[0076]

[0077] Treatment of effluent and recycling effect

[0078]

[0079] 3. Microwave Membrane flux testing of gas-liquid membrane reactor

[0080] Test conditions: Hydrophobic PTFE hollow fiber membrane (pore size 0.1μm), wastewater containing... 150 mg / L + Ni²⁺ 80 mg / L (pH=3.0), operating pressure 0.15 MPa, temperature 50 ± 2℃ (microwave maintained)

[0081] Test data:

[0082]

[0083] Membrane flux decay formula:

[0084] Flux decay rate formula:

[0085] J t / J 0= e -kmt (k) m 无微波 =0.015, k m 微波 =0.003)

[0086] At 120 min, the flux attenuation rate of the microwave group was only 1 / 3 of that of the conventional group, verifying the inhibitory effect of microwave-induced CuS crystal form transformation on membrane fouling; the CuS crystallization energy barrier was reduced by 37.5% at 50 °C by Comsol multiphysics simulation.

[0087] 4. Energy Consumption Comparison Test

[0088]

[0089] Energy consumption breakdown of this method: microwave system 2.2 kW·h (pulse mode saves 40% energy), pumping / stirring 1.5 kW·h, reagent preparation 1.1 kW·h (including...) The generator, after deducting the revenue from metal recycling, has an energy consumption of 0.8 kWh (calculated at 50 yuan / kg for Cu and 120 yuan / kg for Ni), resulting in a net energy consumption of 4.8 kWh.

[0090] Electrochemical method comparison benchmark: Refer to "HJ2002-2018", the operating conditions are plate voltage 5V, current density 50mA / cm², treatment time 40min, energy consumption formula $E=U×I×t / V_water$, the measured energy consumption range is 12-16kW·h / t (typical value 14.2kW·h / t).

[0091] Energy-saving mechanism: Microwave selective heating reduces ineffective energy consumption (traditional electrochemical method >60% of energy consumption is used for water electrolysis), metal recovery reduces net cost (electrochemical method sludge disposal adds an additional 2-3 kW·h), energy consumption calculation complies with the "HJ2008-2017" wastewater treatment energy consumption assessment standard, and references the International Energy Agency (IEA) industrial energy efficiency coefficient (electrochemical method η=45%, microwave system η=85%).

[0092] 5. Regeneration performance of ZIF-8@cellulose adsorption bed

[0093]

[0094] Example 2:

[0095] Based on Example 1, the system for microwave co-treatment of electroplating wastewater and recovery of valuable metals includes a pretreatment unit, a deep treatment unit, a resource recovery unit, and a control module, with the specific structure as follows:

[0096] (a) Pretreatment Unit

[0097] This unit is equipped with dedicated treatment devices for different types of wastewater. Each device operates independently, and the effluent is collected and sent to the advanced treatment unit.

[0098] 1. Acidic cleaning wastewater treatment device

[0099] It consists of a pH adjustment tank (with pH sensor and alkali pump), a microwave-Fenton reaction tank (with built-in 2.45GHz pulse microwave generator and Fenton reagent dosing system), and a manganese dioxide adsorption column. The outlet of the adsorption column is connected to the deep treatment unit.

[0100] 2. Cyanide-containing wastewater treatment device

[0101] For microwave The reaction cell integrates a 2.45GHz pulsed microwave generator and a 254nm UV lamp. Metering dosing pump, equipped with an online ORP monitor (controlling ORP ≥ 800mV), and a bottom panel is installed in the tank. Sedimentation collection tank.

[0102] 3. Chromium-containing wastewater treatment equipment

[0103] Including microwaves Reduction cell (with 2.45GHz pulsed microwave generator) The dosing system and temperature control system (60℃) ensure... Completely restored.

[0104] 4. Copper-nickel wastewater treatment equipment

[0105] Vertical microwave Gas-liquid membrane reactor (φ500mm×1200mm, 316L stainless steel), with built-in hydrophobic PTFE hollow fiber membrane module (pore size 0.1μm, membrane area 2.5m²), and bottom equipped with... It has a gas inlet (with a gas distributor), a wastewater inlet on the side, a tail gas outlet at the top, a CuS precipitation collection tank at the bottom, and is wrapped with an 800W 2.45GHz pulse microwave heating jacket.

[0106] (ii) Deep processing unit

[0107] The core is a coupled reaction tower, connected to the effluent pipeline of the fractional pretreatment unit. The tower body is divided into three layers from bottom to top:

[0108] 1. Microwave radiation layer: Equipped with a 2.45GHz pulsed microwave generator for selective heating of the incoming water;

[0109] 2. Catalytic layer: filling Catalyst particles (ammonia nitrogen degradation rate constant 0.42 min⁻¹ @ 50℃) are fixed by a porous support plate to achieve non-biochemical decomposition of ammonia nitrogen;

[0110] 3. MOF adsorption rotating bed: made of ZIF-8@cellulose material, rotating at 5 rpm, controlled by a drive motor, adsorbing residual heavy metals and organic matter;

[0111] The tower has an inlet (with a flow meter) at the bottom and an outlet (connected to the resource recycling unit) at the top.

[0112] (III) Resource Recycling Unit

[0113] This unit is connected to the corresponding devices in the pretreatment and advanced treatment units to achieve the recovery of metals and target products.

[0114] 1. Copper-nickel recovery unit

[0115] Composed of a two-stage acid elution and desorption column (first stage) Desorption The last section Desorption It consists of a copper electrodeposition cell (titanium anode, stainless steel cathode, current density 200A / m²) and a nickel electrodeposition cell. The feed end of the desorption column is connected to the desorption outlet of the adsorbent material of the MOF adsorption rotating bed.

[0116] 2. Chromium recovery unit

[0117] This is a chromium alum crystallizer (with pH adjustment system and temperature control at 25℃). The feed end is connected to the outlet of a chromium-containing wastewater treatment device, and the bottom has a chromium alum crystal outlet. The crystal purity is determined by XRD (refer to JCPDS01-1013, purity calculation formula:).

[0118] purity ×100% >99%

[0119] 3. Cyanide Conversion Product Processing Unit

[0120] include Calcination furnace (temperature controlled at 450℃, with inert gas inlet), The exhaust gas outlet, ZnO collection box, and sedimentation collection tank of the cyanide-containing wastewater treatment device are connected to the feed end of the calcining furnace.

[0121] (iv) Control and Monitoring Module

[0122] Composed of a PLC controller, online monitoring sensors (pH, ORP, temperature, flow rate, heavy metal concentration), and actuators (pump, valve, microwave generator), it can automatically adjust process parameters (such as microwave pulse mode, dosage, and adsorption bed speed) and record process data through a data acquisition module to ensure stable system operation.

[0123] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals, characterized in that, Includes the following steps: S1: Separate pretreatment: Separate pretreatment is used for acidic cleaning wastewater, cyanide-containing wastewater, chromium-containing wastewater, and copper-nickel wastewater, respectively, employing microwave-assisted corresponding processes. S2: Depth Processing This is achieved by combining catalytic ammonia nitrogen decomposition and MOF adsorption through a coupled reaction tower; S3: Resource Recycling Valuable metals or products are recovered from the copper-nickel, chromium, and cyanide conversion products using corresponding processes. The treatment process for the acidic cleaning wastewater is as follows: First, adjust the pH, then use the microwave-Fenton method to remove COD, while simultaneously recovering the surfactant; The treatment process for the cyanide-containing wastewater is as follows: microwave Oxidation breaks down cyanide, generating and recovering cyanide conversion products during the process; The treatment process for the chromium-containing wastewater is as follows: Microwave-assisted reduction with reducing agent; chromium is recovered by crystallization of the reduction product. The treatment process for the copper-nickel wastewater is as follows: microwave Selective precipitation via gas-liquid membrane reaction; after precipitation, copper and nickel are recovered through adsorption, acid washing and desorption, and electrodeposition.

2. The method for microwave synergistic treatment of electroplating wastewater and recovery of valuable metals according to claim 1, characterized in that, The coupled reaction tower has a multi-layer structure and integrates microwave radiation, catalytic reaction and adsorption functions, and the catalytic decomposition of ammonia nitrogen is carried out under non-biochemical conditions.

3. A system for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals according to claim 1, characterized in that, include: The pretreatment unit for different types of wastewater includes microwave co-treatment devices for acidic cleaning wastewater, cyanide-containing wastewater, chromium-containing wastewater, and copper-nickel wastewater. These devices are a microwave-Fenton reaction system and a microwave system integrating microwave and UV radiation components, respectively. Reaction system, microwave reaction cell and microwave Gas-liquid membrane reactor; A deep processing unit, wherein the deep processing unit includes a coupled reaction tower integrating a MOF adsorption device; And a resource recycling unit, which includes a metal desorption and recovery, crystallization and conversion product processing device.

4. The system for microwave-assisted treatment of electroplating wastewater and recovery of valuable metals according to claim 3, characterized in that, The deep processing unit's coupled reaction tower is provided with a microwave radiation layer, a catalytic layer, and a MOF adsorption rotating bed from bottom to top. The resource recovery unit includes an acid washing and desorption device, an electrowinning device, and a crystallizer.

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