Green treatment method for nickel-phosphorus electroless plating aging solution

Abstract

The application discloses a kind of green treatment methods of nickel-phosphorus chemical plating aging liquid.The method is first reacted with aluminium sulfate and phosphite and hypophosphorous acid in nickel-phosphorus chemical plating aging liquid, respectively generate insoluble in water aluminium phosphite and aluminium hypophosphite, solid-liquid separation and washing solid while hot, recycle solid as the mixture of aluminium phosphite and aluminium hypophosphorous acid, then liquid is frozen so that sodium sulfate is solid, solid-liquid separation while cold, recycle solid sodium sulfate decahydrate, i.e., mirabilite, recycle liquid is used as plating bath evaporation makeup liquid, to make up the evaporation loss of plating solution in plating process.The treatment method of nickel-phosphorus chemical plating aging liquid of the application has little influence on the composition and content of various additives in plating solution, resources are recycled and utilized, simple operation, low cost, environment-friendly.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of treatment and resource recycling of nickel-phosphorus chemical plating aging solution, and relates to a green treatment method for a nickel-phosphorus chemical plating aging solution. BACKGROUND

[0002] The chemical nickel-phosphorus alloy plating technology is widely applied to the manufacturing of components and devices in the fields of aerospace, electronic information and instruments and equipment due to the uniform and dense plating layer, high hardness, corrosion resistance, wear resistance, good brazing property, strong uniform plating and deep plating capacity and no limitation on the geometric shape of the plated parts.

[0003] The nickel-phosphorus chemical plating is usually based on nickel sulfate (NiSO4) as a main salt and sodium hypophosphite (NaH2PO2) as a reducing agent. According to the advancement of the formula, about 1.1-2.0 mol of hypophosphite ions are consumed and 1.1-2.0 mol of phosphite ions are generated for the deposition of 1 mol of nickel ions. In order to ensure the smooth progress of the plating process, the consumed nickel sulfate and sodium hypophosphite need to be continuously added to the plating solution. With the continuation of the plating process, the concentrations of sodium (Na + ) ions (some formulas contain K + ions), sulfate (SO4 2- ) ions (some formulas contain Cl - ions) and phosphite (HPO3 2- ) ions in the plating solution continue to rise. When the concentrations of these by-products accumulate to a certain amount, the deposition rate of nickel-phosphorus, the performance of the plating layer and the stability of the plating solution will be affected. At the current level, the nickel-phosphorus chemical plating solution is usually discarded after 4-10 cycles (Metal Turnovers, MTOs) (mainly different with the requirements for the plating layer quality, and related to the advancement of the plating solution formula, the level of maintenance and other factors), which causes the waste of resources, the increase of production cost and the increase of the risk of environmental pollution.

[0004] The regeneration and treatment of the nickel-phosphorus chemical plating aging solution have always been paid attention to. The current disposal methods include chemical precipitation, oxidation-reduction, ion exchange, adsorption, solvent extraction and electrochemical methods (such as electrodeposition, electrodeionization and electrodialysis). Literature 1 uses a kind of hydrotalcite adsorbent to selectively adsorb and remove SO4 2- and HPO3 2- from the aging solution, and H2PO2 -small. But the source of the adsorbent is limited, and the disposal of phosphorus-containing solid waste after adsorption is not discussed (Yuki Kamimoto, Ryoichi Ichino, Yoshiaki Kiso, et al. Removal of phosphite and sulfate from electroless nickel-phosphorus plating bath with hydrotalcite for the management of watershed [J]. Desalination and Water Treatment, 2013, 51 (19-21): 4050-4055). Patent CN106830452A discloses a method for recovering nickel, buffer salt and water from chemical nickel plating aging solution. First, electrolysis is used to recover nickel in the aging solution, then evaporation concentration-crystallization method is used to recover condensed water, and through the crystallization fluidized bed, a mixture of sulfate and sodium phosphate is obtained. The method is complex, has more equipment and high energy consumption. Patent CN216513270U discloses a chemical nickel plating aging liquid resource treatment system. First, the complex is broken to release nickel ions by using electro-catalytic oxidation equipment, then ion exchange resin adsorption and regeneration are used; at the same time, the hypophosphite and phosphite in the aging solution are oxidized to orthophosphate by electro-catalytic oxidation method, and then reacted with ferric ion to generate iron phosphate. Literature 2 uses a combination of electrodeposition-electrodialysis equipment to achieve nickel ion recovery and phosphate ion removal (Kai Yan, Peisen Huang, Mingzhu Xia, et al. An efficient Two-Chamber Electrodeposition-Electrodialysis combination craft for nickel recovery and phosphorus removal from spent electroless nickel plating bath [J]. Separation and Purification Technology, 2022, 295: 121283). Literature 3 uses hydrogen peroxide to oxidize hypophosphite and phosphite in the waste liquid to orthophosphate (PO4 3-), and then aluminum salt is added to react to generate aluminum phosphate (AlPO4) precipitate, and the phosphorus recovery rate reaches 96% (Wu S, Wang D, Lu S, et al. Recovery of phosphorus from waste nickel plating solution by aluminum salt precipitation method [J]. Electroplating and Finishing, 2013, 35(4): 42-46). The above-mentioned methods are either complex in process, or low in resource recovery rate, or poor in environmental friendliness, and most of them do not consider the recovery and resource utilization of phosphates, and most of the treatment processes seriously interfere with the concentration balance among various additives (such as complexing agent, buffer, stabilizer, wetting agent, accelerator, brightener, etc.) in the plating solution, so that the plating solution loses the possibility of regeneration and reuse. Therefore, it is of great practical significance to explore a green treatment method for the aging solution of nickel-phosphorus chemical plating. SUMMARY

[0005] For the existing treatment methods of the aging solution of nickel-phosphorus chemical plating, most of them are for the purpose of treatment and disposal, and the proportion of recovery and reuse is low, and there are problems of complex equipment, high cost, low recovery rate and serious resource waste. The present application provides a green treatment method for the aging solution of nickel-phosphorus chemical plating, which is simple in operation, low in cost and friendly to the environment, realizes the removal and recovery of by-products phosphite, sulfate and sodium ion in the aging solution of nickel-phosphorus chemical plating, and the reuse of other components in the plating solution.

[0006] The technical scheme of the present application is as follows:

[0007] A green treatment method for the aging solution of nickel-phosphorus chemical plating has the following steps:

[0008] (1) The concentration n(HPO3 2- ) of phosphite ion in the aging solution of nickel-phosphorus chemical plating is determined, and the amount of aluminum sulfate to be added is calculated according to the calculation formula n(Al2(SO4)3) = m x n(HPO3 2- ), m = 1 / 4-1 / 3;

[0009] (2) Aluminum sulfate is added to the aging solution of nickel-phosphorus chemical plating, and heated to react at 50-100℃. After the reaction is completed, hot filtration or centrifugal separation is carried out, then the solid is washed with hot water, and the washing water is added to the filtrate or supernatant. The recovered solid is a mixture of aluminum phosphite and aluminum hypophosphite;

[0010] (3) The filtrate or supernatant is cooled to room temperature, then frozen at -5-0℃ for more than 24h, and then cold filtration or centrifugal separation is carried out. The collected solid is sodium sulfate decahydrate, and the recovered liquid is used as evaporation make-up liquid for the plating bath.

[0011] Preferably, in step (2), the reaction temperature is 70℃.

[0012] Preferably, in step (2), the reaction time is more than 30min.

[0013] Preferably, in step (2), the temperature of the hot water is not lower than the reaction temperature in step (2); under the premise of convenient operation, the washing water is used in small amounts and multiple times, and the number of washing times is not less than 3 times; the more times the washing is performed, the higher the purity of the by-product aluminum phosphite and the smaller the loss of nickel ions.

[0014] Preferably, in step (2), the hot water washing is performed 3 to 5 times.

[0015] This invention utilizes a metathesis reaction between aluminum sulfate and phosphite and hypophosphite ions in a nickel-phosphorus electroless plating aging solution under certain conditions, producing aluminum phosphite (Al2(HPO3)3) and aluminum hypophosphite (Al(H2PO2)3), respectively. Both of these aluminum salts are sparingly soluble in water. Through solid-liquid separation, some of the phosphite ions in the aging solution can be removed, while a certain amount of hypophosphite ions in the solution are also lost. The corresponding reaction equations are as follows:

[0016] 3Na2HPO3+Al2(SO4)3=Al2(HPO3)3↓+3Na2SO4

[0017] 6NaH2PO2+Al2(SO4)3=2Al(H2PO2)3↓+3Na2SO4.

[0018] Aluminum phosphite can be used as a component of halogen-free flame retardants and is also an important component of commonly used non-toxic rust-preventive pigments. Aluminum hypophosphite is a novel halogen-free flame retardant with applications in paints, coatings, textiles, synthetic fibers, carpets, plastics, wood, wood-plastic composites, bamboo-plastic composites, rubber, epoxy resins, unsaturated resins, acrylic resins, and polyurethanes, among others. Therefore, the aluminum phosphate compound obtained by the method of this invention is a mixture of aluminum phosphite and aluminum hypophosphite, which can be used as an additive in non-toxic rust-preventive pigments.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) This invention employs a combination of aluminum phosphite precipitation separation and sodium sulfate freezing separation to separate three byproducts (Na+, sodium sulfate ... + SO4 2- and HPO3 2- Part of it is discharged from the body. The byproducts obtained from precipitation separation are a mixture of aluminum phosphite and a small amount of aluminum hypophosphite. Although trace amounts of nickel ions and other plating solution components are inevitably adsorbed, their content decreases with increasing washing cycles. It can be used as a flame retardant or rust-preventive coating additive. The byproduct obtained from freeze separation, sodium sulfate decahydrate (Glauber's salt), can be used as a basic chemical raw material. Other residual components (including nickel ions, hypophosphite ions, complexing agents, buffers, and residual sulfate, phosphite, sodium ions, etc.) are used together with the recovered solution as makeup water for plating tank evaporation.

[0021] (2) The processing method of the present invention is simple, requires little equipment, is easy to operate, and is economical. The processing process has no emissions of waste gas, waste liquid and solid waste, is environmentally friendly, has little interference with other components in the plating solution, and the aged liquid after treatment is used as evaporation replenishment water and reused in the plating tank. All resources are recovered and applied. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the green treatment method for the nickel-phosphorus electroless plating aging solution of the present invention.

[0023] Figure 2 The graph shows the effect of aluminum sulfate dosage on sulfate removal rate.

[0024] Figure 3 The graph shows the effect of aluminum sulfate dosage on phosphate removal rate.

[0025] Figure 4 This is a solubility curve of sodium sulfate in water.

[0026] Figure 5 This is the phase diagram of the Na2SO4-H2O binary system.

[0027] Figure 6 The image shows the XRD pattern of byproduct S1 in Example 4.

[0028] Figure 7 The image shows the XRD pattern of byproduct S2 in Example 4.

[0029] Figure 8 This is the XPS full spectrum of byproduct S1 in Example 4.

[0030] Figure 9 The image shows the EDX spectrum of the coating of sample 4 (MTO=6) in Example 5.

[0031] Figure 10 The image shows the appearance of several plates in Example 4 (50x magnification). Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. However, the purpose and use of these examples are only for illustrating the present invention and are not intended to limit the actual scope of protection of the present invention in any way, nor to restrict the scope of protection of the present invention to these examples.

[0033] The analytical methods used in the following embodiments include:

[0034] (1) Determination of nickel ions: Standard of the Ministry of Aerospace Industry of the People's Republic of China, Method for Analysis of Chemical Nickel Plating Solution, QJ / Z170-86;

[0035] (2) Determination of hypophosphite: Standard of the Ministry of Aerospace Industry of the People's Republic of China, Analysis Method for Chemical Nickel Plating Solution, QJ / Z170-86;

[0036] (3) Determination of phosphate: Standard of the Ministry of Aerospace Industry of the People's Republic of China, Analytical Method for Chemical Nickel Plating Solution, QJ / Z170-86;

[0037] (4) Determination of sulfate: National Standard of the People's Republic of China, General Test Method for Determination of Sulfate in Salt Industry, GB / T 13025.8-2012;

[0038] (5) Determination of coating thickness: X-ray fluorescence analysis (instrument model Bowman BA-100);

[0039] (6) Corrosion resistance test: National Standard of the People's Republic of China, Artificial Atmosphere Corrosion Test and Salt Spray Test, GB / T 10125-2021;

[0040] (7) Others: Stereo microscope, X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), energy-scattering X-ray spectrometer (EDX), etc.

[0041] There are many common formulations for nickel-phosphorus electroless plating. Besides differences in additives such as complexing agents, stabilizers, buffers, and accelerators, the nickel-phosphorus feed ratio also varies between formulations. Table 1 shows the byproduct concentrations of different MTOs aging solutions used in the following examples.

[0042] Table 1. Concentration of main byproducts in aging solution at different MTOs in the test plating bath.

[0043] Period (MTOs) [c(Na + ) / g·L -1 ]]> [c(SO4 2- ) / g·L -1 ]]> [c(HPO3 2- ) / g·L -1 ]]> 0 (open cylinder) 1.8 6.4 0 1 4.0 12.9 6.3 4 10.1 32.2 26.5 6 13.9 45.0 39.1 8 18.0 57.9 49.7 10 22.3 70.8 68.6 12 26.2 83.6 80.0 15 32.6 102.9 101.8

[0044] Example 1

[0045] 200 mL of an MTO=5.0 electroless nickel-phosphorus aging solution was taken and analyzed. The solution pH was 4.6 and the density d was 1.09 g / cm³. 3 ;c(Ni 2+ )=4.1g / L; c(SO4) 2- )=38.6g / L; c(H2PO2) - )=6.2g / L; c(HPO3) 2- = 34.1 g / L (0.43 mol / L). Add 15 g (0.023 mol) of aluminum sulfate octadeca, stir and react at 70 °C for 30 min, separate by centrifugation while hot, and then wash the solid three times with 10 mL of hot water each time. The recovered solid is a mixture of aluminum phosphite and aluminum hypophosphite. The washing water is added to the centrifugation water and cooled to room temperature to obtain 240.5 mL of aqueous solution.

[0046] The solution was frozen in a refrigerator at -5℃ to 0℃ for 24 hours, then immediately separated to obtain 220.5g of liquid and 43.6g of solid (sodium sulfate containing water of crystallization). The liquid was allowed to stand until room temperature, then recovered and used as replenishment for the plating tank evaporation. Analysis showed a volume V = 210.0mL and a density d = 1.05g / cm³. 3 In the solution, c(Ni) 2+ )=3.7g / L, c(SO4) 2- = 6.4 g / L, c(H2PO2) - =1.1 g / L, c(HPO3) 2- = 7.5 g / L. Nickel recovery rate 94.8% (or loss rate 5.2%), hypophosphite recovery rate 22.2% (or loss rate 77.8%), sulfate removal rate 83.4%, and phosphite removal rate 78.0%.

[0047] Example 2

[0048] 200 mL of MTO=8.0 electroless nickel plating aging solution was taken, and the solution pH was measured to be 4.5; density d = 1.13 g / cm³. 3 ;c(Ni 2+ )=4.5g / L; c(SO4) 2- )=57.9g / L; c(H2PO2) - )=4.8g / L; c(HPO3) 2- = 49.7 g / L (0.62 mol / L). Add 27.0 g (0.04 mol) of aluminum sulfate octadeca, stir and react at 70 °C for 30 min, separate by centrifugation while hot, and then wash the solid three times with 10 mL of hot water each time. The recovered solid is a mixture of aluminum phosphite and aluminum hypophosphite. The washing water is added to the centrifugation water and cooled to room temperature to obtain 249.2 mL of aqueous solution.

[0049] The solution was frozen in a refrigerator at -5℃ to 0℃ for 24 hours, then immediately separated to obtain 201.2 g of liquid and 68.1 g of solid (sodium sulfate in water). The liquid was allowed to stand until room temperature, and then recovered for use as a replenishment solution for the plating tank evaporation. Analysis showed a volume V = 191.6 mL and a density d = 1.05 g / cm³. 3 In the solution, c(Ni) 2+ )=4.2g / L, c(SO4) 2- )=10.4g / L, c(H2PO2) - ) = 2.3 g / L, c(HPO3) 2-= 6.4 g / L. Nickel recovery rate 89.4% (or loss rate 10.6%), hypophosphite recovery rate 45.9% (or loss rate 54.1%), sulfate removal rate 82.8%, and phosphite removal rate 81.7%.

[0050] Example 3

[0051] 200 mL of each MTO=10.0 aging solution was taken, and the pH was measured to be 4.5; density d = 1.16 g / L; c(Ni) 2+ )=4.3g / L; c(SO4) 2- )=70.8g / L; c(H2PO2) - )=6.3g / L; c(HPO3) 2- = 68.6 g / L (0.86 mol / L). Different amounts of aluminum sulfate octahydrate were added, and the same steps were followed as in Example 2. The results are shown in Table 2.

[0052] Table 2. Treatment effects at different dosages of aluminum sulfate octadecyl water.

[0053]

[0054] Note: (1) Since both solid-liquid separations require rapid operation, the volume data of the recovered liquid has a certain error;

[0055] (2)n Al / n P That is, the ratio of the amount of aluminum sulfate octadeca added to the amount of phosphate in the sample;

[0056] (3) In the sixth row of the experiment, the amount of aluminum phosphite generated was relatively large, making separation difficult.

[0057] The removal rates (%) of sulfate and phosphite ions increased with the molar ratio (n) of aluminum sulfate to phosphite ions in the original aging solution. Al / n P The relationships are as follows: Figure 2 and Figure 3 . Figure 2 The results showed that, due to the addition of aluminum sulfate in the precipitation step, the total removal rate of sulfate ions decreased slowly with the increase of aluminum sulfate dosage. Figure 3 The results showed that the removal rate of phosphate ions increased with the increase of aluminum sulfate dosage, and when aluminum sulfate was added in excess (m=n)... Al / n P When the amount of aluminum sulfate is greater than 1 / 3, the removal rate of phosphite can reach 100%, but the residual amount of aluminum ions will undoubtedly increase. Considering both the removal rate of phosphite and the residual aluminum ions, the appropriate amount of aluminum sulfate, n, is selected. Al The amount of phosphate in the aging solution to be treated (n)P The ratio m = n Al / n P = 1 / 4 to 1 / 3.

[0058] Example 4

[0059] 2000 mL of a nickel-phosphorus electroless plating aging solution with MTO = 6.0 was taken, and the solution pH was measured to be 4.5; density d = 1.10 g / cm³. 3 ;c(Ni 2+ )=4.5g / L; c(SO4) 2- )=45g / L; c(H2PO2) - )=4.8g / L; c(HPO3) 2- = 39.1 g / L. Take the aluminum-to-phosphorus ratio (n) 十八水硫酸铝 / n 亚磷酸根 =0.30, that is, add 220g of aluminum sulfate octadeca, stir and react at 80℃ for 30min, separate by centrifugation while hot, then wash the solid 5 times with hot water, each time using 50mL of hot water, and recover solid S1. The washing water is added to the centrifugation water.

[0060] The solution was frozen in a refrigerator at -5℃ to 0℃ for 24 hours, then immediately separated to obtain solid S2. The liquid was allowed to stand until room temperature, and the recovered liquid was used as replenishment solution for plating tank evaporation. The volume was measured to be V = 2120 mL, and the density was d = 1.05 g / cm³. 3 In the solution, c(Ni) 2+ )=3.7g / L, c(SO4) 2- )=9.6g / L, c(H2PO2) - ) = 1.6 g / L, c(HPO3) 2- = 7.4 g / L. Nickel recovery rate 99.5% (or loss rate 0.5%), hypophosphite recovery rate 40.0% (or loss rate 60.0%), sulfate removal rate 77.4%, and phosphite removal rate 80.0%.

[0061] Figure 6 The image shows the XRD pattern of the dried solid S1. Figure 8 The XPS plot of solid S1. Figure 7 (XRD pattern of dried solid S2). Figure 6 and Figure 8 As can be seen, S1 is mainly in an amorphous state (several XRD peaks mainly match Na2SO4), and its composition mainly contains Al, P, and O, as well as small amounts of Na and S (such as Na2SO4). Because the precipitated product particles are very fine, have a large specific surface area, and strong adsorption capacity, a small amount of nickel ions (w) are inevitably adsorbed. Ni =0.3%) and a certain amount of organic compounds (element w) C=14.7%.

[0062] As is customary for new plating tank setup, plating is performed normally according to specifications, maintaining T = 86±2℃; pH = 4.8±0.2; c(Ni 2+ The concentration of nickel ions in the plating solution is 4.7 ± 0.2 g / L. Large components are continuously plated, with a small test piece plated at regular intervals according to specifications. The plating time for the small test piece is t = 60 ± 1 min. The nickel ion concentration in the plating solution is analyzed periodically, and nickel sulfate, sodium hypophosphite, composite additives, pH adjusters, etc., are added according to specifications.

[0063] Due to evaporation, the volume of the plating solution continuously decreases. The recovered solution is continuously or intermittently added to the plating system as makeup water. After adding 2120 mL of the recovered solution, deionized water is added. The appearance, physical properties, and chemical composition of the plating layer on each small sample are observed and analyzed. The results are shown in Table 3. The states of the six corresponding samples under a 50x microscope are shown in Table 3. Figure 10 .

[0064] Table 3 shows the performance of the coating when the recovered solution is used as replenishment water for plating bath evaporation.

[0065]

[0066] The results in Table 3 indicate that although the aging solution treatment process interferes with the chemical composition of the plating solution to some extent, no adverse effects were observed under the premise of limited reuse. The deposition rate decreased slightly with increasing MTOs, which is the typical effect of MTOs on the deposition rate, demonstrating that the reuse of the treated aging solution has no significant impact on the deposition rate.

[0067] Coating composition analysis under MTO=6 conditions ( Figure 9 The results showed that the composition of the coating was within the design range, and no other substances besides Ni and P were co-deposited, indicating that the low concentration of Al remaining in the recovery solution was normal. 3+ With other cations (such as K) + Na + Like other coatings, it cannot be deposited on the surface of the workpiece, and therefore does not affect the composition of the coating.

[0068] When MTO is greater than 8, spots and particles appear on the coating. Figure 10 This is a normal phenomenon. Firstly, it is because the plating solution was not filtered during the plating test. Secondly, it also indicates that the plating solution's tolerance to MTO is less than 8 under the plating conditions. Therefore, it is preferable to change the tank or start aging solution treatment when MTO equals 6.

Claims

1. A green treatment method for a nickel-phosphorus electroless plating aging solution, characterized by, The steps are as follows: (1) Determination of the concentration of phosphite ion in the aging solution of nickel-phosphorus electroless plating n (HPO3 2- ), according to the calculation formula , m =1 / 4 ~ 1 / 3, calculate the amount of aluminum sulfate needed to be added; (2) Add aluminum sulfate into the aging solution of nickel-phosphorus electroless plating, heat and react at 50-100°C, after the reaction, filter or centrifugalize while hot, then wash the solid with hot water, the washing water is mixed into the filtrate or supernatant, and the recovered solid is the mixture of aluminum phosphite and aluminum hypophosphite; (3) Cool the filtrate or supernatant to room temperature, then freeze treat at-5-0°C for more than 24 hours, filter or centrifugalize while cold, collect the solid, which is sodium sulfate decahydrate, and the recovered liquid is used as the evaporation supplement liquid of the plating bath.

2. The green processing method according to claim 1, characterized in that, In step (2), the reaction temperature is 70°C.

3. The green processing method according to claim 1, characterized by, In step (2), the reaction time is more than 30 minutes.

4. The green processing method of claim 1, wherein, In step (2), the temperature of the hot water is not lower than the reaction temperature in step (2), and the hot water washing is not less than 3 times.

5. The green processing method of claim 1, wherein, In step (2), the hot water washing is 3-5 times.

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