Cathode plate protective coating for electrolytic zinc hydrometallurgy and preparation method of cathode plate protective coating

Abstract

The invention relates to a cathode plate protective coating for electrolytic zinc hydrometallurgy and a preparation method thereof. The invention relates to a cathode plate protective coating for electrolytic zinc hydrometallurgy. The cathode plate protective coating is formed by mixing a component A and a component B, the component A comprises self-made radix asparagi polyurea resin, GS-615 fumed silica, chromium oxide green, 2000-mesh mica powder, titanium dioxide, 500-mesh precipitated barium sulfate, KH792, BYK-306, BYK-163 and BYK-066N, and the raw materials are subjected to high-speed dispersion and ball milling to obtain a material system with high solid content and low viscosity (S = 97 + / -2%, and eta < 2000 mPa.s); and the component B is an N-3300 isocyanate curing agent with high solid content and low viscosity (S is 90 + / -2%, and eta is less than 1500mPa. S). By optimizing the formula design, the coating has high adhesive force, excellent permeability resistance, strong corrosion resistance and moderate flexibility, and can be brushed, sprayed or roller-coated on an easily-corroded area of a cathode plate, so that the service life is remarkably prolonged. The preparation and construction processes are simple and efficient, complex multi-layer coating or high-pollution solvents are not needed, the coating is suitable for industrial batch production, and the contradiction between the protection performance and the production cost in the traditional technology is effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of coatings and relates to a cathode plate protective coating for wet smelting electrolytic zinc and a preparation method thereof. Background Art

[0002] In the wet zinc smelting process (accounting for 80% of global production), the aluminum cathode plate faces serious gas-liquid interface corrosion problems during the electrolytic deposition process. The parts of the aluminum plate exposed to the air are exposed to oxygen, acid mist and other media, forming an electrochemical corrosion environment, which leads to localized surface corrosion, difficulty in zinc stripping and accelerated plate loss. When my country produces 7 million tons of zinc annually, 1.4 to 2.1 million plates need to be replaced, which significantly increases production costs. The industry mainly responds through two ways: optimizing the performance of the electrolyte or enhancing the corrosion resistance of the aluminum plate. The international mainstream solution uses organic coating protection technology, and applying a protective layer at the liquid level line has become the standard production process for aluminum cathode plates in Europe and the United States. This measure effectively extends the service life of the cathode plate and has become a key direction for solving the corrosion problem.

[0003] Chinese Patent CN2887892Y: Epoxy resin anti-corrosion coating, easy to operate but only extends life by 60 days, with limited protective effect. Chinese Patent CN102953093A: Three-layer composite coating (epoxy base layer / middle layer / wear-resistant surface layer), which increases life by 30-50%, but has defects such as multiple processes and a long curing cycle. Chinese Patent CN110467866A: Water-based polyurethane / epoxy composite system (montmorillonite nanosheet filler), an environmentally friendly anti-corrosion material with a relatively complex preparation process. Chinese Patent CN108754396A: Ceramic / metal alloy thermal spraying technology, which extends life by 2-3 months, but the coating is brittle and has high porosity and is easy to fall off.

[0004] Existing electrolytic zinc cathode plate anti-corrosion technologies generally have defects such as complex processes (such as multi-layer coating and dependence on special equipment), insufficient coating performance (weak bonding, easy to fall off, and short corrosion resistance life), environmental risks (organic solvent pollution, use of toxic materials) and high costs (nanomaterial preparation, special raw material requirements). It is difficult to balance the contradictions between efficient production, long-term protection, environmental friendliness and low cost. There is an urgent need to develop new protection technologies that take into account high density, strong interface bonding, green process and economy. Summary of the Invention

[0005] This invention addresses the issues of poor coating adhesion, insufficient corrosion resistance, complex processes, and poor environmental performance associated with existing electrolytic zinc cathode plate anti-corrosion technologies. It provides a cathode plate protective coating for hydrometallurgical electrolytic zinc and its preparation method. Through an optimized formulation, this coating combines high adhesion, excellent permeability, strong corrosion resistance, and moderate flexibility. It can be applied by brush, spray, or roller to corrosion-prone areas of the cathode plate, significantly extending its service life. Its preparation and application process is simple and efficient, requiring no complex multi-layer coating or highly polluting solvents. It is suitable for industrial mass production and effectively resolves the conflict between protective performance and production costs encountered in traditional technologies.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A cathode plate protective coating for wet smelting electrolytic zinc is a two-component protective coating, which is prepared by mixing component A and component B in a weight ratio of 1.7 to 1.8:1. Components A and B are both in parts by weight. The component A is a high-solid, low-viscosity (S=97±2%, η<500mPa·s) material system prepared by high-speed dispersion and ball milling of the raw materials, with a formulation of 50-60 parts of homemade asparagus polyurea resin, 2.5-3.5 parts of fumed silica, 10-15 parts of chromium oxide green, 8-12 parts of mica powder, 10-12 parts of titanium dioxide, 3-5 parts of precipitated barium sulfate, 1.5-2 parts of KH792, 0.3-0.5 parts of BYK-306, 0.3-0.6 parts of BYK-163, and 0.4-0.8 parts of BYK-066N. The component B is an N-3300 isocyanate curing agent with high solid and low viscosity (S=90±2%, η<1500mPa·s).

[0008] The mica powder is preferably 2000 mesh mica powder. The precipitated barium sulfate is preferably 500 mesh precipitated barium sulfate. The fumed silica is preferably GS-615 fumed silica.

[0009] The specific formula and preparation method of the protective coating are as follows:

[0010] (1) Synthesis of homemade asparagus polyurea resin

[0011] 50.0g of high-purity N,N-bis(2-aminoethyl)malonamide and 30.0g of triethylamine were dissolved in 800mL of anhydrous DMF and stirred at 40°C under nitrogen. Separately, 45.0g of a highly esterified maleic anhydride ester was dissolved in THF and activated with EDC / HOBt in an ice bath at 0°C. The amine solution was then slowly added dropwise at a rate of 2mL / min. Condensation was carried out at 25°C in the dark for 12 hours. The temperature was then raised to 60°C, and a premix of 5mg of hydroxyl-terminated PCL (Mn=2000) and 0.3g of DBTDL catalyst was added. Simultaneously, 0.5g of a 1010+168 composite antioxidant was added and the mixture was reacted under nitrogen until the -NCO groups were completely consumed. Finally, the aspartame polyurea resin with high solid content and low viscosity (S=97±2%, η<300-500 mPa·s) was obtained by gradient devolatilization in a thin film evaporator (120°C / 10kPa→150°C / 2kPa).

[0012] (2) Preparation of component A

[0013] According to the required proportions, 50-60 parts of homemade asparagus polyurea resin, 2.5-3.5% parts of fumed silica, 10-15 parts of chromium oxide green, 8-14 parts of mica powder, 10-12 parts of titanium dioxide, 3-5 parts of precipitated barium sulfate, 1.5-2 parts of KH792, 0.3-0.5 parts of BYK-306, 0.3-0.6 parts of BYK-163, and 0.4-0.8 parts of BYK-066N were mixed, ultrasonically dispersed at room temperature for 30 minutes, and then ground using a ball mill at a speed of 1500-2000 pm for 1 hour, and the material was filtered to obtain component A.

[0014] (3) Component B: N-3300 isocyanate curing agent with high solid and low viscosity (S = 90 ± 2%, η < 1500 mPa·s).

[0015] (4) Preparation of coating

[0016] Component A and component B are weighed in a weight ratio of 1.7 to 1.8:1, mixed and stirred evenly to obtain the protective coating.

[0017] The method for applying the protective coating in wet smelting electrolytic zinc is as follows: calibrating the position of the liquid level line on the cathode aluminum plate, then defining the area from the upper end of the cathode aluminum plate to 5 cm below the liquid level line as the area where the coating acts, cleaning the surface with xylene to remove dirt and impurities, etc., spraying, rolling or brushing the protective coating on the designated area, and placing it in a ventilated place to dry and solidify.

[0018] The salient features of the present invention are:

[0019] 1. Two-component high solid low viscosity system design

[0020] The optimized ratio of A:B = 1.7-1.8:1 achieves a balance between curing speed and mechanical properties through precise ratio, ensuring the stability of the coating in the harsh environment of electrolytic zinc; ultra-high solid content (A 97%, B 90%): reduces solvent volatilization, conforms to environmental protection trends, and at the same time improves single coating efficiency and reduces construction costs.

[0021] 2. Selection of high-performance resin matrix

[0022] The homemade asparagus polyurea resin has the characteristics of fast curing, chemical corrosion resistance (especially acid electrolyte) and excellent wear resistance, and is suitable for long-term immersion of cathode plates and current shock; aliphatic isocyanate prepolymer provides high hardness, yellowing resistance and weather resistance, avoiding the degradation problem of traditional aromatic isocyanates.

[0023] 3. Synergistic effect of functional fillers

[0024] Chromium oxide green has both anti-corrosion and coloring functions. Its dense oxide film can block the penetration of electrolyte and at the same time act as an inert pigment to enhance the weather resistance of the coating. It is an electrolyte-resistant hard filler that improves the coating's wear resistance, hardness and resistance to electrolyte erosion, thereby extending the service life of the cathode plate.

[0025] 4. Interface enhancement and process optimization

[0026] KH792 silane coupling agent improves the interfacial bonding between the resin and filler / substrate, preventing coating peeling and maintaining adhesion, especially during long-term immersion in electrolyte. High-speed dispersion + ball milling process ensures uniform dispersion of fillers to avoid sedimentation, while controlling viscosity (A < 500mPa·s, B < 1500mPa·s) to facilitate leveling during construction.

[0027] Effects of the Invention

[0028] 1. Highly effective anti-corrosion and wear-resistant protection

[0029] In the electrolyte (sulfuric acid 195g / L, zinc 55-60g / L, copper 0.2mg / L, cadmium 0.2mg / L, cobalt 0.2mg / L, germanium 0.022mg / L, arsenic 0.01mg / L, antimony 0.01mg / L, fluorine 15mg / L, chlorine 1000mg / L, temperature 38-42°C), the cathode plate corrosion area is less than 5% (conventional coating reaches 20%-30%), and the zinc deposition efficiency remains above 92%; the hard filler improves wear resistance by 30%-50%, and can withstand mechanical cleaning and electrolyte erosion.

[0030] 2. Environmentally friendly construction and economic cost reduction

[0031] High-solid, low-viscosity system (solid content A 97%, B 90%), single-layer coating thickness 100-180μm, VOC emission reduction 60%, fast curing (surface drying <30 minutes), saving 2-3 coats of coating costs, and reducing comprehensive maintenance costs by 40%-60%.

[0032] 3. Environmental adaptation and long-term stability

[0033] The aliphatic system is resistant to UV aging and has no yellowing or powdering in open air environments. It is resistant to high salt, hot and humid working conditions, ensuring continuous and efficient operation of the cathode plates and reducing the frequency of shutdowns and replacements. DETAILED DESCRIPTION

[0034] Table 1 Examples of the present invention

[0035]

[0036] Examples 1 to 6 are N-3300 (HDI trimer) curing agent; Comparative Examples 1, 2, and 3 are three different types of isocyanate curing agents, PAPI (crude MDI), PT60 (TDI trimer), and N-3390 (HDI trimer), respectively. Among them, N-3300 (HDI trimer) curing agent is suitable for self-drying or baking systems with high requirements for weather resistance and mechanical strength; N-3390 (HDI trimer) is suitable for industrial coating scenarios that require fast drying and weather resistance. The dosage of the curing agents in the three comparative examples is the same as that in Examples 1, 2, and 3.

[0037] Table 2 Test results of the present invention

[0038]

[0039]

[0040] At the same time, the asparagus polyurea resin of the present invention is compared with common resins on the market. The results are shown in Table 3:

[0041]

[0042]

[0043]

Claims

1. A cathode plate protective coating for hydrometallurgical zinc smelting, characterized in that: It is a two-component protective coating, wherein the A component includes 50-60 parts of aspartame polyurea resin, 2.5-3.5 parts of fumed silica, 10-15 parts of chromium oxide green, 8-12 parts of mica powder, 10-12 parts of titanium dioxide, 3-5 parts of precipitated barium sulfate, 1.5-2 parts of KH792, 0.3-0.5 parts of BYK-306, 0.3-0.6 parts of BYK-163, and 0.4-0.8 parts of BYK-066N; the B component includes N-3300 isocyanate curing agent.

2. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 1, characterized in that: Component A: component B = 1.7-1.8:1 mixed according to weight ratio.

3. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 1, characterized in that: The mica powder is 2000 mesh mica powder.

4. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 1, characterized in that: The precipitated barium sulfate is 500 mesh precipitated barium sulfate.

5. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 1, characterized in that: The fumed silica is GS-615 fumed silica.

6. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 1, characterized in that: The preparation method of asparagine polyurea resin is as follows: 50.0g of high-purity N,N-bis(2-aminoethyl)malonamide and 30.0g of triethylamine are dissolved in 800mL of anhydrous DMF, and the mixture is stirred and dissolved at 40°C under nitrogen protection; 45.0g of high-esterification maleic anhydride ester is dissolved in THF, activated with EDC / HOBt in an ice bath at 0°C, and then the amine solution is slowly added dropwise at a rate of 2mL / min, and condensed at 25°C in the dark for 12 hours; The temperature was then raised to 60°C, and a premix of 5 mg of hydroxyl-terminated PCL and 0.3 g of DBTDL catalyst was added. 0.5 g of a composite antioxidant was simultaneously injected and reacted under a nitrogen atmosphere until the -NCO groups were completely consumed. Finally, the mixture was gradient devolatilized using a thin film evaporator to obtain aspartame polyurea resin.

7. The cathode plate protective coating for hydrometallurgical electrolytic zinc according to claim 6, characterized in that: The composite antioxidant is 1010 and 168 oxidants.

8. The cathode plate protective coating for hydrometallurgical zinc electrolysis according to claim 6, characterized in that: The Mn of hydroxyl-terminated PCL is 2000.

9. The method for preparing a cathode plate protective coating for hydrometallurgical zinc smelting according to claim 1, characterized in that: (1) 50-60 parts of asparagus polyurea resin, 2.5-3.5 parts of fumed silica, 10-15 parts of chromium oxide green, 8-14 parts of mica powder, 10-12 parts of titanium dioxide, 3-5 parts of precipitated barium sulfate, 1.5-2 parts of KH792, 0.3-0.5 parts of BYK-306, 0.3-0.6 parts of BYK-163, and 0.4-0.8 parts of BYK-066N are mixed, and ultrasonically dispersed at room temperature for 30 minutes. Then, the mixture is ground in a ball mill at a speed of 1500-2000 pm for 1 hour, and the material is filtered to obtain component A; component A and component B are weighed in a weight ratio of 1.7-1.8:1, mixed and stirred evenly, and the protective coating is obtained.

10. A method for applying the protective coating according to claim 1 in hydrometallurgical zinc smelting, characterized in that: Mark the position of the liquid level line on the cathode aluminum plate, then define the area from the upper end of the cathode aluminum plate to 5 cm below the liquid level line as the area where the coating acts, use xylene to clean the surface to remove dirt and impurities, spray, roll or brush the protective coating on the designated area, and place it in a ventilated place to dry and solidify.

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