Spent acid purification in the electroplating industry

As a core component of the precision manufacturing sector, the electronic electroplating industry's effectiveness in wastewater treatment and the level of resource recycling directly affect the sustainable development process of the industry. The traditional chemical precipitation method is facing increasingly strict environmental compliance requirements as it generates a large amount of sludge containing heavy metals. Membrane chromatography technology, relying on its core mechanism of membrane separation based on concentration difference, has become a key means to break through the predicament of electroplating wastewater treatment and help the industry steadily move towards the development goal of "zero discharge".

I. Technical Principle: Molecular-level separation mechanism driven by concentration difference
Membrane chromatography technology takes advantage of the selective permeability of ion-exchange membranes to achieve the directional migration of solutes. Its core working principle is as follows:

Membrane material characteristics Anion exchange membranes (referred to as anion membranes) carry positive charges, allowing anions such as sulfate (SO₄²⁻) and chloride ions (Cl⁻) to pass through smoothly. Meanwhile, their pore sizes of 0.1-0.5nm form a "molecular sieve" effect, effectively blocking divalent and higher metal ions such as nickel ions (Ni²⁺) and copper ions (Cu²⁺). Cation exchange membranes (referred to as cation membranes for short) carry a negative charge, allowing cations such as hydrogen ions (H⁺) and sodium ions (Na⁺) to pass through while retaining anions and organic substances.
Concentration difference dynamic The raw liquid chamber (containing waste acid) and the recovery chamber (injected with pure water) are separated by a membrane structure. Driven by a concentration difference of 5% to 25% (ΔC), sulfate ions, chloride ions, etc. diffuse to the low-concentration side, while the hydroxide ions (OH⁻) in the recovery chamber migrate in the opposite direction to the raw liquid chamber and combine with hydrogen ions to form water, ultimately achieving efficient separation of acid and metal ions.
Multistage series design For the complex system where sulfuric acid and hydrochloric acid coexist in electronic electroplating waste liquid, a three-stage series membrane stack structure of "anion membrane + cation membrane + anion membrane" is adopted. The first stage realizes the recovery of sulfuric acid, the second stage completes the recovery of hydrochloric acid, and the third stage is specifically used to intercept copper ions. Eventually, the recovery rate of sulfuric acid can be increased to 85%, and the recovery rate of hydrochloric acid can reach 80%. The copper ion rejection rate shall not be less than 95%.

Ii. Core Application Scenarios in the Treatment of Electronic Electroplating Wastewater
1. Acid recovery and nickel retention from nickel plating waste liquid
The waste liquid produced in the nickel plating process of electronic electroplating contains 15-20g/L of nickel ions, 15% concentration of sulfuric acid and various impurity ions. Membrane chromatography technology achieves dual benefits through the selective separation effect of anion membranes:

Acid recovery: Driven by the concentration difference, sulfate ions pass through the anion membrane and enter the recovery chamber, while hydrogen ions migrate synchronously. The final recovered acid concentration can reach 12%, and the acid recovery rate is stable at 80%.
Nickel retention: Due to its large hydration radius (0.69nm), nickel ions are effectively retained by the anion membrane. After treatment, the nickel ion concentration in the residual liquid drops to 2g/L, and the retention rate reaches 87%.
Economic value: Taking a certain electronic electroplating enterprise as an example, the enterprise processes 5,000 cubic meters of nickel plating waste liquid annually, recovers 600 tons of sulfuric acid (calculated at 350 yuan per ton), saves 210,000 yuan in costs annually, and reduces the generation of nickel sludge by 40% at the same time.
2. Resource utilization of copper plating waste liquid
The waste liquid produced by the copper plating process contains 25-30g/L of copper ions, 18% concentration sulfuric acid and organic additives. By combining membrane chromatography technology with chemical precipitation method, a resource utilization system is constructed:

Acid recovery: A five-stage membrane stack series design is adopted, with a sulfuric acid recovery rate of 82%, and the purity of the recovered acid is no less than 95%, which can be directly returned to the plating tank for recycling.
Copper recovery: Copper ions in the residual liquid after treatment are recovered through electrolytic deposition, with a copper purity of up to 99%. A certain enterprise recovers 20 tons of copper annually (calculated at 50,000 yuan per ton), creating a direct economic benefit of 1 million yuan.
Process optimization: Through the application of the "membrane evolution - electrolytic deposition" integrated system, the cost of copper plating waste liquid treatment for enterprises has been reduced by 35%, and the utilization rate of copper resources has been increased to 98%.
3. Treatment of chemical nickel waste liquid
The composition of chemical nickel waste liquid is complex, containing complexed nickel (Ni²⁺ forms stable complexes with citrate), phosphate and organic matter. Membrane chromatography technology realizes resource utilization through multi-step synergy:

Complexation treatment: Advanced oxidation methods such as Fenton reagent are adopted to disrupt the nickel-citric acid complex structure and release free nickel ions.
Acid recovery: Sulfuric acid (with a concentration of up to 12%) in the waste liquid is recovered through the anion membrane, with a recovery rate of 75%. The recovered acid can be returned to the production process for recycling.
Nickel retention: The nickel ions in the residual liquid are further adsorbed and treated by ion exchange resin, with a retention rate of 99%. The annual nickel sludge production of the enterprise is reduced by 60%.
Iii. Technological Breakthroughs and Process Optimization
1. Innovation in membrane materials
Nickel-resistant membrane development: In response to the industry pain point that nickel ions tend to deposit on the membrane surface, leading to a decrease in flux, Shandong Tianwei Membrane Technology Co., Ltd. has developed a modified anion membrane with surface grafted polyethylene glycol, successfully solving the problem of nickel ion deposition and extending the membrane's service life to 3-5 years.
High-throughput membrane design: Polyphenylene ether-based anion membranes are adopted. Through the optimization of the benzene ring bromination and amination cross-linking process, the selectivity of the membrane is increased to 99.5%, the anti-pollution performance is enhanced by 30%, and the annual depreciation cost of the entire system is reduced to 80,000 yuan.
2. Upgrade of the process mode
Modular systems: Two types of membrane separation systems, namely small mobile ones (with a processing capacity of 10-20m³/d) and large fixed ones (with a processing capacity of 100-500m³/d), have been developed. The cost per ton of water treatment has been reduced to 7-9 yuan, which is much lower than the 12-15 yuan of traditional methods.
Integrated process: By organically combining membrane evolution technology with electrodeposition and crystallization technology, a complete industrial chain of "recycling - purification - reuse" is constructed. For instance, through this integrated process, a certain enterprise has increased the concentration of recovered acid to over 40% and reduced the nickel impurity content to below 0.1g/L.
3. Intelligent control
Integrating Internet of Things (iot) technology and AI algorithms, it can monitor key parameters such as membrane stack voltage, flow rate, and temperature in real time, and automatically and dynamically adjust operating conditions. For instance, by accurately predicting membrane fouling trends through machine learning models and initiating backwashing programs in advance, system downtime can be reduced by 50%, and operational stability can be enhanced by 95%.

Iv. Strategic Value and Industry Impact
The promotion and application of membrane chromatography technology in the treatment of electronic electroplating wastewater not only help enterprises meet environmental protection compliance requirements, but also create significant economic value through resource recycling.

Cost savings: For every ton of waste acid treated, 0.8 tons of sulfuric acid and 0.05 tons of copper can be recovered, saving the enterprise over 1.2 million yuan in costs annually.
Carbon reduction: Compared with traditional evaporation methods, membrane evolution technology reduces carbon emissions per ton of water treatment by 65%, helping enterprises advance their carbon neutrality goals.
Industrial upgrading: Promote the transformation of the electronic electroplating industry from the "end-of-pipe treatment" model to the "resource recycling" model, significantly enhancing the global competitiveness of the industry.
Membrane chromatography technology is reshaping the macro industrial landscape of electronic electroplating wastewater treatment with its "concentration different-driven" micro-separation mechanism. From the efficient separation of sulfuric acid-hydrochloric acid coexisting systems to the deep retention of copper ions, from membrane material innovation to digital process empowerment, this green technology has become the core engine for the high-quality development of China's electronic electroplating industry. In the future, with the deep integration of materials science, digital technology and process integration, membrane chromatography technology is expected to be widely applied and promoted in more specialized fields, contributing a Chinese solution to the green transformation of the electronic electroplating industry.