Innovative Application and Industrial Value of Membrane Chromatography Technology in the Treatment of Waste Liquid from Aluminum foil processing

Aluminum foil, as an indispensable basic material in modern industry, is widely used in food packaging, electronic devices, architectural decoration and other fields. During its processing, if the acidic waste liquid (containing HCl, H₂SO₄ and Al³⁺) produced by the corrosion process is treated by the traditional neutralization method, it will not only cause a waste of resources, but also generate a large amount of aluminum-containing sludge, leading to secondary pollution. Membrane separation technology, with its physical mechanism of "concentration difference-driven + membrane separation", has achieved efficient recovery of acid and deep retention of aluminum ions in the waste liquid of aluminum foil processing without the need for an external electric field and with extremely low energy consumption, thus becoming a key technology for the green transformation of the industry.
Technical principles and core advantages
1. Membrane separation mechanism driven by concentration difference
Membrane chromatography achieves the directional migration of solutes through the selective permeability of ion-exchange membranes:

Anion exchange membrane (anion membrane) : It carries positively charged groups, allowing anions such as SO₄²⁻ and Cl⁻ to pass through. Meanwhile, the pore size (0.1-0.5nm) forms a "molecular sieve" effect, retaining divalent and higher Al³⁺ ions.
Cation exchange membrane (anion membrane) : It is suitable for alkaline systems, but the waste liquid from aluminum foil processing is mainly acidic, so anion membranes are mainly used.
Take the treatment of sulfuric acid waste liquid as an example: The raw liquid chamber (containing H₂SO₄/Al₂(SO₄)₃) and the recovery chamber (pure water) are separated by an anion membrane. Driven by the concentration difference, SO₄²⁻ diffuses towards the lower concentration side, while OH⁻ in the recovery chamber migrates in the opposite direction to the raw liquid chamber and combines with H⁺ to form water, achieving the separation of acid and aluminum.

2. Multi-level series design enhances efficiency
For the waste liquid from aluminum foil processing (H₂SO₄ concentration 15%-20%, Al³⁺ concentration 1%-3%), a three-stage series membrane stack (anion membrane + anion membrane + anion membrane) is adopted:

First-stage recovery: The recovery rate of H₂SO₄ reaches 85%, and the concentration of recovered acid remains stable at over 18%, which can be directly returned to the corrosion process for recycling.
The second-level retention: The retention rate of Al³⁺ is ≥90%, the content of Al³⁺ in the residual liquid is reduced to below 0.1g/L, and the amount of sludge produced is reduced by 60%.
Third-level purification: Trace amounts of Al³⁺ are further removed through nanofiltration membranes, and the purity of the recovered acid is increased to 99%, meeting the production requirements of high-end aluminum foil.

Analysis of Application Scenarios and Benefits in the Aluminum Foil Processing Industry
1. Treatment of waste liquid from foil corrosion
In the production of foil formation, the corrosion section generates a large amount of sulfuric acid/aluminum sulfate wastewater (H₂SO₄ concentration 18%-22%, Al³⁺ concentration 2%-4%). The traditional neutralization method requires a large amount of lime, generates 1.2 tons of aluminum-containing sludge per day, and the recovered acid cannot be directly reused.
Membrane chromatography solution

Process flow: The waste liquid is pre-treated by microfiltration and then enters the three-stage anion membrane dialysis system. The recovered acid is returned to the corrosion tank, and the residual liquid enters the neutralization process.
Economic value: Taking a medium-sized foil formation enterprise as an example, it processes 36,000 cubic meters of waste liquid annually, recovers 30,600 tons of H₂SO₄ (calculated at 800 yuan per ton), saves 24.48 million yuan in costs annually, and reduces sludge disposal costs by 1.8 million yuan per year.
Environmental benefits: The amount of sludge produced has decreased from 4,320 tons per year to 1,728 tons per year, with a reduction rate of 60%, meeting the requirements of the "Hazardous Waste Identification Standard" (GB 5085.3-2007).
2. Treatment of waste liquid from anodizing aluminum profiles
During the anodizing process of aluminum profiles, if the waste sulfuric acid solution (H₂SO₄ concentration 18%-20%, Al³⁺ concentration 1.5%-2.5%) is directly discharged, it not only wastes resources but also corrodes the sewer.
Membrane chromatography solution

Process optimization: The "membrane separation - nanofiltration" integrated system is adopted. The first-stage membrane separation recovers 85% H₂SO₄, and the second-stage nanofiltration further purifies it to 22%, which is then returned to the oxidation tank for use.
Resource recycling: Al³⁺ in the residual liquid is recovered as aluminium hydroxide through sedimentation, with an annual recovery volume of 1,200 tons (calculated at 2,000 yuan per ton), increasing the annual value by 2.4 million yuan.
Process upgrade: After a certain enterprise applied this technology, the service life of the oxidation tank solution was extended by 30%, the number of tank changes was reduced by 4 times per year, and costs were saved by 1.2 million yuan.
3. Resource utilization of waste liquid from high-end aluminum foil production
In the production of aluminum foil for power lithium batteries, the waste liquid contains HNO₃ (15%-18%), HF (3%-5%) and Al³⁺ (2%-3%). The traditional treatment method requires a step-by-step neutralization process, which is complex and costly.
Membrane chromatography solution

Mixed acid separation: A double-membrane method (anion membrane + cation membrane) is adopted in series. The anion membrane recovers HNO₃/HF, while the cation membrane retains Al³⁺.
Recovery effect: HNO₃ recovery rate 82%, HF recovery rate 78%, Al³⁺ retention rate 92%. The recovered acid can be directly used for aluminum foil corrosion.
Industrial upgrading: A certain enterprise processes 12,000 cubic meters of waste liquid annually, recovers mixed acid worth 18 million yuan, and reduces hazardous waste disposal costs by 3 million yuan per year.
Technological breakthroughs and process innovations
The performance of membrane materials has been enhanced
Anti-pollution membrane development: In response to the issue of easy deposition of organic substances (such as surfactants) in aluminum foil waste liquid, a modified anion membrane with fluorocarbon polymer grafted on the surface was developed to solve the membrane pollution problem and extend the membrane life to 3-5 years.
High-throughput membrane design: Polyphenylene ether-based anion membranes are adopted. Through the cross-linking process of benzene ring bromination and amination, the selectivity of the membrane is increased to 99.5%, the anti-pollution performance is enhanced by 30%, and the annual depreciation cost is reduced to 80,000 yuan per set.
2. Upgrade of the process mode
Modular system: Develop small mobile (processing capacity 10-20m³/d) and large fixed (processing capacity 100-500m³/d) membrane separation systems, reducing the cost per ton of water treatment to 6-8 yuan (traditional method is 12-15 yuan).
Integrated process: By combining membrane evolution with evaporation crystallization and ion exchange technology, a "recycling - purification - reuse" chain is formed. For instance, a certain enterprise has increased the concentration of recycled acid to over 25% and reduced the content of aluminum impurities to below 0.01g/L through this process.
3. Intelligent control
Integrating the Internet of Things and AI algorithms, it can monitor parameters such as the voltage, flow rate and temperature of the membrane stack in real time and automatically adjust the operating conditions. For instance, by predicting the trend of membrane fouling through machine learning models and initiating the backwashing program in advance, the system downtime was reduced by 50% and the operational stability was enhanced by 95%.

Strategic value and industry impact
The application of membrane analysis technology in the treatment of waste liquid from aluminum foil processing not only helps enterprises achieve environmental compliance but also creates economic value through resource utilization

Cost savings: For every ton of waste acid treated, 0.9 tons of H₂SO₄ and 0.03 tons of Al(OH)₃ can be recovered, saving over 12 million yuan in costs annually.
Carbon reduction: Compared with traditional evaporation methods, the carbon emissions per ton of water treatment are reduced by 55%, helping enterprises achieve their carbon neutrality goals.
Industrial upgrading: Promote the transformation of aluminum foil processing from "end-of-pipe treatment" to "resource recycling" to enhance global competitiveness.
Membrane analysis technology is reshaping the macroscopic pattern of aluminum foil processing waste liquid treatment with the micro-force of "concentration differation-driven". From the separation of H₂SO₄/Al³⁺ coexistence systems to the deep retention of Al³⁺, from process optimization to digital empowerment, this green technology has become the core engine for China's aluminum foil processing industry to move towards high-quality development. In the future, with the deep integration of materials science, digital technology and process integration, membrane evolution technology is expected to be widely applied and promoted in more fields, contributing solutions to the green development of the aluminum foil processing industry.