Application of Membrane Dialysis in Acid Recovery of Aluminum Processing Industry

Aluminum materials, with significant advantages such as light weight, high strength, and corrosion resistance, are widely used in numerous fields including construction, transportation, and electronics. In the aluminum electronics industry, hydrochloric acid-sulfuric acid mixed acid cleaning is a common process, but it generates a large amount of waste acid liquid. As an efficient acid recovery method, membrane dialysis technology plays a key role in acid recovery for the aluminum processing industry. This paper deeply analyzes the principle of membrane dialysis technology, combined with practical application cases, elaborates on its advantages in acid recovery of the aluminum processing industry, and prospects its future development.

I. Preface

Aluminum materials, with their unique physical and chemical properties, hold a pivotal position in modern industry. In the construction field, aluminum is widely used in doors, windows, curtain walls, etc. Its light weight helps reduce the self-weight of buildings, while high strength and corrosion resistance ensure the safety and durability of buildings. In the transportation field, aluminum is heavily used in vehicles such as cars, trains, and airplanes, helping to reduce energy consumption and improve operational efficiency. In the electronics field, aluminum is used to manufacture components such as casings and heat sinks for electronic products, and its good electrical conductivity and heat dissipation meet the performance requirements of electronic products.

 

In the aluminum electronics industry, hydrochloric acid-sulfuric acid mixed acid is commonly used to remove oxide layers, oil stains, and other impurities from the surface of aluminum electronic products or aluminum materials. After a series of processing steps, a large amount of waste acid liquid is generated. If directly discharged, this waste acid liquid not only causes waste of acid resources but also severely pollutes the environment. Traditional waste acid treatment methods, such as lime neutralization, produce a large amount of waste residue containing heavy metal ions and harmful substances. If improperly treated, these residues can cause secondary pollution to soil and water sources. The emergence of membrane dialysis technology provides an efficient and environmentally friendly solution for acid recovery in the aluminum processing industry, contributing to resource conservation and environmental protection.

II. Principle of Membrane Dialysis Technology

Membrane dialysis is a membrane separation technology based on the selective permeability of ion exchange membranes. In acid recovery for the aluminum processing industry, it mainly utilizes the characteristics of anion exchange membranes (anion membranes) to achieve separation of acids and metal ions.

 

Anion membranes carry positive charges, with fixed positive charge groups inside. Driven by a concentration gradient, anions (such as chloride ions Cl⁻ and sulfate ions SO₄²⁻) in the waste acid liquid are attracted by the positive charge groups of the anion membrane and dialyze into the receiving liquid. Meanwhile, since anions entrain hydrogen ions (H⁺) to pass through the membrane during diffusion, acid recovery is achieved. Metal ions such as aluminum ions (Al³⁺), due to their larger ionic radius, are difficult to pass through the anion membrane and are retained in the original solution chamber. This effectively separates acids from aluminum ions, achieving the goal of acid recovery.

III. Practical Application Cases

(一) Case Background

An aluminum processing plant uses sulfuric acid-hydrochloric acid mixed acid (acid concentration 5.5N) as the etching solution. After a series of processing steps, the concentration of the waste acid liquid drops to about 4N. The plant has a large production scale, with each production line discharging 10 tons of waste acid liquid per day, and there are three such production lines, resulting in a total waste liquid discharge of approximately 30 tons. If the large amount of waste acid liquid is not properly treated, it will not only cause resource waste but also impose a heavy environmental protection burden on the enterprise.

(二) Treatment Process

To recover the waste acid, the plant decided to adopt membrane dialysis technology after in-depth market research and technical evaluation. Among numerous anion membrane products, the plant selected CJAM - 3 anion membrane for experiments. During the experiment, operation conditions such as temperature, pressure, and flow rate were strictly controlled to ensure the accuracy and reliability of experimental results.

 

The experimental results showed that in an acidic system, the DF dialysis anion membrane has an excellent separation effect on aluminum-acid mixtures. It has a high acid recovery rate and a high interception rate for aluminum ions, indicating that the CJAM - 3 anion membrane can effectively separate acid from aluminum ions, meeting the plant's needs for waste acid recovery.

(三) Application Effects

This technology was practically applied in Huaibei Dongci Co., Ltd. in Anhui. The company used 20 sets of 512-square-meter specification devices to build a complete waste acid recovery system. Through the operation of this system, 59,000 cubic meters of waste sulfuric acid are recovered annually, equivalent to saving 9,000 tons of original acid. The recovered sulfuric acid can be reused in the production process, reducing the enterprise's demand for fresh sulfuric acid and cutting raw material procurement costs.

 

Meanwhile, the sales of residual liquid bring an annual profit of 800,000 yuan to the enterprise. The residual liquid can be further processed to extract valuable substances, realizing resource reuse. In addition, 1 million yuan is saved in lime neutralization costs, reducing the treatment costs for waste residues and environmental pollution control costs generated by the traditional lime neutralization method. The investment payback period for this project is within 6 months, demonstrating significant economic and environmental benefits.

IV. Advantage Analysis

(一) Significant Economic Benefits

By recovering waste acid, enterprises reduce the procurement cost of fresh acid. The price of fresh acid is relatively high, and recovering waste acid can lower the enterprise's raw material costs. Meanwhile, the sales of residual liquid and saved neutralization costs also bring considerable economic benefits to the enterprise. Residual liquid may contain valuable substances, which can create additional income for the enterprise through further processing and sales. Saving lime neutralization costs directly reduces the enterprise's treatment costs. The comprehensive effect of these economic benefits lowers the enterprise's production costs and improves its market competitiveness.

(二) Environmentally Friendly

The technology reduces waste acid discharge, thereby decreasing environmental pollution. Waste acid contains a large amount of acid and metal ions, which can cause severe pollution to soil and water sources if directly discharged. Membrane dialysis technology can effectively recover acid, reducing waste acid emissions. At the same time, it avoids the pollution of soil and water sources caused by waste residues from the traditional lime neutralization method. The residues generated by the traditional lime neutralization method contain heavy metal ions and harmful substances, which can have long-term impacts on the ecological environment if not properly treated. Membrane dialysis technology complies with the requirements of sustainable development and is conducive to protecting the ecological environment.

(三) Technical Feasibility

The application of membrane dialysis technology in the aluminum processing industry has been verified by practice, with mature and reliable technology. The equipment is simple to operate and stable in operation, making it suitable for large-scale promotion and application in aluminum processing enterprises. The structure of membrane dialysis equipment is relatively simple, mainly composed of membrane modules, compartments, pipelines, etc. Its operation process does not require complex procedures or professional technicians—ordinary workers can master the operation after simple training. Meanwhile, the equipment operates stably and can maintain good separation effects for a long time, meeting the needs of large-scale production in enterprises.

V. Conclusion

Membrane dialysis technology has obvious advantages in acid recovery for the aluminum processing industry, achieving the dual goals of acid resource recycling and environmental protection. It not only reduces the enterprise's production costs and improves economic benefits but also decreases environmental pollution, conforming to the requirements of sustainable development.

 

With the continuous development of the aluminum industry, the demand for acid resources will continue to increase, and environmental protection requirements will become stricter. As an efficient and environmentally friendly acid recovery technology, membrane dialysis will play a more significant role. In the future, the performance of membranes can be further improved to enhance acid recovery rate and separation effect; the design and operation conditions of devices can be optimized to reduce operation costs; and integration with other technologies can be strengthened to achieve more efficient resource recovery and environmental protection. This will promote the aluminum processing industry toward green and sustainable development, contributing to the construction of a resource-saving and environment-friendly society.