Zero Liquid Discharge for Aluminum Foil Pickling Wastewater

【Project Overview】

In the aluminum processing industry, foil pickling is a key process for ensuring product surface quality and subsequent performance. However, treating the resulting sodium nitrate wastewater has long been a core challenge hindering the industry's green development. Traditional approaches typically use either "Evaporation Concentration + Solidification" or "Neutralization Precipitation + Compliant Discharge." The former allows for partial sodium nitrate recovery but yields only solid salt, which cannot be directly reused in the pickling process, necessitating the additional purchase of fresh nitric acid and sodium hydroxide and leading to raw material waste. The latter directly neutralizes and destroys valuable acid and alkali components, not only forfeiting resource recovery potential but also generating significant solid waste, increasing disposal costs.

This project, leveraging the innovative application of electro-driven membrane technology, has established a comprehensive "Treatment - Recovery - Recycling" process solution. For a sodium nitrate wastewater stream of 22.5 t/h, it achieves efficient recovery and cyclic reuse of acid and alkali resources, with technical indicators and operational benefits far surpassing those of traditional processes.

【Project Highlights】

• Large Treatment Capacity & Strong Continuous Operation Capability
  The project is designed to treat a sodium nitrate wastewater flow rate of 22.5 tons per hour, demonstrating the exceptional processing capacity and stability of the bipolar membrane system in large-flow, industrial continuous operation scenarios, effectively meeting the wastewater treatment demands of scaled production.
• High Resource Recovery Efficiency, Turning "Waste into Treasure"
  The system successfully converts sodium nitrate from the wastewater into valuable ≥7% concentration nitric acid and ≥6% concentration sodium hydroxide solution. The produced acid and alkali are of high quality and can be directly, or after minor adjustment, reused in the production process. This significantly reduces external chemical procurement, achieving internal resource cycling and cost savings.
• Balancing Economic & Environmental Benefits
  The process not only solves the challenge of treating high-salinity wastewater but also transforms it from a "treatment burden" into a "production raw material," creating significant economic value. Simultaneously, it reduces pollutant discharge at the source, achieving the dual objectives of environmental compliance and cost reduction/efficiency improvement.