Corrosiveness of Poly Aluminum Chloride to Equipment

Poly Aluminum Chloride (PAC) is a highly efficient inorganic polymer coagulant widely used in water treatment, papermaking, printing, and dyeing industries. However, PAC can cause certain corrosiveness to equipment during use, especially under high concentration, high temperature, or acidic conditions. Corrosion not only shortens the service life of equipment but may also affect treatment efficiency and operational safety. Therefore, understanding the corrosiveness of polyaluminium chloride to equipment and adopting effective protective measures is crucial. This article will analyze the impact of PAC on equipment and corresponding solutions from two aspects: corrosion mechanisms and protective measures.

Corrosion Mechanism of Polyaluminum Chloride:

1. Acidic Corrosion

Cause: PAC aqueous solution is weakly acidic (pH typically 3.5~5.0), which may corrode metal equipment (e.g., carbon steel, stainless steel) over time.

Manifestation: Pitting, uniform corrosion, or stress corrosion cracks on metal surfaces.

2. Chloride Ion Corrosion

Cause: Polyaluminium chloride contains chloride ions (Cl⁻), which have strong penetrability and can destroy the passive film on metal surfaces, accelerating corrosion.

Manifestation: Localized corrosion (e.g., pitting, crevice corrosion) may occur on stainless steel equipment.

3. High-Temperature Accelerated Corrosion

Cause: Under high-temperature conditions, the corrosiveness of PAC significantly increases, especially for reactive metals like aluminum and copper.

Manifestation: Increased oxidation and accelerated corrosion rates on metal surfaces.

Measures to Prevent Corrosion of Polyaluminum Chloride：

1. Material Selection

Recommended Materials:

For equipment in contact with polyaluminium chloride, prioritize corrosion-resistant materials such as 316L stainless steel, titanium alloy, PVC, or PP plastic.

For critical components (e.g., pumps, valves), ceramic or fluoropolymer-lined materials can be used.

2. Surface Treatment

Methods:

Apply coatings (e.g., epoxy resin, polytetrafluoroethylene) to metal equipment surfaces to isolate direct contact between PAC and metal.

Use electrochemical protection (e.g., cathodic protection) to reduce corrosion rates.

3. Process Optimization

Methods:

Control the concentration and temperature of polyaluminium chloride solutions to avoid long-term operation under high concentration and high temperature.

Regularly clean equipment to prevent PAC residue accumulation.

4. Monitoring and Maintenance

Methods:

Install corrosion monitoring devices (e.g., corrosion coupons, electrochemical probes) to monitor equipment corrosion in real-time.

Regularly inspect equipment surfaces and promptly repair corroded areas.

Although Poly Aluminum Chloride (PAC) is an efficient water treatment chemical, its corrosiveness to equipment cannot be ignored. By selecting appropriate materials, applying surface treatments, optimizing processes, and strengthening monitoring and maintenance, the corrosion risk of PAC to equipment can be effectively reduced, extending equipment service life and ensuring production safety. It is recommended that relevant enterprises adopt comprehensive protective measures based on actual conditions when using PAC to achieve a win-win situation for economic benefits and equipment safety.