Company news about What is Polyaluminium Chloride (PAC), and how dose it work in water treatment

What is Polyaluminium Chloride (PAC), and how dose it work in water treatment

2026-02-28

What is Polyaluminium Chloride (PAC)?

Polyaluminium chloride (PAC) is an inorganic polymer coagulant composed of aluminum ions, hydroxide ions, and chloride ions. Its chemical formula can be represented as [Al₂(OH)ₙCl₆₋ₙ]ₘ, where the degree of polymerization and basicity determine its strength and application range. Unlike traditional aluminum sulfate (alum), PAC contains pre-polymerized aluminum species (mainly Al13), which enhances its charge density and coagulation efficiency.

Common Forms:

Powdered PAC: Light yellow solid with high purity, suitable for drinking water and industrial wastewater treatment.

White PAC: Food-grade or high-purity PAC, suitable for high-purity water such as drinking water.

Liquid PAC: Yellow transparent solution, convenient for metering in industrial applications and suitable for continuous processes.

Each specification is tailored for different industry needs—from municipal plants to mining operations.

How PAC Works as a Coagulant

The working mechanism of PAC as a coagulant involves several key steps, each playing a crucial role in water treatment:

Charge Neutralization

Suspended particles in water are usually negatively charged, which causes them to repel each other and prevents aggregation. Once dissolved in water, PAC hydrolyzes to form various aluminum hydroxide complex ions, such as Al(OH)²⁺ and Al₂(OH)₂⁴⁺, which carry strong positive charges. These quickly neutralize the surface charges of suspended particles, reducing electrostatic repulsion and allowing the particles to stabilize and prepare for aggregation.

Adsorption and Bridging

After charge neutralization, hydroxide complexes in PAC molecules undergo adsorption reactions with the particles. These complexes can bridge between different particles via molecular chains, forming a “bridging” effect that gradually aggregates small particles into larger flocs. This stage often determines the initial structure and stability of the flocs.

Enmeshment or Sweep Flocculation

At higher dosages or lower pH conditions, PAC forms aluminum hydroxide colloids (Al(OH)₃) in water. These floc-like precipitates have strong adsorption and enmeshment capabilities, acting like a “net” to sweep suspended particles, colloids, and organic impurities into settling. This “sweep flocculation” mechanism is especially effective in treating highly turbid water or industrial wastewater.

Floc Formation and Sedimentation

After adsorption and bridging, numerous fine particles form dense and larger flocs. Through slow stirring and other physical actions, the flocs continue to collide and aggregate, becoming larger and heavier, eventually settling under gravity and producing clear water on top. The effectiveness of this stage determines the clarity and solid-liquid separation efficiency of the water treatment.

Filtration and Clarification

Even after sedimentation, tiny particles may remain in the water. Through sand filtration or other fine filtration steps, these residual suspended solids and fine flocs can be effectively removed, resulting in high-clarity water with low impurity content.

These steps make PAC a highly efficient, cost-effective, and environmentally friendly coagulant, widely used in drinking water purification, industrial wastewater treatment, and municipal sewage systems.

Water Treatment Chemicals

Decoloring Agent Water Treatment

Anionic Polyacrylamide

Cationic Polyacrylamide

Nonionic Polyacrylamide

Polyaluminium Chloride

Antifoaming Agent

Polymer Coagulant

Polymer Flocculant

Alumina Flocculant

Drilling Polymer

Mining Flocculants