Polyaluminium Chloride: Properties, Structure, and Applications

What is Polyaluminium Chloride?

Polyaluminium chloride, often abbreviated as PAC, stands out as a versatile inorganic polymer coagulant prized in water treatment, papermaking, and several manufacturing processes. With the chemical formula Al_n(OH)_mCl_3n−m, it features an intricate structure built from polymers of aluminium chloride and aluminium hydroxide. Ranging from yellow to light brown depending on its purity and preparation method, the compound shows up as powder, flakes, solid granules, pearl-like beads, liquids, and even translucent crystals. Each form comes with a targeted use or advantage, depending on the application and storage preference.

Product Forms and Physical Characteristics

Material format matters a great deal with polyaluminium chloride. The powder version flows easily and dissolves quickly in water, which helps in bulk treatment tasks like municipal or industrial water filtration. Flakes and pearls offer slower dissolution and simpler handling, while the liquid solution, typically ranging from colorless to pale amber, allows for effortless dosing and mixing without any dust. Solid crystals often appear in precise measuring and in applications needing minimal impurities. The density of solid PAC ranges between 0.9 and 1.3 grams per cubic centimeter, depending on preparation, and liquid forms sit around 1.15 grams per milliliter. The material generally sports a molecular weight that varies with the polymerization level—reflecting how the manufacturing process dramatically shapes the product’s technical parameters and practical performance.

Chemical Properties and Structure

Behind its effectiveness, PAC’s polymeric structure offers a web of aluminium-oxygen bonds that actively capture and neutralize fine particles, heavy metals, and organic impurities. Each molecule brings together multiple aluminium atoms bridged by oxygen, boosting coagulation efficiency over traditional alum. Neutrality or slight positiveness in the polymer’s charge gives Polyaluminium Chloride the edge in destabilizing suspended solids or emulsified oil droplets—leading to swift and comprehensive water clarification. Chloride ions maintain the compound’s stability and help control the solution’s pH, keeping reactions predictable and manageable. PAC generally falls into a mildly acidic to near-neutral pH range, reinforcing practical safety during handling and storage.

Specifications and HS Code

The technical side comes in numbers and codes that help buyers and policymakers. Typical PAC products deliver basicity between 40% and 85%, measured as the fraction of aluminium present as hydroxide rather than chloride. Purity swings from around 28% to 32% Al₂O₃ content by weight for commercial water treatment grades, sometimes reaching up for food-grade or high-demand industrial uses. The HS Code for polyaluminium chloride sits at 2827.49.90, a designation that streamlines logistics, safety reporting, and customs processing. Solution concentrations run from 5% to 20% Al₂O₃ by weight, with density and viscosity shifting accordingly; this directly impacts dosing rates and application method selection.

Raw Materials and Manufacturing

Manufacturers build polyaluminium chloride from aluminium hydroxide or bauxite, hydrochloric acid, water, and—in high-purity grades—supplemental filtration or acidification agents. The process creates polynuclear hydroxy-aluminium complexes, and, depending on the balance of input chemicals, the finished product can favor higher basicity and fewer impurities or slide toward cost savings at the expense of consistency. Sloppy raw material choice can yield unwanted contaminants such as residual iron, silica, or organic carbon; reputable producers work with tight controls and rigorous post-processing to minimize these. Renewable or by-product hydrochloric acid sources, along with green chemistry processing, are starting to trickle into the manufacturing mix to answer both environmental criticisms and shifting regulatory landscapes.

Storage, Safety, and Hazards

Safety with polyaluminium chloride starts with understanding its moisture affinity and chemical reactivity. Solid forms should always stay sealed and dry to prevent caking, clumping, and unwanted hydrolysis, which can release hydrogen chloride gas. Liquid forms, while less prone to reacting with air, require proper drum or tank storage to guard against leaks and spills. Direct skin or eye contact with PAC can trigger irritation or mild burns, and inhalation of powder dust brings about respiratory discomfort—basic workplace protections like gloves, goggles, and local ventilation should never be skipped. On the hazard spectrum, PAC sits below strong acids but can turn harmful if misused or in accidental pollution cases, especially in fish-bearing streams or agricultural drainage zones. People working with the chemical rely on clear labeling, careful dilution, and well-maintained secondary containment to reduce risk.

Applications, Importance, and Solutions

Polyaluminium chloride’s story mainly unfolds in water and wastewater treatment. Its ability to latch onto suspended solids, color bodies, and dissolved phosphorus means city water systems, pulp mills, and food factories depend on regular PAC dosing for regulatory compliance and clean discharge. In my community, PAC performs as the backbone of the drinking water plant, ensuring millions drink safely every day even when upstream contamination spikes. Problems like dosing mistakes, poor mixing, or substandard chemical supply can tip the balance into secondary pollution or ineffective treatment, threatening public health and plant efficiency. Investing in automation, staff training, and robust sourcing practices helps dodge those pitfalls. Downstream users—farmers, wildlife, and recreational boaters—benefit from thoughtful PAC use, too, since clearer water sustains ecosystems and brightens rural economies.

Future of Polyaluminium Chloride

Market pressures and environmental regulations push PAC producers to keep raising the bar on quality, cost, and sustainability. Emerging research blends PAC with organic polymers or alternative metals to tackle ever-finer particles, micropollutants, or uncharged toxins now driving global water anxiety. Sustainable raw material sourcing, better recycling of process wastewater, and new low-carbon production pathways continue to reshape the competitive landscape. Stakeholders—industry, government, and citizens—need to stay informed and involved, pushing not just for technical compliance but for substantial improvements in how essential chemicals like PAC fit into the world’s water security puzzle.