Roller drying polyaluminum chloride

Roller-dried polyaluminum chloride (PAC), a highly efficient flocculant for water treatment, is widely used in both water purification and wastewater management. As a solid form of polyaluminum chloride (PAC), it is manufactured through a drum-drying process, offering advantages such as convenient storage and high efficiency. Below I will elaborate on key aspects:

1. Basic definitions and core concepts

Roll-dried polyaluminum chloride (PAC) is an inorganic polymer compound with the chemical formula [Al₂(OH)nCl₆−n]m[Al₂​(OH)n​Cl₆−n​]m​ (where nn ranges from 1 to 5 and mm indicates the degree of polymerization). Produced by dehydrating liquid PAC slurry in high-temperature drum drying equipment, it forms light yellow or brown powder or granules. Compared to traditional liquid PAC, this form boasts higher concentration (typically ≥30% alumina content) and a longer shelf life (up to 1-2 years). Its primary function is as a flocculant, rapidly adsorbing impurities in water to form flocs for subsequent sedimentation separation. Notably, under modern environmental standards, roll-dried PAC has become the preferred alternative to traditional aluminum salts (such as aluminum sulfate) due to its low heavy metal residue and superior flocculation efficiency.

2. Production process and process

Drum drying process is a key step in the production of solid PAC, which mainly includes four stages: raw material preparation, polymerization reaction, drum drying and post-treatment:

• Raw material preparation: aluminum bauxite, aluminum hydroxide or aluminum-containing waste are used as raw materials to dissolve in hydrochloric acid to make liquid PAC solution.
• Polymerization: The temperature (80-100°C) and pH value (3.5-4.5) are controlled in the reactor to hydrolyze and polymerize aluminum ions to form a highly alkaline slurry (usually 50-70%).
• Drum drying: the slurry is evenly coated on the surface of the high temperature drum (temperature 150-200°C), and the water is evaporated by rotation to form a thin sheet solid, and then the powder or particles are obtained after crushing and screening.
• Post-processing: The product is cooled and packaged to ensure no lumping and stability.
• The advantages of this process are energy saving and high efficiency (short drying time, low energy consumption) and high product purity (less impurities), but there are also challenges such as large equipment investment and high dust control requirements. According to statistics, this production method accounts for about 40% of the global PAC market, especially in developing countries (such as China).

3. Main features and advantages and disadvantages

The characteristics of drum dryer PAC determine its high efficiency in water treatment, and the core advantages include:

• Efficient flocculation: high charge density and large molecular weight can quickly neutralize the colloidal charge in water, fast flocculation speed (2-3 times faster than traditional aluminum salt), and a wide range of pH (5-9).
• Environmental safety: low residual aluminum ion (<0.2mg/L), reduce secondary pollution; non-toxic, in line with drinking water standards (e.g., China GB 15892-2020).
• Storage convenience: small volume in solid form, not easy to leak, low transportation and storage cost; in humid environment, moisture-proof packaging is required to avoid lumping.
• Disadvantages: High production cost (high energy consumption for drying); if improperly used, a small amount of by-products (such as hydrogen chloride gas) may be generated, and it needs to be operated in a ventilated environment. Generally speaking, its cost performance is better than liquid PAC in long-term use, especially suitable for remote areas or large-scale water plants.

4. Application fields and practical uses

The application of drum dryer PAC is extensive, mainly in the following fields:

• Drinking water treatment: to remove turbidity, organic matter and pathogens, suitable for urban waterworks and rural water purification systems.
• Industrial wastewater treatment: treat wastewater from printing and dyeing, paper making, mining and other industries, effectively settle heavy metals and suspended solids.
• Other uses: including sludge dewatering (as a dewatering aid), petroleum extraction (as a drilling fluid additive), and construction industry (as a accelerator).
• In practice, it is recommended that the dosage be 0.1-10mg/L (depending on water quality), and it can be added directly to the water body after dissolution. Supplementary information: With the aggravation of global water shortage, the demand for drum drying PAC in reuse water and zero discharge projects is increasing, and the market is expected to grow by 8% annually in 2025.

As a green water treatment agent, drum drying polyaluminum chloride combines high efficiency, safety and economy, and is especially suitable for large-scale industrial and municipal projects.