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Water Treatment
Water Treatment > Quality
Water Solutions > FAQ > What alum and PACl
qualities are important for water treatment? Should I be concerned with the
iron content of alum?
Alum strength and purity have traditionally been equated to equivalent alumina (Al2O3). Recent standards prefer to measure the active metal present (as percent aluminum. Dry alum typically contains about 9% active aluminum, while liquid alum has somewhat over 4%. Typical properties for liquid alum and PACl follow.
| |
Liquid Alum |
PACl* |
| Solution Strength, % (as dry alum) |
48.5 |
>20 to <50 |
| Total Al2O3 Equivalent, % |
8.3 |
6 to 23 |
| Specific Gravity, 0 °F, (at 15.6 °C) |
1.335 |
1.1 to 1.4 |
| pH Liquid Alum |
2.3 (approx.) |
1 to 3 |
| Density, lb/gal, U.S. |
11.13 |
10 to 12 |
| Concentration, lb. As dry alum/gal, U.S. |
5.4 |
N/A |
| Viscosity (cps), at 32 °F |
52 |
20 to >100 |
| at 70 °F |
21 |
10 to 50 |
| Freezing Point, °F |
5 |
5 to 20 |
As regards iron content, most alum is made from chemical grade bauxite which imparts about 0.1% iron to the product. This iron level does not hinder coagulation or cause alum to crystallize and precipitate out. Crystallization depends on solution strength and occurs if evaporation causes the solution to become too concentrated. The best way to prevent crystallization is to confirm solution concentration upon delivery (it should be less than 48.5%) and inventory no more than a 30-day supply, or one 4,000-gallon truck for small users.
* Properties vary by PACl type and vendor.
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