The scale formed will depend upon the type of dissolved salts present and which incompatible salts they are mixed with;
- Calcium ion + sulphate ion = calcium sulphate (sulphate type scale)
- Calcium ion + carbonate ion = calcium carbonate (carbonate type scale)
The resulting scale formed will determine which type of chemical product is needed to treat it and hence the treatment method
Carbonate type scales are easily treated with an acid based product as they are readily solubilised in this type of product which is fast acting. However, they can also be treated with an alkali based chelating product. This is especially useful if there are other materials present in the scale mix that are acid insoluble or are other materials present in the scaled up system that can be damaged by acid treatment.
Sulphate type scales are not soluble in acid based products so need to be treated with alkaline based chelating products. These target the low solubility ions and effectively bind and remove them from the water allowing more to solubilise etc. This type of product typically needs to be used at temperature 50-90°C to work in a time effective manner but will still work at lower temperatures. However, treatment times will be longer.