Aluminum Sulfate (alum or also known as alumina) as a precipitating agent, plays an important role in papermaking. The first is the need for sizing, but it also satisfies the other requirements in papermaking. Alumina is acidic solution, the amount of Aluminum Sulfate directly affects the pH value of slurry. Although papermaking is shifting to neutral or alkaline, but Aluminum Sulfate’s role still can not be ignored.
In the Aluminum Sulfate, the relative content of Al2O3 is about 8%, when pH <3, Al (H2O) 63+ is the main form of aluminum’s present in the solution. If the solution’s pH increased (-OH ions concentration increases), water molecules will gradually be replaced by the -OH ions.