Adding phosphate (PO4--) to the boiler drum is another method of treating suspended solids in the boiler feedwater stream. The activated PO4 treatment results in the formation of insoluble precipitates in the boiler drum. Unlike the chelation treatment, this process is carried out solely in the boiler drum. The goal of the treatment is to precipiate calcium and hardness ions in the phosphate form. The PO4 is particularly effective for the treatment of iron deposits on boiler surfaces. These deposits act as miniature boilers taking liquid from the feedwater and producing steam. During this process iron deposits act to hold caustics and suspended solids within the deposit. This causes depositional growth on the surface of the boiler. PO4 acts to remove the deposits and buffer the pH when the caustic is released. In order to control the size of the precipitate that is formed, Dispersing agents are used to control the particle size of the precipitate. Dispersants interfere with the crystal complex of the suspended solid.
An activated PO4 treatment is not as effective as chelation for treating magnesium hardness. Magnesium Phosphate formed by this process adheres to the surface of the boiler and reduces its effectiveness.