Deposition of hematite particles on polypropylene walls in dynamic conditions.

An experimental circulating water loop has been constructed to study the deposition of hematite particles of average diameter 320 nm on polypropylene pipe walls in the ranges pH 4-11, Re 3300-17,700 at 25 degrees C. Real-time turbidimetric measurements were used to measure the deposited concentrations. Results showed that the deposition rate increased when pH decreased and when the flow rate increased. Adhesion was observed even under repulsive electrostatic conditions (pH>7), where the surfaces of hematite and polypropylene were both negative, indicating that the kinetic energy of at least a part of the particles surpassed the electrostatic repulsive potentials. The experimental curves were fitted by a model assuming simultaneous adhesion and removal of particles, leading to adhesion and removal rate constants, whose values depend on pH and flow rate. Removal is negligible below pH 9.