Fouling by aqueous suspensions of magnetite particles: the effect of pH and ionic strength

Abstract

Particles adhesion Is one of the fundamental steps in heat exchanger fouling. Surface Interactions are affected by a con siderable number of factors related to the nature of the surfaces Involved. and to the composition and dynamics of the fouling fluid. Although quantitative predictions of U1e rate of adhesion are still not feasible !n practical situations. the evaluation of the potential energy of Interaction between two surfaces "in each vicinity" can be a valuable tool for the qualitative assessment of the fouling tendencies. For that purpose experimental determination of the parameters characterizing the physico-chemical properties of the Interacting surfaces are required. The present paper reports studies on particulate fouling caused by aqueous suspensions of magnetite on copper surfaces. A series of experiments were carried out at different pH values in the range of 7.5 - 9.5. For each pH two distinct types of experiments were performed: In one case the pH was controlled wlth NaOH and In the other the pH controlling medium was Na2co3. Each run lasted 20 days and at the end the thi ckness of the deposits was measured by means of a micrometer coupled to an electrical circuit. The zeta potentials and surface tensions of the solids were measured and used !n the Interpretation of the results. which was carried out In terms of the DLVO Theory.