Interaction of kaolin and magnetite particles with copper surfaces at different pH values

Abstract

The deposition of particles from flowing suspensions is gove·rned by lhe combined action of surface interactions and hydrodynamic forces. Among lhe great numberof factors affecting surface interactions th•e pH plays an important role when aqueous suspensions are concerned. This work reports lhe results obtained in severa! deposition experirnents carried out with aqueous suspensions of kaolin and magnetite particles, flowing at a velocity of 0.42 m/s, in the pH range 7.5 - 1 0.5. Copper was chosen as surface of deposition, due to lhe importance of particle deposits on heat transfer equipment, where copper is widely used. - Foreach type of parficles and pH v alue two different runs were performed. ln one case the pH was kept constant via addition of sodium hydroxide and in the other lhe controlling medium was sodium carbonate. Each run had a duration of 20 days and at the end lhe thickness of lhe deposits was measured by means of a micrometer based device. Zeta potentials and surface tensions of til e interacting species were also measured. The .interpretation of the results has been tried by associatin~~ lhe effects predicted by DL VO theory with lhe action of short range repulsivE! interactions and hydrodynamic forces acting on the deposited particles. The better agreement with experimental observations is obtaineci considering that the interactions take place at constant potential. However, th1~re are some situations of difficult explanation, forwhich it would be necessary to quantify t11e hydration forces.