MAGNETIC AMELIORATION OF SCALE FORMATION

Process industry remains sceptical of antiscale magnetic treatment (AM T) despite its long history. Manufacturer's claims concerning AMT comp rise: (a) a reduction in the amount of scale formed, (b) production of a less tenacious scale due to a change in its crystal morphology, (c) removal of existing scale, and (d) a retention of the antiscaling pro perties of the treated water for hours following treatment. Scientific research has both substantiated and refuted these claims, creating wi despread controversy as to the credibility of this type of water condi tioning. Positive results indicate effects on: (a) colloidal systems w here aggregation is generally enhanced and (b) crystallisation where l arger hydrophilic crystals, usually with modified crystal growth, are generated. Investigations have incorporated scaling kinetics, scale mo rphology, scale solubility, particle coagulation and corrosion. Effect s have been reported for different scale-forming compounds and for var ious microscopic and macroscopic parameters in single-phase systems. A MT appears to be enhanced by prolonged or repeated magnetic exposure, and is more effective above a threshold magnetic field contact time an d in flowing systems. Effects have been reported in treated waters up to 130 h after exposure has ceased. Industrial case studies indicate t hat the most successful implementations are in hot recirculating syste ms. Mechanisms presented to account for the observed effects comprise (a) intramolecular/intraionic interaction, (b) Lorentz force effects, (c) dissolution of contaminants, and (d) interfacial effects. The most plausible of these is the latter, in which the interaction of the mag netic field with the charged species present (ion clusters and crystal lites) affects crystal nucleation and subsequent growth. The reported scale inhibition (and descaling) then occurs as a result of magnetical ly-produced hydrophilic discrete scale particles of substantially diff erent size and crystal morphology to untreated systems, in which more adherent crystals are generated.