Process industry remains sceptical of antiscale magnetic treatment (AMT) despite its long history. Manufacturer's claims concerning AMT comprise: (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 properties of the treated water for hours following treatment. Scientific research has both substantiated and refuted these claims, creating widespread controversy as to the credibility of this type of water conditioning. Positive results indicate effects on: (a) colloidal systems where aggregation is generally enhanced and (b) crystallisation where larger hydrophilic crystals, usually with modified crystal growth, are generated. Investigations have incorporated scaling kinetics, scale morphology, scale solubility, particle coagulation and corrosion. Effects have been reported for different scale-forming compounds and for various microscopic and macroscopic parameters in single-phase systems. AMT appears to be enhanced by prolonged or repeated magnetic exposure, and is more effective above a threshold magnetic field contact time and in flowing systems. Effects have been reported in treated waters up to 130 h after exposure has ceased. Industrial case studies indicate that the most successful implementations are in hot recirculating systems. 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 magnetic field with the charged species present (ion clusters and crystallites) affects crystal nucleation and subsequent growth. The reported scale inhibition (and descaling) then occurs as a result of magnetically-produced hydrophilic discrete scale particles of substantially different size and crystal morphology to untreated systems, in which more adherent crystals are generated.
