In some hydrometallurgical operations, the removal of iron from process liquors can be critical, with the method of choice commonly being crystallization (precipitation). It has been recently discovered that if the removal of iron occurs at pH 3, ferrihydrite, a complex and disordered compound, will generally be precipitated. A laboratory scale, computer controlled, continuous crystallizer was constructed to investigate the removal of iron from low pH solutions (precipitation). The significance of ferrihydrite precipitation and the effect of pH and silica concentration on the properties of the precipitate were investigated. Considerable insight has been gained concerning the crystallization and growth mechanisms under these conditions, including the unusual limit of ferrihydrite crystal growth. The use of in situ focussed beam reflectance measurement (FBRM) analysis has allowed the particle size differences experienced at low pH in ferrihydrite precipitation to be studied. The improved understanding of the crystallization of iron from hydrometallurgical process liquors has resulted in a methodology for more effective removal of iron. (C) 2002 Elsevier Science B.V. All rights reserved.