Comment on: ‘Is the fish-hook effect in hydrocyclones a real phenomenon?’ by F. Bourgeois and A. K. Majumder [Powder Technology 237 (2013) 367–375]

•Normal efficiency curves of hydrocyclones show monotonic increase with size.•It is logical to expect that near zero sized particles follow water.•Efficiency of near zero particles may be equated/approximated to water recovery.•Errors in size analyses could cause anomalous efficiency curves.

Recently, an unusual shape of the efficiency curve for a hydrocyclone classifier is reported by Bourgeois and Majumder [Powder Technology 237 (2013) 367–375]. They report actual recovery of near zero sized particles to underflow as zero. Such perfect separation of the finest particles is in total disagreement with the knowledge base and experience accumulated over many years of hydrocyclone practice. However, the authors assert that the efficiency curves reported by them are determined from a carefully generated experimental data followed by a rigorous statistical analysis. It is likely that their anomalous observations are due to systematic errors in size analyses.

Graphical abstractNormal efficiency curve of a hydrocyclone classifierFigure optionsDownload full-size imageDownload as PowerPoint slide