Analysis of Scale from Some South African

Several samples of evaporator scale collected during the 1993 and 1994 milling seasons were analysed using x-ray diffraction, x-ray fluorescence, scanning electron microscopy and optical microscopy. The results were evaluated in terms ofcurrent knowledgeofevaporator foulingand similar trends were found to those published in the literature. From these results, typical evaporator scale profiles could be proposed for Southern African mills, depending on whether hydroxyl apatite is formed. Nevertheless each mill has its own characteristics. FX displayed a distinctly high silica content in its early effect scale while calcium aconitate was identified as a major phase in scale from NB. Microscopic examination found that scale was formed in layers. These analytical techniques were used to evaluate the effect of additives to the process streams on scale formed.