Flow cytometry as a tool to assess inhibitor performance for calcium oxalate scale control

Flow cytometry (FCM) and on-line turbidity monitoring have been used as tools to evaluate the performance of anti-scaling agent components, used for inhibition of calcium oxalate crystallization. The focus was on the precipitation rate, as well as on the crystal size and form. Sodium oxalate and calcium chloride solutions were mixed together in the presence of different chemical additives in an aqueous test solution. Addition of filtrate from peroxide-bleached groundwood pulp to the system was also tested. Finally, a method for evaluation of the calcium oxalate precipitation potential in paper mill process waters was developed and tested. The precipitation kinetics, size distribution and hydrophobicity of the formed precipitates were analysed. Based on the results, it was concluded that the combination of flow cytometry and turbidimetric monitoring gives new insights into the calcium oxalate precipitation process, and the function mechanisms of different additives. An effective combination of anti-scaling agents could be identified using this methodology, and this product was used in a full-scale trial at a paper mill. What is even more important, the results could be verified using real process waters from a mechanical pulp mill. A strong interaction between the calcium oxalate precipitation and dissolved and colloidal substances present in pulp was also shown.