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Crystallization Fouling of the Aqueous Two-Component System CaSO4/CaCO3 Fouling of Salt Mixtures
Volker Hofling, Wolfgang Augustin and Matthias Bohnet

In the present study batch and continuous fouling experiments with the aqueous two component system CaSO4/CaCO3 were carried out, investigating especially the influence of pH-value on the fouling behaviour. The composition of the obtained fouling layers was analysed by x-ray diffraction and scanning electron microscopy (SEM). Further the strength of the crystalline deposits was determined in abrasion experiments. In the experiments a strong effect of the pH-value on crystallization fouling was observed. Lowest fouling tendency was seen for experiments at pH 7.0. At different pH-values the crystalline layers showed big differences in their macroscopic as well as in their microscopic structure. Below pH 6.0 only calcium sulphate was detected by x-ray diffraction. At higher pH values besides calcium sulphate also calcium carbonate was found in different modifications. The different layer composition leads to different strength of the layers. At the moment it is difficult to correlate the fouling behaviour clearly to the different experimental conditions.

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