Surface Processes At The Membrane Scaling
SURFACE PROCESSES AT THE MEMBRANE SCALING
I. Atamanenko, A. Kryvoruchko, L. Yurlova, B. Kornilovich
Institute of Colloid Chemistry and Chemistry of Water, Ukrainian National Academy of Sciences, Vernadsky avenue 42, 03142 Kiev, Ukraine
The effect of inhibitor addition on the calcium sulphate crystallization process has been studied by the differential scanning calorimetry method (DSC). Starting from CaSO4 concentration of 1.7 g/l, alongside with the main peak corresponding to its homogeneous solution at a temperature of 270 K there appears one more water peak in the DSC thermograms. It is likely due to the crystalline phase formation of CaSO4. Appearance of nuclei of the CaSO4 crystals having the highly active surface affects the state of surrounding water. As a result, there arises the peak of the structured water at the temperature of 249 K.
The increase in CaSO4 concentration in its solution up to 4.4 g/l results in both the growth of water peak in the low-temperature range (249 K) and splitting of its main peak in the DSC thermograms. The former testifies to the increase in the nucleus amount of calcium sulphate. As for the latter, it may be due to the growth of CaSO4 crystals.
Carboxymethyl cellulose (CMC), polyacrylamide (PAA) and specific cation-exchange polyelectrolyte (termed hereafter as PE-1) have been taken as the inhibitors. Addition of any of them at the concentration of 5 ppm into the CaSO4 solution (4.4 g/l) leads only to disappearance in splitting of water peak at 270 K. In the DSC thermograms, there is the water peak in the low temperature range, and it is observed at the same temperature of 249 K. In the thermograms of all the solutions under study [CaCl2, Na2SO4 and all the inhibitors (CMC, PAA and PE-1)], there is only a single peak around 270 K, whereas the low temperature peak is absent. An increase in the concentration of inhibitors up to 75 ppm in the CaSO4 solution leads to decrease in the water peak two times at a temperature of 249 K.
Therefore, in the supersaturated CaSO4 solutions in the presence of inhibitors, appearance of the new phase comes only to pass, i.e., the nuclei of
CaSO4. The low temperature peak in the DSC thermograms testifies to that. An introduction into a solution of the different inhibitors (CMC, PAA, PE-1) is accompanied by their sorbtion onto the surface of CaSO4 nuclei, precluding their aggregation and growth. No peak splitting is observed at a temperature of 270 K.
Thus, the initial stages of CaSO4 crystal nucleation have been determined by use of the DSC method in the presence of inhibitors. Effectiveness in the inhibitor application to avert growth of the crystalline phase of CaSO4 is shown.
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