CATEGORY: FOULING
Proceedings of International Conference on Heat
Exchanger Fouling and Cleaning, June 9-14, 2013, Budapest, Hungary
The
influence of phosphate on calcium carbonate formation in hard water
S. Noda (1), T. Saito1, K. Miya (1), S. Furukawa (1), S. M. Clarke
(2) and D. I. Wilson (3)
1 Advanced Technology R&D Center, Mitsubishi Electric Corp., Hyogo, Japan
2 BP Institute and Dept. of Chemistry, University of Cambridge, Cambridge, UK
3 Dept. of Chemical Engineering and Biotechnology, University of Cambridge,
Cambridge, UK
Abstract
Calcium carbonate fouling layers form when the concentration of scaling ions in
solution exceeds their solubility limit. Although small amounts of phosphate
ions are found in tap water in some parts of Europe, the effect of these
species on the kinetics and characteristics of calcium carbonate scale
generated from a supersaturated aqueous salt solution containing phosphate is
not reliably understood.
In
this study, a series of experiments using model solutions containing phosphate
were conducted to study the chemical characteristics of the scale formed. The results suggest that the time constant of
scale formation in solution at 65 C with 2.0 mg/L phosphate ions was about 17
times longer than that in solutions without phosphate. X-ray diffraction and
SEM/EDX analysis of the scale layers confirmed that deposits formed in the
presence of phosphate were calcite, containing trace amounts of phosphorous,
while those formed in the absence of phosphate were a mixture of aragonite and
calcite.
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