A SOLUBILITY AND THERMODYNAMIC STUDY OF STRUVITE

Accumulation of magnesium ammonium phosphate hexahydrate (struvite) on surfaces in contact with wastewater, especially in anaerobic sludge digestion and post-digestion processes, is a widely reported problem in the wastewater treatment industry. The solubility and thermodynamic properties of struvit...

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Bibliographic Details
Published in:Environmental technology 2007-09, Vol.28 (9), p.1015-1026
Main Authors: Bhuiyan, M. I. H., Mavinic, D. S., Beckie, R. D.
Format: Article
Language:English
Subjects:
Anaerobic treatment
Applied sciences
ENTHALPY
Exact sciences and technology
Exact solutions
General purification processes
IONIC STRENGTH
Magnesium
Magnesium Compounds - chemistry
Mathematical models
Osmolar Concentration
Phosphates - chemistry
Pollution
Sodium Chloride - chemistry
SOLUBILITY
Strength
STRUVITE
TEMPERATURE
Thermodynamics
Waste water
Wastewaters
Water treatment and pollution
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Summary:Accumulation of magnesium ammonium phosphate hexahydrate (struvite) on surfaces in contact with wastewater, especially in anaerobic sludge digestion and post-digestion processes, is a widely reported problem in the wastewater treatment industry. The solubility and thermodynamic properties of struvite at different temperatures was studied. Struvite thermodynamic solubility products at temperatures between 10 and 60 °C were determined by variation of solution ionic strength and extrapolation to zero ionic strength, using an appropriate activity coefficient model. The pK sp value of struvite at 25°C was found to be 13.36(±0.07). The pKsp value for a temperature range of 10-60 °C varies from 14.36(±0.05) to 14.01(±0.03) with the minimum value of 13.17(±0.05) at 30°C. The effect of ionic strength, pH and temperature on struvite solubility was also studied. The solubility of struvite determined in deionized water was found to be 169.2 (±4.3) mg l -1 at 25°C, with the maximum value of 212.7 (±3.8) mg l -1 at 35°C. Standard enthalpy of reaction, ΔH γ °, calculated from the average K sp values for the temperature range of 10-30 °C, was 23.62 Kcal mol -1 . An analytical expression for the K sp as a function of temperature has been developed by fitting experimental data.
ISSN:0959-3330
1479-487X
DOI:10.1080/09593332808618857