Extension of the ionic strength range application

of Legrand and Poirier model


M. A. Ben Farh, Ch. Hannachi, B. Hamrouni*

UR Dessalement et Traitement des Eaux, Faculté des sciences de Tunis, 2092 Manar II, Tunisia,

* Corresponding author. E-mail: bhamrouni@gmail.com

Received: 03 February 2012; revised version accepted: 22 July 2012



     Aggressiveness and scaling cause decrease in performances and deterioration of installations. The model of Legrand and Poirier allows the study of the calco-carbonic system in natural waters having low salinities. This model allows the determination of both the water character and the treatment bringing water to equilibrium. Despite its advantages Legrand and Poirier model is unreliable for waters having high ionic strengths. The objective of this study is the extension of the ionic strength range application of Legrand and Poirier model. A thermodynamic model taking into account the formation of ion pairs is then developed. The model is embodied in a computer program. Characters of water samples was studied and determined with this model at different temperatures from 10 to 40°C and 0 to 1 mol L-1. Moreover it permits the determination of the amount of calcium hydroxide necessary to bring water to calco-carbonic equilibrium. Our results shows also the efficiency of determining the amount of sodium hydroxide necessary to bring water to equilibrium in the range of 0 to 1 mol L-1 when temperature is between 10 to 25°C and 0 to 0.260 mol L-1 at 40°C.


Keywords: Calco-carbonic equilibrium; Legrand and Poirier model; Ionic strength; Calcium hydroxide; Sodium hydroxide.



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