An accurate calculation model for Na+ concentration in seawater desalination solution

Based on the Nernst equation, the relationship between the electromotive force (EMF) of NaCl (denoted as Esw) and the concentration of sodium ion (denoted as c(Na+)swcNa+sw) in seawater desalination solution was derived as follow: Esw=E0+Slg((γsw±NaCl)2c(Na+)swc(Cl-)sw)Esw=E0+Slgγsw±NaCl2cNa+swcCl-sw. The value of the standard EMF (E0) and the parameter S can be obtained with the binary system of NaCl–H2O by correcting electrode. The activity coefficient of NaCl in seawater desalination solution (denoted as γsw±NaClγsw±NaCl) was calculated by the simplified Pitzer equation, and shown good agreement with the experimental result. Through this model, the functional relationship between c(Na+)swcNa+sw and Esw can be obtained once the functional relationship between γsw±NaClγsw±NaCl and c(Na+)swcNa+sw is regressed and E0, S are available. Compared with the direct potentiometry method, this model can provide wider measuring range including linear and nonlinear parts and higher accuracy whose deviation is 1.37%, as well as no need for standard buffer solution.

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► A model is proposed for determination of c(Na+) in seawater desalination solution.
► Activity coefficient is considered in the model.
► The model provides wider measuring range, higher accuracy, and no buffer solution.