Modelisation of fluoride removal in Donnan dialysis

Excess or lack of levels of fluoride in drinking water being harmful to the human health, the concentration of F− ions must be maintained in the range 0.5–1.5 mg l−1. Donnan dialysis (DD) using as driving force a concentration gradient is an effective and simple technique for fluoride removal. The purpose of the present study is to apply a mathematical treatment to DD results obtained with NaF synthetic solutions. In the proposed model, the exchange phenomena were described by an equation of exchange kinetics at the membrane–solution interface. The selectivity coefficient of the anion exchange membrane and the rate constant of the exchange reaction used in the mathematical treatment were determined from kinetics measurements. The concentration profiles in the feed compartment were plotted. The simulated values for the fluoride concentrations at the outlet of the dialyzer agree well with the experimental results and show that the modelisation based on a simple mathematical model could be used to predict the dimension of DD pilot.