Chemical interaction between industrial acid effluents and the hydrous medium

Several industrial effluents are acid and contain numerous chemical ions like fluorides and some heavy metals (Cd, Pb, etc.). These solutions are harmful to the receiving medium according to the Tunisian norm N.T.106 002. In this work, we examined the interaction between an industrial effluent and a hydrous medium. This interaction is predominantly an acid-base reaction type; this is due to the acid character of the industrial effluent and the slightly basic character of the natural solution (groundwater and seawater). We have, in particular, studied the concentration evolution of two elements (Cd2+ and F−) according to the pH in the range of 2.5-6. Especially, we highlight the formation of a solid precipitate during this interaction. The chemical analysis followed by the X-ray diffraction showed that the precipitated solid phase was CaF2. Two advantages of the formed precipitate are to be mentioned, firstly it contributes to the decrease of F− rate and secondly to the retention of part of Cd2+ initially existing in the industrial effluent. The optimal experimental conditions of decreasing these two ions have been determined for each of the studied waters. We established in particular that the formed solid phase may constitute a barrier against the diffusion of Cd2+ in the hydrous medium.