Défluoruration des eaux de boisson du sud algérien par adsorption et filtration.

Abstract

The objective of this work is defluoridation study of drinking water in southern Algeria by, two techniques, adsorption by local clay of the Tabalbala region in Béchar provenice, which can be used for the production of small water quantities at the domestic scale and membrane filtration for larger needs (urban populations) at industrial scale using the reverse osmosis membrane in demineralisation station of Tindouf city. At first, Tindouf groundwater quality was studied. The results show that fluoride ions concentration in groundwater varies between 0.16 and 3.31 mg / L. In addition, groundwater is characterized by the presence of three hydrochemical facies (sodiumpotassium, sodium-chloride and bicarbonate-calcium) according to the Piper diagram. Chemical quality of the water is poor, resulting from high salinity influenced water aquifer lithology, climatic factors (evaporation) and anthropogenic factors (urban discharges). Clay was characterized by various methods such as infrared spectroscopy (FTIR), the X-ray diffraction (XRD), the X fluorecence and determination of physicochemical analysis pHZCP, CEC and specific surface. Results show that kaolin clay nature has the chemical composition SiO2 (53.83%) and Al2O3 (39.81%). The pHZCP, CEC and specific surface area of this kaolin are equal to 6.4, 8 meq / 100g and 10, respectively. The batch adsorption shows that a greater elimination of fluoride was noted in the pH between 4.5 and 6 in a contact time of 120 min. Thermodynamic parameters (ΔH, ΔS and ΔG)of the floride ions indicate that the process is endothermic and proceeds spontaneously. Presence of nitrate and chloride ions did not influence the fluoride adsorption; while sulphates and carbonates decreased fluoride adsorption by kaolinite, showing that these ions could compete with each other. The kinetic and isotherm study shows that the process of fluoride adsorption follow the pseudosecond order model and Freundlich isotherm model. In study region, defluorination membrane process is reverse osmosis. Demineralising water is obtained at high retention rate for all the ions such as fluorine (98%) in order to better understand reverse osmosis membrane selectivity. The osmosis water is clearly below the criteria of potability of human water consumption on the physicochemical level, a re-mineralization is essential to obtain water respecting the norms.