The adsorptive removal of azo dye molecules from textile effluents by the powdered mineral hematite has been largely studied in the literature, but this mechanism of interaction with the mineral hematite surface is still to date not revealed, hence the need for a theoretical study. The crystal structure model of Hematite adopted is α − Fe2O3 (111). The DFT method and MDs(Molecular Dynamics simulations) have been employed to elucidate the mechanism of interaction. The azo-dye molecule chosen for this study is the reactive red RR141. Geometry minimization of RR141 was performed at the DFT / B3LYP / 6 −31+ +g(d,p) level of theory. The reactivity and performance of RR141-vacuum and RR141-aqueous media in isolated state were evaluated on basis of their planarity, global and local electronic properties as well as deformation ability to adhesion to the mineral surface. The Azo (> N− −N <) and hydroxyl (-O--H) groups are the main active centers for the adsorption of RR141 in a vacuum and aqueous media. Azo and hydroxyl groups of RR141 dye are electron donors, while the sulphonic acid (-SO3--Na+) group is an electron acceptor. The RR141 is found more reactive in the vacuum than in an aqueous medium. The interfacial interaction is the combined effect of the hydrogen bond and the interactions between Fe & −O−, C, −S−,= N− atoms. The whole system is interacting on the first layer through (π-π)-bonds in the nearly parallel adsorption geometries and through the single pair electrons of the heteroatoms.

The assessment of major elements and stable isotopes of groundwater in the Laayoune-Dakhla region was carried out in order to determine the various geochemical processes that contribute to the mineralization of these waters. A total of 30 groundwater samples were collected from wells in the Laayoune-Dakhla region (southern Sahara, Morocco). Using a hydrogeochemical assessment technique, this study will look at the general conditions of groundwater for drinking reasons. The statistical results of the major cations (Na+, Ca2+, Mg2+, K+) of the major anions (Cl−, SO42−, HCO3−, NO3−), show that the abundant cations and anions are of the order of Na+ > Ca2+ > Mg2+ > K+ and Cl− > SO42− > HCO3− > NO3−, respectively. The EC value of the water in the study area ranges from 1290 to 6895 µS/cm with an average of 3341.53 µS/cm. The pH value of the water samples is between 6.88 and 7.75. The waters of the study area were determined to be hydrogeochemical facies Na-Cl (86.66%) and Ca-SO4 (13.33). Their chemistry seems to be mainly controlled by sulphate, calcium, chloride and sodium and is explained by the dissolution of the evaporative formations characteristic of the Saharan regions. Ionic reports show that rock weathering and mineral dissolution and evaporation control the chemical evolution of groundwater. In addition, a good correlation between calcium and sulphate suggests leaching of gypsum and anhydrite. The values of δ18O vary from − 6.96 to -8.93‰ while those of δ2H vary between − 51.5 and − 65.56‰. The presence of evaporation was confirmed by stable isotope levels (δ18O, δ2H). The variation in oxygene-18 levels can be interpreted in terms of the difference in altitude between the recharge altitudes.