Utilização de adsorventes argilominerais visando redução de dureza como alternativa de pré- tratamento ao uso da osmose reversa.

Abstract

The quantitative availability of groundwater in northeastern Brazil is usually quite restricted, and these waters are highly mineralized. These two factors are associated with numerous health, economic, social and environmental problems in the Brazilian semiarid region. In this context, the present research evaluated samples from five deep wells located in the Municipality of Caucaia - CE between the years 2018 and 2020. The physical-chemical quality data from the deep wells were submitted to principal component analysis (PCA). The waters of all evaluated wells have high levels of total hardness (TH > 300mgCaCO3/L) representing a potential risk of reduction in the useful life of the membranes of reverse osmosis desalinators installed in the locations. The water from the wells was classified as sodium chloride according to the Piper Diagram. The use of this type of water is associated with problems of corrosion, sodification and salinization soil due to the high levels of electrical conductivity (>2250 μS/cm) and Sodium Adsorption Ratio (RAS>26). Adsorption tests were carried out in order to evaluate the potential of natural clays (AS, AF, ATA, AVB and VLC) and with chemically activated clays with basic (NaOH), acid (HCl) and saline (NaCl) treatments aiming at the hard water softening. The results indicated that the natural Sodic (AS) and Ferric (AF) clays showed efficiency in the removal of total hardness (TH) a little over 40% in the adsorption tests with synthetic solution (1000mgCaCO3/L) while AS reached an efficiency removal rate of approximately 65% for the P1 deep well sample (TH = 533mgCaCO3/L). The experimental results for the Langmuir and Freundlich isotherms suggest that there is a reasonable fit of the isotherm models to the experimental data; Langmuir (r2=0.986 and Qe=29.03mg/g) and Freundlich (r2=0.946 and Qe=33.56mg/g). The acid treatment (HCl 1.0 mol/L) reduced the efficiency of all clays in removing the cations associated with total hardness. On the other hand, the saline treatment (NaCl 1.0 mol/L) did not promote a significant increase in the efficiency of clays in softening the water. Finally, AF and AS clays showed total hardness removal efficiencies of 79% and 88%, respectively, after chemical activation with 1.0mol/L NaOH. Therefore, the results of the adsorption tests suggest that the use of natural or chemically activated clays is an alternative in the pre- treatment of groundwater, aiming at increasing the useful life of reverse osmosis desalination membranes in order to enhance water supply and quality of treated wate