RESUMO A caracterização geoquímica de águas salinas em reservatórios localizados em regiões semiáridas é uma questão importante a ser abordada, pois permite compreender a deterioração da qualidade da água causada pela evaporação. Neste estudo, o diagrama de Gibbs, razões iônicas e modelagem geoquímica foram empregados para decifrar os processos geoquímicos que afetam a evolução química da água de três reservatórios salinos localizados no semiárido do estado de Sergipe, Nordeste do Brasil. Os principais processos geoquímicos envolvidos na composição química da água dos reservatórios foram a dissolução do sal marinho, intemperismo dos silicatos, troca iônica, com uma contribuição limitada da dissolução de carbonatos. A modelagem geoquímica confirmou que a evaporação-cristalização é o principal mecanismo que controla a composição química da água, levando ao aumento das concentrações de Na+, Mg2+, Ca2+ e Cl-, e redução do HCO3- pela precipitação de calcita e dolomita. Além disso, os modelos simulados reproduziram a tendência observada nos dados hidroquímicos reais e indicaram excelente concordância entre as concentrações iônicas simuladas e as concentrações iônicas reais, para a maioria dos íons maiores. O maior desvio foi observado para o HCO3-, cujas concentrações reais foram muito mais elevadas que as previstas pela modelagem e isso tem sido atribuído a restrições cinéticas na precipitação da calcita.

ABSTRACT The geochemical characterization of saline water in reservoirs located in semi-arid regions is an important issue to be addressed, as it allows us to understand the deterioration of water quality caused by evaporation. In this study, the Gibbs diagram, ionic ratios and geochemical modeling were employed to decipher the geochemical processes that affect the chemical water evolution of three saline reservoirs located in the semi-arid region of Sergipe state, Northeastern Brazil. The reservoirs geochemical processes mainly include sea salt dissolution, silicate weathering, ion exchange, with a limited contribution from the dissolution of carbonates. Geochemical modeling confirmed that evaporation-crystallization is the main mechanism that controls the chemical composition of water, leading to increased concentrations of Na+, Mg2+, Ca2+ and Cl-, and reduction of HCO3- by precipitation of calcite and dolomite. Furthermore, the simulated models reproduced the trend observed in the real hydrochemical data and indicated excellent agreement between the simulated ion concentrations and the real ion concentrations for most of the larger ions. The highest deviation was observed for HCO3 whose actual concentrations were much higher than those predicted by the modeling, attributed to kinetic restrictions concerning calcite precipitation.

The organic matter (OM) contained in a natural aquatic environment, located in a tropical region in Notheastern Brazil, was characterized using synchronous fluorescence spectroscopy and UV-Vis absorbance. The synchronous fluorescence spectra did not show qualitative differences for samples collected during dry and rainy seasons. They also revealed two peaks, one at 390 nm and other at 460 nm, associated with humic substances. The lack of peaks with significant fluorescence intensity at 270 - 300 nm and at 320 - 370 nm confirms it is an environment with natural OM. The A254/A436 ratios obtained during the dry and rainy seasons (13.55 to 14.97) indicate the presence of allochthonous OM of terrestrial origin, with high level of aromatic carbon associated with humic substances. The OM photodegradation by natural sunlight was more pronounced in the first five days, with a decrease of FImax from 23.6 to 55.4%. Also, titration with Cu(II) ions was used to determine the complexation ability of the two fluorescent sites, obtaining log K values of 4.26 and 4.27.

ABSTRACT Oil is an important source of energy, mainly in developing countries. Important research has been conducted to find cementing procedures that guarantee safe and cost-effective oil exploration below pre-salt layers. This work aimed to make a new cement paste with cement, seawater, silica, biopolymers (chitosan and sodium alginate) and hydroxyapatite (HA), found in nature. For comparison purposes, slurry without additives was prepared and characterized. The HA used was extracted from fish scales (Cynoscion acoupa) in optimized condition NaOH concentration, temperature and reaction time. Both slurry were prepared with ratios water/cement (w/c) and silica/cement (s/c) equal to 0.50 and 0.35, respectively. The new cement slurry was obtained with proportions of 5% of each biopolymer and HA with respect to the total weight of the cement. In the immersion tests, specimens were immersed in samples of hyper production of saline water by 35°C for 15 days. Thereafter, they were washed, dried and its surface layers were scraped. Before, the resulting materials were characterized. The values of the ratios Ca/Si of new cement slurry (3.38 ± 0.06) were superior compared to standard (2.58 ± 0.05). The new slurry had high thermal stability and low amounts of small crystallite-type portlandite (35.70 nm). Conversely, a slurry standard formed larger crystals of about 50.3 nm. Significantly, after continuous long-term contact of both slurries with hyper-saline produced water from oil well fields operations, in comparison with standard slurry structural characteristics, the new slurry has practically maintained its pristine chemical structure, as well as has shown crystallite-type particles of NaCl and Friedel's/Kuzel's salts with lower proportion. The presence of the biopolymers and HA has driven the improved the self-healing properties observed in the new cement slurry. In this first study, the new slurry has shown adequate characteristics to contribute to cost effective and environmental-friendly oil well operations.

Surface sediments from the River São Francisco were analyzed to investigate the impact, due to the presence of metals (Cd, Cu, Pb, Zn) in wastes from a metallurgical industry in the city of Três Marias/MG, Brazil. The concentrations and geochemical associations of Pb, Zn and trace metals associated with the minerals employed in zinc production were measured. Sediments close to discharge locations were highly contaminated with Pb (332-512 μg g-1) and Zn (7872-10780 μg g-1), with values decreasing rapidly due to dilution and hydraulic sorting. Evaluation of toxicity according to the Consensus-based Sediment Quality Guidelines indicated for Cd, Pb and Zn a high probability of adverse effects on aquatic biota at these sites.