Análise da influência da introdução de resíduos de granito e mármore no desempenho de destiladores solares do tipo simétrico de dupla inclinação

Abstract

Due to the problematic caused by the scarcity of drinking water on the planet, solar distillation has been presented as a simple and non-polluting alternative for the production of potable water from sources contaminated by salts, sewage and pathogenic microorganisms. However, solar stills devices are characterized by a low efficiency performance in the production of potable water. Searching for alternatives in the development of more efficient solar stills, the present work aimed to analyze the influence of the concentration of mining waste from granite and marble on the performance of symmetric double slope solar distillers. Initially, the main properties of the rocks of the granite and marble were identified from the analysis of their mining waste/chips by means of Pycnometry, humidity measurement, Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), Thermogravimetry, Sedimentation/Sieving test, macroscopic petrographic description of the granite, and of the marble response to hydrochloric acid attack. For the evaluation of the effect of the mining waste on solar distillation, tests were performed in an eight-hour interval (8:00 am to 4:00 pm) using three distillers containing 300 mL of aqueous solution containing mineral rejects in the concentrations of 2, 4, 8, 12, 24 mg/mL, in which granite waste was added in the first distiller, marble in the second, and no residue in the third distiller, functioning as a control system. In the experiments, the water to be distilled was collected from an artesian well located on the campus of the Universidade Federal do Ceará (UFC) in Crateús. The evaluation of the potability of the distilled water was performed through laboratory tests of pH, electrical conductivity and color. According to the characterization tests, the granite waste used in the distillation experiments is a monzogranite with a density of 2.52 g/cm3, while the marble residue has a dolomitic character and density of 2.65 g/cm3. In both wastes, the particles are irregularly shaped, there was no significant mass variation in the temperature range of 23 to 498°C, the humidity was less than 1% and granulometry in the silt fraction (0.002 - 0.006 mm) presented with highest percentage. As for distillation, for all concentrations analyzed, the distillers that operated in the presence of the mining wastes were more efficient than the control system, with the distiller containing the granite waste being the most efficient of the three systems. Furthermore, the results revealed that the concentration with 8 mg/mL of mineral residues was the one that led to the maximum distillation performance, corresponding to 56.04% for granite and 52.73% for marble, which meant an increase of 26.20% and 22.89%, respectively, when compared to the control system. The results of the physical-chemical analysis of the water produced by the distillers presented values within the limits indicated by current health safety standards. In this perspective, it is evident that the use of granite and marble residues can be an alternative for the improvement of the solar stills in terms of the production of potable water, which makes solar distillation a possible solution for the adequate destination of wastes from the mining activity.