Candiota city, in the south of Brazil, is located near the largest reserves of mineral coal of the country. This coal is used for thermoelectric power generation. The extraction of coal from open-cut mines involves operations may generate at least some particulate matter into the atmosphere. These particles retained on the surface of metallic structures exposed to the atmosphere, may adsorb gases such as CO, CO2, SO2 and NO, which, in combination with humid air form corrosive substances, such as HNO3 and H2SO4. This paper aims to evaluate the influence of Candiota coal on the corrosion of buried steel structures and exposed to atmosphere containing particulate matter from coal combustion. The coal sample was characterized by SEM (scanning electron microscopy), thermogravimetric analysis (TGA), surface area analysis (BET method), electrical conductivity (EC) analysis, FTIR and Raman spectroscopy. Corrosion was simulated by exposure of steel samples to coal particles and thermoelectric industrial atmosphere. Electrochemical tests of solutions leached from the coal were conducted by voltammetry to evaluate the soluble compounds corrosiveness. The corrosion rate was determining following the technical standard ASTM G1-90. Localized attacks and corrosion products formations were detected in API 5L Grade B steel exposure to coal. The average corrosion rate for the samples in direct contact to the pulverized coal was 0.15 mm/year, while in samples exposed to the atmosphere from industrial power plant was 0.30 mm/year. It is concluded that API 5L Grade B steel metal structures, exposed to atmospheres rich in Candiota coal and its derivatives, must be properly protected and monitored to avoid future damage caused by corrosion.
Olive leaf is a residue in olive oil and fruits production, which is considered with bioactive potential due to the high antioxidant activity attributed mainly to the phenolic compounds. The research aimed to investigate the Brazilian olive leaf drying, and also study its influence on the bioactive potential of the leaf. The desorption isotherms of olive leaves were determined and experimental curves were fitted to GAB, BET and Peleg models. Convective drying in a fixed bed dryer was used in different conditions of air temperature (50 ºC and 70 ºC) and air speed (0.9 m s-1 and 1.5 m s-1). Drying curves were obtained for each experimental test. The bioactive potential was reflected in the determination of total phenolic content, antioxidant activity and color parameters. Among the moisture equilibrium predictions between the GAB, BET and Peleg models, the first showed a better predictable capability. The results showed that in the drying operation, the increase in air temperature and speed influenced the increase in the drying rate and the reduction of time. The values of the effective diffusivity of the olive leaves varied between 2.61 x 10- 9 m2 s-1 and 10.12 x 10-9 m2 s-1. The samples dried until 10% of moisture (wet-basis) showed a good antioxidant activity, higher than 85%, and maintenance of the phenolic compounds regarding the fresh leaves around 70%. Bleaching and yellowing of leaves after drying were observed for all studied conditions and a decrease in green color at 70 ºC and 1.5 m s-1, in this condition the L*a*b* color parameters were 35.39, -5.00 and 42.66, respectively. This study demonstrated that the proper drying condition was at 70 ºC and 1.5 m s-1 for olive leaf drying and these conditions were important to maintain the original characteristics of the leaves and to spend less time in operation. Thus, this paper describe a viable drying process to take advantage of the olive leaf for the benefit of the environment and human health.
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