Detecção de ferro em água por imagem digital com dispositivo portátil

Abstract

Iron is the fourth most abundant element in the Earth's crust and can be found in soils, streams, and groundwater. It occurs in minerals such as hematite, magnetite, taconite, and pyrite, and is widely used in steel and alloys. In water bodies, its presence originates from rock dissolution; however, anthropogenic interferences can increase iron levels in surface waters, making them unsuitable for more noble uses. Water bodies suffer from iron contamination mainly due to human activities, especially those located near mining areas. With a focus on monitoring iron content, this work aims to develop a low-cost, portable mobile colorimetric device integrated with a smartphone, capable of performing iron measurements in mg/L. After constructing the device, colorimetric calibration was carried out using the adapted method by Paiva et al. (2012). The calibration curve was prepared with the following soluble iron concentrations: 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, and 8 mg/L, all in duplicates, showing a reddish-orange color with a gradient from lighter to darker shades. The absorption inherent to concentration was measured by spectrometry and subsequently recorded as images using the rear camera of a smartphone, positioned inside the compartment of the portable device, 3D printed to block external light interference, using only the smartphone’s flash as the light source. These colors can be numerically represented through the RGB (Red, Green, Blue) system, in which the primary colors (red, green, and blue) create secondary colors defined on a scale from 0 to 255 for each. To determine the RGB numerical value, a mobile application was used to analyze each photograph, identify the colors present, and convert them to grayscale, allowing comparison of the obtained values with the absorbance corresponding to each concentration. It is expected that the modifications made will be sufficient to yield improved results for determining iron content in water from images, as the setup contains fewer interferences from the compartment and the cuvette holding the sample.