Desenvolvimento de procedimento analítico para a caracterização de resíduos eletrônicos
Bezana, Thiago Berti
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In the production of printed circuit boards large amounts of base and precious metals with high purity are used in their composition. The growing generation of electronic waste together with the scarcity of mineral resources around the world demand the development of technologies that allow minimizing the environmental impact caused by the disposal of these wastes as well as the extraction of mineral resources from nature. In this context an analytical procedure was developed for elemental analysis of silver, gold and copper. Sample preparation includes steps of grinding, homogenization and representative sampling, followed by microwave-assisted acid digestion. Silver, gold and copper, were determined by inductively coupled plasma optical emission spectrometry (ICP OES). Grinding tests of samples indicated as the best alternatives to obtain particles with particle sizes smaller than 0.150 mm, a combination between cryogenic mill, ideal for sample fractions with high amount of polymers and resins, and vibrating cup mill, used for sample fractions with high amounts of metals. The techniques of homogenization by conical stacks and division by pyramidal longitudinal stacks were efficient to obtain representative samples. This technique allowed representative samples to be obtained by taking into account standard deviations 6-fold lower for Au concentrations. After microwave-assisted acid digestion, analytes were determined by ICP OES. A complete 33 factorial design was carried out to evaluate effects of the following variables: sample mass, acid mixture and heating program. The experimental conditions that led to the best results based on the efficiency of the digestion procedure focused on the target metals was the use of 10 mL of aqua regia, 750 mg of sample and heating at 230 °C with ramp of 8 min and plateau during 30 min. ICP OES was efficient for determination of Ag, Au and Cu in e-wastes. Palladium determination was affected by spectral interferences caused by Fe and Ar for the two most intenses emission lines. The developed analytical procedure was adequate and complied with the demand of the project. The limits of detection of the developed procedure were: Ag – 0.0035 mg kg-1, Au – 0.0288 mg kg-1 and Cu – 0.0017 mg kg-1, and the concentration ranges obtained to printed circuit boards of desktop computers e-waste were: Ag - 290 mg kg-1 ; Au - 90 mg kg-1 and Cu - 18%.