Análise de especiação química de cromo em fertilizantes orgânicos

Abstract

Tannery waste is constituted of organic materials of animal origin mixed with inorganic salts. Among them, nutrients that are essential to plants and microorganisms, such as nitrogen, calcium, sulfur, phosphorus, magnesium and potassium, enabling their use as fertilizers, as well as their reuse. Although, chromium salts are largely applied in leather tanning, making monitoring its concentrations in fertilizers indispensable. Chrome can be found in various stages of oxidation, with its to most stable species being Cr(III) and Cr(VI). They significantly differ by their biological and chemical action, highlighting that Cr(III) is essential to humans, while Cr(VI) is toxic. For that reason, Ministry of Agriculture, Livestock and Supply (MAPA) defined its maximum level as 2 mg kg-1. Many speciation analytical techniques are described in literature, among them are determination by electroanalytical methods, atomic spectrometry, such as liquid chromatography associated with inductively coupled plasma mass spectrometry LCICP-MS, and spectrophotometric determination. Spectrometry is the most used because of its low cost, robustness, and large scale usage. Thus, this research had as its objective the development of a chrome speciation method by visible (VIS) spectrometry, based in the NaOH/Na2CO3 alkaline extraction, described in the United States Environmental Protection Agency (EPA) 3060a method, activated charcoal sample stratum clean up. The method analytical characteristics were stablished, which comply with MAPA’s Cr(VI) maximum level. Between the analyzed samples, only one of the fertilizers complies with the defined limit. Thereby, the method shows itself to be efficient, robust, and low cost.