Microwave Acid Extraction to Analyze K and Mg Reserves in the Clay Fraction of Soils

• Autor(a) principal: Batista,Araína Hulmann
• Data de Publicação: 2016
• Outros Autores: Melo,Vander Freitas, Gilkes,Robert
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Revista Brasileira de Ciência do Solo (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832016000100431
• topic: EPA 3051A; EPA 3052; aqua regia; boiling nitric acid; microwave extraction; nonexchangeable K

ABSTRACT: Extraction of K and Mg with boiling 1 mol L-1 HNO3 in an open system for predicting K and Mg uptake by plants is a method of low reproducibility. The aim of this study was to compare the extraction capacity of different acid methods relative to hydrofluoric acid extraction for K and Mg. A further objective was to develop a chemical extraction method using a closed system (microwave) for nonexchangeable and structural forms of these nutrients in order to replace the traditional method of extraction with boiling HNO3 on a hot plate (open system). The EPA 3051A method can be used to estimate the total content of K in the clay fraction of soils developed from carbonate and phyllite/mica schist rocks. In the clay fraction of soils developed from basalt, recoveries of K by the EPA 3051A (pseudo-total) method were higher than for the EPA 3052 (total hydrofluoric extraction) method. The relative abundance of K and Mg for soils in carbonate rocks, phyllite/mica schist, granite/gneiss, and basalt determined by aqua regia digestion is unreliable. The method using 1 mol L-1 HNO3 in an closed system (microwave) showed potential for replacing the classical method of extraction of nonexchangeable forms of K (boiling 1 mol L-1 HNO3 in an open system - hot plate) and reduced the loss of Si by volatilization.