Characterization of verdete rock as a potential source of potassium

Abstract

RESUMOPotassium is a nutrient found at low levels in Brazilian soils, requiring large inputs of fertilizers to achieve satisfactory crop yields. Brazil has high external dependence and limited reserves of soluble K mineral, which is traditionally exploited for the production of fertilizers. On the other hand, it is common the occurrence in the country of potassium-rich silicate minerals which are not commercially exploited. This study aimed to characterize mineralogically and chemically samples of verdete rock separated into size fractions and evaluate its potential as potassium fertilizer. The mineral composition of verdete rock is based on glauconite, quartz and feldspar. The total K 2 O content in verdete rock ranged from 5.18 to 9.0 dag/kg. The K content extracted in water or 2% citric acid was 2.4% below the total of K, indicating low reactivity of verdete rock and limitations for direct use as K source. The processes of physical fractionation and sedimentation in water are inefficient to promote the concentration of K in the different verdete rock fractions. The total K content in some samples are considerable and may enable the use of this rock as raw material for production of more reactive potassium fertilizers. Caracterização do verdete como fonte potencial de potássioO K é um nutriente encontrado em baixos teores em solos brasileiros, sendo necessário grande aporte via fertilização para alcançar produtividades satisfatórias das culturas. O Brasil apresenta elevada dependência externa e possui limitadas reservas de minerais solúveis de K, tradicionalmente explorados para a produção de fertilizantes. Por outro lado, é comum a ocorrência no país de minerais silicatados ricos em K não explorados comercialmente. Neste trabalho, objetivou-se caracterizar mineralógica e quimicamente amostras de verdete, separadas em frações granulométricas e avaliar seu potencial de uso com fertilizante potássico.A composição mineral do verdete é à base de glauconita, quartzo e feldspatos. Os teores totais de K 2 O no verdete variaram de 5,18 a 9,0 dag/kg. O teor de K extraído em água ou em ácido cítrico a 2% foi inferior a 2,4% do K total, indicando baixa reatividade do verdete e limitações para seu uso direto como fonte de K. O fracionamento físico e a sedimentação em água são processos ineficientes para promover a concentração de K nas diferentes frações do verdete. Os teores totais de K em algumas amostras de verdete são consideráveis, podendo viabilizar o uso desta rocha como matéria prima para produção de fertilizantes potássicos mais reativos.Palavras-chave: glauconita, K, fertilizante.

Potassium extraction from the silicate rock Verdete using organic acids

“…Brazil has been depleting K reserves of potash ores of high solubility, such as sylvinite (KCl/NaCl mixture) and carnallite (KCl.MgCl 2 .6H 2 O) (DNPM, 2018). Nevertheless, there are large reserves of easily extractable K-silicate rock resources near the soil surface, such as Verdete rock, which contains around 10 % K 2 O and its reserves are estimated at 10 8 t (Luz et al, 2010;Safatle et al, 2020;Santos et al, 2015a). Since Brazilian deposits of soluble K sources supply less than 10 % of the demand for K, silicate rocks, such as Verdete rock, have been suggested as alternative K sources for agriculture (Luz et al, 2010;Santos et al, 2015a).…”

“…Nevertheless, there are large reserves of easily extractable K-silicate rock resources near the soil surface, such as Verdete rock, which contains around 10 % K 2 O and its reserves are estimated at 10 8 t (Luz et al, 2010;Safatle et al, 2020;Santos et al, 2015a). Since Brazilian deposits of soluble K sources supply less than 10 % of the demand for K, silicate rocks, such as Verdete rock, have been suggested as alternative K sources for agriculture (Luz et al, 2010;Santos et al, 2015a). However, due to the low solubility, these K-rich silicate rocks need physical, chemical, or biological treatment to make K available to plants in a short term (Ciceri et al, 2017;Matias et al, 2019;Santos et al, 2015b).…”

Nutrient availability in phosphate and potassic rocks induced by Acidithiobacillus oxidizing bacteria to produce biofertilizers

“…Biotite, mineral of the mica group is common in soils and igneous rocks comprise the original source of mica (Kämpf et al, 2009). More than 90% of the potassium soluble fertilizer used in Brazilian agriculture is purchased from the international companies, because the production does not satisfy the great demand (Barbosa Filho et al, 2007;Santos et al, 2015). Due to importance of soluble fertilizers for increasing plant yield, studies are needed to develop biofertilizers that can serve as alternatives for P and K sources (Duarte et al, 2012).…”

Grain-size mineral analysis of verdete rock coarse and fine aggregates and adjustment to two granulometric distribution models

“…Verdete is a greenish and banded rock, which has fine granulometry and clay matrix, and it is composed essentially by glauconite, quartz, and kaolinite minerals and potassium feldspars 15 . According to Santos et al 16 , the rock occurs in Serra da Saudade, Alto Paranaíba Region (MG), geologically located in the San Francisco Craton. The municipality of Cedro do Abaeté is known to have reasonable reserves of verdete (57.4 million tons) 17 .…”