Potassium recovery from Brazilian glauconitic siltstone by hydrothermal treatments

Abstract

Silicate rock Verdete, collected in the central region of Minas Gerais state (Brazil) and composed mostly of micas (glauconite and muscovite) and tectosilicates (Kfeldspar and quartz), was hydrothermally treated with several reactants in order to release and recover potassium. The hydrothermal products were characterized by flame photometry, XRD, XRF, SEM and EDS. Treatment with sulfuric acid was effective to break the crystal lattice of micas before 1 h of reaction and recovered 24% of potassium in the form of sulfates. The K-feldspar appears to have remained intact during the process. Treatment with a Ca(OH) 2 (86 wt.%)-CaCO 3 (14 wt.%) mixture did not consume the micas, but K-feldspar was gradually consumed over the 24 h reaction period. The K recovery was probably due to a concurrent hydrolytic framework dissolution of K-feldspar mediated by OH − ions and by the exchange of K + with Ca 2+. The K-bearing species are carbonaceous materials with variable K + /Ca 2+ ratios, such as K 2 Ca(CO 3) 2 .

Potassium extraction from the silicate rock Verdete using organic acids

“…Verdete samples were collected from a rock outcrop on the border between the municipalities of Quartel Geral and Serra da Saudade, in Minas Gerais State, Brazil (19°17'59.0" S, 45°44'16.9" W, altitude of 842 m) (Figure 1). Previous works have characterized Verdete as a sedimentary rock composed mainly by glauconite (40-80 %), whose origin may be related to marine transgression, resulting in diagenetic substitution with K + into clay minerals (Moreira et al, 2016;Safatle et al, 2020).…”

“…The chemical composition of Verdete rock (Table 1) was previously determined by X-ray fluorescence (XRF) (Schimicoscki et al, 2020). Mineralogical characterization by X-ray diffraction (XRD) indicated that Verdete rock is composed mainly by aluminosilicates, with typical diffraction peaks of K feldspar, mica (muscovite and glauconite), and quartz (Safatle et al, 2020…”

“…Most XRD lines for glauconite overlapped those of muscovite. However, the greenish color and softness, due to a laminar structural organization, indicate that the rock was also composed of glauconite (Safatle et al, 2020). XRD peaks at 20.7° and 26.5° (q) demonstrated the presence of quartz.…”

“…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).…”

Feasibility of concentrating potassium minerals from Verdete ore by cell flotation

“…Mass compositions were determined by Wavelength Dispersive X-Ray Fluorescence spectrometry (WDXRF) on a Bruker S8 Tiger equipment, as previously described by Safatle et al (2020). Prior to characterization, samples were macerated and sieved in a 200-mesh sieve.…”