Abstract

Although Brazil is one of the world's leading exporter of agricultural products, the country is highly dependent on the importation of potassic fertilizers. K-bearing silicate rocks are reported as potential solutions to reduce external K dependency. This work evaluated K extraction from silicate Verdete rock, a glauconite-bearing rock containing 10 % of K2O, by solubilization with organic acids. Firstly, Verdete rock was reacted during 3-120 h with solutions of citric or oxalic acid at 2 % (m/v) in Erlenmeyer flasks by shaking. Oxalic acid extracted 6.5 % of K in Verdete, while citric acid extracted 2.3 %. Another experiment was performed to evaluate the effect of various oxalic acid concentrations (2, 4, 6, 8, and 10 %) and differing reaction times (12, 24, 48, and 72 h) on K extraction from Verdete rock. Soluble K concentration nearly doubled with the increase of reaction time from 12 to 72 h, rising from 20 to 37 mg L–1. Increments in K extraction were obtained by increasing oxalic acid concentrations up to 6 % and above this concentration, no significant gain was observed. The X-ray diffraction data showed that K extraction resulted from the formation of oxalate-metal complexes with metals in Verdete rock.

Highlights

  • Potassium (K) is a critical nutrient for croplands worldwide

  • Oxalic acid extracted 6.5 % of K in Verdete, while citric acid extracted 2.3 %. Another experiment was performed to evaluate the effect of various oxalic acid concentrations (2, 4, 6, 8, and 10 %) and differing reaction times (12, 24, 48, and 72 h) on K extraction from Verdete rock

  • 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)

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Summary

Introduction

Potassium (K) is a critical nutrient for croplands worldwide. Brazil is considered a ‘global farm’ (Tollefson, 2010), most potash fertilizer applied in Brazilian agriculture is imported (ANDA, 2017). 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). Most of these treatments rely on high temperatures to achieve K solubilization (Ciceri and Allanore, 2020; Santos et al, 2015a), which is energetically unfavorable

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