Thermal and chemical solubilization of verdete for use as potassium fertilizer

• An alternative non-conventional source of K was evaluated by thermal and chemical treatments.
• The fluxing agents: LiCl, CaCl2.2H2O and Na2CO3 were most efficient in the release of K from verdete.
• Solubilization of K from verdete was greater in an alkaline medium compared to an acidic medium.
• The heated treatments were most effective in releasing K from verdete whether in acid or alkaline media.

Thermal and chemical treatments were used to investigate the solubilization of potassium from verdete, a glauconitic rock. Fluxing agents were evaluated at distinct temperatures and proportions. Chemical dissolution of verdete was studied with increasing amounts of acids or bases at different temperatures and reaction times. In the calcination test, the presence of fluxing agents was critical to increasing the rock solubility, in addition to the effects of temperature and material ratios. The content of water-soluble K was 100, 100, 85, and 42% when using the salts LiCl, CaCl2.2H2O, Na2CO3, NaCl, respectively, as fluxing agents. The salts CaSO4, CaCO3 and Ca3(PO4)2 were ineffective as fluxing agents. In the chemical treatments, the reaction with the base NaOH was more efficient than the acids to solubilize K. It was possible to solubilize up to 60% of K from verdete with 4.0 mol L− 1 NaOH, at 150 °C for 120 min. Among the acids, H3PO4 was the most efficient, promoting solubilization of up to 42% K, with 4.0 mol L− 1 H3PO4, at 225 °C, for 120 min. When using the concentrated acid waste and shaking for 144 h, up to 75% of K could be solubilized from the rock. It was concluded that the heated treatments were most effective in solubilizing verdete, followed by the acid waste, which are processes required for the production of soluble potassium fertilizers from unconventional sources of low reactivity.