Fluoride aided potassium extraction from Verdete rock by thermal processing with ferrous sulfate heptahydrate. / Extração de potássio auxiliada por flúor da rocha de Verdete por processamento térmico com sulfato ferroso hepta-hidratado

• Autor(a) principal: Pereira, Antônio Clareti
• Data de Publicação: 2019
• Outros Autores: Becheleni, Emily Mayer de Andrade, Gomes, Marta Ribeiro dos Santos, Rocha, Sônia Denise Ferreira
• Tipo de documento: Artigo
• Idioma: por
• Título da fonte: Brazilian Applied Science Review
• Texto Completo: https://ojs.brazilianjournals.com.br/ojs/index.php/BASR/article/view/1565
• topic: fertilizer; potassium; fluoride; glauconite; ferrous sulfate.

Glauconite is a green-colored monoclinic mineral with hydrated phyllosilicate of potassium and iron. It has low resistance to weathering and is usually found in sandstones and shales, as well as in marls and impure limestones. It is a secondary mineral formed from the modification of iron-rich micas, such as biotite. Even though it is an alternative source of potassium, it is still not extracted commercially on a large scale due to the lack of commercial technology that makes the business viable economically.Ferrous sulfate heptahydrate is a residue or by-product formed during the pickling of iron and steel and also in the manufacture of titanium dioxide from the ilmenite.Iron, as a raw material for the production of reagents, is abundant in the tailings of this metal.The use of ferrous sulfate as a sulfating agent has the advantage of being more selective and less aggressive during processing, in addition to the property of being thermosensitive.Fluorine accelerates this sulfation process due to an ionic substitution action on the structure of glauconite and on compounds that prevent the reaction, such as calcium sulfate.This work has investigated the release of potassium by dissolution in a 2% (w/w)citric acid solution in water, after previous thermal and chemical processing of glauconite rock (10% K2O) from Cedro doAbaeté - MG - Brazil with ferrous sulfate heptahydrate and NaF in the ratio (1.00: 0.70: 0.01), respectively.Potassium soluble in citric acid and not soluble in water characterizes a slow acting fertilizer.Thermal processing was performed at temperatures of 500°C and 700°C for 6h in a fluidized bed oven.The selection of ferrous sulphate was based on a thermodynamic evaluation of the system.The results showed that the thermal processing of the rock and ferrous sulfate mixture alone was not effective for the release of potassium in aqueous solution and in citric acid.The extraction of potassium from raw rock in citric acid was 7%.The mixture of rock and ferrous sulfate, without fluoride, in citric acid had an extraction rate of 6.8%.However, the same mixture with addition of 29ppm of fluorine had different results, in water (20% at 700°C) and mainly in citric acid (52.1% at 700°C), increasing the availability of potassium in more than 7 times when compared to the availability of rock potassium in natura.This study confirms that the combined effects of fluorine and temperature of thermal processing increase the release of potassium from glauconite.