Abstract: The extraction of potassium from a tablet mixture of K-feldspar ore and CaSO₄ by roasting was studied with a focus on the effects of the decomposition behavior of CaSO₄ on the potassium extraction process. The roasted slags were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and thermogravimetric (TG) analysis. The XRD analysis revealed that hydrosoluble mischcrystal K₂Ca₂(SO₄)₃ was obtained by ion exchange of Ca²⁺ in CaSO₄ and K⁺ in KAlSi₃O₈. Meanwhile, the intermediate product, SiO₂, separated from KAlSi₃O₈ and reacted with CaSO₄ to decompose CaSO₄. The SEM results showed that some blowholes emerged on the surface of the CaSO₄ particles when they reacted with SiO₂ at 1200℃, which indicates that SO₂ and O₂ gases were released from CaSO₄. The TG curves displayed that pure CaSO₄ could not be decomposed below 1200℃, while the mixture of K-feldspar ore and CaSO₄ began to lose weight at 1000℃. The extraction rate of potassium and decomposition rate of CaSO₄ were 62% and 44%, respectively, at a mass ratio of CaSO₄ to K-feldspar ore of 3:1, temperature of 1200℃, tablet-forming pressure of 6 MPa, and roasting time of 2 h. The decomposition of CaSO₄ reduced the potassium extraction rate; therefore, the required amount of CaSO₄ was more than the theoretical amount. However, excess CaSO₄ was also undesirable for the potassium extraction reaction because a massive amount of SO₂ and O₂ gas were derived from the decomposition of CaSO₄, which provided poor contact between the reactants. The SO₂ released from CaSO₄ decomposition can be effectively recycled.

Key words: K-feldspar, Calcium sulfate, Potassium extraction, Calcium sulfate decomposition, Roasting

摘要： The extraction of potassium from a tablet mixture of K-feldspar ore and CaSO₄ by roasting was studied with a focus on the effects of the decomposition behavior of CaSO₄ on the potassium extraction process. The roasted slags were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and thermogravimetric (TG) analysis. The XRD analysis revealed that hydrosoluble mischcrystal K₂Ca₂(SO₄)₃ was obtained by ion exchange of Ca²⁺ in CaSO₄ and K⁺ in KAlSi₃O₈. Meanwhile, the intermediate product, SiO₂, separated from KAlSi₃O₈ and reacted with CaSO₄ to decompose CaSO₄. The SEM results showed that some blowholes emerged on the surface of the CaSO₄ particles when they reacted with SiO₂ at 1200℃, which indicates that SO₂ and O₂ gases were released from CaSO₄. The TG curves displayed that pure CaSO₄ could not be decomposed below 1200℃, while the mixture of K-feldspar ore and CaSO₄ began to lose weight at 1000℃. The extraction rate of potassium and decomposition rate of CaSO₄ were 62% and 44%, respectively, at a mass ratio of CaSO₄ to K-feldspar ore of 3:1, temperature of 1200℃, tablet-forming pressure of 6 MPa, and roasting time of 2 h. The decomposition of CaSO₄ reduced the potassium extraction rate; therefore, the required amount of CaSO₄ was more than the theoretical amount. However, excess CaSO₄ was also undesirable for the potassium extraction reaction because a massive amount of SO₂ and O₂ gas were derived from the decomposition of CaSO₄, which provided poor contact between the reactants. The SO₂ released from CaSO₄ decomposition can be effectively recycled.

关键词: K-feldspar, Calcium sulfate, Potassium extraction, Calcium sulfate decomposition, Roasting