Syntheses and high temperature phase transformations of alunite-Natroalunite solid solution series.

KAWANO Motoharu, SHIMODA Susumu, TOMITA Katsutoshi

doi:10.2465/gkk1952.20.13

The alunite-natroalunite solid solution series were synthesized by precipitation from mixed solutions of K₂SO₄, Na₂SO₄, and Al₂ (SO₄)₃ for 2 days' reaction at boiling temperature. The K ions in the initial solution were preferentially taken into structure during crystallization of the alunite, and amounts of products formed in this reaction decreased with decreasing K mol% of the solution. The calculated structural formulae on the basis of SO₄=2 indicate that the synthetic alunites contain H₃O ions in the A sites, which increased from 11 to 19 mol% with decreasing K mol%. In addition, the slight deficiency of Al ions suggests the presence of vacancies in the B sites. Structural changes of alunites were observed by the thermal treatment. At 530°C, formation of KAl (SO₂)₂ from alunite and Al₂ (SO₄)₃ from natroalunite occurred simultaneously with the removal of OH ions. Removal of SO₄ ions from the dehydroxylated phases led to formation of amorphous phases at about 803°C for alunite run and about 765°C for natroalunite run. The amorphous phases then recrystallized into K₂SO₄ and Al₂O₃ in the alunite run and Na₂SO₄ and Al₂O₃ in the natroalunite run. The thermal behavior suggests the existence of compositional immiscibility between alunite and natroalunite.

Syntheses and high temperature phase transformations of alunite-Natroalunite solid solution series.

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