The effect of aluminium fluoride on the formation of calcium sulfate hydrates

Emile T.M.J. Martynowicz; Geert Jan Witkamp; Gerda M. Van Rosmalen

doi:10.1016/0304-386x(95)00066-p

The effect of aluminium fluoride on the formation of calcium sulfate hydrates

Emile T.M.J. Martynowicz, Geert Jan Witkamp^*, Gerda M. Van Rosmalen

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

28 Scopus citations

Abstract

Different phases, hydrates or polymorphs are often developed in mineral ore conversion processes where sparingly soluble salts are formed. Their development not only depends on the operating conditions but also on the specific composition of the ore. In this study the effect of aluminium fluoride, a constituent encountered in fluorapatite rock in varying concentrations, on the formation of calcium sulfate hydrates during phosphoric acid processing is presented. Solubility experiments and continuous crystallization experiments of calcium sulfate hemihydrate (CaSO₄ · 1/2H₂O, HH) and calcium sulfate dihydrate (CaSO₄ · 2H₂O, DH) were performed in concentrated phosphoric/sulfuric acid solutions at 75°C and 90°C in the presence of small amounts of aluminium fluoride or hydrogen fluoride. Both AlF₃ and HF increase the solubilities of HH and DH via their effect on the activity coefficients of calcium and sulfate. Aluminium fluoride retards the HH and DH growth rate and an AlF₃ concentration of 95 mmol (kg solution)^-1 increases the calcium sulfate concentration far above the DH solubility line. This leads to DH formation under conditions where normally HH is formed. The presence of aluminium fluoride also results in crystal habit modification and agglomeration of the HH and DH crystals formed.

Original language	English (US)
Pages (from-to)	171-186
Number of pages	16
Journal	Hydrometallurgy
Volume	41
Issue number	2-3
DOIs	https://doi.org/10.1016/0304-386x(95)00066-p
State	Published - Jun 1996
Externally published	Yes

ASJC Scopus subject areas

Industrial and Manufacturing Engineering
Metals and Alloys
Materials Chemistry

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title = "The effect of aluminium fluoride on the formation of calcium sulfate hydrates",

abstract = "Different phases, hydrates or polymorphs are often developed in mineral ore conversion processes where sparingly soluble salts are formed. Their development not only depends on the operating conditions but also on the specific composition of the ore. In this study the effect of aluminium fluoride, a constituent encountered in fluorapatite rock in varying concentrations, on the formation of calcium sulfate hydrates during phosphoric acid processing is presented. Solubility experiments and continuous crystallization experiments of calcium sulfate hemihydrate (CaSO4 · 1/2H2O, HH) and calcium sulfate dihydrate (CaSO4 · 2H2O, DH) were performed in concentrated phosphoric/sulfuric acid solutions at 75°C and 90°C in the presence of small amounts of aluminium fluoride or hydrogen fluoride. Both AlF3 and HF increase the solubilities of HH and DH via their effect on the activity coefficients of calcium and sulfate. Aluminium fluoride retards the HH and DH growth rate and an AlF3 concentration of 95 mmol (kg solution)-1 increases the calcium sulfate concentration far above the DH solubility line. This leads to DH formation under conditions where normally HH is formed. The presence of aluminium fluoride also results in crystal habit modification and agglomeration of the HH and DH crystals formed.",

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AU - Van Rosmalen, Gerda M.

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Y1 - 1996/6

N2 - Different phases, hydrates or polymorphs are often developed in mineral ore conversion processes where sparingly soluble salts are formed. Their development not only depends on the operating conditions but also on the specific composition of the ore. In this study the effect of aluminium fluoride, a constituent encountered in fluorapatite rock in varying concentrations, on the formation of calcium sulfate hydrates during phosphoric acid processing is presented. Solubility experiments and continuous crystallization experiments of calcium sulfate hemihydrate (CaSO4 · 1/2H2O, HH) and calcium sulfate dihydrate (CaSO4 · 2H2O, DH) were performed in concentrated phosphoric/sulfuric acid solutions at 75°C and 90°C in the presence of small amounts of aluminium fluoride or hydrogen fluoride. Both AlF3 and HF increase the solubilities of HH and DH via their effect on the activity coefficients of calcium and sulfate. Aluminium fluoride retards the HH and DH growth rate and an AlF3 concentration of 95 mmol (kg solution)-1 increases the calcium sulfate concentration far above the DH solubility line. This leads to DH formation under conditions where normally HH is formed. The presence of aluminium fluoride also results in crystal habit modification and agglomeration of the HH and DH crystals formed.

AB - Different phases, hydrates or polymorphs are often developed in mineral ore conversion processes where sparingly soluble salts are formed. Their development not only depends on the operating conditions but also on the specific composition of the ore. In this study the effect of aluminium fluoride, a constituent encountered in fluorapatite rock in varying concentrations, on the formation of calcium sulfate hydrates during phosphoric acid processing is presented. Solubility experiments and continuous crystallization experiments of calcium sulfate hemihydrate (CaSO4 · 1/2H2O, HH) and calcium sulfate dihydrate (CaSO4 · 2H2O, DH) were performed in concentrated phosphoric/sulfuric acid solutions at 75°C and 90°C in the presence of small amounts of aluminium fluoride or hydrogen fluoride. Both AlF3 and HF increase the solubilities of HH and DH via their effect on the activity coefficients of calcium and sulfate. Aluminium fluoride retards the HH and DH growth rate and an AlF3 concentration of 95 mmol (kg solution)-1 increases the calcium sulfate concentration far above the DH solubility line. This leads to DH formation under conditions where normally HH is formed. The presence of aluminium fluoride also results in crystal habit modification and agglomeration of the HH and DH crystals formed.

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The effect of aluminium fluoride on the formation of calcium sulfate hydrates

Abstract

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