An investigation of gypsum precipitation-dissolution in acid water samples gave certain results about gypsum produced on the industrially used limestone surfaces.
The gypsum solubilities were measured in the range of 25 - 60°C. In H₂SO₄ with concentrations over 5 × 10^-3 mol/l, greater solubilities were observed in higher temperatures, when 0.245g CaSO₄/100g solution was used at 60°C. In acid waters over pH 3, solubilities were almost the same as those in water samples, irrespective of temperature.
The solubility of gypsum is less in CaCl₂ solution than in water. In HCl-CaCl₂ solution thesolubility is affected by CaCl₂ in lower temperatures and by HCl in higher temperatures.With the concentrations of SO₄^2- over 1400mg/l, gypsum precipitation tends to increase rapidly. The produced gypsum, with 60°C, SO₄^2-- 1650mg/l, coats the limestone surfaces closely and perpendicularly in a short crystal-columnar form; with 25°C, SO₄^2- 1500mg/l, in a rough and needle crystal form.