Hi all,
I tried to determine gypsum in soil through water evaporation. in the interval 40°C - 100°C the result is 83%, in the interval 70-100°C the result is 53%. How to interpret it? I did the test with the same sample: i) heated on 40°C, ii) heated on 70°C, iii) heated on 104°C.
I would believe that this soil could contain 83% of gypsum. Does somebody have experience with this Artieda method?
Gypsum is always correlated with temperature, Gypsum calcium sulphate dehydrate CaSO4. is 2H2O. When gypsum is heated to a temperature of 70-100°C it loses 3/4 of its water of crystallization and becomes plaster of Paris., The result of Gypsum is reduced. Gypsum has calcium sulphate dehydrate (2H2O), whereas Plaster of Paris has calcium sulphate hemihydrates(1 / 2 H 2 O ). Hence Plaster of Paris has mole of crystallization water whereas moles of crystallization water are present in Gypsum.
Hi,
I do not know which soil you have, but sometimes gypsum is associated with anhydrite (CaSO4) while gypsum has CaSO4 · 2 H2O. formula. Evaporation systematically causes a modification in the gypsum structure but also requires high pressure!
Regards
Prem Baboo thank you for answer. Sure, this is the principle of Artieda thermogravimetric method (Artieda et al., 2006). Still, which portion of evaporated water determines better gypsum present in soil? i) 40-104°C, or ii) 70-104°C? the result of first interval is 83% "gypsum" in soil, second interval resulted in 53% "gypsum" in soil. I read that 10-15% of gypsum could be "degraded" due to heating, anyway, difference here is 30%. I expect high content of gypsum, therefore, both values are in the range of my expectation.
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