METHOD OF PRODUCING GYPSUM Russian patent published in 2009 - IPC C01F11/46 C04B11/00 

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing gypsum, meant for use as binder in the production of construction materials, as well as in chemical, medical and other industries. The method is characterised by that, calcium-containing raw material used is natural and/or synthetic chalk, which is decomposed using nitric acid, taken in stoichiometric amount of 80 to 95%. The process is carried out for 30 to 60 minutes. The obtained suspension is mixed with lime or a mixture of lime and chalk in amount which provides for pH=6.5 to 11.5. The mixture is heated to T=45 to 80°C and separated by filtering. The filtered solution of calcium nitrate and sulphuric acid in stoichiometric amount of 97 to 105% are simultaneously added to a solution of nitric acid with concentration 15 to 25%, obtaining a mixture with solid to liquid ratio of 1:(3.5 to 4.5). The mixture is kept for 4.5 to 5.5 hours at temperature of 45 to 50°C while stirring. The solid product formed is separated by filtering and washed.

EFFECT: invention increases strength, whiteness and content of base material in the obtained gypsum.

3 cl, 1 ex, 6 tbl