Abstract: The invention relates to a spacer with mixing elements, particularly for membrane modules.

Abstract: Method of production of synthetic fluorite with a selected specified grain size to be obtained, by submitting the calcium carbonate to a reaction with fluoride ions present in an aqueous solution, consists therein that calcium carbonate is used having a grain size substantially the same as the selected grain size for the synthetic fluorite to be obtained. The fluoride ions for the reaction with the calcium carbonate are supplied in the form of a solution of ammonium fluoride and/or potassium fluoride and/or sodium fluoride. The process is conducted at a temperature chosen within the range of 50.degree. C to 150.degree. C, under a pressure reduced, atmospheric or elevated, within the range of 0.5 to 10 atm, and preferably at the boiling temperature or at a temperature not too far from the boiling point, especially in a reaction system containing ammonium fluoride.