ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Calcium sulphate scaling in membrane distillation process

Marek Gryta

Department of Water Technology and Environment Engineering, Institute of Chemical and Environment Engineering, Szczecin University of Technology, ul. Puŀaskiego 10, 70-322 Szczecin, Poland

E-mail: marek.gryta@ps.pl

Received: 30 March 2008  Revised: 3 July 2008  Accepted: 21 July 2008

Abstract: Formation of precipitates containing CaSO₄ during membrane distillation, applied to the concentration of aqueous salt solutions, is discussed in this paper. It was found that the concentration of SO₄²⁻ ions in such solutions should not exceed 600 mg L⁻¹ when they are subjected to concentration. However, concentration of sulphates at the level of 800 mg L⁻¹ in the feed is permissible provided that the excess of CaSO₄ is removed in a crystallizer. Crystallisation of salts, mainly CaSO₄ · 2H₂O, on the surface and inside the membrane was observed at higher feed concentrations, causing damage of the module. Precipitation of calcium sulphate was also observed during the production of demineralised water when high values of the water recovery coefficient (above 90 %) were used. In this case, the formed precipitate also contained CaCO₃, the co-precipitation of which significantly changed the properties of the scaling layer. The precipitate containing both CaSO₄ and CaCO₃ was formed mainly on the membrane surface and it could easily be removed by rinsing the module with a HCl solution.

Keywords: membrane distillation - scaling - calcium sulphate - water pretreatment

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-008-0095-y

Chemical Papers 63 (2) 146–151 (2009)