Abstract: A gaseous species can be separated from an aqueous donor mixture and absorbed in an aqueous recipient mixture using a membrane separation apparatus while maintaining a large temperature difference (e.g. greater than 30° C.) between the two aqueous mixtures. A composite membrane is employed which comprises a non-porous membrane adjacent a porous membrane. The non-porous membrane is permeable to the gaseous species. The porous membrane has a porosity greater than 50% and is hydrophobic. In one embodiment, the composite membrane is oriented such that the porous membrane faces the aqueous recipient mixture and is impermeable thereto at the recipient mixture pressure. The invention is particularly suitable for separating chlorine dioxide from chlorine dioxide reaction liquor and absorbing in chilled water.

Abstract: Fluoride ions can be removed from an aqueous stream to desirable levels (e.g. less than 1 ppm) using two precipitation reactions in series. In this method, calcium chloride and a phosphate salt are added to form a first precipitate and then a carbonate salt is added to form a second precipitate. However under certain circumstances, the conventional stoichiometries employed have been found to remove insufficient fluoride. Instead, sufficient fluoride can be removed by employing unconventional stoichiometries, specifically excessive calcium chloride or deficient carbonate salt.

Abstract: A gaseous species can be separated from an aqueous donor mixture and absorbed in an aqueous recipient mixture using a membrane separation apparatus while maintaining a large temperature difference (e.g. greater than 30° C.) between the two aqueous mixtures. A composite membrane is employed which comprises a non-porous membrane adjacent a porous membrane. The non-porous membrane is permeable to the gaseous species. The porous membrane has a porosity greater than 50% and is hydrophobic. In one embodiment, the composite membrane is oriented such that the porous membrane faces the aqueous recipient mixture and is impermeable thereto at the recipient mixture pressure. The invention is particularly suitable for separating chlorine dioxide from chlorine dioxide reaction liquor and absorbing in chilled water.