The characteristics of the composite membranes of three types in reverse osmosis of the concentrated CaSO4 solutions containing sodium carboxymethyl cellulose, an acidic polyelectrolyte (APE) at different concentrations have been studied. An effect of the concentration of this APE on the characteristics of the comparatively coarsely porous membranes has been demonstrated. We also showed the data indicating how to prevent formation of the irreversible scaling of the low soluble salt at the APE concentrations under study.