Inhibition features of calcium scaling on composite membranes by an acidic polyelectrolyte

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.

1. Research on the effect of acidic polyelectrolyte — Na-CMC in RO of CaSO4 solutions on the composite membranes of three types showed that Na-CMC in concentrations under study — 16 and 32 mg/l prevent crystallization of low soluble salt. 2. An important effect of the porous structure of composite membranes on RO indices has been established. On making use of comparatively coarsely porous membranes OFM-K (No. 2) and OFAM-K (No. 3) in RO of CaSO4 solutions, containing 16 mg/l Na-CMC, a reverse scaling takes place. Scale is formed mainly on the membrane surface. Starting membrane characteristics of OFM-K are re-established completely. As for OFAM-K an unnoticeable irreversible lowering of flux (2.7%) and rejection increase according to Na+ (2.5%) have been marked. 3. It has been shown that with concentration increase of Na-CMC till 32 mg/l a scaling on the surface of the coarsely porous membranes is strengthened. For OFM-K re-establishment of starting indices without membrane rinsing is characteristic; membrane OFAM-K irreversibly loses 3.4% of rejection. 4. It has been established that characteristics of membrane No. 1 with a more compact structure are not changed in RO of solutions of the low soluble salt both at concentration of 16 mg/l and at 32 mg/l Na-CMC and they practically do not differ from the starting ones. 5. Thus, on making use of comparatively coarse reverse osmosis composite membranes, into whose selectivity an electrochemical mecha- nism of ions inhibition because of locating in their pores of ionized functional groups makes a main contribution; a RO of the lowly soluble salt (CaSO4) in the presence of a sodium carboxymethylcellulose as an inhibitor of CaSO4 crystal formation, can be accompanied by reverse surface scale formation and also changing of features of membrane porous space.