Diffusion Dialysis Membranes

Does anyone know if it is possible to use cation membranes in a diffusion dialysis system to remove free NaOH and retain sodium aluminate (dissolved aluminium in caustic).

s this process possible? Can the membranes withstand the 25% NaOH soln and the pH 13? Are there companies out there that manufacture such systems?

ny help on the topic is greatly appreciated.

Thank you,

Jim Pejoski
- Canning Vale, Western Australia

Probably not.

The difference between diffusion dialysis for acids is that you are trying to recover an anion, which is a large molecular compound in most cases, and also usually divalent, which gives it greater propensity to "attach" itself to water passing throught the membrane. Your trying to recover caustic in the cation application - which competes with hydrogen ions for transport (even in the highly alkaline background). Sodium is a poor transport ion as it is stable and only monovalent.

Have you tried to seed the material and filter it out?

Tom Baker
wastewater treatment specialist
Warminster, Pennsylvania

Yes you can recover NaOH using cation membrane, if your solution is NaOH and sodium aluminate the problem is that as you recover the sodium hidroxide the sodium aluminate precipitates, therefore you can only recover as much as 40 % during dialysis. If you cristalization of your high aluminum discharge, you can recover the rest of your NaOH. You have to play with the water inflow to reduce the dilution of your NaOH. I had the chnace to do this process about 11 years ago at the University of Rhode Island.

Best regards

Dr. Belzahet Treviño Arjona
Water Studies Center, ITESM - Monterrey, Nuevo león México

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