Acid stable membranes for nanofiltration
Semi-permeable membranes are described that allow for the efficient processing of many liquid based feed solutions, particularly those that contain acids. The membranes of this invention are able to process such feeds with high permeate rates while maintaining excellent retention of dissolved metals, cations, and organic compounds, even in the presence of hot concentrated acids. The semi-permeable membranes of this invention are able to conduct such separations for a useful period of time due to their chemical stability towards acids and their ability to permeate acids.
1. A nanofiltration membrane comprising a polysulfonamide polymer matrix which after exposure to a 20% sulfuric acid solution for either, 24 hours at 90° C. or 30 days at 40° C.; is capable of meeting the test of: removing at least 50% of the copper ions from a feed solution consisting of 9.5% CuSO 4 and 20% sulfuric acid at a flux of at least 1 gallon per foot 2 per day; wherein the feed solution is applied to the membrane at a pressure of 600 psig and a temperature of 25° C., wherein the nanofiltration membrane is prepared from the reaction of 1) a naphthalene disulfonyl reactant, a naphthalene trisulfonyl reactant, a benzene disulfonyl reactant, or a benzene trisulfonyl reactant, or mixtures thereof; with 2) diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexaethylenepentamine, or tris-(2-aminoethyl)amine, or mixtures thereof.
2. A membrane according to claim 1 wherein the test flux is at least 6 gallons per foot 2 per day.
3. A membrane according to claim 2 wherein the test copper retention value is at least 90%.
4. The membrane according to claim 1 , wherein at least 80% of the copper ions from the feed solution are removed.
5. A separation method comprising contacting a membrane according to claim 1 with an acid-containing feed solution having a pH less than about 4 that comprises dissolved cations, wherein the membrane removes at least a portion of the dissolved cations from the feed solution.
6. A method for treating a metal ore sample comprising contacting a membrane according to claim 1 with an acid-containing feed solution comprising a dissolved metal ore; wherein the feed solution comprises metal ions; and wherein the membrane removes at least a portion of the metal ions from the feed solution.