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.