Ion separation of binary metallic aqueous solutions at acidic Langmuir monolayer surfaces

We focused on analyzing the capability of the acidic monolayer surfaces for separation of toxic metal ions out of house-prepared binary inorganic ioni c solutions such as calcium-lead, calcium-chromium, calcium-copper, and cal cium-zinc aqueous systems. The affinities of the films to toxic metal ions were analyzed by using Fourier transform infrared spectroscopy. A model con sidering both the electrochemical and thermodynamic aspects was also applie d to quantify the surface ion affinities. It is noted that surface ion bind ing capability for binary ionic solutions can be much different from that f or pure ionic solutions. As a result, surface binding constants were found to be 4.5 x 10(6), (++) for lead ions, 1.5 x 10(6) for chromium ions, 5.5 x 10(5) for copper ions, and 6 x 10(4) for zinc ions, respectively, at pH=5. 5. For the separation experiments done at pH=5.5, lead, copper, zinc ions w ere separated more efficiently from the mixed ionic solutions by the factor s of ca. 30,000, 10,000, 3,700, and 400, respectively, compared to calcium ions of which binding constant is 1.5 x 10(2). Interestingly, when compared to corresponding pure ionic systems, copper and lead ions were separated a s much, while chromium and zinc ions were less by the factor of 500 and 50, respectively.