The recovery of noble metals is important from a practical viewpoint for the effective use of natural resources. Generally, a variety of disposed industrial products containing small amounts of noble metals are first leached in aqua regia, followed by extraction with classical chemical separation methods using inorganic collectors and/or precipitants. [1][2][3][4][5][6][7] This recovery process produces large volumes of waste solutions, which usually contain extremely large amounts of various base metals, ammonium salts, sodium salts, chlorides, nitrates, sulfates, formates, acetates and so on. Contrarily, much smaller amounts of noble metals that are not completely recovered and still remain in the waste solutions are finally collected and removed as their metals by adding into the slightly acidic waste solution a zinc metal plate as a metallic precipitant for a long period of time.
1It is essential to know the efficiency of the recoveries of each noble metal and simultaneously the content of each noble metal still remaining in the final waste solution, just before the solution is transferred to the subsequent recovery process of the base metals as their hydroxides. However, it is very difficult to rapidly and accurately determine the contents of the noble metals in the final waste solution, because of the very low abundances of noble metals and of the extremely high concentrations of associated base metals and many other salts. Usually, any procedure has included the use of a variety of methods of concentration and/or separation prior to the analysis of such waste solutions for noble metals by means of modern and highly sensitive instruments. 3,[6][7][8][9] It has recently been revealed that chromatographic systems 10-16 consisting of a chelate-forming resin or a cellulose anion exchanger and a thiourea solution as an eluant are applicable to the separation of noble metals and base metals in various sample solutions. We have also demonstrated that an anion-exchange method 17 using a common anion-exchange resin and a dilute thiourea solution is more effective than the others, because of much stronger adsorption of the noble metals on the anion-exchange resins.In the present study, anion-exchange methods already developed for the separation of noble metals from various base metals were applied to the determination of Au(III), Pd(II), and Pt(IV) in the industrial waste solutions obtained in the final stage of the noble-metal recovery process. Noble metals were collected on a small anion-exchange column, and recovered with an effluent containing small amounts of thiourea. The effluent was directly analyzed for each noble metal by graphite furnace atomic absorption spectrometry (GFAAS). The present method will allow the simple and accurate determination of trace amounts of noble metals in industrial waste solutions containing excessively large amounts of associated base metals and salts to be performed simply and rapidly.
Experimental
Reagents and solutionsStandard solutions of gold(III), palladium(II), and platinu...