Catalytic selective separation of chloride ions from acidic wastewater

Abstract

A new two-step technique was developed for selective separation of chloride ions from acidic aqueous solutions. The process is operated at ambient temperature and pressure, and it is powered by H2 gas and atmospheric oxygen. The Pt-Ag-AC catalyst comprises activated carbon (AC) loaded with platinum (Pt) nano size crystals and metallic silver (Ag) particles. The aeration of acidic chloride solution results in the oxidation of Ag0 to Ag+, which in turn reacts with chloride ions to form an insoluble AgCl precipitate on the catalyst. The regeneration of the Pt-AgCl-AC is performed by hydrogenation, that leads to reduction of AgCl into Ag0, followed by the release of Cl− ions. The process was studied in a batch mode system using acidic NaCl-H2SO4 solutions (500 mgCl/L, [H2SO4]0 = 0.5 M) and Pt-Ag-AC made of granular activated charcoal. The carbon was loaded with 0.5 %Pt and 3.22, 6.25 or 9.09 % of metallic silver. A maximal chloride adsorption capacity of 16.31 mgCl/g was recorded. Full (100 %) separation of Cl− ions from NaCl solutions with [Cl−]0 = 200 mg/L and [H2SO4]0 = 0.5 M was demonstrated.