Abstract: A process for the separation of pentavalent arsenic from an aqueous solution using an N-alkyl pyridinium-containing adsorption medium is disclosed. An oxidizing medium and process for the oxidation of trivalent arsenic to pentavalent arsenic with removal of the pentavalent arsenic so formed is also disclosed.

Abstract: A process for removing contaminating levels of selenium from a contaminated aqueous solution is disclosed. That process includes providing a vessel or flow-permissive container containing a water-insoluble polymeric adsorption medium having a plurality of polymerized C.sub.1 -C.sub.4 N-alkylated pyridinium-containing adsorption sites. An influent of an aqueous solution having a total selenium concentration of about 10 to about 1000 parts per billion is introduced to the vessel or flow-permissive container to contact the insoluble polymeric adsorption medium. The solution is maintained in contact with that insoluble adsorption medium for a time period sufficient for the medium to bind the selenium in the contacting solution. The resulting aqueous solution is discharged from the vessel as an effluent having a total selenium concentration whose ratio to the total selenium concentration of the influent is about zero to about 10.sup.-3.

Abstract: A process for removing contaminating levels of hexavalent chromium ion ?Cr(VI)! from a concentrated aqueous solution of sodium sulfate. That process includes providing a vessel containing a water-insoluble adsorption medium having a plurality of polymerized pyridyl-containing adsorption sites. An influent of an aqueous solution of about 1.0 to about 2.0 molar (e.g., saturated) sodium sulfate having a total hexavalent chromium ion concentration of up to about 1000 parts per million, to the vessel to contact the insoluble adsorption medium. The solution is maintained in contact with that insoluble adsorption medium for a time period sufficient for the medium to bind the hexavalent chromium ions in the contacting solution. The resulting aqueous solution is discharged from the vessel as an effluent having a total hexavalent chromium ion concentration whose ratio to the total hexavalent chromium ion concentration of the influent is about zero to about 25.0.times.10.sup.-6.