Sorption extraction of cobalt ions from nitrate media by the iminodiacetate chelating resins Lewatit TR-207 and TR-260

Cobalt-ion sorption from nitrate media by the macroporous chelating resins Lewatit TR-207 and TR-260, which contain active functional groups based on iminodiacetic acid, is studied. Both resins are shown to sorb cobalt from nitrate solutions rather efficiently at pH 1.5–2.0, and the degree of cobalt extraction reaches ～100% for a solid to liquid ratio of ≥0.3. Under optimal conditions, the cobalt capacity of the resins is ～160 mg/g. The system under study is equilibrated within 240 min, and >70% Co is extracted during the first hour of sorption. On heating to 40–40°C, cobalt sorption enhances; however, upon further heating to 50–52°C, the extraction of cobalt decreases, which is probably caused by thermal destruction of the resin. The estimated change in the enthalpy of cobalt sorption in the temperature range 21–41°C is about +84 kJ/mol. The results obtained are employed to test the cobalt sorption under dynamic conditions in a laboratory column packed with Lewatit TR-207 resin in the H⁺ form (the working volume of the column is 100 ml) using the real mother liquor (24.5 mg Co/l) of cobalt oxalate precipitation. Quantitative desorption of cobalt is conducted with a solution of HNO₃ (400 g/l). During dynamic tests, about nine specific volumes of the initial mother liquor are passed through the column. After this, the cobalt content in the purified solution is lower than 0.4–0.5 mg/l; i.e., the total degree of cobalt extraction is >98%. In the desorption solution, the cobalt concentration increases to ～0.3 g/l, which corresponds to a more than tenfold degree of cobalt enrichment. Thus, the resins under study can be recommended for the extraction of cobalt microamounts (20–50 mg/l) from foul and reused waters.