Selective separation of chromium(Ⅲ) and iron(Ⅱ) by extraction

Chromium (Ⅲ) and iron (Ⅱ) were extracted together by saponified P204 + sulfonated kerosene system, and were selectively stripped to recover chromium from sulfuric acid leaching solutions of electroplating sludge. The effects of the factors were studied, such as saponification rate, P204 concentration, initial pH value, extraction time, temperature and extraction phase ratio on the extraction efficiency, as well as the effects of such factors as the composition, concentration and the ratio of the stripping agent on the stripping efficiency. The results show that the extraction rate of chromium is predominated by the saponification rate and concentration of P204. Under the following optimum conditions: Using 30 %P204+70 %sulfonated kerosene as the extractant, saponification rate is 70 %, pH value of 2.42, V_O/V_A=1/1, in 28 ℃ and reaction time is 5min, the chromium concentration in the outlet water phase was about 0.9 mg/L and the extraction rate of chromium was 99.99 %by six-stage countercurrent extraction. Effective separation of chromium and iron by two stripping processes: The loaded organic can be stripping using 2mol/L H2SO4, V_O/V_A=5/1, the temperature is 32 ℃ and reaction time is 5min, stripping rate of chromium was 97.5 %, concentration of chromium enriched to 29.5 g/L and concentration of iron close to 10 mg/L by three-stages countercurrent stripping with 2 mol/L sulfuric acid. After chromium stripping, iron in the loaded organic can be stripped using sodium hydroxide solution.