In a liquid-liquid system for the separation and recovery of individual rare earths, co-extraction of ferric iron is a serious problem. This study was done to determine whether the problem could be solved by converting the iron to the ferrous state, as opposed to precipitating the ferric iron to remove it from solution. In the precipitation of ferric iron, some co-precipitation of rare earths occurs. A synthetic iron solution, and a uranium barren solution containing 3.17 g Fe 4-2/1 and 0.34 g Fe +3/1, were used in the test work. The ferric iron in the barren solution was reduced by 90% at 90 °C in 31 minutes by addition of twice the stoichiometric amount of S02. An alternate method used 1.5 times the stoichiometric amount of SO2 at room temperature and 15 g/1 activated carbon; retention time was 15 minutes. All of the test work was carried out in an oxygen-free system. On the basis of this work the activated carbon-S02 method was the more economical. Measurement of the oxidation potential can be used as a method of control.