The mother-liquor after precipitating cobalt by the oxalic acid contains the oxalic acid of 0.20~0.25mol/L, and the hydrochloric acid of 1mol/L.If it was used to dissolve the raw materials, which was easy to produce deposition of the oxalate, the leaching proportion of the valuable metal would be reduced.P350 was studied to separate the oxalic acid and the hydrochloric acid, and its extraction mechanism was discussed.