Excessive standard solution of calcium was added to precipitate oxalic acid in waste solution.After filtration,the content of oxalic acid in waste solution from rare earth separation process was determined by EDTA back titration method.The pH of sample solution was adjusted to 7.0-10.0with400g/L NaOH solution.After adding 10 mL of NH3-NH4 Cl buffer solution at pH 10.0,the excessive standard solution of calcium was added to precipitate the oxalic acid in waste solution.The pH of filtrate was adjusted to 12.0...