In order to extract aluminum from bauxite, the aluminum ore is exposed with a caustic soda solution under pressure in the temperature range of 150 to 200 °C. Dilution and pH value setting are implemented by the addition of 170 mmol/L citric acid prior to calcium determination with ion chromatography in the Bayer caustic soda. Doing so establishes a pH value of 4.5 and prevents precipitation of aluminum hydroxide. The IC separation takes place on the Metrosep C 4 - 150/4.0 column with a citric acid eluent.