Method of recovering cerium

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PROBLEM TO BE SOLVED : To recover cerium from an etching waste solution at high efficiency. SOLUTION : The method consists of : a reduction stage where a reducing agent is added to the solution to be treated in such a manner that the oxidation-reduction potential lies in the range of 0 to 800 mV; and a chromium removal stage where alkali is fed to the solution after the reduction stage, and chromium is precipitated as chromium precipitates to separate a cerium recovery solution. As the reducing agent, nitrite can be used. A cerium oxidation stage where an oxidizer and alkali are fed to the solution after the chromium removal stage, and cerium is recovered as cerium (II) hydroxide by its oxidation at pH in the range of 3 to 9 or a cerium re-recovery stage where the chromium precipitates separated in the chromium removal stage are subjected to acid dissolution and are thereafter fed with alkali so as to be chromium re-precipitates, so that cerium is separated from the chromium precipitates to obtain a cerium re-recovery solution, can be added thereto. The cerium re-recovery solution separated in the cerium re-recovery stage can be returned to the solution to be treated or the solution after the reduction stage. COPYRIGHT : (C)2004, JPO&NCIPI