Volatile Separation and Recovery of Iridium from Oxygen Evolution Electrodes Using Calcium Oxide

Abstract

Iridium is a platinum-group metal with unique catalytic properties and chemical stability. Because of these characteristics, the metal is used in the form of iridium–tantalum oxides in the catalytic layer of oxygen evolution electrodes. Recovering Ir from end-of-life products is important because of its low production volume, the uneven geographical distribution of Ir sources, and high supply risks. However, Ir recovery requires its dissolution in aqueous solution using a strong acid, making the procedure not only dangerous but also hazardous to the environment. Moreover, if metals other than Ir are dissolved in the aqueous solution during its recovery, harmful effluents and gases could be generated. Separating Ir from such other metals would be difficult. Accordingly, we developed a method to extract Ir only from the catalyst layer and, simultaneously, recover Ir as a Ca–Ir composite oxide that is soluble in hydrochloric acid. Only iridium oxide was volatilized from the catalyst layer of the oxygen evolution electrodes and brought into contact with CaO in the gas phase. The composite oxide obtained was dissolved in hydrochloric acid and subsequently analyzed. The result revealed that Ir is highly soluble in hydrochloric acid, and the composite oxide does not contain Ta.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 243–248.

Fig. 1 Schematic diagram of Ir separation and recovery in this experiment.