The electrochemical behavior of cerium(III) in nitric acid solutions of rare-earth elements was studied. The activation energy and reaction order of cerium(III) oxidation were determined for various levels of anodic polarization.Published data [13 6] on cerium(III) recovery from a mixture of rare-earth elements (REEs) and preparation of its pure compounds show that the method of preliminary electrochemical oxidation of Ce(III) to Ce(IV), followed by separation by precipitation or extraction, is the most promising. The comparative simplicity of separation is based on the substantial difference in the chemical properties of REE(III) and Ce(IV). The advantages of the electrochemical oxidation are the absence of chemical oxidants, possibility of preparation of stable Ce(IV) solutions, feasibility of a continuous process, higher equipment productivity, and smaller working area. However, this method has been insufficiently developed for industrial application [7]. The high yield of Ce(III) oxidation is achieved at a low current efficiency.In this study, we examined how the electrochemical oxidation of Ce(III) in nitric acid solutions depends on the current density i, Ce(III) concentration, and electrolyte stirring intensity (characterized by the Reynolds number Re). The conditions ensuring complete Ce(III) oxidation with a current efficiency exceeding 92% were determined.
We have studied the influence of Nb content (0.35-60 wt %) and heat treatment on the phase composition, texture, and photocatalytic activity (PCA) of composites based on titanium(IV) and nio bium(V) oxides and obtained materials that possess PCA under illumination at λ ≥ 900 nm.
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