Rare earths are used in the renewable energy technologies such as wind turbines, batteries, catalysts and electric cars. Current mining, processing and sustainability aspects have been described in this paper. Rare earth availability is undergoing a temporary decline due mainly to quotas being imposed by the Chinese government on export and action taken against illegal mining operations. The reduction in availability coupled with increasing demand has led to increased prices for rare earths. Although the prices have come down recently, this situation is likely to be volatile until material becomes available from new sources or formerly closed mines are reopened. Although the number of identified deposits in the world is close to a thousand, there are only a handful of actual operating mines. Prominent currently operating mines are Bayan Obo in China, Mountain Pass in the US and recently opened Mount Weld in Australia. The major contributor to the total greenhouse gas (GHG) footprint of rare earth processing is hydrochloric acid (ca. 38%), followed by steam OPEN ACCESS Resources 2014, 3 615 use (32%) and electricity (12%). Life cycle based water and energy consumption is significantly higher compared with other metals.

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The application of wet oxidation to the removal of organic impurities from Bayer-process liquors has the potential to deliver major benefits to the alumina industry. Previous work has identified the malonate anion as especially reactive under WO conditions, a property ascribed to its ability to form a carbanion in alkaline conditions. Understanding of the reaction mechanism involved in this effect is of importance to the development of improved WO technology. The current work confirms carbanion formation as the first step in the reaction. Deuterium exchange experiments and 13 C NMR spectroscopy are used to demonstrate the weak acidity of the R-hydrogen atoms which leads to carbanion formation. The acidity of the R-hydrogen atoms in malonate is induced by the electron-withdrawing effect of the two adjacent carboxylate groups. Substituting an electrondonating group such as methyl or ethyl at the R-position reduces this effect, resulting in reduced oxidation rates for the substituted malonates. The role of the carbanion in the reaction mechanism is confirmed by analysis of the products and reaction kinetics.

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