The validity of the electrochemical series for metal sulfides decomposition in their standard state has been tested experimentally at 1500 K for La2S3, Cu2S, MoS2, and ReS2 in a molten electrolyte with the following molar composition: (BaS)54-(Cu2S)31-(La2S3)15 (electrolyte B). Voltammetry measurements indicated the presence of faradaic reactions in the investigated electrolyte with and without the addition of MoS2 and/or ReS2. Electrolysis experiments showed that the addition of La2S3 to BaS-Cu2S increases the faradaic efficiency for liquid copper production with respect to a previously studied (BaS)54-(Cu2S)46 electrolyte, and enabled isolation of elemental sulfur as the anodic product. Electrochemical measurements suggested the need to take into account the activity of dissolved Cu2S in order to explain the observed cell voltage during electrolysis. Electrolysis in the presence and absence of ReS2 and/or MoS2 confirmed their relative stability as predicted by assuming decomposition in their standard states. Analysis of the metal products electrowon from an electrolyte containing Cu2S, MoS2, and ReS2 indicated the simultaneous production of solid and liquid phases with nonequilibrium compositions.

The electrochemistry of anodic oxygen evolution on iridium in silicate-containing molten oxides at 1570 °C was experimentally investigated using both direct and alternating current methods. Static and rotating electrode results show the presence of anodic reactions of iridium in addition to oxygen evolution. In the context of electrochemical engineering of molten oxide electrolysis, the results confirm prior theoretical calculations (Allanore, 2013) that suggested an essential role of convection and electrolyte composition on the ability to sustain oxygen evolution at high current densities. In addition, the reported results show that electrochemical measurements in molten oxides coupled with mass-transfer models are complementary characterization tools for oxygen chemistry.

The anticipated increase in demand for potassium fertilizers and alumina from developing nations experiencing a high-rate of population growth brings a global sustainability concern. Most of these countries do not have economically viable resources for both commodities; and the environmental footprint of existing technologies may compromise local ecosystems. Alternatives, both in terms of resources and extraction technologies, are therefore needed. Aqueous alteration of potassium-bearing aluminosilicate minerals has been proposed as an alternative to both traditional K-fertilization and alumina production. This work discusses the mechanism of aqueous alteration of aluminosilicate minerals, and the chemical processes that have been proposed to date. Although extensive studies are found in the fields of geochemistry and materials chemistry, their results have rarely been analysed and engineered to allow a proper control and design of chemical processing. The review suggests that such a multi-disciplinary approach is required to enable new technologies that both comply with green chemistry principles and are economically viable.

•The interplay between geology, comminution and leaching of agrominerals is elucidated.•Prolonged comminution of ultrapotassic syenites results in enhanced K+ leaching.•Comminution of agrominerals can be engineered to provide maximum agronomic benefit.Growth of world population and consequent growth of food demand are drivers of expansion and intensification of agriculture. High-yield agriculture relies on fertilizers that, therefore, become a key focus to address concerns on global food security. Currently, potassium fertilizers are produced in the northern hemisphere. These fertilizers do not suit the deep leached soils of tropical countries, partly due to their high solubility. The use of geological materials (agrominerals) such as K-bearing silicates could be an option to develop slow release potassium fertilizers from abundant and readily available geologic sources. Thus far, both laboratory and agronomic field tests on such materials have been inconclusive, meaning that a clear relationship between the application of agrominerals to soil and the fertilizing effect could not be established. Novel interdisciplinary approaches are needed to predict the release of nutrients from agrominerals. This study presents one such approach, proposing a detailed analysis of the relationship between petrographic characteristics of twelve samples of ultrapotassic syenite (K-feldspar ore), and the leaching of potassium from their powders. The correlation between petrographic features, comminution and leaching proposed here, is expected to play a major role in the assessment of the fertilizing properties of agrominerals in the field.