Jose Ignacio Robla

Among the strategic materials considered by the EU, tungsten is included; thus, investigations about the recovery of this metal both from natural and recyclable sources are of interest. In this work, we presented an investigation about the recovery of tungsten based on the treatment of three tungsten-bearing concentrates: scheelite (29% W), wolframite (50% W), and mixed scheelite–wolframite (29% W). All of these come from a cassiterite ore of Spanish origin. The characteristics of each concentrate pave the procedure to be followed in each case. In the case of the wolframite concentrate, the best results were derived from the leaching of the ore with NaOH solutions, whereas the treatment of the scheelite concentrate benefits from an acidic (HCl) leaching. The attack of the mixed concentrate is only possible by a previous roasting step (sodium carbonate and 700–800 °C) followed by a leaching step with water. In the acidic leaching, tungstic acid (H₂WO₄) was obtained, and the alkaline–water leaching produces Na₂WO₄ solutions from which pure synthesized scheelite is precipitated.

In the final stage of zinc calcines processing, zinc is recovered by zinc electrowinning. However, the presence of germanium in the electrolyte seriously affects the current density in the electrowinning step. Since germanium is a critical and strategic material for the European Union according to the most recent foresight studies, this research has focused on an alternative route for the treatment of germanium concentrates (0.1 %wt Ge) obtained after the roasting step in conventional zinc processes. The results showed that this concentrate can be treated by leaching in mild acidic medium (90% germanium efficiency)-solvent extraction with an ionic liquid and alkaline stripping (99% germanium recovery), followed by neutralization and precipitation steps to yield GeO2 as end-product. The overall germanium recovery was around 85%.

Among the strategic materials considered by the EU, tungsten is included, thus, investigations about the recovery of this metal both from natural or recycle sources is of interest. In this work we presented an investigation about the recovery of tungsten based on the treatment of three tungsten-bearing concentrates: scheelite, wolframite and a mixed scheelite-wolframite. All of these come from a cassiterite ore of Spanish origin. The characteristics of each concentrate of each concentrate pave the procedure to be followed in each case. In the case of the wolframite concentrate, best results were derived from the leaching of the ore with NaOH solutions, against, the treatment of the scheelite concentrate benefits of an acidic (HCl) leaching. The attack of the mixed concentrate is only possible by a previous roasting step (sodium carbonate and 700-800º C) followed by a leaching step with water. Whereas in the acidic leaching tungstic acid (H2WO4) was obtained, the alkaline-water leaching produces Na2WO4 solutions from which pure synthesized scheelite is precipitated.

Not having the same grade of popularity as other metals like rare earth elements, gold, copper, etc., strontium is a chemical element with wide uses in daily life, which is why it appears in the EU 2023 list of Critical Raw Materials. Among the sources (with celestine serving as the raw material) used to recover the element, the recycling of some Sr-bearing secondary wastes is under consideration, and it is also worth mentioning the interest in the removal of strontium from radioactive effluents. To reach these goals, several technological alternatives are being proposed, with the most widely used being the adsorption of strontium or one of its isotopes on solid materials. The present work reviews the most recent advances (for 2024) in the utilization of diverse technologies, including leaching, adsorption, liquid–liquid extraction, etc., in the recovery/elimination of Sr(II) and common ⁹⁰Sr and ⁸⁵Sr radionuclides present in different solid or liquid wastes. While adsorption and membrane technologies are useful for treating Sr-diluted solutions (in the mg/L order), liquid–liquid extraction is more suitable for the treatment of Sr-concentrated solutions (in the g/L order).

Both natural gas production and fossil fuels production are the main sources to most of the energy consumption, this gas presented a series of impurities, i.e. CO2, which needed to be eliminated in order to prevent several concerns as the corrosion of equipments, greenhouse gas emissions and others. It is thus clear, that the development of efficient CO2 capture and storage processes are important to reduce both CO2 production and its contribution to global warming. CO2 can be capture from gas streams by three technologies: absorption, adsorption and membranes, however, they have some challenges in its utilization to be resolved, and some groups of scientist try to resolve it by the inclusion of deep eutectic solvents in them. In the present work, the most recent developments (2024 year) in CO2 capture using deep eutectic solvents (DESs) jointly to absorption, adsorption or membrane-based technologies have been reviewed.

Both natural gas production and fossil fuels production are the main sources to most of the energy consumption, this gas presented a series of impurities, i.e. CO2, which needed to be eliminated in order to prevent several concerns as the corrosion of equipment, greenhouse gas emissions and others. It is thus clear, that the development of efficient CO2 capture and storage processes are important to reduce both CO2 production and its contribution to global warming. From gaseous streams CO2 can be captured by three technologies: absorption, adsorption and membranes, however, they have some challenges in its utilization to be resolved, and some groups of scientists try to resolve it by the inclusion of deep eutectic solvents in them. In the present work, the most recent developments (2024 year) in CO2 capture using deep eutectic solvents (DESs) jointly to absorption, adsorption or membrane-based technologies have been reviewed.

Most of our energy consumption proceeds from the use of fossil fuels and the production of natural gas. However, the presence of impurities in this gas, like CO₂, makes treatment necessary to avoid further concerns, such as greenhouse gas emissions, the corrosion of industrial equipment, etc.; thus, the development of CO₂ capture and storage procedures is of the utmost importance in order to decrease CO₂ production and mitigate its contribution to global warming. Among the CO₂ capture processes available, three separation technologies are being used to achieve this goal: absorption, adsorption and membranes. To overcome some limitations of these methodologies, the joint use of these technologies with ionic liquids is gaining interest. The present work reviewed the most recent developments (for 2024) in CO₂ capture using ionic liquids coupled to absorption-, adsorption- or membrane-based processes.

Being not as popular as other elements, such as cobalt, lithium, and rare earth elements, both gallium and germanium have wide use in target developments/industries, thus making them valuable and strategically critical metals. The principal sources for the recovery of both metals are secondary wastes of the bauxite (gallium) or zinc (germanium) industries; also, their recycling from waste materials is necessary. The characteristics of these materials make hydrometallurgical operations widely useful in recovering both gallium and germanium from the various sources containing them. The present work reviews the most recent applications (in 2024) of the various operations applied to the recovery of gallium or germanium from various resources.

The presence of organic dyes in aqueous environments is extremely hazardous to life due to the toxicity of these compounds. Thus, its removal from these various aquatic media is of the utmost importance, and several technologies are constantly being tested to meet this goal. Among these technologies, various types of degradation and adsorption techniques are typically used, and of the various types of materials used within these technologies, nanomaterials are constantly being developed and investigated, likely due to the various properties that these nanomaterials have. This work reviewed recent developments (in 2023) about the use of these nanomaterials in the treatment of solutions contaminated with these toxic organic dyes.

The importance of rare earth elements as a basis for the development of new technologies or the improvement of existing ones makes their recovery from raw and waste materials necessary. In this recovery, hydrometallurgy and its derivative solvometallurgy play key roles due to their operational characteristics, which are emphasized with the use of ionic liquids. This manuscript reviews the most recent advances (2023 and 2024) in the use of ionic liquids in unit operations (leaching and separation technologies) aimed at the recovery of these valuable and strategic metals. Moreover, a comprehensive review is presented of the use of these chemicals in the development of advanced materials containing some of these rare earth elements.