Evaluation of Selective Sorbents for the Extraction of Valuable Metal Ions (Cs, Rb, Li, U) from Reverse Osmosis Rejected Brine

Metal Recovery from Natural Saline Brines with an Electrochemical Ion Pumping Method Using Hexacyanoferrate Materials as Electrodes

The electrochemical ion pumping device is a promising alternative for the development of the industry of recovering metals from natural sources-such as seawater, geothermal water, well brine, or reverse osmosis brine-using electrochemical systems, which is considered a non-evaporative process. This technology is potentially used for metals like Li, Cu, Ca, Mg, Na, K, Sr, and others that are mostly obtained from natural brine sources through a combination of pumping, solar evaporation, and solvent extraction steps. As the future demand for metals for the electronic industry increases, new forms of marine mining processing alternatives are being implemented. Unfortunately, both land and marine mining, such as off-shore and deep sea types, have great potential for severe environmental disruption. In this context, a green alternative is the mixing entropy battery, which is a promising technique whereby the ions are captured from a saline natural source and released into a recovery solution with low ionic force using intercalation materials such as Prussian Blue Analogue (PBA) to store cations inside its crystal structure. This new technique, called "electrochemical ion pumping", has been proposed for water desalination, lithium concentration, and blue energy recovery using the difference in salt concentration. The raw material for this technology is a saline solution containing ions of interest, such as seawater, natural brines, or industrial waste. In particular, six main ions of interest-Na+, K+, Mg2+, Ca2+, Cl-, and SO42--are found in seawater, and they constitute 99.5% of the world's total dissolved salts. This manuscript provides relevant information about this new non-evaporative process for recovering metals from aqueous salty solutions using hexacianometals such as CuHCF, NiHCF, and CoHCF as electrodes, among others, for selective ion removal.

Extraction of strategically important elements from brines: Constraints and opportunities

Strategically important elements are those that are vital to advanced manufacturing, low carbon technologies and other growing industries. Ongoing depletion and supply risks to these elements are a critical concern, and thus, recovery of these elements from low-grade ores and brines has generated significant interest worldwide. Among the strategically important elements, this paper focuses on rare earth elements (REEs), the platinum-group metals and lithium due to their wide application in the advanced industrial economics. We critically review the current methods such as precipitation, ion exchange and solvent extraction for extracting these elements from low-grade ores and brines and provide insight into the technical challenges to the practical realisation of metal extraction from these low-grade sources. The challenges include the low concentration of the target elements in brines and inadequate selectivity of the existing methods. This review also critically analyzes the potential applicability of an integrated clean water production and metal extraction process based on conventional pressure-driven membrane and emerging membrane technologies (e.g., membrane distillation). Such a process can first enrich the strategically important elements in solution for their subsequent recovery along with clean water production.

Synthesis of porous resorcinol-formaldehyde resins and study of their sorption characteristics toward Cs in highly mineralized alkaline media

The present work was devoted to study of sorption parameters of resorcinol-formaldehyde resins synthesized through introduction of an inorganic filler (in amounts of 10 and 25 wt.%) with its subsequent leaching. The surface morphology and composition of ion-exchange resins have been investigated by means of the method of scanning electron microscopy. The effect of internal diffusion on the peculiarities of the ion-exchange process has been determined. It has been revealed that the ion-exchangers destruction upon a prolonged contact with highly alkaline solutions is followed by the decrease of internal diffusion coefficients and selectivity toward Cs-137 micro-quantities. The sorption properties of resins under dynamic conditions at high solution feeding rates have been studied. A sample with the highest efficiency of Cs-137 removal from highly mineralized solutions has been identified.

Towards the Extraction of Radioactive Cesium-137 from Water via Graphene/CNT and Nanostructured Prussian Blue Hybrid Nanocomposites: A Review

Cesium is a radioactive fission product generated in nuclear power plants and is disposed of as liquid waste. The recent catastrophe at the Fukushima Daiichi nuclear plant in Japan has increased the 137Cs and 134Cs concentrations in air, soil and water to lethal levels. 137Cs has a half-life of 30.4 years, while the half-life of 134Cs is around two years, therefore the formers' detrimental effects linger for a longer period. In addition, cesium is easily transported through water bodies making water contamination an urgent issue to address. Presently, efficient water remediation methods towards the extraction of 137Cs are being studied. Prussian blue (PB) and its analogs have shown very high efficiencies in the capture of 137Cs+ ions. In addition, combining them with magnetic nanoparticles such as Fe3O4 allows their recovery via magnetic extraction once exhausted. Graphene and carbon nanotubes (CNT) are the new generation carbon allotropes that possess high specific surface areas. Moreover, the possibility to functionalize them with organic or inorganic materials opens new avenues in water treatment. The combination of PB-CNT/Graphene has shown enhanced 137Cs+ extraction and their possible applications as membranes can be envisaged. This review will survey these nanocomposites, their efficiency in 137Cs+ extraction, their possible toxicity, and prospects in large-scale water remediation and succinctly survey other new developments in 137Cs+ extraction.

Porous Resorcinol-Formaldehyde Resins

Porous ion-exchanging resorcinol-formaldehyde resins were prepared by removing an inorganic template (CaCO3) and by polymerization of a highly concentrated emulsion with toluene as a dispersing phase. As compared to original resorcinol-formaldehyde resins, the porous one is characterized with higher values of internal diffusion, providing exceptional purification coefficients. However, the amounts of the introduced CaCO3 and toluene have to be below 10 wt.% and 25 wt.%, respectively, to avoid fast degradation of the ion-exchanger. Under dynamic conditions, average purification coefficients in the model solution of Cs-137 are twice higher than those of the non-porous sample. The prepared porous ion-exchange resin can be used in cases when high Cs-137 uptake from liquid media should be realized at increased rates of solution percolation.

Mining Critical Metals and Elements from Seawater: Opportunities and Challenges

The availability and sustainable supply of technology metals and valuable elements is critical to the global economy. There is a growing realization that the development and deployment of the clean energy technologies and sustainable products and manufacturing industries of the 21st century will require large amounts of critical metals and valuable elements including rare-earth elements (REEs), platinum group metals (PGMs), lithium, copper, cobalt, silver, and gold. Advances in industrial ecology, water purification, and resource recovery have established that seawater is an important and largely untapped source of technology metals and valuable elements. This feature article discusses the opportunities and challenges of mining critical metals and elements from seawater. We highlight recent advances and provide an outlook of the future of metal mining and resource recovery from seawater.