Unlocking hidden mineral resources: Characterization and potential of bitterns as alternative sources of critical raw materials

Mineral extraction from seawater brines has emerged as a viable solution to reduce Europe's reliance on imported Critical Raw Materials (CRM). However, the economic viability of this approach hinges on the local demand for sodium chloride, the primary product of such extraction processes. This study investigates the potential of residual brines, commonly known as "bitterns," generated during solar sea-salt extraction in traditional saltworks, as an alternative source of minerals. The Mediterranean region, encompassing South-European, NorthAfrican, Near East coasts, and parts of the Atlantic regions, is particularly conducive to exploring this prospect due to its extensive solar sea salt industry. Saltworks in the region, adopting various operational strategies based on feed quality or local climate conditions, produce different types of bitterns, each holding a latent resource potential that has remained largely unexplored. Within the framework of the EU-funded SEArcularMINE project, it was conducted an extensive analytical campaign to characterize bitterns collected from a diverse saltworks network. The analysis revealed the presence of sodium, potassium, magnesium, chloride, sulfate, and bromide in concentrations ranging from g/ kg, while boron, calcium, lithium, rubidium, and strontium were found in the mg/kg range. Additionally, trace elements (TEs) such as cobalt, cesium, gallium, and germanium were detected at concentrations in the order of mu g/kg. Detailed results on the composition of bitterns are presented, emphasizing the distinct characteristics observed at different sites. The estimated potential for mineral recovery from these bitterns is approximately 190 euro/m3, considering the production capacity of about 9 Mm3 per year in the Mediterranean area. This finding underscores the significant contribution that mineral recovery from bitterns could make in securing access to CRMs for the European Union

Boosting sustainable water production by upstream integration of desalination with saltworks in the Mediterranean region

SEArcularMINE is an EU project that is focused on mineral extraction from saltwork bitterns, adopting a circular approach. Within this context, this work shows the possibility of completing the circular scheme with an upwind integration of seawater desalination that can provide freshwater to the local community but also use the brine reject to feed the saltwork in order to increase its productivity. In this study, a specific case of a natural saltwork in Trapani (Italy) is presented, assuming to place a desalination plant very close to the saltworks, so that the brine can be sent there without an additional energy input. After choosing the best desalination technology, demonstrating that Reverse Osmosis (RO) is more suitable than thermal processes from both economic and environmental point of view, the details of the RO design are presented. Then, preliminary calculations using a simple model for the saltwork ponds have been performed, showing that the brine feed can either increase the salt productivity by more than 50% or that the ponds surface can be reduced by more than 40%. Finally, evaporation experiments on desalination brines have been performed to demonstrate that no changes in salt quality occur compared to the standard seawater fee

Pd-C surface phase as an essential parameter of selective alkyne hydrogenation: a high-pressure XPS study

Appropriate reaction selectivity is likely the biggest issue on the way to economically feasible industrial catalytic processes. Palladium particles are able to add one hydrogen molecule to both alkenes and alkynes, hence the question may arise how the catalyst prohibits total hydrogenation of alkynes and multiple unsaturated hydrocarbon. We investigated the hydrogenation of various alkenes and alkynes on palladium catalysts by catalytic reaction and high-pressure XPS experiments, and found that the active surface of selective alkyne hydrogenation consist of a Pd-C surface phase. Carbon embedded in the palladium lattice inhibits the emergence of bulk-dissolved hydrogen to the surface, which is reactive but unselective. Moreover, Pd-C does not build up from alkenes

Pd-C surface phase as an essential parameter of selective alkyne hydrogenation

Palladium is one of the most widely applied metals in catalytic processes both in homogeneous and heterogeneous systems. In either case selectivity is a major concern to make industrial processes economically feasible. Palladium particles are able to add one hydrogen molecule to both alkenes and alkynes, hence the question may arise how the catalyst prohibits total hydrogenation of alkynes and multiple unsaturated hydrocarbon. Most of the explanations offered for this question consider the presence of carbonaceous overlayer on the palladium surface. We studied the hydrogenation of 1-pentyne over various palladium catalysts under different conditions. In line with the literature data on alkyne hydrogenation, 1-pentyne hydrogenation on palladium catalysts is characterized by two significantly different regimes: at high pressures (and) with high hydrogen excess pentane is by far the main product. At lower pressures or/and with lower H2/C5 ratios, hydrogenation is much slower, but almost totally selective to 1-pentene. Pulse hydrogenation, in-situ TEOM, in-situ XPS and HRTEM reveals that this turn of selectivity is related to an especial carbon retention. It is unequivocally established that carbon dissolves into the palladium lattice (mainly in the near-surface region) and a palladium-carbon surface phase (PdC) builds up in the early stage of the reaction. This, and not the clean palladium surface, is the active phase in the regime of selective hydrogenation of alkynes on a typical catalyst. The formation of Pd-C is strongly suppressed at high p(H2), at which condition hydrogenation is non-selective. We propose that the role of dissolved carbon and the Pd-C surface phase is to exclude bulk dissolved hydrogen participating to the reaction. The genesis of the active surface includes the total fragmentation of significant amount of reactant molecules. Further experiments with C2/C3/C5 alkynes and alkenes indicate that Pd-C formation is a general process during selective triple bond hydrogenation, but it does not build up from the corresponding alkenes, making the hydrogenation sites different from alkynes and alkenes

Potentials for critical raw materials recovery from Mediterranean saltworks bitterns

Minerals extraction from seawater brines is currently regarded as the most practical approach to reduce European dependency from the import of many Critical Raw Materials. The technical feasibility of such approach has been widely demonstrated in several different research and development projects but the economic sustainability has always been found to depend on the local demand for sodium chloride, which is always the most abundant product of the extraction. Starting from this crucial node, the SEArcularMINE project has investigated the possibility to use the residual brines originated by sea-salt extraction in traditional saltworks, regarded as an already well-established marketplace. The Mediterranean area as a whole, can rely on a diffused industry including South-European coast, North-African and Close East coast and portions of the Atlantic regions. Additionally, many inland salt-lakes and subsoil waters are traditionally operated in the same way as the coastal facilities to produce solar-salt. Interestingly, each saltworks have a slightly different approach, adapted to feed quality or local climate conditions. Accordingly, different types of brine are produced, having unique features. These “bitterns” are extremely interesting to characterize, focusing on their hidden potential. In this work, an extensive analytical campaign has been conducted exploiting the wide saltworks network established within the SEArcularMINE project. Main results are here reported, highlighting the possibility of contributing to secure the access to some Critical Raw Materials for E