Daniel Winter’s research while affiliated with Fraunhofer Institute for Solar Energy Systems and other places

Im MALEG Verbundprojekt wird an der Effizienzsteigerung von geothermischer Energieproduktion mit Hilfe von künstlicher Intelligenz geforscht. In diesem Zusammenhang wird sowohl ein Digitaler Zwilling des Geothermiekraftwerks, mit dessen Sensoren und Aktoren, als auch ein Digitaler Zwilling der hydrogeochemischen Prozesse innerhalb des Thermalwasserkreislaufes entwickelt. Die Energieproduktion in Geothermiekraftwerken ist an die hydrochemischen Grundbedingungen des Fluides geknüpft. Dabei wird durch Druck-, Temperatur-, oder pH-Änderungen das chemische Gleichgewicht des geförderten Thermalwassers verändert, welches zu unkontrollierten Prozessen wie Mineralausfällungen, Ausgasen und Korrosion führen können. Um diese Prozesse besser abbilden zu können, wurde ein Digitaler Zwilling entwickelt. Dieser Zwilling basiert auf der Kopplung eines geochemischen Modellierprogramms (IPhreeqc) und eines numerischen Berechnungsprogramms (MATLAB) via Component Object Model Servers. Dabei werden Modellierungen automatisiert berechnet, übertragen und ausgewertet. Somit lassen sich die neuen geochemischen Gleichgewichtsverhältnisse durch die Parameteränderung direkt ermitteln und interpretieren. Diese Ergebnisse bilden die Grundlade für die Implementierung einer Künstlichen Intelligenz zur Effizienzsteigerung von Geothermiekraftwerken.

Seawater mining presents a potential option for recovering the European Union’s Critical Raw Materials (CRMs), but direct extraction from seawater is challenging due to their low concentrations, as most of them are Trace Elements (TEs) (at levels of mg/L or µg/L). Saltworks bitterns (ultraconcentrated brines resulting from the sea salt production process) offer an alternative solution, naturally concentrated up to 40 times more than seawater. These bitterns can be further processed with chelating Ion Exchange (IX) sorbents to selectively extract TEs. However, this process requires an acidic elution stage with strong acids, followed by neutralization, to recover TEs through precipitation, demanding extensive chemicals consumption. Diffusion Dialysis (DD) could be used to recover the excess acid without external reagents, using an acid-resistant Anion Exchange Membrane (AEM). This study evaluates DD through batch and once-through tests for acid recovery from simulated IX eluate generated in the elution stage of TEs (B, Ga, Ge, Co, Sr) recovery from saltworks bitterns. Batch tests achieved high recoveries for HCl (45–50 %) and H2SO4 (30–37 %), being the theoretical maximum attainable recovery equal to 50 %. B and Ge only partially permeated through the membrane (82 % rejection) by a diffusion mechanism in their neutral form (H3BO3(aq), H4GeO4(aq)). Ga, Co and Sr, in cationic form, were highly rejected (>96 %). Permeability followed the order Ga < Sr < Co ≪ Ge < B, due to the relevant charge and size. HCl permeability correlated linearly with concentration, while H2SO4 was inversely proportional. Once-through tests showed higher acid (74 % HCl, 62 % H2SO4) and oxoacid (66 % H3BO3(aq), 52 % H4GeO4(aq)) recovery at a low specific flow rate, or apparent flux, (0.38 L/(m2membrane·h)) due to increased residence time. Water to acid flow rate ratios did not affect species transport when an excess of water was guaranteed. Conversely, an influence was observed when the ratio was below 1, with a minimum at 0.18, where a very low passage of species was observed due to the reduced dilution volume of the dialysate solution (water). A 1D transport model, incorporating the solutes permeabilities determined experimentally, effectively described the system performance, especially for HCl and B, albeit slightly overestimating the other TEs’ transport.

Geothermal fluids are a proven resource for sustainable baseload energy worldwide. Recently the fluids circulated in large volume streams in geothermal power plants have also come into focus for the potential of raw material extraction, such as Lithium. Geothermal fluids are the product of high-temperature and high-pressure water-rock interaction. This results in varying degrees of enrichment of different elements. Among them are elements of economic or strategic interest as lithium (Li), magnesium (Mg), cesium (Cs), but also elements typically causing unwanted mineral precipitations (scaling) within geothermal power plants such as silicon (Si). The extraction of specific target elements is still challenging in terms of integrating the process technology in a geothermal cycle. Especially in volcanic geothermal systems target elements are lower concentrated than in conventional brine resources and further the fluids tend to silica scaling. To enable the efficient extraction of the target elements, a treatment strategy was developed, consisting of an effective precipitation unit for silica reduction and two combined concentration steps for the enrichment of the target elements. The method uses the controlled precipitation of Si as Calcium-Silica-Hydrate phases and the concentration is conducted by reverse osmosis (RO) and membrane distillation (MD) using geothermal heat. The treatment approach was incorporated in a field demonstrator and tested in a geothermal system in the Southern Volcanic Zone in Chile. The results showed an effective silica reduction, enabling concentration rates up to a concentration factor of 16 under continuous flow-through conditions. The concentration of the dissolved solids on one side of the membranes enabled further the production of freshwater from geothermal fluids on the other side. Moreover, the MD process shows high energy efficiency in comparison to conventional evaporation processes and by geothermal sourcing also has direct potential for fossil fuel saving. Since volcanic resources are the most used in the global geothermal sector in terms of in­stalled capacity, the effective handling of the fluids has the potential for unleashing a global geothermal raw material potential.

Möglichen Effizienzsteigerungen von geothermischer Energieproduktion durch Verringerung der Reinjektionstemperatur stehen meist hydrochemische Randbedingungen entgegen. Hoch mineralisierte Thermalwässer tendieren verstärkt zu unkontrollierten Mineralausfällung (Scalings) bei größerer Druckentlastung oder Abkühlung. Sie sind ein stark limitierender Faktor für den effizienten und kontinuierlichen Betrieb von Geothermieanlagen. Komplexe standortspezifische Thermalwasserchemie erschwert deren Vorhersage und Quantifizierung mittels deterministischer geochemischer Modelle. Im MALEG Projekt werden geochemische Modelle durch eine künstliche Intelligenz ergänzt, welche mit hydrogeochemischen Daten aus vor Ort Experimenten trainiert wird.

Desalinization of seawater can be achieved by membrane distillation techniques (MD). In MD, the membranes should be resistant to fouling, robust for extended operating time, and preferably provide a superhydrophobic surface. In this work, we report the preparation and characterization of a robust and superhydrophobic polyvinylidene fluoride membrane containing fluoroalkyl-capped CuONPs (CuONPs@CF) in the inner and fluorinated capped silicon oxide nanoparticles (SiO2NPs@CF) on its surface. SiO2NPs@CF with a mean diameter of 225 ± 20 nm were prepared by the sol method using 1H,1H,2H,2H-perfluorodecyltriethoxysilane as a capping agent. Surface modification of the membrane was carried out by spraying SiO2NPs@CF (5% wt.) dispersed in a mixture of dimethyl formamide (DMF) and ethanol (EtOH) at different DMF/EtOH % v/v ratios (0, 5, 10, 20, and 50). While ethanol dispersed the nanoparticles in the spraying solution, DMF dissolved the PVDF on the surface and retained the sprayed nanoparticles. According to SEM micrographs and water contact angle measurements, the best results were achieved by depositing the nanoparticles at 10% v/v of DMF/EtOH. Under these conditions, a SiO2NPs covered surface was observed with a water contact angle of 168.5°. The water contact angle was retained after the sonication of the membrane, indicating that the modification was successfully achieved. The membrane with SiO2NPs@CF showed a flux of 14.3 kg(m²·h)⁻¹, 3.4 times higher than the unmodified version. The method presented herein avoids the complicated modification procedure offered by chemical step modification and, due to its simplicity, could be scalable to a commercial membrane.

The availability of raw mineral resources containing elements included in the critical raw materials (CRMs) list is a growing concern for the European Union. Sea mining has been identified as a promising secondary source. In particular, brines obtained in solar saltworks contain relevant amounts of valuable CRMs such as Mg(II), B(III), other alkaline/alkaline-earth metals (Rb(I), Cs(I), Sr(II)) and transition/post-transition elements (Co(II), Ga(III), Ge(IV)). However, the low concentration of some of these elements (µg/L) requires an effort to develop recovery routes that are sustainable and economically feasible where the required chemicals and energy are produced on-site from the saltworks bitterns (i.e. HCl and NaOH). Even the conventional recovery processes such as ion exchange, sorption and precipitation, which have proved to be competitive for metals recovery, are challenged in the case of trace elements (TEs). This work studies the recovery of TEs included in the CRMs list from saltworks bitterns after ion exchange processes. First, batch crystallisation and reactive precipitation were tested for some target elements in single-component solutions: Sr(II), Co(II), Ga(III), Ge(IV) and B(III). Then, the experiments were carried out with multi-component synthetic solutions assuming different scenarios of bittern streams coming out a selective extraction stage using sorption and ion exchange processes. The targeted elements were recovered except for Ge(IV), where alternatively routes need to be evaluated as its precipitation involves the use of tannic acid or sulphide solutions that could not be produced from the bitterns. However, a further concentration step would be necessary to achieve element concentrations closer to the mineral phases saturation. Moreover, model simulations were performed using the PHREEQC program, which provided a good prediction of the experimental trends obtained in most cases.

An extensive experimental campaign on Li recovery from relatively dilute LiCl solutions (i.e., Li+ ∼ 4000 ppm) is presented to identify the best operating conditions for a Li2CO3 crystallization unit. Lithium is currently mainly produced via solar evaporation, purification, and precipitation from highly concentrated Li brines located in a few world areas. The process requires large surfaces and long times (18-24 months) to concentrate Li+ up to 20,000 ppm. The present work investigates two separation routes to extract Li+ from synthetic solutions, mimicking those obtained from low-content Li+ sources through selective Li+ separation and further concentration steps: (i) addition of Na2CO3 solution and (ii) addition of NaOH solution + CO2 insufflation. A Li recovery up to 80% and purities up to 99% at 80 °C and with high-ionic strength solutions was achieved employing NaOH solution + CO2 insufflation and an ethanol washing step.