Combined study of mineral deposits and deep geothermal for energy production or urban heating – Comparison between the Portuguese (Neves-Corvo) and the Hungarian (Recsk) case studies

Energy and metals are essential resources in the 21st century and with the economic and technical development are more and more required. The fulfilling of these requirements leads to the need to produce both more ore and energy. Considering these goals, the project CHPM2030 (“Combined Heat, Power and Metal extraction”) was launched in January 2016, focused on the characterization of European mining regions that can be linked to both metal extraction and renewable energy production. The aim of this project is to convert ultra-deep metallic mineral formations into an “orebody-enhanced geothermal system” to co-produce energy and metals. This study will focus on two mining areas (Recsk in Hungary and Neves-Corvo in Portugal), considered CHPM2030 case studies, comparing them regarding mineral (ore) and geothermal potential in terms of heat-flow density values and their implication in temperatures in depth estimations. Especially, when it concerns geothermal energy, the surface demand is an important factor to consider, so wider studies are required

Laboratory leaching tests to investigate mobilisation of metals within engineered geothermal reservoirs

Combining geothermal energy utilization with the extraction of metals in a single interlinked process offers a way to improve the economics of engineered geothermal systems. Here we describe laboratory experiments used to assess the effectiveness of a range of leaching fluids by quantifying metal release from various mineralised rocks. The main findings of this study include: enhanced mobilisation of metals typically found in sulphide minerals (Pb, Zn, Cu), lesser mobilisation of some critical elements (such as Co, Sr and W), and the efficacy of organic additives in mobilising metals

Laboratory leaching tests to investigate mobilisation and recovery of metals from geothermal reservoirs

The H2020 project “Combined Heat, Power and Metal extraction” (CHPM2030) aims at developing a novel technology which combines geothermal energy utilisation with the extraction of metals in a single interlinked process. In order to improve the economics of geothermal-based energy production, the project investigates possible technologies for the exploitation of metal-bearing geological formations with geothermal potential at depths of 3–4 km or deeper. In this way, the coproduction of energy and metals would be possible and could be optimized according to market demands in the future. This technology could allow the mining of deep ore bodies, particularly for critical metals, alongside power production, while minimizing environmental impact and costs. In this paper, we describe laboratory leaching experiments aimed at quantifying the relative rates and magnitudes of metal release and seeing how these vary with different fluids. Specific size fractions (250–500 μm) of ground mineralised rock samples were investigated under various pressures and temperatures up to 250 bar and 250°C. Initial experiments involved testing a variety of potential leaching fluids with various mineralised samples for a relatively long time (up to 720 h) in batch reactors in order to assess leaching effectiveness. Selected fluids were used in a flow-through reactor with shorter contact time (0.6 h). To ensure possible application in a real geothermal reservoir, a range of fluids were considered, from dilute mineral acid to relatively environmentally benign fluids, such as deionised water and acetic acid. The main findings of the study include fast reaction time, meaning that steady-state fluid compositions were reached in the first few hours of reaction and enhanced mobilisation of Ca, Cd, Mn, Pb, S, Si, and Zn. Some critical elements, such as Co, Sr, and W, were also found in notable concentrations during fluid-rock interactions. However, the amount of these useful elements released is much less compared to the common elements found, which include Al, Ca, Fe, K, Mg, Mn, Na, Pb, S, Si, and Zn. Even though concentrations of dissolved metals increased during the tests, some remained low, and this may present technical challenges for metal extraction. Future efforts will work toward attaining actual fluids from depth to more tightly constrain the effect of parameters such as salinity, which will also influence metal solubility

Manipulation of lipid content in algae biomass at the Blue Lagoon R&D Center

Microalgae have long been recognized as a potentially good source for biofuel production because of their high oil content and rapid biomass production. There are two main objectives of this research: one is to explore the effect of growth conditions on the lipid content in algae biomass and the other is to convert the algae biomass into lipid by using so-called hydrothermal liquefaction, (HTL, a process where long chain polymers of hydrogen, oxygen and carbon decompose into short-chain petroleum hydrocarbons, under heat and high pressure). The optimal circumstances for the HTL both in terms of temperature, pressure and running time during the HTL were investigated, with the aim maximizing the lipid content. Microalgae strain, isolated from the geothermal environment of the Blue Lagoon in Iceland was cultivated at the Blue Lagoon R&D Center in geothermal seawater. Algae were harvested and subsequently processed by HTL by exposing the algae to high pressure (more than 50 bar) and high temperature (up to 270 °C) at the same time, to achieve the chemical conversion of the biomass. An induction-heated autoclave, available from a previous M.Sc. project carried out at the Blue Lagoon R&D Center, was used. To investigate the highest amount of lipids naturally accumulated in the microalgae cells, growth conditions (nutrition concentration and pH) were manipulated in small-scale bioreactors. As the best outcome, oil content increased to 9.03% from the initial 0.46% in algae biomass, during hydrothermal processing at 280 °C temperature and under 56-61 bar pressure. This research confirmed that, microalgae cultivated with low nutrition concentration has the most lipid content per produced mass. However, unfavorable circumstances are limiting the growth rate of the biomass in a way, the absolute mass of produced lipids in are the lowest in the case of nutrition limitation. The thesis also gives an overview of geothermal systems and the most common methods and technologies used to harness geothermal energy

Kombinált hő- áram és fémtermelés ultramély érctestekből – rétegcsúsztatás jövőbeni alkalmazása

Az Európai Uniónak „tiszta” energiára van szüksége, ami hosszú távon gazdaságosan fenntartható. Ugyanakkor szükség van nyersanyagokra is, azonban a bányászat elérhetősége limitált. Ennek a megoldására az Európai Bizottság pályázatot írt ki, aminek a feladata új technológia fejlesztése a geotermikus energiatermelés és fém bányászat együttes megvalósulására. A három és fél éves periódus végére laboratóriumi méretben üzemelő, gazdaságilag fenntartható technológia kidolgozása a cél. A tervezett erőmű a hazai geotermikus szektor által rétegcsúsztatásnak nevezett technológiát fogja alkalmazni, amely során – a réteg repesztéssel szemben – nem használnak kitámasztó anyagot, mert a meglévő feszültségtér és a lesajtolt víz súrlódás csökkentő hatására elmozdulás történik a már meg-lévő repedéseken, és ezek a repedések nem záródnak vissza az egyenetlen felület és a továbbra is ható feszültségtér miatt. Így a technológia új törések kialakítása nélkül repeszti tovább a már meglévő töréseket

Biofilm Forming Bacteria during Thermal Water Reinjection

Reinjection of heat-depleted thermal water has long been in the center of scientific interest in Hungary regarding around 1000 operating thermal wells. While the physical and chemical aspects of reinjection have partly been answered in the past years, the effects of biological processes are still less known. We carried out our investigations in the surface elements of the Hódmezővásárhely geothermal system which is one of the oldest operating geothermal systems in Hungary. About one-third of the used geothermal water has been reinjected since 1998 by two reinjection wells at the end of the thermal loops. During the operation, plugging of the surface system was experienced within a few-day-long period, due to biological processes. The goal of our research was to find the dominant species of the microbial flora and to make a proposal to avoid further bacterial problems. We found that the reinjected, therefore the produced, water’s chemical oxygen demand, phenol index, and BTEX composition basically determine the appearing flora on the surface. When the concentration of these compounds in the thermal water is significant and residence time is long enough in the buffer tank, certain bacteria can be much more dominant than others, thus able to form a biofilm which plugs the surface equipment much more than it is expected