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Ocean-Floor Sediments as a Resource of Rare Earth Elements: An Overview of Recently Studied Sites

Publication . Milinovic, Jelena; Rodrigues, Francisco J. L.; Barriga, Fernando J A S; Murton, Bramley J.

The rare earth elements (REE), comprising 15 elements of the lanthanum series (La-Lu) together with yttrium (Y) and scandium (Sc), have become of particular interest because of their use, for example, in modern communications, renewable energy generation, and the electrification of transport. However, the security of supply of REE is considered to be at risk due to the limited number of sources, with dependence largely on one supplier that produced approximately 63% of all REE in 2019. As a result, there is a growing need to diversify supply. This has resulted in the drive to seek new resources elsewhere, and particularly on the deep-ocean floor. Here, we give a summary of REE distribution in minerals, versatile applications, and an update of their economic value. We present the most typical onshore methods for the determination of REE and examine methods for their offshore exploration in near real time. The motivation for this comes from recent studies over the past decade that showed ΣREE concentrations as high as 22,000 ppm in ocean-floor sediments in the Pacific Ocean. The ocean-floor sediments are evaluated in terms of their potential as resources of REE, while the likely economic cost and environmental impacts of deep-sea mining these are also considered.

2021-01-30Journal article

Open access

The role of climate, marine influence and sedimentation rates in late-Holocene estuarine evolution (SW Portugal)

Publication . Costa, Ana Maria; Freitas, Maria da Conceição; Leira, Manel; Costas, Susana; Costa, Pedro JM; Andrade, César; Bao, Roberto; Duarte, João; Rodrigues, Aurora; Cachão, Mário; Araújo, Ana Cristina; Diniz, Mariana; Arias, Pablo

Estuaries are sensitive to changes in global to regional sea level, to climate-driven variation in rainfall and to fluvial discharge. In this study, we use source and environmentally sensitive proxies together with radiocarbon dating to examine a 7-m-thick sedimentary record from the Sado estuary accumulated throughout the last 3.6 kyr. The lithofacies, geochemistry and diatom assemblages in the sediments accumulated between 3570 and 3240 cal. BP indicate a mixture between terrestrial and marine sources. The relative contribution of each source varied through time as sedimentation progressed in a low intertidal to high subtidal and low-energy accreting tidal flat. The sedimentation proceeded under a general pattern of drier and higher aridity conditions, punctuated by century-long changes of the rainfall regime that mirror an increase in storminess that affected SW Portugal and Europe. The sediment sequence contains evidence of two periods characterized by downstream displacement of the estuarine/freshwater transitional boundary, dated to 3570–3400 cal. BP and 3300–3240 cal. BP. These are intercalated by one episode where marine influence shifted upstream. All sedimentation episodes developed under high terrestrial sediment delivery to this transitional region, leading to exceptionally high sedimentation rates, independently of the relative expression of terrestrial/marine influences in sediment facies. Our data show that these disturbances are mainly climate-driven and related to variations in rainfall and only secondarily with regional sea-level oscillations. From 3240 cal. BP onwards, an abrupt change in sediment facies is noted, in which the silting estuarine bottom reaches mean sea level and continued accreting until present under prevailing freshwater conditions, the tidal flat changing to an alluvial plain. The environmental modification is accompanied by a pronounced change in sedimentation rate that decreased by two orders of magnitude, reflecting the loss of accommodation space rather than the influence of climate or regional sea-level drivers.

2019Journal article

Restricted access

Impact of fine particle pollution on the natural ventilation potential of commercial buildings

Publication . Martins, Nuno R.; Graça, Guilherme Carvalho Canhoto Carrilho da

The majority of office and other non-domestic buildings use mechanical cooling and ventilation, even when an optimized natural ventilation (NV) system could meet cooling and fresh air requirements. However, in most large cities, the outdoor environment is contaminated with a combination of noise, fine particles, heat and toxic gases. This contaminated environment has a detrimental impact on naturally ventilated buildings due to their lack of filtration and outdoor noise attenuation systems. This thesis presents a numerical analysis of the effect of fine particle pollution (PM2.5) on the NV potential of office buildings in California, Europe and Asia. Several years of measured weather and PM2.5 concentration data were used to perform statistical and dynamic thermal and airflow simulation analysis. In California and Europe, the outdoor temperature is suitable for NV during between 40 and 95 % of the annual working hours. In Asia, that fraction is lower, but can be increased by the availability of personal comfort systems (PCS). Nonetheless, in most cities, PM2.5 levels are high during a majority of those working hours. Detailed simulation results show that a hybrid NV system can reduce the air-conditioning and ventilation electricity consumption of a well-designed office building by up to 83 % (93 % if combined with PCS), in comparison to an office using, during all working hours, a mechanical cooling and ventilation system equipped with a high-efficiency particle filter. Unfortunately, in this hybrid approach, high levels of outdoor PM2.5 penetrate the indoor environment, increasing occupant cumulative exposure by up to six times. To overcome this problem, two exposure control approaches were tested. Using NV only during moments of low outdoor PM2.5 concentrations limits the exposure increase to up to three times but at the cost of reducing energy savings. Equipping NV openings with an electrostatic filter would result in a similar exposure reduction, but at a very low energy cost, taking full advantage of NV’s saving potential.

2018Doctoral thesis

Open access

Caracterização e avaliação do recurso hidromineral das Quenturas, vulcão das Furnas, ilha de S. Miguel (Açores)

Publication . Freitas, Ana Rita Regalo; Carvalho, Maria do Rosário da Encarnação de,1963-; Nunes, João Carlos Carreiro,1962-

A ilha de São Miguel, e em particular a região das Furnas, têm sido alvo de diversos estudos desde o século XVI, em parte devido aos fenómenos de termalismo que aqui ocorrem e à forma como afetam as populações, nomeadamente no que toca à utilização destas águas para fins terapêuticos e de lazer. A ocorrência de nascentes de água mineral e termal é um fenómeno conhecido desta região, cuja origem está associada a fenómenos de carácter vulcânico e à existência de sistemas hidrotermais superficiais ou profundos, bem como à interação entre ambos. A variabilidade composicional das águas do Vulcão das Furnas traduz-se no aparecimento de águas frias, com maior ou menor componente gasocarbónica, águas termais ácidas e básicas e fumarolas, todas no interior da Caldeira do Vulcão das Furnas. Dada a importância destes recursos minerais foi demarcada uma concessão hidromineral, designada por “Concessão Mineromedicinal Estância Termal das Furnas”, que englobava, em 1964, uma área de 50 hectares e trinta e três nascentes mineromedicinais, cuja licença de exploração foi atribuída à antiga Junta Geral. Entre estas trinta e três está contemplada a nascente das Quenturas (ou da Água Férrea das Quenturas), que atualmente se encontra captada e é utilizada no abastecimento do Furnas Boutique Hotel – Thermal & Spa, localizado nas suas imediações. O objetivo do presente trabalho é promover um conhecimento mais aprofundado do recurso hidromineral das Quenturas, quer quantitativo, quer qualitativo, por forma a contribuir para a correta gestão do mesmo. Para tal procedeu-se a uma atualização dos dados da “Concessão Mineromedicinal Estância Termal das Furnas”, com levantamento e amostragem das diversas nascentes que dela fazem parte atualmente, com vista ao estudo geoquímico e isotópico das mesmas. O estudo do comportamento das nascentes localizadas na área envolvente da “Concessão Mineromedicinal Estância Termal das Furnas” permite melhor compreender o aquífero termal associado ao recurso hidromineral das Quenturas. A Caldeira do Vulcão das Furnas é dotada de grande variabilidade composicional no que se refere às águas que nela emergem, sendo estas geralmente classificadas como águas frias, águas frias gasocarbónicas, águas termais de menor temperatura (mesotermais) ou maior temperatura (hipertermais) e fumarolas. Neste enquadramento, a nascente das Quenturas representa uma água termal de pH ácido, cuja temperatura de emergência é próxima de 59°C, apresentando-se muito mineralizada. É descrita como o resultado da contaminação de aquíferos pouco profundos por vapor hidrotermal que ascende do aquífero termal mais profundo.

2017Master thesis

Open access