Avaliação de um biossorvente à base de fibra de ráfia na sorção de hidrocarbonetos

Oil spills and discharges of petroleum products have severely polluted aquatic ecosystems, oceans, rivers, groundwater and even soil. In August 2019, more than 2,000 km of the northeast and southeast coast of Brazil were struck by a major oil spill in the country’s largest ever environmental disaster. Spill remediation is a significant environmental challenge and the economic and socioenvironmental impacts of these events are diverse. Oil spills in oceans and rivers severely affect the fishing and tourism industries of the areas in question, with damage including severe short and long-term effects on plants and animals, such as respiratory and digestive disorders, reduced growth and reproductive capacity as well as weakened immunity due to the bioaccumulation of toxic contaminants. There are several proposed strategies for removing crude oil and petroleum products from surface water. Contaminated areas can be remediated in-situ or ex-situ, with the former considered the best option in terms of cost and efficiency. In this respect, absorbent materials obtained from biomass have received widespread attention due to their ease of use, buoyancy and low cost. Raffia is a natural fiber abundant in eastern Africa with excellent physical properties, such as low specific weight, good liquid sorption and low conductivity. As such, the present study investigated the application of raffia fiber with different particle sizes (< 300 µm, 300 - 850 µm, 850 - 1000 µm, 1000 - 1400 µm and 1400 - 2000 µm) and fiber/hydrocarbon ratios (1, 2, 3 and 4% w/v) as an absorbent for hydrocarbons, using n-heptane as a model molecule. Microscopic analysis of micronized raffia fiber indicated the presence of honeycomb-shaped cells with well-defined borders and an irregular geometry. These honeycomb structures are preserved, especially in large particle size ranges. Among the granulometries assessed, the highest sorption capacities were obtained for 1000 to 1400 µm raffia fibers, suggesting that honeycomb-shaped structures favor hydrocarbon sorption. Additionally, the fact that smaller particles do not require micronization is economically beneficial and facilitates application of the absorbent material to remediate hydrocarbon-contaminated areas. The results obtained under the conditions studied indicate that sorption capacity increases as the absorbent content rises. Comparison of fiber contents of 1% and 3% w/v for 1000 - 1400 µm particles showed an increase of approximately 43% in sorption capacity when content rose to 3% w/v. The results of the present study demonstrate the potential of natural raffia fiber as an alternative absorbent for hydrocarbons.O derramamento de óleo e derivados de petróleo leva a graves efeitos de poluição em sistemas aquáticos, oceanos, rios e águas subterrâneas e, até mesmo, no solo. Recentemente, em agosto de 2019, mais de 2 mil quilômetros do litoral do Nordeste e Sudeste brasileiro foram atingidos por um grande derramamento de petróleo, caracterizando o maior desastre ambiental já ocorrido no Brasil. Um grande desafio ambiental é a remediação de incidentes envolvendo derramamento de óleo e derivados de petróleo. Os impactos econômicos e socioambientais desses incidentes são os mais diversos. Considerando os desastres de derramamento em áreas marítimas e fluviais, os danos podem gerar sérios problemas na indústria pesqueira ou até mesmo em atividades turísticas da região. Entre estes danos, efeitos gravíssimos em plantas e animais a curto e longo prazo, como problemas nos sistemas respiratório e digestivo, na capacidade de crescimento e reprodução e na imunidade devido aos processos de bioacumulação de contaminantes tóxicos. Atualmente, muitas abordagens são propostas para remoção de contaminantes de óleo e derivados de petróleo de superfícies aquosas. A remediação de áreas contaminadas pode ocorrer in-situ ou ex-situ, sendo que as tecnologias in-situ são sempre consideradas as melhores opções devido ao custo e eficiência. Com relação a isso, materiais absorventes provenientes de biomassa têm atraído muita atenção pela sua facilidade de utilização, pois normalmente possuem boa flutuabilidade e baixo custo. A ráfia é uma espécie de fibra natural encontrada em abundância na região ocidental da África e que possui propriedades físicas interessantes, como a baixa massa específica, boa sorção a líquidos e baixa condutividade. Dentro deste contexto, o presente trabalho estudou a aplicação da fibra natural de ráfia em diferentes faixas granulométricas (< 300 µm, 300 - 850 µm, 850 - 1000 µm, 1000 - 1400 µm e 1400 - 2000 µm) e em diferentes razões fibra/hidrocarboneto (1, 2, 3 e 4% m/v) como material absorvente para hidrocarbonetos, utilizando o n-heptano como molécula modelo. A análise microscópica da fibra de ráfia micronizada indica a presença de células formadas com fronteiras bem definidas e fechadas, mas com geometria irregular, cuja forma lembra uma colmeia de abelha. Essas estruturas de colmeia foram preservadas, principalmente nas maiores faixas granulométricas. Dentre as diferentes granulometrias avaliadas, as maiores capacidades de sorção foram obtidas com partículas de ráfia na faixa de 1000 - 1400 µm, sugerindo que a presença de estruturas na forma de colmeia favorece a sorção de hidrocarboneto. Além disso, o fato de não haver necessidade de micronizar a fibra em partículas muito finas, gera vantagens do ponto de vista econômico e de aplicação do material absorvente na remediação de áreas contaminadas por hidrocarbonetos. Os resultados obtidos nas condições estudadas indicam que a capacidade de sorção cresce à medida que a quantidade de absorvente aumenta. Comparando-se os teores de 1% e 3% m/v de ráfia, na faixa de 1000 - 1400 µm verificou-se um aumento de aproximadamente 43% na capacidade de sorção, quando o teor de fibra aumentou para 3% m/v. Os resultados do presente trabalho evidenciam a potencialidade da fibra natural de ráfia como material absorvente alternativo para hidrocarbonetos

Wellbore integrity in a saline aquifer : experimental steel-cement interface degradation under supercritical CO2 conditions representative of Brazil’s Parana basin

From our work, significant progress has been made in understanding the degradation of cement-casing systems. The CO2 degradation process was evaluated in specimens with a large interfacial defect, such as large annular spaces, voids and/or channels, which may be the result of a poor cementing job. From the experiments showing no interfacial defect, no signs of degradation were observed, while from experiments showing interfacial defect, both the cement and steel undergo significant degradation. In the well casing, the CO2-rich brine affects the steel phase, leaching Fe2+ ions into solution and promoting FeCO3 precipitation on the material surface, while on the cement sheath, two processes are occurring: (i) the portlandite dissolution and (ii) the cement carbonation process. Then, iron (Fe2+) starts to migrate into the cement structure, compromising the material’s self-healing and pore-blocking features, while calcium (Ca2+) starts to compose the corrosion film from the formation of mixed carbonates (FexCayCO3) so reducing the corrosion layer’s protection. Finally, both ions (Ca2+ and Fe2+) become so abundant in the material vicinity that they may form calcium carbonate (CaCO3) on the corrosion layer and iron carbonate (FeCO3) in the cement matrix. Thus, from our results, the degradation mechanisms of the cement-casing system in CO2-rich brine was revised

The role of hydrogenotrophic iron-reducing bacteria on the corrosion process in the context of geological disposal

L’objectif principal de cette étude est d’évaluer le rôle de l’activité de bactéries hydrogénotrophes et ferri-réductrices sur le processus de corrosion anoxique en utilisant des indicateurs géochimiques. Il est considéré que le couple redox H2/Fe(III) est un moteur important pour les activités bactériennes qui peuvent ainsi affecter les vitesses de corrosion par la déstabilisation des couches de passivation (i.e. magnétite, Fe3O4). Les résultats indiquent que la magnétite de synthèse est déstabilisée en présence de bactéries hydrogénotrophes et ferri-réductrices due à la réduction du Fe(III) structural couplée à l’oxydation de l’H2. La quantité de Fe(III) bioréduit est augmentée en présence de concentrations croissantes en H2 dans le système: 4% H2 < 10% H2 < 60% H2. De plus, les résultats indiquent que la réaction de corrosion est différente selon la composition de la solution et la surface de contact de l’échantillon métallique (poudre de fer ou coupon en acier au carbone). Les produits de corrosion solides sont différents pour chaque échantillon étudié: vivianite, sidérite et chukanovite sont les principales phases minérales identifiées dans les expériences avec de la poudre de fer, tandis que vivianite et magnétite sont identifiées en présence de coupons en acier au carbone. Les résultats montrent que la vitesse de corrosion est quasiment deux fois plus importante en présence de bactéries après 5 mois de réaction. Cette étude apporte une nouvelle approche sur la compréhension des phénomènes de biocorrosion, l’identification des mécanismes physico-chimiques et la détermination des paramètres contrôlant la vitesse de corrosion.The main objective of this study is to evaluate the role of hydrogenotrophic and IRB activities on anoxic corrosion process by using geochemical indicators. It is assumed that the redox couple H2/Fe(III) is an important driver for bacterial activities potentially affecting the corrosion rate by destabilization of passive layers (i.e. magnetite, Fe3O4). Our results indicate that synthetized Fe3O4 is destabilized in the presence of hydrogenotrophic IRB due to structural Fe(III) reduction coupled to H2 oxidation. The extent of Fe(III) bioreduction is notably enhanced with the increase in the H2 concentration in the system: 4% H2 < 10% H2 < 60% H2. Moreover, the results indicate that corrosion extent changes according to the solution composition and the surface of metallic sample (iron powder and carbon steel coupon). The solid corrosion products are different for each sample: vivianite, siderite and chukanovite are the main mineral phases identified in the experiments with iron powder, while vivianite and magnetite are identified with carbon steel coupons. Our results demonstrate that corrosion rate is increased almost two-fold in the presence of bacteria after 5 months of reaction. This study gives new insights regarding the understanding of biocorrosion phenomena, identification of physicochemical mechanisms, and determination of key parameters controlling the corrosion rate

Impact of microbial activity on the radioactive waste disposal: long term prediction of biocorrosion processes

International audienceThis study emphasizes different experimental approaches and provides perspectives to apprehend biocorrosionphenomena in the specific disposal environment by investigating microbial activity with regard to themodification of corrosion rate, which in turn can have an impact on the safety of radioactive waste geologicaldisposal.It is found that iron-reducing bacteria are able to use corrosion products such as iron oxides and “dihydrogen” asnew energy sources, especially in the disposal environment which contains low amounts of organic matter.Moreover, in the case of sulphate-reducing bacteria, the results show that mixed aerobic and anaerobicconditions are the most hazardous for stainless steel materials, a situation which is likely to occur in the earlystage of a geological disposal. Finally, an integrated methodological approach is applied to validate theunderstanding of the complex processes and to design experiments aiming at the acquisition of kinetic dataused in long term predictive modelling of biocorrosion processes