Oil–mineral Aggregates Formation Research Articles

Using Machine Learning to Predict Oil–Mineral Aggregates Formation

The formation of oil–mineral aggregates (OMAs) is essential for understanding the behavior of oil spills in estuaries and coastal waters. We utilized statistical methods (screening design) to identify the most influential variables (seven factors in total) during OMA formation. Time was the most important factor, followed by temperature and oil/clay ratio. Moreover, machine learning was applied to predict the OMA median diameter (D50). Among the three tested algorithms, the Random Forest (RF) algorithm showed the highest accuracy, with a training R2 of 0.99 and testing R2 of 0.93. An open-source software tool that integrates the RF algorithm was developed, allowing users to easily estimate the OMA D50 based on input variables. The valuable results and the practical tool we have developed enhance the understanding and management of environmental impacts associated with oil spills.

STABILIZATION OF OIL-IN-WATER EMULSIONS WITH HIGHLY DISPERSED MINERAL PARTICLES: BIODEGRADATION AND TOXIC EFFECT ON AQUATIC ORGANISMS

For the processes of natural self-purification from oil spills, the presence of suspended solids in the water column is essential to form so called oil-mineral aggregates (OMA) followed by their migration to the bottom layers and subsequent oil biodegradation. The literature contains a sufficient number of publications devoted to OMA formation conditions and feasibility of their application in oil spill response technologies. However, the impact of OMAs on marine ecosystems and their representatives is poorly studied. The lack of systematic studies focused on the estimation of ecological risk of the consequence OMAs entail for marine ecosystems, and the efficiency of oil biodegradation involving OMA formation, leads to quite contradictory conclusions. This review presents an attempt to summarize the available reports on the ecological risk of OMAs for aquatic ecosystems and estimations of the effect of OMA formation on oil biodegradation. Factors that influence the toxicity of OMAs for suspended and benthic aquatic organisms, and the prospects for further research in the field of environmental impact of these structures with a view to use them more actively in oil spill response technologies are described. This review are based on the analysis of scientific publications over a period of 1999 to 2021 by ScienceDirect search tool. For citation: Grechishcheva N.Yu., Korolev A.M., Zavorotny V.L., Starodubtseva K.A., Ali M.S. Stabilization of oil-in-water emulsions with highly dispersed mineral particles: biodegradation and toxic effect on aquatic organisms. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 2. P. 23-35. DOI: 10.6060/ivkkt.20236602.6729.

Experimental investigations on the vertical distribution and properties of oil-mineral aggregates (OMAs) formed by different clay minerals

After oil spills, the floating oil may interact with suspended minerals to form the oil-mineral aggregates (OMAs) in turbulent environments. In this work, a flume was used in conjunction with a settling device to investigate the vertical distribution and properties of OMAs formed by different clay minerals. The density and size of OMAs depend on the density and surface properties of the constituent particles, which also affect the vertical distribution of dispersed oil. Density of oil-montmorillonite aggregates increased from 1165 to 1897 kg/m3 within 6 h test. Among the four minerals, montmorillonite displayed the highest affinity with dispersed oil and the most significant modification of oil-water interfacial tension. Oil dispersion efficiency was significantly greater and reached 39.3% in the presence of montmorillonite at 300 mg/L compared with the control group (17.6%). Particle concentration is the most important factor for the capture of oil and participation of particles during the OMA formation, while the zeta potential and hydrophobicity have nonsignificant effect on the two processes. Cation exchange capacity has a moderate effect on the sunken oil formation, which is also the second main factor governing the particle participation. Particle size plays a second leading role in governing the sunken oil formation but with a minor contribution of the particle participation.

The Role of Biophysical Stickiness on Oil-Mineral Flocculation and Settling in Seawater

Biophysical cohesive particles in aquatic systems, such as extracellular polymeric substances (EPS) and clay minerals, play an important role in determining the transport of spilled oil contamination and its eventual fate, particularly given that suspended sediment and microbial activities are often prevalent and diverse in natural environments. A series of stirring jar tests have been conducted to understand the multiple structures characteristics of the oil-mineral aggregates (OMAs) and EPS-oil-mineral aggregates (EPS-OMAs). OMAs and EPS-OMAs have been successfully generated in the laboratory within artificial seawater using: Texas crude oil (Dynamic viscosity: 7.27 × 10–3Pa⋅s at 20°C), two natural clay minerals (Bentonite and Kaolin clay), and Xanthan gum powder (a proxy of natural EPS). A magnetic stirrer produced a homogeneous turbulent flow with a high turbulence level similar to that under natural breaking waves. High-resolution microscopy results show that EPS, kaolinite, and bentonite lead to distinguished oil floc structures because of the different stickiness character of EPS and mineral clay particles. With relatively low stickiness, kaolinite particles tend to attach to an oil droplets surface (droplet OMAs) and become dominant in small-sized flocs in the mixture sample. In contrast, the more cohesive bentonite particles stickiness could adsorb with oil droplets and are thus dominated by larger sized flocs. Biological EPS, with the highest stickiness, demonstrated that it could bond multiple small oil droplets and form a web structure trapping oil and minerals. Generally, adding EPS leads to flake/solid OMAs formation, and individual oil droplets are rarely observed. The inclusion of ESP within the matrix, also reduced the dependence of settling velocity on floc size and mineral type.

An OMA-SIM Approach to Study OMA Kinetics for the Cleanup of Marine Oil Spill

Breaking waves can break oil slicks into fine droplets and entrain them in the water column. An interesting hypothesis has emerged in recent years that oil droplets and mineral fines may form Oil-Mineral Aggregates (OMAs) and enhance oil dispersion in aquatic environments. The present research investigated physical processes of marine oil spills, including oil slick breakup, the formation of OMAs, and oil/OMAs vertical mixing. In this study, a modeling approach is developed for simulating the formation and vertical mixing of oil droplets and OMAs, namely Oil Droplet and OMAs Simulation (OMA-SIM). This integrated modeling tool combines the oil vertical mixing model and density-based OMAs formation model to examine the dispersion of oil droplets and OMAs. The OMA-SIM is validated using data obtained from a mesoscale wave tank experimental study. Simulation results show that the energy dissipation rate of breaking waves is the predominant factor affecting the concentration and particle size of formed oil droplets and OMAs. It also confirms that oil viscosity has a significant influence on dispersed oil concentration. High temperature, low oil viscosity, together with more formed OMAs lead to a higher concentration of dissolved oil. Other findings based on the validated OMA-SIM approach include that: the dispersants reduce oil/water interfacial tension and decrease the size of oil droplets and OMAs, and the application of mineral fines facilitates the formation of OMAs. This study indicates that the OMA-SIM is an effective modeling tool for examining the vertical dispersion of spilled oil with or without the use of dispersant and other green particle materials like mineral fines under breaking waves.

Effects of weathering on the dispersion of crude oil through oil-mineral aggregation

Crude oil that is inadvertently spilled in the marine environment can interact with suspended sediment to form oil-mineral aggregates (OMA). Researchers have identified OMA formation as a natural method of oil dispersion, and have sought ways to enhance this process for oil spill remediation. Currently there is a lack of understanding of how the weathering of oil will affect the formation of OMA due to a lack of published data on this relationship. Based on literature, we identified two conflicting hypotheses: OMA formation 1) increases with weathering as a result of increased asphaltene and polar compound content; or 2) decreases with weathering as a result of increased viscosity. While it is indeed true that the viscosity and the relative amount of polar compounds will increase with weathering, their net effects on OMA formation is unclear. Controlled laboratory experiments were carried out to systematically test these two conflicting hypotheses. Experimental results using light, intermediate, and heavy crude oils, each at five weathering stages, show a decrease in OMA formation as oil weathers.

Chemical dispersion of oil with mineral fines in a low temperature environment

The increasing risks of potential oil spills in the arctic regions, which are characterized by low temperatures, are a big challenge. The traditional dispersant method has shown limited effectiveness in oil cleanup. This work studied the role of mineral fines in the formation of oil–mineral aggregates (OMAs) at low temperature (0–4°C) environment. The loading amount of minerals and dispersant with different dispersant and oil types were investigated under a full factorial design. The shapes and sizes of OMAs were analyzed. Results showed that the behavior of OMA formation differs when dispersant and mineral fines are used individually or together. Both the experimental and microscopic results also showed the existence of optimal dispersant to oil ratios and mineral to oil ratios. In general, poor oil removal performance was observed for more viscous oil. Corexit 9500 performed better than Corexit 9527 with various oils, in terms of oil dispersion and OMA formation.

Influence of Seasonal Variability of Lower Mississippi River Discharge, Temperature, Suspended Sediments, and Salinity on Oil‐Mineral Aggregate Formation

Under certain conditions, oil droplets that have separated from the main oil slick may become coated by suspended sediments forming oil-mineral aggregates (OMAs). The formation of these aggregates depends on suspended particulate characteristics, temperature, salinity, mixing energy, droplet size and number, and oil properties. The OMAs do not re-coalesce with the slick and tend not to adhere to surfaces, potentially evading surface cleanup measures, enhancing opportunity for biodegradation and reducing shoreline oiling. Potential OMA formation was quantified during four distinct states of the Lower Mississippi River during a typical year using empirical relationships from laboratory and field studies for three common oils and different combinations of discharge, temperature, suspended sediments, and salinity. The largest potential OMA formation for the two lighter oils, up to 36% of the total release volume, was in the winter and spring, when high sediment availability promotes formation. For the denser, high-viscosity oil, the peak potential OMA formation, 9% of the release volume, occurred in the summer, when the salinity was higher. These results provide some evidence that, depending on environmental and spill characteristics, the formation of OMAs could be an important, but unaccounted for, process in the fate and transport of oils released in the Lower Mississippi River and should be included in oil spill dispersion models and post-spill site assessment and remediation actions.

Investigation of OMA formation and the effect of minerals

Oil–mineral-aggregates (OMA) have been shown to be effective in oil spills cleanup. Experimental work was carried out to study the effects of physical–chemical properties of natural minerals and chemically modified minerals on OMA formation and oil removal. The results showed that the hydrophobicity, particle sizes and specific surface of minerals played an important role in OMA formation. Appropriate hydrophobicity of minerals can enhance the formation of OMA. The surface property of minerals can also influence the shape of OMA. Spherical mineral–oil aggregates were frequently formed with hydrophilic minerals while irregular shaped OMA were observed with hydrophobic minerals. The sizes of OMA also increased when the minerals changed from hydrophilic to hydrophobic. The effects of dispersant and mixing energy were also carefully studied. The results showed that dispersant were a dominant factor. When dispersant was applied, effects of other factors became minimal.

Laboratory investigation of the effects of mineral size and concentration on the formation of oil–mineral aggregates

Controlled laboratory studies of the formation of oil–mineral aggregates (OMA) in seawater demonstrate that sediment concentration and sediment size are key variables for determining the quantity of oil droplets stabilised by OMA formation. Experiments with a single sediment size and a range of sediment concentrations show that as sediment concentration increases, the quantity of oil trapped in OMA increases abruptly. In experiments with a single sediment concentration and a range of sediment sizes, the quantity of oil trapped in OMA decreases as sediment size increases. These results provide direct support to the hypothesis that there is a critical sediment concentration for OMA formation. Below this concentration, stabilisation of oil droplets by OMA decreases rapidly, while above this concentration, stabilisation is extensive. The results also support simple geometric models of OMA formation that predict that the critical sediment mass concentration increases linearly with sediment particle diameter. These results will help to place quantitative constraint on predictions of where and when OMA formation will be a factor in the natural dispersal of oil accidentally spilled into the ocean.

BIODEGRADATION AT A LAND-FARMING SITE AT 14,000 FEET IN THE HIGH BOLIVIAN ALTIPLANO

ABSTRACT Approximately 30,000 m3 of contaminated soil recovered from cleanup operations after a 29,000 barrel oil spill in the Desaguadero River (January 2000) was stored in temporary pits. Waste disposal plans explored several options for final disposal, including incineration and land farming. Initial concerns about the ability to landfarm the contaminated soil centered on the biodegradation potential at altitudes of 14,000 ft (4,300 m) and in a region with seasonally low day and nighttime temperatures. The Bolivian Altiplano has a semiarid climate where daily fluctuations of 15°C in temperature are common while average temperatures range between −6 C (July) and 21.0°C (November). The technical experts at the Bolivian Ministry of Sustainable Development were reluctant to grant permission for Land Farming to be used at high altitude and instead insisted that all the contaminated soil be sent by truck across Bolivia to lower altitudes where the proposed a Land Farm was to be created. As an operational response a series of experiments was set up to demonstrate that indeed Land Farming was possible at high altitude. This paper presents the results of these experiments but it should be clearly noted that the testes were conducted under operational conditions without the rigour normally found in laboratory or scientific experiments. Results showed that it was not only possible to deplete the total petroleum hydrocarbon (TPH) content from 40,000 ppm to below 1,000 ppm required by Bolivian law, but that it also could be completed within 4 months under specific technical conditions of the biodegradation process. Previous studies documented the formation of oil-mineral aggregates (OMAs) in the contaminated soils from the Rio Desaguadero spill1. We hypothesized that OMA formation and presence of aluminum polysilicate would provide an effective combination to increase the biodegradability of the soils under specific control conditions. This paper explains the high-altitude biodegradation process and the results of monitoring tests from the land farming under operational field conditions. ©2004 Transredes S.A. All Rights Reserved.

A COMPREHENSIVE NUMERICAL APPROACH TO PREDICT OIL-MINERAL AGGREGATE (OMA) FORMATION FOLLOWING OIL SPILLS IN AQUATIC ENVIRONMENTS

ABSTRACT Aggregation between suspended sediment grains and oil droplets, which leads to the formation of agglomerates commonly referred to as Oil-Mineral Aggregates (OMA), is widely acknowledged as a natural process that enhances dispersion of spilled oil in aquatic environments. A comprehensive numerical approach is developed to predict the contribution of OMA formation to the dispersal of spilled oil. The model comprises four modules to calculate maximum size of oil droplets, to predict formation of oil droplets from a slick, to predict formation of sediment floc, and to calculate density of oil-sediment flocs. The inputs of the model are environmental conditions, oil properties and concentration and grain-size distribution of suspended sediments. Sensitivity analysis performed using five crude oils covering a range of viscosities from 8 10−3 to 68 10−3 kg/ms, a kinetic energy dissipation rate from 10−3 to 102 m2/s3, a sediment grain size of 3 μm and a sediment concentration of 250 mg/l showed that formation of OMA is strongly dependent on the oil-water interfacial tension and the kinetic energy dissipation rate. Under breaking wave conditions, the contribution of OMA formation to the dispersal of spilled oil varies between 31 and 97 % depending on characteristics of the individual test oils, in particular oil-water interfacial tension. Results show also that OMA formation is enhanced when the Weber number approaches a value of 0.05.

The OSSA II Pipeline Oil Spill: Natural Mitigation of a Riverine Oil Spill by Oil–Mineral Aggregate Formation

Previous studies have documented enhanced rates of oil removal from marine sediments by physical dispersion and biological degradation processes following the formation of oil–mineral aggregates (OMAs), which are microscopic particles of oil stabilized by fine minerals. In January 2000, approximately 29,000 bbl of crude oil were accidentally released from the OSSA II pipeline in the Bolivian Altiplano at a point crossing the Rı́o Desaguadero. Mineralogical analysis of sediments from the Rı́o Desaguadero basin revealed the presence of clay minerals known to readily interact with oil to form OMA. In support of laboratory tests that showed a significant amount of OMA formation in low salinity waters (0.35 ‰), OMA formation was observed when samples of Rı́o Desaguadero water and sediment were mixed with pipeline oil. Oil dispersion and enhanced biodegradation rates facilitated by rapid OMA formation after the spill incident may explain the oil fraction (27–37%) that was unaccounted in mass balance models that considered factors such as evaporative loss and oil recovered by clean up operations.

The Influence of Salinity on Oil–Mineral Aggregate Formation

The formation of microscopic oil–mineral aggregates (OMA) has been linked to the natural removal of stranded oil in coastal marine environments and to the efficacy of surf washing (relocation of oiled sediment into the zone of wave action) as an oil spill remediation procedure. To predict the significance of this process in estuarine and freshwater environments, OMA formation was tested in the laboratory with seawater diluted to obtain a salinity range of 0–35. Quantification of the amount of oil incorporated into OMA shows that the extent of OMA formation is not significantly different from that of seawater for salinity values as low as 1.5–0.15 (1/20 to 1/200 of pure seawater). The precise value of this threshold depends on parameters including oil type and the nature of the mineral present. Below this salinity threshold, there is a linear decrease in the amount of oil incorporated in OMA, to practically zero in distilled water. It is concluded that oil spill remediation by natural or induced OMA formation (i.e. surf washing) is applicable to marine, estuarine and possibly inland hyper-saline environments.

Formation and Characterization of Oil–Mineral Aggregates

Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed onto mineral surfaces, but also as a discrete phase to form microscopic oil–mineral aggregates (OMA). As it promotes the dispersion of stranded oil, this process is now believed to be instrumental in the natural recovery of oiled shorelines and in the efficacy of spill countermeasure techniques such as surf-washing (relocation of oiled sediment into the zone of wave action). To predict the fate of residual oil following spills and the effectiveness of such countermeasures, an improved understanding of the nature and properties of OMA and of the factors influencing their formation is required. Laboratory protocols and microscopical methods have been refined for the detection and classification of OMA. Three OMA types have been identified: droplet, solid and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or flocculated mineral particles. Solid aggregates are mixed oil and mineral bodies of various shapes (scale of tens of μm). Flake aggregates are thin sheets that can reach the mm size range in which mineral and oil are arranged in an ordered configuration. The parameters controlling the quantity, type and size of OMA include mineral type and surface properties, quantity, viscosity and composition of the oil, and oil/mineral ratio. It is also evident that water turbulence (i.e. breaking waves, strong flood currents) greatly enhances OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate. OMA being on average less dense than mineral-only aggregates and even buoyant, they will be kept in suspension longer and be dispersed further than unoiled sediment. Mineral particles in OMA act as a surfactant preventing the oil from recoalescing. As OMA formation increases the surface to volume ratio of spilled oil, it prolongs and enhances oil weathering processes such as dissolution, evaporation and biodegradation.

Time Scale for Oil Droplet Stabilization by Mineral Particles in Turbulent Suspensions

An equation is presented that defines the time required to coat and stabilize oil droplets with mineral particles suspended in a turbulent medium. The physical model underlying the proposed expression successfully explains variability in the formation rates of oil–mineral aggregates (OMA) observed previously in laboratory studies. Constraint is placed on the coalescence efficiency between oil droplets and mineral particles by reconciling the magnitudes of theoretical and observed coalescence rates. Example stabilization times are calculated for a range of conditions typical of the coastal marine environment. In general, stabilization times are less than one day, supporting the hypothesis that OMA formation is an important process in the cleansing of oiled shorelines. For the range of oil concentrations used in the model (0.01–0.1 kg m −3) OMA stabilization does not occur when sediment concentration is of order 0.01 kg m −3. The finding that OMA form rapidly given adequate sediment concentration indicates that intervention to increase sediment concentration is an effective response on oiled shorelines. The proposed equation will assist the oil-spill countermeasures community by providing a quantitative tool for establishing the importance of OMA formation relative to other oil dispersion processes in the coastal zone.

Application of Ultraviolet Fluorescence Spectroscopy to Monitor Oil–Mineral Aggregate Formation

At an excitation wavelength of 320 nm, the ultraviolet fluorescence (UVF) spectra emitted by reference oils dispersed in seawater with mineral fines yielded two important results: (1) Resuspended negatively-buoyant oil–mineral aggregates (OMAs) exhibited maximum fluorescence at an emission wavelength of 450 nm and, (2) the hydrocarbons dispersed and/or dissolved in the seawater that remained after the aggregates had settled out exhibited maximum fluorescence at 355 nm. Data from UVF analysis (450 nm emission) and microscopical observations of seven reference oils suggest that higher-viscosity oils are less likely to form aggregates with mineral fines. This decline in OMA formation with increased oil viscosity could be predicted from a decrease in the ratio of emission at 450–355 nm. The data suggest that direct UVF spectroscopy of dispersed/dissolved oil and OMAs in seawater can be used to predict and verify the extent of OMA formation.

CHARACTERIZATION OF OIL-MINERAL AGGREGATES

ABSTRACT Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed on mineral surfaces, but also as a discrete phase to form microscopic oil-mineral aggregates (OMA). On the basis of recent studies, OMA formation now is believed to be instrumental in the natural recovery of oil spill impacted shorelines and in the efficacy of cleanup techniques such as surf washing. A better understanding of the nature and properties of OMA will help predict the fate of oil spilled in the aquatic environment. This work describes the various instruments and methods currently available for the detection and identification of OMA. Three types of OMA have been characterized by microscopy techniques: droplet, solid, and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or aggregated mineral particles. Solid aggregates are a mixture of oil and minerals blended into microscopic bodies of various shapes. Flake aggregates are thin sheets reaching several millimeters across in which mineral and oil are arranged in a regular pattern. Energy from breaking waves facilitates OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate.