Recovery Observations from Alkali, Nanoparticles and Polymer Flooding as Combined Processes.

We have studied wettability alterations through imbibition/flooding and their synergy with interfacial tension (IFT) for alkalis, nanoparticles and polymers. Thus, the total acid number (TAN) of oil may determine the wetting-state of the reservoir and influence recovery and IFT. Data obtained demonstrate how the oil TAN number (low and high), chemical agent and reservoir mineralogy influence fluid-fluid and rock-fluid interactions. We used a laboratory evaluation workflow that combines complementary assessments such as spontaneous imbibition tests, IFT, contact angle measurements and selected core floods. The workflow evaluates wettability alteration, IFT changes and recovery when injecting alkalis, nanoparticles and polymers, or a combination of them. Dynamics and mechanisms of imbibition were tracked by analyzing the recovery change with the inverse bond number. Three sandstone types (outcrops) were used, which mainly differed in clay content and permeability. Oils with low and high TANs were used, the latter from the potential field pilot 16 TH reservoir in the Matzen field (Austria). We have investigated and identified some of the conditions leading to increases in recovery rates as well as ultimate recovery by the imbibition of alkali, nanoparticle and polymer aqueous phases. This study presents novel data on the synergy of IFT, contact angle Amott imbibition, and core floods for the chemical processes studied.

Sorption of Nanomaterials to Sandstone Rock.

We investigated the interaction of silica nanostructured particles and sandstone rock using various experimental approaches, such as fluid compatibility, batch sorption and single-phase core-floods. Diol and polyethylenglycol (PEG) surface-modified nanostructured silica materials were tested using two brines differing in ionic strength and with the addition of sodium carbonate (Na2CO3). Berea and Keuper outcrop materials (core plug and crushed samples) were used. Core-flood effluents were analysed to define changes in concentration and a rock's retention compared to a tracer. Field Flow Fractionation (FFF) and Dynamic Light Scattering (DLS) were performed to investigate changes in the effluent's size distribution. Adsorption was evaluated using UV-visible spectroscopy and scanning electron microscopy (SEM). The highest adsorption was observed in brine with high ionic strength, whereas the use of alkali reduced the adsorption. The crushed material from Berea rock showed slightly higher adsorption compared to Keuper rock, whereas temperature had a minor effect on adsorption behaviour. In core-flood experiments, no effects on permeability have been observed. The used particles showed a delayed breakthrough compared to the tracer, and bigger particles passed the rock core faster. Nanoparticle recovery was significantly lower for PEG-modified nanomaterials in Berea compared to diol-modified nanomaterials, suggesting high adsorption. SEM images indicate that adsorption spots are defined via surface roughness rather than mineral type. Despite an excess of nanomaterials in the porous medium, monolayer adsorption was the prevailing type observed.

Wettability Changes Due to Nanomaterials and Alkali-A Proposed Formulation for EOR.

We investigated the usage of two silica nanomaterials (surface-modified) and alkali in enhanced oil recovery through Amott spontaneous imbibition tests, interfacial tension (IFT) measurements, and phase behavior. We evaluated the wettability alteration induced by the synergy between nanomaterials and alkali. Moreover, numerical analysis of the results was carried out using inverse Bond number and capillary diffusion coefficient. Evaluations included the use of Berea and Keuper outcrop material, crude oil with different total acid numbers (TAN), and Na2CO3 as alkaline agent. Data showed that nanomaterials can reduce the IFT, with surface charge playing an important role in this process. In synergy with alkali, the use of nanomaterials led to low-stable IFT values. This effect was also seen in the phase behavior tests, where brine/oil systems with lower IFT exhibited better emulsification. Nanomaterials' contribution to the phase behavior was mainly the stabilization of the emulsion middle phase. The influence of TAN number on the IFT and phase behavior was prominent especially when combined with alkali. Amott spontaneous imbibition resulted in additional oil recovery ranging from 4% to 50% above the baseline, which was confirmed by inverse Bond number analysis. High recoveries were achieved using alkali and nanomaterials; these values were attributed to wettability alteration that accelerated the imbibition kinetics as seen in capillary diffusion coefficient analysis.

River-derived humic substances as iron chelators in seawater.

The speciation of iron(III) in oxic seawater is dominated by its hydrolysis and sedimentation of insoluble iron(III)-oxyhydroxide. As a consequence, many oceanic areas have very low iron levels in surface seawater which leads to iron deficiency since phytoplankton require iron as a micronutrient in order to grow. Fortunately, iron solubility is not truly as low as Fe(III) solubility measurements in inorganic seawater would suggest, since oceanic waters contain organic molecules which tend to bind the iron and keep it in solution. Various iron-binding organic ligands which combine to stabilize dissolved iron have been detected and thoroughly investigated in recent years. However, the role of iron-binding ligands from terrestrial sources remains poorly constrained. Blackwater rivers supply large amounts of natural organic material (NOM) to the ocean. This NOM (which consists mainly of vascular plant-derived humic substances) is able to greatly enhance iron bioavailability in estuaries and coastal regions, however, breakdown processes lead to a rapid decrease of river-derived NOM concentrations with increasing distance from land. It has therefore been argued that the influence of river-derived NOM on iron biogeochemistry in offshore seawater does not seem to be significant. Here we used a standard method based on 59Fe as a radiotracer to study the solubility of Fe(III)-oxyhydroxide in seawater in the presence of riverine NOM. We aimed to address the question how effective is freshwater NOM as an iron chelator under open ocean conditions where the concentration of land-derived organic material is about 3 orders of magnitude smaller than in coastal regions, and does this iron chelating ability vary between NOM from different sources and between different size fractions of the river-borne NOM. Our results show that the investigated NOM fractions were able to substantially enhance Fe(III)-oxyhydroxide solubility in seawater at concentrations of the NOM ≥ 5 µg L- 1. Terrigenous NOM concentrations ≥ 5 µg L- 1 are in no way unusual in open ocean surface waters especially of the Arctic and the North Atlantic Oceans. River-derived humic substances could therefore play a greater role as iron carriers in the ocean than previously thought.

Asymmetrical Flow-Field-Flow Fractionation coupled with inductively coupled plasma mass spectrometry for the analysis of gold nanoparticles in the presence of natural nanoparticles.

Flow-Field-Flow Fractionation (Flow-FFF), coupled with online detection systems, is one of the most promising tools available for the analysis and characterization of engineered nanoparticles (ENPs) in complex matrices. In order to demonstrate the applicability of Flow-FFF for the detection, quantification, and characterization of engineered gold nanoparticles (AuNPs), model dispersions were prepared containing AuNPs with diameters of 30 or 100nm, natural nanoparticles (NNPs) extracted from a soil sample, and different concentrations of natural organic matter (NOM), which were then used to investigate interactions between the AuNPs and the NNPs. It could be shown that light scattering detection can be used to evaluate the fractionation performance of the pure NNPs, but not the fractionation performance of the mixed samples that also contained AuNPs because of specific interactions between the AuNPs and the laser light. A combination of detectors (i.e. light absorbance and inductively coupled plasma mass spectrometry (ICP-MS)) was found to be useful for differentiating between heteroaggregation and homoaggregation of the nanoparticles (NPs). The addition of NOM to samples containing 30nm AuNPs stabilized the AuNPs without affecting the NP size distribution. However, fractograms for samples with no added NOM showed a change in the size distribution, suggesting interactions between the AuNPs and NNPs. This interpretation was supported by unchanged light absorption wavelengths for the AuNPs. In contrast, results for samples containing 100nm AuNPs were inconclusive with respect to recovery and size distributions because of problems with the separation system that probably related to the size and high density of these nanoparticles, highlighting the need for extensive method optimization strategies, even for nanoparticles of the same material but different sizes.

Spot the difference: engineered and natural nanoparticles in the environment--release, behavior, and fate.

The production and use of nanoparticles leads to the emission of manufactured or engineered nanoparticles into the environment. Those particles undergo many possible reactions and interactions in the environment they are exposed to. These reactions and the resulting behavior and fate of nanoparticles in the environment have been studied for decades through naturally occurring nanoparticulate (1-100 nm) and colloidal (1-1000 nm) substances. The knowledge gained from these investigations is nowhere near sufficiently complete to create a detailed model of the behavior and fate of engineered nanoparticles in the environment, but is a valuable starting point for the risk assessment of these novel materials. It is the aim of this Review to critically compare naturally observed processes with those found for engineered systems to identify the "nanospecific" properties of manufactured particles and describe critical knowledge gaps relevant for the risk assessment of manufactured nanomaterials in the environment.

Accessibility of humic-associated Fe to a microbial siderophore: implications for bioavailability.

Microorganisms in aerobic, circum-neutral environments are challenged to acquire sufficient nutrient Fe due to low solubilities of Fe oxides. To overcome this challenge, many aerobic microbes produce low molecular weight (MW) organic ligands, or siderophores, with extremely high Fe-binding affinities. This research expands the existing understanding of siderophore-mediated Fe acquisition from minerals by examining the effects of the siderophore desferrioxamine B (DFOB) on Fe removal from aquatic humic substances (XAD-8-isolated) and other organic matter (OM) isolates (reverse osmosis, RO; and "transphilic", XAD-4) from several rivers including the Suwannee River (GA, USA). Analysis of samples by asymmetrical flow field-flow fractionation (AsFlFFF) with in-line ICP-MS and UV-vis detectors showed that Fe was naturally abundant and primarily associated with intermediate to high MW OM. An excess of DFOB (relative to naturally present Fe) removed ∼ 75% of Fe and shifted the OM MW distribution to lower MWs, perhaps due to removal of "bridging" Fe, although additional mechanistic study of MW shifts is needed. Removal of other OM-associated metals (e.g., Al, Cu, Zn) by DFOB was minimal for all but a few samples. Fe bound to humic substances and other more "transphilic" organic components therefore should be considered readily bioavailable to aerobic, siderophore-producing microorganisms.

Natural organic matter and iron export from the Tanner Moor, Austria.

Samples from a pristine raised peat bog runoff in Austria, the Tannermoor creek, were analysed for their iron linked to natural organic matter (NOM) content. Dissolved organic carbon < 0.45 µm (DOC) was 41-64 mg L-1, iron 4.4-5.5 mg L-1. Samples were analysed applying asymmetric field flow fractionation (AsFlFFF) coupled to UV-vis absorption, fluorescence and inductively coupled plasma mass spectrometry (ICP-MS). The samples showed an iron peak associated with the NOM peak, one sample exhibiting a second peak of iron independent from the NOM peak. As highland peat bogs with similar climatic conditions and vegetation to the Tanner Moor are found throughout the world, including areas adjacent to the sea, we examined the behaviour of NOM and iron in samples brought to euhaline (35‰) conditions with artificial sea salt. The enhanced ionic strength reduced NOM by 53% and iron by 82%. Size exclusion chromatography (SEC) of the samples at sea-like salinity revealed two major fractions of NOM associated with different iron concentrations. The larger one, eluting sharply after the upper exclusion limits of 4000-5000 g mol-1, seems to be most important for iron chelating. The results outline the global importance of sub-mountainous and mountainous raised peat bogs as a source of iron chelators to the marine environment at sites where such peat bogs release their run-offs into the sea.

Effect of pH and stream order on iron and arsenic speciation in boreal catchments.

Riverine transport of iron (Fe) and arsenic (As) is affected by their associations with natural organic matter (NOM) and suspended iron (oxy)hydroxides. Speciation has a strong influence on element transport from the headwaters to the ocean because NOM may be transported over longer distances compared to iron (oxy)hydroxides. We show that Fe speciation changes along the flow path of a boreal watercourse, as water moves from NOM-rich, acidic first-order streams with pH as low as 3.9 to less acidic higher-order systems (up to pH 6.4). Analysis by Flow Field-Flow Fractionation and chemical equilibrium modeling revealed that Fe from wetland-dominated headwaters was mainly exported as Fe-NOM complexes; in catchments with a stream order >1 and with higher pH, Fe was present in Fe-NOM complexes and precipitated as nanoparticulate iron(oxy)hydroxides which aggregated as the pH increased, with their size eventually exceeding the membrane filters cutoff (0.2 µm). The measured NOM-bound Fe decreased with increasing pH, from 0.38 to 0.16 mmol Fe·g(NOM)(-1). The high concentrations of NOM-bound Fe emphasize the importance of boreal catchments to Fe export to the oceans. Concentrations of As in the <0.2 µm fraction but larger than what is usually considered "truly dissolved" (<1000 g·mol(-1)), decreased from 75% to 26% with increasing pH. The As in this size range was mainly associated with NOM but at pH >4.5 became associated with iron(oxy)hydroxides, and its transport thus became more coupled to that of the iron(oxy)hydroxides downstream in the circumneutral streams.

The influence of pH on iron speciation in podzol extracts: iron complexes with natural organic matter, and iron mineral nanoparticles.

The quantities of natural organic matter (NOM) and associated iron (Fe) in soil extracts are known to increase with increasing extractant pH. However, it was unclear how the extraction pH affects Fe speciation for particles below 30 nm. We used flow field-flow fractionation (FlowFFF) and transmission electron microscopy (TEM) to investigate the association of Fe and trace elements with NOM and nanoparticulate iron (oxy)hydroxides in podzol extracts. For extracts prepared at the native soil pH (~4), and within a 1-30 nm size range, Fe was associated with NOM. In extracts with a pH≥7 from the E and B soil horizons, Fe was associated with NOM as well as with iron (oxy)hydroxide nanoparticles with a size of approximately 10 nm. The iron (oxy)hydroxide nanoparticles may have either formed within the soil extracts in response to the increase in pH, or they were mobilized from the soil. Additionally, pH shift experiments showed that iron (oxy)hydroxides formed when the native soil pH (~4) was increased to 9 following the extraction. The iron (oxy)hydroxide nanoparticles aggregated if the pH was decreased from 9 to 4. The speciation of Fe also influenced trace element speciation: lead was partly associated with the iron (oxy)hydroxides (when present), while copper binding to NOM remained unaffected by the presence of iron (oxy)hydroxide nanoparticles. The results of this study are important for interpreting the representativeness of soil extracts prepared at a pH other than the native soil pH, and for understanding the changes in Fe speciation that occur along a pH gradient.

Using FLOWFFF and HPSEC to determine trace metal-colloid associations in wetland runoff.

Natural organic matter (NOM) and iron colloids can coexist in surface water. These colloids might exhibit different affinities to metals and metalloids. Previously it has been shown, that organic and inorganic colloids in the low nanometer range can be fractionated using Flow Field-Flow Fractionation analyzes (FlowFFF), but it is not yet understood how the presence of inorganic colloids influences results obtained by High Performance Size Exclusion Chromatography (HPSEC). Studies that compare the use of these size-separation techniques for the analyzes of organic and inorganic colloids and associated elements are needed in order to interpret results obtained by either of these methods. Therefore, associations between colloids from a small stream draining a wetland area and a selected range of elements (Fe, Al, Ti, Pb, Cu, Ni, As, U, and Rare Earth Elements (REE)) have been investigated. FlowFFF analyzes and HPSEC analyzes were combined with ultrafiltration, functional group titration and arsenic speciation analysis. NOM and, in a sample with a pH > 5.2, slightly larger iron organo-mineral colloids, were present in the <0.2 µm fraction in the surface water. Both exhibited notably different affinities for trace elements. Cu, Ni, Al, and the REE all showed similar modes (i.e. peak maxima) and size distributions to the NOM, while Pb and As showed a preferential association with iron organo-mineral colloids. It was not possible to differentiate between NOM and iron-organo mineral colloids with HPSEC. The differences in the results regarding the apparent molecular mass distributions obtained by FlowFFF and HPSEC are discussed.