Iron Oxide-coated Sand Research Articles

Biological arsenite oxidation on iron-based adsorbents in groundwater filters

Iron-based adsorbents are commonly used to remove arsenic (As) from water for drinking water purposes. Here, we study the role of biological As(III) oxidation on iron-based adsorbents in filters and its effect on overall As uptake. A lab-scale filter with iron oxide coated sand (IOCS), a commonly used adsorbent, was operated with water containing As(III) and As(V), while water samples were taken periodically over its height. As(III) oxidation initiated after approximately 10 days and increased to a first order rate constant of 0.09 s−1 after 57 days resulting in full oxidation of As(III) in <50 s. Consequently, the filter shifted from an As(III) to an As(V) adsorbing filter. Oxidation was not observed after inhibiting the microbial activity using sodium azide confirming its biogenic nature. This implies that As(III) oxidizing biomass can grow on iron-based adsorbents in water filters without requiring inoculation. As the experimental conditions were similar to full-scale As treatment plants, we believe that biological As(III) oxidation is widely overlooked in these systems. Occurrence of biological oxidation is, however, beneficial for removal, as at pH <8 the adsorption capacity for As(V) can be up to 10-fold higher than for As(III). With these new insights, arsenic treatment using iron-based adsorbents can be further optimized. We suggest a more robust new design with a biological active As(III) oxidizing top layer and an As(V) adsorbing bottom layer.

Transport of polystyrene microplastics in bare and iron oxide-coated quartz sand: Effects of ionic strength, humic acid, and co-existing graphene oxide

This research explored the effects of widely utilized nanomaterial graphene oxide (GO) and organic matter humic acid (HA) on the transport of microplastics under different ionic solution strengths in bare sand and iron oxide-coated sand. The results found transport of polystyrene microplastics (PS) did not respond to the presence of HA in sand that contains large amounts of iron oxide. Compared to bare quartz sand, ionic strength had little effect: <20 % of PS passed through Fe sand columns. There was a significant promotion of PS transport in the presence of GO, however, which can be attributed to the increased surface electronegativity of PS and steric hindrance. Moreover, GO combined with HA significantly promoted the transport of PS in the Fe sand, and transport further increased when the concentration of HA increased from 5 to 10 mg/L. Interestingly, the degree of this increase exactly corresponded to the change in the surface charge of the microplastics, demonstrating that electrostatic interaction dominated the PS transport. Further results indicated that co-existing pollutants had significant impacts on the transport of microplastics under various conditions by altering the surface characteristics of the plastic particles and the spatial steric hindrance within porous media. This research will offer insights into predicting the transport and fate of microplastics in complex environments.

A framework for estimating soil water characteristic curve and hydraulic conductivity function of permeable reactive media

The unsaturated behavior of permeable reactive barriers (PRB) is a critical component in predicting the removal efficiency through the adsorption of contaminants. This study investigates the framework to estimate the soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) for iron oxide-coated sand (IOCS) and zeolite, which are common materials used in PRBs. A multistep outflow (MSO) experiment was performed and the results of the MSO experiment were used to optimize associated parameters in Kosugi's SWCC and HCF. In addition, three scenarios of optimization analysis were investigated to evaluate the best-fitting model for estimating SWCC and HCF. The low root mean square error (RMSE) of fitted parameters indicates the Kosugi model well described the observed suction profiles in MSO experiments. In addition, the lowest RMSE and coefficient of variation suggested the inclusion of the additional parameter β provided the best estimation of the three materials (clean sand, IOCS, and zeolite). The physically reasonable estimation of SWCC and HCF of the three materials from the optimized parameters suggests the proposed framework is a reasonable model for the unsaturated behavior of PRBs.

Molecular Structure and Conformation of Biodegradable Water-Soluble Polymers Control Adsorption and Transport in Model Soil Mineral Systems.

Water-soluble polymers (WSPs) are used in diverse applications, including agricultural formulations, that can result in the release of WSPs to soils. WSP biodegradability in soils is desirable to prevent long-term accumulation and potential associated adverse effects. In this work, we assessed adsorption of five candidate biodegradable WSPs with varying chemistry, charge, and polarity characteristics (i.e., dextran, diethylaminoethyl dextran, carboxymethyl dextran, polyethylene glycol monomethyl ether, and poly-l-lysine) and of one nonbiodegradable WSP (poly(acrylic acid)) to sand and iron oxide-coated sand particles that represent important soil minerals. Combined adsorption studies using solution-depletion measurements, direct surface adsorption techniques, and column transport experiments over varying solution pH and ionic strengths revealed electrostatics dominating interactions of charged WSPs with the sorbents as well as WSP conformations and packing densities in the adsorbed states. Hydrogen bonding controls adsorption of noncharged WSPs. Under transport in columns, WSP adsorption exhibited fast and slow kinetic adsorption regimes with time scales of minutes to hours. Slow adsorption kinetics in soil may lead to enhanced transport but also shorter lifetimes of biodegradable WSPs, assuming more rapid biodegradation when dissolved than adsorbed. This work establishes a basis for understanding the coupled adsorption and biodegradation dynamics of biodegradable WSPs in agricultural soils.

Groundwater Purification Using Bio-Sand Filter Modified with Iron Oxide-Coated Sand and Activated Carbon

Groundwater is the most used natural resource which serves different diverse purposes and alternative water supply for households mainly in rural areas. However, it is polluted by contaminants such as heavy metals, total hardness and coliform bacteria. One such promising water treatment technology for households in rural areas is the Bio-sand Filter (BSF) because of its low cost and efficient removal of contaminants. Although BSF is efficient to remove contaminants, there is still needed to improve the flow rate and the performance of removing pollutants from groundwater. Therefore, this study focused on the development of a laboratory-scale Modified Bio-sand Filter (MBSF) that was combined with Iron-oxide Coated Sand (IOCS) with Granular Activated Carbon (GAC) made from coconut shells to purify groundwater. Laboratory scale of filters were performed in this study. Groundwater was collected from household’s well water in Kean Svay district, Kandal province. The filters were operated by filling the water source with 10 liters per day and operated for 20 days. Heavy metals were measured by Atomic Absorption Spectroscopy (AAS) and Arsenator. Total hardness was analyzed by Ion Chromatography (IC). Target coliform bacteria such as E. coli and total coliform were cultured by spread plate method. Flow rate was observed by setting time for 1 minute and measure the volume of effluent water. By the results, all physicochemical parameters of MBSF were within the standard limit of drinking water. MBSF showed significantly better removal efficiency for arsenic with 100% than BSF while MBSF can also remove Mn and Fe which was under the drinking water standard of WHO and MIME. Total hardness was achieved more than 80% in MBSF, while BSF with only 40%. MBSF also performed slightly better than BSF as well in removing both E. coli and total coliform with more than 90% reduction. The flow rate of the MBSF was faster about two and a half times than the flow rate of BSF with the average of 0.15 L/min for MBFS and 0.06 L/min for BSF. The results from this study contributed to the improvement of household water treatment method for purifying groundwater efficiently in rural areas.

Prototype Experiments Assessing Arsenic and Iron Removal Efficiencies through Adsorption Using Natural Skye Sand

Based on earlier batch and column experimental results, it was established that Skye sand is suitable for removing arsenic from water through adsorption. As a real-size prototype may not always replicate results from batch and column experiments, this paper presents experimental results on arsenic removal through a prototype arsenic filter using the same Skye sand used in the batch and column experiments. As arsenic-contaminated water is often associated with a high concentration of iron, which causes blockage of the filter system, this study also investigates the removal of iron from the water through the same filter media. First, several physical properties of the Skye sand were established through XRF, XRD, SEM and EDX analyses. Then, a real-size prototype was made based on an earlier design of a similar filter made of iron oxide-coated sand (IOCS). It was found that the current filter is capable of removing arsenic consistently to a level below the detection limit (0.05 µg/L) for a considerable period (up to 150 bed volumes). Additionally, the same filter is capable of removing iron to a level below the WHO-acceptable limit (0.3 mg/L). Analytical calculation suggests that the current prototype filter with Skye sand can produce arsenic-free water continuously for 600 days (100 L per day) with a feed arsenic concentration of 500 µg/L.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries.

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Evaluation of iron coated natural sand for removal of dissolved arsenic from groundwater and develop sustainable filter media

Drinking of untreated arsenic contaminated groundwater has suspected many inhabitants at the verge of chronic arsenicosis diseases. Develop a sustainable filter media has become an urgent need. In developing countries, practice of local sand material as filter media for removal of iron and arsenic is a common technique used daily. In this study, a relative capacities of the iron oxide-coated sand (IOCS) usually used in the conventional household filters was evaluated for removal of arsenic. The experimental study results have showed that the initial As (III) concentration of 500 μg L−1 was removed by IOCS at 10 g L−1 dose with an efficiency of 92% and natural sand removed at 68% of As (III) by a dose of 20 g L−1. Freundlich isotherm results for IOCS showed maximum adsorption at 7.2 μg g−1. The conversion of ferrous to ferric iron in natural groundwater system suggest that due to co-precipitation, ferric dosage of 10 mg L−1 at pH 7 for 2 hrs has showed that the optimum conditions for removing arsenic. Experimental results suggested that the iron flocs can remove up to 62% of As(III) from groundwater. The adsorption capacities of IOCS bed at a depths of 3 cm, 4 cm and 5 cm could remove initial arsenic concentrations of 100 μg L−1 at pH 7 as 66.87 μg g−1, 63.49 μg g−1, 57.08 μg g−1, respectively, by following the Thomas model. The results of iron coated sand suggest that IOCS material provide an economical and sustainable solution to remove the dissolved arsenic concentration from groundwater.

Iron oxide coated sand (IOS): Scale-up analysis and full-scale application for phosphorus removal from goat farm wastewater

Effective eutrophication control, especially for decentralized wastewater treatment, has received increasing attention in recent years. In view of this, iron oxide coated sand (IOS) granules, a recycled waste product from the drinking water industry, was investigated for phosphorus removal from goat farm wastewater, both at laboratory-scale and at full-scale. Brunauer-Emmett-Teller adsorption revealed a high specific surface area (249 m2/g) of the IOS. Fourier Transform Infrared Spectroscopy and X-ray Diffraction demonstrated that Fe(III) compounds are the main functional component and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy showed that Fe and O elements covered more than 84% of the surface of the IOS. The IOS granules showed good phosphorus adsorption capacity over a wide pH range during laboratory-scale batch tests. Moreover, the phosphorus adsorption was very fast and the residual phosphorus concentration dropped below 0.02 mg/L within an hour at a dosage of 20 g/L. After adsorption, the exhausted IOS could be regenerated by using 0.5 M KOH, and more than 80% adsorption capacity remained. Laboratory-scale column tests with real wastewater originating from a goat farm were run and Bed Depth Service Time and Bohart–Adams models were applied in view of scale-up. Based on this, a full-scale IOS based fixed bed reactor was designed, built and tested at a goat farm. A TP removal efficiency of 99% with a 0.87 m3 IOS fixed bed reactor (fed at 2.2 m3/d) was obtained. The TP concentration in the effluent remained below 0.3 mg/L for nearly 400 days, achieving long term TP removal. This study demonstrates that IOS based treatment is an ecological and environmentally friendly method, suitable for full-scale (decentralized) wastewater treatment.

Repurposing spent filter sand from iron and manganese removal systems as an adsorbent for treating arsenic contaminated drinking water

Waterworks which utilise river bank filtration water sources often have to apply aeration and sand filtration to remove iron and manganese during the drinking water treatment process. After some time, the sand becomes saturated and the spent filter sand (SFS) must be disposed of and replaced. In order to valorize this waste stream, this paper investigates the reuse of SFS as an adsorbent for the treatment of arsenic contaminated drinking water. The arsenic removal performance of SFS is compared with two synthetic iron oxide coated sands (IOCS). The sorbents were first characterized by SEM, EDS, BET specific surface area, and point of zero charge (pHpzc) measurements, and then investigated under a variety of conditions. The surface of the SFS was revealed to be coated with iron manganese binary oxide. The Freundlich model best described the isotherm experiment data, indicating a non monolayer adsorption model for arsenic adsorption on the three IOCS investigated. As(III) and As(V) removals were negatively effected by the presence of PO43− and HA anions as they competed with the arsenic species for adsorption sites. However, given the status of SFS as a waste material, the results obtained in this paper suggest it may be successfully reused as a very economically and environmentally sustainable solution for small waterworks requiring both As(V) and As(III) removal during drinking water treatment.

Effects of iron oxide coatings on the mobility and retardation of U(VI) in water saturated media

Iron oxide coatings occur commonly in the environment and affect significantly the fate of heavy metals. However, U(VI) transport in water saturated iron oxide-coating porous media has been seldom investigated. In this study, the adsorption and retardation of U(VI) on iron oxide-coated sand were comparatively investigated over a wide range of experimental conditions by batch and column experiments combined with modelling. The presence of iron oxide coatings significantly enhanced U(VI) adsorption which could be described by a two-site surface complexation model. The breakthrough curves of U(VI) in iron oxide coated quartz sand column show a two-plateau profile, which could not be directly reproduced by the commonly used two-site kinetic model. More sites for U(VI) have to be considered, implying that the heterogeneity of surface sites might be more significant in the non-equilibrium transport system than that in the equilibrium adsorption system. In addition, the presence of salicylic acid (SA) facilitated the transport of U(VI) at acidic pH, due to the competition between surface complexation of U(VI) and the complexation of U(VI) with SA in aqueous phase. Overall, this study provides a comprehensive understanding of the migration behavior of U(VI) in water saturated iron oxide-coated sand system.

Removal of iron from water using iron oxide coated hollow polymethylmethacrylate microspheres

Functional hollow poly (methyl methacrylate) microspheres (HPMM) coated with iron oxide (FHPMM) were synthesized as a highly efficient material for the removal of iron from water. The material was characterized by using Optical Microscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and Vibrating Sample Magnetometer (VSM). The most intriguing feature of this material is low bulk density of the order of 0.60 gm/cc for uncoated HPMM and 1.27 gm/cc for FHPMM resulting in the enhanced surface area leading to enormously high adsorption capacity revealed from the adsorption isotherm study compared to the conventional iron oxide coated sand used for separation of iron from water. Optimum conditions of adsorption were determined by carrying out batch experiments. Under batch studies, investigation of the effect of various operational parameters such as initial metal ion concentration, pH, and contact time were carried out. Kinetic studies showed that the adsorption equilibrium time was reached within 30 min and the adsorbent showed a high affinity for Fe (II) ions at a pH value of 7.5. The adsorption isotherm was well fitted by the Langmuir model. The maximum adsorption capacity of FHPMM for iron was 2.322 mg/g. Based on the results, this low-density high-performance material can be advocated as a superior adsorbent to replace the conventional iron oxide-coated sand used in water purification systems.

Adsorption of dissolved copper and zinc on sand and iron oxide coated sand (IOCS) for urban stormwater treatment: effects of pH, chloride, and sulfate

Adsorption of dissolved copper and zinc on sand and iron oxide coated sand (IOCS) for urban stormwater treatment: effects of pH, chloride, and sulfate

Batch experiments on arsenic removal efficiencies through adsorption using synthetic and natural sand samples

Recently it has been unearthed that many potable water sources around the world are contaminated with arsenic, which has got long-term health hazards for the consumers. Among different arsenic removal techniques, adsorption is widely used and easily achievable. Through the use of suitable adsorbent, arsenic can be significantly removed from potable water, which is a dire need for many distant communities where there is scarcity of alternative potable water source. This paper presents arsenic removal characteristics of different synthetic and natural sand samples through adsorption. To replicate the Skye sand which was found to be effective in removing arsenic, two synthetic sand samples (one coated with iron and the other coated with aluminium) were prepared in the laboratory. Different combinations of these samples were tested through batch experiments to evaluate their arsenic removal efficiencies under different conditions. It is found that among the synthetic adsorbents, the ones dried at 80 °C (during their preparation) showed the highest arsenic removal efficiencies. Also, among all the samples, iron oxide-coated sand (IOCS) showed the highest arsenic removal efficiencies, varying from 71 to 100% depending on the amount of doses, whereas with the use of natural Skye sand with the same variation in doses, arsenic removal efficiencies varied from 26 to 90%.

Effects of phosphate on the transport of graphene oxide nanoparticles in saturated clean and iron oxide-coated sand columns

In this study, transport behaviors of graphene oxide (GO) in saturated uncoated (i.e., clean sand) and goethite-coated sand porous media were examined as a function of the phosphate. We found that phosphate enhanced the transport of GO over a wide range of solution chemistry (i.e., pH 5.0–9.0 and the presence of 10 mmol/L Na+ or 0.5 mmol/L Ca2+). The results were mainly ascribed to the increase of electrostatic repulsion between nanoparticles and porous media. Meanwhile, deposition site competition induced by the retained phosphate was another important mechanism leading to promote GO transport. Interestingly, when the phosphate concentration increased from 0.1 to 1.0 mmol/L, the transport-enhancement effect of phosphate in goethite-coated sand was to a much larger extent than that in clean sand. The observations were primarily related to the difference in the total mass of retained phosphate between the iron oxide-coated sand and clean sand columns, which resulted in different degrees of the electrostatic repulsion and competitive effect of phosphate. When the background solution contained 0.5 mmol/L Ca2+, phosphate could be bind to sand/ goethite-coated sand surface by cation bridging; and consequently, promoted competition between phosphate and nanoparticles for deposition sites, which was an important mechanism for the enhanced effect of phosphate. Moreover, the DLVO theory was applicable to describe GO transport behaviors in porous media in the absence or presence of phosphate. Taken together, these findings highlight the important status and role of phosphate on the transport and fate of colloidal graphene oxide in the subsurface environment.

Removal of microcystin-LR and other water pollutants using sand coated with bio-optimized carbon submicron particles: Graphene oxide and reduced graphene oxide

Sand is the most used filter adsorbent material in a drinking water treatment plant (DWTP) or household purpose filters. However, sand poses challenge for the micropollutant removal in presence of metals, natural organic matter, total organic carbon, ammonia and other macro-pollutants. In this study, sand was coated using laboratory-synthesized graphene oxide (GO) and reduced graphene oxide (rGO) to enhance its surface properties in terms of hydrophobicity, roughness and specific surface area (6 times higher for GO/rGO as compared to 5.5 m2/g for sand), that allowed an enhanced adsorption of macro pollutants as well as one target micropollutant: Microcystin-LR (MC-LR). A more electropositive surface than sand (zeta potential: −43.2 mV) in form of iron oxide-coated sand (IOCS or Fe: −21.2 mV) and its combination with GO (FeGO: −13.4 mV) was tested to validate the hypothesis of enhanced MC-LR adsorption due to electrostatic attraction. Two known MC-LR degraders (Arthrobacter ramosus and Bacillus sp.) were screened before bioaugmentation, based on the biofilm forming potential for each coated sand composite. Additionally, the dosage of GO and rGO were bio-optimized before coating them over the sand grains (400 mg/L for GO and 520 mg/L for rGO), to obtain a non-toxic and non-disruptive effect and providing at least 60% cell viability. A highest MC-LR removal of 91% was obtained under biodegradation phase using rGO-coated sand that showed an increase of 47.2% in MC-LR removal when compared to physical adsorption phase. Sand filter (control) showed a maximum MC-LR removal of 54.7%. The highest saturation adsorbent constants of 8.5 mg/kg and 7.4 mg/kg were obtained for GO and rGO-coated sand media, respectively, which was 5–6 times higher than the uncoated sand.

Influences of pH on transport of arsenate (As5+) through different reactive media using column experiments and transport modeling

This research aims to evaluate the effects of pH, including both acidic and neutral conditions to simulate an acid mine environment, on the sorption and transport of As(V) in contaminated groundwater through different reactive materials by using column experiments and mathematical modeling. Six saturated columns were set up to evaluate the migration and removal efficiency of As(V) with three different materials acting as permeable reactive barrier (PRB) media under different pH conditions (pH 4 and pH 7). The reactive materials consisted of pure sand (control column), iron oxide-coated sand (IOCS) and a combination of IOCS and zero-valent iron-coated sand (ZVICS) (ZVICS + IOCS). According to the column experiments, the descending order of removal capacity (mg As/g) for ZVICS + IOCS, IOCS and sand was 0.452 > 0.062 > 0.0027 mg As/g at pH 4 and 0.117 > 0.0077 > 0.0022 mg As/g, respectively, at pH 7. The column experiments showed that the removal and retardation factor (RF) of As(V) generally increased with decreasing pH. The SEM images and the corresponding EDX spectra of acid-washed natural sand, IOCS and ZVICS + IOCS from the columns showed that the peak of As was detectable on the reactive materials. The mechanism of As(V) sorption onto sand at pH 4 and pH 7 corresponded to the uniform (equilibrium) solute transport model, whereas the IOCS and ZVICS + IOCS columns corresponded to the two-site model (TSM) with the Freundlich isotherm. The fraction of instantaneous sites (f) for As(V) sorption onto IOCS and ZVICS + IOCS appeared to decrease with increasing pH, especially for ZVICS + IOCS, which indicates that nonequilibrium sorption/desorption mainly dominated during As(V) migration.

Cotransport of Cu with Graphene Oxide in Saturated Porous Media with Varying Degrees of Geochemical Heterogeneity

Graphene oxide (GO) is likely to encounter heavy metals due to its widespread use and inevitable release into the subsurface environment, where the ubiquitous presence of iron oxides (e.g., hematite) would affect their interaction and transport. The present study aimed to investigate the cotransport of GO (20 mg L−1) and copper (0.05 mM CuCl2) in the presence of varying degrees of geochemical heterogeneity represented by iron oxide-coated sand fractions (ω = 0‒0.45) in water-saturated columns under environmentally relevant physicochemical conditions (1 mM KCl at pH 5.0‒9.0). The Langmuir-fitted maximum adsorption capacity of Cu2+ by GO reached 137.6 mg g−1, and the presence of 0.05 mM Cu2+ decreased the colloidal stability and subsequent transport of GO in porous media. The iron oxide coating was found to significantly inhibit the transport of GO and Cu-loaded GO in sand-packed columns, which can be explained by the favorable deposition of the negatively charged GO onto patches of the positively charged iron oxide coatings at pH 5.0. Increasing the solution pH from 5.0 to 9.0 promoted the mobility of GO, with the exception of pH 7.5, in which the lowest breakthrough of GO was observed. This is possibly due to the fact that the surface charge of iron oxide approaches zero at pH 7.5, suggesting that new “favorable” sites are available for GO retention. This study deciphered the complicated interactions among engineered nanomaterials, heavy metals, and geochemical heterogeneity under environmentally relevant physicochemical conditions. Our results highlight the significant role of geochemical heterogeneity, such as iron oxide patches, in determining the fate and transport of GO and GO-heavy metal association in the subsurface environment.

Pilot Test of the Permeable Reactive Barrier for Removing Uranium from the Flooded Gunnar Pit

This work reports on applying iron oxide coated sand (IOCS) media in an experimental permeable reactive barrier to remove uranium (U) species from uranium containing water. A field study was conducted at the legacy Gunnar uranium mine & mill site that was abandoned in the 1960s with limited to no decommissioning. The flooded Gunnar mine pit presently contains about 3.2 million m3 of water contaminated by dissolved U (1.2 mg/L), Ra-226 (0.4 Bq/L), and minor concentrations of other contaminants (As, Se, etc.). The water is seeping over the pit rim into Lake Athabasca, posing potential environmental and health concerns. IOCS media can be used to immobilize uranium species through an adsorption process. Herein, the preparation of hydrous ferric oxide sorbents and their supported forms onto silica sands is described. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (pXRD) were used for structural characterization. The adsorption properties of the IOCS sorbent media were modeled by the Langmuir adsorption isotherm, where a maximum uranium uptake capacity was estimated. Bench-scale adsorption kinetic experiments were also performed before moving to a field trial. Based on these lab results and input on field-scale parameters, a pilot permeable reactive barrier was fabricated and a field test conducted near the Gunnar pit in June 2019. This pilot test provided technical data and information needed for designing a full-scale permeable barrier that employs the IOCS media. This approach can be applied for in-situ water treatment at Gunnar and other legacy uranium sites.

Heavy metal removal from stormwater runoff by sorption

In this study, several sorbents (i.e. alumina, activated bauxsol coated sand (ABCS), bark,bauxsol coated sand (BCS), fly ash (FA), granulated activated carbon (GAC), iron oxidecoated sand (IOCS), natural zeolite (NZ), sand, and spine!) are investigated with the longterm goal of developing a feasible technology for heavy metal removal during secondarytreatment of storm water. The sorbents are tested in batch tests for their As, Cd, Cr, Cu, Ni andZn removal efficiency from synthetic stormwater samples, where all of these metals coexisted at a starting pH of 6.5. It is found that each sorbent has different affinity to the heavymetals, with heavy metal cations (i.e. Cd, Cu, Ni and Zn) removed more effectively thanheavy metal anions (i.e. As and Cr) by all sorbents except IOCS, which has a high affinitytowards As. The results further indicated that alumina and BCS outperform the other sorbents,possibly due to high surface area of alumina and the favourable sorption sites of BCS;whereas NZ, sand and bark were the least efficient. On the other hand, although FAeffectively retained Cd, Ni and Zn, the leaching of As, Cr, and Cu is a concern.