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•For the first time, vivianite was separated from sludge via a wet magnetic technique.•The study focuses on the analysis of the extracted vivianite and recovered P.•The product ...contains vivianite (50–60%), organic matter (20%), quartz and siderite.•Phosphorus was recovered and purified from vivianite through alkaline treatment.•After purification, heavy metals are in line with P rock and future legislation.
To prevent eutrophication of surface water, phosphate needs to be removed from sewage. Iron (Fe) dosing is commonly used to achieve this goal either as the main strategy or in support of biological removal. Vivianite (Fe(II)3(PO4)2 * 8H2O) plays a crucial role in capturing the phosphate, and if enough iron is present in the sludge after anaerobic digestion, 70–90% of total phosphorus (P) can be bound in vivianite. Based on its paramagnetism and inspired by technologies used in the mining industry, a magnetic separation procedure has been developed. Two digested sludges from sewage treatment plants using Chemical Phosphorus Removal were processed with a lab-scale Jones magnetic separator with an emphasis on the characterization of the recovered vivianite and the P-rich caustic solution. The recovered fractions were analyzed with various analytical techniques (e.g., ICP-OES, TG-DSC-MS, XRD and Mössbauer spectroscopy). The magnetic separation showed a concentration factor for phosphorus and iron of 2–3. The separated fractions consist of 52–62% of vivianite, 20% of organic matter, less than 10% of quartz and a small quantity of siderite. More than 80% of the P in the recovered vivianite mixture can be released and thus recovered via an alkaline treatment while the resulting iron oxide has the potential to be reused. Moreover, the trace elements in the P-rich caustic solution meet the future legislation for recovered phosphorus salts and are comparable to the usual content in Phosphate rock. The efficiency of the magnetic separation and the advantages of its implementation in WWTP are also discussed in this paper.
In this study, an innovative suspension magnetization roasting (SMR) technology was developed and utilized for the recovery of iron from a typical refractory iron ore. The effects of the roasting ...temperature, CO reducing gas flow rate, N2 fluidizing gas flow rate, and feeding rate on the iron recovery were investigated. Under the optimal roasting conditions, a continuous and stable pilot scale SMR test was conducted for 72 h, and a staged grinding and staged low-intensity magnetic separation (LIMS) process was designed to upgrade the roasted product. The results showed that with the appropriate SMR conditions — a roasting temperature of 520 °C, CO flow rate of 4.0 m3/h, N2 flow rate of 2.0 m3/h, and feeding rate of 100 kg/h — an iron concentrate with a total iron grade (TFe) of 60.18% and iron recovery of 90.17% could be obtained. Compared to the traditional process of shaft furnace magnetization roasting (SFMR) followed by LIMS, the novel technique developed here could improve the TFe and iron recovery of the iron concentrate by 12–14% and 17–22%, respectively, with well-functioning equipment. During the SMR process, hematite and siderite were transformed into magnetite, which enhanced the magnetism of the iron minerals. The utilization of the SMR method has the potential to provide a significant technological advance in the field of refractory iron ore recovery in China and globally.
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•Utilization of suspension roasting provides a technological advance for iron recovery.•Roasting reactor performs stable production, with high-quality roasted product.•Hematite and siderite were converted into magnetite, enhancing magnetism of iron ore.•Good performance both in technical and equipment.
In this investigation, the coal fires in different Colombian coal mines were studied using advanced electron beam and X-ray diffraction techniques. The results were compared with information from ...high-resolution transmission electron microscopy (HR-TEM) equipped with a dispersive X-ray detector (EDS). Amorphous phases, salammoniac, anatase, muscovite, goethite, jarosite, calcite, gypsum, kaolinite, illite, and quartz are the dominant mineral matter constituents in almost all of the coal fires, with minute quantities of native sulfur, magnetite, siderite, pyrite, pickeringite, epsomite, hexahydrite, halotrichite being present in around half of the investigated coal fire samples. Other minerals that are present in some particular samples are chlorite, ankerite, and dolomite. Fe-sulfides were also detected particularly in the pyrite-bearing coal fires, possibly indicating oxidation of the Fe-sulfides occurring with coal fires. Exhaust discharge data indicate an overall trend of reducing carbon dioxide (CO2) and carbon monoxide (CO) releases (between 1.5 and 34%) from the coal fires. This is the first report on Colombian coal fires, which would be important for different perspectives of the research in the area.
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•Coal fires showed various degrees of contamination by anthropogenic activities.•Nanoparticles in Colombian coal areas were critical compared with the probable effect level.•Human activities played a dominant role, to coal pollution.•Community health surveys from mining and non-mining communities were aggregated for analysis.
Models of mineral-reagent complex (a) before and (b) after oleate adsorption.
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•Flotation of siderite, hematite and quartz with sodium oleate.•Molecular dynamic simulation of ...reagent-mineral complex models in solution.•Relative concentration analysis of carbon and oxygen in oleate ions.•Close relationship between flotation and molecular simulation.
Models of sodium oleate adsorption on siderite, hematite and quartz were investigated by molecular dynamic simulation, respectively. Surface energy was calculated to confirm the cleavage plan of hematite and quartz. Both natural cleavage plane of siderite and calculated plane were used to investigate the flotation of the three minerals. Based on the molecular simulation in solution with water as medium, adsorption quantity and interaction capability of oleate ions on the three minerals indicated that siderite could be collected efficiently by sodium oleate at neutral pH. Results of flotation experiments were further demonstrated by analysis of relative concentration of carbon atoms and oxygen atoms.
A significant number of industries produce large volumes of aqueous effluents containing heavy metals that discharge into the environment threatening biodiversity and human life. However, such ...effluents pose serious problems for the industry because of the high cost of metal decontamination using conventional technologies. The aim of this work is to study a suitable alternative through the use of iron compounds generated by a natural consortium with adsorptive properties appropriated for metal removal. The biogenic iron precipitates were identified as a mixture containing mainly siderite and magnetite. The use as sorbent was investigated to remove copper, zinc, arsenate and chromate from aqueous solutions. Variables such as the initial pH, contact time and initial metal concentration were evaluated. Three models were used to study the adsorption kinetic: pseudo first order, pseudo second order and Elovich models. Equilibrium data were fitted to Langmuir and Freundlich isotherm models. Higher metal uptakes were obtained with arsenic. Metal sorption was also investigated in the bimetallic system As-Cu.
•The natural consortium produced mainly siderite and magnetite.•Biogenic iron compounds can be used as adsorbents for heavy metals.•Biogenic compounds showed a higher uptake of As and Cr.•Zinc and copper were adsorbed by the organic matter bound to nanoparticles.•Other metals in solution affected the uptake compared to the monometallic systems.
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•The effects of adding ZVI on batch and continuous experimental systems are analyzed.•ZVI corrosion increases CH4 production and promotes the formation of Fe precipitates.•A model is ...developed and tested describing main biological and physicochemical processes.•Evaluation results show the impact of ZVI addition on potential energy and P recovery.
The influence of Zero Valent Iron (ZVI) addition on the potential resource recovery during the anaerobic digestion (AD) of domestic waste sludge is assessed. Potentially recoverable resources analyzed were nutrients such as struvite to recover P, and energy as biogas to recover C. Short term (biochemical methane potential tests, BMP) and long term (AD1, AD2) experiments are conducted using two types of set-up (batch, continuous). Process data (influent, effluent and biogas) is continuously collected and the dry digested sludge is analyzed by XPS. A mathematical model is developed based on a modified version of the Anaerobic Digestion Model No 1 upgraded with an improved physicochemical description, ZVI corrosion, propionate uptake enhancement and multiple mineral precipitation. The results of all experiments show that ZVI addition increases methane production and promotes the formation of siderite (FeCO3) and vivianite (Fe3(PO4)2), which causes changes in the biogas composition (%CH4 versus %CO2) and reduces P release. The model can satisfactorily reproduce the dynamics of AD processes, nutrient release, pH and methanogenesis in AD1. The proposed approach also describes the changes in the overall performance of the process because of ZVI addition in AD2. A model-based scenario analysis is included balancing chemical-ZVI addition and increased methane production/struvite precipitation. This scenario analysis allows concluding that: (a) the improvement of methane production does not compensate the costs of ZVI purchase, and (b) ZVI dramatically decreases the P recovery potential in the digestate of the AD systems. This is the first study to experimentally and mathematically describe the effect of ZVI on biogas production/composition and on the fate of phosphorus compounds, and its potential implications for potential energy and phosphorus recovery in AD systems.
Hydraulic fracturing of unconventional hydrocarbon reservoirs is critical to the United States energy portfolio; however, hydrocarbon production from newly fractured wells generally declines rapidly ...over the initial months of production. One possible reason for this decrease, especially over time scales of several months, is the mineralization and clogging of microfracture networks and pores proximal to propped fractures. One important but relatively unexplored class of reactions that could contribute to these problems is oxidation of Fe(II) derived from Fe(II)-bearing phases (primarily pyrite, siderite, and Fe(II) bound directly to organic matter) by the oxic fracture fluid and subsequent precipitation of Fe(III)-(oxy)hydroxides. The extent to which such reactions occur and their rates, mineral products, and physical locations within shale pore spaces are unknown. To develop a foundational understanding of potential impacts of shale iron chemistry on hydraulic stimulation, we reacted sand-sized (150–250 μm) and whole rock chips (cm-scale) of shales from four different formations (Marcellus Fm., New York; Barnett Fm., Central Texas; Eagle Ford Fm., Southern Texas; and Green River Fm., Colorado) at 80 °C with synthetic fracture fluid, with and without HCl. These four shales contain variable abundances of clays, carbonates, and total organic carbon (TOC). We monitored Fe concentration in solution and evaluated changes in Fe speciation in the solid phase using synchrotron-based techniques. Solution pH was the most important factor affecting the release of Fe into solution. For reactors with an initial solution pH of 2.0 and low carbonate content in the initial shale, the sand-sized shale showed an initial release of Fe into solution during the first 96 h of reaction, followed by a plateau or significant drop in solution Fe concentration, indicating that mineral precipitation occurred. In contrast, in reactors with high pH buffering capacity, little to no Fe was detected in solution throughout the course of the experiments. In reactors that contained no added acid (initial pH 7.1), there was no detectable Fe release into solution. The carbonate-poor whole rock samples showed a steady increase, then a plateau in Fe concentration during 3 weeks of reaction, indicating slower Fe release and subsequently slower Fe precipitation. Synchrotron-based X-ray fluorescence mapping coupled with X-ray absorption spectroscopy (both bulk and micro) showed that when solution pH was above 3.25, Fe(III)-bearing phases precipitated in the shale matrix. Initially, ferrihydrite precipitated on and in the shale, but as experimental time increased, the ferrihydrite transformed to either goethite (at pH 2.0) or hematite (pH > 6.5). Additionally, not all of the released Fe(II) was oxidized to Fe(III), resulting in the precipitation of mixed-valence phases such as magnetite. Idealized systems containing synthetic fracture fluid and dissolved ferrous chloride but no shale showed that in reactors open to the atmosphere at low pH (<3.0), Fe(II) oxidation is inhibited. Surprisingly, the addition of bitumen, which is often extracted by organic compounds in the fracture fluid, can override this inhibition of Fe(II) oxidation caused by low pH. Nonetheless, O2 in the system is still the most important factor controlling Fe(II) oxidation. These results indicate that Fe redox cycling is an important and complex part of hydraulic fracturing and provide evidence that Fe(III)-bearing precipitates derived from oxidation of Fe(II)-bearing phases could negatively impact hydrocarbon production by inhibiting transport.
Arsenic (As) release and mobility in groundwater is coupled to the iron (Fe) cycling and the associated transformation of Fe-oxides present in sediments. Recent in situ experiments have provided ...observations on arsenic mobilization and co-occurring reductive mineral transformation when placing As-loaded ferrihydrite-coated sand for 80 days in wells of an As-contaminated aquifer of Northern China. However, the complex temporal change in solid-associated arsenic and the multiple geochemical processes occurring when the flowing groundwater contacts the As-loaded ferrihydrite-coated sand hamper a detailed evaluation of the experimental data set. In this study, we develop a modeling approach that allows a quantitative interpretation of arsenic release and ferrihydrite transformation observed during the in situ experiments. The model accounts for the interplay of abiotic and biotic geochemical processes (i.e., surface complexation, reductive dissolution, formation of secondary iron minerals, and arsenic sequestration into the newly formed minerals) involved in the transformation of Fe-oxides and controlling arsenic mobility. The results show the capability of the proposed approach to reproduce the temporal trends of solid arsenic and ferrihydrite concentrations, as well as the spatial variability of mineral transformation, observed in different wells using a common set of surface complexation parameters and kinetic rate constants. The simulation outcomes allowed us to disentangle the specific contribution of the different mechanisms controlling the release of arsenic. It was possible to identify an initial rapid but minor release of As (13–23% of the initial surface concentration) due to desorption from ferrihydrite, as well as the reduction of adsorbed As(V) to As(III) upon contact with the flowing anoxic groundwater. Successively, reductive dissolution of ferrihydrite caused the decrease of the amount of the Fe mineral phase and led to a major depletion of solid-associated arsenic. The produced Fe(II) catalyzed the ferrihydrite conversion into more crystalline Fe(III) oxides (i.e., lepidocrocite and goethite) through Ostwald ripening, and resulted in the formation of siderite and mackinawite upon reaction with carbonates and sulfides naturally present in the groundwater. The model results also showed that, whereas the decrease in surface sites during reductive dissolution of ferrihydrite promoted arsenic mobilization, the mineral transformation limited As release through its sequestration into the newly formed secondary mineral phases.
Oil adsorption on the pore surface of tight shale affects the transport and even recovery of oil through shale reservoir. In this paper, an innovative model evaluating the n-alkane adsorption on ...shale was developed theoretically according to the hydrocarbon vapor adsorption (HVA) process and was verified by the n-decane (i.e., n-C10) adsorption on continental oil shale obtained from the Dongying sag of the southeastern Bohai Bay basin of China. The model considered the multilayer adsorption of hydrocarbon and the microscopic characteristics of the shale pore system. For a case study, several parameters in the models were determined by low temperature nitrogen adsorption/desorption (LT-N2A/D) and HVA tests combined with recently reported molecular dynamics simulation. Next, optimal values of the coefficients k and β were determined by fitting the experimental data with the model and were used to calculate the n-C10 adsorbed amount under 0.8 P/P0 and 298.15K condition. Simultaneously, the n-C10 condensed (i.e., free-phase-like) amount was obtained. The primary results demonstrate that (1) n-C10 adsorbed amount is obviously lower than condensed amount and varies from 0.097 to 0.619mg/g (mean 0.311mg/g), accounting for 1.68–3.76% (mean 2.32%) of the total amount. (2) Both the adsorbed and condensed amounts are directly controlled by total pore volume, which are mainly contributed by organic matters and secondarily by pyrite and siderite in shale. The model will be potential useful to evaluate the shale oil adsorption.
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