Presence Of SO2 Research Articles

The kinetics and pore structure of sorbents during the simultaneous calcination/sulfation of limestone in CFB

The interaction of calcination and sulfation in the simultaneous calcination/sulfation of limestone sorbent under circulating fluidized bed boiler conditions was studied. A specially designed constant-temperature reactor which can stop the reaction at a given time was employed. When limestone entered the furnace of mixed gases of CO2, O2, SO2, etc., its weight went down first, then up, so there was a minimum weight point. The whole reaction period could be divided into two stages by this minimum weight point, named the weight-loss stage and the weight-growth stage, which were dominated by the calcination reaction and by the sulfation reaction, respectively. In the weight-loss stage, the sulfation reaction took place and CaSO4 formed simultaneously together with limestone calcination as long as SO2 was present. In the weight-growth stage, the sulfation ratio at 60min in simultaneous calcination/sulfation is 30.7% higher than that in the sequential calcination then sulfation process. The weight loss rate of limestone calcined in the presence of SO2 was lower than that without SO2 present but the final weight was higher. The calcination of limestone was slowed by the presence of SO2; a probable mechanism was proposed, namely that the CaSO4 formed may fill or plug the pores in the CaO layer, and impede the transfer of CO2 and, therefore, retard the calcination reaction. This mechanism was supported by the observation that the effective diffusion coefficient of CO2 in CaO produced in the presence of SO2 was reduced. The impeding effect increased with increasing SO2 concentration (0–3000ppm), while, when the particle size decreased from 0.4–0.45mm to 0.2–0.25mm, the calcination rate of limestone was higher, no matter whether there was SO2 present or not. The impeding effect was less pronounced at 880°C than at 850°C. The reason for this appears to be the fact that there was less CaSO4 formed at 880°C and, therefore, fewer pores of the particle were filled or plugged.

Sulfuric Acid Aerosol Formation and Collection by Corona Discharge in a Wet Electrostatic Precipitator

A wet electrostatic precipitator (ESP) is considered as an effective technology for the control of dust and acid mist after wet flue gas desulfurization. In this study, a lab-scale wet ESP was designed to investigate dust collection with residual SO2 in the flue gas. Results showed that dust collection efficiency was reduced in the presence of SO2. This finding is attributed to the sulfuric acid aerosol formation during the corona discharge process. An exponential increase of the aerosol number concentration was observed with the increasing applied voltage, which could be 2 orders of magnitude higher than that without corona discharge. Fractional aerosol size distribution indicated that the aerosol penetration ratio was extremely low, in the size range of 0.1–1.0 μm. The formation of sulfuric acid aerosol could only be detected when the specific energy density exceeded a threshold value. Dust collection efficiency decreased by 13.5% when the SO2 concentration increased from 0 to 25 ppm as a consequence of...

NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures

Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction (SCR) of NO. The results showed that the addition of Nb2O5 could improve the SCR activity at low temperatures and the 6wt.% additive was an appropriate dosage. The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures. The resistances to SO2 of 3V6Nb/WTi catalyst at different temperatures were investigated. FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures, which still exhibited the reactivity with NO above 200°C on the catalyst surface. There was a synergistic effect among NH3, H2O and SO2 that NH3 and H2O both accelerated the catalyst deactivation in the presence of SO2 at 175°C. The thermal treatment at 400°C could regenerate the deactivated catalyst and get SCR activity recovered. The particle and monolith catalysts both kept stable NOx conversion at 225°C with high concentration of H2O and SO2 during the long time tests.

Removal of nitric oxide using combined Fe II EDTA and coal slurry in the presence of SO 2

Abstract Nitric oxide was removed by aqueous coal slurry containing FeIIEDTA in the presence of SO2 using a bubbling reactor. The effects of NO and O2 concentrations, temperature and pH on NO removal and coal pyrite leaching were studied. NO removal efficiency and coal pyrite leaching rate increased with the increase of NO concentration. The overall effect of high oxygen concentration is unfavorable to the removal of NO. The reduction rate of the complexed NO by coal pyrite increased with increasing temperature up to 60 °C, resulting in higher NO removal efficiency and coal pyrite leaching rate. Further increase in temperature was unfavorable to NO removal and coal pyrite leaching because the absorption of NO became the rate-determining step. The optimal pH was determined to be about 5.8. When pH was greater than 5.8, the reduction of FeIIEDTA-NO was inhibited, and therefore the NO removal efficiency decreased with further increase of pH. The reduction of FeIIEDTA-NO by coal pyrite played a significant part in coal pyrite leaching. Nevertheless, the leaching of coal pyrite was still controlled by chemical reaction.

Optimization of Promoter and Support for Co-based/zeolites Catalysts in Catalytic Reduction of NOx by CH4

Catalytic behavior of Co-based/zeolites catalysts was investigated in NOx reduction by CH4. Optimization of promoter and support was investigated by catalytic tests, and the relationship between catalytic activity and catalyst structure was illustrated by catalyst characterization. Co-Fe/SAPO-34 exhibited the highest activity among various Co-base/zeolites catalysts. The maximum conversion of NOx with 52.7% was obtained on Co-Fe/SAPO-34 at 450℃. The inhibition of activity of Fe/zeolites became severe in the presence of SO2, CO2, and H2O. CO2 exerted virtually no effect on the SCR activity of Co-Fe/zeolites. The inhibition of NOx conversion by H2O was reversible for Co-Fe/zeolites catalysts. Cobalt species were mainly present in CoO and Co(OH)2 states in Co-Fe/SAPO-34. Co3O4and Co(OH)2 were the main cobalt species of Co-Fe/ZSM-5, while CoO, CoAl2O4 and Co3O4 might be present in Co-Fe/Beta. The ratio of Fe2+/Fe3+ in the surface layer of Co-Fe/zeolites decreased in the order of Co-Fe/ZSM-5(3.98) > Co-Fe/SAPO-34(0.52) > Co-Fe/Beta(0.43). The active states of cobalt species and suitable ratio of Fe2+/Fe3+ were important for the activity of Co-Fe/zeolites in CH4-SCR. CH4-SCR over Co-Fe/zeolite catalysts started with the adsorption of NO and CH4 on Brønsted acid sites of the zeolite to produce NO+and carbon-containing species(-C=O and -COO) in the presence of oxygen, respectively. Subsequently, the important intermediates of nitrate species were generated from NO+ at the active sites. Finally, nitrate species reacted with carbon-containing species to form N2 and CO2.

Prevention of Mist Formation in Amine Based Carbon Capture: Field Testing Using a Wet ElectroStatic Precipitator (WESP) and a Gas-Gas Heater (GGH)

This study presents the results of two field tests that aimed at evaluating two countermeasures (WESP and GGH) to avoid acid mist formation. A WESP is shown to be very efficient for the removal of nuclei from the flue gas (100% efficient) and thus can prevent aerosol formation inside an amine based absorber. This is however only valid in the absence of SO2 in the flue gas entering the WESP. A decreasing WESP efficiency is noted in the presence of SO2 with increasing voltages as a result of newly formed aerosols inside the WESP. This implies that no or very low levels of SO2 should be present in the flue gas entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue gas leaving the power plant's Flue Gas Desulphurisation) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it. Having a Gas-Gas Heater (or any type of flue gas cooling such as a Low Temperature Heat Exchanger) installed upstream of the wet scrubbing may prevent homogenous nucleation and thus prevent the conversion of H2SO4 into sulfuric acid aerosols and consequently mist formation issues in the amine based carbon capture installation. Which option to choose amongst the two countermeasures presented in this study will depend on whether a new built installation is being considered or whether a carbon capture is planned as a retrofit into an existing installation.

CrO –MnO –TiO2 adsorbent with high resistance to SO2 poisoning for Hg0 removal at low temperature

Abstract Chromium modified MnO x –TiO 2 (CMT), MnO x –TiO 2 (MT) and CrO x –TiO 2 (CT) adsorbents were prepared by a sol–gel method and were investigated for Hg 0 removal in the absence and presence of SO 2 . The fresh and used adsorbents were characterized by N 2 physisorption, XRD, FTIR, H 2 -TPR, XPS and TG. The results showed that the addition of Cr into MT can not only increase the activity of Hg 0 removal, but also improve its SO 2 resistance performance. The amount of manganese sulfate formed onto spent CMT was much higher than that of chromium sulfate, meaning that sulfate species were formed preferentially on Mn rather than Cr.

Mercury capture by a structured Au/C regenerable sorbent under oxycoal combustion representative and real conditions

The environmental implications of mercury do not correspond only to the emissions to the atmosphere; the quality of the captured CO2 to be transported and sequestered has been subject of research, concerning trace quantities of heavy metals participating in mineralization and precipitation reactions in sequestration conditions. For oxycoal combustion, mercury is not an environmental issue alone but also an operational issue, particularly about where mercury could accumulate within the CO2 processing unit. Therefore, Hg removal is necessary to prevent its attack on the aluminium heat exchangers.In this work, a regenerable sorbent based on carbon supported Au nanoparticles (0.1%wt) has been used for Hg capture under oxycoal combustion atmosphere. The influence of the presence of O2, NO, SO2 and HCl in a gas containing Hg and CO2 on the sorbent as well as on the Hg oxidation (Au can act as an oxidation catalyst) has been evaluated under a simulated flue gas. The presence of either NO or HCl in the simulated flue gas led to mercury oxidation, with oxidized mercury not evolving in the gas, indicating that it is retained on the sorbent; the oxidized mercury is well stabilized on Au surfaces of the sorbent and favours the Hg-Au amalgam formation. This sorbent has been also evaluated in 3kWth oxycoal bubbling fluidized bed combustor. A lignite with high sulphur content was burned in presence of limestone. Despite high SO2 concentration that reached the Au/C sorbent, high capture efficiency was achieved and breakthrough occurred after 3.5h and 10% breakthrough is not reached during the experiments. Bearing in mind that regeneration time can be adjusted near 1h, two swing sorbent beds could be used to control mercury emissions under oxycoal combustion conditions.

Crown Ether Complexes of Alkali-Metal Chlorides from SO2.

The structures of alkali-metal chloride SO2 solvates (Li-Cs) in conjunction with 12-crown-4 or 1,2-disila-12-crown-4 show strong discrepancies, despite the structural similarity of the ligands. Both types of crown ethers form 1:1 complexes with LiCl to give [Li(1,2-disila-12-crown-4)(SO2 Cl)] (1) and [Li(12-crown-4)Cl]⋅4 SO2 (2). However, 1,2-disila-12-crown-4 proved unable to coordinate cations too large for the cavity diameter, for example, by the formation of sandwich-type complexes. As a result, 12-crown-4 reacts exclusively with the heavier alkali-metal chlorides NaCl, KCl and RbCl. Compounds [Na(12-crown-4)2 ]Cl⋅4 SO2 (3) and [M(12-crown-4)2 (SO2 )]Cl⋅4 SO2 (4: M=K; 5: M=Rb) all showed S-coordination to the chloride ions through four SO2 molecules. Compounds 4 and 5 additionally exhibit the first crystallographically confirmed non-bridging O,O'-coordination mode of SO2 . Unexpectedly, the disila-crown ether supports the dissolution of RbCl and CsCl in the solvent and gives the homoleptic SO2 -solvated alkali-metal chlorides [MCl⋅3 SO2 ] (6: M=Rb; 7: M=Cs), which incorporate bridging μ-O,O'-coordinating moieties and the unprecedented side-on O,O'-coordination mode. All compounds were characterised by single-crystal X-ray diffraction. The crown ether complexes were additionally studied by using NMR spectroscopy, and the presence of SO2 at ambient temperature was revealed by IR spectroscopy of the neat compounds.

Simultaneous NO and mercury removal over MnOx/TiO2 catalyst in different atmospheres

In this study, manganese oxides supported on titania was prepared by sol-gel method and employed as SCR catalyst for simultaneous NO and mercury removal from coal combustion flue gas. The simultaneous NO and Hg0 conversion rate on MnOx/TiO2 was evaluated in different atmospheres, and the interaction between denitration and demercuration was investigated. The results indicated that MnOx/TiO2 had good activity in simultaneously removing NO and Hg0 in SCR atmosphere (NH3+NO+O2+N2). However, both NO conversion and Hg0 removal efficiency were inhibited in simulated coal combustion flue gas compared to that in SCR atmosphere because of the presence of SO2 leading to the generation of sulfite and sulfate on the catalyst. H2O in simulated coal combustion flue gas had negative effect on the catalytic performance as well. NO conversion in oxy-fuel combustion flue gas was lower than that in air combustion flue gas, while Hg0 removal efficiency in oxy-fuel combustion flue gas was higher than that in air combustion flue gas. Hg0 displayed no obvious influence on NO conversion and N2 selectivity over SCR process. And SCR atmosphere showed almost no inhibition to Hg0 removal when the temperature was below 300°C. At the optimal temperature for NO conversion (250°C), the inhibition of SCR atmosphere on Hg0 removal became stronger as the space velocity (GHSV) increased, but the inhibitive effect could be ignored when GHSV slowed down to 50,000h−1 or less.

Study of SO2 effect on selective catalytic reduction of NOx with NH3 over Fe/CNTs: The change of reaction route

Fe/CNTs catalyst exhibits perfect performance when it is used in selective catalytic reduction of NOx with NH3 (NH3-SCR), meeting the requirements of low-temperature conversion and no vanadium use, which is thought to be a potential candidate for traditional V2O5–WO3 (MoO3)/TiO2 catalysts. However, small amount of SO2 remained after the desulfurization process severely impacts the activity of Fe/CNTs. TGA, XPS and TPD tests were used to investigate the properties of SOx-species formed on the catalysts; TPSR tests were proceeded to reveal the difference of reaction pathway between normal SCR reaction and that in presence of SO2. The results showed that ferric sulfate was the major sulfate species accumulated on Fe/CNTs, which enhanced the adsorption of NH3 species while constrained the adsorption of NOx species. Reaction pathway study suggested the adsorption and activation of NOx species over Fe/CNTs were conductive to the formation of intermediates which was the key to its excellent low-temperature performance. While this effective reaction pathway was inhibited with SO2 in the feed gas and led to the low-temperature activity loss (<275°C). Instead, ferric sulfates formed on Fe/CNTs promoted the reaction between adsorbed NH3 species and gaseous NO through which SCR performance at higher reaction temperature was promoted and this became the dominating reaction pathway. The transform of dominating reaction route was the reason for the change of de-NOx performance over Fe/CNTs in presence of SO2.

Nitrosamine Formation in Amine-Based CO2 Capture in the Absence of NO2: Molecular Modeling and Experimental Validation.

A computational chemistry approach was used to elucidate and verify the different nitrosamine formation mechanisms and pathways. These included nitrosamine formation under acid or basic environments in the presence of NO, O2, SO2 and CO2 without NO2. The results clearly showed that nitrosamine could be formed without NO2 via 2 different types of mechanisms, namely, addition and elimination forming N-N bond before proton transfer and proton transfer before N-N bond formation, respectively. The essence of these mechanisms identified in this work was that two reaction steps were required to complete both reaction mechanisms with different nitrosating agents. Two steps were both necessary neither of which could be neglected, if the nitrosamine formation reaction was to be completed. Computational simulation performed on the reactant, intermediate, transition state, and product for each set of reactions also validated the proposed mechanisms. Experiment also detected nitrosamine from the reaction of diethylamine and NO, SO2, O2, and CO2 in both liquid and gas phase. Thus, NO2 is not necessary for nitrosamine formation to occur in the CO2 capture system.

Effect of Ce/Y Addition on Low-Temperature SCR Activity and SO2 and H2O Resistance of MnOx/ZrO2/MWCNTs Catalysts

The effects of SO2 and H2O on the low-temperature selective catalytic reduction (SCR) activity over MnOx/ZrO2/MWCNTs and MnOx/ZrO2/MWCNTs catalysts modified by Ce or Y was studied. MnCeZr and MnYZr catalysts reached nearly 100% and 93.9% NOx conversions at 200 °C and 240 °C, respectively. They displayed a better SO2 tolerance, and the effect of H2O was negligible. The structural properties of the catalysts were characterized by XRD, H2-TPR, XPS, and FTIR before and after the reaction. The results showed that Ce could increase the mobility of the oxygen and improve the valence and the oxidizability of manganese, while the effect of Y was the opposite. This might be the main reason why the catalytic activity of MnCeZr was better than MnYZr in the presence or absence of SO2 and H2O. Doping Ce or Y broadened the active temperature window. Ce or Y, which existed in the catalysts with a high dispersion or at the amorphous state, preferred to react with SO2 to form sulfate species, and protected the manganese active sites from combing with SO2 to some extent, which coincided with the theory of ionic polarization.

A comparative study on the Mn/TiO2-M(M = Sn, Zr or Al) Ox catalysts for NH3-SCR reaction at low temperature

ABSTRACTA series of TiO2-M(M = Sn, Zr or Al) Ox were prepared and manganese oxide (MnOx) was supported on the carrier by the traditional impregnation method for low-temperature selective catalytic reduction (SCR) of NOx with ammonia as a reductant. The obtained catalysts were characterized by XRD, BET, high-resolution transmission electron microscope (HRTEM), H2-TPR, NH3-TPD, X-ray photoelectron spectroscopy (XPS) and in situ Fourier-transform infrared (FT-IR) and their catalytic activities for NOx reduction with NH3 in the presence of SO2 were investigated comparatively. The results showed that the highest NOx conversion of over 90% could be obtained with the Mn/Ti-Sn catalyst at a wide range of temperature window of 150–270°C. The combination of characterization techniques, such as BET, XRD and HRTEM, revealed that manganese oxides were well dispersed on Ti-Sn. H2-TPR suggested that Ti-Sn and Ti-Zr supports could enhance the reduction ability of catalysts. Accordingly, Mn/Ti-Al exhibited worse activity at low temperature. XPS results were in good agreement with H2-TPR results, and Mn/Ti-Sn had more surface-reducible species of Mn4+ ions and more surface-adsorbed oxygen species, which was conducive to SCR reaction. The in situ FT-IR spectra of NH3 adsorption indicated that all the modified catalysts had more Lewis acid sites and the amide species at 1506 cm−1 had a certain influence on the catalytic reaction at low temperature. Mn/Ti-Zr showed a stronger resistance to SO2 but Mn/Ti-Al was affected more adversely and all the catalysts could not be restored to the initial catalytic activity after stopping feeding SO2. NH3-TPD revealed that the total acid amount of the Mn/Ti-Sn sample was larger than other samples, which indicated that the Ti-Sn solid solution could provide more surface acid sites over the catalyst.

Reaction mechanism for the influence of SO2 on Hg0 adsorption and oxidation with Ce0.1-Zr-MnO2

The removal of Hg0 from flue gas has been one of the primary challenges in the control of mercury emission. The presence of even small amounts of SO2 has a significant influence on the Hg0 removal process, and the mechanism of this process has not been thoroughly explained to date. To understand the mechanism for SO2 influence, the influence of SO2 on the Hg0 adsorption and Hg0 oxidation components of the Hg0 removal process were investigated separately based on Ce0.1-Zr-MnO2. SO2 was shown to have serious negative effects on the Hg0 adsorption process due to the reaction between SO2 and Mn-based active sites, as determined by TGA and XPS results. In contrast, for the Hg0 oxidation process Mn-SO42− formed through the reaction between SO2 and Mn-based active sites, and Mn-SO42− had a certain contribution to Hg0 oxidation. Moreover, XPS results indicated that SO2 reacts with O2 to form SO3 which adsorbed on the catalyst surface and act as new active sites, promoting Hg0 oxidation via: Hg+SO3+1/2O2→HgSO4. This phenomenon caused the catalyst to retain Hg0 oxidation activity in the presence of SO2 for a relatively long time.

Removal of chromium (VI) from water using nanoscale zerovalent iron particles supported on herb-residue biochar

A composite material consisting of nanoscale zerovalent iron particles supported on herb-residue biochar (nZVI/BC) was synthesized and used for treatment of Cr(VI)-contaminated water. The effects of initial pH, chromium concentration, contact time, and competition with coexisting anions and natural organic matter (NOM) were also investigated. nZVI/BC was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy analysis (SEM), and the Brunauer-Emmett-Teller surface area was measured. TEM and X-ray photoelectron spectroscopy (XPS) analysis before and after reaction with Cr(VI) showed that reduction and coprecipitation occurred during hexavalent chromium adsorption. The removal of Cr(VI) was highly pH-dependent and the adsorption kinetics data agreed well with the pseudo-second-order model. The presence of SO42− and humic acid promoted Cr(VI) removal at both low and high concentrations, while the HCO3− inhibited the reaction. These results prove that nZVI/BC can be an effective reagent for removal of Cr(VI) from solutions.

Effects of seed particles Al2O3, Al2(SO4)3 and H2SO4 on secondary organic aerosol

Seed particles Al2O3, Al2(SO4)3 and H2SO4 were selected to investigate their effects on secondary aerosol (SA) formation in toluene/NOx photooxidation under sulfur dioxide (SO2) and ammonia (NH3). Effect of seed particles on SA formation was related to their acid-base properties and the presence of acid or alkaline gases. Under NH3-poor condition, SA formation increased with increasing SO2 concentration due to the acid-catalyzing effect of the oxidation products of SO2 (i.e. H2SO4). The enhancing effect of SO2 became unobvious under NH3-rich condition, because NH3 would eliminate the acid-catalyzing effect by neutralizing the acid products. Acidic seeds H2SO4 accelerated SA formation under either SO2 or NH3 condition. Weak acidic Al2(SO4)3 seeds didn’t affect obviously on SA formation. The inhibiting effect of amphoteric seeds Al2O3 on SA formation was related to the presence of SO2 / NH3 due to their acid-base property. Under NH3-poor condition, the inhibiting effect of Al2O3 on SA formation decreased with increasing concentration of SO2, while under NH3-rich condition, the inhibiting effect wasn’t remarkable.

Luminescence of ferrocene-modified pyrene derivatives for turn-on sensing of Cu2 + and anions

Detection and identification of metal ions by fluorescent turn-on sensors are challenging due to the quenching effect of most of the tested metal ions. In the present work, three ferrocene-modified pyrene-based probes 2–4 were synthesized to act as turn-on fluorescent sensors for Cu2+. The measurements of fluorescence quantum yield and fluorescence lifetime reveal that ferrocenyl unit can efficiently reduce the fluorescence emission of pyrene moiety. Steady-state fluorescence measurements find that the three ferrocene-modified fluorophores exhibit selective turn-on responses to Cu2+. Moreover, this turn-on effect to Cu2+ is highly influenced by the type of the counter ion. It is found that the presence of Cl− or NO3− could realize the turn-on response to Cu2+, whereas, the presence of SO42− or Ac− could not induce any fluorescence enhancement to Cu2+. Control experiments with ferrocene-free pyrene-based probe 1 reveal that the ferrocenyl unit plays the key role in the turn-on response to Cu2+. The possible mechanism for the turn-on responses is attributed to the oxidation behavior of Cu2+ to the ferrocene unit, which is confirmed by the control experiments with sodium ascorbate. Cyclic voltammetry measurements show that Cu2+ can influence the redox behaviors of ferrocenyl derivatives, which is also highly dependent on the anion of the copper salts. The influence of anion on the turn-on responses to Cu2+ was further used for anion detection and fluorescent logic gate.

Enhancing Oil Recovery from Chalk Reservoirs by a Low-Salinity Water Flooding Mechanism and Fluid/Rock Interactions

Different Low Salinity Waters (LSWs) are investigated in this work to understand the role of some ions, which were recognized from our previous work and the literature for their effect on wettability alteration. Different flooding stages were followed. The primary stage was by injecting synthetic seawater (SSW) and the secondary stage was with SSW diluted by 10 (LSW 1:10) and 50 (LSW 1:50) times, single and two salt brines, such as Na2SO4, MgCl2, and NaCl+MgCl2 at 70 °C. The flooding sequence was due to that most of the fields in the North Sea were flooded with seawater. Two flooding rates were followed, 4 PV/day (PV = Pore Volume) and 16 PV/day in all the experiments. One of the observations was the increase of the pH during the flooding with LSW and single salt brines. The increase of the pH was attributed to mineral precipitation/dissolution as the results of ionic interactions. The effluent ion concentrations measured to understand the most likely oil recovery mechanisms. The results showed that the higher the SSW dilution the slower the oil recovery response. In presence of SO42−, Ca/Mg, higher oil recovery. The exchange between Ca/Mg, was in line with field observations. A geochemical simulation was done for a comparison with the experimental data.

Dissolved Selenium(VI) Removal by Zero-Valent Iron under Oxic Conditions: Influence of Sulfate and Nitrate.

Dissolved Se(VI) removal by three commercially available zero-valent irons (ZVIs) was examined in oxic batch experiments under circumneutral pH conditions in the presence and absence of NO3– and SO42–. Environmentally relevant Se(VI) (1 mg L–1), NO3– ([NO3—N] = 15 mg L–1), and SO42– (1800 mg L–1) were employed to simulate mining-impacted waters. Ninety percent of Se(VI) removal was achieved within 4–8 h in the absence of SO42– and NO3–. A similar Se(VI) removal rate was observed after 10–32 h in the presence of NO3–. Dissolved Se(VI) removal rates exhibited the highest decrease in the presence of SO42–; 90% of Se(VI) removal was measured after 50–191 h for SO42– and after 150–194 h for SO42– plus NO3– depending on the ZVI tested. Despite differences in removal rates among batches and ZVI materials, Se(VI) removal consistently followed first-order reaction kinetics. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analyses of reacted solids showed that Fe(0) present in ZVI undergoes oxidation to magnetite [Fe3O4], wüstite [FeO], lepidocrocite [γ-FeOOH], and goethite [α-FeOOH] over time. X-ray absorption near-edge structure spectroscopy indicated that Se(VI) was reduced to Se(IV) and Se(0) during removal. These results demonstrate that ZVI can be effectively used to control Se(VI) concentrations in mining-impacted waters.