Selenate Removal Research Articles

Removal of selenate from wastewater using a bioelectrochemical reactor: The importance of measuring selenide and the role of competing anions

Removal of selenate (SeO42-) from selenate-contaminated wastewater is challenging due to the commonly co-existing and competing anions of sulfate (SO42-) and nitrate (NO3-). This study investigates SeO42− reduction to elemental selenium (Se0) in a cathode-based bioelectrochemical (BEC) reactor and a conventional biofilm reactor (i.e., an upflow anaerobic reactor). The simulated wastewater contained SeO42− at a typical concentration of 5 mg Se/L, SO42− at a typical concentration of 1000 mg S/L, and NO3− at concentrations that varied from 0 to 10 mg N/L. The impact of sulfate on the BEC reactor was much lower than that on the conventional reactor: The selenium removal, defined as (selenate in influent – dissolved selenium in effluent)/selenate in influent, was 99 % in the BEC reactor versus 69 % in the conventional biofilm reactor. The lower selenium removal in the conventional reactor was mainly due to the >10 times higher reduction of sulfate, which directly caused competition between sulfate and selenate for the common resources such as electrons. The more reduction of sulfate in the conventional reactor further led to 45 times higher production of selenide. Selenide is usually assumed to be minimal and therefore not measured in the literature. This simplification may significantly overestimate selenium removal when the influent sulfate concentration is very high. NO3- in the influent of the BEC reactor promoted selenium removal when it was less than 5.0 mg N/L but inhibited selenate removal when it was more than 7.5 mg N/L. This was supported by the microbial community analysis and intermediate (nitrite) analysis.

Effective selenate removal using pH modulated synthesis of biogenic jarosite: Comparative insight with non-biogenic jarosite and biogenic schwertmannite

Selenium, a crucial trace element for many organisms, including prokaryotes and humans, is toxic at high concentrations, necessitating its removal from wastewater. This study investigates the use of jarosite, a naturally occurring iron sulfate mineral with excellent heavy metal attenuation properties, for selenate (Se(VI)) removal for the first time. Biogenic jarosite was synthesized through Fe(II) oxidation by Acidithiobacillus ferrooxidans at an initial pH ranging from 1.5 to 4.0 (J-1.5 to J-4.0). This resulted in the formation of morphologically diverse particles of biogenic jarosite owing to varying Fe(II) oxidation and precipitation rates. For comparative analysis, non-biogenic jarosite (J-90C) and biogenic schwertmannite (S-2.5) were also synthesized. At 0.2 mM initial Se(VI) concentration, J-2.5 demonstrated superior Se(VI) removal compared to J-3.5 and J-90C. At 2.0 mM Se(VI), J-2.5 still outperformed J-3.5 and J-90C although its overall removal efficiency decreased. Notably, at 0.2 mM concentration, Se(VI) removal by J-2.5 was 63 %, which is comparable to 77 % removal by S-2.5. Furthermore, sulfate release from J-2.5 was significantly lower than that from S-2.5 in both Se-free and Se-containing solutions. This study provides critical insights into the synthesis and application of biogenic jarosite as a replacement for metastable schwertmannite, emphasizing its potential as an excellent Se sink for wastewater treatment.

Changes in microbial communities during high-rate microbial selenate reduction in an up-flow anaerobic fluidized bed reactor

Biological fluidized bed reactor (FBR) is a promising treatment option for removing selenium oxyanions from wastewater by converting them into elemental selenium. The process can achieve high rates and be efficiently operated at low hydraulic retention times (HRT). However, the effects of HRT on the changes in microbial community in the FBR process have not been previously explored. In this study, dynamic changes of microbial communities both on biofilm carrier and in suspension of a selenate-reducing FBR were explored at various HRTs (0.3–120 h). Based on partial 16S rRNA gene sequencing of the microbial communities, alpha diversity of microbial communities in suspension rather than in the biofilm were impacted by low HRTs (0.3 h–3 h). Members from genera Geobacter, Geoalkalibacter, and Geovibrio were the main selenate-reducing bacteria on carrier throughout the FBR process. Genus Geobacter was dominant in FBR carrier at HRT of 24 h–120 h, whereas Geoalkalibacter and Geovibrio dominated at low HRT of 0.3 h–6 h. Suspended microbial communities detected in the FBR effluent were more sensitive to HRT changes than that in biofilm. “Shock loading” at HRT of 0.3 h had a great impact on microbial community compositions both in the biofilm and effluent. Reactor operation in batch mode and long HRT of 24 h helped recover the community from “shock loading” and improved selenite reduction and ethanol oxidation. Redundancy analysis revealed that HRT, influent pH and selenate loading were key operational parameters impacting both the FBR performance and the composition of microbial communities associated with both the FBR carrier and effluent. Overall, the microbial communities in FBR biofilm flexibly responded to the changes of HRT and showed resilience to the temporary shock loading, enabling efficient selenate removal.

Efficient selenate removal from impaired waters with TiO2-assisted electrocatalysis

Aquatic selenium (Se) oxyanions have profound ecosystem and human health impacts, necessitating their conversion and immobilization into elemental Se(0) to mitigate the aquatic Se pollution. While thermodynamically favorable, this transformation encounters kinetic limitations, especially for selenate (SeO42−) or Se(VI). To lower the activation barrier, we investigated the electrocatalytic Se(VI) transformation using five affordable catalysts on graphite cathodes, including TiO2, underpotentially deposited Cu (UPD Cu), underpotentially deposited Cd (UPD Cd), Co, and CuFe. Among these five catalysts, we identified characteristic Se(VI) reduction peaks for TiO2 through cyclic voltammetry. Other catalysts removed less than 5% of 1-mM Se(VI) in 24-h chronoamperometry tests while leaching ppm-level metal cations in the treated water. In contrast, TiO2 as the electrocatalyst could remove more than 80% of 1-mM Se(VI) with negligible catalyst dissolution. Mechanistic investigations revealed a six-electron Se(VI)/Se(0) reduction pathway at -0.30 V (vs. Ag/AgCl), resulting in red Se(0) deposits on the TiO2-coated graphite cathode. Further potential decrease to more negative than -0.45 V led to Se(-II) formation, triggering cathodic Se(0) dissolution and surface regeneration. Electrochemical impedance spectroscopy indicated that Se(VI) reduction was optimal with a moderate TiO2 loading of 0.55 mg cm−2 and acidic environments (pH=1.0∼2.5), achieving an optimized removal of 88.7 ± 2.3% under -0.70 V and an energy input of 3.6 kWh kg−1 Se. These findings lay the foundation for efficient selenate removal from impaired waters. Future efforts should evaluate catalyst performance over time and refine electrode and reactor designs to improve efficiency.

Reduction-orientated selective removal of selenate by thiourea-functionalized polystyrene material

Efficient removal of trace selenate [Se(VI)] from contaminated water is still challenging because of the inevitable interference from the coexisting anions toward the adsorption or ion-exchange process. Herein, a bifunctional material (NCS@CMPS) was proposed for selective removal of Se(VI) from a complex matrix. NCS@CMPS was subtly prepared by grafting a chloromethylated polystyrene substrate (CMPS) with thiourea, resulting in reductive groups (C-SH and C=S) and adsorptive sites (–NH-, –NH2, and C=NH2+) anchored on the skeleton of CMPS. Batch studies demonstrated an excellent removal efficiency and anti-interference capabilities of NCS@CMPS toward Se(VI), even with very high levels of competing anions (chloride, sulfate, phosphate, nitrate, and bicarbonate) over a wide pH range (3 ∼11). The in-situ reductive removal and the unique pH-buffering effect of NCS@CMPS were responsible for the high selectivity and the wide applicability. The XPS analyses identified the removal mechanisms of concentrating, reducing, and sequestrating of Se species inside NCS@CMPS, where the majority of Se species was reduced to Se(IV) (80.9%). In column mode, NCS@CMPS can treat over 10,000 bed volumes (BV) of a simulated Se(VI) wastewater ([Se]ini = 200 μg/L) to below 10 μg/L, whereas the capacity of its substrate (i.e., CMPS) was only 28 BV. Additionally, the exhausted NCS@CMPS can be regenerated by NaBH4-NaOH-HCl treatment for repeated use. Moreover, the effectiveness of NCS@CMPS in treating actual industrial Se(VI) wastewater was also validated.

Coupling protein recovery to methane and lactic acid production to valorize duckweed used in selenate remediation

Duckweed (DW) can be used for metal bioremediation, but can also serve as a renewable feedstock for various processes such as protein production, acidogenesis and methanogenesis. In this study, a selenate (3 mg L−1) supplemented modified Steinberg medium was used as a feed for DW cultivation, which gave a selenate removal efficiency of 55%. Thereafter, an optimized protein extraction protocol was developed yielding a∼20% protein extraction efficiency from both the control and selenate-enriched DW. The solid fraction obtained during protein extraction was utilised for lactic acid (LA) production (upto 5 g L-1), whereas the liquid fraction (after protein extraction) was used as the substrate for methane production (∼150 mL gCOD−1). Selenate enriched DW achieved faster LA production and showed better methane production kinetics when compared to the control DW. This study shows that bioenergy and biocommodity production can be efficiently coupled to selenium removal from polluted wastewaters using DW.

Integrated bioprocess for Se(VI) remediation using duckweed: Coupling selenate removal to biogas production

The use of phytoremediation as a method for wastewater treatment or removal of pollutants is garnering significant interest and duckweed (DW), a free floating macrophyte, depicts significant potential for the removal of nutrients and toxic compounds from contaminated waters. The present work aimed to develop an integrated process for remediating selenate (Se(VI)) using DW biomass and subsequent use of Se(VI) enriched DW for biogas production. The main objective is to extend the application of selenium (Se) enriched DW biomass for biogas production. Se(VI) enriched DW biomass (Se-DW) gave higher methane production (48.38 ± 3.6 mL gCOD−1) than control DW biomass (C-DW) (24.46 ± 3.6 mL gCOD−1). To further enhance methane production, three pre-treatment approaches (acid, alkali and hydrothermal) were assessed and the solid and liquid fractions obtained after pre-treatment were used as a substrate. Pre-treatments increased biogas production in both Se-DW and C-DW than untreated conditions. Liquid fractions gave higher biogas production than solid fractions. In Se-DW, highest biogas production was observed in hydrothermal pre-treated Se-DW, while in C-DW, acid pre-treatment gave higher biogas production. Methane production was shown to be enhanced up to a Se(VI) concentration of 1.7 mg L−1, whereas a concentration beyond this lowered biogas production.

Microbial community dynamics in a feedback-redox controlled bioreactor process that enabled sequential selenate, nitrate and sulfate removal, and elemental selenium recovery

Oxidation reduction potential (ORP) feedback-control by ethanol-dosing was recently proved effective in facilitating a two-stage fluidized bed reactor (FBR) process to remove selenate, nitrate, and sulfate from wastewater, and recover high-purity elemental Se without the formation of carcinogenic SeS. However, further optimization requires knowledge on the relationship between microbial community composition and process performance. Here, changes of microbial communities during the reduction of selenate and nitrate in the first FBR (FBR1) under various ORP conditions (−240 to −520 mV vs. Ag/AgCl), sulfate reduction in subsquent FBR (FBR2) and sulfide oxidation in sulfide oxidation reactor (SOR) were examined. Based on 16S rRNA gene sequencing, high ORP (stage i without sulfate: >−360 mV; stage ii with sulfate: >−440 mV) and elevated sulfate at ORP ≤ −480 mV (stage iii) in FBR1 altered the microbial communities both on fluidized carrier and bulk liquor. Selenate reducers (Geoalkalibacter and Geovibrio genera) were impacted at ORP > −360 mV (stage i) or >−440 mV (stage ii), when selenate removal in FBR1 declined. However, nitrate reducers (Caenispirillum and Paracoccus genera) were not affected in the FBR1, and facilitated ~100 % nitrate removal. At ORP ≤ −480 mV, selenate reducers were readily enriched in FBR1. In the FBR2, the major sulfate reducing genera were Desulfomicrobium, Desulfovibrio and Desulfuromonas, whereas the dominant sulfide-oxidating genera in SOR were Paracoccus, Thiobacillus and Acholeplasma. This study suggested that both nitrate- and selenate-reducing communities could remain active under elevated sulfate concentrations, enabling sequential oxyanions removal and elemental Se recovery from wastewater.

Selenate removal via continuous fixed-bed column with nanoscale zero-valent iron supported on bentonite-zeolite pellets

Excessive levels of selenium in water are caused by discharging from fossil fuels combustion, coal-fired power plant activity, and mining operations. Selenium contamination poses considerable hazards to human health. Selenate (Se6+) is the most oxidized and common form of selenium in contaminated water. Zeolite-supported nanoscale zero-valent iron (Z-NZVI) coated onto bentonite-zeolite pellets (BZ-NZVI) was prepared for the removal of Se6+. The BZ pellets were coated with Z-NZVI powder at a ratio of 1:5. The BZ-NZVI was characterized using X-ray diffraction, point of zero charge analysis, Brunauer-Emmett-Teller method, field emission scanning electron microscopy, and X-ray fluorescence spectrometry techniques. The BZ-NZVI samples were tested in the batch reactor for kinetics and adsorption isotherm studies and subsequently in a continuous fixed-bed column. The kinetic models and adsorption isotherms were best described by the pseudo-first-order kinetics and Langmuir adsorption isotherm, respectively. Both boundary layer diffusion and intraparticle diffusion appeared to affect the intraparticle diffusion process. The efficiency of Se6+ removal in fixed-bed column of BZ-NZVI fitted well with Yoon-Nelson model. The adsorption rate decreased according to the Se6+ breakthrough proportion. The maximum Se6+ adsorption breakthrough capacity was 0.034 mg/g under the test run of 0.5 mg/L-Se6+ solution, pH 7, the flow rate of 5 mL/min, and the temperature of 303 K. Breakthrough times increased with decreasing flow rate and Se6+ initial concentration but decreased as the mass of BZ-NZVI increased. Se6+ contaminated in wastewater was removed by reduction and adsorption mechanisms over BZ-NZVI, which is a promising new area of research.

Microbial Enhancement of Selenium Removal in Chemically Modified Zeolite Columns

Selenium (Se) is an essential micro-nutrient for living organisms, but elevated concentrations in water can adversely affect health. In this research, we investigate the removal of selenium oxyanions (selenate and selenite) in aqueous systems by integration of adsorption on modified zeolites and microbial reduction. Dynamic sorption-reduction experiments were conducted using two sets of zeolite columns for the removal of selenite and selenate oxyanions, respectively. In each case, one column was fully packed with natural, unmodified zeolites, while the other column was composed of 80% natural and 20% iron-coated zeolites, by mass. The initial selenium concentration, selenite (SeIV) or selenate (SeVI), was 790 μg/L, the pH was 7.5, and the flow rate was 3 mL/min. Initially, as expected, the higher selenate removal (34%) was observed with coated zeolite, twice as high compared to the results with unmodified zeolite. Maximum selenite removal was 89% in the column with modified zeolite. Within approximately 14 days, as the biofilm developed inside the columns, selenium reduction in all four columns reached approximately 99%. Biofilm microbial community composition, assessed by 16S rRNA sequencing, is consistent with the presence of mainly selenium-reducing bacteria (Veillonella, Bacteroides, and Escherichia). Selenium oxyanions were reduced to elemental selenium, visible within the bioreactors as red-color aggregates.

Understanding the positive effects of dissolved Fe2+ and limited aeration on selenate removal from water by nano zero-valent iron supported on biochar

ABSTRACT Batch test was conducted to investigate Se(VI) removal by nano zero-valent iron supported on biochar (BC@nZVI) prepared by a one-step carbothermal synthesis in the presence of ferrous ions and limited aeration. The presence of ZVI and biochar was confirmed in the synthesised material by X-ray diffraction and Raman spectroscopy. TEM analysis revealed that nZVI with a diameter of about 50 nm was dispersed well on the biochar. The Effects of BC@nZVI dosage, initial solution pH, Fe2+ concentration, limited aeration, and coexisting anions on Se(Ⅵ) removal were investigated. The role of Fe2+ on Se(VI) removal have been examined by sequential Fe2+ and Se(VI) dosing tests. More than 98% of Se(VI) (10 mg/L) was removed with BC@nZVI dosage of 1.0 g/L at pH 4.0. The removal percentage of Se(VI) decreased with an increasing in pH from 4.0 to 9.0. The strong electrostatic attraction between Se(VI) and nZVI and the high nZVI activity at low pH are responsible for the significant selenium removal. The removal efficiency of Se(VI) increased with increasing Fe2+ concentration from 0 to 0.5 mmol/L. Fe2+ promotes a shift in the passive layer on nZVI surface towards a medium that favours electron transfer. Se(VI) reduction by ZVI is thought to be accelerated under limited aeration. The positive effect of O2 on selenate reduction can be attributed either to mechanical removal of the oxide layer on the ZVI particles, or to a difference in electron transfer rates, or to a reactive Fe(II)-bearing solid formed when ZVI was oxidised by O2. Cl−, NO3 −, SO4 2− and HA can inhibit the removal of Se(VI) on BC@nZVI in different degrees. The results of XRD, Raman, and XPS characterisation showed that the removal mechanism of Se(VI) include the adsorption and reduction ed of Se(VI) on BC@nZVI. Fe2+ and limited aeration would play a critical role in Se(VI) removal by BC@nZVI.

Near Quantitative Removal of Selenate and Sulfate Anions from Wastewaters by Cocrystallization with Chelating Hydrogen-Bonding Guanidinium Ligands.

Selenium (Se) has become an environmental contaminant of aquatic ecosystems as a result of human activities, particularly mining, fossil fuel combustion, and agricultural activities. By leveraging the high sulfate concentrations relative to Se oxyanions (i.e., SeO n 2-, n = 3, 4) present in some wastewaters, we have developed an efficient approach to Se-oxyanion removal by cocrystallization with bisiminoguanidinium (BIG) ligands that form crystalline sulfate/selenate solid solutions. The crystallization of the sulfate, selenate and selenite, oxyanions and of sulfate/selenate mixtures with five candidate BIG ligands are reported along with the thermodynamics of crystallization and aqueous solubilities. Oxyanion removal experiments with the top two performing candidate ligands show a near quantitative removal (>99%) of sulfate or selenate from solution. When both sulfate and selenate are present, there is near quantitative removal (>99%) of selenate, down to sub-ppb Se levels, with no discrimination between the two oxyanions during cocrystallization. Reducing the selenate concentrations by 3 orders of magnitude or more relative to sulfate, as found in many wastewaters, led to no measurable loss in Se removal efficiencies. This work offers a simple and effective alternative to selective separation of trace amounts of highly toxic selenate oxyanions from wastewaters, to meet stringent regulatory discharge limits.

Biomineralization of indium to indium selenide by anaerobic granular sludge in the presence of selenium oxyanions for sustainable recovery

This study examined simultaneous removal of indium (In(III)) and selenium oxyanions (Se(IV) and Se(VI)) using anaerobic granular sludge in batch and sequencing batch experiments. The indium removal efficiency was very high (>95%) throughout the experimental period, whereas the selenite removal values (78.9–98.2%) were considerably higher than the values obtained for selenate removal (15.5–70.0%) in the absence of In(III). The presence of In(III), however, increased the selenite and selenate removal efficiency to values up to 96–98%. The removal mechanism involved adsorption onto granular sludge followed by biomineralization to indium selenide. The presence of indium selenide in granular sludge treating indium and either of the selenium oxyanions was confirmed by SEM-EDX, XRD and XPS analysis. The granular sludge biomass exposed to only indium, mineralized it to form indium hydroxide. The microbial community analysis showed dominance of methanogenic microorganism in the granular sludge exposed to different combinations of indium and selenium. This study demonstrated the potential of anaerobic granular sludge biomass for production of indium selenide from co-mineralization of indium in the presence of selenium oxyanions Se(IV) and Se(VI) which provides an alternative novel strategy for its recovery from waste streams.

Removal of arsenic and selenium from brackish water using electrodialysis for drinking water production

Arsenic (As) and selenium (Se) are hazardous elements contaminating groundwater resources. In this work, arsenite (AsIII), selenite (SeIV) and selenate (SeVI) removal from brackish water by a batch electrodialysis (ED) system was investigated with varied water quality (pH, feed concentration and feed salinity) and operative parameters (flowrate and electric potential). The results showed that As and Se removal was pH dependent. Rising salinity increased the amount of chloride ions and therefore delayed As and Se removal. Higher As and Se feed concentrations led to higher molar flux, although removal rates were independent of ion concentration. ED boundary layer thickness was reduced at higher flowrates (30 to 70 L/h), but this did not affect the removal of contaminants significantly (<5 %). Electromigration transport was the dominant mechanism for both Se and As species removal, as long as the compounds were charged. The ionic characteristics (diffusivity, ionic mobility, hydration number) were the determinant principle for removal. As and Se real contaminated groundwater samples were tested showing that ED can potentially be used as a resource recovery method for selective removal of more mobile ions.

Synthesis and selenate removal of magnesium–aluminum-layered double hydroxide particle using magnesium oxide

Synthesis and selenate removal of magnesium–aluminum-layered double hydroxide particle using magnesium oxide

Non-demineralized paper waste sludge derived magnetic biochar as sorbs for removal of methylene blue, phosphorus, and selenate in wastewater

Pollution has continued to be the source of elevated nutrient levels in catchment areas, causing eutrophic conditions that threaten human health. Adsorption has been seen as a cost-effective and simple process of removing and recovering nutrients from wastewater. Biomass feedstocks have received significant research interest in recent years on the production of biochar and its magnetized variants for wastewater treatment. However, there have been minimal studies on the use of paper waste sludge obtained from the recycling industry as a feedstock for biochar production used in wastewater treatment. Hence this study focused on the production of magnetic biochar composites as an adsorbent for nutrient removal and recovery from wastewater. Neat non-demineralized biochar and its magnetized variant were produced using paper waste sludge through co-pyrolysis at 450 °C and for the magnetized variant, the feedstock was synthesized using Fe3+ and Fe2+ salts. The biochar produced exhibited good structural and chemical properties suitable for adsorption. Hence further analysis was performed using MBC-SPS-450 for the removal of phosphorus (P), selenate (Se), and methylene blue (MB) from wastewater. The observed efficiencies for P, Se, and MB were 48.83, 58.43, and 5.92 mg g − 1 respectively. From the results obtained, the magnetized variant (MBC-SPS-450) displayed excellent adsorption efficiencies, lower loading requirements with an optimum loading of 5 g L − 1, easy removal from solution by magnets, and was regenerated with excellent adsorption efficiencies. These excellent results position paper waste sludge-derived biochar as a good and low-cost adsorbent for the removal and recovery of nutrients from wastewater with the added benefit that it is part of the recycling process.

Novel triazine-based cationic covalent organic polymers for highly efficient and selective removal of selenate from contaminated water

Selenium (Se) removal from contaminated water has become a major environmental problem in recent years. Designing efficient and selective materials for selenium adsorption is urgent and still represents a great challenge. Herein, two novel cationic covalent triazine frameworks (CTFS-Cl and CTFL-Cl) are developed for the first time and employed as a new class of Se adsorbents. The results from systematic adsorption experiments indicate that these materials can adsorb SeO42- in a wide range of pH values (2−11) with fast kinetics (5 min), outstanding adsorption capacity, and excellent selectivity over other competing anions. The maximum adsorption capacity achieved (149.3 mg/g by CTFS-Cl) constitutes one of the highest values among the organic polymeric materials. More importantly, after a single step adsorption, these materials can reduce the Se concentrations to lower than 10 μg/L, the lowest drinking water standard in the world. The adsorption mechanism was probed by XPS technique, EDS analysis, adsorption experiments, and DFT calculations, which reveals that anion exchange between Cl- and SeO42- is the main driving force for Se adsorption. Additionally, CTFS-Cl and CTFL-Cl perform well toward real contaminated river water sample with the residual Se being less than 8.49 μg/L. This work demonstrates the excellent performance of CTFs-based materials with great application prospect for Se removal in contaminated water treatment.

Surface water H-bonding network is key controller of selenate adsorption on [0 1 2] α-alumina: An Ab-initio study

Selenate adsorption onto metal oxide surfaces is a cost-effective method to remove the toxin from drinking water systems. However, the low selectivity of metal oxides requires frequent sorbent replacement. The design of selective adsorbents is stymied because the surface factors controlling selenate adsorption remain unknown. We calculate adsorption energies of selenate on the (012) α-Al2O3 surface using density functional theory to unravel the physics that controls adsorption. Our model is validated against experiment by correctly predicting selenate removal efficiency as a function pH. We find that the selenate adsorption energy on the anhydrous α-Al2O3 surface is surprisingly anti-correlated with the fully solvated adsorption energy; therefore, the direct interaction between adsorbate and sorbent is eliminated as the controlling mechanism. Rather, the change in number of surface hydrogen bonds after adsorption is the factor most correlated with the adsorption energy (R2 > 0.8); and is thus determined to be the factor controlling selenate adsorption. We find that pH affects adsorption by controlling the number of surface protons available for H-bonding to selenate. This work demonstrates that adsorption prediction should not be made based on gas phase sorption energies and suggests that surface engineering which increases surface protonation may be an effective strategy for increasing selenate sorption.

Novel Triazine-Based Cationic Covalent Organic Polymers for Highly Efficient and Selective Removal of Selenate from Contaminated Water

Novel Triazine-Based Cationic Covalent Organic Polymers for Highly Efficient and Selective Removal of Selenate from Contaminated Water

Reductive removal of selenate (VI) in aqueous solution using rhodium metal particles supported on TiO2.

Selenium and its compounds in high concentration are toxic for humans, especially selenate (VI) is the most toxic due to its high solubility in water. To promote the reductive reaction of Se(vi) to Se(iv) or Se(0), which is relatively easy to remove in water, noble metal particles were added as reaction sites with a reductant. The highest removal performance of selenate in aqueous solution was achieved using rhodium particles supported on TiO2 (Rh/TiO2). Selenate was rapidly reduced with hydrazine on the metal particle, leading to a selenium deposition on the particle inhibiting the stable reductive reaction. On the other hand, when a weaker reductant such as formaldehyde was used for the selenate reduction, the selenium deposition was suppressed due to its low reactivity, resulting in a stable reductive reaction of selenate in water.