Initial Sulfate Research Articles

Sulphate removal by membrane filtration minimizes the risk of hydrogen sulphide formation in fixed bed biofilters

Hydrogen sulphide (H2S) is one of the suspected reasons behind sudden mass fish mortalities in recirculating aquaculture systems (RAS) in recent years. H2S production in aquaculture systems depends on sulphate and organic matter availability, presence of specific microbial groups, and local anoxic conditions. Specific potential H2S production hotspots in RAS have been identified within biofilters and in accumulated sludge. Current H2S control methods have been identified, such as improved hydrodynamics, increasing degassing efficiency, chemical addition of hydrogen peroxide or ozone, but have not been efficient or widespread applied. In this study, a nanomembrane filtration system was installed at a brackish water (mixture of seawater and freshwater to 15 ppt) smolt production site in Norway to remove sulphate ions from the seawater intake line (15 times reduction). The hydrogen sulphide production potential of the nanofiltered seawater mixed with freshwater (n = 3) was compared to an unfiltered seawater and freshwater mixture (15 ppt, n = 3) for 42 days in experimental scale biofilters using industrial fixed bed media. In both treatments, the linear production of H2S started around the time that bulk water measurements of oxidation-reduction potential (ORP) and dissolved oxygen (DO) dropped below 0 mV and 1 mg/L, respectively. As expected, the highest H2S concentration was observed in unfiltered water reactors, which also reached the highest concentration faster than filtered-water reactors. A 15 times reduction in initial sulphate levels by the nanofiltration membrane led to overall three times lower H2S production and delayed the onset of production by two days. Hence, membrane-filtering intake water decreased the risk of H2S production. A limitation in this study, however, was that sulphate was not completely removed from the intake water, and the next steps should evaluate how increasing the effort of membrane operation to completely remove sulphate affect the dynamics of H2S production in RAS.

Surface properties of schwertmannite with different sulfate contents and its effect on Cr(VI) adsorption

Sulfate is a critical component of schwertmannite. However, the sulfate content of schwertmannite decreases with the increase in AMD-polluted river pH value, and its impact on the surface properties and Cr(VI) adsorption of schwertmannite remains unclear. To address this issue, different methods, including batch adsorption, N2 physisorption, scanning electron microscopy (SEM), potentiometric titration, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) in combination with two-dimensional correlation spectroscopy (2D-COS) analysis, and surface complexation modeling (SCM) were employed. Our results showed that sulfate existed as both non-protonated bidentate-binuclear complexes and non-protonated outer-sphere complexes in schwertmannite. The surface morphology and particle size of schwertmannite were unaffected by the sulfate content. However, a decrease in sulfate content resulted in a drop in the negative charge on the surface of schwertmannite, which is conducive to particle aggregation. An increase in pH, on the other hand, raised the negative charge and encouraged the dispersion of the particles. And then, reducing the sulfate content of schwertmannite led to a decrease in acid-base buffer and Cr(VI) adsorption capacity of schwertmannite. The adsorption process of Cr(VI) by schwertmannite can be divided into two stages. In the first stage, Cr(VI) was adsorbed primarily through anion exchange reactions with the sulfate; however, the contribution of surface complexation gradually increased as the initial sulfate content decreased because of a reduced likelihood of anion exchange and an increase in the specific surface area of schwertmannite. Additionally, the behavior of sulfate and Cr(VI) in this stage could be predicted based on the initial sulfate content of schwertmannite. In the second stage, surface complexation with hydroxyl sites became the predominant mechanism of adsorption, which still exhibited great potential at higher Cr(VI) concentrations. Finally, the aforementioned hypothesis was used to establish a CD-MUSIC model, and the fitting results demonstrated that the density and Cr(VI) adsorption capacity of the sulfate site dropped as the sulfate content decreased, while the hydroxyl site was less impacted. The findings have provided insights into further understanding the properties of schwertmannite and its adsorption of Cr(VI).

Paired electrocatalytic H2O2-persulfate activation for sulfamethoxazole mineralization in a filter-press cell using BDD and air diffusion electrodes

This paper deals with the paired electrocatalytic H2O2-persulfate (H2O2-PS) activation to yield SO4– and OH for the antibiotic sulfamethoxazole (SMX) mineralization. A filter-press cell with a boron-doped diamond (BDD) anode and a gas diffusion cathode (GDE) was used to form the PS (through the anodic oxidation (AO) of sulfate) and H2O2 (via oxygen reduction reaction, ORR). Bulk electrolysis in the flow cell reached accumulation values of 1.48 mM PS and 4.80 mM H2O2 in 100 mM Na2SO4 at pH 3, with current density and mean linear flow velocity of j = 10 mA cm−2, andu = 39.5 cm s−1. On the other hand, the influence of the initial sulfate concentration 50 ≤ CSO42-≤ 500 mM), applied current density (5 ≤ j ≤ 15 mA cm−2), initial PS and SMX concentrations (0 ≤ CPS ≤ 1 mM, 5 ≤ CSMX ≤ 20 mg L–1) was systematically addressed on the H2O2-PS process performance. The best trial achieved the total abatement of 20 mg L–1 of SMX in a 100 mM Na2SO4 + 0.5 mM PS at pH 3, u = 39.5 cm s−1, and j = 10 mA cm−2. Lastly, a degradation pathway of SMX was proposed in which most of the by-products consisted of short-chained carboxylic acids and ammonium. Scavenger tests revealed that the degradation of SMX is provoked by OH (68.3 %), SO4– (3.9 %), and other oxidants (27.8 %).

Evaluation of a granular Cu-modified chitosan biocomposite for sustainable sulfate removal from aqueous media: A batch and fixed-bed column study

Adsorption-based treatment of sulfate contaminated water sources present challenges due to its favourable hydration characteristics. Herein, a copper-modified granular chitosan-based biocomposite (CHP-Cu) was prepared and characterized for its sulfate adsorption properties at neutral pH via batch equilibrium and fixed-bed column studies. The CHP-Cu adsorbent was characterized by complementary methods: spectroscopy (IR, Raman, X-ray photoelectron), thermal gravimetry analysis (TGA) and pH-based surface charge analysis. Sulfate adsorption at pH 7.2 with CHP-Cu follows the Sips isotherm model with a maximum adsorption capacity (407 mg/g) that exceeds most reported values of granular biosorbents at similar conditions. For the dynamic adsorption study, initial sulfate concentration, bed height, and flow rate were influential parameters governing sulfate adsorption. The Thomas and Yoon-Nelson models yield a sulfate adsorption capacity (146 mg/g) for the fixed bed system at optimized conditions. CHP-Cu was regenerated over 5 cycles (33 % to 31 %) with negligible Cu-leaching. The adsorbent also displays excellent sulfate uptake properties, regenerability, and sustainable adsorbent properties for effective point-of-use sulfate remediation in aqueous media near neutral pH (7.2). This sulfate remediation strategy is proposed for other oxyanion systems relevant to contaminated environmental surface and groundwater resources.

Aerobic biotransformation of 6:2 fluorotelomer sulfonate in soils from two aqueous film-forming foam (AFFF)-impacted sites

Although 6:2 fluorotelomer sulfonate (6:2 FTS) is a common ingredient in aqueous film-forming foam (AFFF) formulations, its environmental fate at AFFF-impacted sites remains poorly understood. This study investigated the biotransformation of 6:2 FTS in microcosms prepared with soils collected from two AFFF-impacted sites; the former Loring Air Force Base (AFB) and Robins AFB. The half-life of 6:2 FTS in Loring soil was 43.3 days; while >60 mol% of initially spiked 6:2 FTS remained in Robins soil microcosms after a 224-day incubation. Differences in initial sulfate concentrations and the depletion of sulfate over the incubation likely contributed to the different 6:2 FTS biotransformation rates between the two soils. At day 224, stable transformation products, i.e., C4C7 perfluoroalkyl carboxylates, were formed with combined molar yields of 13.8 mol% and 1.2 mol% in Loring and Robins soils, respectively. Based on all detected transformation products, the biotransformation pathways of 6:2 FTS in the two soils were proposed. Microbial community analysis suggests that Desulfobacterota microorganisms may promote 6:2 FTS biotransformation via more efficient desulfonation. In addition, species from the genus Sphingomonas, which exhibited higher tolerance to elevated concentrations of 6:2 FTS and its biotransformation products, are likely to have contributed to 6:2 FTS biotransformation. This study demonstrates the potential role of biotransformation processes on the fate of 6:2 FTS at AFFF-impacted sites and highlights the need to characterize site biogeochemical properties for improved assessment of 6:2 FTS biotransformation behavior.

Investigation of leaching behaviors of carbonation-cured CSA cements using an electrically accelerated leaching test

The present study provides the investigation of leaching behaviors of carbonation-cured calcium sulfoaluminate (CSA) cements with varying initial sulfate contents using an electrically accelerated leaching test. The CSA cement samples were normally or carbonation-cured for 28 days before subjecting them to an electrically accelerated leaching condition for 14 days. The samples were characterized experimentally before and after accelerated leaching. In addition, the leaching behaviors of the CSA cement samples over a wide range of cumulative leached water were thermodynamically modeled to determine their likely performance in repository environments. The results indicate that the reaction of ye'elimite was significantly promoted by accelerated leaching, resulting in the formation of ettringite after leaching, regardless of the curing regime used. Calcium sulfates and C-(A)-S-H formed in the carbonation-cured samples were the first phases to decompose upon accelerated leaching, which is in good agreement with the thermodynamic modeling calculations. For the normally cured samples, the use of higher calcium sulfate in the mixture is preferred, considering the amount of leached ions, yet the opposite holds true for the carbonation-cured samples. In particular, the changes in the calculated volumes of the reaction products upon simulated leaching were smaller for the carbonation-cured samples than for the normally cured samples.

The initiation stage of thermochemical sulfate reduction: An isotopic and computational study

Thermochemical sulfate reduction (TSR) is one of the most important organic-inorganic reactions in petroleum reservoirs which significantly affects production and processing risks. The initiation (non-catalyzed) stage of TSR is critical in constructing a reliable kinetic model to predict this reaction. There is a large gap in our understanding of the mechanisms involved in this stage. In the present study, we used hydrous pyrolysis experiments with Na2SO4 and 1-dodecene as model compounds at pH= 1, and temperatures of 250 °C and 300 °C to simulate this early TSR stage. We measured and calculated the sulfur isotopic fractionations of sulfate, H2S and individual organic sulfur compounds (OSC). A thermodynamic model was used to determine the concentrations of the different sulfate species (H2SO4, HSO4¯, SO42-) at the experimental conditions. We then used ab initio calculations to determine possible radical and non-radical reaction mechanisms to explain the experimental results. During all the experiments, sulfate was consumed gradually while H2S and OSC were produced. The residual sulfate was 34S enriched up to 10.7‰ relative to the initial sulfate as pyrolysis time advanced. The produced H2S and OSC were typically about 21‰ 34S depleted relative to co-existing sulfate. The formation of OSC, such as C24 sulfides and C12 thiophenes, during the experiments and their similar δ34S values, suggest a common precursor and that radical mechanisms are involved in their formation. Calculated activation energies and free energies (Ea and ∆G‡, respectively) for the radical TSR mechanisms (20.6–34.1 and 32.3–44.4 kcal mol−1, respectively) yielded lower values than the non-radical TSR mechanisms (53.5–68.5 and 59.7–78.1 kcal mol−1, respectively). However, the calculated kinetic fractionation factors for the non-radical mechanism correlated better with the 11–12‰ experimental fractionation factor of current and previous studies. This similarity between the experimental and computational results indicates that these non-radical rather than radical mechanisms were likely involved in the reduction of sulfate in our experiments. Despite the lower activation energies, the radical TSR mechanisms are not dominant in our experimental system, probably due to competing reactions of the active radical species (alkyl and allyl radicals). Nevertheless, under natural conditions, the significantly lower amount of alkenes is expected to reduce the competition on the active alkyl and allyl radicals for alkylation, making these radical mechanisms competing pathways for the initiation stage of TSR.

Empirical models to determine ions concentrations in lithium brines with high ionic strength

Argentina Puna brines are complex systems in which ions such as Na+, K+, Li+, Mg2+, Ca2+, SO42−, and B4O72− are presents. To obtain lithium carbonate from brines, they must be treated in order to increase its lithium concentrations and to eliminate the others ions that are presents in the brines. During concentration some salts can reach their solubility products (kps) and crystallize, producing different solid-liquid equilibriums. In order to design and select the process to purify the brine before lithium salts precipitation, it is necessary to know the other ions concentrations.Ion concentrations in solutions can be calculated based on the salts coefficient activities using Pitzer's model and its modifications. These methods have the restriction that can only be applied to solutions with ionic strength values up to 6 molal. The state of the art shows that the approach to study the equilibrium in complex system is to consider it as binary, ternary, quaternary and quinary systems. When ionic strength values are higher than 6 m the systems studied are binaries or have symmetrical ions.Brines of the Argentina Puna have, in general, initial ionic strength values around 6 molal and it increases when the brine is concentrated by evaporation, so the available thermodynamical models cannot be used to determine, beforehand, the final composition of a certain brine. In this work four different brines from four different Puna plateau in Argentina were evaporated to several degrees and ionic strength was calculated from the chemical brine's composition after each evaporation test. Ionic strength was found to correlate with the percentage of eliminated water following two different simple mathematical models, depending on the initial sulphate concentration of the brine and the possibility of its precipitation. Models to estimate the concentration of diluted ions of commercial value such as Li+, K+, and Mg2+ as function of ionic strength were also proposed. Ion concentrations could be modeled as function of the amount of eliminated water, once the correct relationship between this parameter and the ionic strength of the brine is established. These models correlate accurately ionic strength and ion concentrations for an ionic strength range from 4.8 to 15.4 molal; corresponding to percentages of water evaporated from 0% up to 60%.With these models it is possible to calculate beforehand the final ions concentrations after a given percentage of evaporated water. It allows to design brines processing and select the purification techniques without exhausting and time-consuming tests. Nowadays there are no tools that allows to do that, in consequence, each company must perform rigorous and numerous tests with its brines. Results of these work show that ionic strength is the parameter that unified brines behavior even if initial composition could be different. In consequence, it could be used as a parameter to describe brine behavior during evaporations.

Isotopic constraints on the sulfur cycle of the Bottom Convective Layer in the Black Sea

The Black Sea is the largest euxinic seawater basin with H2S at depths of below 90 m. Previously found that the presence of H2S in water was caused by microbial sulfate reduction. Herein, we report the sulfur isotopic composition of sulfate and sulfide in seawater at stations in the central part of the Black Sea, especially from the Bottom Convective Layer (BCL) located below a water depth of 1750 m. Our study shows that the sulfur isotopic composition of sulfate (δ34S(SO4)) in the surface layer of the oxic zone is +21.1‰ ± 0.1‰ relative to the Vienna Canyon Diablo troilite (VCDT), and does not differ from sulfate in the Mediterranean Sea. In the BCL, the average δ34S(SO4) value is +23.0‰ ± 0.2‰, which does not change vertically or laterally owing to effective convective mixing. The sulfur isotopic composition of H2S varies from −40.0‰ to −41.9‰ between 200 m water depth down to the seafloor with an average δ34S(H2S) value of −40.6‰ ± 0.4‰ for the BCL.Based on the water mass balance and sulfur isotopic composition of sulfate in the relevant water masses affecting the BCL, we have formulated a model to calculate the sulfate reduction rate in the BCL. After evaluating the sulfate and sulfide sources in the BCL, we assumed that the only apparent sulfide source is a bacterial sulfate reduction in the water column, and the main sulfate source is a mixture of water from the Black Sea and the lower Bosporus current with an initial sulfate isotopic composition of +21‰. The weak water exchange in the BCL leads to the largest observed isotopic difference ΔSR = δ34S(SO4) − δ34S(H2S) of 63.6‰ between sulfate and sulfide in the sulfidic water column of the Black Sea. To achieve a steady state with respect to the sulfate isotopic composition +23‰ in the BCL, an average sulfate reduction (SR) rate of 1.1 ± 0.1 nmol L−1 day−1 is required. A steady state relative to sulfur isotopic composition of sulfate in the BCL water was established 4200 years ago. The estimated residence time of H2S was 1.5 times shorter (946 years) than that of sulfate (1390 years). The latter is close to the water renewal time of the BCL (1432 years). Different residence times of sulfide and sulfate in the BCL are explained using their different fluxes from the BCL. Sulfate is mainly removed from the BCL via vertical advection, while a considerable part of the sulfide generated in the BCL (1/3 of total annual production) is probably spent on the sulfidation (FeS → FeS2) of muddy turbidites. The estimated annual H2S production in the BCL is 0.78 ± 0.07 Tg. The developed model predicts that the sulfide concentration in the BCL remains practically unchanged (380 ± 5 μM) over the last 1800 years (after 5700 years from the onset of anoxia).

A Fixed-Bed Column with an Agro-Waste Biomass Composite for Controlled Separation of Sulfate from Aqueous Media

An agro-waste composite with a pelletized form was prepared and characterized via IR and 13C solids NMR spectroscopy. Thermal gravimetry analysis (TGA) was used to study the weight loss profiles, while SEM images provided insight on the biocomposite morphology, along with characterization of the sulfate adsorption properties under equilibrium and dynamic conditions. The sulfate monolayer adsorption capacity (qe = 23 mg/g) of the prepared agro-waste pellets was estimated from the adsorption isotherm results by employing the Langmuir model, and comparable fitting results were obtained by the Freundlich model. The dynamic adsorption properties were investigated via adsorption studies with a fixed bed column at pH 5.2. The effects of various parameters, including flow rate, bed height and initial concentrations of sulfate, were evaluated to estimate the optimal conditions for the separation of sulfate. The experimental data of the breakthrough curves were analyzed using the Thomas and Yoon–Nelson models, which provided satisfactory best-fits for the fixed bed kinetic adsorption results. The predicted adsorption capacities for all samples according to the Thomas model concur with the experimental values. The optimum conditions reported herein afford the highest dynamic adsorption capacity (30 mg/g) as follows: 1100 mg/L initial sulfate concentration, 30 cm bed height and 5 mL/min flow rate. The breakthrough time was measured to be 550 min. This study contributes to a strategy for controlled separation of sulfate using a sustainable biocomposite material that is suitable for fixed-bed column point-of-use water treatment systems.

Phase development of hydrated cement pastes with SCMs under delayed heating conditions below 100 °C

This paper focuses on studying the effect of the delayed heating of cementitious materials on the phase assemblage variations in three types of cement paste. Two heating temperatures of the order of 65 °C and 80 °C were used to thermal treat the samples. Our results show that the thermal treatment induces the modification of the phase assemblage(particularly degradation of AFt and AFm phases) as well as the polymerization of the C-(A)-S-H. The observed variations depend mainly on the initial sulfate, aluminate and carbonate content in each cement. Finally, it is shown that the thermal treatment-related phenomena such as adsorption of aluminates on C-(A)-S-H are almost completely reversible after the temperature drop and re-immersion in water for 3 months, meanwhile other phenomena such as the formation of the hydrogarnet and hydrotalcite are only partially reversible. This modifies the free elements proportion and influences the probability of the DEF occurrence.

Study of early-age performance of cementitious backfills with alkali activated slag under internal sulfate attack

The vulnerability to internal sulfate attack of calcium-rich ordinary Portland cement (OPC) and its relative high cost force mines to explore technically effective and low cost alternative binders to solidify sulfate-containing tailings. Alkali activated slag (AAS) has been established to be a promising substitute for OPC due to its superior strength, good resistance to chemical attack and low cost. This study shows results of a laboratory research dealing the characteristics of cemented paste backfill (CPB) with AAS under internal sulfate attack. A blend of two alkali activators (SS: sodium silicate, SH: sodium hydroxide) was considered. To assess the behavior of CPB materials subjected to diverse conditions, a total of 4 different SS/SH ratio (e.g., 0.5, 0.75, 1, and 1.25) were used within CPB. Results shows that initial/final setting times tend to drop with growing sulfate content up to 5000 ppm, followed by gradual increases. Increasing sulfate content leads to higher yield stresses and viscosities and the degree of this negative impact is much severer in samples having the high SS/SH ratio. The presence of sulfate can enhance or deteriorate the strength of AAS-CPB depending on activator type, cure age and initial sulfate content. CPB with high SS/SH ratio reveals weaker resistance to internal sulfate attack due to their lower pH values. The key outcome of this work will be beneficial to optimally design of sulfate bearing CPB-AAS structures.

ВИЗНАЧЕННЯ ЕФЕКТИВНОСТІ ВИЛУЧЕННЯ СУЛЬФАТІВ НА ЗВОРОТНООСМОТИЧНІЙ МЕМБРАНІ НИЗЬКОГО ТИСКУ

The dependence of the efficiency of the low-pressure reverse osmosis membrane Filmtec TW30-1812-50 on the initial concentrations of sodium sulfate in the range of 10-650 mg/dm3 at permeate recovery rates of 1-90 % using a pressure of 4 atm was determined. The effect of increasing the permeate recovery rate on selectivity, membrane performance, and the in-crease in the sulfate content of concentrates was determined. It is shown that the concentration of sulfates in permeate depends on their initial concentration in solutions and increases both with an increase in the initial concentration and with an increase in the degree of permeate extraction. The latter factor is quite significant at initial sulfate concentrations of 650 mg/dm3. The membrane performance increases with decreasing salt content in water and decreases with increasing permeate removal rate, which leads to an increase in salt concentration in the pre-membrane space. The selectivity of the membrane for sulfates is 94.9-99.3 % and increases with increasing concentration of sodium sulfate solutions in solutions, despite a certain increase in salt concentrations in permeates. It is shown that as the degree of permeate selection increases, the selectivity for solutions with low initial sulfate concentrations increases. A FFP-based process modeling was performed to determine the sulfate con-centration in the permeate and concentrate at any initial sulfate concentration in a certain range. It was found that the con-centrate solutions are stable in the entire range of concentrations used with an increase in the degree of permeate recovery from 10 to 90 %. Based on the research results, a method for determining the capacity of the plant and the osmotic and oper-ating pressures based on the salt concentration and the set pressure in the system was proposed. From the data obtained, it can be concluded that the permissible level of mineralization at which the use of low-pressure reverse osmosis membranes is ad-visable.

Shear characteristics of the rock/cemented tailings interface exposed to sulfate attack

A clear understanding and accurate assessment of the mechanical properties of the interface between backfill material and the adjacent rock mass is paramount to a safe and economical design of cemented paste backfill (CPB) structures. With the CPB being a cementitious material, sulfate compounds prevalent in the mining environment may affect the shear characteristics of the CPB–rock interface. However, there are currently no research studies on the long-term shear behaviour of the CPB–rock interface exposed to sulfate attack, although CPB often contains a relatively large amount of sulfate ions. This paper presents and discusses the findings obtained through experimental investigation of the impact of the initial sulfate concentration in CPB on the shear characteristics of the interface between rock and CPB cured for long durations. The obtained results show that sulfate considerably influences the long-term shear strength and behaviour of the interface. Sulfate can either negatively or positively alter the shear properties of the mature CPB–rock interface due to the competition between the processes that reduce or increase the strength at the interface. The dominant process is a function of the initial sulfate content and the curing time.

Biological selenate and selenite reduction by waste activated sludge using hydrogen as electron donor

Biological reduction of selenium oxyanions is widely used for selenium removal from wastewater. The process is, however, limited by the availability of a suitable, efficient and low cost electron donor. In this study, selenite and selenate reduction by waste activated sludge using hydrogen as the electron donor was investigated. Both selenite and selenate (80 mg/L) were completely removed using H2 within 8 days of incubation. In the presence of sulfate in the medium, the Se removal efficiency decreased to 77.8–95.4% (for selenite) and 88.2–99.4% (for selenate) at different temperatures and initial sulfate concentrations. Thermophilic conditions (50 °C) were better suited for both selenite and selenate reduction using H2 as electron donor with a 0.8–13.5% increase in overall Se removal. Similarly, sulfate reduction also increased from 69.1– 88% at 30 °C to 72–94.6% at 50 °C. Most of the H2 utilized was diverted towards Se and sulfate reduction with minimal production of byproducts such as methane (<0.32 mM) or volatile fatty acids (<0.92 mg/L). The elemental Se produced from selenite and selenate reduction ranged between 33.9 and 52.1 mg/L. The elemental selenium nanoparticles produced as a result of selenite and selenate reduction were characterized using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and dynamic light scattering (DLS) spectroscopy. Furthermore, characterization of the biomass using Fourier-transform infrared spectroscopy (FTIR) and excitation emission matrix (EEM) spectra of the extracellular polymeric substances (EPS) produced by the waste activated sludge were performed to elucidate the mechanism of selenium oxyanion reduction to elemental selenium nanoparticles.

Comparative Evaluation of Industrial Phosphoric Acids Desulfation Capabilities of Limes and Barium Carbonate

Industrial phosphoric acid is an omnipresent product in the food industry and in the production of fertilisers and detergents. The presence of impurities in the raw material results in a relatively charged acid with various chemical species at the expense of its quality and use. These impurities include sulfate ions that precipitate into phosphoric acid during its manufacture. A desulfation is thus necessary. This study focuses on the reduction of free sulfates in phosphoric acid as impurities. This resulted in the use of three different adjuvants: lime, limestone, and barium carbonate. Three initial sulfate levels mainly contained in phosphoric acid were investigated: 2%, 4% and 6%. After experimentation, the comparison between the resulting yields allows considering barium carbonate as the most effective adjuvant. The desulfation efficiency was 95% in a very short stirring time of 15 min, independently of the initial sulphate content of phosphoric acid. The tests carried out with lime and limestone also lead to very interesting desulfation rates for phosphoric acid with an initial sulfate content of 2 or 4%.

Evaluation of a sulfidogenic system fed with microalgal biomass of Chlorella pyrenoidosa as an electron donor: Sulfate reduction kinetics

In this study, a sulfidogenic reactor fed with microalgal biomass of Chlorella pyrenoidosa as an electron donor was operated in a continuous mode. This study evaluated the influence of various initial sulfate concentration from 1.0 to 2.5 g/L on anaerobic sulfate reduction kinetics by a sulfidogenic enrichment culture predominantly Desulfovibrio sp. VSV2. It was observed that volumetric sulfate reduction rate (VSRR) was consistently increasing with an increase in volumetric sulfate loading rate (VSLR) across the retention time of 7–10 days. For a retention time of 7 days, the maximum VSRR was noted as 0.0050 g/(L.h) with a corresponding VSLR of 0.0089 g/(L.h). When retention time was maintained for 10 days, a maximum sulfate reduction of 65% and a maximum bacterial concentration of 1.632 g/L were achieved for an initial sulfate concentration of 1.5 g/L. It was concluded that VSLR facilitated through both dilution rate and initial sulfate concentration had a significant influence over sulfate reduction kinetics. The results of the study suggested that the microalgal-fed sulfidogenic system could be effectively employed for reduction of sulfate from sulfate-rich wastewater.

Combined solar activated sulfate radical-based advanced oxidation processes (SR-AOPs) and biofiltration for the remediation of dissolved organics in oil sands produced water

• Effective degradation of dissolved organics in produced water by solar activated SR-AOPs. • SO 4 •− , • OH and 1 O 2 reactive species were formed during solar activated SR-AOPs. • Better performance by solar activated peroxymonosulfate compared to persulfate. • Excellent mineralization of dissolved organic by post-treatment biofilm filtration. • Microbial profiling indicated presence of hydrocarbons and carboxylic acid degraders. This study reported for the first time the potential of sequential solar activated sulfate radical advanced oxidation processes (SR-AOPs) and fixed bed biofiltration for the enhanced remediation of dissolved organics in oil sands process water (OSPW). The effect of initial sulfate precursors namely persulfate (PS) and monopersulfate (PMS) was examined on the degradation of naphthenic acid (NA) surrogates and various classes of organics in real OSPW. Effluents from solar activated SR-AOPs treatment of OSPW at specific conditions were subjected to biofiltration for 45 days. Fast and complete degradation of 5-phenylvalveric acid (PVA) and up to 99% degradation of various organics in OSPW were achieved by the solar activated SR-AOPs. Radical scavenger and spin-trap electroparamagnetic spectrometry analysis showed that hydroxyl ( • OH) and sulfate (SO 4 •− ) radicals were the major reactive species generated and participated in the oxidation of organics in SR-AOPs treatment with either PS or PMS along with a small proportion of singlet oxygen. The biofiltration post-treatment showed significant mineralization of dissolved organics in treated OSPW, achieving over 60% and 40% reduction in DOC and COD, respectively, surpassing most of the reported studies for such combined approach. The bacterial metataxonomic analysis indicated significant enrichment of hydrocarbons and carboxylic acid degraders ( Sphingomonas and Sphingopyxis ) in the biofilters treating PMS pre-treated OSPW. However, for biofilters treating raw OSPW and PS, the bacterial community was dominated by hydrocarbon degraders and methanotrophs. The treated OSPW was found completely non-toxic for the OSPW treated with PMS-9 h and biofiltration. This demonstrates the potential of combined treatment for the effective remediation of the oil sand industry effluent.

In‐depth understanding the hydration process of Mn‐containing ferrite: A comparison with ferrite

AbstractManganese (Mn) is inevitably incorporated into cement from raw materials, and is mainly incorporated into the ferrite phase of cement. In this paper, the hydration kinetic was investigated for Mn‐containing ferrite and unmodified ferrite. The evolution of the solid phases, aqueous species, and both conductivity and pH were investigated for unmodified ferrite and Mn‐containing ferrite by a diluted suspension experiment. Isothermal calorimetry, transmission electron microscopy, and mechanical property measurements were conducted to explore the influence of Mn on the hydraulic activity of ferrite. The results showed that the incorporation of Mn enhances the hydraulic activity, alleviates the influence of gypsum on the retardation of ferrite, and improves the early strength in the presence of gypsum. Mn‐containing ferrite also accelerates dissolution, influencing the initial sulfate adsorption. Mn ions eventually incorporate into (Al, Fe)‐AFt and (Al, Fe)‐AFm. During the first several hours of hydration of ferrite, there is no sulfate consumption after the initial adsorption, accompanied by a decrease of Ca2+ and Al3+ concentration. And an “adsorption‐barrier” hypothesis is proposed to explain the dormant period of sulfate consumption.

Sulfate Removal from Water by Ion Exchange Method Using Purolite A200 Resin

In this study, sulfate removal by ion exchange method using Purolite A200 resin was investigated. In the study, the effect of resin amount, temperature, initial pH of the solution, initial sulfate concentration of the solution and mixing speed were selected as parameters. As a result, in sulfate removal; it was observed that the initial pH value was not very effective, but the temperature, initial sulfate concentration, mixing speed and resin amount were effective and the removal efficiency increased with the increase in the values of these parameters. The qm value was found as -0.381, while the Langmuir coefficient KL value was found as -0.227. For Freundlich isotherm, the Kf value was found to be 0.617, while the n coefficient value was found to be 0.705. These result was show that Langmuir isotherm was found to be a more suitable adsorption isotherm than Freundlich isotherm for this system.