H2O2 Dosage Research Articles

Preparation of CuFe2O4 composite metal oxides and selective oxidation of benzyl alcohol

Using iron nitrate and copper nitrate as raw materials, mesoporous material SBA-15 as template agent and n-hexane as solvent, CuFe2O4 samples of mesoporous loaded composite metal oxide catalysts were successfully prepared by calcination at 600 °C. The samples were characterized by X-ray diffraction (XRD), thermogravimetric-differential scanning analysis (TG-DSC), and scanning electron microscopy (SEM). The selective oxidation of benzyl alcohol by CuFe2O4 under different catalytic conditions was investigated using benzyl alcohol as a model compound, and the oxidation products were analyzed by high performance liquid chromatography (HPLC). The results showed that the CuFe2O4 catalyst prepared by calcination at 600°Cwas the best. The best selective oxidation conditions were achieved at a reaction system temperature of 90 °C, a catalyst dosage of 4 g/L, a molar ratio 1:1 of H2O2 dosage to benzyl alcohol, and a reaction time of 4 h. The conversion of benzyl alcohol under this condition was 66.95%, and the selective conversion of benzaldehyde was 96.07%. This indicates that CuFe2O4 is a composite metal oxide with high selective oxidation of benzyl alcohol and has wide application prospects.

Tuning the intrinsic catalytic sites of magnetite to concurrently enhance the reduction of H2O2 and O2: Mechanism analysis and application potential evaluation

Heterogeneous Fenton-like process based on H2O2 activation has been widely tested for water purification, but its application still faces some challenges such as the use of high doses of chemicals (including catalysts and H2O2). Herein, a facile co-precipitation method was utilized for small-scale production (∼50 g) of oxygen vacancies (OVs)-containing Fe3O4 (Vo-Fe3O4) for H2O2 activation. Experimental and theoretical results collaboratively verified that H2O2 adsorbed on the Fe site of Fe3O4 tended to lose electrons and generate O2•-. While the localized electron from OVs of Vo-Fe3O4 could assist in donating electrons to H2O2 adsorbed on OVs sites, this allowed more H2O2 to be activated to •OH, which was 3.5 folds higher than Fe3O4/H2O2 system. Moreover, the OVs sites promoted dissolved oxygen activation and decreased the quenching of O2•- by Fe(III), thus promoting the generation of 1O2. Consequently, the fabricated Vo-Fe3O4 achieved much higher oxytetracycline (OTC) degradation rate (91.6%) than Fe3O4 (35.4%) at a low catalyst (50 mg/L) and H2O2 dosage (2 mmol/L). Importantly, further integration of Vo-Fe3O4 into fixed-bed Fenton-like reactor could effectively eliminate OTC (>80%) and chemical oxygen demand (COD) (21.3%∼50%) within the running period. This study provides promising strategies for enhancing the H2O2 utilization of Fe mineral.

Hydroxylamine facilitated catalytic degradation of methylene blue in a Fenton-like system for heat-treatment modified drinking water treatment residues.

Rational treatment of drinking water treatment residues (WTR) has become an environmental and social issue due to the risk of secondary contamination. WTR has been commonly used to prepare adsorbents because of its clay-like pore structure, but then requires further treatment. In this study, a Fenton-like system of H-WTR/HA/H2O2 was constructed to degrade organic pollutants in water. Specifically, WTR was modified by heat treatment to increase its adsorption active site, and to accelerate Fe(III)/Fe(II) cycling on the catalyst surface by the addition of hydroxylamine (HA). Moreover, the effects of pH, HA and H2O2 dosage on the degradation were discussed with methylene blue (MB) as the target pollutant. The mechanism of the action of HA was analyzed and the reactive oxygen species in the reaction system were determined. Combined with the reusability and stability experiments, the removal efficiency of MB remained 65.36% after 5 cycles. Consequently, this study may provide new insights into the resource utilization of WTR.

Electrical Energy Consumption of Multiscale UV-AOP Reactors for Micropollutant Removal in Drinking Water: Facilitated Prediction by Reaction Rate Constants Measured on a Mini-Fluidic Photoreaction System.

Electrical energy consumption per order (EEO) is an important figure-of-merit for the selection and optimization of ultraviolet (UV)-based advanced oxidation processes (UV-AOPs). However, EEO applications are limited by the lack of an accurate and facilitative evaluation method because EEO presents reactor property dependence. In this study, we developed an EEO prediction method for multiscale UV-AOP reactors for micropollutant removal in water. The method utilized the reaction rate constants determined in a reference reactor (e.g., mini-fluidic photoreaction system), complemented by a scale-up method that clarified the dependence of EEO on reactor properties. The predicted results of various UV-AOPs were verified experimentally in four bench/pilot-scale reactors in laboratory and a full-scale flow-through reactor (FFR) in field using sulfamethazine as a model micropollutant. For example, EEO values of 0.105 and 0.058 kWh m-3 order-1 were predicted in the FFR at H2O2 doses of 5 and 10 mg L-1, respectively, which generally agreed with verification results. Additionally, the developed method could assist the identification of appropriate reactors in the laboratory for EEO measurements, providing a valuable supplement for the EEO prediction in practice. The developed method presents acceptable accuracy, convenience, and low cost, which would significantly facilitate EEO evaluations for practical UV-AOP applications.

Green sludge dewatering and recycling technology for generating renewable energy and liquid nutrients: Bench- and pilot-scale studies

In this study, ultrasonication was performed under a low H2O2 dosage for dewatering and reducing activated sludge. Moreover, torrefaction was performed to convert the sludge remaining after ultrasonication into biochar, which is a renewable energy source. Factors including the H2O2 concentration, ultrasonication time and power, and torrefaction temperature and reaction time were systematically evaluated. The results of bench-scale tests indicated that high sludge volume and mass reductions (>50%) as well as high-carbohydrate and -protein content in the supernatant could be achieved through 20-s ultrasonication under a H2O2 dosage of 1.5% and ultrasonication power of 70-W. In these tests, the produced biochar exhibited a HHV of 12.8–14.4 MJ kg−1, a return of energy investment (ROEI) of 7.7–14.2, and 65.4% lower greenhouse gas (GHG) emissions upon combustion than did bituminous coal. In the pilot-scale tests, the produced biochar exhibited an ROEI of 10.4, and its GHG emissions on combustion were 74.8% lower than those of bituminous coal. The cost of the developed method is 84.6% lower than that of the conventional dewatering and disposal method. In summary, the proposed method is an energy-efficient, environment-friendly, and economically feasible method for producing biochar and recovering nutrients from supernatants without considerable GHG emissions.

Optimized photodegradation of palm oil agroindustry waste effluent using multivalent manganese-modified black titanium dioxide.

This article presents a methodological approach to use manganese (Mn3+Mn7+)-modified black titanium dioxide (Mn/BTiO2) as a photocatalyst to optimize and improve visible-light-driven photodegradation of treated agro-industrial effluent (TPOME). A modified wet chemical process was used to prepare BTiO2. The BTiO2 was then wet impregnated with Mn and calcined at 300 °C for 1 h to produce Mn/BTiO2. The activity of Mn/BTiO2 was investigated in terms of photo-assisted elimination of chemical oxygen demand (COD), phenolic compounds (PCs), color, and total organic carbon (TOC). Using the design of experiments (DOE), the conditions of the photocatalytic process, including photocatalyst loading, Mn concentration, hydrogen peroxide (H2O2) dose, and irradiation time, were optimized. Under the optimum conditions (0.85 g/L photocatalyst loading, 0.048 mol/L H2O2 dose, 0.301 wt.% Mn concentration, and 204 min irradiation time) COD, PCs, color, and TOC removal efficiencies of 88.87%, 86.04%, 62.8%, and 84.66%, respectively, were obtained. Statistical analysis showed that the response variable's removal from TPOME estimation had high R2and low RMSE, MSE, MAD, MAE, and MAPE values, indicating high reliability. This study demonstrated the significant potential of the developed photocatalytic system for the treatment of waste effluent generated by the palm oil industry and other agro-industries, with the ability to simultaneously reduce a number of organic pollution indicators (OPIs).

Modified nanoarchitectonics of activated carbon derived from the Astragalus shrub for efficient photocatalytic degradation of methylene blue from water

ABSTRACT In this study, the photocatalytic degradation of methylene blue (MB) dye was explored by applying biochar/Ag nanocatalyst.Biochar (activated carbon) was produced from the Astragalus shrub by a slow pyrolysis procedure. Preparation of biochar/Ag nanoparticles was performed using the sol-gel technique, and the physical properties of the prepared nanocatalyst were studied using BET, FTIR, XRD, FESEM, and EDX analyses. According to the analyses, Ag was successfully placed on the biochar particles.Investigations on the Ag/activated carbon (AC) ratio, initial concentration dye, lamp power, pH, catalyst dosage, and amount of H2O2 were conducted to acquire the highest removal efficiency of MB. The maximum degradation rate of MB dye was attained under optimal conditions, including initial dye concentration of 5 mg/L, pH 9, 20 mL of H2O2, 60 mg of AC/Ag nanoparticle dosage, and 100 min under 80 W lamp power. The highest MB dye degradation in the mentioned circumstances was achieved at 96.09%.The kinetic survey likewise represented that the elimination of MB dye using AC/Ag nanocatalysts follows the first-order model, and the optimum time for the photocatalytic removal procedure of methylene blue through biochar/Ag nanocatalysts is 100 min. The stability of the AC/Ag nanoparticles during five rounds was favourable, and only 5.79% of MB dye degradation yield was diminished.

Treatment of net washing wastewater by Fenton process

<p>The discharge of wastewater from net washing is one of the most significant problems in the marine ecosystem because of its high organic and saline content. Sea water quality is deteriorated every day due to the high amount of organic matter produced in the aquaculture sector. The aim of this study was to investigate the treatability of net washing wastewater by Fenton process. The efficiency of advanced oxidation processes (AOPs) in the treatability of net washing wastewater was evaluated through chemical oxygen demand (COD) and color removal. The effects of H2O2, and Fe (II) dosages, pH and reaction time were investigated, and the parameters were optimized by 23 full factorial design principles and variance analysis (ANOVA). The results showed that H2O2 dosage was the most effective parameter for Fenton process. The maximum COD removal was found at Fe (II)/H2O2 concentration ratio of 1/5 and the 180 minutes reaction time. The COD removal increased from 77 % to 88 % by increasing the peroxide dose from 80 mM to 400 mM. The total R2 for the three factors was calculated to be 59.67%. According to the experimental results, in the factor analysis between the three variables and COD removal, only the variation in peroxide concentration was statistically significant. Since the efficiency of biological treatment is unstable in treating of high organic matter and saline wastewaters, the Fenton process has great potential in the treatment of net washing wastewater.</p>

Magnetic hydrochar from the extract and residue of herbal medicines for adsorption and Fenton reaction

Residues of herbs medicines are potential resources to prepare hydrochar. However, problems such as limited adsorption capacity and difficulty in recovery restrict the application of residues. Here, Ferrous sulfate heptahydrate (FeSO4·H2O) was used to load Fe3O4 to prepare Fe3O4-modified hydrochar (Fe-CBC). Herbal extract (silymarin) was used to prepare functionalized hydrochar (Sil-Fe-CBC) for the first time by using the residue of clematis. Sil-Fe-CBC was used to remove methylene blue (MB) and tetracycline (TC) from water. The MB adsorption quantity was increased to 124.7 mg/g within 30 min, and the removal was increased to 84.26%. The TC removal was achieved approximately 91% in 120 min at an optimum pH of 3, an H2O2 dosage of 0.4 mL, a Sil-Fe-CBC dosage of 0.6 g/L, and a temperature of 30 °C. The FTIR spectra and XRD spectrum studies confirm that the form of ·OH is linked to Fe2+ in the catalysis process via the reduction of silymarin. Silymarin functionalization is a new approach to promote the efficiency of Fenton. Herbal medicine residues are potential raw materials in hydrochar preparation, and the extracts can improve hydrochars' performance.

Kinetics of three commercial textile dyes decomposition by UV/H2O2 and UV/acetone processes: An experimental comparative study and DFT calculations

Acetone photolysis was investigated and compared with the UV/H2O2 process for the removal of three commercial textile dyes, Reactive Red 184 (RR184), Reactive Orange 4 (RO4), and Direct Red 80 (DR80), in aqueous solution at 254 nm, pH = 6.5–6.8, and T = 20 ± 2 °C. The removal efficiency of RR184, RO4, and DR80 by UV/H2O2 was 35 %, 59 %, and 69 %, respectively, whereas UV/acetone exhibited a removal efficiency of 81 %, 99 %, and 88 %, within 30 min ([Dye]0 = 0.1 mM and [acetone]0 = [H2O2]0 = 50 mM). However, as the initial doses of H2O2 and acetone were increased, the decolorization increased, and the experimental kinetic data always agreed with the pseudo-first-order reaction model (R2 = 0.94–0.99). Additionally, UV/acetone was consistently shown to be significantly more efficient than UV/H2O2 under all conditions tested. For instance, the rate constant ratios kUV/acetone/kUV/H2O2 are 3.19, 1.95, and 1.67 for RR184, RO4, and DR80, respectively ([Dye]0 = 0.1 mM and [acetone]0 = [H2O2]0 = 50 mM). Scavenging tests using specific probes revealed that •OH and •CH3 radicals were the main responsible for dyes degradation (greater than80 %) in the UV/H2O2 and UV/acetone processes, respectively. In both systems, the dyes' reactivity order was found to be RO4 > DR80 > RR184, indicating that chemical structure is an important factor in evaluating the efficiency of the degradation process. This reactivity order was supported by the density functional theory (DFT)-based thermodynamic calculations used to explain the HO•-initiated degradation of the studied azo dyes in the UV/H2O2 process.

A comparative study of hydrogen peroxide oxidation and electrocoagulation using aluminum, iron, and zinc electrodes for urban sludge disintegration

ABSTRACT Municipal and industrial wastewater treatment plants produce large amounts of sludge containing high levels of organic, chemical, and microbial pollutants. Unless stabilized completely and discharged safely, they may become potential pollution sources threatening soil and water bodies. This study investigated H2O2 oxidation and electrocoagulation as pretreatments to improve stabilization of an urban sludge. The H2O2 oxidation was optimized with respect to H2O2 dosage and initial sludge pH-H2O2. Batch electrocoagulation experiments were conducted using aluminum, iron, and zinc electrodes to investigate the effect of treatment period, current density, and pH. The effectiveness was compared in terms of solubilization of sludge, disintegration degree, and reduction of total solids. Sludge settling velocity after disintegration by both H2O2 oxidation and electrocoagulation were measured with respect to the operating conditions. The obtained results indicated that the high rate of sludge disintegration (63.3%) was obtained with aluminum electrodes, which has lower operating costs than iron and zinc electrodes. The H2O2 oxidation reached a maximum disintegration degree of 50%. Additionally, with aluminum and iron electrodes, sludge settleability was enhanced with both H2O2 oxidation and electrocoagulation.

Process optimization of BTEX degradation from petrochemical effluent using integrated advanced oxidation

In this study, an integral treatment consisted of UV/Fenton/ TiO2 system in the batch systems was developed to perform degradation of synthetic Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX). Initially, the efficiency of photo Fenton catalytic degradation was compared with conventional treatment methods. Later, optimum levels of selected variables such as the initial concentration of BTEX, pH, temperature, reaction time, and initial dosage of TiO2 were analyzed using one factor at a time method. Further, screening of variables and optimization were performed using Planckett-Burman design and central composite design, respectively. Photo Fenton catalytic process showed about 1.15 fold increase in efficiency when compared with photo Fenton process. Among the selected seven variables, four variables namely, initial pH, BTEX concentration, H2O2 dosage and TiO2 dosage were identified as significant factors. Under the optimal conditions, chemical oxygen demand reduction reached about 84.54 ± 2.57% using UV/Fenton/ TiO2 system. Finally, first-order kinetic model resulted in prediction of 19.43 kJ/mol of activation energy. Thus, process optimization and kinetic study using the developed photo Fenton catalytic system could be beneficial for real time waste containing BTEX pollutants.

Highly efficient decomplexation of chelated nickel and copper effluent through CuO–CeO2–Co3O4 nanocatalyst loaded on ceramic membrane

A novel CuO–CeO2–Co3O4 nanocatalyst loaded on Al2O3 ceramic composite membrane (CCM-S) was synthesized through spraying-calcination method, which can be beneficial to the engineering application of scattered granular catalyst. BET and FESEM-EDX testing revealed that CCM-S possessed a porous character with high BET surface area of 22.4 m2/g and flat modified surface with extremely fine particle aggregation. The CCM-S calcined above 500 °C presented excellent anti-dissolution effect due to the formation of crystals. XPS indicated that the composite nanocatalyst possessed the variable valence states, which were conducive to exert the catalytic effect of Fenton-like reaction. Subsequently, the effects of experimental parameters including fabricate method, calcination temperature, H2O2 dosage, initial pH value, and CCM-S amount were further investigated considering the removal efficiency of Ni(II)-complex and COD after decomplexation and precipitation (pH = 10.5) treatment within 90 min. Under the optimal reaction condition, the residual Ni(II)-complex and Cu(II)-complex concentration from actual wastewater was all lower than 0.18 mg/L and 0.27 mg/L, respectively; meanwhile, the removal efficiency of COD was all higher than 50% in the mixed electroless plating effluent. Besides, the CCM-S could still maintain high catalytic activity after a six-cycle test, and the removal efficiency was slightly declined from 99.82% to 88.11%. These outcomes indicated that CCM-S/H2O2 system was provided with a potential applicability on treatment of real chelated metal wastewater.

Degradation of iohexol in the Co(II)/peracetic acid system under neutral conditions: Influencing factors, degradation pathways and toxicity

Advanced oxidation processes based on peracetic acid (PAA) activation have received more attention in water treatment recently. In this study, the degradation of iohexol (IOH, a classical iodinated X-ray contrast media) in the Co(II)/PAA system under neutral conditions, which mainly produced carbon-centric radicals, was investigated. Results showed that IOH decomposition follows the pseudo-first-order kinetic with a rate constant of 0.283 min−1. Appropriately increasing concentrations of PAA or Co(II) could promote the removal of IOH, while elevating the dosage of H2O2 inhibits the elimination of IOH in the Co(II)/PAA system. The IOH elimination was affected by pH, with the best response in pH between 5 and 7 in the Co(II)/PAA system. Additionally, low Cl− doses have negligible effects whereas high Cl− impeded the breakdown of IOH. Br−, I−, HCO3−, H2PO4− and humic acid suppressed the degradation of IOH. Removal of IOH was significantly inhibited in three selected real water samples. Furthermore, six IOH degradation pathways, including H-abstraction, amide hydrolysis, amino oxidation, deiodination reaction, hydroxylate and elimination reaction, were proposed on the basis of the liquid chromatography-tandem mass spectrometry, ion chromatography and DFT theoretical calculations (Frontier electron densities and fukui functions) results. Finally, the ECOSAR assessment showed that some degradation byproducts were much more toxic than IOH parent, but were much more biodegradable. Overall, this study indicates a potential risk when applying the carbon-centric radicals involved in PAA-based AOPs to remediate halogenated organic pollutants in water.

Potential of the Biomass Waste Originating from Saccharum officinarum as a Fenton Precursor for the Efficient Oxidation of Azo Dye from an Aqueous Stream

In the current investigation, elements extracted from Saccharum officinarum were identified as exporters of Fenton catalysts. Saccharum officinarum was soaked in an alkali prior to acidic treatment and then subjected to pyrolysis for elemental recovery. X-ray diffraction (XRD) and scanning electron microscopy (SEM) augmented with energy-dispersive X-ray spectroscopy (EDX) were used to identify the prepared catalyst. The material was combined with hydrogen peroxide, which led to Fenton’s reaction. Then, the modified Fenton system was applied to eliminate the textile dye, named Bismarck Brown Azo dye, contaminating the aqueous effluent. Response surface methodological model (RSM) analysis was used to identify the most effective operational parameters, and the model set the optimized values as 39 and 401 mg/L for Saccharum officinarum and H2O2 doses, respectively, at pH 2.9. The maximum Bismarck Brown Azo dye removal achieved was 85%. Increasing the temperature to 60 °C improved the dye oxidation efficiency. However, the dye treatment efficacy was reduced when the dye loading increased. Additionally, the kinetic rate order was investigated and the system was fitted to second-order rate reaction kinetics. The thermodynamic variables show that the reaction is endothermic and non-spontaneous.

Experimental and modelling approach to the design of chemical absorption columns with fast gas-liquid reaction: A case-study on flue-gas desulfurization with H2O2 oxidative solutions

In this work, we propose a methodology to approach the design of chemical absorption columns with fast gas-liquid reactions by an experimental and modelling study, which accounts for thermodynamic (solubility) data, mass-transfer phenomena, and the reaction kinetics contribution. As a reference case, the SO2 absorption in aqueous solution of H2O2 at different concentrations, which oxidizes SO2 to sulfuric acid, is considered. A lab-scale fed-batch bubble column is used to evaluate SO2 solubility dataset in absorbing solutions of distilled water containing different dosages of H2O2. A thermodynamic model is developed and validated in a Thermodynamic Flash block of ASPEN PLUS®, allowing to describe the experimental results with optimum agreement. For kinetic experiments, a lab-scale falling-film absorber is used to investigate both SO2 mass-transfer rates and the fundamental kinetic aspects of an absorption process with chemical reaction. The physical contribution to the mass-transfer rate is evaluated through a set of dedicated experiments, which allowed determining gas-side (kGa) and liquid-side (kLa) coefficients in the falling-film absorber. Subsequently, the Enhancement factor (EL) of the SO2 oxidative absorption is evaluated for the oxidizing reaction (SO2 + H2O2 → H2SO4) under the explored experimental conditions, using the equilibrium dataset and the mass transfer coefficients previously obtained. Finally, EL is correlated to the Hatta number (Ha) with the Danckwerts kinetic model as a pseudo-mth-nth-order non-reversible reaction type and the model kinetic parameters are calculated.

Synthesis, characterization and heterogeneous photo-Fenton-like catalyst activity of a novel inorganic-organic 2D framework based on reduced α-Keggin phosphomolybdate

A novel inorganic-organic 2D framework [CuI2CuII2(L)4(PMoV3MoVI9O40)(H2O)] (CuLPMo12) [L = 4-(4H-1,2,4-triazol-4-yl)pyridine)] based on reduced α-Keggin phosphomolybdate was hydrothermally synthesized and fully characterized. CuLPMo12 was found to be an efficient heterogeneous photo-Fenton-like catalyst for the degradation of dyes including methyl orange (MO), methylene blue (MB) and rhodamine B (RhB). The Fenton-like catalyst activity study of CuLPMo12 was carried out by employing RhB as model dye, because it had the best catalytic effect on RhB degradation. The degradation of RhB was affected by initial pH value and concentration of RhB solution, concentration of H2O2 and CuLPMo12 dosage. The optimum conditions for RhB degradation in the photo-Fenton-like progress were determined, the color of RhB could be completely removed in 5 min and the total organic carbon (TOC) removal was up to about 81.8% in 3 h under these conditions. These data were superior to that of similar compounds reported by other groups. Moreover, this system could work in a wide pH range and the optimum pH value was 7. Working at neutral pH made it be more convenient to operate than the acidic traditional Fenton system. UV–Vis spectroscopy results confirm that the N-deethylation and the conjugated chromophore cleavage reactions occurred simultaneously in a stepwise manner during RhB degradation process. Mechanism research indicates that the active species, such as 1O2,•OH, and •O2H/O2•− were responsible for RhB degradation. The better stability and recyclability of CuLPMo12 suggest that the present photo-Fenton-like system has potential in practical wastewater treatment.

Novel Gemini ionic liquid for oxidative desulfurization of gas oil

The N1,N1,N3,N3-tetramethyl –N1,N3-diphenylpropane-1,3-diaminium dichloride ionic liquid (ILc) is an environmentally friendly catalyst for oxidative–extractive desulfurization of gas oil (sulfur content = 2400 ppm) in the presence of H2O2 as an oxidizing agent. The precise structure of the prepared IL was confirmed using FT-IR spectroscopy, and1H-NMR. The reaction temperature, IL ratios, H2O2 dosage, and reaction time were studied to assess their effects on the desulfurization efficiency. The thermodynamic parameters of the oxidation reaction were determined. A desulfurization efficiency of 84.7% was obtained after the extractive desulfurization process using acetonitrile as an organic solvent at a solvent to feed ratio of 1:1 (v/v). Furthermore, the prepared IL may be reused for at least six cycles without any significant change in its desulfurization performance or chemical structure, which confirms its high reusability.

Ozone-activated peroxymonosulfate (O3/PMS) process for the removal of model naphthenic acids compounds: Kinetics, reactivity, and contribution of oxidative species

Due to their recalcitrance, naphthenic acids (NAs) are one of the constituents of interest in oil sands process water (OSPW). In this study, peroxymonosulfate (PMS) activated by ozone was employed to degrade NA model compounds in buffer solutions. At an ozone/PMS ratio of 2:1, a removal of 85 % was observed for a model diamondoid NA compound (1-adamantanecarboxylic acid; ACA) after 45 s of reaction. Compared with ozone alone, the degradation of ACA was accelerated in the presence of ozone/PMS, with an overall pseudo-first order rate constant (kobs) increasing from 8.02 × 10−4 s−1 during ozone treatment to 6.74 × 10−2 s−1 in the ozone/PMS system. Although ozone/hydrogen peroxide (H2O2) showed high degradation for ACA, the ozone/PMS system showed a higher kobs of 5.44 × 10−2 s−1at a PMS dose of 0.042 mM, while at the same dose of H2O2, kobs was equal to 3.62 × 10−2 s−1 for ozone/H2O2. This result showed the synergetic effect of ozone and PMS on the degradation of ACA. Relative kinetics studies using mixtures of model NA compounds showed better performance for ozone/PMS to degrade aromatic NAs compared to ozone/H2O2. Hydroxyl radicals and sulfate radicals were found to be responsible for the removal of ACA, with limited effect of molecular ozone. The proposed degradation pathways for ACA included hydroxylation, carboxylation, and polymerization under ozone/PMS, while hydroxylation and carboxylation were the main degradation pathways under ozone/H2O2. The results of this study emphasize the potential of ozone/PMS process to treat OSPW by accelerating the degradation of recalcitrant organic compounds.

Kinetic mechanism of selenium leaching from selenium-rich acid sludge in NaOH solution

ABSTRACT Recovery of selenium from selenium-containing materials by metallurgical techniques is important. In this paper, the selenium was leached from the selenium-rich acid sludge via a direct NaOH leaching method. In order to analyze the leaching rate of various experimental conditions, certain parameters such as dosage of H2O2, NaOH concentration, leaching temperature, reaction time and liquid–solid ratio were also investigated. Particularly, the leaching rate of Se reached 98.94% under the optimal leaching condition, such as the H2O2 dosage of 75 mL·L−1, the NaOH concentration of 6.25 mol·L−1, the leaching temperature of 363 K, the reaction time of 120 min, and the liquid–solid ratio of 10. The unreacted nuclear dynamical model and homogeneous reaction kinetic model were then respectively utilised to describe the leaching kinetics of the Se leaching process. The results indicated that the homogeneous reaction kinetic model was more suitable than the unreacted nuclear dynamical model. Based on an analysis of leach kinetics, the leach was shown to proceed via homogeneous reaction. This work is of great practical value in terms of recovery of selenium from selenium-rich acid sludge with efficient and low cost methods.