Toxic heavy metal removal from sulfide ores using potassium permanganate: Process development and waste management

A monolithic new attitude utilizing Aspen Plus software and Taguchi method has been applied to evaluate a novel configuration for removal of toxic heavy metals during sulfide ores recovery using potassium permanganate (KMnO₄). In this new configuration, KMnO₄ has been produced by sludge recovery of cobalt purification step containing manganese (IV) oxide (MnO₂). Also, in this suggested configuration, the required sulfuric acid (H₂SO₄) solvent has been provided by recovery of sulfur compounds released during leaching process of sulfide ores. The optimum condition obtained by Taguchi experimental design has been used as initial data for the simulation and sensitivity analysis of process via Aspen Plus software. A systematic study of the design and operating condition has been made for key performance metrics such as removal of toxic heavy metal from sulfide ores, recovery of KMnO₄ from sludge containing MnO₂ and conversion of released sulfide gases to H₂SO₄ at the different operating condition such as H₂SO₄ concentration of 60-90 g/L, operating temperature of 60-150 °C, agitation rate of 100-400 rpm, reaction time of 0.5-2 h, solid to liquid ratio of 1:1-1:4, particle size of 10-500 μm, additive amount of 10-40 wt% and oxygen pressure of 0.5-2 MPa. The optimum condition for removal of toxic heavy metal have been found to be H₂SO₄ concentration of 70 g/L, temperature of 90 °C, agitation rate of 200 rpm, reaction time of 1.5 h, particle size of 500 μm, solid to liquid ratio of 1:2, additive amount of 40 wt% and oxygen pressure of 1.5 MPa. According to simulation results, the maximum conversion of released sulfide gases to H₂SO₄, recovery of KMnO₄ and toxic heavy metals removal during designed process at optimized condition are 98%, 91% and 99%, respectively.

Phase-transfer catalysis enhanced remediation of trichloroethylene polluted groundwater by potassium permanganate

As one of the remediation reagents, potassium permanganate (KMnO₄) is injected to the aquifer, degrading trichloroethylene (TCE) by chemical oxidation. This study investigated the kinetics of TCE degradation by series of batch experiments, as well as the influence of medium size. Moreover, phase-transfer catalyst (PTCs), such as pentyltriphenylphosphonium bromide (PTPP) and sodium hexametaphosphate (SHMP) were used for enhancing oxidation. The batch experimental results showed that in the absence of PTC, the removal efficiency of TCE was 36.14% and 86.79% within 4 and 30 min, respectively. However, the removal rate of TCE was up to 67.48% and 49.90% within 4 min for 15 mol% PTPP- and SHMP-added system, respectively. The results indicated that PTPP and SHMP promoted the depletion of M n O 4 - to oxidize DNAPL TCE, but its effectiveness varied with the addition ratio of PTPP or SHMP. Its promotion was more remarkable when PTC added with a higher proportion. The alleviation of MnO₂ by phosphates ( P O 4 3 - , H P O 4 2 - and H 2 P O 4 - ) or PTC in the presence of media was qualitatively investigated. Results showed that the content of MnO₂ in the dissolved phase during the same reaction period decreased by PTC. Moreover, H P O 4 2 - and SHMP have apparent beneficial effects of reducing MnO₂ formation. The presence of aquifer media has a pH buffer and a negative influence on the reaction between TCE and the oxidant; moreover, as particle size of media decreased, the negative effect increased.

MnO2 Heterostructure on Carbon Nanotubes as Cathode Material for Aqueous Zinc-Ion Batteries

Due to their cost effectiveness, high safety, and eco-friendliness, zinc-ion batteries (ZIBs) are receiving much attention nowadays. In the production of rechargeable ZIBs, the cathode plays an important role. Manganese oxide (MnO2) is considered the most promising and widely investigated intercalation cathode material. Nonetheless, MnO2 cathodes are subjected to challenging issues viz. limited capacity, low rate capability and poor cycling stability. It is seen that the MnO2 heterostructure can enable long-term cycling stability in different types of energy devices. Herein, a versatile chemical method for the preparation of MnO2 heterostructure on multi-walled carbon nanotubes (MNH-CNT) is reported. Besides, the synthesized MNH-CNT is composed of δ-MnO2 and γ-MnO2. A ZIB using the MNH-CNT cathode delivers a high initial discharge capacity of 236 mAh g-1 at 400 mA g-1, 108 mAh g-1 at 1600 mA g-1 and excellent cycling stability. A pseudocapacitive behavior investigation demonstrates fast zinc ion diffusion via a diffusion-controlled process with low capacitive contribution. Overall, the MNH-CNT cathode is seen to exhibit superior electrochemical performance. This work presents new opportunities for improving the discharge capacity and cycling stability of aqueous ZIBs.

Influences of the micropollutant erythromycin on cyanobacteria treatment with potassium permanganate

Cyanobacteria blooms and micropollutants (e.g., antibiotics) in source waters are two increasing environmental issues worldwide. This study hypothesized that the coexisting antibiotics may possibly alter the efficiency of water treatment processes through affecting the physiological and biochemical characteristics of cyanobacterial cells. A toxic strain of Microcystis aeruginosa was exposed to the common antibiotic erythromycin (ERY) at environmentally relevant concentrations; then, samples were collected on days 1, 4 and 6 to assess the efficiency of potassium permanganate (KMnO₄) in cyanobacteria oxidation. The percentage of intact cells remained constant after treatment with 2 mg L^-1 KMnO₄ in M. aeruginosa samples dosed with 0-5.0 μg L^-1 ERY. Although 6 mg L^-1 KMnO₄ could damage cyanobacterial cells, its ability was considerably reduced as the concentrations of ERY increased. KMnO₄ oxidation degraded the intracellular microcystins (MCs) in all of the cyanobacterial samples, even the samples with intact cells, possibly resulting from the stimulation of intracellular reactive oxygen species (ROS). The highest amounts of total MCs remained after oxidation with 2 and 6 mg L^-1 KMnO₄ in 0.2 μg L^-1 ERY-treated cyanobacterial samples, which may be due to large amounts of MC production. The 5.0 μg L^-1 ERY inhibited the growth of cyanobacterial cells and downregulated the expression of the MC synthesis gene (mcyB), which resulted in the lowest amounts of total MCs. However, it led to the highest concentration (4.6 μg L^-1) of extracellular MCs after treatment with 2 mg L^-1 KMnO₄ for 300 min. Generally, this study indicates that the effectiveness of KMnO₄ oxidation in cyanobacteria treatment decreased when the concentration of ERY increased. Hence, the possible risks caused by the coexistence of cyanobacteria and antibiotics, such as reduced efficiency of water treatment processes in cyanobacteria inactivation and degradation of the dissolved MCs, need to be taken into account.

Mechanisms that influence the interactions between remediation agent injection and contamination plume variation

To study the interactions between remediation agent injection and hydrodynamic dispersion as well as the expansion of a contamination plume, a two-dimensional sandbox experiment was conducted to simulate and monitor the mixing of a remediation agent in the contamination plume and the expansion of the contamination plume over time. Potassium permanganate is a purple solution, and it represents the remediation agent; Perchloroethylene (PCE), is dyed green and was used to observe the migration and diffusion of the contaminant and the overlap of contamination and the agent-plume. Six quantitative characterization parameters: migration distance, (d_M), migration area, (A_M), initial area ratio, (K_i), spreading speed difference, (SSD), area ratio, (K_A) and migration distance ratio, (K_d), are proposed to comprehensively analyse the influence of the three factors of injection pressure, particle size and viscosity change on the mixing of a remediation agent and the expansion of the contamination plume over time. The results show that these six parameters can effectively characterize the mixing of the remediation agent and the expansion of the contamination plume, where d_M, A_M and K_i characterize the expansion and the other three parameters characterize the mixing. The factors increasing the expansion of the contamination plume follow the order: 40 cm > 30 cm > 20 cm, for injection pressure (water head); coarse sand > medium sand > fine sand for particle size; and no polymer added > added polymer 200 mg/L > added polymer 800 mg/L > added polymer 400 mg/L for viscosity adjustment. The factors that intensify the mixing of the remediation agent in the contamination plume follow the order: 20 cm > 30 cm > 40 cm (water head); coarse sand > medium sand > fine sand; and added polymer 400 mg/L > added polymer 200 mg/L > no polymer added> added polymer 800 mg/L. Finally, conclusions from the TOPSIS method show that under optimal injection conditions, mixing is enhanced without increasing plume expansion and that the optimum injection conditions are injection pressure = 20 cm, use of a coarse sand medium, and added polymer concentration = 400 mg/L.

Characteristics and mechanisms of controlled-release KMnO4 for groundwater remediation: Experimental and modeling investigations

Controlled release materials (CRMs) are emerging oxidant delivery techniques for in-situ chemical oxidation (ISCO) for groundwater remediation. Successful implementation of CRM relies on good understandings of the kinetics and mechanism of controlled release of reactive agents. In this study, batch experiments and model simulations were conducted to explore the impacts of CRM properties (composition and size) and environmental conditions (temperature, pH, water volume and anions) on KMnO₄ release from KMnO₄ -paraffin controlled release beads. Experimental results indicated that higher KMnO₄: paraffin mass ratio resulted in shorter release longevities and higher release rate. Larger bead resulted in lower release rate, longer release longevity, and more KMnO₄ released. Higher incubation temperature resulted in higher release rate and shorter release longevity, but did not affect the total mass of KMnO₄ released. Acidic pH decreased the total mass of KMnO₄ released while alkaline pH did not affect KMnO₄ release. The presence of SO₄^2-, CO₃^2-, Cl^- and Br^- had negligible impacts on KMnO₄ release. A dissolution-diffusion conceptual model was developed. The above experimental observation and the associated controlled release mechanisms can be qualitatively explained by the conceptual model. A more detailed two-film boundary mathematical model was developed to simulate KMnO₄ release process. Comparison of modeling results with experimental data suggest that the new mathematical model gave a good quantitatively predication. Overall, this study shows that properly designed CRM can sustain release for years, thus representing a cost-effective and low-maintenance groundwater remediation technology. Both CRM properties and environmental conditions significantly affect the release kinetics and longevity, therefore these factors should be considered in the design and maintenance of CRM-based ISCO system.

Impacts of antibiotic contaminants on Microcystis aeruginosa during potassium permanganate treatment

Application of KMnO₄ for preventing the formation of cyanobacterial bloom at early growth stage has not been reported. Antibiotics generate hormesis effects in cyanobacteria at currently reported concentrations, which may negatively affect the control of cyanobacterial bloom. This study assessed the treatment performance of KMnO₄ in Microcystis aeruginosa with and without the existence of the antibiotic mixture composed of four simultaneously detected antibiotics in aquatic environments (sulfamethoxazole, ciprofloxacin, amoxicillin and tetracycline). KMnO₄ downregulated two chlorophyll a synthetases (chlG and chlM), 14 photosynthesis-related proteins and two microcystin synthetases (mcyB and mcyD) in M. aeruginosa, and reduced chlorophyll a content, photosynthetic activity and microcystin concentration in a dose-dependent manner. Inhibition of photosynthesis and biosynthesis resulted in extended lag phase and decreased growth rate in KMnO₄-treated Microcystis aeruginosa. In contrast, mixed antibiotics upregulated 6 oxidation-reduction proteins, a cell division regulatory protein (MAE_37210), 14 photosynthesis-related proteins, 14 biosynthesis-related proteins (including microcystin synthetases mcyA and mcyB) and a microcystin transport protein (mcyH), which consequently reduced oxidative stress, shortened lag phase as well as significantly stimulated (p < 0.05) cyanobacterial growth, photosynthetic activity, microcystin synthesis and microcystin release in KMnO₄-treated M. aeruginosa. An optimal dose of 3 mg L^-1 was suggested for KMnO₄ treatment. Mixed antibiotics should be controlled below a no-impact threshold of 20 ng L^-1 (5 ng L^-1 for each antibiotic) for eliminating their adverse effects during KMnO₄ treatment of cyanobacteria in antibiotics polluted environments.

Enhancement of biological oxygen demand detection with a microbial fuel cell using potassium permanganate as cathodic electron acceptor

When dual-chamber microbial fuel cell (MFC) is used to detect biochemical oxygen demand (BOD), dissolved oxygen is traditionally used as cathodic electron acceptor. The detection limit of this MFC-based BOD biosensor is usually lower than 200 mg/L. In this paper, the startup of MFC-based BOD biosensor was researched and the external resistor of MFC was optimized. Results showed that the MFC started up with the dissolved oxygen as cathodic electron acceptor within 10 d, and the external resistor was optimized as 500 Ω to ensure the maximum output power of MFC. Dissolved oxygen and potassium permanganate (KMnO₄) were used as cathodic electron acceptor to run MFC for detection of wastewater BOD, and the performances of two kinds of BOD biosensors were compared. The MFC-based BOD biosensor using KMnO₄ (10 mmol/L) as cathodic electron acceptor exhibited an excellent performance, compared with that using dissolved oxygen. The upper limit of BOD detection was greatly broadened to 500 mg/L, the response time was shortened by 50% for artificial wastewater with a BOD of 100 mg/L, and the relative error of BOD detection was reduced to less than 10%. The MFC-based BOD biosensor using KMnO₄ as cathodic electron acceptor showed a better linear relationship (R² > 0.992) between the electric charge and BOD concentration within a BOD range of 25-500 mg/L. The MFC-based BOD biosensor using the KMnO₄ as cathodic electron acceptor is promising with a better application prospect.

Impact of copper sulphate, potassium permanganate, and hydrogen peroxide on Pseudanabaena galeata cell integrity, release and degradation of 2-methylisoborneol

Frequent off-flavor events caused by geosmin and 2-methylisoborneol have caused concern among consumers about the quality of potable water. Pseudanabaena galeata, a filamentous cyanobacterium, is a known producer of 2-methylisoborneol in lakes and reservoirs. The use of algicides to control cyanobacteria must consider the potential release of contaminants into the water. This is the first study to systematically investigate the effectiveness of copper sulphate (CuSO₄), potassium permanganate (KMnO₄), and hydrogen peroxide (H₂O₂) on the cell viability and integrity of Pseudanabaena galeata. Following algicide or oxidant treatment, the release and degradation of 2-methylisoborneol was also examined. It is evident that all of these chemicals can decrease Pseudanabaena galeata viability and damage cell membranes and the filamentous Pseudanabaena galeata was more susceptible to treatment by these three algicides than unicellular colonial Microcystis aeruginosa. Of the three compounds used, KMnO₄ showed the stronger ability to compromise cell integrity and 5.0 mg/L KMnO₄ could induce 91 ± 1.5% lysis of Pseudanabaena galeata within 2 h. It was found that H₂O₂ had the potential to degrade 2-methylisoborneol with 16.0 ± 0.4% degraded by 20.0 mg/L H₂O₂ within 8 h. In contrast, 2-methylisoborneol could not be degraded by CuSO₄ (dosage: ≤ 1.5 mg/L; reaction time: ≤ 8 h) and KMnO₄ (dosage: ≤ 5.0 mg/L; reaction time: ≤ 3 h) basically. Results showed that the oxidation capacity of H₂O₂ against Pseudanabaena galeata was enhanced under sunlight. The results will help drinking water utilities to better understand the risk of Pseudanabaena galeata lysis and 2-methylisoborneol release during raw water treatment.

Removal of cyanotoxins by potassium permanganate: Incorporating competition from natural water constituents

In recent years, harmful algal blooms capable of producing toxins including microcystins, cylindrospermopsin, and saxitoxin have increased in occurrence and severity. These toxins can enter drinking water treatment plants and, if not effectively removed, pose a serious threat to human health. The work here investigated the efficacy of permanganate oxidation as a treatment strategy, with a focus on incorporating competition by cyanobacterial cells and dissolved organic matter (DOM). We report rate constants of 272 ± 23 M^-1 s^-1 for the reaction between permanganate and microcystin-LR, 0.26 ± 0.05 M^-1 s^-1 for the reaction between permanganate and cylindrospermopsin, and, using chemical analogs, estimate a maximum rate constant of 2.7 ± 0.2 M^-1 s^-1 for the reaction between permanganate and saxitoxin. We conclude that permanganate only shows potential to remove microcystins. No pH (6-10) or alkalinity (0-50 mM) dependence was observed for the rate of reaction between microcystin-LR and permanganate; however, a temperature dependence was observed and can be characterized by an activation energy of 16 ± 5 kJ mol^-1. The competition posed by cyanobacterial cells was quantified by an apparent second order rate constant of 2.5 ± 0.3 × 10^-6 L μg chl-a^-1 s^-1. From this apparent second order rate constant, it was concluded that cyanobacterial cells are not efficient scavengers of permanganate within typical contact times but this second order rate constant can be used to accurately predict microcystin degradation in algal-impacted waters. The competition posed by DOM depended on both the amount of DOM present (as measured by TOC) and its electron donating capacity (as predicted by SUVA-254 or E2/E3 ratio). DOM was concluded to scavenge permanganate efficiently and we forward that this should be considered in permanganate dosing calculations.

Kinetics and mechanism of Pseudoanabaena cell inactivation, 2-MIB release and degradation under exposure of ozone, chlorine and permanganate

The organic pollutants produced by cyanobacteria cells, such as off-flavor compounds (e.g. 2-methylisoborneol, 2-MIB) and hazardous toxins (e.g. microcystins), are commonly detected in water sources. Although studies have shown that oxidation using potassium permanganate (KMnO₄), chlorine and ozone helps to remove cyanobacteria cells, the potential effects of these oxidants on cell viability and the release of off-flavor substances have scarcely been explored. This study investigated the impacts of three widely used oxidants on Pseudanabaena sp. (a common species of 2-MIB producing cyanobacteria) inactivation, and on the release and degradation of intracellular 2-MIB. Experiments using KMnO₄ showed that both the cell viability and 2-MIB release fit to a two-stage second-order kinetic model with a threshold of KMnO₄ exposure (ct). No significant variations in the cell viability and 2-MIB release occurred until the exposure reached ct because KMnO₄ was primarily consumed by the dissolved and cell-bound organic matters before it damaged the cell. However, chlorine permeates the cell membrane more easily, causing rapid algae inactivation and the subsequent cell lysis and 2-MIB release. Unlike permanganate and chlorine, which are unable to degrade the released 2-MIB because of their insufficient oxidation potentials, ozone is capable to inactivate the cell and degrade 2-MIB as well. When the initial O₃ concentration is above a certain level (1.0 mg ·L^-1 in this study), the released 2-MIB can be substantially oxidized. Therefore, the choice of a suitable oxidant and a proper dose is highly important in the control of off-flavor compounds during the treatment of algae-containing raw water.

Rapid oxidation of iodide and hypoiodous acid with ferrate and no formation of iodoform and monoiodoacetic acid in the ferrate/I-/HA system

Toxic and odorous iodinated disinfection byproducts (I-DBPs) could form in the chemical oxidation of iodine-containing water. A critical step for controlling the hazardous I-DBPs is to convert the iodine species into stable and harmless iodate (IO₃^-) while inhibiting the accumulation of highly reactive hypoiodous acid (HOI). Herein, the oxidation of I^- and HOI with ferrate was investigated, and the formation profile of HOI was determined based on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) coloring method through a stopped-flow spectrophotometer. The second-order rate constants (k_app) of ferrate with HOI decreased from 1.6 × 10⁵ M^-1s^-1 to 8.3 × 10² M^-1s^-1 as the solution pH varied from 5.3 to 10.3, which were 7.5, 7.2 and 13.8 times higher than that of ferrate with I^- at pH 6.0, 7.0 and 8.0, respectively. Compared with other oxidants such as ozone, hypochlorous acid, chloramine and potassium permanganate, ferrate would swiftly oxidize HOI formed in the I^- oxidation process. For the ferrate oxidation of I-containing water, HOI was swiftly oxidized to IO₃^- from pH 5.0 to 9.0. Phosphate buffer promoted the oxidation of I^- while inhibited the oxidation of HOI with ferrate. When 5 mgC/L of humic acids (HA) existed in the solution, no formation of iodoform and monoiodoacetic acid (MIAA) was observed in the oxidation of iodide (20 μM) with ferrate (from 10 μM to 80 μM). These results suggested that ferrate oxidation could be an effective method for the control of I-DBPs in iodine-containing water treatment.

Intricate Estimation and Assessment of Surface Conditioning of Posts to improve Interfacial Adhesion in Post-core Restorations: An in vitro Study

INTRODUCTION

Post and core restorations are routinely used for restoring grossly decayed tooth structures. Various chemical agents are known to affect the interfacial adhesions between the post and the core. Hence, we planned the present study to evaluate the effect of various post-surface treatments on the interfacial strength between the posts and composite materials that are used for building up the core portion.

MATERIALS AND METHODS

The present study included assessment of the effect of surface conditioning of posts on the interfacial adhesion in post-core restorations. A total of 80 clear post-tapers were included and were divided broadly into four study groups based on the type of chemical testing protocols used. Various chemical treatments included alkaline potassium permanganate, hydrogen peroxide, and phosphoric acid. The fourth group was the control group. The composite core material was used for building up the core. Testing of the tensile load was done on a universal testing machine. All the results were analyzed by the Statistical Package for the Social Sciences (SPSS) software.

RESULTS

The highest bond strength was observed in the study group treated with alkaline potassium permanganate, while the lowest was observed in the control group followed by the hydrogen peroxide group. While comparing the mean bond strength in between various study groups, significant results were obtained.

CONCLUSION

Chemical treatment protocol significantly alters the mean bond strength of the post and core restoration.

CLINICAL SIGNIFICANCE

Potassium permanganate significantly increases the bond strength between the fiber post and core restoration.

Elimination of microcystin-LR and residual Mn species using permanganate and powdered activated carbon: Oxidation products and pathways

The oxidation of microcystin-LR (MC-LR) in deionized water (DI) and river water using potassium permanganate (KMnO₄) at a neutral pH and at 23 ± 2 °C was investigated. These two aqueous systems (i.e., DI and river water) gave comparable second-order rate constants (289.9 and 285.5 M^-1s^-1 (r² > 0.99), respectively), which confirmed the effectiveness of this oxidation process for the treatment of natural surface water. The presence of either humic or fulvic acid reduced the removal efficiency of MC-LR, with the latter exhibiting a greater inhibitory effect. Monitoring of MC-LR and residual Mn²⁺ levels with adding KMnO₄ (1 mg/L) and powdered activated carbon (PAC, 5-20 mg L^-1) before and during coagulation, respectively, revealed that 60 min of permanganate pre-oxidation followed by coagulant addition with PAC was the most effective approach for reducing both levels below limits stated by WHO guidelines. The MC-LR degradation products were the result of oxidation occurring at the diene and aromatic moieties of the Adda (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid) side-chain, in addition to amine bond hydrolysis of the Mdha (N-methyldehydroalanine) moiety. Several toxic by-products with an intact Adda chain were observed during the reaction, but completely disappeared after 60 min. This further supports the conclusion that sufficient contact time with permanganate (i.e., >60 min) is essential to reducing the residual toxicity and maximizing the efficiency of MC-LR oxidation when treating raw water.

Analytical model for the design of in situ horizontal permeable reactive barriers (HPRBs) for the mitigation of chlorinated solvent vapors in the unsaturated zone

In this work we introduce a 1-D analytical solution that can be used for the design of horizontal permeable reactive barriers (HPRBs) as a vapor mitigation system at sites contaminated by chlorinated solvents. The developed model incorporates a transient diffusion-dominated transport with a second-order reaction rate constant. Furthermore, the model accounts for the HPRB lifetime as a function of the oxidant consumption by reaction with upward vapors and its progressive dissolution and leaching by infiltrating water. Simulation results by this new model closely replicate previous lab-scale tests carried out on trichloroethylene (TCE) using a HPRB containing a mixture of potassium permanganate, water and sand. In view of field applications, design criteria, in terms of the minimum HPRB thickness required to attenuate vapors at acceptable risk-based levels and the expected HPRB lifetime, are determined from site-specific conditions such as vapor source concentration, water infiltration rate and HPRB mixture. The results clearly show the field-scale feasibility of this alternative vapor mitigation system for the treatment of chlorinated solvents. Depending on the oxidation kinetic of the target contaminant, a 1m thick HPRB can ensure an attenuation of vapor concentrations of orders of magnitude up to 20years, even for vapor source concentrations up to 10g/m³. A demonstrative application for representative contaminated site conditions also shows the feasibility of this mitigation system from an economical point of view with capital costs potentially somewhat lower than those of other remediation options, such as soil vapor extraction systems. Overall, based on the experimental and theoretical evaluation thus far, field-scale tests are warranted to verify the potential and cost-effectiveness of HPRBs for vapor mitigation control under various conditions of application.

Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Multi-component reactive transport in heterogeneous media and its decoupling solution

The multi-component reactive transport model is widely used in contaminant transport, water-rock interaction, and other earth science fields. Since its complexity lies in its solution, a decoupling approach is used to simplify the model to enhance computational efficiency. A decoupling approach is presented for heterogeneous media, and used to solve the model in this situation. The whole domain is divided into several sub-domains due to the different reactions which may occur and the corresponding component matrix was obtained. The boundary between sub-domains could be divided into two parts, inflow and outflow, which are defined as the Neumann condition and the Dirichlet one, and the concentration of the latter could be calculated by the component in the adjacent sub-domain. Then the models in each sub-domain can be connected and solved. Taking a heterogeneous porous media as an example in which permanganate is partially dissolved during the process, firstly the result obtained by this method without considering porosity variation is compared to that from PHAST: good agreement is achieved, then while considering the change of porosity caused by the dissolution of the permanganate, the flow field, species concentration and porosity of the whole domain and typical sections and points during the reaction are analysed. It is concluded that: the decoupling approach to heterogeneous media is appropriate, and the results from the model could reflect the variation of physical fields due to groundwater in heterogeneous media.

The effects of various control and water treatment processes on the membrane integrity and toxin fate of cyanobacteria

Cyanobacterial blooms are one of the main contaminants that can degrade drinking water quality with the associated taste, odour and toxic compounds. Although a wide range of techniques have shown promise for cyanobacterial bloom control and cyanobacterial cell/metabolite removal in reservoirs and water treatment plants (WTPs), these treatments may have negative consequences through release of intracellular metabolites into the surrounding water. This study assessed the impact of copper sulphate (CuSO4), chlorine, potassium permanganate (KMnO4), hydrogen peroxide (H2O2) and ozone on Microcystis aeruginosa culture and the toxins it produced. All of these agents induced the loss of cyanobacterial membrane integrity. However, no associated increase in dissolved toxins was detected during chlorine and H2O2 treatments which may be due to faster toxin oxidation rates than release rates. KMnO4 doses of 1 and 3mgL(-1) degraded dissolved toxins while having no impact on cyanobacterial membrane integrity. In contrast, ozone induced a significant increase in extracellular toxins but it was unable to degrade these toxins to the same degree as the other oxidants which may due to the lack of residual. All chemicals, except CuSO4, were able to reduce cyanotoxins and chlorine was the most effective with a rate up to 2161M(-1)s(-1).

Arsenic and iron removal from groundwater by oxidation-coagulation at optimized pH: laboratory and field studies

A three-step treatment process involving (i) mild alkaline pH-conditioning by NaHCO₃; (ii) oxidation of arsenite and ferrous ions by KMnO₄, itself precipitating as insoluble MnO₂ under the pH condition; and (iii) coagulation by FeCl₃ has been used for simultaneous removal of arsenic and iron ions from water. The treated water is filtered after a residence time of 1-2 h. Laboratory batch experiments were performed to optimize the doses. A field trial was performed with an optimized recipe at 30 households and 5 schools at some highly arsenic affected villages in Assam, India. Simultaneous removals of arsenic from initial 0.1-0.5 mg/L to about 5 μg/L and iron from initial 0.3-5.0 mg/L to less than 0.1 mg/L have been achieved along with final pH between 7.0 and 7.5 after residence time of 1h. The process also removes other heavy elements, if present, without leaving any additional toxic residue. The small quantity of solid sludge containing mainly ferrihydrite with adsorbed arsenate passes the toxicity characteristic leaching procedure (TCLP) test. The estimated recurring cost is approximately USD 0.16 per/m(3) of purified water. A high efficiency, an extremely low cost, safety, non-requirement of power and simplicity of operation make the technique potential for rural application.

Catalasic activity in fish liver: improvement of the UV to visible analytic method

Antioxidative defenses and more especially catalasic activity (CAT) are studied in a large range of scientific research thematics. In environmental sciences, the problematic of oxidative stress is of great interest as pollutants can induce perturbations of redox homeostasis. Consequently, changes in antioxidative defenses levels in fish tissues and particularly in liver are used as potential biomarkers of pollution. In most studies, the CAT was assayed by following during 5 min the consumption of H2O2 in cytosolic buffered extracts at 240 nm (UV-method). This study proposed a development of this method in the visible, using permanganate and a 525-nm detection, which was more accurate, sensitive, and rapid. Moreover, the hepatic CAT of six different fish species [a cyclidae (Nimbochromis linni), 3 cyprinidae (Brachydanio rerio, Rutilus rutilus, Cyprinus carpio), an anguillidae (Anguilla anguilla), and a percidae (Perca fluviatilus)] was evaluated with the two protocols (UV- and KMnO4-method). The results but also the thermal optimum of the reaction and the interest of CAT as biomarker in ecotoxicology were discussed.

Fluorescent sensing of colloidal CePO4:Tb nanorods for rapid, ultrasensitive and selective detection of vitamin C

Vitamin C is an essential biological molecule for living organisms. The detection of vitamin C is always required due to its wide use in chemical, biological and pharmaceutical engineering. Here, we established a novel sensing system for rapid, ultrasensitive and highly selective detection of vitamin C based on a 'turn-on' fluorescent method. The turn-on fluorescent sensing system was built up of a colloidal CePO(4):Tb nanocrystalline solution with its fluorescence quenched by KMnO(4). The addition of vitamin C leads to a linear increase of fluorescence. The sensing principle of nanocrystalline CePO(4):Tb is based on a redox reaction via simply modulating the surface chemistry of nanocrystals. Our present sensing system for vitamin C exhibits a rapid response rate of less than 2 min, and highly selective and ultrasensitive detection with a detection limit of 108 nM, which is two orders of magnitude lower than that acquired by previously reported methods. The repeated reversibility of fluorescence quenching/recovery with time revealed a high reproducibility and long-term stability of our sensing materials. Furthermore, our developed sensing material overcomes the disadvantages such as complex surface modification/immobilization and serious biotoxicity compared to quantum-dot-based fluorescent sensing systems.

Examination of electron stains as a substitute for uranyl acetate for the ultrathin sections of bacterial cells

Electron staining reagents were examined to find a possible substitute for uranyl acetate (UA) in electron microscopy of bacterial ultrathin sections. Four kinds of stains, platinum blue (Pt-blue), oolong tea extract (OTE), potassium permanganate (KMnO(4)) and phosphotungstic acid (PTA), were examined in comparison with UA either with or without post-staining with lead citrate (Pb). Electron microscopy was performed on sections from Spurr-embedded cells of a Gram-positive bacterium, Bacillus cereus NBRC 13597, and a Gram-negative bacterium, Escherichia coli NBRC 3301. Both Pt-blue and OTE showed staining similar to each other and to that of double staining with UA and Pb in B. cereus, while in E. coli the cytoplasmic membrane appeared less dense when compared with UA and Pb. KMnO(4) stained excessively to some extent, but showed images of the best contrast in the cytoplasmic membrane comparable with UA and Pb among the four reagents. PTA could stain the peptidoglycan layer but gave images of low quality for both bacteria. This study demonstrated that none of the reagents examined showed staining results of the same quality or better than the conventional method with UA and Pb. However, stains of Pt-blue, OTE and KMnO(4) could possibly be an alternative candidate for the UA according to the structure in question.