Fe Leaching Research Articles

Degradation of anti-inflammatory drug diclofenac using cobalt ferrite as photocatalyst

Emerging pollutants, among them pharmaceutical compounds, are found in surface and ground waters, suggesting their ineffective removal by conventional wastewater treatment technologies. In this paper, the removal of sodium diclofenac, a widely used non-steroidal anti-inflammatory drug, was explored by a heterogeneous Photo-Fenton process using CoFe2O4, H2O2 and Uv germicide radiation (254nm). Cobalt ferrites, were obtained by Pechini method and calcined at 600°C and 800°C. They were characterized by X-ray diffraction, Uv visible spectroscopy, Mössbauer and X-ray photoelectron spectroscopy, temperature-programmed reduction and specific surface area. The inverse spinel structure was obtained, and both materials presented good performance in the photo-Fenton reaction. A degradation mechanism based on the generation of OH groups is suggested. The complete sodium diclofenac degradation and 86% of mineralization of the total organic carbon were obtained using cobalt ferrite calcined at 800°C. This catalyst was used in three cycles, without activity loss showing a negligible Fe leaching.

Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

Low temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

Al-Doped magnetite encapsulated in mesoporous carbon: a long-lasting Fenton catalyst for CWPO of phenol in a fixed-bed reactor under mild conditions

Al substituted magnetite was identified as a promising heterogeneous Fenton catalyst for CWPO of 200 ppm phenol in a continuous system under mild conditions (pH 5, 40 °C, 0.1 ml min−1, 1.2S H2O2) for 500 h with 80% TOC conversion, 1 ppm Fe leaching.

Synthesis of Fe0/Fe3O4@porous carbon through a facile heat treatment of iron-containing candle soots for peroxymonosulfate activation and efficient degradation of sulfamethoxazole

Developing highly efficient, reusable, non-toxic and low-cost catalysts is of great importance for persulfate-based advanced oxidation processes (AOPs). In this work, ferrocene was mixed into paraffin to prepare a candle, and the iron-containing candle soots were collected and heated at 500 °C~900 °C under N2 atmosphere for 1 h to prepare magnetically recyclable Fe0/Fe3O4@porous carbon (Fe0/Fe3O4@PC) catalysts. The Fe0/Fe3O4@PC-700 obtained after pyrolysis at 700 °C exhibited the best catalytic activity for sulfamethoxazole (SMX) degradation. 10 mg/L SMX could be completely degraded within 10 min by 0.2 g/L of Fe0/Fe3O4@PC-700 and 0.5 mM PMS at pH 5.0. The carbon shell effectively inhibited the Fe leaching of Fe0/Fe3O4@PC-700, and 99.73% of Fe was retained after five consecutive cycles. In the Fe0/Fe3O4@PC-700/PMS system, SMX was degraded through the sulfate radical (SO4·¯), hydroxyl radical (·OH), superoxide radical (O2·¯) dominated radical pathway, and the singlet oxygen (1O2) dominated non-radical pathway. The coexisting inorganic ions and natural organic matters (NOM) in actual water inhibited the degradation of SMX. Finally, four possible degradation pathways were proposed based on the degradation intermediates of SMX. This work provides a facile heat treatment of iron-containing candle soots strategy to prepare the metal@carbon catalysts for PMS-based AOP.

A High-Efficient Carbon-Coated Iron-Based Fenton-Like Catalyst with Enhanced Cycle Stability and Regenerative Performance

Carbon coated iron-based Fenton-like catalysts are now widely studied in wastewater treatment. However, their poor stability is still a big challenge and the related regenerative performance is seldom investigated. Herein, a carbon-coated Fe3O4 on carbon cloth (cc/Fe3O4@C) was prepared with glucose as carbon source via electrodeposition and ethanol solvothermal methods. An amorphous carbon layer with polar C-groups covers the surface of Fe3O4, which presents a flaky cross-linked network structure on the carbon cloth (cc). The cc/Fe3O4@C exhibits an improved catalytic activity with nearly 84% phenol was removed within 35 min with polar C-groups. What’s more, around 80% phenol can still be degraded in 120 min after 14 degradation cycles. After the regeneration treatment, the degradation performance was restored to the level of the fresh in the first two regenerations. The enhanced cycle stability and regeneration performance of the catalyst are as follows: Firstly, the catalyst’s composition and structure were recovered; Secondly, the reduction effect of the amorphous carbon layer ensuring timely supplement of Fe2+ from Fe3+. Also, the carbon layer reduces Fe leaching during the Fenton-like process.

Preparation and application of a novel biochar-supported red mud catalyst：Active sites and catalytic mechanism

A novel catalyst RM-BC(HP) was synthesized by hydrothermal treatment and pyrolysis (800 ℃) using red mud and coconut shells. Influence of different preparation conditions on catalyst performance was explored. SEM showed that RM-BC(HP) was porous and RM was successfully loaded on the outside surface and inside the pores of BC. XRD revealed that Fe2O3 in RM was reduced to Fe0 and Fe3O4 in the pyrolysis process, in which pyrolysis temperature and addition ratio of coconut shells were critical. TGA-MS, FT-IR and XPS were also applied to character the catalyst. 100% of AO7 was removed within 30 min with conditions of 2 mM PS, 50 mg/L AO7 and 0.5 g/L RM-BC(HP), and the Fe leaching was negligible. High removal rate was obtained in tap, river, and lake water. RM-BC(HP)/PS system also exhibited excellent degradation performance for other dyes (MB, MG and RhB) and antibiotics (TC, OTC and CTC). The mechanism studies demonstrated that PS was mainly activated by Fe0 and Fe2+ in RM-BC(HP) to produce different radicals, then 1O2 was generated by the reactions among these radicals to degrade AO7. Finally, nine intermediate products of AO7 were identified by FT-ICR-MS and a probable degradation pathway was proposed.

Ti-Modified LaFeO3/β-SiC Alveolar Foams as Immobilized Dual Catalysts with Combined Photo-Fenton and Photocatalytic Activity.

Ti-modified LaFeO3/β-SiC alveolar foams were used as immobilized, highly robust dual catalysts with combined photocatalytic wet peroxide oxidation and photocatalytic activity under UV-A light. They were prepared by incipient wetness impregnation of a β-SiC foam support, by implementing a sol-gel Pechini synthesis at the foam surface in the presence of dried amorphous sol-gel titania as a titanium source. The physicochemical and catalytic features suggest the stabilization at the foam surface of a substituted La1-xTixFeO3 catalyst analogous to its powdery counterpart. Taking 4-chlorophenol removal in water as a model reaction, its dual nature enables both high reaction rates and full total organic carbon (TOC) conversion because of a synergy effect, while its macroscopic structure overcomes the drawback of working with powdery catalysts. Further, it yields photonic efficiencies for degradation and mineralization of ca. 9.4 and 38%, respectively, that strongly outperform those obtained with a reference TiO2 P25/β-SiC foam photocatalyst. The enhancement of the catalyst robustness upon Ti modification prevents any Fe leaching to the solution, and therefore, the optimized macroscopic foam catalyst with 10 wt % catalyst loading operates through pure heterogeneous surface reactions, without any activity loss during reusability test cycles.

Improving the catalytic activity of bentonite-based bismuth ferrites composite via mechanical activation for photo-Fenton process

A bentonite-based bismuth ferrites (BiFe/Bent) composite has been fabricated by a sol-gel process in our previous study. To further improve the catalytic activity of BiFe/Bent in photo-Fenton reaction, the activation of BiFe/Bent by mechanical activation process was studied in this work. The effects of on the catalytic activity and physicochemical change of activated composite (A-BiFe/Bent) were investigated. The optimum conditions for activation of BiFe/Bent were as follows: filling ratio of grinding medium 30%, Ф10 balls as grinding medium, rotation speed of planet carrier 600 rpm, milling time 30 min, and mass of composite activated 5 g L−1 (per unit volume of milling chamber). After mechanical activation, besides the improvement from the activity components of BiFeO3 and Bi2Fe4O9, the changes in the microstructure of activated composite, including enhanced specific surface area, improved pore structure, high defectiveness in structure, and small size of activity components, were the main reasons for the improved catalytic activity of A-BiFe/Bent. Compared with that of BiFe/Bent, the catalytic activity of A-BiFe/Bent was improved about by 1-fold, and the A-BiFe/Bent exhibited good stability and low Fe leaching. It was advisable to implement mechanical activation as a strategy to promote the catalytic efficiency of BiFe/Bent.

Photocatalytic oxidation of tetracycline by magnetic carbon-supported TiO2 nanoparticles catalyzed peroxydisulfate: Performance, synergy and reaction mechanism studies

TiO2 decorated on ferroferric oxides coupled with activated carbon (TFOC), as a magnetic heterogeneous catalyst, was synthesized and its photocatalytic ability was assessed in coupling with UV light towards peroxydisulfate (PS) activation to degrade tetracycline (TC). Main properties of the catalyst were analyzed by using UV–visible DRS, FESEM, VSM, PL, EDS, TEM, XRD and BET techniques. A proposed reaction mechanism was suggested for activating PS and TC degradation. Both TiO2 and Fe3O4 (FO) were synthesized and dispersed successfully on the carbon surfaces in nano-sized scale. It was found that the photocatalytic activity of TiO2 was accelerated significantly after loading on the magnetic carbon. TFOC showed an excellent magnetic response in the presence of a magnet. According to PL analysis, FO nanoparticles and carbon played a critical role in the suppression of recombination of excited electrons and holes. TFOC in coupling with UV showed a best performance, compared to the other single and binary processes for TC decontamination. After 15 min reaction, the highest level of elimination, 96% TC (60 mg/L) and 72.1% TOC were obtained at optimum operational conditions: pH:5.0, TFOC: 0.3 g/L and PS:1.0 mM. A noticeable synergistic effect was found for TFOC in combination with UV and PS. Both negligible Fe leaching and high efficiency of degradation were achieved with reused times, illustrating that TFOC has an excellent durability and reusability. Based on trapping tests, the importance of involved oxidizing species during TC decontamination over TFOC/PS/UV system was in order of 1O2 > SO4•– > h+ > O2•– > HO•. Among studied anions, the highest quenching impact was observed for chloride ions. Particularly, TFOC composite showed the high catalytic activity as well excellent potential in recovery and its coupling with UV light and PS can be introduced as a promising strategy for efficient destroying TC antibiotic.

A heterogeneous photocatalytic sulfate radical-based oxidation process for efficient degradation of 4-chlorophenol using TiO2 anchored on Fe oxides@carbon

A photocatalytic sulfate radical-based advanced oxidation process was studied to degrade 4-chlorophenol (4-CP) using persulfate (PS) catalyzing UV light and heterogeneous catalyst. In this regards, ferroferric oxide nanoparticles anchored on activated carbon (FOC) was applied as a supporter of TiO2 nanoparticles for fabricating of a recoverable photocatalyst (FOCT). Some analysis techniques including PL, UV–vis DRS, XRD, FESEM-EDS, BET, TEM and VSM were utilized to determine the optical, structural, textural and physicochemical characteristics of FOCT. The reaction mechanisms of PS activation and the generation of free radicals were described in details. Moreover, degradation intermediate products were identified and reaction pathway were proposed. It was found that photocatalytic activity and oxidation performance of pure TiO2 were improved after decoration on FOC. An excellent elimination efficiency was achieved in coupling of FOCT and UV irradiation with PS. Over 99 % of 4-CP (60 mg/L) and 49 % of TOC were removed by FOCT/UV/PS at optimum operational conditions. Furthermore, high PCP decontamination rate (> 86 %) was obtained, even at high concentrations (100 mg/L). During consecutive five runs of catalyst use, the degradation rate was decreased slightly to 88 % with a negligible decline in Fe and Ti leaching, demonstrating the excellent reusability and durability of FOCT in oxidation process. SO4– and HO radicals were detected as main reactive species that involved in the degradation of 4-CP over FOCT/UV/PS system. Thanks to good performance and easy recovery of catalyst, FOCT/UV/PS hybrid system has a great potential for environmental remediation perspectives.

Heterogeneous electro-Fenton-like oxidation for the degradation of 4-nitrophenol characterized by immobilized Fe(III): Performance, mechanism and chlorinated organic compounds formation

Degradation of 4-nitrophenol was carried out by a novel electrochemical process, in which a carbon nanotube-containing cathode was employed for the electro-generation of hydrogen peroxide (H2O2) and immobilized Fe(III) served as the heterogeneous catalyst. The catalyst of immobilized Fe(III) prepared by dipping molecular sieves into Fe(NO3)3 solution exhibited a well catalytic activity and a weak Fe(III) leaching. By the major function of electro-Fenton-like oxidation and the secondary function of anodic oxidation, TOC removal of 77 % and 4-nitrophenol removal of 100 % were achieved under the optimum conditions. The degradation efficiency decreased in the presence of chloride ions (Cl−), and this unfavorable effect was relevant to the electro-generation of chlorine (Cl2). It was confirmed that hydroxyl radical (OH) was the major oxidizing specie in the heterogeneous electro-Fenton-like oxidation. During the degradation, firstly nitro-group was replaced by hydroxyl forming quinol and the further oxidation generated p-benzoquinone. Afterwards, benzene ring was destroyed and oxidized leading to the mineralization. The generation of inorganic ions mainly presented as nitrate ions (NO3−) and ammonium ions (NH4+) at the end. Moreover, some chlorinated organic compounds were found during the degradation in the presence of chloride ion (Cl−), and they could be completely destroyed by the successive oxidation degradation. This paper indicates that the presented process is able to effectively degrade organic compounds as well as avoid the generation of iron sludge.

Selective Leaching of LiFePO4 by H2SO4 in the Presence of NaClO3

Herein, problems commonly observed for the wet leaching of waste LiFePO4 cathode materials, namely extensive Fe leaching and impurity removal, are mitigated through the use of NaClO3, and the effects of leaching parameters on Fe, P, Li, and Al leaching efficiencies are probed. As a result, optimal leaching conditions are determined as temperature = 90�C, H2SO4 concentration = 1 M, liquid-to-solid ratio = 5:1, leaching time = 1 h, stirring speed = 150 rpm, and NaClO3 dosage = 25 g per 100 g raw material, with the corresponding Fe, P, Li, and Al leaching efficiencies obtained as 0.21, 0.03, 97.23 and 11.87%, respectively.

In-situ formed N-doped bamboo-like carbon nanotubes encapsulated with Fe nanoparticles supported by biochar as highly efficient catalyst for activation of persulfate (PS) toward degradation of organic pollutants

In this study, N-doped bamboo-like carbon nanotubes encapsulated with Fe nanoparticles (Fe NPs) on the surface of soybean dregs-derived biochar (Fe@NCNT − BC) was synthesized via a low-cost and facile strategy. The unique composites behaved as efficient catalysts for the degradation of various organic pollutants by the activation of persulfate (PS). Under the conditions of [PS] = 5 mM, [RhB] = 20 mg/L, [Fe@NCNT-BC-800] = 1.0 g/L, pH = 7.0, the RhB degradation rate was very fast reaching up to 100% within 10 min. The system also exhibited significant high activity in a broad pH window (3.0–11.0). Meanwhile, the recycling experiments and Fe leaching tests further demonstrated the stability of Fe@NCNT − BC during the activation of PS. Most interestingly, the Fe nanoparticles played a key role in promoting the degree of graphitization and the formation of bamboo-like N-doped carbon nanotubes. Besides, the introduction of biochar significantly improved the dispersion ability to the Fe@NCNT − BC. The competitive radical quenching tests and electron paramagnetic resonance measurements (ESR) illustrated that instead of the traditional radicals (sulfate radicals and hydroxyl radicals), the non-radical singlet oxygen (1O2) was the dominant reactive oxidative species (ROS) in the Fe@NCNT-BC/PS system. A mechanistic study suggested that pyridinic N, graphitic N, sp2-hybridized carbon structure and C = O bond in the Fe@NCNT − BC − 800 promoted the generation of the ROS. This study successfully provides an economic and feasible method for synthesis of a novel catalyst as an eco-friendly and efficient material for the degradation of organic pollutants in the environment.

Simultaneously accelerating the regeneration of FeII and the selectivity of 2e- oxygen reduction over sulfide iron-based carbon aerogel in electro-Fenton system

The regeneration of surface FeII and the electro-formation of H2O2 play crucial roles for determining the degradation efficiency of heterogeneous electro-Fenton process. The sulfide iron-based carbon aerogel was synthesized directly as cathode. The main composition of iron compounds were Fe3O4 and FeS∙FeS2, which were embedded in the matrix of carbon aerogels. Most of sulfur was evenly distributed on carbon, favoring the formation of −COOH groups. The nature of existed sulfur were investigated by temperature-programmed reaction spectroscopy respectively under the CO2 and air. The S-doping promoted the regeneration of FeII and improved the selectivity of 2e− oxygen reduction with iron-based carbon materials. As high as 99 % removal of dimethyl phthalate and 3-chlorophenol were obtained in 240 min. Meanwhile, the EPR results demonstrated that HO∙ was formed by on site decomposing H2O2 with FeSCA, which exhibited high stability with low Fe leaching (< 2 ppm) and high recyclability even in acidic medium.

Direct Hydroxylation of Phenol to Dihydroxybenzenes by H2O2 and Fe-based Metal-Organic Framework Catalyst at Room Temperature

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70 °C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditions.

One-pot fabrication of sludge-derived magnetic Fe,N-codoped carbon catalysts for peroxymonosulfate-induced elimination of phenolic contaminants

The use of waste sludge as a precursor of catalysts for environmental applications has been encouraged during the past few years. In this study, a series of magnetic Fe,N-codoped carbon catalysts (UBC-x) were successfully prepared by a facile one-pot pyrolysis method using Fe-rich sludge and N-rich urea as the raw materials. By carefully controlling the mass ratio of urea/dry sludge (x = 0–3), a significant amount of N (1–10 mass%) were incorporated, and the UBC-x catalysts, especially UBC-0.5 and UBC-0.75, could be imparted with high catalytic activity, convenient magnetic separation and high recycle stability. Phenolic contaminants like phenol and bisphenol A (BPA) could be nearly completely removed through peroxymonosulfate (PMS)-induced degradation by using UBC-x as the catalysts under a wide pH range (2–11) and with the co-existence of water constituents (chloride Cl− and sodium humate NaH, 0–50 mM). Among the several reactive oxidative species (ROS), singlet oxygen (1O2) was deemed as the main reactive species responsible for BPA degradation. Both Fe and N active sites contributed to the high catalytic activity of UBC-x, and their coordination made the catalysts rather stable with no significant Fe leaching under a wide pH range. Therefore, after an easy magnetic separation, the UBC-x could be recycled and reused efficiently in another BPA removal cycle. The as-synthesized magnetic Fe,N-codoped carbon catalysts provided a new route for sludge reutilization and showed potential applications in wastewater treatment.

Study of the leaching and pore evolution in large particles of a sulfide ore

A long-term leach investigation was undertaken on particles of a sulfide ore to determine the nature of solution transport into large particles and to identify the primary roles concentrations of acid and oxidant on controlling solution transport. Bulk leaching results showed that in the case of Fe leaching, both [Fe3+] and [H2SO4] promoted the extent of Fe extraction whereas the extent of Zn and Pb extraction was dependent only on [H2SO4]. Based on the bulk extraction of Al and Mg, it appears that [H2SO4] drives the expansion of inner particle pores by promoting the dissolution of gangue minerals. The findings indicated that the generation of cracks and/or pores to enhance solution contact with the value minerals remains the critical factor in improving value metal recovery from this type of material during heap leaching. Comparative laboratory and synchrotron X-CT studies were also undertaken on single ore particles using a novel in–situ leach cup technique. Similar to the solution results, the acid concentration was shown to be critical in creating effective porosity and pore networks through the centre of the particles for the transport of solution to value minerals and subsequent leaching and transport to the bulk solution. This occurred primarily through the dissolution of auxiliary aluminosilicate gangue minerals, which in turn created networks of porosity for effective bulk solution transport into large particles during heap leaching. This, in turn, enables local solution micro-environments where leaching occurs at the solid-liquid interface. Following the accessibility of bulk solution into the particle, the reaction is then governed by surface-mineral reactions between the sulfidic minerals.

MOF-Derived Fe2O3/Nitrogen/Carbon Composite as a Stable Heterogeneous Electro-Fenton Catalyst

Heterogeneous Electro-Fenton (EF) enables rapid elimination of recalcitrant organic pollutants without producing undesirable byproducts, but stable functioning of this process remains challenging. In this work, a porous composite of ferric oxide/nitrogen/carbon (Fe2O3/N–C) with good EF activity and stability was fabricated from iron-based metal–organic framework compounds (MOFs) and polyaniline via one-step pyrolysis. The incorporated Fe2O3 nanocrystals and the pyridinic and pyrrolic-N species endow the material with high catalytic activity for hydrogen peroxide (H2O2) generation and activation. The efficient degradation of bisphenol A and several other organic pollutants, dominated by a heterogeneous EF pathway, was achieved in acidic solution. The catalyst had low Fe leaching (0.52 mg/L after 2 h of reaction) and retained 98% of its original activity after four cycles of repeated use. Therefore, Fe2O3/N–C may serve as an efficient, stable, and environmentally benign heterogeneous EF catalyst for wastewater treatment and environmental remediation applications.

Regeneration of a deactivated surface functionalised polyacrylonitrile supported Fenton catalyst for use in wastewater treatment.

Successful attempts to regenerate a used surface functionalised nanocoated polyacrylonitrile (PAN) catalyst are described here. During use in wastewater treatment, the novel Fenton catalyst (F1) is deactivated due to iron loss caused by acid hydrolysis. In this study the deactivated catalyst (D1) is subjected to reactions with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC), followed by reactions with either hydroxylamine to give sample T1 or hydroxylamine and hydrazine to give sample T2. The samples were then impregnated with iron(iii) salt to give either Fe-T1 or Fe-T2. The catalysts were characterized by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR), Atomic Absorption (AA) and UV/VIS spectroscopies, Scanning Electron Microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy and Electron Spin Resonance (ESR) spectroscopy. The iron on the regenerated catalyst was found to be in complexed form but had deposited iron oxide species as well. The catalysts were tested in batch mode and compared with the fresh modified PAN catalyst in the degradation of the dye Reactive Orange 16 (RO-16) with analysis by UV/VIS spectroscopy. The reactivated catalysts prepared with EDC were found to be more active and faster (as measured at 120 min) in decolourising RO-16 than the fresh catalytic mesh but also with a higher degree of Fe leaching (0.85% loss of iron per gram of Fe-T2 catalyst over 6 cycles compared to 0.32% loss of Fe per gram of F1 catalyst over 6 cycles). This leaching was found not to contribute significantly to degradation of the dye and the preliminary results suggest that the regime can be used for catalyst regeneration encouraging industrial uptake.

Freezing/thawing effects on geochemical behavior of residues from acid mine drainage passive treatment systems

Passive systems are promising for the treatment of acid mine drainage (AMD) but generate metal-rich solids or residues. In subarctic climate, freezing/thawing (F/T) cycles may influence the chemical stability of waste, including residues from AMD passive treatment. The objective of this study was to assess and better understand the effect of F/T cycles on contaminants (metal and sulfates) leaching from AMD post-treatment residues. To do so, samples of residues WA50 (50 % wood ash and 50 % wood chips), PBR (30 % inorganic materials and 70 % organic substrate) and C50 (50 % calcite and 50 % wood chips) were collected from a laboratory tri-unit passive treatment system for iron-rich AMD (Fe-AMD) operated for over 1-year. To better understand the effect of freezing upon contaminant leaching, kinetic tests in weathering cells under wetting/drying (W/D) and F/T cycles were performed. Results showed that F/T cycles are likely to enhance the potential of metal leaching from post-treatment residues. The Fe leaching was 1.6-(for WA50), 3.2-(for C50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles. Similarly, Zn leaching was 2.4-(for WA50), 4.9-(for PBR) and 5-(for C50) times higher under F/T cycles compared to the W/D cycles. Finally, Mn leaching was 2.4-(for WA50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles but no difference in Mn concentration was observed for C50 residues. These findings suggest that during snow melt or early spring significant metal concentrations could be released while disposing AMD passive treatment residues.