Regeneration Kinetics Research Articles

The Influence of Minority Carrier Density on Degradation and Regeneration Kinetics in Multicrystalline Silicon Wafers

The rate at which silicon solar cells and wafers degrade and regenerate when subjected to light and elevated temperatures (LeTID) is known to depend on the minority carrier concentration. In this article, we utilize spatial differences in the rate of degradation and regeneration in multicrystalline silicon wafers to estimate the dependence of these rates on minority carrier concentration. We apply the relation obtained from spatial investigations in a model describing temporal LeTID defect evolution. With the updated model in which the evolving minority charge carrier density during degradation and regeneration is considered, we obtain a drastically improved fit between measured and modeled data. The activation energy for the regeneration process determined from our proposed model (0.56±0.12eV at 1 sun) is lower than most values reported in the literature but correspond perfectly to the activation energy reported by Graf et al. by whom evolving carrier injection is accounted for experimentally. Hence, our results underpin the importance of taking the evolution of charge carrier injection into account in the evaluation of LeTID kinetics. Finally, we use our updated model to obtain spatial maps of degradation and regeneration parameters. Clear correlations are shown between LeTID kinetics parameters and local processing conditions.

Microbiota regulate the induction and proliferation of revival intestinal stem cells through inflammatory cytokines

Abstract Gut microbiota are critical mediators of inflammation and regeneration of the intestinal epithelium. Intestinal restitution is a coordinated response that involves the dedifferentiation of mature epithelial cell lineages, the proliferation of Lgr5+ intestinal stem cells, and the induction of Clu+ revival stem cells (RSCs). How the gut microbiota directly impacts this regenerative process remains unclear. Using irradiation as a model for small intestinal epithelium restitution, we demonstrate that microbiota regulate the induction and subsequent proliferation of Clu+ RSCs. Our results report that specific pathogen-free (SPF) mice induce greater RSCs 3 days post-IR in comparison to germ-free (GF) mice. This microbiota-dependent increase in RSCs was matched by an increase in BrdU+ proliferating cells and an increase in TUNEL+ apoptotic cells in SPF mice. Using intestinal organoids as an in vitro model of intestinal restitution, SPF and GF intestinal crypts demonstrated equal propensity to generate mature organoids. Transcriptional analysis of GF and SPF RSCs by single-cell RNA sequencing highlighted unique regenerative and inflammatory gene signatures. The altered regeneration kinetics observed in SPF mice was accompanied by an increase in Tnfa and Cxcl1 at the peak of RSC induction and an increase in Ifnγ post RSC induction. Altogether, these findings suggest that microbiota-dependent expression of inflammatory cytokines may be key regulators in facilitating the expansion and proliferation of RSCs to efficiently repair the intestinal epithelium following damage.

Carbon dioxide capture with aqueous amino acids: Mechanistic study of amino acid regeneration by guanidine crystallization and process intensification

CO2 capture from powerplant-generated flue gas via a phase-changing process involving absorption with aqueous amino acids (e.g., glycine or sarcosine) and bicarbonate crystallization with bis-iminoguanidines (e.g., glyoxal-bis-iminoguanidine or GBIG) is investigated in this paper. This process is of high interest due to its potential to decrease the energy penalty for CO2 capture by significantly reducing the solvent regeneration energy typically associated with aqueous amine solvents. A critical step in the proposed CO2 capture mechanism is the regeneration of the amino acid by removal of protons and bicarbonate ions from solution through crystallization of GBIGH22+ bicarbonate salt. Here, we investigated the thermodynamics and kinetics of glycine regeneration by crystallization of GBIGH22+(HCO3–)2(H2O)2. A theoretical model was developed and compared to experimental data to simulate and predict the glycine regeneration and determine its reaction mechanism. This combined experimental and theoretical study led to the conclusion that, while the GBIGH22+ bicarbonate crystallization step provides most of the thermodynamic driving force for the glycine regeneration, the rate-limiting step is the protonation of GBIG prior to crystallization. The CO2 loading and amino acid regeneration steps were combined into a single, intensified process using a bubble column reactor. The CO2 loading capacity of GBIG was experimentally determined to be roughly 1.36 mol CO2 per mol GBIG. These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine absorbents.

Sonicated zeolitic imidazolate Framework-8 derived nanoporous carbon for efficient capture and reversible storage of radioiodine

Iodine plays a significant role in industry and in chemical processes within living organisms. However, radioiodine exposure possess threats such as thyroid cancer to humans, when released into the environment through using nuclear technology, used nuclear fuel reprocessing and nuclear accidents. Its capture and storage is critical to safeguard industrial applications, prevent harm to human health, while preventing environmental damage. Herein we report efficient radioiodine capture using a large surface area, nanoporous carbon derived from ultra-sonication of ZIF-8. The carbon exhibited high adsorption capacity of 434 ​wt% gravimetrically with reusability of 96% after 3 cycles, and 1418 mgg-1 in cyclohexane solution with fast kinetics and high recoverability and reusability. We deduced the high adsorption capacity to be due to the large surface area with micro and mesopores, presence of OH- acting as electron donors and the presence of nitrogen, which interacts strongly with the electron-deficient iodine (I2). Moreover, the process best fits the pseudo-second-order and Freundlich models with multilinearity observed with Weber-Morris model. Because of its comparatively lower cost, large surface area, facile preparation, good regeneration and fast kinetics, the as-prepared porous carbon shows exceptional promise as radioiodine adsorbent.

Lanthanum biosorption using sericin/alginate particles crosslinked by poly(vinyl alcohol): Kinetic, cation exchange, and desorption studies

Nowadays, lanthanum removal from wastewater has received attention due to its importance in various industrial applications. Biosorption has been considered a promising process for lanthanum removal from secondary sources. This study aimed to evaluate the use of sericin/alginate/poly(vinyl alcohol) (SAPVA) particles for lanthanum biosorption in batch system. The effect of pH on the biosorption of lanthanum showed that both lanthanum‐uptake (0.103 mol/kg) and calcium‐release (0.155 mol/kg) reach a maximum at equilibrium pH 5.22. Biosorption kinetics was carried in three lanthanum initial concentrations (0.0005, 0.0011, and 0.0017 mol/dm3). The results revealed that the equilibration time was reached between 210 and 450 min and biosorption capacity at equilibrium between 0.050 and 0.152 mol/kg. The kinetic followed the pseudo-second order model and the external diffusion was the main limiting step. Evaluation of cation exchange mechanism showed that the lanthanum biosorption is related to a stoichiometric reaction (2:3 ratio) between calcium and lanthanum. Calcium nitrate under acidic conditions was able to retrieve lanthanum biosorbed in the particles with high efficiency (96.07 ± 2.02%). Regeneration kinetics showed a longer equilibration time (630 min) and lower biosorption capacity at equilibrium (0.138 mol/kg) for the lanthanum initial concentration of 0.0015 mol/dm3. In this case, the experimental kinetic profile of calcium released throughout the lanthanum biosorption was not stoichiometric. Characterization analyzes suggest that the main mechanism involved in lanthanum capture and calcium release was cation exchange between functional groups on the biosorbent particles and lanthanum. Thus, SAPVA particles are a promising biosorbent for lanthanum removal from aqueous solutions.

Mass transfer enhanced CaO pellets for CO2 sorption: Utilization of CO2 emitted from CaCO3 pellets during calcination

• Mass transfer enhanced CaO pellets were prepared and applied to capture CO 2 . • CO 2 evacuation from CaCO 3 pellets created mass transfer channels. • Developed channels significantly enhanced CO 2 sorption kinetics. • Enhanced mass transfer caused fast regeneration of CaO pellets after CO 2 sorption. In the preparation of CaO-based CO 2 sorbents, particle densification during pelletization significantly limits the mass transfer of CO 2 , thereby decreasing the CO 2 sorption performance. In this study, mass transfer enhanced CaO pellets (CaO–PC) were prepared through the formation of channels using CO 2 evacuation from the inside of the pellets. Calcination of CaCO 3 pellets induced CO 2 evacuation and the remaining evacuation pathways provided excellent mass transfer channels for CaO–PC. Conventional CaO pellets (CaO–CP) were also prepared for comparison. Unlike the severely agglomerated (or blocked) morphology of CaO–CP, well-developed channels were observed in CaO–PC. It was experimentally confirmed that these channels directly contributed to the initial stage of CO 2 sorption in CaO–PC, which significantly accelerated the CO 2 sorption kinetics. CaO–PC had increased CO 2 sorption uptakes of 58.9, 65.1, and 67.0 wt% at 500, 600, and 700 °C, respectively, whereas those for CaO–CP were 47.6, 55.4, and 56.8 wt%. In addition to CO 2 sorption, enhanced mass transfer had a positive effect on CO 2 release after capture. Under CO 2 flow, the regeneration of CaO–PC was faster than that of CaO–CP, even at lower temperatures. Both the fast CO 2 sorption and regeneration kinetics of CaO–PC significantly enhance the energy efficiency of continuous CO 2 capture processes. These improvements were accomplished easily without the need of any additional energy-consuming treatments other than the conventional preparation methods.

High adsorption and high catalyst regeneration kinetics observed for Flyash-Fe3O4-Ag magnetic composite for efficient removal of industrial azo reactive dyes from aqueous solution via persulfate activation

The degradation of industrial azo reactive dyes (Corafix Red ME4B, Corazol Golden Yellow, and Corazol Black BX) has been demonstrated via the activation of persulfate (S2O82−) by using the Flyash (FA)-Fe3O4, FA-Fe3O4-Ag, and FA-Fe3O4-Ag-Cu magnetic composites as the activators. No significant dye decomposition has been observed for the thermal (30 °C) activation process and with the use of FA as an activator which involve no anchoring of the dye on the catalyst-surface. Nevertheless, FA-Fe3O4-Ag catalyst (100 g L−1) shows the maximum catalytic activity (98.6%) for the degradation of Corafix Red ME4B at the initial dye concentration of 0.3 g L−1 which has been attributed to its largest adsorption capacity (29.6 mg g−1) and the highest catalyst regeneration kinetics. Former is the result of pore-filling sorption process involving the electrostatic attraction mechanism caused by the presence of the highest surface oxygen-ion vacancy concentration and the largest pore volume (0.1654 cm3 g−1). The mechanism of dye degradation via the activation of S2O8●− involves the generation of SO4●− and ●OH which are responsible for the dye decomposition and the catalyst regeneration respectively. The kinetics of catalyst regeneration is enhanced by the relatively higher pore volume of catalyst and smaller change in its oxidation state.

Prospective principles of catalyst utilization using supercritical fluid media

An overview of prospective principles of catalyst utilization using supercritical fluid media is presented. The processes in which these working media act as solvents and extractants, reagents and reaction media are considered. At the same time, we are talking about both heterogeneous catalysts and catalytic complexes dissolved in the water runoff of industrial enterprises. Using the LD-145 catalyst as an example, we studied the possibility of extending its service life instead of recycling, due to a change in the physical and chemical principles of its regeneration. We are talking about replacing the high-temperature process of vapor-air oxidation of catalyst-deactivating compounds with a supercritical fluid extraction process. At the same time, the extractant used is not widespread carbon dioxide, but propane/butane mixture, the use of which makes the process significantly more efficient. This is because a number of binary systems “deactivating compound – extractant” change the type of phase behavior from V-VI to I-II when changing carbon dioxide to propane/butane mixture. Thus, these systems, for example, involving naphthalene, phenol and some other substances in the supercritical fluid state fall outside the binodal of the binary system into the region of unlimited miscibility of components, which significantly increases the kinetics of the catalyst regeneration.

Dye Regeneration Kinetics of Sensitized Nickel Oxide Films under Illumination Investigated by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) feedback mode has been used to investigate regeneration kinetics on P1 (4-(bis-{4-[5-(2,2-dicyanovinyl) thiophene-2-yl] pH-enyl} amino) benzoic acid) dye sensitized nickel oxide (NiO) electrodes in contact with reduced iodide liquid electrolyte in different electrolyte solvents. We were used acetonitrile, ethanol, methanol and propylene carbonate solvents for comparison under illumination of different wavelengths. We found significant variation of regeneration kinetics parameters such as regeneration rate constant (keff), the reduction rate constant (kred) and absorption cross-section (Φhv) in different illumination intensity and different solvents.

The impact of insufficient time resolution on dye regeneration lifetime determined using transient absorption spectroscopy.

Dye regeneration lifetimes of a combination of dyes and redox mediators were determined by two transient absorption (TA) spectrometers with 0.5 ns (sub-ns) and 6 ns (ns) time resolutions to elucidate the impact of insufficient time resolution on the measurements of dye regeneration kinetics in dye-sensitised semiconductor electrodes. Due to the disordered nature of the dye-sensitised electrodes, the dye regeneration lifetime is often characterised by half-decay time (τ1/2) of the initial signal magnitude. Alternatively, τ1/2,S is calculated from stretched-exponential lifetime (τww) and the distribution of lifetimes characterised by the stretch parameter (β). Stretched-exponential functions were numerically modelled, showing that to keep the error in τ1/2 ≤ 10%, τww needs to be at least 20 times longer than the time resolution in case of non-dispersive transients (β = 0.9) but at least 870 times longer when dispersive (β = 0.5). To test the predictions, TA decays of a combination of organic and porhyrin dyes and three cobalt-complex mediators are analysed, spanning a range of τww and β. These examples show that a 262% error in τ1/2 is possible if the time resolution of the TA setup is only 13 times faster than τww and smaller β results in larger error when τww is similar. Determining τ1/2,S by stretched-exponential fitting generally reduces the error compared to that determined directly from the graph. However, if the stretched-exponential function does not correctly describe the early signal transient, even a larger error by stretched-exponetial fitting is introduced. The key requirement for accurate measurement is to have a fast-enough TA setup to resolve the initial plateau of the TA signal. To demonstrate the impact of the measured errors, the measured regeneration lifetimes are plotted versus the driving force of the reaction and modelled using Marcus theory. Erroneous regeneration rates lead to an underestimated electronic coupling term by 2.2 times in case of a series of porphyrin dyes matched with Co complex electrolytes, a significant impact when the interpretation of factors affecting electron transfer at dye-sensitised semiconductor/electrolyte interface is discussed.

The role of intraparticle diffusion path length during electro-assisted regeneration of ion exchange resins: Implications for selective adsorbent design and reverse osmosis pretreatment

Inorganic membrane scaling is a major cause of process failure for reverse osmosis (RO). Pretreatment using selective ion exchangers can reduce membrane scaling by removing scale-forming ions such as calcium (Ca2+) and phosphate (P). Ca- and P-selective ion exchangers also enable calcium phosphate recovery via precipitation from spent regenerants enriched with both ions. However, conventional regeneration approaches require substantial chemical and energy inputs. In this study, we designed a RO pretreatment process using electro-assisted regeneration of a column train containing a hybrid anion exchanger (HAIX) and a weak acid cation exchanger (WAC) to selectively remove > 90% Ca2+ and P from synthetic secondary effluent. HAIX and WAC were regenerated using pH 11 catholyte and pH 3 anolyte produced via electrochemical water splitting. HAIX contains ferric oxide nanoparticles (FeOnp) in a parent strong base anion exchanger (SBA). By comparing P regeneration efficiency of HAIX and SBA, we identified that FeOnp dopants reduced intraparticle diffusivity by 85% from SBA to HAIX. However, HAIX exhibited faster column regeneration kinetics than SBA, potentially due to the shortened intraparticle diffusion path length caused by the surface-distributed P in saturated HAIX, which overcompensated for low intraparticle diffusivity. Regenerability enhancement caused by the reduced intraparticle diffusion path length was also confirmed by comparing WAC with shallow-shell WAC (SSWAC), which has surface-distributed carboxylate functional groups. We anticipate that this study will inform selective adsorbent design by identifying strategies to improve regenerability, facilitate process intensification by replacing chemical inputs with electricity, and enhance resource recovery from wastewater.

Experiment and regeneration kinetic model study on CO2 adsorbent prepared from fly ash

• Loaded potassium-based CO 2 adsorbent was prepared from fly ash. • Temperature programmed desorption of adsorbent was performed. • Experiment and model fitting were combined to study desorption regeneration. • Avrami fractional kinetic model was used to simulate regeneration kinetics. • Diffusion models were used to analysis desorption mechanism. Using power plant fly ash to prepare CO 2 adsorbent can not only realize low-carbon power in power plants, but also effectively use solid waste to achieve the objective of treating the waste with waste. Regeneration characteristic is an important performance of adsorbent. Through the temperature programmed desorption experiment, the influence of different regeneration conditions on performance and regeneration kinetics can be studied, and the optimal calculation of regeneration conditions can be carried out, so as to realize the recycling of adsorbent with economic benefits. The optimal regeneration temperature and heating rate were 150 °C and 10 °C/min, respectively. Under these conditions, the desorption capacity was 1.7454 mmol/g, and the desorption efficiency was 86.38%. Avrami fraction kinetic model was used to simulate and calculate the regeneration kinetics of adsorbent. The results showed that the regeneration temperature affected the regeneration mechanism. High regeneration temperature and high heating rate could promote the desorption kinetic rate to increase. When the regeneration temperature was 90 °C and 190 °C, k a was 0.000885 min −1 and 0.001318 min −1 respectively. Three kinds of diffusion were used to study the regeneration mechanism. It was concluded that after the regeneration temperature was higher than the chemical desorption temperature, the desorption regeneration could be divided into early, middle and final stages, and the rate controlling steps were respectively: intraparticle diffusion control, joint control of surface chemical reaction and intraparticle diffusion, and membrane diffusion control. Physical desorption occured when the regeneration temperature was lower than 110 °C. The desorption time was longer and CO 2 concentration released was always low.

Scalpel edge roughness affects post-transection peripheral nerve regeneration

BackgroundGentle and precise tissue dissection reduces collateral tissue damage and preserves its structural quality for optimizing healing. This is particularly true for peripheral nerve neurorrhaphy. Axon regeneration kinetics across the repair is dependent on the amount of intraneural fibrosis. The purpose of this study was to determine whether scalpel blade smoothness was a deterministic factor in the kinetics of postneurorrhaphy peripheral axon regeneration. MethodsScalpel transection of the saphenous nerve was performed in 18 female Hartley guinea pigs either by a standard #15 stainless steel scalpel blade or a highly polished version of the same blade. Compound nerve action potential recordings and histochemical assay of neurofilament density proximal and 1 cm distal to the site of nerve transection were quantified postneurorrhaphy at postoperative weeks 5, 9, and 12. ResultsThere was no action potential transmission observed in the distal axons immediately after neurorrhaphy. A substantial acceleration of axonal conduction recovery was observed in nerves transected with polished scalpel blades observed by high compound nerve action potential amplitudes at postneurorrhaphy weeks 5 and 9 (P < .05). In addition, an increased recovery of intra-axonal neurofilament density in nerves transected with polished scalpel blades was observed by postoperative week 5 (P < .05). ConclusionThe quality of the scalpel blade is an important determinate of postsurgical healing. Gentle handling of tissue matters.

Simultaneous magnesia regeneration and sulfur dioxide generation in magnesium-based flue gas desulfurization process

A method was proposed for simultaneously regenerating magnesia from the Mg-based flue gas desulfurization byproducts in the power plant and generating the high concentration of sulfur dioxide. Elemental sulfur particles were evaporated to sulfur vapor and the latter one was used as the reductive agent to regenerate magnesia from the magnesium gypsum. The experiments were carried out in a successive fixed-bed system to study the concentration of sulfur dioxide in the exhaust gas and the activity of the regenerated magnesia under different reaction conditions. Sulfur vapor effectively reduced the magnesia regeneration temperature from above 950 °C to merely 650 °C. The concentration of sulfur dioxide in the exhaust gas could achieve 20% by volume when the sulfur vapor partial pressure was 1674 Pa, the regeneration temperature was 750 °C, the gas hourly space velocity was 1200 h−1 and the loading of the reaction materials in the regeneration reactor was 16 g, respectively. The activity of the regenerated magnesia after the decomposition of the magnesium gypsum at 750 °C was satisfactory. Both the magnesium gypsum and the regenerated magnesia were characterized using X-ray fluorescence spectroscopy, thermogravimetric analyzer, X-ray diffraction spectroscopy, BET surface area analyzer, scanning electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The kinetics of the magnesia regeneration from the magnesium gypsum in the presence of the sulfur vapor was analyzed and the nucleation model was determined to be the most appropriate kinetic model. The activation energy and the pre-exponential factor were determined to be 76.51 kJ/mol and 228.66 min−1, respectively. All the results demonstrate that there is considerable potential for the application of this proposed method in flue gas desulfurization process.

Study on NOx removal from simulated flue gas by an electrobiofilm reactor: EDTA-ferrous regeneration and biological kinetics mechanism

The regeneration of EDTA-FeII is a key step in electrobiofilm reduction-integrated systems for NOx removal from industrial boiler flue gas. The current and carbon sources are proposed to be the two crucial electron donors for EDTA-FeII regeneration. These parameters strongly influence the reactivity of EDTA-FeII-generated products in the system. Therefore, their effects on EDTA-FeII-NO and EDTA-FeIII reduction and the EDTA-FeII generation mechanism were studied. The results showed that the electrobiofilm method has obvious advantages over biological or electrochemical methods used alone for EDTA-FeII regeneration. Under the optimal conditions at a current of 22.9A m-3 net cathode chamber, the rate of EDTA-FeII regeneration reached 98.35%. The glucose concentration is the primary factor influencing the reduction of both EDTA-FeII-NO and EDTA-FeIII, while the current significantly promotes both processes. Comparison of the Km values of the two substrates indicated that microbial activity was crucial to the reduction of EDTA-FeII-NO, but the biological reduction of EDTA-FeIII had a competitive influence on EDTA-FeII-NO reduction, which limited the abundance and effectiveness of the bacteria responsible for EDTA-FeII-NO reduction in the electrobiofilm system.

PFAS and DOM removal using an organic scavenger and PFAS-specific resin: Trade-off between regeneration and faster kinetics

Treatment technologies such as ion exchange (IX) process exhibit promising potentials for the removal of toxic per- and poly-fluoroalkyl substances (PFAS) from natural waters. In recent years, industries have started manufacturing PFAS-specific resins which are typically operated in a single use-and-dispose mode until exhaustion. However, this increases the resin demand and the consequent operational cost and environmental burden of the IX process. In this study, the performance of a PFAS-specific resin (A592) was compared with that of a regenerative organic scavenger resin (A860) which is traditionally employed for dissolved organic matter (DOM) and micorpollutant removal. Comparative studies were performed to examine the removal of multiple long- and short-chain carboxylic, sulfonic, precursor and emerging PFAS (including GenX) from synthetic and natural waters. The A592 resin exhibited faster uptake kinetics for PFAS while simultaneously removing 10–15% of DOM. The A860 resin removed ~60–70% of DOM; however, it required approximately 3-fold higher contact times for achieving the same degree of PFAS removal when compared to the PFAS-specific resin. The resin breakthrough (Ctreated (PFAS) > 70 ng/L) was observed around 125,000 ± 5000 bed volumes (BVs) for the PFAS-specific resin (via multiple loading tests), while it ranged between 15,000–27,000 BVs for the organic scavenger. Yet, a mass balance on PFAS and DOM removal indicated ~90–98% site saturation (in milli-equivalents (meqs)) on both IX resins before exhaustion. More importantly, the regenerated organic scavenger resin (A860) exhibited PFAS and DOM removal capabilities for longer operational BVs when compared to A592 operated in a single-use-mode in natural waters.

Implications of feeding or cofeeding bio-oil in the fluid catalytic cracker (FCC) in terms of regeneration kinetics and energy balance

Feeding or cofeeding bio-oil (biomass pyrolysis oil) into the fluid catalytic cracking (FCC) has a direct impact on product distribution, reaction kinetics and deactivation of this key catalytic valorization strategy. In this work, we have analysed the impact in terms of the catalyst regeneration kinetics and energy balance of the unit. These factors are linked to the holistic viability of revamped refineries turned into biorefineries. Deactivated catalysts were obtained in FCC experiments using vacuum gasoil and raw bio-oil. The regeneration kinetics of coke combustion were analysed in a thermobalance, whereas the heats dissipated throughout the combustion (high heating values) were analysed in a calorimeter. Overall, the regenerator does not require major design amendments to treat bio-oil. We found a linear correlation between the higher heating value of the reactants and the coke produced, which enables to predict possible scenarios in the FCC unit. When incorporating higher amounts of bio-oil, the heat balance of the unit changes significantly: the temperature in the regenerator rises up to +36 K, requiring significant energy input for heating the bio-oil but offering the chance to recover more (electrical) energy when the proportion of bio-oil is greater than ca. 50%.

Sulphate Removal from Flotation Process Water Using Ion-Exchange Resin Column System

Water chemistry is one of the most important parameters affecting flotation performance. Various types of ions can dissolve and accumulate in process water depending on ore mineralogy, reagent scheme, grinding medium and chemistry of mine site water. Sulfur-based ions (sulfate, thiosulfate, polythionate) are generally observed in flotation of sulfide ores. High concentrations of these ions may reduce efficiency of the flotation process, causing scale problems. Removal of these ions from process water often requires complex water treatment plants with high capital and operating costs. In this study, partial cleaning of water was investigated as an alternative approach for decreasing high sulphate concentrations of 3000–3800 mg/L down to 1000–1500 mg/L, an acceptable concentration for most sulfide ore flotation plants, by using an ion-exchange resin. For this purpose, detailed adsorption tests were performed using a laboratory-scale column system to determine the most suitable type of resin for adsorption of sulfate and thiosalts, kinetics of adsorption and regeneration of the resins. A strong base anion ion exchange resin (Selion SBA2000) was used in the experiments. The findings from the laboratory scale studies were validated in a Cu-Pb-Zn Flotation Plant in an Iberian mine using a larger scale of column set-up. The results showed that 60–70% of sulphates could be successfully removed from process water. Adsorption capacity of the resin was determined as 80.3 mg SO4/g resin. Concentrations of thiosalts and polythionates were also reduced to nearly zero value from 500 mg/L and 1000 mg/L, respectively. Flowrate of water had a significant effect on adsorption performance. The resin could be regenerated successfully using 2% (w/v) NaOH solution and used multiple times for water treatment.

Carrier-Induced Degradation in Monocrystalline Silicon: Dependence on the Temperature and Irradiance

The dependence of the carrier-induced degradation on the temperature and irradiance is studied. The stability of samples after accelerated degradation and regeneration at different temperature and irradiance are studied also. Minority carrier lifetime and normalized defect density are used to characterize the degradation and regeneration kinetics. The mechanism of temperature and irradiance on degradation is studied and discussed.

Photocatalysts for H2 Generation from Starburst Triphenylamine/Carbazole Donor-Based Metal-Free Dyes and Porous Anatase TiO2 Cube.

A series of novel triphenylamine/carbazole-based D-D-π-π-A dyes DH1-4 and a mesoporous anatase cubic "microcage" TiO2 material (denoted as MC-TiO2 ) were synthesized and combined to obtain dye-sensitized photocatalysts (denoted as DHn/Pt/MC-TiO2 , n=1-4). These catalysts showed better performances in visible-light-driven H2 evolution from water than DHn/Pt/P25-TiO2 catalysts based on commercial P25-TiO2 bulk semiconductor under similar conditions. Compared with P25-TiO2 particles, the porous MC-TiO2 had a large Brunauer-Emmett-Teller surface area, porosity, and exposed {0 0 1} crystal plane, which greatly contributed to the photocatalytic activity. The optimized DH2/Pt/MC-TiO2 photocatalyst exhibited an attractive H2 production rate (16.28 mmol g-1 h-1 based on catalyst mass), and the optimized DH4/Pt/MC-TiO2 photocatalyst showed good stability [turnover number (TON) of 16 699 in 105 h based on dye number], which represents one of the best performances among all reported visible-light-driven heterogeneous catalytic systems. Compared with the other dyes in this series, the high H2 production rate of DH2 on Pt/MC-TiO2 can be attributed to its size-matching effect and thus high dye loading amount, whereas the high TON and durability of DH4/Pt/MC-TiO2 are probably related to the rapid regeneration kinetics of DH4.