Chlorine Pressure Research Articles

Plasmid-mediated transfer of antibiotic resistance genes and biofilm formation in a simulated drinking water distribution system under chlorine pressure

The effects of disinfectants and plasmid-based antibiotic resistance genes (ARGs) on the growth of microorganisms and the plasmid-mediated transfer of ARGs in the water and biofilm of the drinking water distribution system under simulated conditions were explored. The heterotrophic plate count of the water in reactors with 0.1 mg/L NaClO and NH2Cl was higher than in the control groups. There was no similar phenomenon in biofilm. In the water of reactors containing NaClO, the aphA and bla genes were lower than in the antibiotic resistant bacteria group, while both genes were higher in the water of reactors with NH2Cl than in the control group. Chloramine may promote the transfer of ARGs in the water phase. Both genes in the biofilm of the reactors containing chlorine were lower than the control group. Correlation analysis between ARGs and water quality parameters revealed that the copy numbers of the aphA gene were significantly positively correlated with the copy numbers of the bla gene in water and significantly negatively correlated in biofilm (p < 0.05). The results of the sequencing assay showed that bacteria in the biofilm, in the presence of disinfectant, were primarily Gram-negative. 1.0 mg/L chlorine decreased the diversity of the community in the biofilm. The relative abundance of some bacteria that may undergo transfer increased in the biofilm of the reactor containing 0.1 mg/L chlorine.

Long-term trial of a community-scale decentralized point-of-use drinking water treatment system

Two billion people lack access to safely managed drinking water services, many of these are in low/middle income countries where centralised systems are impractical. Decentralised point-of-use drinking water treatment systems offer alternative solutions in remote or resource constrained settings. The main aim of this study was to assess the long-term (3 year) operation and performance of a point-of-use drinking water treatment system (POU-DWTS). A biologically contaminated urban drainage pond was used as a water source and the quality of the produced drinking water was assessed over two independent trials. The decentralised POU-DWTS combined ultrafiltration membranes with disinfection from electrochemically generated hypochlorous acid (HOCl). The operational parameters, such as flow rate, free available chlorine and transmembrane pressure, were monitored in real-time and recorded via a remote monitoring system. Water quality from the source and treated water was assessed over two trial periods within the 3-year operational trial: an 11-week period at the start and a 22-week trial at the end. All water samples were assessed for a range of basic, chemical, microbiological and metal water quality parameters. The results demonstrate that the decentralised POU-DWTS is capable of continuously producing high quality drinking water when HOCl is continuously used to dose water prior to entering the ultrafiltration [UF] membranes. Over the 3-year operational study, the continuous dosing of HOCl pre-UF membranes resulted in stable permeability, indicating no occurrences of irreversible biofouling within the UF membranes and that good membrane ‘health’ was maintained throughout. As such, there was no need to replace the UF membranes nor undertake acid/alkaline chemical cleans at any point throughput the three-year study. The POU-DWTS continuously produced high quality drinking water, resulting in 6453 m3 of drinking water produced over the trial period, that met international water quality standards, at a community scale within the location studied.

Response mechanisms of pipe wall biofilms in water supply networks under different disinfection strategy pressures and the effect of mediating halogenated acetonitrile formation

Residual chlorine and biofilm coexistence is inevitable in drinking water transmission and distribution networks. Understanding the microbial response and its mediated effects on disinfection byproducts under different categories of residual chlorine stress is essential to ensure water safety. The aim of our study was to determine the response of pipe wall biofilms to residual chlorine pressure in chlorine and chloramine systems and to understand the microbially mediated effects on the formation and migration of haloacetonitriles (HANs), typical nitrogenous disinfection byproducts. According to the experimental results, the biofilm response changes under pressure, with significant differences noted in morphological characteristics, the extracellular polymeric substances (EPS) spatial structure, bacterial diversity, and functional abundance potential. Upon incubation with residual chlorine (1.0 ± 0.2 mg/L), the biofilm biomass per unit area, EPS, community abundance, and diversity increased in the chloramine group, and the percentage of viable bacteria increased, potentially indicating that the chloramine group provides a richer variety of organic matter precursors. Compared with the chloramine group, the chlorination group exhibited increased haloacetonitrile formation potential (HANFP), with Rhodococcus (43.2%) dominating the system, whereas the prediction abundance of metabolic functions was advantageous, especially with regard to amino acid metabolism, carbohydrate metabolism, and the biodegradation and metabolism of foreign chemicals. Under chlorine stress, pipe wall biofilms play a stronger role in mediating HAN production. It is inferred that chlorine may stimulates microbial interactions, and more metabolites (e.g., EPS) consume chlorine to protect microbial survival. EPS dominates in biofilms, in which proteins exhibit greater HANFP than polysaccharides.

Modeling of titania slag carbochlorination

AbstractTitanium tetrachloride, a product of titanium slag chlorination in the presence of carbon, is an intermediate product for high grade TiO2 pigment preparation and titanium metallurgy. The chlorination of carbon‐titanium dioxide pellets with gas mixtures of N2 and Cl2 was studied at high temperatures (750‐1050 oC) and various partial pressures of chlorine (0.1‐0.8 atm) in a fixed‐bed reactor with the inner diameter of 80 mm. Based on the comparison of experimental and computational studies, a principal mechanism of the TiO2 carbochlorination was proposed, and chlorine concentration profile at different reaction conditions was clearly understandable. Porous diffusion of chlorine inside the C‐TiO2 pellet structure played an important role in the kinetic reaction model.

Homo- and hetero-epitaxial growth of β-gallium oxide via GaCl3-O2-N2 system

β-gallium oxide (Ga2O3) was grown by tri-halide vapor phase epitaxy (THVPE) using gaseous GaCl3 and O2 as precursors. The growth rate linearly increased with increasing ratios of input partial pressure of O2 against GaCl3, and further, it was found the β-Ga2O3 growth by THVPE successfully suppressed the gas phase reaction and decreased Ga2O3 particles observed in halide vapor phase epitaxy (HVPE) by changing the ratio of the supply partial pressure of the second chlorine against that of the first during the GaCl3 generation. An epilayer with high crystalline quality and high purity equivalent to that grown via HVPE was obtained by newly developed THVPE without any particle formation.

THERMODYNAMIC RIPHEAN-PHANEROZOIC EVOLUTION OF THE UPPER GEOSPHERES: ATMOSPHERE, EARTH’S CRUST, HYDROSPHERE AND BIOSPHERE

A new concept of thermodynamic Riphean-Phanerozoic evolution of upper geospheres: atmosphere, earth’s crust, hydrosphere and biosphere is presented. This evolution from Riphean to Phanerozoic is determined by the consistent cooling of the earth’s surface. For the hydrosphere (starting from 2.0 billion years), this is manifested in the appearance and increase in the Riphean and Phanerozoic of the mass of liquid water (mainly in the seas and oceans), which gradually decreases its acidity and increases its oxidizing properties. The primary atmosphere in the Early Proterozoic about 2 billion years ago mainly consisted of gaseous water and chlorine, with water gas pressure at about 230 bar and the chlorine pressure at about 5 bar at a temperature of 375 °С. At this, an acidic hydrosphere (pH = 0.15) was formed, with a pressure of about 1 bar of free oxygen in the atmosphere. In the acidic ocean in Riphean to Vendian, with little sedimentation, almost all components were removed from the rocks of the ocean floor, except for silica, with the formation, for example, of Ovruch quartzites. Since Vendian (from 620 million years ago, and especially in the Phanerozoic), the land area and the height of the continents rapidly increased, which are eroded by the seas with the deposition of thick sediments, including carbonates. At the same time, more and more volcanics are accumulating, which is associated with active plate tectonics. The modern composition of the Earth’s atmosphere was formed due to chemical reactions of oxidation in the hydrosphere and atmosphere and volcanism, followed by a change in pH, Eh, and temperature (below 60 °С) in the hydrosphere and atmosphere and the appearence of life. This led to a decrease in carbon dioxide in the hydrosphere and atmosphere, especially due to plants, as well as to stabilization of the oxygen content in the atmosphere at 0.2 bar and to the predominance in it of nitrogen, which has substantial stability in the atmosphere Views of some geologists that Archean banded ferruginous quartzites have originated as sedimentary rocks are contradicted by significant temperatures in the surface layers of the Earth in the Archean (about 600-700 °С), when active processes of regional metamorphism and gas formation took place.

Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Xylazine and remifentanil in constant rate infusion (CRI) could be used for sedation in horses without adverse effects. The objective was to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine and remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed after 3 minutes by a CRI of xylazine and remifentanil (0.65 mg/kg/h and 6 μg/kg/h, respectively) was administered in 10 healthy horses for 60 minutes. Sedation, ataxia, and cardiopulmonary, hematological, and blood gases variables were evaluated. Heart rate decreased significantly during the first 25 minutes after CRI of xylazine and remifentanil, whereas the respiratory rate showed a significant decrease at 20 minutes and remained significantly low until the endpoint. There were no statistically significant fluctuations in blood arterial pressure, blood pH, partial pressure of arterial carbon dioxide, lactate, creatinine, calcium, chlorine, and sodium, compared with baseline values. Blood partial pressure of arterial oxygen and bicarbonate values were significantly higher compared with baseline values, whereas potassium decreased. Sedation and ataxia developed immediately after the administration of xylazine in all horses. All horses recovered successfully within 10 minutes after interruption of the CRI of xylazine and remifentanil, with no ataxia. No adverse effects were observed. The use of a combination of xylazine and remifentanil as sedation protocol has no adverse effects at the described dosage.

Insights on the stability of cuprous chloride under high pressure: An equilibrium ab initio atomistic thermodynamics study

Density functional theory, in conjunction with ab initio atomistic thermodynamics, were used to investigate the stability of the low index cuprous chloride surfaces, and predict the morphology of CuCl nanocrystals under high pressures of chlorine. The rocksalt orientation of the lattice was adopted to resemble a CuCl crystal under high pressure. Under Cl-lean conditions, the defective CuCl(100)+Cl structure was found to be the most stable configuration among all surfaces investigated. Under Cl-rich conditions, a flawless, CuCl(111) surface with Cl-termination becomes the most stable configuration. It was shown that in a diluted chlorine environment, the CuCl in zinc blende structures are more stable than the CuCl in rocksalt configurations, while under a chlorine rich environment, the CuCl in rocksalt structures are more stable than the CuCl in zinc blende configurations. At low pressure of chlorine, it was found that the (100) facets are the most dominant to the Wulff construction, giving the crystal a coffin shape. As the pressure of chlorine increases, however, the involvement of the (111) facet increases giving the crystal a semi dodeca-hedron shape. At high pressure of chlorine, the major contributors to the Wulff construction were found to be the (111) facets, resulting in the formation of dodeca-hedron nanocrystals.

Selective extraction of vanadium from pre-oxidized vanadium slag by carbochlorination in fluidized bed reactor

Abstract Most of the vanadium (V) is industrially extracted from vanadium slag, a byproduct in steelmaking, via the sodium roasting-water leaching or calcification roasting-acid leaching process, which usually suffers from environment pollution or decrease in product purity. In this paper, a novel process of vanadium extraction featuring carbochlorination of pre-oxidized vanadium slag with chlorine (Cl2) and nitrogen (N2) mixture in a fluidized bed reactor was proposed. And the selectivity between vanadium and iron (Fe) in the slag was primarily concerned, due to the high content of the latter in vanadium slag. The thermodynamic analysis reveals that there exists a favorable zone for selective chlorination of V from Fe compounds. Subsequently, carbochlorination experiments were conducted to investigate the influences of chlorination temperature and time, addition amount of petroleum coke and pressure fraction of chlorine on extraction of V and Fe. And 87.47% of V together with 18.79% of Fe can be extracted from the pre-oxidized vanadium slag by chlorination at 650 °C for 120 min with chlorine pressure fraction [P(Cl2)/P(Cl2+N2)] = 0.5 and petroleum coke mass fraction in raw materials for chlorination Rc = 10%. The results demonstrate that the selective chlorination process has good potential to recover vanadium from vanadium slags in efficient and clean ways.

Electronic Absorption Spectra of Uranium(V) Species in Fused Alkali Chlorides

Alkali chloride based melts can be used in pyrochemical reprocessing various types of spent nuclear fuels, especially those of fast neutron reactors. There is a possibility of refabricating uranium oxide or mixed uranium-plutonium oxide fuel by electrodeposition of UO2 or (U,Pu)O2 from chloride melts containing uranyl (or a mixture of uranyl and plutonyl) ions. At high temperatures uranyl chloro species undergo decomposition yielding UO2 + ions and finally UO2. Increasing temperature and lowering partial pressure of chlorine in the atmosphere above the melt shifts the equilibrium towards the decomposition products. In fact, uranium(V) ions are often present in uranyl-containing melts and, if unaccounted for, result in increased current efficiency of UO2 electrodeposition process. Electronic absorption spectroscopy allows a convenient method for detecting and measuring concentration of uranium(V) in uranyl-containing electrolytes. Absorption spectra of uranium(V) species in fused salts were reported over fifty years ago but still remain the least studied especially from the quantitative side concerning molar absorption (extinction) coefficient values. Uranium(V), f 1-electron configuration, absorbs in the visible region of the spectrum and the spectra have there two broad bands with the maxima around 620 and 775 nm not overlapping with the absorption of uranium(VI) ions, Fig. These bands correspond to two f–f transitions in UO2Cl4 3– complex ion, i.e., φ5u → 3π1u and φ5u → 3π3u. The aim of the present work was studying the effect of temperature and cationic melt composition on the absorption spectra of uranium(V) ions and determining molar absorption coefficients. The measurements were performed in individual alkali chlorides and their mixtures of various compositions including LiCl, CsCl, LiCl–KCl, LiCl–KCl–CsCl, NaCl–KCl, NaCl–CsCl. The temperature range varied from 350 to 850 oC depending on the melt. Uranium(V) ions were obtained in situ by reducing uranium(VI) ions with hydrogen. Uranium dioxide was also produced but no soluble uranium(IV) species in the melt were detected. After recording the spectrum a sample of the melt was taken and analyzed for the total uranium concentration and the mean uranium oxidation state which always was between five and six. From that, concentration of U(V) and V(VI) ions in the melt were calculated and U(V) extinction coefficients determined. The results obtained allow determination of U(V) concentration in technological electrolytes. Acknowledgement. This work was supported by the Ministry of Education and Science of the Russian Federation (project No. 4.5062.2017/8.9). Fig. Electronic absorption spectra of LiCl–KCl based melts containing U(VI) ions (line 1) and a mixture of U(VI) and U(V) ions at a 3 : 2 ratio (line 2). Total uranium concentration 0.038 mol/l, T = 550 oC. Figure 1

An Electrochemical Study of Divalent Ytterbium Species in NaCl–KCl and NaCl–KCl–Cscl Based Melts

A usual oxidation state of rare earth metals in chloride melts is +3. A number of lanthanides (particularly europium, ytterbium, samarium, and thulium) can also form thermodynamically stable ions in the oxidation state +2. Ln(II)/Ln(III) redox processes are normally investigated employing transient electrochemical techniques where the formation of Ln(II) ions is limited to the near electrode surface layer. The present work was aimed at studying the reduction of Yb(III) ions in the bulk of the melt and assessing the stability of Yb(II) chloro species in molten chloride media. The experiments were carried out in the melts based on NaCl–KCl–CsCl eutectic and NaCl–KCl equimolar mixtures at 550–850 and 700–850 oC, respectively, employing stationary and transient electrochemistry and high temperature spectroscopy methods. Concentration of ytterbium in the melt was varied from 1 to 10 wt. %. Ytterbium(II)/(III) formal standard redox potentials were obtained from the results of electrochemistry measurements (cyclic voltammetry and potentiometry). Electronic absorption spectra of Yb(II) species were recorded both in molten and quenched electrolytes. Reduction of Yb(III) to Yb(II) can be achieved by shifting the equilibrium of the reaction YbCl6 3– + Cl– ↔ YbCl6 4– + ½ Cl2 to the right by lowering partial pressure of chlorine in the atmosphere above the melt. Here, zirconium, as a metal with high affinity for chlorine, was used as a getter. The reduction process was followed by measuring the absorption spectra. As the reaction proceeded, the color of the melt changed from colorless of YbCl6 3– to brown. Analysis of the resulting melts showed that the mean oxidation state of ytterbium was below three, the value depended on temperature, duration of the reduction and melt composition. Increasing temperature or reduction time expectedly resulted in a greater degree of reduction. Ytterbium(III) can also be reduced with a suitable reductant and hydrogen was chosen here as an example. Sparging the melt containing Yb(III) ions with hydrogen resulted in decreasing mean oxidation state of ytterbium: YbCl6 3– + Cl– + ½ H2 ↔ YbCl6 4- + HCl. The course of the reduction process was followed by measuring the redox potential. The efficiency of hydrogen as a reducing agent was comparable to the thermal decomposition in the presence of zirconium getter. Hydrogen reduction was also a very convenient way of preparing the melts with a low Yb(II) content for spectroscopy measurements. Another way of reducing Yb(III) to Yb(II) is electrolysis: YbCl6 3– + e– ↔ YbCl6 4-. In a series of preliminary experiments Yb(II)/Yb(III) redox potentials were determined from the results of cyclic voltammetry measurements. Reduction of Yb(III) to Yb(II) was carried out by potentiostatic electrolysis under an inert (argon) or a reducing (hydrogen) atmosphere with and without agitating the melt. The lowest mean oxidation state of ytterbium in the melt thus obtained was 2.33 showing that two thirds of Yb(III) could be reduced to Yb(II). Acknowledgement. This work was supported by the Ministry of Education and Science of the Russian Federation (project No. 4.5062.2017/8.9).

An electron transfer in CuCl-CuCl2 melt at different Cl2 partial pressures

Electron and ion transference numbers, conductivity, and Cu+/Cu2+ concentration ratio in the CuCl-CuCl2 melt are measured at temperature of 560 °C and partial pressure of chlorine from 0.1 to 1 atm. The electron transference numbers and the total conductivity grow with chlorine partial pressure; that is accompanied by decreasing of ionic conductivity both in contribution and absolute values. The total conductivity changes from ∼6 to ∼8 S cm−1 while pCl2 increases from 0.1 to 1 atm. The electron transference numbers increase from 67 to 95% in the same chlorine partial pressure range. The electronic conductivity is evaluated by two independent methods. Values of electronic conductivity obtained from the concentrations of Cu2+ ions are close to that obtained by Faraday efficiency measurements.

Tuberculosis/cryptococcosis co-infection in China between 1965 and 2016

Cases of tuberculosis/cryptococcosis co-infection are rapidly increasing in China. However, most studies addressing this co-infection have been published in Chinese journals, and this publication strategy has obscured this disease trend for scientists in other parts of the world. Our investigation found that 62.9% of all co-infection cases worldwide were reported in the Chinese population (n=197) between 1965 and 2016, and 56.3% of these Chinese cases were reported after 2010. Nearly all cases originated from the warm and wet monsoon regions of China. HIV-positive subjects tended to correlate with more severe manifestations of a tuberculosis/cryptococcosis co-infection than those without HIV. Notablely, dual tubercular/cryptococcal meningitis was the most frequent (54.0%) and most easily misdiagnosed (95.2%, n=40/42) co-infection. We also found that the combined use of cerebrospinal fluid pressure and concentrations of glucose, protein and chlorine might be an inexpensive and effective indicator to differentiate tubercular/cryptococcal co-infection meningitis from tubercular meningitis and cryptococcal meningitis.Emerging Microbes & Infections (2017) 6, e73; doi:10.1038/emi.2017.61; published online 23 August 2017

Selective chlorination of CaO from titania slag by CO+Cl2 mixtures in fluidized bed

This paper presents a facile approach to selectively decrease the CaO content in titania slag from 1.09 to 0.18wt.% under a selective chlorination atmosphere of Cl2 and CO. Thermodynamic analysis indicated that a predominance area exists to selectively chlorinate CaO with a low reduction potential. The intrinsic chlorination kinetics indicated that both the high partial pressure of chlorine and high temperature were advantageous to increase the chlorination selectivity of CaO. Under the guidance of the thermodynamic and intrinsic kinetics, selective chlorination kinetics of CaO from titania slag were conducted at 1173–1273K and were represented by the pore-blocking rate law. The present study indicated that a high concentration of reactant gases with a low reduction potential at high temperature could simultaneously overcome the inner mass transfer resistance while maintaining a high chlorination selectivity. The optimized partial pressures of Cl2 and CO were 0.8 and 0.2atm, respectively, and the temperature was 1273K.

Stability field diagrams for Ln–O–Cl systems

Isothermal stability field diagrams for Ln−O−Cl systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) are developed by taking partial pressures of volatile components oxygen and chlorine as variables. Thermodynamic properties of all the oxides and trichlorides (LnCl3) are available in the literature. However, data for oxychlorides (LnOCl) and dichlorides (LnCl2) are limited. Based on systematic trends in stability of these compounds across the lanthanide series, missing data are estimated to construct the diagrams for 13 Ln−O−Cl systems at 1000 K. All the lanthanide elements form stable LnCl3 and LnOCl. Dichlorides of Nd, Sm, Eu, Dy, Tm and Yb are stable. For systems in which dichlorides are unstable (Ln = La, Ce, Pr, Gd, Tb, Ho, Er), the LnOCl is in equilibrium with the metal (Ln) and the stability field of LnOCl is sandwiched between those of oxides and trichlorides. Stability field diagrams of lanthanide systems forming stable LnCl2 are of two kinds: in the first kind (Ln = Nd, Dy) the stability fields of Ln and LnOCl are in contact and the stability field of LnOCl separates the fields of chlorides and oxides. In diagrams of the second kind (Ln = Sm, Eu, Tm, Yb) there is a direct equilibrium between the oxides and dichlorides at low partial pressures of oxygen and chlorine. There is no contact between the stability fields of Ln and LnOCl; the stability field of LnOCl intervenes between the oxide and chloride phases only at higher partial pressures.

Integrated chemical and toxicological investigation of UV-chlorine/chloramine drinking water treatment.

As the use of alternative drinking water treatment increases, it is important to understand potential public health implications associated with these processes. The objective of this study was to evaluate the formation of disinfection byproducts (DBPs) and cytotoxicity of natural organic matter (NOM) concentrates treated with chlorine, chloramine, and medium pressure ultraviolet (UV) irradiation followed by chlorine or chloramine, with and without nitrate or iodide spiking. The use of concentrated NOM conserved volatile DBPs and allowed for direct analysis of the treated water. Treatment with UV prior to chlorine in ambient (unspiked) samples did not affect cytotoxicity as measured using an in vitro normal human colon cell (NCM460) assay, compared to chlorination alone when toxicity is expressed on the basis of dissolved organic carbon (DOC). Nitrate-spiked UV+chlorine treatment produced greater cytotoxicity than nitrate-spiked chlorine alone or ambient UV+chlorine samples, on both a DOC and total organic halogen basis. Samples treated with UV+chloramine were more cytotoxic than those treated with only chloramine using either dose metric. This study demonstrated the combination of cytotoxicity and DBP measurements for process evaluation in drinking water treatment. The results highlight the importance of dose metric when considering the relative toxicity of complex DBP mixtures formed under different disinfection scenarios.

Modelling approach to quickly assess polyethylene ageing by chlorine dioxide in distribution systems

A prediction model for the life of polyethylene (PE) has been developed as a function of chlorine dioxide concentration and pressure. It can be coupled with an existing hydraulic model covering chlorine dioxide residuals and pressure values in the network. It allows a quick identification of the areas of highest PE failure risk. The methodology is applied successfully to a real distribution system in France.

Kinetic Study of Europium Oxide Chlorination

The kinetics of europium oxide (Eu2O3) chlorination using gaseous chlorine as a chlorination agent was studied between 523 K and 1223 K (250 °C and 950 °C). The relative mass change during the chlorination reaction was continuously monitored using a high resolution thermogravimetric system. The starting temperature for the reaction of Eu2O3(s) with chlorine was determined at about 523 K (250 °C) with the formation of solid europium oxychloride (EuOCl). For temperatures above 1123 K (850 °C), the EuOCl(s) is chlorinated producing EuCl3(l). The influence of gaseous flow rate, sample mass, chlorine partial pressure, and temperature on the reaction rate was analyzed. The results showed that for 673 K (400 °C) and temperatures below, the system is under chemical control. Concerning the influence of chlorine partial pressure, it was determined that pressures greater than 50 kPa do not modify the kinetic regime. For the experiment at 673 K (400 °C), it was found that the chlorination rate was proportional to a potential function of the partial pressure of chlorine whose exponent is 0.54. The conversion curves were analyzed with the Johnson–Mehl–Avrami description. Intrinsic activation energy of 115 kJ mol−1 was obtained for the temperature range of 573 K to 673 K (300 °C to 400 °C). Finally, a global rate equation that includes these parameters was developed.

Kinetic study of neodymium oxide chlorination with gaseous chlorine

The kinetics of the chlorination of neodymium oxide has been investigated by thermogravimetry between 312°C and 475°C, and for partial pressures of chlorine ranging from 10kPa to 50kPa. The starting temperature for the reaction of neodymium oxide with chlorine was determined to be about 250°C, leading to neodymium oxychloride as product. The results showed that, for temperatures below 425°C, the system is under chemical control and the formation of the oxychloride progresses through a nucleation and growth mechanism. The influence of chlorine mass transport through the bulk gas phase and through the boundary layer on the overall reaction rate was analyzed. In the absence of these two mass-transfer steps, a reaction order of 0.39 with respect to chlorine partial pressure, and an activation energy of 161±4kJmol−1 were determined. A complete rate equation has been successfully developed.

Kinetic study of Hubnerite (MnWO4) chlorination

The kinetics of Argentinean Hubnerite (MnWO4) chlorination using gaseous chlorine as chlorination agent was studied between 750 and 950°C. The relative mass change during the chlorination reaction was continuously monitored using a high resolution thermogravimetric system. The starting temperature for the reaction of the manganese tungstate with chlorine was determined at about 650°C. The influence of gaseous flow rate, sample mass, chlorine partial pressure, and temperature on the reaction rate was analyzed. The dependence of the reaction rate with sample mass clearly indicates that the reaction is not occurring under chemical control, so the reaction proceeds under mixed control for sample masses greater than 0.5mg. In those conditions, an apparent activation energy of 198±9kJmol−1 was obtained with an isoconversional method. Concerning the influence of chlorine partial pressure, it was determined that pressures greater than 35kPa do not modify the kinetic regime. For the experiment at 850°C, it was found that the chlorination rate was proportional to a potential function of the partial pressure of chlorine whose exponent is around 0.85. Finally, a global rate equation that includes these parameters was developed.