Letteratura scientifica selezionata sul tema "Liquid iron"

ABSTRACT Avian pathogenic Escherichia coli (APEC) strains are a subset of extraintestinal pathogenic E. coli (ExPEC) strains associated with respiratory infections and septicemia in poultry. The iroBCDEN genes encode the salmochelin siderophore system present in Salmonella enterica and some ExPEC strains. Roles of the iro genes for virulence in chickens and production of salmochelins were assessed by introducing plasmids carrying different combinations of iro genes into an attenuated salmochelin- and aerobactin-negative mutant of O78 strain χ7122. Complementation with the iroBCDEN genes resulted in a regaining of virulence, whereas the absence of iroC, iroDE, or iroN abrogated restoration of virulence. The iroE gene was not required for virulence, since introduction of iroBCDN restored the capacity to cause lesions and colonize extraintestinal tissues. Prevalence studies indicated that iro sequences were associated with virulent APEC strains. Liquid chromatography-mass spectrometry analysis of supernatants of APEC χ7122 and the complemented mutants indicated that (i) for χ7122, salmochelins comprised 14 to 27% of the siderophores present in iron-limited medium or infected tissues; (ii) complementation of the mutant with the iro locus increased levels of glucosylated dimers (S1 and S5) and monomer (SX) compared to APEC strain χ7122; (iii) the iroDE genes were important for generation of S1, S5, and SX; (iv) iroC was required for export of salmochelin trimers and dimers; and (v) iroB was required for generation of salmochelins. Overall, efficient glucosylation (IroB), transport (IroC and IroN), and processing (IroD and IroE) of salmochelins are required for APEC virulence, although IroE appears to serve an ancillary role.

Imidazolium ionic liquids containing acetylacetone, thenoyltrifluoroacetone, or 8-hydroxyquinoline, respectively, were used as the extracting agents for the separation of traces of iron (III) from its aqueous solutions with or without citric and oxalic acids. The results show that 8-hydroxyquinoline in imidazolium ionic liquids extract iron quantitatively from all the tested solutions including complexing ones, regardless of indications of unexpected iron behavior/speciation.

The smooth drainage of produced iron and slag is a prerequisite for stable and efficient blast furnace operation. For this it is essential to understand the drainage behavior and the evolution of the liquid levels in the hearth. A two-dimensional Hele–Shaw model was used to study the liquid–liquid and liquid–gas interfaces experimentally and to clarify the effect of the initial amount of iron and slag, slag viscosity, and blast pressure on the drainage behavior. In accordance with the findings of other investigators, the gas breakthrough time increased and residual ratios for both liquids decreased with an increase of the initial levels of iron and slag, a decrease in blast pressure, and an increase in slag viscosity. The conditions under which the slag–iron interface in the end state was at the taphole and not below it were finally studied and reported.

Background: In recent years, iron supplementation has increased significantly because of the damaging systemic effects of iron deficiency anaemia (IDA) being reported. The standard first-line therapy is oral iron tablets, with over 70% of recipients experiencing gastrointestinal adverse effects. Methods: This recent review of high-quality literature compares the effectiveness and adverse effects of tablet and liquid forms of iron supplementation in patients with IDA. Findings: The evidence to date indicates that both forms of iron supplementation are equally effective. However, the literature consistently and strongly supports the use of the liquid form of iron supplementation (ferrous sulfate) over the tablet form (ferrous sulphate or ferrous fumarate) in terms of adverse effects. Conclusions: Healthcare professionals should consider recommending the use of liquid iron formulation for the management of IDA and switch patients to this form if they experience gastrointestinal adverse effects. This may help to effectively manage IDA.

The simplest model of the structure and interatomic interaction is applied to nitrogen solutions in liquid alloys of Fe – Ni system, which earlier (2019) was used by the authors for nitrogen solutions in alloys of Fe – Cr system. The principles of statistical mechanics are used in this model. Thus, three formulas were obtained. The first formula expresses the Sieverts law constant for the solubility of nitrogen in liquid nickel through a similar constant for the solubility of nitrogen in liquid iron and the Wagner interaction coefficient of nitrogen with nickel in low-concentration liquid iron-base alloys. The second formula expresses the partial enthalpy of dissolution of nitrogen in liquid nickel during the formation of an infinitely dilute solution through a similar value for dissolution of nitrogen in liquid iron and the Wagner interaction coefficient of nitrogen with nickel in iron-base liquid alloys. The third formula expresses the Wagner interaction coefficient of nitrogen with iron in low-concentration liquid nickel-base alloys through the Wagner interaction coefficient of nitrogen with nickel in liquid iron-base alloys. The constant of the Sieverts law for the solubility of nitrogen in liquid iron at T = 1873 K is assumed to be 0.044 mass. %. The partial enthalpy of dissolution of nitrogen in liquid iron assumed to be 5.0 kJ/mol. For Wagner interaction coefficient of nitrogen with nickel in iron-base liquid alloys at 1873 K three variants of values were studied: 2.4, 2.6, and 2.85. For the first option, theoretical value of the Sieverts law constant for solubility of nitrogen in liquid nickel at T = 1873 K, equal to 0.00195 mass. % was obtained. Theoretical value of the enthalpy of dissolution of nitrogen in liquid nickel is 52.7 kJ/mol. Theoretical value of the Wagner interaction coefficient of nitrogen with iron in nickel-base liquid alloys is –4.0. The agreement of theory with experiment seems to be satisfactory.

Interaction of liquid copper with sintered iron is important in brazing, liquid phase sintering and infiltration. In brazing, the penetration of liquid copper into the pores is to be `avoided', whereas in infiltration processes it is `encouraged', and in liquid phase sintering it should be `controlled' so that optimum mechanical properties are achieved. The main objective of the research is to model the interaction by studying the effect of the process variables on the mechanisms of copper interaction in Fe-Cu and Fe-Cu-C systems. This involves both theoretical and experimental considerations. Dilatometric investigations at 950, 1125 and 1200oC, together with metallographic analyses were carried out to clarify the copper growth phenomenon. It is shown that penetration of liquid copper into the iron grain boundaries is the major cause of dimensional changes. Infiltration profiles revealed that copper penetration between the iron interparticle contact points and along iron grain boundaries is a rapid process. The extent of copper penetration depends on the dihedral angle. Large dihedral angles hinder, and small angles promote copper penetration into the grain boundaries. Dihedral angle analysis shows that the addition of 0.6wt.% graphite reduces the number of zero dihedral angle from 27 to 3o and increases the mean dihedral angle from 9.8 to 41.5o. The dihedral angle was lowest at 1125oC and then increased to higher values as the system approached its equilibrium condition. Elementally mixed (E.M.) Fe-Cu compacts showed a rapid expansion at the copper melting point. However, graphite additions reduced compact growth by increasing the mean dihedral angle. In order to reduce the copper growth phenomenon, iron powder was coated with a thin layer of copper by an immersion coating (I.C.) technique. The dilatometric curves revealed an overall shrinkage in the I.C. compacts compared to their corresponding E.M. compacts. Multiple regression models showed that temperature had the most effect on dimensional changes and density had the most contributing effect upon the copper penetration area in the infiltrated powder metallurgy compacts.

Cast iron and steel alloys are commonly used for tooling and structural components in Al production, Al die-casting and the aluminizing industry due to their favourable properties including high strength, good formability and low cost. However, the iquid Al corrosion of these materials is one of the crucial concerns in maintaining the efficient production. Al is produced by the electrolytic smelting of alumina. Cast iron and/or cast steel pipes - commonly known as „tapping pipes‟ - are used to extract the liquid Al produced by smelting. Tapping pipes mainly degrade by material loss because liquid Al reacts with nearly all metals. Failure of tapping pipes is a significant contributor to the maintenance expenses; therefore, the primary aim of this research is to develop a material to enhance the life time of tapping pipes. Various test methods were developed in order to examine the effect of molten Al environment on cast iron and steel alloys. The corrosion resistance of these alloys was determined under different conditions of Al flow and temperature. The intermetallic compounds formed by exposing the ferrous to liquid Al were characterized using the Energy Dispersive X-ray Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) techniques. The formation, growth and nature of reaction products were revealed to establish a link to the liquid Al corrosion resistance. A relationship between the chemical composition and liquid Al corrosion resistance of cast irons could not established in the past. In the present work, the corrosion rate was found to depend upon the graphite morphology and fraction of each Fe-C phase of cast iron matrix, which can be controlled by selecting the chemical composition. Moreover, present research suggested the guidelines for producing a cast iron with enhanced liquid Al corrosion resistance. The presence of C-rich phases, graphite flakes and cementite was found to be effective in enhancing the liquid Al corrosion resistance of gray cast irons. Conversely, a higher Si content was found to enhance the susceptibility of cast irons to liquid Al corrosion. The corrosion mechanisms for ferrous alloys in liquid Al are not fully understood. Thus the subsequent analysis of the dissolution data was supported by investigating the reaction products formed between Al and substrate materials. In addition to commonly existent ε-Fe2Al5 and ζ-FeAl3 phases, the formation of Al4C3 and κ-Fe3AlC compounds was confirmed for the first time in the intermetallic layers of ferrous alloys. The Fe3Si phase in the intermetallic layers of high Si cast irons was found, which was believed to facilitate the high corrosion rates of high Si cast irons. Moreover, the mechanism by which C in Fe-substrates affects the liquid Al corrosion resistance can be better understood given the present work. Furthermore, the analysis presented here gives an understanding of the nature, growth and dissolution of intermetallic compounds in several cast iron alloys. Higher Si additions to cast irons played an important role in molten metal corrosion by accelerating the material loss and changing the nature of intermetallic layers. The results of this study clearly indicated that the dissolution and the growth of intermetallic compounds are interrelated and the dissolution and/or spallation of the intermetallic layers may be the primary mode of liquid Al corrosion of ferrous alloys.

The present work was initiated to investigate runnerrefractory corrosion by molten steel. The aim was to understandthe mechanism of inclusion formation during ingot casting. Thework is also of interest to other unit processes in steelmaking, where refractory corrosion and erosion are seriousproblems. The oxides investigated in the present work werealumina, silica and mullite, which are the main components inrunner refractory. In addition, industrial refractory materialwas investigated.

Two types of experiments were conducted. The first, "rodexperiments", involved dipping a rod of the oxide into an ironbath containing varying amounts of oxygen. After quenching, therods were examined through SEM/EDS analysis. In the second setsof experiments, the wetting behaviour of molten iron onrefractory oxides was investigated by means of the sessile-dropmethod. The reactions were followed in static as well asdynamic modes through contact angle measurements. Temperatureand oxygen partial pressure were, besides time the parametersthat were investigated in the present study. Oxygen partialpressure was defined by introducing a gas mixture of CO-CO₂-Ar into the furnace.

The experimental studies were preceded by a thermodynamicinvestigation of the refractory systems, in order to get afundamental understanding of the reactions that occurred. Phasestability diagrams for the systems were constructed based onthe data available in literature. The diagrams showed that thereaction between alumina and oxygen containing iron would leadto the formation of hercynite at a critical oxygen level in themetal. With silica, the reaction would lead to the formation offayalite. In the mullite case, the reaction products would behercynite at moderate oxygen levels in the melt and hercynitetogether with fayalite at slightly higher oxygenpotentials.

For all substrates, the contact angles started decreasing asthe surface-active oxygen came into contact with the iron drop.At a critical level of oxygen in the metal, a reaction productstarted forming at the drop/substrate interface. The reactionproducts were identified through SEM/EDS analysis and werefound to be in agreement with thermodynamic predictions. In thecase of SiO₂substrate, there were also deep erosion tracksalong the periphery of the drops, probably due to Marangoniflow.

Alumina-graphite refractory reactions with molten iron werealso investigated through Monte Carlo simulations. The resultsshowed that, with increased alumina content in the refractory,the carbon dissolution into the melt decreased. Further, thewetting behaviour at the interface was found to be an importantfactor to considerably reduce the carbon dissolution fromalumina-graphite refractories.

The experimentation was extended to the commercialrefractories used in the ingot casting process at UddeholmTooling AB, Sweden. The analysis of the plant trial samplesindicates that there is less likelihood of a strong corrosionof the refractories that could lead to a significant populationof inclusions in the end product. The impact of the presentexperimental results on refractory erosion is discussed. Theimportance of the results to clean steel processing anddevelopment of new generation refractories are alsopresented.

Iron is an essential nutrient for growth of photosynthetic microorganisms such as cyanobacteria and algae. Iron is required for proteins involved in the important processes of carbon and nitrogen assimilation. Low concentrations of iron in cultures or natural waters can lead to iron limitation which affects many aspects of algal metabolism. In natural waters, iron limitation can have effects on the patterns and rates of primary productivity. The cellular content of certain proteins can be affected by media iron concentrations. Methods have been used that assay components of the cell as an indirect measure of iron nutritional status. For example, spectroscopy can be performed to determine the cellular concentration of iron-containing proteins involved in photosynthesis. Organisms grown in media that imitate natural conditions, or organisms collected from their natural habitat are usually dilute. Methods that assay iron nutritional status such as spectroscopy and column chromatography require large sample sizes which are difficult to obtain from natural samples. In addition, methods that utilize techniques such as immunology or radioactive labelling are complex and time-consuming. These considerations led to the necessity of developing a technique that would be simple, rapid and effective on dilute samples. The method developed here utilized fast protein liquid chromatography (FPLC), which fulfilled these requirements. A complete analysis could be done within two to three hours with minimal sample treatment. The FPLC was simple to operate and was effective on a sample containing less than 100 μg of protein. Some photosynthetic organisms, when iron-depleted, can produce the flavin-containing protein flavodoxin (Flv). This protein substitutes for the iron-containing protein ferredoxin (Fd) in Fd-dependent reactions such as the light-induced reduction of NADP. The FPLC technique identified and quantified, in relative terms, Fd and Flv in the cell. Optical spectroscopy was used to verify FPLC retention time assignments. The results illustrated how the FPLC could be used to observe the changes in relative Fd and Flv content as a function of media iron concentration in cultures of the cyanobacterium Anabaena grown in the laboratory. It was found that Fd content decreased and Flv content increased with decreasing media iron concentration. In addition, samples of the cyanobacterium Trichodesmium collected from the ocean near Barbados were analyzed using FPLC to assay relative Fd and Flv content. By analogy with Anabaena, Fd and Flv retention times were identified. Using this technique conclusions could be drawn regarding the changing iron nutritional status of Trichodesmium in its natural habitat .

La synthèse de nano-object connait un essor grandissant depuis ces 20 dernières années. Les études fondamentales de système a permis (et permet encore) de trouver de nombreux domaines d'application aux nanotechnologies, que ces soit en catalyse, en électronique, dans le domaine biomédical...La thèse se déroule autour de deux axes de recherches: la synthèse et la description des propriétés magnétique de nanoparticules de fer stabilisé par des liquides ioniques, et la synthèse, l'étude magnétique, et leur évaluation en tant qu'agent de contraste et médiateur d'hyperthermie de nanoparticules de de ferrite fonctionnalisé par des dérivées carbohydrates
The synthesis of nano-object is growing in the last 20 years. Basic research system has (and still allows) to find many areas of application for nanotechnology that is in catalysis, electronics, biomedical ...The thesis proceeds along two lines of research: the synthesis and the description of magnetic properties of iron nanoparticles stabilized by ionic liquids, and the synthesis, magnetic study, and their evaluation as a contrast agent and hyperthermia mediator of functionalized carbohydrate derivatives ferrite nanoparticles

A significant body of work exists around coke dissolution into liquid iron, however there are key aspects of this important reaction that are not well described. This study was focused on gaining the answers to the questions “How does the coke mineral matter behave during coke dissolution?” and “Can the effects of sulphur and oxide layer formation on the dissolution rate be separated and quantified?”. Issues that must be addressed if the understanding of the kinetics of this reaction is to be advanced and coke's use in the blast furnace further optimised.To this end, a detailed investigation was conducted examining the influence of coke mineral matter on coke (carbon) dissolution into liquid iron. This project was focused on the mineral matter layer that forms at the coke/iron interface and how the presence of this layer affects the kinetics of carbon dissolution from the coke into the liquid iron. A range of experimental techniques were used to identify and characterise the mineral layer as it formed at the coke/iron interface and to assess the layers influence on the carbon dissolution kinetics.Carbon dissolution experiments, utilising a carburiser cover technique, were carried out where carbon and sulphur transfer to an iron-carbon melt was measured over time at temperatures of 1450°C, 1500°C and 1550°C. This technique allowed fundamental data on the dissolution rate constant to be calculated, and the effects of temperature, melt sulphur and different carbonaceous materials to be explored.Development of the mineral layer at the coke/iron interface as a function of both time and temperature was studied utilising a quenched carbon dissolution technique that was developed during the project. This technique had the additional benefit of allowing the composition of the melt to be determined for a larger range of elements than the dissolution experiments. The quenched carbon dissolution experiments complemented the carbon dissolution experiments and allowed direct comparisons between the dissolution behaviour measured in the dissolution experiments and the composition and morphology of the mineral layer observed in the quenched samples.The dissolution studies were further complemented by sessile drop measurements of the wetting behaviour of iron on the mineral phases that were identified in the mineral layer present at the coke/iron interface, thermodynamic modelling utilising the MTDATA software package and a conceptual model of the interfacial mineral layer.A mineral layer was observed to have formed at the coke/iron interface during coke dissolution into liquid iron at experimental temperatures ranging from 1450°C to 1550°C. The mineral layer was solid at these temperatures and persistent at the interface. The amount of mineral matter present in the mineral layer was observed to be increasing with increased reaction time. The composition and structure of the mineral layer changed with both experimental time and temperature. The composition of the mineral layer was principally composed of oxides of aluminium and calcium, present as various calcium aluminates and calcium sulphides. Initially the mineral layer was a loose agglomeration of particles of which a majority were alumina particles. As the dissolution reaction proceeded, the loose agglomeration of particles was replaced by an open acicular layer that was predominantly the calcium aluminate CaO.6Al2O3 (CA6). As the dissolution reaction continued further, the calcium aluminates became increasingly richer in calcium oxide, with the predominate phase present in the mineral layer progressing through the calcium aluminates phases CA6 to CaO.2Al2O3 (CA2) and onto CaO.Al2O3 (CA). The apparent calcium enrichment of the mineral layer was observed to occur more rapidly as the experimental temperature increased. Accompanying the compositional changes in the mineral layer, the morphology of the mineral layer was also observed to change. The mineral layer was formed as an initial loose agglomeration of alumina particles, changing to an open acicular structure consisting of CA6/CA2 before being converted to a dense layer as the dissolution reaction proceeded and the composition of the mineral layer changed to CA and calcium sulphide (CaS) appeared at the interface.It was found that the formation of the calcium sulphide layer was preceded by the formation of the calcium aluminate layer. Only after the calcium aluminate layer had experienced progressive calcium enrichment and the CA and CA2 phases had formed did the CaS phase appear at the iron interface. Thermodynamic analysis of the experimental results confirmed that the formation of the calcium enriched calcium aluminates, CA2 and CA, were a necessary requirement to stabilise the calcium sulphide layer for the coke composition studied.The kinetics of carbon dissolution from the coke to the liquid iron were observed to be dependent on the structure of the interfacial mineral layer. This dependence was manifest as two stage behaviour in the first order mass transfer plots. The initial stage, characterised by rapid carbon dissolution, was observed while the mineral layer was developing or had the open acicular structure of the CA6/CA2 layer. The second stage was characterised by a significant reduction in the rate of carbon dissolution. The onset of the second stage was coincident with the change in the composition of the mineral layer from CA6/CA2 to CA2/CA and the associated densification of the mineral layer. In stating that the nature of the mineral layer affects the dissolution kinetics, a change in the reaction control mechanism is implied. This represents a change in the coke dissolution kinetics from simple mass transfer control to a mixed control regime where both mass transfer and the mineral (product) layer are active.In an attempt to overcome the problems associated with the heterogeneity of coke a coke analogue was developed. In the coke analogue the composition and dispersion of the carbonaceous and mineral matter (oxides) are controlled and the porosity is fixed. When single phase calcium aluminates were introduced into the coke analogues, calcium enrichment of the resulting calcium aluminate mineral layer was observed. The observed carbon dissolution kinetics were dependant on the structure of the interfacial calcium aluminate layer. Consistent with the coke dissolution studies, the calcium aluminate layer formed at the coke analogue iron interface during carbon dissolution was at least in part rate controlling the carbon dissolution reaction for the coke analogues studied.Utilising the sessile drop experimental technique the wettability with liquid ironcarbon-sulphur alloys of the predominate phases that were observed in the mineral layer were measured. It was observed that the contact angle decreased as the proportion of lime (CaO) in the calcium aluminate increased. Further it was observed that while the presence of sulphur in the melt increased the contact angle for the alumina and CA6 substrates, on the CA2 and CA substrates the contact angle was decreased. The improvement in the wetting of the CA2 and CA substrates with sulphur was attributed to the formation of CaS at the substrate/droplet interface.This study has produced new fundamental data on the growth and development of the mineral layer and the wettability of the predominate calcium aluminates observed in the mineral layer. These detailed studies have illuminated the changing nature of the layer in terms of both composition and morphology and found that the kinetics of carbon dissolution from the coke to the liquid iron were dependant on the structure of the interfacial mineral layer.

Abstract For the mass production of astatine-211, a promising radiopharmaceutical for cancer treatment, the National Institute for Quantum and Radiological Science and Technology has proposed the innovative “Liquid Bismuth Target System.” The target window in this system must be made from a material that resists the highly corrosive liquid bismuth environment. To meet this requirement, a promising target window material was selected in corrosion experiments performed in stagnant liquid bismuth. Based on knowledge of corrosion in liquid lead–bismuth eutectic gained during the development of fast reactors and accelerator-driven subcritical systems, FeCrMo–alloy, FeCrAl–alloy, and austenitic stainless steel (as a reference) were selected as the specimen materials. Experiments were carried out under saturated dissolved oxygen and low oxygen conditions, and the corrosion behaviors of the specimens were evaluated, mainly by scanning electron microscopy. The FeCrAl–alloy exhibited the most excellent corrosion resistance, followed by FeCrMo–alloy. Both materials are suitable candidates for the target window. Although austenitic stainless steel was less corrosion resistant than the former two materials, it is a likely applicable for the target window under appropriately limited operation conditions (such as irradiation current and exposure time) of the liquid bismuth target system.

High amount of basic oxygen furnace (BOF) slag in steelmaking process is a big challenge, therefore, recycling of the slag have been extensively concerned by not only steelmakers but also researchers. One of the promising methods is to use the slag as a flux in the pretreatment process because the basicity of slag is high and it contains high amount of MgO and CaO. This study examines recycling ability of the BOF slag as a part of the flux adding to the pretreatment process. In the experiment procedure, the flux was combination of the slag (59 mass%), CaO (32 mass%) and SiO2 (9 mass%). The flux and the iron sample were put into the crucible, and then set up in the resistance furnace. The experiments were carried out at different temperatures of 1450, 1500 and 1550 °C with holding time of 15 minutes. The results shown that the S content in the iron significantly decreased in all cases of temperatures. S content in the iron in the pretreatment process reduced from the initial value to 0.007 mass% at the temperature of 1450 °C. However, at temperature of 1550 °C, the S content in the iron was 0.012 mass%. Besides, Si content in the iron reduced with increasing temperature; Si content in the iron significantly decreased from initial value of 2.67 mass% to 0.05 and 0.06 mass% once the temperatures were 1500 and 1550 °C, respectively. Additionally, it was indicated that Fe content in the slag after reaction dropped from the initial value of 6.20 mass% to 0.62 mass% at the temperature of 1550 °C.

The project was originally aimed at investigating and developing new efficient methods for cost effective removal of ammonia (NH₃) and hydrogen sulfide (H₂S) from Concentrated Animal Feeding Operations (CAFO), in particular broiler and laying houses (NH₃) and hog houses (H₂S). In both cases, the principal idea was to design and operate a dedicated air collection system that would be used for the treatment of the gases, and that would work independently from the general ventilation system. The advantages envisaged: (1) if collected at a point close to the source of generation, pollutants would arrive at the treatment system at higher concentrations; (2) the air in the vicinity of the animals would be cleaner, a fact that would promote animal growth rates; and (3) collection efficiency would be improved and adverse environmental impact reduced. For practical reasons, the project was divided in two: one effort concentrated on NH₃₍g₎ removal from chicken houses and another on H₂S₍g₎ removal from hog houses. NH₃₍g₎ removal: a novel approach was developed to reduce ammonia emissions from CAFOs in general, and poultry houses in particular. Air sucked by the dedicated air capturing system from close to the litter was shown to have NH₃₍g₎ concentrations an order of magnitude higher than at the vents of the ventilation system. The NH₃₍g₎ rich waste air was conveyed to an acidic (0<pH<~5) bubble column reactor where NH₃ was converted to NH₄⁺. The reactor operated in batch mode, starting at pH 0 and was switched to a new acidic absorption solution just before NH₃₍g₎ breakthrough occurred, at pH ~5. Experiments with a wide range of NH₃₍g₎ concentrations showed that the absorption efficiency was practically 100% throughout the process as long as the face velocity was below 4 cm/s. The potential advantages of the method include high absorption efficiency, lower NH₃₍g₎ concentrations in the vicinity of the birds, generation of a valuable product and the separation between the ventilation and ammonia treatment systems. A small scale pilot operation conducted for 5 weeks in a broiler house showed the approach to be technically feasible. H₂S₍g₎ removal: The main goal of this part was to develop a specific treatment process for minimizing H₂S₍g₎ emissions from hog houses. The proposed process consists of three units: In the 1ˢᵗ H₂S₍g₎ is absorbed into an acidic (pH<2) ferric iron solution and oxidized by Fe(III) to S⁰ in a bubble column reactor. In parallel, Fe(III) is reduced to Fe(II). In the 2ⁿᵈ unit Fe(II) is bio-oxidized back to Fe(III) by Acidithiobacillus ferrooxidans (AF).In the 3ʳᵈ unit S⁰ is separated from solution in a gravity settler. The work focused on three sub-processes: the kinetics of H₂S absorption into a ferric solution at low pH, the kinetics of Fe²⁺ oxidation by AF and the factors that affect ferric iron precipitation (a main obstacle for a continuous operation of the process) under the operational conditions. H₂S removal efficiency was found higher at a higher Fe(III) concentration and also higher for higher H₂S₍g₎ concentrations and lower flow rates of the treated air. The rate limiting step of the H₂S reactive absorption was found to be the chemical reaction rather than the transition from gas to liquid phase. H₂S₍g₎ removal efficiency of >95% was recorded with Fe(III) concentration of 9 g/L using typical AFO air compositions. The 2ⁿᵈ part of the work focused on kinetics of Fe(II) oxidation by AF. A new lab technique was developed for determining the kinetic equation and kinetic parameters (KS, Kₚ and mₘₐₓ) for the bacteria. The 3ʳᵈ part focused on iron oxide precipitation under the operational conditions. It was found that at lower pH (1.5) jarosite accumulation is slower and that the performance of the AF at this pH was sufficient for successive operation of the proposed process at the H₂S fluxes predicted from AFOs. A laboratory-scale test was carried out at Purdue University on the use of the integrated system for simultaneous hydrogen sulfide removal from a H₂S bubble column filled with ferric sulfate solution and biological regeneration of ferric ions in a packed column immobilized with enriched AFbacteria. Results demonstrated the technical feasibility of the integrated system for H₂S removal and simultaneous biological regeneration of Fe(III) for potential continuous treatment of H₂S released from CAFO. NH₃ and H₂S gradient measurements at egg layer and swine barns were conducted in winter and summer at Purdue. Results showed high potential to concentrate NH₃ and H₂S in hog buildings, and NH₃ in layer houses. H₂S emissions from layer houses were too low for a significant gradient. An NH₃ capturing system was designed and tested in a 100-chicken broiler room. Five bell-type collecting devices were installed over the litter to collect NH₃ emissions. While the air extraction system moved only 10% of the total room ventilation airflow rate, the fraction of total ammonia removed was 18%, because of the higher concentration air taken from near the litter. The system demonstrated the potential to reduce emissions from broiler facilities and to concentrate the NH₃ effluent for use in an emission control system. In summary, the project laid a solid foundation for the implementation of both processes, and also resulted in a significant scientific contribution related to AF kinetic studies and ferrous analytical measurements.

Introducción En 2023 el Banco de la República celebra 100 años de su fundación. Este es un aniversario de gran significado, el cual ofrece la oportunidad de resaltar el aporte que el Banco ha hecho al desarrollo del país. Su trayectoria como garante de la estabilidad monetaria lo ha consolidado como la institución estatal independiente que genera mayor confianza entre los colombianos por su transparencia, capacidad de gestión y el cumplimiento efectivo de las funciones de banca central y culturales encomendadas en la Constitución y la Ley. En una fecha tan importante como esta, la Junta Directiva del Banco de la República (JDBR) hace un reconocimiento a las generaciones de directivos y funcionarios que con su compromiso y dedicación contribuyeron a engrandecer esta institución1. El mandato del Banco de la República se consolidó en la Asamblea Nacional Constituyente de 1991, para cuya integración los ciudadanos tuvieron la oportunidad de elegir a las setenta personas que tendrían como tarea redactar una nueva constitución. Los dirigentes de los tres movimientos políticos más votados fueron elegidos presidentes de la Asamblea, y esta presidencia tripartita reflejó la pluralidad y la necesidad de consenso entre las diferentes fuerzas políticas para sacar adelante la reforma. Entre los asuntos considerados, la Asamblea Nacional Constituyente le otorgó especial importancia a la estabilidad monetaria. Por esta razón decidió incluir el tema de banca central y dotar al Banco de la República de la autonomía necesaria para utilizar los instrumentos a su cargo sin injerencia de otras autoridades. El constituyente entendió que velar por la estabilidad de precios es un deber del Estado y que la entidad responsable de este cometido debe estar consagrada en la Constitución y contar con la capacidad técnica y autonomía institucional necesaria para adoptar las decisiones que considere pertinentes para alcanzar este objetivo fundamental, en coordinación con la política económica general. En particular, el artículo 373 estableció que “el Estado, por intermedio del Banco de la República, velará por el mantenimiento de la capacidad adquisitiva de la moneda”, disposición que coincidía con el esquema de banca central adoptado por países exitosos en el control de la inflación. En 1999, mediante sentencia 481, la Corte Constitucional indicó que “el deber de mantener la capacidad adquisitiva de la moneda no solo se predica de la autoridad monetaria, crediticia y cambiaria, esto es de la Junta del Banco de la República, sino también de quienes tienen responsabilidades en la formulación y ejecución de la política económica general del país” y que “la finalidad constitucional básica del Banco de la República es la protección de la moneda sana, pero esa autoridad debe tomar en consideración en sus decisiones los otros objetivos económicos de la intervención del Estado, como el pleno empleo, pues sus funciones deben coordinarse con la política económica general.” La reforma al Banco de la República concertada en la Constituyente de 1991 y en la Ley 31 de 1992 se puede resumir en los siguientes aspectos: i) asignó al Banco un mandato específico: mantener la capacidad adquisitiva de la moneda, en coordinación con la política económica general; ii) designó a la JDBR como autoridad monetaria, cambiaria y crediticia; iii) otorgó al Banco y a su Junta Directiva un importante grado de independencia frente al Gobierno; iv) prohibió al Banco otorgar crédito al sector privado distinto del financiero; v) estableció que para otorgar crédito al Gobierno se requería del voto unánime de su Junta Directiva, a menos que se trate de operaciones de mercado abierto; vi) determinó que el legislador, en ningún caso, podrá ordenar cupos de crédito a favor del Estado o de los particulares; vii) designó al Congreso, en representación de la sociedad, como principal destinatario del ejercicio de rendición de informes del Banco; y viii) delegó en el presidente de la República la función de inspección, vigilancia y control sobre el Banco de la República. Los miembros de la Asamblea Nacional Constituyente entendieron claramente que los beneficios de una inflación baja y estable se extienden a toda la sociedad y contribuyen al buen funcionamiento del sistema económico. Entre los más importantes cabe mencionar que una inflación baja promueve el uso eficiente de los recursos productivos, al permitir que los precios relativos guíen de mejor forma la asignación de recursos, lo cual promueve el crecimiento económico y aumenta el bienestar de la población. Igualmente, una inflación baja reduce la incertidumbre sobre la rentabilidad esperada de la inversión y sobre el precio futuro de los activos, lo que aumenta la confianza de los agentes económicos, facilita la financiación de largo plazo y estimula la inversión. Una inflación baja evita redistribuciones arbitrarias del ingreso y la riqueza, debido a que los estratos de ingresos bajos de la población no pueden protegerse de la inflación mediante la diversificación de sus activos, y concentran una elevada proporción de su ingreso en la compra de alimentos y otros bienes básicos, ítems que generalmente son los más afectados por los choques inflacionarios2. Por otra parte, una baja inflación facilita las negociaciones salariales, lo cual crea un buen clima laboral y reduce la volatilidad del nivel de empleo. Finalmente, una inflación baja contribuye a que el sistema de impuestos sea más transparente y equitativo, al evitar las distorsiones que la inflación introduce sobre el valor de los activos y de los ingresos que componen la base tributaria. Desde el punto de vista de la autoridad monetaria, uno de los beneficios más relevantes de una inflación baja es la credibilidad que los agentes económicos adquieren en la meta de inflación, lo que la convierte en un ancla nominal efectiva sobre el nivel de precios. Al recibir su mandato, y en uso de su autonomía, el Banco de la República empezó a anunciar metas puntuales de inflación anual a partir de 1992. Si bien en esta primera etapa las metas de inflación propuestas no se lograron cumplir de forma precisa, sí se consiguió imprimirle a la inflación una tendencia descendente, que la llevó desde un nivel del 32,4% en 1990 al 16,7% en 1998. Para aquella época la tasa de cambio se mantenía dentro de una banda, lo cual limitaba la efectividad de la política monetaria, que buscaba cumplir simultáneamente una meta de inflación y un objetivo de tasa de cambio. La crisis asiática se contagió a las economías emergentes y afectó de manera importante a la economía colombiana. La tasa de cambio presentó una fuerte presión a la depreciación al cerrarse el acceso al financiamiento externo en condiciones de un elevado desequilibrio externo. Lo anterior, junto con la falta de flexibilidad cambiaria, impidió hacer una política monetaria contracíclica, lo que condujo a una contracción del PIB del 4,2% en dicho año. En este contexto de desaceleración económica, la inflación anual se redujo al 9,2% a finales de 1999, situándose por debajo de la meta del 15% que se había fijado para ese año. Este episodio reveló plenamente lo costoso que podría ser, en términos de actividad económica, el tener simultáneamente metas para la inflación y para la tasa de cambio. Hacia finales de 1999 el Banco de la República anunció la adopción de un nuevo régimen de política monetaria que denominó Esquema de Inflación Objetivo. Este régimen, conocido internacionalmente como ‘Inflation Targeting,’ venía ganando creciente aceptación en países desarrollados, al haber sido adoptado a partir de 1991 por Nueva Zelanda, Canadá e Inglaterra, entre otros, logrando importantes avances en el manejo de la inflación, sin incurrir en costos en términos de actividad económica. En América Latina, Brasil y Chile también lo acogieron en 1999. En el caso colombiano, el último requisito pendiente por cumplir para adoptar dicho esquema de política era la flexibilidad de la tasa de cambio, la cual se materializó hacia septiembre de 1999, cuando la JDBR decidió abandonar las bandas cambiarias para permitir que la tasa de cambio se determinara libremente en el mercado. De forma coherente con el mandato constitucional, el objetivo fundamental de este nuevo esquema de política consistía en “el cumplimiento de una meta de inflación que contribuya a mantener un crecimiento del producto alrededor de su capacidad potencial”3. Dicha capacidad potencial se entendía como aquel crecimiento del PIB que la economía puede obtener si utiliza plenamente sus recursos productivos. Para cumplir este objetivo la política monetaria debe cumplir necesariamente un papel contracíclico en la economía. Ello porque cuando la actividad económica está por debajo de su potencial y existen recursos ociosos, la autoridad monetaria puede reducir la tasa de interés ante la ausencia de presiones inflacionarias para estimular por esa vía la economía y, de manera inversa, cuando el producto supera su capacidad potencial. Este principio de política, que está inmerso en los modelos para guiar la postura de política monetaria, hace que, en el mediano plazo, sean totalmente compatibles los objetivos del cumplimiento de la meta de inflación y de un nivel de actividad económica compatible con su capacidad productiva. Para alcanzar este propósito, en el esquema de inflación objetivo se utiliza la tasa de interés del mercado monetario (a la cual el banco central suministra liquidez primaria a los bancos comerciales), como el instrumento primordial de política. Con ello se sustituyó la cantidad de dinero como meta intermedia de política monetaria, que el Banco de la República, al igual que varios otros bancos centrales, utilizaron por mucho tiempo. En el caso colombiano, el objetivo del nuevo esquema de política monetaria implicaba, en términos prácticos, que la recuperación de la economía, luego de la contracción ocurrida en 1999, debía lograrse al tiempo que se cumplían las metas decrecientes de inflación establecidas por la JDBR. De manera notable este propósito se cumplió. En la primera mitad de la década del 2000 la actividad económica logró una recuperación importante, hasta alcanzar un crecimiento del 6,8% en 2006. Entretanto, la inflación fue descendiendo gradualmente, en línea con las metas de inflación. Fue así como la tasa de inflación se redujo desde el 9,2% en 1999 al 4,5% en 2006, cumpliendo con la meta de inflación establecida para ese año, mientras que el PIB alcanzó su nivel potencial. Después de lograrse este equilibrio en 2006, la inflación repuntó al 5,7% en 2007, por encima de la meta del 4% fijada para ese año, debido a que el crecimiento del PIB del 7,5% superó su capacidad potencial4. Luego de comprobarse la eficacia del esquema de inflación objetivo en sus primeros años de operación, este régimen de política continuó consolidándose a medida que la JDBR y el equipo técnico ganaron experiencia en su manejo y se incorporaron modelos económicos de última tecnología para diagnosticar el estado presente y futuro de la economía, y evaluar la persistencia de los desvíos de la inflación y sus expectativas con respecto a la meta de inflación. A partir de 2010 la JDBR estableció la meta de inflación anual de largo plazo del 3%, que continúa vigente en la actualidad. La menor inflación ha contribuido a crear un entorno macroeconómico más estable, que ha favorecido el crecimiento económico sostenido, la estabilidad financiera, el desarrollo del mercado de capitales y el funcionamiento de los sistemas de pagos. Gracias a ello se lograron reducciones en la prima por riesgo inflacionario y menores tasas de interés de los TES y de crédito. A su vez, la duración de la deuda interna pública aumentó de forma importante pasando de 2,27 años en diciembre de 2002 a 5,86 años en diciembre de 2022 y la profundización financiera, medida como el nivel de la cartera como porcentaje del PIB, pasó de cerca del 20% a mediados de la década de los noventa a valores superiores al 45% en años recientes, en un contexto saludable de los establecimientos de crédito. Los logros tangibles alcanzados por el Banco de la República en el manejo de la inflación al haber contado con la autonomía que le otorgó la Constitución para cumplir con el mandato de preservar el poder adquisitivo de la moneda, junto con los importantes beneficios que se derivaron del proceso de llevar la inflación a su meta de largo plazo, hacen que el reto que actualmente enfrenta la JDBR de retornar la inflación a la meta del 3% sea aún más exigente y apremiante. Como es bien conocido, a partir de 2021, y especialmente en 2022, la inflación en Colombia volvió a convertirse en un serio problema económico, con elevados costos de bienestar. El fenómeno inflacionario no ha sido exclusivo de Colombia y es así como muchos otros países desarrollados y emergentes han visto alejarse sus tasas de inflación de las metas propuestas por sus bancos centrales5. Las razones de este fenómeno se han analizado en los recientes Informes al Congreso, y en esta nueva entrega se profundiza al respecto con información actualizada. La sólida base institucional y técnica que soporta el esquema de inflación objetivo bajo el cual opera la estrategia de política monetaria le da a la JDBR los elementos necesarios para enfrentar con confianza este difícil reto. Al respecto, en su comunicado del 25 de noviembre la JDBR reiteró su compromiso con la meta de inflación del 3,0%, la cual prevé alcanzar hacia finales de 20246. La política monetaria continuará enfocada en cumplir este objetivo, al tiempo que velará por la sostenibilidad de la actividad económica, tal y como lo ordena la Constitución. Las encuestas a analistas llevadas a cabo en marzo mostraron un incremento importante (del 32,3% en enero al 48,5% en marzo) en el porcentaje de respuestas que sitúan las expectativas de inflación a dos años o más en un rango entre el 3% y 4%. Este es un indicativo claro de recuperación de credibilidad en la meta de inflación a mediano plazo, lo cual guarda coherencia con el anuncio de la JDBR de noviembre pasado. La moderación de la tendencia alcista de la inflación que se observó en enero, y especialmente en febrero, contribuirá a reforzar esta revisión de expectativas de inflación, y ayudará a cumplir los objetivos propuestos. Luego de registrarse una inflación del 5,6% a finales de 2021, la inflación mantuvo una tendencia alcista a lo largo de 2022 debido a las presiones inflacionarias tanto de origen externo, asociadas con las secuelas de la pandemia y las consecuencias del conflicto bélico en Ucrania, como de origen interno, resultantes de: el fortalecimiento de la demanda local; los procesos de indexación de precios estimulados por el aumento de las expectativas de inflación; las afectaciones a la producción de alimentos provocadas por el paro de mediados de 2021, y el traspaso de la depreciación a los precios. Los aumentos del salario mínimo del 10% en 2021 y del 16% en 2022, que en ambos casos superaron la inflación observada y el incremento de la productividad, acentuaron los procesos de indexación al haber establecido un elevado referente de ajuste nominal. De esta forma, la inflación total aumentó al 13,1% a finales 2022. La variación anual de alimentos, que subió del 17,2% al 27,8% entre esos dos años, fue el factor que más influyó en la aceleración del Índice de Precios al Consumidor (IPC). Otro rubro que contribuyó de manera importante a las alzas de precios fue el de regulados, cuya variación anual aumentó del 7,1% en diciembre de 2021 al 11,8% a finales de 2022. Por su parte, la medida de inflación básica sin alimentos ni regulados subió del 2,5% al 9,5% entre finales de 2021 y finales de 2022. El aumento sustancial de la inflación básica muestra que la presión inflacionaria se extendió a la mayoría de los rubros de la canasta familiar, lo cual es característico de procesos inflacionarios con una indexación de precios generalizada, como ocurre en Colombia. La política monetaria empezó a reaccionar tempranamente a estas presiones inflacionarias. Fue así como a partir de su sesión de septiembre de 2021 la JDBR inició un cambio progresivo de la postura de la política monetaria a partir del mínimo histórico del 1,75% de la tasa de interés de política al cual se había llegado para estimular la recuperación de la economía. Este proceso de ajuste prosiguió sin interrupción a lo largo de 2022 y hasta inicios de 2023, cuando la tasa de política monetaria alcanzó el 12,75% en enero pasado, con lo cual acumuló un incremento de 11 puntos porcentuales (pp). El público y los mercados se han mostrado sorprendidos de que la inflación continuara aumentando, a pesar de los significativos incrementos de la tasa de interés. Pero como lo ha explicado la JDBR en sus diversas comunicaciones, la política monetaria actúa con rezago. Así como en 2022 la actividad económica se recuperó hasta alcanzar un nivel superior al de prepandemia, impulsada, entre otros factores, por el estímulo monetario otorgado durante el período de pandemia y de los meses subsiguientes, así también los efectos de la actual política monetaria restrictiva se irán dando paulatinamente, lo que permite esperar que hacia finales de 2024 la tasa de inflación converja hacia el 3%, como es el propósito de la JDBR. Los resultados de la inflación en enero y febrero de este año mostraron incrementos marginales decrecientes (13 pb y 3 pb respectivamente), en comparación con la variación observada en diciembre (59 pb). Esto sugiere que se aproxima un punto de inflexión en la tendencia de la inflación. En otros países de América Latina, como Chile, Brasil, Perú y México, la inflación llegó a su techo y ha empezado a descender lentamente, aunque con algunos altibajos. Es previsible que en Colombia ocurra un proceso similar durante los próximos meses. El descenso previsto de la inflación en 2023 obedecerá, entre otros factores, a las menores presiones de costos externos por cuenta de la progresiva normalización de las cadenas de suministro, a la superación de los choques de oferta por razones de clima y por los bloqueos viales de años anteriores, lo que se reflejará en menores ajustes en los precios de los alimentos, como ya se observó en los primeros dos meses del año y, por supuesto, al efecto rezagado de la política monetaria. El proceso de convergencia de la inflación a la meta será gradual y se extenderá más allá de 2023. Dicho proceso se facilitará si se revierten las presiones a la devaluación, para lo cual resulta esencial que se continúe consolidando la sostenibilidad fiscal y se eviten mensajes en diferentes frentes de la política pública que generan incertidumbre y desconfianza. _______________________________________ 1 Este Informe al Congreso contiene el recuadro 1 que resume la trayectoria del Banco de la República en estos 100 años. Adicionalmente, con auspicio del Banco, varios libros que profundizan diversos aspectos de la historia de esta institución fueron publicados en años recientes. Véase, por ejemplo: Historia del Banco de la República 1923-2015; Tres banqueros centrales; Junta Directiva del Banco de la República: grandes episodios en 30 años de historia; Banco de la República : 90 años de la banca central en Colombia. 2 Es por ello que una menor inflación se ha reflejado en la reducción de la desigualdad del ingreso medida a través del coeficiente de Gini al pasar de 58,7 en 1998 a 51,3 en el año previo a la pandemia. 3 Véase Gómez Javier, Uribe José Darío, Vargas Hernando (2002). “The Implementation of Inflation Targeting in Colombia”. Borrador de Economía, núm. 202, marzo, disponible en: https://repositorio.banrep.gov.co/handle/20.500.12134/5220 4 Véase López-Enciso Enrique A.; Vargas-Herrera Hernando y Rodríguez-Niño Norberto (2016). “La estrategia de inflación objetivo en Colombia. Una visión histórica”, Borrador de Economía, núm. 952. https://repositorio.banrep.gov.co/handle/20.500.12134/6263 5 Según el FMI, la variación porcentual de los precios al consumidor entre 2021 y 2022 pasó del 3,1 % al 7,3 % para las economías avanzadas, y del 5,9 % al 9,9 % para las economías de mercados emergentes y en vías de desarrollo. 6 https://www.banrep.gov.co/es/noticias/junta-directiva-banco-republica-reitera-meta-inflacion-3