Mixing, Mass Transfer, and Numerical Models

We want to eliminate dissolved impurities to another phase: slag, gas, solid, or a molten metal that has limited solubility in the main metal. The various phases may be in the form of droplets, bubbles, particles, or walls. The contact areas with metal should be large. The aim in reactor design and operation is to achieve relatively high velocities and small dimensions. Relations for mass transfer are also included since the behaviour of systems with molten metals may be different from that usually treated in chemical engineering. In the field of turbulence the Prandtl eddy length is important for describing removal to walls. Hydrogen in aluminium and the pick-up of hydrogen in aluminium from water vapour is studied in some detail, measured, and modelled. It is taken into account that hydrogen gas is two-atomic. The approach concerning aluminium may be applied to a range of metals.

Effective Removal of Barrier Layer on the Surface of Low-Nickel Matte in an FeCl3-HCl-H2O Solution

Using ferric chloride as an oxidant, here, we investigated the leaching effect of low-nickel matte in a flow field produced by mechanical agitation. The factors affecting a leaching reaction, such as stirring speed, leaching time, low-nickel matte particle size, and inert abrasive quartz sand, were studied. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), a laser particle size analyzer, optical microscopy (OM), a scanning electron microscopy (SEM) with an energy dispersive X-ray detector (EDS), and a Raman spectrometer were used to characterize the materials before and after the leaching reaction. The contents of the main metal ions such as Ni, Cu, and Co in the leaching solution were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Using the control variable method, the optimal experimental conditions were as follows: 2 mol/L FeCl3—0.5 mol/L HCl-H2O system with low-nickel matte and quartz sand (mass ratio is 1:5) and leaching at 90 °C for 8 h. The results showed that the blocking effect of the solid product sulfur layer was effectively removed and continuous leaching was realized. The leaching efficiencies of Ni, Cu, and Co were 98.9%, 99.3%, and 98.1%, respectively.

Reduction Characteristic of CaSO4-CuO Combined Oxygen Carrier Under CO Atmosphere

CaSO4 oxygen carrier is considered to be a potential oxygen carrier (OC) for Chemical Looping Combustion because of its high oxygen capacity and low price. But its reactivity is lower than the main metal oxide oxygen carriers, and it deactivates due to sulfur loss as well as sintering at high reaction temperatures above 920 ℃. To improve the performance of CaSO4-based oxygen carrier, small amounts of CuO particles were mixed mechanistically with CaSO4 particles to use as combined oxygen carrier in this work. The reduction reactions of CaSO4 oxygen carrier, CuO oxygen carrier and CaSO4-CuO combined oxygen carrier under CO atmosphere were investigated. The effects of reaction factors including reaction temperature, the oxygen-carrying ratio of CuO to CaSO4 and mass of oxygen carrier, on the reductions have been investigated in this study. XRD, SEM-EDS, BET and gas analyses were performed to investigate the variations of solid phase, element compositions in solid residual and sulfur release with reaction time. The results show that the addition of CuO increases the reactivity of the CaSO4-based oxygen carrier while also suppressing the release of the gas sulfur. For the individual reduction of CaSO4 by CO, with the increase of CaSO4 mass (500 - 1200 mg), CO2 yield also increases until 1000 mg stops and SO2 released rises remarkably; An increase in the reaction temperature aggravated the SO2 emission. The carbon dioxide generation efficiency also increases with an increase in temperature, but decreases when the temperature exceeds 950 ℃ due to sintering of the oxygen carrier particles; With respect to the reaction of CuO with CO, CO2 yield does not change significantly with increasing temperature, due to the sintering of the CuO oxygen carrier in a high temperature reaction environment;For the combined oxygen carrier: a.As the reduction reaction temperature increases, the reduction reaction performance of the combined oxygen carrier is enhanced within the reaction temperature range of 750~900℃. b. CaO the use of CuO additives not only improves the CO conversion rate, but also inhibits the release of gas sulfide. As the oxygen carrying fraction of CuO increases, SO2 released is reduced and the SO2 release time is delayed. What� more, the solid products after reduction reaction mainly contain CaS, CaO, CuO, Cu2O and CaSO4, and no copper sulfide is detected. c. When the oxygen-carrying ratio of CuO to CaSO4 is increasing from 15% to 20%, CO2 yield increases greatly.

Ensuring the reliability of metal smoke and veintilation pipes and their carrying towers

The problem of ensuring the reliability of the work of metal smoke and ventilation pipes and their bearing towers has recently gained special significance in connection with the large number of accidents at industrial enterprises. Methods of estimation of residual resource of bearing elements of high-rise buildings with various damage detected during diagnostics are developed. The formulas for determining the residual life of metal chimneys are given, the actual reserves of the residual resource are determined after long periods of operation for specific structures. In this work, variants of reinforcement of the elements of chimneys and towers with the most dangerous injuries (category A) – gaps, with cracks in the main metal and welds, with loss of the overall stability of the trunk of the pipe, have been developed and substantiated. On the basis of the analysis of the summation of internal and external stresses, we obtain formulas for calculating the elastic-deformation state of metal chimneys in the zone of through cracks and holes when performing construction reinforcement works by means of welds for overlays. The variants of amplification of smoke pipes after the destruction of stops of towers, which perceive wind loads, and as consequences of the loss of overall stability of the pipe are given. The research results make it possible to assess the reliability of metal smoke and ventilation pipes and their bearing towers after long operating periods, as well as used in the development of regulatory documents when assessing the technical condition and residual life of high-rise buildings.

A metasedimentary source of gold in Archean orogenic gold deposits

The sources of metals enriched in Archean orogenic gold deposits have long been debated. Metasedimentary rocks, which are generally accepted as the main metal source in Phanerozoic deposits, are less abundant in Archean greenstone belts and commonly discounted as a viable metal source for Archean deposits. We report ultralow-detection-limit gold and trace-element concentrations from a suite of metamorphosed sedimentary rocks from the Abitibi belt and Pontiac subprovince, Superior Province, Canada. Systematic decreases in the Au content with increasing metamorphic grade indicate that Au was mobilized during prograde metamorphism. Mass balance calculations show that over 10 t of Au, 30,000 t of As, and 600 t of Sb were mobilized from 1 km3 of Pontiac subprovince sedimentary rock metamorphosed to the sillimanite metamorphic zone. The total gold resource in orogenic gold deposits in the southern Abitibi belt (7500 t Au) is only 3% of the Au mobilized from the estimated total volume of high-metamorphic-grade Pontiac sedimentary rock in the region (25,000 km3), indicating that sedimentary rocks are a major contributor of metals to the orogenic gold deposits in the southern Abitibi belt.

Superior Hydrogen Sorption Kinetics of Ti0.20Zr0.20Hf0.20Nb0.40 High-Entropy Alloy

High entropy alloys (HEAs) are composed of multiple main metal elements and have attracted wide attention in various fields. In this study, a novel Ti0.20Zr0.20Hf0.20Nb0.40 HEA was synthesized and its hydrogenation properties were studied, including sorption thermodynamics and hydrogen absorption/desorption kinetics. The maximum hydrogen absorption capacity was 1.5 H/atom at 573 K. X-ray diffraction (XRD) analysis indicated that the crystal structure of Ti0.20Zr0.20Hf0.20Nb0.40 HEA transformed from body-centered cubic (BCC) to body-centered tetragonal (BCT) with increasing hydrogen content, and to face-centered cubic (FCC) after hydrogen absorption to saturation. As a multi-principal element alloy, the Ti0.20Zr0.20Hf0.20Nb0.40 HEA possesses unique hydrogen absorption characteristics. The hydrogen absorption platform pressure rises gradually with the increase of the hydrogen absorption amount, which is caused by multiple kinds of BCT intermediate hydrides with consecutively increasing c/a. The full hydrogen absorption of the Ti0.20Zr0.20Hf0.20Nb0.40 HEA was completed in almost 50 s, which is faster than that of the reported hydrogen storage alloys in the literature. The experimental results demonstrate that the Ti0.20Zr0.20Hf0.20Nb0.40 HEA has excellent kinetic properties, unique thermodynamic hydrogen absorption performance, as well as a low plateau pressure at room temperature.

Calciothermal reduction of tantalate iron and manganese

Processes of calciothermal reduction of metals from iron (FeTa2O6) and manganese (MnTa2O6) tantalates as well as tantalum oxide (Ta2O5) were studied in this work. According to the results of thermodynamic analysis performed in the temperature range 373 – 2773 К, the interaction of FeTa2O6 and MnTa2O6 with calcium proceeds with complete reduction of metals. By the calculation and comparison of the lgK equilibrium constants for the reactions of alumino- and calciothermal reduction of iron and manganese tantalates were showed the thermodynamic advantage of using metallic calcium as a reducing agent. Experimental investigations of calciothermal reduction on samples of synthesized oxides were carried out by the method of combined thermogravimetry and differential thermal analysis in the mode of non-isothermal heating to 1473 K in an argon flow. X-ray powder diffraction was used to determine the phase composition of the initial samples and interaction products. It was shown that the calciothermal reduction of metals from the synthesized manganese tantalate proceeds actively at temperatures above 1196 K, while iron tantalate and tantalum oxide with the appearance of molten calcium. Tantalum and its solid solutions with iron or manganese, corresponding to the structural type Ta7Fe6, were included in the main metal components of the products of the interaction of FeTa2O6 and MnTa2O6 with calcium.

Assessment of the Bioavailability and Speciation of Heavy Metal(loid)s and Hydrocarbons for Risk-Based Soil Remediation

For the assessment of the environmental and sanitary risks deriving from contamination of agricultural soils, it is crucial to identify and characterize the contaminants and study the soil chemical properties influencing their mobility and bioavailability. This information is essential for the selection of the best site remediation and securing strategy. The study site of this work is agricultural land of 6 ha in the province of Naples (Italy) subject to the past illegal burial of industrial wastes, principally from tanneries. With the aim of identifying the contaminants and assessing their mobility and bioavailability, the soil of the site was characterized for the main chemical and physical properties and for the concentration of potentially toxic elements and hydrocarbons. The readily and potentially bioavailable fractions of the main metal contaminants and their distribution in the soil geochemical fractions were determined by extraction in 1 M of NH4NO3, 0.05 M of ethylenediaminetetraacetic acid (EDTA) pH 7, and European Community Bureau of Reference (EU-BCR) sequential fractionation. Further, the speciation of heavy hydrocarbons and chromium was carried out. The agricultural soil was widely contaminated by chromium, zinc, and heavy hydrocarbons (up to 4487, 1846, and 1800 mg/kg, respectively). In some sub-areas, contaminations by cadmium, lead, and copper (up to 283, 417, and 1183 mg/kg, respectively) were also observed. The chromium was found to be scarcely mobile and bioavailable and was mainly associated with the oxidizable, residual, and reducible fractions of the soil (on average 56%, 25%, and 19% of the total, respectively). However, chromium speciation revealed the presence of a significant amount of highly toxic Cr(VI) (above the legal threshold of 2 mg/kg), despite the low oxidizing power of the soil. Zinc was more mobile and bioavailable than chromium and was mainly distributed among the acetic acid-extractable and reducible fractions of the soil (on average 28% and 47% of the total, respectively). Cadmium was found to be very mobile and bioavailable, and was mainly distributed in the acetic acid-extractable and reducible fractions of the soil (on average 40% and 45% of the total). The speciation of heavy hydrocarbons showed that they consist almost entirely of long-chain aliphatic hydrocarbons, considered not very toxic and immobile. These results suggest that the use of not-edible plant coverage might be the best securing and remediation action for the study site, with the potential to preserve the soil ecosystem services, contain the risk of soil erosion and particle dispersion, and phytoextract the bioavailable metals.

IMPACT ASSESSMENT OF MODERNIZATION OF STEAM TURBINE END SEALS ON THE RESIDUAL RESOURCE

Modernization of sealing units with a change of design is carried out in order to improve the technical and economic parameters of steam turbines. It is known from experience of operation of the turbine equipment that, ring cracks in rotors arise in sealing areas. This is due to both seals design features and the accumulation of thermocyclic fatigue. The research is devoted to the study of resource parameters of the high-pressure rotor of the T-250/300-240 turbine equipped with seals of labyrinth, honeycomb and direct-flow type. Numerical experiments were performed on the basis of three-dimensional geometric models of interflow end seals of the high pressure rotor. The finite element method is used to discretize the computational area. The thermal state of the turbine is calculated for the starting mode from the cold state of the metal by solving the boundary value problem of thermal conductivity in a non-stationary setting. The calculation of the stress-strain state of the turbine takes into account the obtained data on temperature stresses and forces from the non-uniformity of temperature fields, as well as centrifugal forces and steam pressure. Differences in the stress-strain state of the rotor for different seal designs are established. It is indicated that after grooving of labyrinth interflow seals to the honeycomb structure, the stress level in the rotor decreased by 8 %, and when grooving to the direct-flow structure — by 21 %. The accumulated damage in the main metal of the turbine was determined using experimental curves of long-term strength of steel 25Cr1Mo1V. The calculation of resource indicators showed that in the transition from the labyrinth to the honeycomb design of the seals, the individual resource of the high-pressure rotor increases by 6.1 %, and in the transition to direct-flow — by 14.4 %. Ref. 10, Fig. 5, Tab. 1.

Quality of bio-solids produced in a Spanish Wastewater Treatment Plant (Córdoba-Spain) and its use in agronomy along 2000-2019

Bio-solids are the final fate of pollution present in urban wastewater, reaching the production of these ones in Spanish WWTPs 701,751 T/year (dates of 2018). Considering that 85% of Spanish bio-solids are used in agronomy, it is important to know characteristics of biosolids there produced, and in this way, we have investigated bio-solids generated in La Golondrina´s WWTP (Córdoba, Spain) along 2000-2019. This WWTP is a conventional facility operated by activated sludges (26.55x106 m3/year treated) which has produced 1.43 kg of bio-solids per m3 of treated wastewater (38.000 T/year). Our results indicated that bio-solids had a dryness over initial mass of 22.3%, and 74.9% of organic matter over dried matter (o.d.m.). At the same time, major components detected in bio-solids were N, P and Ca which levels were 5.0%, 3.5% and 3.7%, respectively. On the other hand, concentration of total metals in bio-solids ranged 13,024 mg/kg o.d.m., being the main metal Fe (11.749 mg/kg o.d.m.) followed by Zn, Cu and Mn, with levels as mg/kg o.d.m. of 463.1, 392.8 and 265.7, respectively. Evolution per year of all the investigated parameters are shown in the paper. Taking into account the use of bio-solids in agronomy, we have evaluated levels of metals limited by the Spanish normative to this respect: thus, the seven metals restricted (Cd, Cu, Ni, Pb, Zn, Hg and Cr) exhibited concentration in bio-solids very lower than parametric values established. Moreover, we have estimated the ratios of accumulation of organics and metals from wastewater to bio-solids: thus, organic matter, N and P, were accumulated in bio-solids respectively, 342, 356 and 643 times, and total metals, 2,632 times. Finally, levels of Escherichia coli slightly varied from wastewater to bio-solids: 1.5x108 colony-forming units/L in the first one, and 0.9x108/g (o.d.m.) in the second ones.