Influence of Different Carbon Content on Reduction of Zinc Oxide via Metal Bath

Electric arc furnace dust (EAFD) is an important secondary resource for the zinc industry. The most common process for its recycling is the pyro-metallurgical treatment in the Waelz process. However, this process focuses on the recycling of the zinc, whereas the recovery of other metals from the EAFD—such as iron and other alloying elements—is neglected. An up-to-date version of reprocessing can involve multi-metal recycling by means of a metal bath containing carbon. The use of a liquid iron alloy requires a higher processing temperature, which enables the reduction and melting of iron oxides as well as other compounds occurring in the dust. Furthermore, the Zn yield is higher and the reduction kinetics are faster than in the Waelz process. This paper is only focused on the zinc reduction in such a metal bath. In order to determine the influence of the carbon content in the molten metal on the reduction rate, experiments were carried out on the reduction behavior of zinc oxide using a synthetic slag. This slag, with a basicity B2 = 1, was applied to an iron bath with varying carbon contents. (0.85%, 2.16%, 2.89%, and 4.15%) The decrease in the zinc oxide concentration was monitored, along with the reaction rates calculated from these data. It was found that the reaction rate increases with rising carbon content in the melt.

CATALYST PROCESSING AND RECYCLING

Discussed auto catalysts contain interesting quantities of platinum noble metals, palladium and rhodium according to the type of auto catalyst, thereby becoming a possible source of these metal aims to acquaint themselves with catalysts in general, their history and last but not least the possibilities of processing and obtaining noble metals for further use. The article deals with knowledge at the theoretical level of use of methods in processing depleted catalysts. It is pyrometallurgical and hydrometallurgical methods. The platinum group metals (PGMs) palladium, platinum, and rhodium represent the key materials for automotive exhaust gas treatment. Since there are currently no adequate alternatives, the importance of these metals for the automotive industry is steadily rising. The high value of PGMs in spent catalysts justifies their recycling. The state-of the-art technology is to melt the ceramic carrier and collect the precious fraction in a liquid metal bath. As the feed material has quite high melting points, huge amounts of energy are required for this process. Hydrometallurgical treatments of the spent catalysts offer the possibility to recycle the PGMs with less energy and time demands. Moreover, automotive catalysts contain further valuable materials to improve the exhaust gas treatment. These compounds, like cerium oxide, cannot be recovered in pyrometallurgical processes.

Modeling the behavior of direct current electromagnetic forces acting on a drop of liquid metal during electroslag remelting

The article presents mathematical and computer modeling of the behavior of liquid electrode metal drops during the process of electroslag remelting (ESP) at a constant current source. The study of the effect of electric field created by direct current allowed us to show the deviation of the drop trajectory from the electrode axis. The flow of electrons and drops of the electrode metal are exposed to electromagnetic forces, which leads to their displacement relative to the remelted electrode axis. This effect entails destabilization of the liquid metal bath and crystal heterogeneity. In turn, the use of external influence on the flow of ESR process can make it possible to stabilize the liquid metal bath even with the use of direct current. Centrifugal forces can act as such forces. They can arise when implementing the technology with the consumable electrode rotation around its own axis. To establish the optimal parameters of rotation speed, it is necessary to estimate the magnitude of impact of the magnetic field that occurs during direct current remelting process. The modeling was carried out using the Ansys Fluent 16.0 software package on the example of remelting 12Kh18N10T steel under the flux ANF-6. The algorithm for calculating of Ansys Fluent is based on the finite element method. In this paper, the mathematical apparatus was not changed and was used in its initial form. The method of magnetic induction was used. The database of information about the ongoing process was built on a grid of finite elements with certain, but sufficient level of adequacy and quality. Each element contains information about the model at a given point, specified for this modeling process. We have revealed the change in the trajectory of the electrode metal drop by electric field from the opposite direction along which the drop flows. The average length of the path traversed by liquid metal drop from the mold axis to the inner surface is from 5 to 15 cm. The motion of an electrode metal drop without an external magnetic field was simulated. This simulation made it possible to determine (estimate) the direction of movement of electrode metal drops and the indicator of necessary external force to stabilize the liquid metal bath during ESP process at direct current equal to 0.067 N.

CFD Investigation of Rotational Sloshing Waves in a Top-Submerged-Lance Metal Bath

Computational fluid dynamics (CFD) is applied to investigate rotational sloshing waves in a top-submerged-lance (TSL) cylindrical metal bath. The study is an extension of a recent work of the authors, where the top injection of Ar into a metallic bath was examined in a quasi-2D flat setup, allowing the numerical model to be extensively validated against experimental data based on x-ray radiography. The new analysis of top gas injection in a cylindrical vessel reveals the appearance of rotational sloshing in the bath, which is maintained by a condition of synchronism between the gas bubbles and the free surface of the bath. A numerical quantification is achieved with specific post-processing of the simulation results, showing the effect of control parameters such as the lance immersion depth and the gas flow rate. This fundamental research study demonstrates the capability of CFD modeling to predict bath dynamics known from literature and practice, the understanding of which is essential for the design of TSL furnaces.

Carbothermic Reduction of Zinc Containing Industrial Wastes: A Kinetic Model

Effective recycling of zinc-containing industrial wastes, most importantly electric arc furnace dust, is of tremendous importance for the circular economy of the steel and zinc industry. Herein, we propose a comprehensive kinetic model of the combined carbothermic and metallothermic reduction of zinc oxide in a metal bath process. Pyro-metallurgical, large-scale lab experiments of a carbon-saturated iron melt as reduction agent for a molten zinc oxide slag were performed to determine reaction constants and accurately predict mass transfer coefficients of the proposed kinetic model. An experimentally determined kinetic model demonstrates that various reactions run simultaneously during the reduction of zinc oxide and iron oxide. For the investigated slag composition, the temperature-dependent contribution of the metallothermic zinc oxide reduction was between 25 and 50 pct of the overall reaction mechanism. The mass transfer coefficient of the zinc oxide reduction quadrupled from 1400 °C to 1500 °C. The zinc recovery rate was > 99.9 pct in all experiments.

An acceptable method to evaluate the analytical performance of real-time fluorescent RT-PCR targeting SARS-CoV-2

It was necessary to carry out methodologies evaluations of real-time fluorescent reverse-transcription PCR (RT-PCR) targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Considering biosafety issues and lack of positive specimens in some special locations in China, the routine specimens from healthy individuals were used to perform methodologies evaluations, in which the indexes were the differences of quantification cycle values (ΔCq) between human derived internal reference control (IRC) genes of a specimen and quality control (QC). Serial experiments were carried out to evaluate various factors that might affect aforementioned methodologies, such as types of virus transport mediums, methods of specimen pretreatment and template preparation, specimen vortex strength, specimen storage temperature and duration. The results showed that using ΔCq values as indexes, among various factors that might affect analytical performance, it was better to store specimens in the normal saline transport mediums, inactivate pathogens using water or metal bath, release more virus particles from swabs by vortex mixing, extract nucleic acids with centrifuge methods, and perform amplification assays timely. Aforementioned opinions and optimum conditions were further confirmed by SRAS-CoV-2 pseudovirus and clinical positive specimens. Altogether, the results of this study indicated that the routine specimens from healthy individuals could be used to evaluate the analytical performance of real-time fluorescent RT-PCR targeting SRAS-CoV-2, of which the indexes were the ΔCq values between IRC genes of a specimen and QC. This acceptable method was extremely valuable in both theoretical and practical significance under current pandemic of coronavirus disease 2019 (COVID-19).