Kinetics of reduction and oxidation reactions during pyrometallurgical metal extraction

The article deals with a sophisticated approach to the study of basic kinetic dynamic process in metal production. It is concerned with three agendas: study of reduction reactions of iron oxides and carbon as reducing agents with secondary created oxides; study of the effect of catalyst occurrence on the reaction space; study of the effect of variable temperature and pressure gradients on the processes. The main experiments were carried out in the newly established Laboratory for Research on High Temperature Properties equipped with testing setup and upgraded with interpretive model system, enabling a generalization of experimentally obtained information to theoretical conclusions about processing of non-standard alternative and waste materials.Web of Science2442018200

Study on reducibility and porosity of metallurgical sinter

The paper dealt with research on structural properties of metallurgical sinter. It was aimed at studying of sinter porosity and density in relation to its reducibility. For porosity determination was used immersion technique using Archimedes principle. Density was measured by gas pycnometer and apparent density was calculated from results of measured porosity. These properties were studied in relation to temperature 950 degrees C at which reducibility tests of every sample were carried out according to ISO 4695:2007. For the study 7 batches of 5 samples of sinter originated from industrial metallurgical plant were sorted. The porosity and density were discussed for virgin samples before the test of reducibility and for reduced samples after ISO test. The effect of 950 degrees C on the properties was contemplated and SEM analysis was carried out. The samples porosity before reduction test was in range from 5.1% to 9.82% and for the samples after reduction test it was 32.77-44.12%. The density of samples was not significantly affected by temperature with values ranging from 3.65 to 3.82 g cm(-3) for virgin samples, resp. 4.87-5.37 g cm(-3) for samples after reduction.Web of Science5731664165

Hydrogen embrittlement of welded joint made of supermartensitic stainless steel in environment containing sulfane

The work is focused on evaluation of resistance of the welded joint made of supermartensitic 13Cr6Ni2.5Mo stainless steel to sulfide stress cracking. Testing method A and solution B in accordance with NACE TM 0177 were used. All the testing samples were ruptured in a very short time interval but welded joint samples were fractured primarily in the weld metal or in heat affected zone and not in the basic material. Material analysis of samples were made with use of a ZEISS NEOPHOT 32 light microscope and a JEOL 6490LV scanning electron microscope.Web of Science61271170

Influence of selected rare earth metals on structural characteristics of 42CrMo4 steel

The influence of rare earth metals (REM) addition on solidification structure of the low-carbon 42CrMo4 steel was investigated. Alloys were prepared by means of a centrifugal casting. The addition of cerium, praseodymium or mischmetal in the steel produced greatly improved solidification structure with a suppressed columnar grain zone, finer grain size in the equiaxed grain zone. The additions occurred in the steel bath in the form of REM oxide and/or oxide-sulphide inclusions and as dissolved REM segregated along with other elements at prior grain boundaries and interdendritic spaces. Microstructure (light microscope), SEM/EDX chemical microanalysis, and TOF-SIMS analysis – mapping of elements in the structure of alloys were obtained.Web of Science55476075

Disparities in methods used to determine microplastics in the aquatic environment: A review of legislation, sampling process and instrumental analysis

Plastic particles smaller than 5 mm, i.e., microplastics, have been detected in a number of environments. The number of studies on microplastics in marine environments, fresh water, wastewater, the atmosphere, and the human body are increasing along with a rise in the amounts of plastic materials introduced into the environment every year, all contributing to a range of health and environmental issues. Although the use of primary microplastics has been gradually reduced by recent legislation in many countries, new knowledge and data on these problems are needed to understand the overall lifecycle of secondary microplastics in particular. The aim of this review is to provide unified information on the pathways of microplastics into the environment, their degradation, and related legislation, with a special focus on the methods of their sampling, determination, and instrumental analysis. To deal with the health and environmental issues associated with the abundance of microplastics in the environment, researchers should focus on agreeing on a uniform methodology to determine the gravity of the problem through obtaining comparable data, thus leading to new and stricter legislation enforcing more sustainable plastic production and recycling, and hopefully contributing to reversing the trend of high amounts of microplastics worldwide.Web of Science1814art. no. 760

Hydrometallurgical recycling process for mobile phone printed circuit boards using ozone

Printed circuit boards (PCBs) can be an important source of non-ferrous metals (Al, Sn, Zn, and Ni) and precious metals (Au, Ag, Cu, and Pd). With the continuous increase in demand for metals due to the depletion of ores, recycling of this waste is becoming an attractive alternative. The printed circuits also contain hazardous metals, such as Pb, Hg, As, and Cd. Due to the huge increase in the amount of e-waste, the processing of printed circuit boards for metal recovery and proper handling of hazardous substances has a positive effect on the environment. Pyrometallurgical and hydrometallurgical methods are used for the treatment of this waste. Various oxidizing agents are used in the hydrometallurgical processes, including ozone. PCBs from mobile phones were assessed for the recovery of Cu, Sn, and precious metals. The ground and sieved materials were leached in nitric acid, hydrochloric acid, and sulfuric acid at various process parameters, such as leaching time, leaching agent, and temperature. It was found that the best result was obtained using hydrochloric acid with the addition of ozone at 353 K for a period of 4 h to obtain 68.45 g/dm(3) of copper. Preliminary results of electrolysis and cementation are also presented.Web of Science115art. no. 82

Study of mass motion on vibrating device: Design and process simulation.

The simulation of mass motion using a vibrating device that was laboratory designed was the main idea of the work. The construction of an experimental vibrating device and the associated measuring station along with the measurement of dynamic properties of the vibrating device depending on preselected input parameters of the device of bulk material on this experimental model is presented. The simulation of the general behavior of particles on an experimental vibrating device at rotational frequencies of 20 Hz, 25 Hz and 35 Hz, and the rotation of contact vibrators at 30°, 45° and 75° by mass flow modeling using software ROCKY DEM is done. It was observed that the particles were moving at the fastest speed at 45° and at 35 Hz and that the top layers fall to the bottom especially at higher rotational frequencies, which may ultimately cause aeration of the particulate matter, thus reducing the angle of internal friction of the bulk material.Web of Science20236380637

The effect of organic acids as leaching agents for hydrometallurgical recovery of metals from PCBs

The hydrometallurgical treatment, compared to other recycling processes, is of great interest due to its higher efficiency and better economy. In hydrometallurgy, popular agents used in the leaching processes of e-waste include inorganic acids, ammonia, chlorides, thiourea, thiosulphates. Organic acids are also becoming more and more popular. The article presents an overview of possible paths of the metal recovery from e-waste with the use of various organic acids. The results of own research on the leaching of printed circuit boards with the use of organic acids including citric acid, oxalic acid, acetic acid, formic acid, malic acid, lactic acid are also presented.Web of Science613-461260

Processing of metal waste-sludge from the galvanizing plants

This paper deals with the possibility of obtaining zinc from waste galvanic sludge, which is formed during galvanic plating. The aim of the experimental and practical part was to obtain zinc after the leaching of galvanic sludge. Leaching was performed in sulfuric acid, nitric acid and hydrochloric acid at different temperatures and time intervals with the addition of oxidizing agents as hydrogen peroxide or ozone. A separation of the leach and filtrate using filtration followed. The leach was further processed by a precipitation of iron and other metals using various agents. After a further filtration, the electrolysis was performed in order to obtain pure zinc on the cathode at the electrical voltage of approximately 3.5 V. Leaching using a solution of sodium hydroxide or potassium hydroxide was also performed when the prior dissolving of a major part of zinc into the leach occurred, while iron and non-ferrous metals remained in the leaching residue. After the filtration of the leach, the electrolysis with a high zinc yield of a purity of more than 99% followed. This way seems to be an optimal one for building a semi-industrial line for galvanic sludge recycling. All the partial products, i.e., the leach, the leaching residue, the filtrate, the solid precipitate and the separated metal on the cathode were subjected to chemical analyses. The analyses results are presented in tables and graphs.Web of Science1211art. no. 194

Phase transformation after heat treatment of Cr-Ni stainless steel powder for 3D printing

Today, Ni-Cr steel is used for advanced applications in the high-temperature and electrical industries, medical equipment, food industry, agriculture and is applied in food and beverage packaging and kitchenware, automotive or mesh. A study of input steel powder from various stages of the recycling process intended for 3D printing was conducted. In addition to the precise evaluation of the morphology, particle size and composition of the powders used for laser 3D printing, special testing and evaluation of the heat-treated powders were carried out. Heat treatment up to 950 degrees C in an air atmosphere revealed the properties of powders that can appear during laser sintering. The powders in the oxidizing atmosphere change the phase composition and the original FeNiCr stainless steel changes to a two-phase system of Fe3Ni and Cr2O3, as evaluated by X-ray diffraction analysis. Observation of the morphology showed the separation of the oxidic phase in the sense of a brittle shell. The inner part of the powder particle is a porous compact core. The particle size is generally reduced due to the peeling of the oxide shell. This effect can be critical to 3D printing processing, causing defects on the printed parts, as well as reducing the usability of the precursor powder and can also change the properties of the printed part.Web of Science1515art. no. 534