This article presents the results of a study on metallurgical slag reduction using biomass such as Spent Coffee Grounds (SCGs). The proposed solution is a new aspect of searching for alternatives to standard reducers used in pyrometallurgical processes of metal production. Its gasification yields significant amounts of hydrocarbons, which are excellent reducing agents in such processes. The research results of copper slag reduction with the use of SCG biomass indicate this process is characterised by lower carbon dioxide emissions compared with the process using solid fuels such as coke and coke breeze. The addition of SCG as the reducer ensures the decrease in copper content in the slag to 0.32 wt.%, which corresponds to the increase of so-called relative decopperisation degree even up to 96.9%. As the decopperisation degree of slag increases, significantly more intense reduction in lead oxides during the reduction process is observed. The smallest lead content in waste slag of 0.91 wt.% was obtained for the slag reduction process with 7.56 wt.% of SCG as the reducer and the process duration of 1.5 h.

The article presents a study on the removal of petroleum fractions from reprocessed and decommissioned petrochemical catalysts used in refineries. Petrochemical catalysts are hazardous waste due to their content of petroleum fractions (organic fraction), while also containing high concentrations of Ni, Mo and V. The process of removing petroleum fractions from catalysts was carried out by solvent extraction using hexane. Its purpose was to prepare the catalysts for subsequent steps involving pyrometallurgical processes leading to the recovery of Ni, Mo, V. At the same time, the extraction process was aimed at reducing CO₂ emissions during melting by deriving the oil fraction before the pyrometallurgical step. The realized studies showed that the degree of removal of the petroleum fraction from catalysts depends on temperature, catalyst/solvent ratio and extraction time. The study showed that it is possible to remove > 40% by weight of the oil fraction initially contained in the catalysts. The research presented in this article is being carried out as part of the LIDER13/0133/2022 project funded by the National Centre for Research and Development, which aims to develop a complete technology for the recovery of Ni, Mo and V from spent petrochemical catalysts.

The Joule heat generated by current flow between electrodes in a resistance furnace not only melts and heats the charge but also induces mixing of the molten material. Increased mixing promotes improved chemical and temperature uniformity within the bath. This paper presents a novel approach to effectively optimizing electrode geometry in resistance furnaces. The method relies on a surrogate criterion derived exclusively from an electromagnetic submodel, which governs the process hydrodynamics. This criterion is based on the location of the Joule heat generation center in the bath. Its idea is to lower this center as much as possible while keeping it close to the vertical bath axis. Owing to this, the best conditions for the development of natural convection were obtained. The developed methodology was demonstrated through an application to a two-electrode furnace. The results showed that the influence of forced MHD convection is negligible in this furnace (with a Lorentz force of only about 0.0015 N/kg). The validation of the optimized geometry, derived using solely the electromagnetic submodel, was carried out using a full process model, including time-consuming hydrodynamic calculations. The proposed optimization methodology enabled a 10-fold increase in the average mixing velocity (from 0.0008 to 0.0084 m/s). The main significance of the presented study is the introduction of a surrogate criterion that allows for a multiple reduction in the time of numerical optimization of the mixing intensity in electrode resistance furnaces in comparison to the standard solution based on the flow velocity criterion determined from the hydrodynamic model.

The production of copper based on a direct-to-blister flash smelting process made it necessary to introduce the technology for the reduction of flash smelting slag and subsequent refining of the resulting Cu–Fe–Pb alloy. Refining of Cu–Fe–Pb alloy produces a converter slag containing 7 ÷ 25 wt pct Cu, 3 ÷ 20 wt pct Fe , and 15 ÷ 45 wt pct Pb. This material is directed to the reduction (de-coppering) process, which allows the recovery of copper in the form of Cu–Pb alloy as well as the removal of lead from the copper material cycle in the form of lead-bearing material. The copper recovery rate in the form of Cu–Pb alloy depends on a number of factors, of which one of the primary ones is the viscosity of the medium (slag), which determines the rate of coalescence and sedimentation of the reduced metal droplets. The investigations on how the degree of reduction of metal oxides from the converter slag affects its viscosity are presented in the study. Viscosity tests were conducted in the range of 1000 ÷ 1450 °C and showed that the main factor affecting viscosity is the Cu₂O content in the slag. Slags directed to the reduction process with a high Cu₂O content have a lower viscosity than slags after the reduction process, which is due to a decrease in the copper oxide content of the slag. The viscosity of slags after reduction depends on the PbO content, the higher the PbO content the lower the slag viscosity. Furthermore, studies have shown that the viscosity of slags can be reduced by adding CaO to the slag.

The article presents an electrical model of a resistance furnace with two electrodes encompassing the generation of Joule heat. The characteristic feature of this model was the consideration of contact resistance between the electrodes and the slag. A series of analyses were conducted based on this model. Firstly, the impact of contact resistance on current flow and Joule heat generation in the furnace was assessed, demonstrating its significant importance. A separate group of analyses focused on the spatial configuration of the furnace and its interaction with the aforementioned phenomena. The impact of symmetric and asymmetric electrodes immersion was analysed. In addition to the impact on current flow, the study also demonstrated the influence on the natural convection mechanism described by the proposed measures of the spatial non-uniformity of heat generation. The research showed that symmetric electrode immersion allows for the generation of more heat in the system at a constant voltage. Asymmetric electrodes immersion causes an increase in the non-uniformity of heat generation, which translates into a higher intensity of natural convection.

Shaft sludge is a lead-bearing material produced by the wet dedusting of shaft furnace process gases generated during copper smelting from concentrates. It is a material with a high concentration of lead and hydrocarbon compounds, the melting of which in short rotary furnaces causes many problems. This paper presents the results of thermodynamic modelling of the melting process of shaft sludge and other lead-bearing materials. Computations were carried out using HSC Chemistry 8 software by calculating thermodynamic equilibrium by minimising the free enthalpy of the system. Calculations showed that, as a result of the change in technology and the introduction of technical improvements, it is possible to increase the Pb recovery to raw lead from 55.4–70.7%, while maintaining a total Pb recovery of approximately 93%. The calculations presented in the article are realised within the framework of project No. POIR.01.01.01-00-1300/20 − 01 funded by the National Centre for Research and Development, entitled „Environmentally friendly technology for vitrification of lead-bearing slag by intensifying the work of a short rotary furnace with the dust and process gas conditioning system”.