The Use of Coniferous Tree Cone Biomass as an Energy Source and a Reducing Agent in the Recycling of Metals from Oxide Secondary Raw Materials

The challenges faced by the metallurgical industry implicate that actions aimed at reducing negative impacts on the environment are becoming extremely important. This is justified both in the search for economically competitive methods of producing basic construction materials, consistent with the circular economy policy, and in improving the efficiency of metal production technology. An essential aspect of biomass use is the introduction of an energy source that naturally reduces the energy supplied to the reactor, thereby reducing the carbon footprint of the metal produced. In this case, the research undertaken aims to determine the possibility of using a bioreductant that will allow for the reduction or elimination of the fossil raw material, which is coal, thus reducing the costs associated with ETS and ETS II (European Union Emissions Trading System). This paper presents the results of research on the reduction process of oxide metal-bearing raw material, the chemical composition of which is similar to slags from the copper industry. The effects of slag reduction time on the degrees of copper and lead removal were examined. The process was carried out at 1300 °C, with the constant addition of a reducing agent, in the form of crushed pine cones. After processing for 1 h, the copper content in the waste slag was 1.30 wt%, whereas extending the process to 5 h reduced the copper content to 0.15 wt%. For lead, at the exact reduction times, the element's contents in the slag after processing were 1.92 wt% and 0.79 wt%, respectively. The results of the studied process showed that, in the first stage of the slag reduction process, intensive reduction of copper and lead oxides occurs. Research was also conducted to characterize the biomaterial during the high-temperature process. Results show high degrees of removal for basic metals at the following levels: 99% for Cu and 72% for Pb. The waste slag is characterized by low metal content, which allows for safe storage or use in other sectors of the economy. This type of biomaterial is, therefore, recommended for research in large-scale laboratories or on a semi-industrial scale, particularly in relation to the gas phase formed and its possible impacts on the structural elements of industrial installations. It should be noted that there is a lack of data in the literature on the use of forest biomass in the form of pine cones as an alternative to coke as a reducing agent for use in pyrometallurgical processes.