As the grade of mineral resources continues to decline and production costs rise, increasing attention is being paid to ore sorting technologies, aiming to enhance the feed grade entering the crushing, grinding, and beneficiation stages, reduce the ore throughput in downstream processing chains, and improve overall efficiency. Microwave infrared (MW-IR) has been proposed as an excitation–discrimination technique for developing a novel ore sorting method. Consequently, understanding the thermal contrast of ore and waste rock after microwave heating is particularly critical. Microwave heating experiments were conducted under varying process conditions, including microwave power, heating duration, and sample size. The surface temperature distribution characteristics, non-uniformity, and the thermal contrast between ore and waste rock were analyzed. The results showed that both ore and waste rock exhibited pronounced temperature non-uniformity after microwave exposure, with evaluation indices differing by several to tens of times. Significant variation was also observed across different surfaces of the same sample in parameters such as maximum temperature, average temperature, temperature range, temperature non-uniformity index, and coefficient of variation. Notably, microwave power and heating time did not alter the temperature distribution trend on the same surface, while the effect of sample size on non-uniformity indices of ore and waste rock exhibited the opposite trend. Moreover, no significant correlation was found between the permittivity at different locations on the ore surface and the temperature distribution. It is recommended that numerical simulation methods are employed to investigate the factors influencing temperature distribution. These findings offer important insights into the distinct thermal responses of ore and waste rock to microwave heating and provide a scientific basis for advancing MW-IR-based ore sorting technology.

Microwave-infrared (MW-IR) ore sorting has been demonstrated to effectively separate ore from waste, enabling the rejection of low-grade material from ore streams or the enrichment of valuable ore from waste. Consequently, this technology presents substantial research value and market potential. It should be emphasized that the intrinsic heterogeneity of ores is a critical factor that must be considered in sorting. In this study, a heterogeneous ore geometric model was developed to achieve bidirectional coupling between the electromagnetic field and solid heat transfer. The microwave heating behavior was systematically analyzed under varying mineral contents, mineral assemblages, and ore orientations, and the implications for MW-IR ore sorting were discussed. The results indicate that the temperature field distribution is highly dependent on the electric-field distribution. Increasing the content of high-loss minerals intensifies the “corner effect” during microwave heating. Furthermore, the dielectric properties of microwave-absorbing minerals significantly modulate the temperature field distribution of mineral assemblages; specifically, the weak dielectric response of sphalerite leads to anomalous heating behavior in the Quartz + Sphalerite assemblages. Ore orientations appear to have little influence on the spatial distribution of thermal hotspots. Moreover, no clear correlation was observed between ore temperature or non-uniformity metrics and mineral content. Notably, even with identical mineral types and contents, changes in ore orientation can significantly affect temperature levels and non-uniformity. Accordingly, heterogeneous particle-packing models that more closely represent real ore morphologies are recommended for further investigation of additional factors governing microwave heating behavior.

In modern nickel mineral processing operations, the aim is to separate pentlandite from gangue minerals. One of these gangue minerals, pyrrhotite, contains up to 1 wt% Ni but is disposed of as waste, i.e., as tailings. Declining sulfide ore grades and increasing nickel demand have led to renewed interest in extracting nickel from pyrrhotite tails. One proposed process is thermal concentration, which aims to recover the nickel as a ferronickel alloy via thermal treatment at temperatures greater than 900 °C. Achieving these temperatures requires substantial energy input as the reactions involved are highly endothermic. In the present research, microwave radiation was used to process a reaction mixture consisting of a concentrate of pyrrhotite tails, iron ore, and metallurgical coke. The fundamental property that determines the interaction of microwaves with a material is complex permittivity. It was found that the reaction mixture had very high real and imaginary permittivities, making it a good candidate for microwave treatment. An input power of 800 W of microwave radiation (2450 MHz) was then employed to heat various reaction mixtures for thermal treatment times of 120, 300, and 600 s. The ferroalloy grades (6–7.5 wt% Ni) were comparable to those produced by conventional heating and to those obtained by other authors using conventional heating techniques. The microwaved samples had increased metallization of nickel, which was attributed to increased melting due to the higher internal temperatures.

As the global demand for nickel transitions from ferronickel to nickel sulfate for batteries, the nickel sulfide ore reserves are becoming increasingly more difficult to mine. Although, the mining of the nickeliferous laterite ores is much simpler, the extraction of the metal is more challenging, with limited process options. Furthermore, the current processing techniques are costly and have environmental issues, resulting in the need to develop alternative technologies through laboratory research and pilot plant testing. In this paper, firstly, an overview is provided of the composition plus mineralogy of both the limonitic and the saprolitic nickeliferous laterite ores and of the current commercial techniques that are employed to process these ores. Secondly, the pyrometallurgical research work reported in the literature on the production of a nickel concentrate by selective reduction followed by magnetic separation is reviewed. The main objectives are to achieve a high nickel recovery and to produce a concentrate with a high nickel grade. Thirdly, the role of additives, in particular the sulfur-containing species, is evaluated. Fourthly, the main issues involved in the processing of these ores and of particular importance, the areas that require further research and development are discussed. Finally, the potential of these new developing processes to replace the current commercial operations is assessed.

In pyrometallurgical processes, the temperatures attained are amongst the highest of all industrial chemical processes and consequently the energy requirements are considerable. Although in the last few decades there have been significant improvements in the thermal efficiencies of these processes, some limitations are imposed by the innate characteristics of both the energy sources and the pyrometallurgical raw materials. Currently, there exist significant incentives for innovative and efficient processes that harness electricity from renewable energy sources. Furthermore, this electricity can be converted into electromagnetic radiation, such as microwaves, which can be utilized as a source of thermal energy. The fundamental properties which determine the interaction of microwaves with any given material are the real and the imaginary permittivities. This data is required for microwave process development, particularly numerical modeling. In the present research, these permittivities were determined for a number of raw materials of pyrometallurgical interest as a function of temperature and frequency by the cavity resonance perturbation technique. The materials studied were oxides, carbonates and sulphides. Also, the permittivity changes during the reduction of hematite by hydrogen were investigated. In order to interpret the permittivity variations as a function of temperature and also in the reduction process, the changes in the composition were modelled using HSC Chemistry®7.1. Some conclusions are drawn regarding the utilization of microwaves for the heating of pyrometallurgical materials.

ABSTRACT An understanding of the decomposition processes in the Mn-O and the Mn-O-H systems is important for several applications such as the reduction of manganese ores or the production of pure manganese oxides. Precise thermodynamic data is required for modelling these thermal processes and in particular data is lacking for Mn5O8. It would be advantageous to more accurately model these processes, but this depends on the availability of reliable thermodynamic data. In the present research, the currently available data for the Mn-O system was evaluated in order to obtain consistent decomposition temperatures of the various manganese oxides, as calculated using the Equilibrium Composition program of HSC Chemistry® 7.1. Subsequently, these temperatures were compared to the experimentally determined values in the literature. Also, the effects of variables such as atmospheric composition and pressure on the temperatures were evaluated. Additionally, the thermal conditions required for the formation of Mn5O8, were delineated. The thermodynamic data utilized for Mn5O8 were as follows: ΔH° = −2444.5 kJ/mol, ΔS° = 280.2 J/(mol·K) and J/(mol·K). The selected data utilized in this research, can be used for accurate thermodynamic calculations and as examples, phase stability diagrams for the Mn-O, Mn-O-H and Mn-O-N systems were determined.

High temperatures are required in pyrometallurgical processes and consequently they are extremely energy intensive. Microwaves can offer several potential thermal energy efficiency advantages such as selective and/or rapid internal heating. The fundamental parameters which determine the interaction of microwaves with any given non-magnetic material are the real and the imaginary permittivities. In the current research, the permittivities of various mixtures of several pyrometallurgical raw materials plus carbonaceous reducing agents were determined as a function of both temperature and frequency, using the cavity perturbation technique. The raw materials investigated were an oolitic iron ore, an electric furnace dust and a chromite ore. As the temperature of a mixture increased, the permittivities began to increase rapidly, at temperatures lower than for the raw material alone. Subsequently, as the temperatures increased even further, the permittivities began to decrease and consequently peaks were typically observed in both the real and the imaginary permittivities. The changes in the permittivities of the mixtures were interpreted in terms of reduction reaction information available in the literature and also the amounts of the various species present as calculated by the Equilibrium Module of HSC Chemistry & REG; 7.1. The initial rapid rise in the permittivities of the mixtures was attributed to the presence of the carbonaceous reducing agent, while the decrease was ascribed to the consumption of the carbonaceous reducing agent and also the reduction of metal oxides to metal. The permittivity data can be utilized to better understand the heating behaviour of the mixtures and also can be employed in numerical modelling.

The global demand for nickel metal continues to grow, while the resource base for nickel is transitioning from the nickel sulphide ores to the nickeliferous laterite oxide ores. Considerable research is being performed on developing innovative processes for extracting the nickel from the oxide ores. One potential new energy source for these processes could be microwave radiation. The interaction of microwaves with a given material is mainly determined by the permittivities. In the present research, the permittivities of a nickeliferous silicate laterite ore and both activated charcoal-ore and segregation reaction mixtures were measured as a function of both temperature and frequency using the cavity perturbation technique. In general, the ore permittivities increased slowly at low temperatures and more rapidly at higher temperatures. For the reaction mixtures, the rapid rise in the permittivities occurred at a temperature lower than for the ore and there was a characteristic peak in the permittivities. In order to understand the behaviours of the mixtures, the relevant thermodynamic literature was reviewed and also reaction simulations were performed using HSC Chemistry® 7.1. The initial rapid rise in the permittivities was attributed to the presence of the charcoal. For the activated charcoal-ore mixtures, at high temperatures the amounts of carbon and iron oxide decreased as a result of the reduction reactions and thus the permittivities decreased. Similarly, for the segregation mixture, the carbon was consumed due to the water-gas reaction and once more the iron oxide decreased. The permittivity information can be utilized to better understand the heating behaviours of the mixtures and also can be employed in numerical modelling for process development.

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. It is a challenging component in the leach solution as it impedes gold recovery from the residue. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based resin, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulfur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 resin from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔGadso = −1.9 kJ/mol, ΔHadso = −9.1 kJ/mol, and ΔSadso = −0.1 kJ/(mol K). The negative free energy and enthalpy changes demonstrated that the adsorption of elemental sulfur was both spontaneous and exothermic over the temperature range studied.

Ferroalloys, such as ferrochromium, ferromanganese and ferrosilicon are pyrometallurgically produced in energy intensive submerged arc furnaces. In turn, these materials can be used as reagents in a number of pyrometallurgical processes, where the energy requirements are typically supplied by electricity or by the combustion of hydrocarbons. Presently, there are significant incentives to develop more efficient pro-cesses, which utilize renewable energy. The electricity from these renewable sources can be converted into electromagnetic radiation, such as microwaves, which in turn can be used as a thermal energy source. The amount of energy absorbed from the electromagnetic field and the amount converted into heat are determined by the real and the imaginary permittivities, respectively. These permittivity results are needed for process development, in particular for numerical modelling. In this research, the permit-tivities of selected ferroalloys and reaction mixtures were determined as a function of temperature and frequency using the cavity perturbation technique. Also, the limitations of the cavity perturbation tech-nique for these types of measurements are highlighted. In order to interpret the permittivity changes for the reaction mixtures, HSC Chemistry & REG;7.1 was utilized to model the compositional changes as a function of temperature. The results indicate that microwaves are a potential heating source for ferroalloy produc-tion and also in processes which utilize ferroalloys as a reagent.& COPY; 2023 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Recently, the demand for lithium metal and its associated compounds has been growing exponentially, mainly due to the increased consumption of lithium ion batteries. Consequently, to meet this demand, minerals such as spodumene have become the most important lithium-bearing resources. Although numerous methods have been studied for the extraction of lithium from spodumene, the conventional process of spodumene decrepitation followed by leaching in sulfuric acid, remains the proven commercial process. In the high temperature decrepitation process, alpha-spodumene is converted into beta-spodumene and also some intermediate gamma-spodumene can form. In the current research, a comprehensive thermodynamic analysis of the decrepitation of spodumene has been performed using HSC Chemistry (R) 7.1. Firstly, the thermodynamic data available in the literature for the various relevant lithium aluminosilicates was evaluated and then this data was incorporated into the HSC data base. Secondly, using the experimental data available in the literature, the non-ideal behaviour of spodumene was accounted for by the incorporation of activity coefficients. Finally, the model was applied to the decrepitation of both pure spodumene and also a spodumene concentrate. The modelled conversion results were in good agreement with the process data available in the literature.

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based catalyst, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulphur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 catalyst from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔGadso = -1.9 kJ/mol, ΔHadso = -9.1 kJ/mol, and ΔSadso = -0.1 kJ/(mol·K). The negative free energy and enthalpy changes demonstrate that the adsorption of elemental sulfur is both spontaneous and exothermic over the temperature range studied.

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated.

Microwave radiation is a relatively new energy source that is being considered for several applications in mineral processing and extractive metallurgy. In the present research, various gibbsite-type bauxite ores were subjected to microwave radiation. The main objective was to assess the effect of microwave dewatering on the compressive strength indices of the ores and to compare the results obtained to those for conventional heating. Firstly, the fundamental interactions of the microwaves with the ores were evaluated by determining both the real and the imaginary permittivities as a function of temperature, and these were related to the water content. Secondly, the microwave heating behavior was modeled using a 24 factorial statistical analysis. Thirdly, the effect of dewatering by microwave heating on the compressive strength indices of roughly spherical bauxite ore pisoids was studied, and these results were compared to those obtained using conventional heating. Fourthly, the effect of particle size on the compressive strengths of irregular-shaped single particles of bauxite ore was investigated using both heating techniques. Finally, the energy requirements for dewatering of the ores, and hence reducing their compressive strengths, were compared for both processes. On the laboratory scale, the results showed that in comparison to conventional dewatering, microwave dewatering resulted in lower strength indices at both lower moisture removals and energy inputs.

The removal of elemental sulfur from the final leach residue produced during the atmospheric oxidative leaching of chalcopyrite concentrates is both a technical and an economic challenge. Lanxess Lewatit (R) AF 5 catalyst is a promising candidate material that can collect this elemental sulfur during the leaching process. However, to be cost-effective it is necessary to develop methods to regenerate and recycle the AF 5. In the present research, toluene and tetrachloroethylene were studied as potential organic solvents for the removal of the sulfur from the sulfur loaded AF 5. Also, the recovery of elemental sulfur from the resulting liquor was investigated. The effects of temperature, time and AF 5 to solvent ratio on sulfur removal from the sulfur loaded AF 5 were examined. The optimum desulfurization conditions were 100 degrees C for toluene and 110 degrees C for tetrachloroethylene for an AF 5 to solvent ratio of 1:50 and a processing time of 120 min. For toluene and tetrachloroethylene, the sulfur removals were 89.8% and 88.1%, respectively. Toluene was considered to be the most promising solvent due to its higher sulfur removal efficiency and a reduced effect on the behavior of the recycled AF 5 in the leaching process. After three consecutive leaching and regeneration cycles the sulfur absorption capacity and the copper and iron leaching recoveries were essentially unchanged. Copper and iron recoveries of greater than 95% and greater than 80%, respectively, were achieved with the recycled AF 5.

Elemental sulfur is a key component in the acidic Albion chalcopyrite atmospheric leaching process and is a challenging issue in the residue. It has been proposed to use Lanxess Lewatit® AF 5 (AF 5) catalyst during the leaching of copper concentrates in the acidic Albion leach process, to eliminate the elemental sulfur from the leach residue. When using AF 5 during leaching, the copper and the iron recoveries were above 95% and 80%, respectively. The AF 5 collected 100% of the elemental sulfur and for a 1:1 ratio of AF 5 to concentrate, the loaded AF 5 gained 12.3 wt% sulfur after the first acidic Albion leach test and contained 24.3 wt% sulfur after two leaching tests.In this study, the optimum conditions for the removal of sulfur from the catalyst were investigated using a high temperature process in a laboratory tube furnace. The results indicated that the maximum desulfurization of 90.1% was achieved at 550 °C after 10 min. The regenerated AF 5 could be reused for several chalcopyrite leaching-AF 5 cycles. For the recycled AF 5, the sulfur absorption decreased by only 1.0% while the recoveries of copper and iron were not affected. The kinetic study showed that the activation energy for AF 5 desulfurization was 164.5 kJ/mol;

In the last few decades there has been increasing interest in the application of microwaves as an energy source in extractive metallurgy for the treatment of ores and concentrates. The fundamental parameters required for the design of industrial systems are the real and the imaginary permittivities, which are both frequency and temperature dependent. However, there is a dearth of data on the permittivities, of not only the ores and the concentrates, but also the minerals that comprise the ores. In the present research, the permittivities of selected hydroxide minerals were determined using the cavity perturbation technique as a function of both temperature and frequency. The behaviours of the permittivities were interpreted using both thermogravimetric analysis (TGA) and thermodynamic modelling. The water in these minerals, in its various forms, makes a significant contribution to the permittivities. Also, generally, the higher iron-bearing hydroxides have higher permittivities than the magnesium silicates or aluminosilicates. It is shown that the permittivities of the hydroxide minerals are low, but the hydroxyl ion makes a significant contribution. The effect of frequency is more pronounced both during dehydroxylation and at high temperatures and, in both cases, is attributed to increases in the ac conductivity.

An increasing amount of nickel is currently being extracted from the nickeliferous laterite ores, rather than from the sulfide deposits. Consequently, new processes are being developed to extract the nickel from these ores and selective reduction is one possibility. In these processes, it has been shown that the addition of sulfur can improve the grade and/or the recovery. In the current work, the mechanism of the carbothermic reduction of a sulfur-containing nickeliferous limonitic laterite ore was investigated by utilising TGA/DTA and both thermodynamic and kinetic analyses. It was found that, in addition to dehydroxylation and reduction, the reaction sequence also consisted of the following major stages: (1) conversion of pyrite to pyrrohtite and (2) subsequent desulfurisation. Analyses of the reacted samples showed that both the particle size and the amount of ferronickel increased with both particle growth temperature and retention time at temperature. The thermodynamic predictions were in general agreement with the experimental findings and were consistent with the postulated formation of an iron-sulfur-oxygen solution.

The mineral processing and extractive metallurgy industries are under increasing pressure to develop more energy efficient and sustainable technologies. As a result, there is increasing interest in the application of alternative energy sources, such as microwave technology. While bench scale testing has been conducted in this area for over thirty years, scale-up has remained a key challenge. One barrier to implementation has been the lack of understanding of the fundamental interaction of microwaves with ores. Key parameters include the real and the imaginary permittivities, which influence both the heating rate and the microwave penetration depth. Over the last decade, high temperature permittivity measurements have been performed on various ores using the cavity perturbation technique. In this paper, this permittivity data is presented as a function of temperature primarily at 912 MHz. Based on the interpretation of this data, recommendations are made for the sustainable utilization of microwave technology in metallurgical processing.