According to the 2018 report of the Intergovernmental Panel on Climate Change (IPCC) on the impacts of global warming up to 1.5°C above pre-industrial levels, CO2 emissions need to decline by about 45% by 2030 and reach net zero in 2050. In the 2019 pronouncement of the United Nations,1 over 50 countries committed to carbon neutrality by 2050, and the decarbonization of metal production processes was identified as crucial to achieving the carbon neutrality goal.Footnote 1

Metal production technologies are carbon and energy intensive, but it can be argued that the bulk of the carbon footprint of metal processes comes from energy sources and reductants. This is especially intensive in the iron and steel industries, where the heavy dependence on carbon sources for reductive smelting is a major contributor to high CO2 emissions. As illustrated in Fig. 1, decarburizing industrial processes requires a convergence of an array of the following strategies:

  1. (i)

    Improved energy efficiency in processes

  2. (ii)

    Alternative reductants such as bioreductants and hydrogen

  3. (iii)

    Capturing of carbon

  4. (iv)

    Renewable energy sources

Fig. 1
figure 1

A schematic diagram showing main components contributing to the decarburization of the metal industry.

Full size image

Improving process energy efficiency and capturing process carbon remain challenging and still require intensive study to scale-up and deploy enabling technologies.

Research and development efforts to take extractive metallurgy to the next level generally aim at (1) effective utilization of the energy content of feedstock, (2) minimization/elimination of carbon-based fuel consumption, (3) efficient environmental pollution control and the production of controlled gases as a side stream resources, e.g., as a feed stock for acid plants, and (4) near 100% extraction and recovery of the primary and minor metals from different feedstock. These efforts will eventually lead to creating adaptive and energy efficient metallurgical processes.

For the March 2022 issue, JOM Advisors of the Energy Committee, Recycling and Environmental Technologies Committee, and Process Technology and Modeling Committee of The Minerals, Metals & Materials Society organized a special topic with a focus on improved extractions and recoveries of the strategic metals, “Recovery of Rare Earth and Critical Metals from Unconventional Sources”.2 For this May issue, original research and review papers focusing on energy efficiency and low carbon footprint in the metals processing industries were invited and five papers were selected for publication after a peer review.

The first article in the list, “Electroreduction of Antimony Sulfide Enhanced by Nitrogen Bottom Blowing in Molten NaCl-KCl-Na2S,” by Zhu et al. proposes a novel nitrogen bottom-blowing method to enhance mass transfer in the molten salt electrolysis process, which also improves current efficiency and reduces electrolysis energy consumption. The authors have also investigated the effect of nitrogen agitation on the dissolution of Sb2S3 and Sb. According to their observation, nitrogen agitation can obviously accelerate the dissolution of Sb2S3. They reported the current efficiency of the cathode to be 92.76%, the energy consumption to be 1.78 kWh kg−1, and the grade of crude antimony to be 98.5%. The overall electrolytic current efficiency improved by 19.87% and energy saving improved by 20.89% because of the nitrogen stirring. Additionally, authors suggest that appropriate flow rate of nitrogen to accelerate the removal of sulfur from the reactor avoids the formation of high-priced antimony compounds.

The second article, entitled “CO2 Gasification of Densified Biomass: The Influence of K on Reaction Rate,” by Kaffash and Tangstad examined the reactivity of metallurgical coke and densified charcoals. They designed experimental procedures to simulate conditions occurring in an industrial furnace of Mn-alloys production. To determine the catalytic effect of potassium, samples were impregnated using a gaseous impregnation technique with K2CO3, with concentration of up to 5 wt.% K. They reported that increasing potassium content led to an increase in the CO2 reactivity of coke and charcoal. The CO2 reactivities of the coke and densified charcoal were comparable when the maximum 5 wt.% K was applied.

The article entitled “Oscillating Currents Stabilize Aluminum Cells for Efficient, Low Carbon Production” by Mohammad et al. described a new invention for manufacturing aluminum while using 12% less heat and 4% less electricity. According to the authors, their invention works by thinning the high-resistance electrolyte layer through which electrical current must pass to liberate Al from dissolved aluminum oxide. This method could allow Al production at lower cost with less energy and smaller carbon footprint.

The article entitled “Thermal Degradation of Poly (Styrene-co-methyl Methacrylate) in the Presence of AlI3 Nanoadditive” by Bahadur et al. presented results of the study of the effect of AlI3 nanoadditive (NA) on the thermal degradation of poly (styrene-co-methyl methacrylate) PSCMMA. They produced the PSCMMA nanocomposites with the addition of AlI3 NA in an acetone common solvent by varying the added amount by up to 5 wt.%. Using thermo-analytical techniques (TGA, DTG, DTA), they determined the thermal degradation of PSCMMA with different concentrations of AlI3 NA. As a result, they reported that the thermal degradation temperature increased proportionally with increasing concentration of AlI3 NA, and the pure PSCMMA to burned five times faster than PSCMMA6 nanocomposite (which has 5 wt.% AlI3).

The fifth article, titled “Thermoeconomic Dyanamics of Orange Hydrogen Production, an Energy Matter,” by Neelameggham et al. presents a detailed thermo-economics and -dynamics of energy-efficient orange hydrogen production. Their analysis revealed that a spectrum of costs in the production exists primarily from the energy conversion costs and economics of such energy conversions. The analytical results reported in the article suggest low-cost hydrogen production possibilities from hydrocarbons called 'orange' hydrogen, which is CO2 free, along with the ease of making it from the ground using the present-day renewable energy technologies.

The peer-reviewed papers in this special topic should be of interest to a broad readership including those considering a more sustainable production of metals such as Al and hydrogen for decarbonizing the metal-making industry. The titles of the articles published under this topic in the fourth issue of JOM this year (vol. 74, no. 5) are listed below and can be fully accessed via the journal’s page at: https://link.springer.com/journal/11837/74/5/page/1.

  • “Electroreduction of Antimony Sulfide Enhanced by Nitrogen Bottom Blowing in Molten NaCl-KCl-Na2S” by Q. Zhu, J. Yang, C. Tang, T. Nan, R. Ding, and J. Liu

  • “CO2 Gasification of Densified Biomass: The Influence of K on Reaction Rate” by H. Kaffash and M. Tangstad

  • “Oscillating Currents Stabilize Aluminum Cells for Efficient, Low Carbon Production” by I. Mohammad, M. Dupuis, P.D. Funkenbusch, and D.H. Kelley

  • “Thermal Degradation of Poly (Styrene-co-methyl Methacrylate) in the Presence of AlI3 Nanoadditive” by A. Bahadur, S. Iqbal, H.O. Alsaab, N.S. Awwad, H.A. Ibrahium, F.H. Alshammari, N. Alwadai, and M.T. Alotaibi

  • “Thermoeconomic-dynamics of Orange Hydrogen Production, an Energy Matter” by N. Neelameggham, G. Subramanian, and P. Kalamegham