Update: The relationship between the characteristics of Mn ores and their behaviour in hydrogen reduction

Pre-reduced Mn Ore after H2 reduction
Alok Sarkar PhD candidate Supervisor- Jafar Safarian

Alok Sarkar

PhD Candidate | NTNU, Norway

Supervisor: Prof. Jafar Safarian

We are excited to share groundbreaking news about the metal and mining industry’s commitment to environmental sustainability. The EU-funded HAlMan project is set to revolutionize manganese production, this initiative investigates the viability of a sustainable hydrogen reduction process to produce pre-reduced manganese ores. Specifically, it concentrates on the pre-reduction step of manganese ores using hydrogen before proceeding to the aluminothermic reduction step, facilitating the production of manganese and its alloys.

I concentrate on examining the mineralogical traits of raw manganese ore using SEM, ICP-MS, XRF, and XRD. I then investigate their response to hydrogen reduction and analyze the pre-reduced samples by using various characterization techniques such as SEM, XRD, XRF and BET. Recently I conducted experiments using Nchwaning manganese ore, a South African manganese ore supplied by our partner, Assmang. Our results indicate promising findings.

The experiments were executed using a vertical thermogravimetric (TG) setup (Entech VTF 80/15). The reduction experiments were standardized at a 120-minute reduction time for temperatures ranging from 600℃ to 900℃. Each experiment utilized a 150g dried Nchwaning manganese ore sample. A schematic view of the TG furnace is shown in Figure 1. Figure 1(A) shows a sketch of the crucible, and the overall setup of the furnace is shown in Figure1(B). 

In our exploration, we discovered that the Nchwaning ore is highly dense and features Mn and Fe oxides in the forms of Mn2O3 and Fe2O3. Notably, the ore exhibits low porosity (0.0013cm3/g) and a minimal BET surface area (0.49m2/g).

DisVadri Furnace Setup
Figure 1: (A) Crucible overall set up (B) Schematic of thermogravimetric furnace setup.

Our investigation further unveiled the impact of temperature on the pre-reduction kinetics of the ore with hydrogen, indicating that higher temperatures result in a faster and more extensive reduction process. The pre-reduction process with hydrogen at temperatures of 800℃ and 900℃ over two hours yielded complete reduction. This transformation led to the formation of metallic Fe and MnO from Mn2O3 and Fe2O3 in the ore. The pre-reduction temperature played a pivotal role in altering the pore volume and structure of the ore. 

Additionally, a decline in BET surface area and pore volume at temperatures surpassing 700℃ was seen, reaching their lowest values at 900℃. Microscopic examination highlighted sintering in the ore above 700℃, resulting in a pre-reduced ore characterized by reduced porosity and increased density.

We are proud to be part of this transformative initiative that not only addresses environmental concerns but also fosters innovation in the metal and mining sector. Stay tuned for updates as the HAlMan project paves the way for a greener and more sustainable future.