Sequential Extraction of Critical Metals in Variably Altered Ultramafic Rocks for Economic Geology Applications

Nickel (Ni), Cobalt (Co), and Chromium (Cr) are useful critical metals in industry, specifically in manufacturing rechargeable batteries, stainless steel, and superalloys. As many countries are transitioning to alternative forms of energy, critical metals are becoming even more important, with the demand for these elements projected to increase significantly. Since Ni, Co, and Cr are not unlimited resources, finding more efficient and environmentally conscious extraction mechanisms to facilitate the transition to a sustainable world is incredibly valuable. Critical mineral data was collected using sequential extraction methods to characterize the mineral host phases for these metals. Ultramafic rocks of variable alteration mineralogy, such as serpentinite/saprolite (Puerto Rico, Oman), laterite (Puerto Rico), talc-rich soapstone (Oman), and carbonated ultramafics (Oman), were used for analysis. Ultramafic rocks are ideal sources as they are widespread and tend to contain significant amounts of Ni, Co, and Cr compared to other available rocks. Samples were chemically treated with reagents that sequentially leached out metals from 6 fractions: exchangeable, absorbed/carbonate, organic, amorphous oxyhydroxide, crystalline oxides, and residual silicates. Each round of treatment went through an X-ray diffractometer (XRD) for mineralogical compositions. A high resolution inductively coupled plasma mass spectrometer (ICP-MS) was used to determine concentrations of Ni, Co, and Cr. Initial XRD data shows that after each extraction, there is a decrease in sharp peaks. Minerals identified include chromite, lizardite, andradite, chrysotile, and goethite. Initial ICP-MS data depicts a significant contrast between Ni, Co, and Cr during extraction. The laterite samples show that 45-65% of Ni and >97% of Co remain in the residual for each sample. In contrast, less than 30% and 43% of Co remain in the residual in the serpentinized bedrock and saprolite layer, respectively. As for Cr, 82-98% remains in the residual with the larger percent in the laterite layers. If these ultramafic samples contain sufficient concentrations of Ni, Co, and Cr in specific mineral phases, an alternative and targeted method for metal extraction may be explored to aid future energy transition goals.

• Inductively Coupled Plasma Mass Spectrometry

• Sequential Extraction using Chemical Reagents

• X-ray Diffraction

The chemical reagents utilized need to be altered to result in a better extraction. The reagents were based on the Canadian Geological Society standards and can be adapted based on other researchers' and organizations' findings. Research will be continued through PhD student Lucas Abernathy. 

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Trainings were conducted by Dr. Marion Lytle. Each step of sequential extraction was monitored and aided by Dr. James Leong. There were no external protocols that were required.