Review of the extraction of key metallic values from black shales in relation to their geological and mineralogical properties

The aim of this paper is to provide geologists, metallurgical engineers, or mineral resource strategists with a first overview of the currently available state-of-the-art knowledge of the extraction of key metallic values from black shales. The key metallic values considered were vanadium (V), molybdenum (Mo), uranium (U), nickel (Ni), zinc (Zn), as well as platinum group elements and gold. First, a global geological and mineralogical overview is given. Following this, each technological approach is explained and, finally, a summary is provided. Each topic also includes brief overview of the possible environmental impacts. All information was sourced from academic papers, patents, and technological reports. The main conclusions are: (i) black shales are enriched in different sets of metals, yet the V-Mo-U-Ni-Zn association is relatively universal, (ii) mineralization is mostly disseminated and rocks are very fine grained, (iii) hosts of key metals are either sulfides of organometallic complexes, V is often associated with silicates, (iv) the latter 3 along with additional factors result in poor opportunities for beneficiation (flotation, etc.), (v) extraction methods range from conventional hydrometallurgy, bio-leaching, and in-situ leaching in many combinations with roasting, microwave, autoclave or other aiding steps. The final choice of technology is site-specific and there are no rule-of-thumb solutions. There is only one fully operational production unit that exploits black shale as a raw material - Talvivaara/Terrafame in central Finland.

Automated summary

This paper provides a comprehensive overview of the extraction of key metallic values from black shales, covering geological and mineralogical aspects, technological approaches, environmental impacts, and main conclusions.