Heterogenite

Heterogenite is a natural tri-valent cobalt oxyhydroxide mineral.^[2] It is the most abundant oxidised cobalt mineral in the Katanga Copperbelt, a region in the Democratic Republic of the Congo.^[3] About 70% of known heterogenite is located in the DRC.^[4]

Heterogenite
General
Category	Minerals
Formula	CoO(OH)
IMA symbol	Htg[1]
Strunz classification	04.FE.20
Dana classification	06.01.04.02
Crystal system	Trigonal or Hexagonal
Identification
Color	Black, reddish, blackish-brown
Cleavage	{0001}
Mohs scale hardness	4–5
Density	4.13 – 4.47, Average = 4.3
Common impurities	Mn, Ni, Zn, Cu, Fe

The name heterogenite came from Greek, "of another kind", as the mineral differs in composition from similar minerals.^[5] Its formation is likely related to the weathering of carrollite (CuCo₂S₄).^[6] In nature it is found coexisting with other minerals like smaltite, pharmacosiderite, calcite, linnaeite, sphaerocobaltite, malachite and cuprite.^[2]

Composition

Heterogenite has an average grade of 64.1% cobalt, one of the highest rates among cobalt-containing minerals.^[7]

Similar to most oxyhydroxides, heterogenite acts as a chemical 'sponge', trapping many trace elements such as Ni, Zn, V, As, Mo, and Pb. Amongst these trace elements is also uranium, whose concentration in the mineral can be as high as a few percent.^[8]

Heterogenite contains cobalt in both Co²⁺ and Co³⁺ oxidation states.^[6]

Occurrence

Heterogenite is formed by the oxidation of cobalt-sulfides and accumulated as residual deposits during a Pliocene weathering event.^[6] Many studies highlight that heterogenite was formed in oxidizing conditions under the surface.^[9] In several locations, primary sulfides have been oxidised due to surface weathering down to about 100 meters below the surface, which resulted in significant cobalt enrichment and transformation to oxidic ore minerals, such as heterogenite.^[10]

Treatment

The preferred concentration technique for treating heterogenite is surface sulfidation followed by flotation. Sulfidation typically requires sodium sulfide (Na₂S), ammonium sulfide (NH₄)₂S), or sodium sulfydrate (NaSH) in order to make heterogenite suitable for collection with sulfydryl-type collectors.^[9]