Critical Raw Materials supply in the EU: the case of Sb-rich Pb-Zn-Au mineralization, Chalkidiki, Greece

Antimony is a strategic element, widely used in the production of alloys, halogen-bearing flame retardants and semiconductors. As the main antimony supplier is China, new providers in the EU are necessary in order to decrease its criticality.

The present study aims to evaluate the antimony enrichment of the Pb-Zn-Au carbonate replacement Stratoni deposit, Chalkidiki, Greece. The mineral assemblage comprises galena, sphalerite, pyrite and arsenopyrite ± subordinate phases such as boulangerite, bournonite, chalcopyrite, pyrrhotite and graphite.

Boulangerite (Pb₅Sb₄S₁₁) is the most abundant Sb phase, and occurs as long acicular crystals within galena, the matrix or massive pyrite. Crystal size ranges between 10 and >100 µm. Bournonite (PbCuSbS₃) is less abundant, and occurs associated with boulangerite, included in pyrite as small crystals (<20 µm).

Boulangerite shows Sb contents ranging between 25.64 and 26.45 wt%, whereas bournonite shows Sb contents between 23.37 and 25.23 wt%. Base metal sulfides contain low amounts of Sb: up to 0.44 wt% within pyrite, up to 0.21 wt% within sphalerite and up to 0.28 wt% within galena. Arsenopyrite and chalcopyrite Sb contents are even lower.

The enrichment plant works in three consecutive stages, producing galena, sphalerite and pyrite concentrates. Each stage comprises conditioning, roughing, scavenging and cleaning flotation cells.

Grain size analyses show similar granulometric curves for the concentrates, with uniformity coefficients lower than 3. D90, D50 and D10 are respectively 400, 110 and 45 µm for galena, 127, 60 and 42 µm for sphalerite and 240, 105 and 49 µm for pyrite concentrates.

Whole rock major (XRF) and trace element (ICP-MS) analyses show that most of the antimony, and therefore of boulangerite and bournonite, reports to the galena concentrate. Starting from 1169 ppb in the initial feed Sb is highly enriched in the galena concentrate (20633 ppm), not enriched in the sphalerite concentrate (1170 ppm) and relatively depleted in the pyrite concentrate (334 ppm), making the galena concentrate a suitable candidate for Sb recovery.

The presence of Sb mostly in its own phases opens up the potentiality to recover the metal as a by-product of galena production. The crystal size of boulangerite is large enough to allow separation through flotation. Further tests are necessary in order to evaluate the amount of Sb phases in tiny inclusions within base metal sulfides and Sb enrichment in base metal phases, that can negatively affect the metal recovery.