Mineralogy of Ga- and Ge-bearing metallurgical slags from Tsumeb, Namibia

Abstract

Gallium (Ga) and germanium (Ge) are technologically important critical elements. Lead blast furnace slags from Tsumeb, Namibia, comprise over two million metric tons of material that contains high levels of Ga (135–156 ppm) and Ge (128–441 ppm) in addition to significant Zn concentrations (up to 11 wt.%) and represent a potential resource for these elements. A combination of mineralogical and chemical methods (PXRD, FEG-SEM-EPMA and LA-ICP-MS) indicated different partitioning of Ga and Ge within the individual slag phases. Gallium is predominantly bound in small euhedral crystals of Zn–Fe–Al spinels (<10 μm in size), exhibiting concentrations in the range of 480–1370 ppm (up to 0.004 atoms per formula unit, apfu). Concentrations of Ga in other phases (e.g. melilite) are systematically below 90 ppm. The principal host of Ge is the silicate glass and, to a lesser extent, silicates (melilite and olivine group phases). Concentrations of Ge in glass attained a concentration of 470 ppm (EPMA), but the LA-ICP-MS analysis of glass matrix containing submicrometre spinel crystallites indicated that average Ge levels vary in the range of 113–394 ppm. In the potential extraction of Ga and Ge, the results indicate that ultrafine milling is needed to liberate the Ga- and Ge-hosting phases prior to metallurgical processing of the slag.

Review on operation of spinel-containing slags of the non-ferrous metallurgy

“…[33] For recovery of those elements from slags the understanding of the partitioning of the elements between the phases available in slags is key. For example, the critical element Ga is found to be predominantly bound to Zn–Fe–Al spinels within lead blast furnace slags from Tsumeb, Namibia as reported by Ettler et al [35] Ni-containing spinel is observed in Ni converter slags by Yu and Chattopadhyay [36], which is relevant for metal loss in slag. The melting point of oxyspinels is usually higher than the process temperature of non-ferrous pyrometallurgical operation, so they occur in the slag as solid particles.…”

Leaching of liquation-feeding furnace dross as a first step for germanium recovery

“…Examples of materials from zinc metallurgy with elevated germanium concentrations include residues from hydrometallurgical processes obtained during the leaching of zinc ores and purification of zinc electrolytes [ 7 – 11 ]. In pyrometallurgical operations, such by-products as alloy and slag from lead blast furnaces [ 12 , 13 ], flue dust from flash copper smelting [ 14 ], polymetallic alloy from New Jersey process [ 15 ] or dust from fuming of leaching residue [ 16 – 18 ] may be generated. In subsequent stages, the Ge-bearing material is firstly leached, then germanium is selectively recovered from the solution by tannin precipitation, and cementation with iron or zinc powder, either by solvent extraction.…”