GERMANIUM REDISTRIBUTION DURING WEATHERING OF ZN MINE WASTES: IMPLICATIONS FOR ENVIRONMENTAL MOBILITY AND RECOVERY OF A CRITICAL MINERAL

Germanium (Ge), an element critical to energy, defense, and communication technologies, is produced both from coal fly ash and as a byproduct of zinc (Zn) mining. Although many Zn ores are enriched in Ge relative to average upper continental crustal abundance, Ge has been discarded in Zn mining wastes for centuries. It is therefore essential to investigate the distribution, element speciation, and mineral hosts of Ge to understand its environmental behavior and its potential for recovery from legacy mine wastes. The Tar Creek Superfund Site in Oklahoma, a former Zn, lead (Pb), and Ge producing area, is a natural laboratory for understanding the behavior of Ge. Using bulk and microanalytical techniques, we studied Ge in bulk and size-fractionated surface samples from Tar Creek Superfund Site mine wastes, which are locally known as chat. In the sampled chat, Ge has been redistributed from sphalerite (ZnS), its original host mineral, to hemimorphite (Zn₄Si₂O₇(OH)₂·H₂O), a weathering product that forms rinds of fine needle-like particles on both quartz and sphalerite grains. Hemimorphite hosts over half of the Ge in the chat sampled (64% on average), while sphalerite hosts only ~10% of the Ge. In sphalerite, Ge exists both as Ge⁴⁺ and Ge²⁺, while hemimorphite contains only Ge⁴⁺. Quartz, an abundant mineral with low Ge concentration (2 ppm), hosts ~25% of the Ge. Geochemical modeling shows that hemimorphite is more stable than sphalerite in waste piles and provides a thermodynamically stable secondary repository for Ge. However, hemimorphite is fine-grained, and if ingested or inhaled is readily soluble, with the potential to release Ge. While Ge has been linked to adverse health impacts, acute toxicity from ingestion of chat is unlikely at this site. However, little is known about low-level, chronic toxicity of Ge, or effects from its inhalation. This study shows how weathering can directly influence the distribution, speciation, and mineral hosts of Ge in mine wastes, which in turn can control the environmental stability, potential bioavailability, and metallurgical recovery strategies for Ge.