Abstract:

The ongoing global transition to a net-zero economy will increase demand on mine production for critical metals to support green technology growth, with a consequent increase in production of mine waste volumes. Mine wastes typically contain various combinations of reactive sulfides and carbonate minerals, which have the potential to consume O₂ and emit CO₂ as well as influence discharge water quality, and reactive silicates which have potential to sequester CO₂via mineral carbonation.

Numerous previous research studies have documented evidence of both CO₂ sequestration and emissions within mine waste storage facilities (both operating and closed sites) around the globe, but despite this, the concept and related policies and implications for reporting and regulation are underdeveloped. Further, to date there is no well developed or standardised empirical testing method to directly estimate the relative change in pore gases (e.g., O₂ and CO₂) and long-term flux rates of these gases within both waste rock and tailings facilities.

This study presents a novel and potentially scalable method of measuring the relative balance between sulfide oxidation (and oxygen consumption), carbonate dissolution (and CO₂ release) and carbonation (CO₂ sequestration) rates within mine waste. The method includes the use of bespoke sealed and instrumented experimental cells and larger barrels to carry out short to medium term testing programs, along with the use of analytical geochemical methods to validate instrumentation data. The paper will outline the workings of the measurement method and present results from testing carried out on mine waste from sites in Northern Europe.

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Ben Gersten