Behaviour of Metals during Bioheap Leaching at the Talvivaara Mine, Finland

Hanna Tuovinen,David Read,Esa Pohjolainen,Janne Lempinen,Dina Solatie,Jukka Lehto,Mila Pelkonen

doi:10.3390/geosciences8020066

Abstract

The behaviour of base metals Ni, Zn, Cu, Co, Fe, and Mn, potentially toxic metals Pb, Cr, and Cd, and the radioactive elements, U and Th, in the Talvivaara mining process, Finland has been studied by tracing metal concentrations from the black schist ore, through ores subjected to bioheap leaching of varying duration, to pregnant leach solution (PLS), and solid process waste material deposited on site in gypsum waste ponds. It is apparent that Zn, Cu, Co, and Cd are leached from the ore in a similar manner and recovered efficiently in the PLS; however, Ni, though leached, was also found in the gypsum pond at relatively high concentrations. Relatively little Pb is released from the ore, but the small fraction that is mobilised accumulates in the gypsum pond. Of the radioactive constituents, Th is essentially immobile, whereas U is readily leached from the ore, again accumulating in gypsum pond waste. In addition, a laboratory-based sequential leach test was applied to assess the future leaching potential of metals from residual ore and process waste material under different environmental conditions.

Highlights

Heap leaching is an advantageous method to extract metals from low-grade ores and it has been utilized at large scales to extract gold, uranium, and copper [1]
In our previous paper we reported on the behaviour of radionuclides in the Talvivaara mining process [9]
The present paper focuses on the behaviour of associated metals, including base metals (Ni, Zn, Cu, Co) and potentially toxic metals (Cd, Cr, Pb), which were measured in the ore heaps, pregnant leach solution, and solid process waste to evaluate their fate through the various stages of the mining process

Summary

Introduction

Heap leaching is an advantageous method to extract metals from low-grade ores and it has been utilized at large scales to extract gold, uranium, and copper [1]. A special type of heap leaching, bioheap leaching makes use of microbially-induced enhancement of the metals leaching from the ore. Cause more severe environmental effects than conventional processing, especially with respect to contamination of surrounding water systems during ore processing and after closure of a mine [3]. The volumes of both the process waters and the solid waste materials left on site after mine closure are very high and can lead to severe environmental impacts if not properly managed. Acidic environments can further dissolve potentially-toxic metals from surrounding materials and cause contamination of natural water systems. Due to Geosciences 2018, 8, 66; doi:10.3390/geosciences8020066 www.mdpi.com/journal/geosciences

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