Recovery and remediation potential of copper and other PTEs in tailings from the Zambian copperbelt

Chisala, Precious

Thesis

Recovery and remediation potential of copper and other PTEs in tailings from the Zambian copperbelt

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Creator

Chisala, Precious

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2023

Thesis identifier

T17419

Person Identifier (Local)

201753532

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Civil and Environmental Engineering

Abstract

Mining activities generate large amounts of waste that can be detrimental to human health and the environment. In Zambia, mining has been ongoing since 1920 and potentially toxic elements (PTEs) have been left in mine wastes including copper mine tailings. Tailings of the Copperbelt including the bottom soil where they are currently sitting contain high enough levels of copper that they can be regarded as ore in other regions. This research focuses on recovery and remediation of copper and other PTEs in some tailings of the Copperbelt Province. Tailings were collected from three tailings sites in the Zambian Copperbelt: Akatiti, Kitwe, and Uchi. These tailings were thought to be from different time periods of mining with Akatiti coming from the second-oldest tailings dam in Zambia and Kitwe and Uchi coming from more recent activities. Physical and chemical characterisation of the tailings were carried out. All tailings and underlying soil material were classified as coarse-grained sands with some gravel and silt present at times. All were neutral to mildly alkaline (7.2≤pH ≤8.5). Copper content in tailings varied from 0.2-0.8% by mass, comparable to ore in other regions, and cobalt contents varied from 0.008-0.05% by mass. Underlying soils had copper and cobalt contents of 0.07-0.8% and 0.008-0.05%, respectively, indicating some mobilisation had likely occurred already. These levels indicated both opportunity for copper and cobalt recovery and need for remediation. Copper recovery from mined materials is normally carried out by pyrometallurgical or hydrometallurgical processes. Analogous to these methods, thermal treatments and soil washing were explored for potential copper-cobalt recovery and remediation in Akatiti and Uchi tailings. Thermal treatments involved smouldering or roasting. Treating the tailings via smouldering made the PTEs become more immobile and resistant to leaching, including copper. Roasting at 600°C and 1000°C had similar effects to differing extents. Smouldering and roasting affected the mineralogy of the tailings, changing the native pH and availability of PTEs including copper to differing extents. In contrast, soil washing with 0.5 M hydrochloric acid for 24 hours recovered 94%, 100%, and 58% of copper from Akatiti, Kitwe, and Uchi tailings, respectively, while also recovering 7-45% of other PTEs. This work shows that a combined remediation and resource recovery approach is feasible for Zambia’s copper tailings and should be explored to contribute to the 2030 national vision of Zambia for creating jobs for the local communities.

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