Abstract
This paper introduces the concept of ‘Precision Mining’ of metals which can be defined as a process for the selective in situ uptake of a metal from a material or media, with subsequent retrieval and recovery of the target metal. In order to demonstrate this concept nanoscale zerovalent iron (nZVI) was loaded onto diatomaceous earth (DE) and tested for the selective uptake of Cu from acid mine drainage (AMD) and subsequent release. Batch experiments were conducted using the AMD and nZVI-DE at 4.0–16.0 g/L. Results demonstrate nZVI-DE as highly selective for Cu removal with >99% uptake recorded after 0.25 h when using nZVI-DE concentrations ≥12.0 g/L, despite appreciable concentrations of numerous other metals in the AMD, namely: Co, Ni, Mn and Zn. Cu uptake was maintained in excess of 4 and 24 h when using nZVI-DE concentrations of 12.0 and 16.0 g/L respectively. Near-total Cu release from the nZVI-DE was then recorded and attributed to the depletion of the nZVI component and the subsequent Eh, DO and pH recovery. This novel Cu uptake and release mechanism, once appropriately engineered, holds great promise as a novel ‘Precision Mining’ process for the rapid and selective Cu recovery from acidic wastewater, process effluents and leach liquors.
Highlights
BET surface area analysis determined that the surface area of the diatomaceous earth (DE) was 29.7 m2/g compared to 6.5 m2/g recorded for the nanoscale zerovalent iron (nZVI)-DE, with the lower surface area of the latter material attributed to agglomeration of the material
high resolution transmission electron microscopy (HRTEM) analysis determined that the DE comprised Si bearing frustules of various shapes and sizes in addition to a minor component of fragmented Si bearing material, which were likely frustules which have been mechanically broken, with sizes ranging from submicron scale to hundreds of microns in diameter (Fig. 1 and S1)
This suggests that each nZVI particle was likely to have formed directly upon the surface of the DE, i.e. as an ultra-small nanoparticle nuclei which subsequently grew upon the DE surface into the final nZVI product
Summary
Popescu et al, 2013) This method has been applied at various scales (up to field scale) and its major limitation is that the surface amendment often isolates or interferes with the ability of nZVI to react with aqueous contaminants (Crane and Scott, 2012). Another approach is to immobilise the nanomaterial onto a matrix support, which has the additional benefit of curtailing concerns regarding the escape of nanomaterials into the environment. This study has been established in order to bridge this gap in our understanding and investigate whether nZVI-DE could be applied for the Precision Mining of Cu from AMD, which is one of the most prominent environmental issues currently facing the mining industry, and regarded by the European Environment Bureau and the US Environmental Protection Agency as rated “second only to global warming and stratospheric ozone depletion in terms of global ecological risk” (European Environment Bureau, 2000)
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