Selective formation of copper nanoparticles from acid mine drainage using nanoscale zerovalent iron particles

R.A Crane,D.J Sapsford

doi:10.1016/j.jhazmat.2017.12.014

Abstract

Nanoscale zerovalent iron (nZVI) has been investigated for the selective formation of Cu nanoparticles from acid mine drainage (AMD) taken from a legacy mine site in the UK. Batch experiments were conducted containing unbuffered (pH 2.67 at t = 0) and pH buffered (pH < 3.1) AMD which were exposed to nZVI at 0.1–2.0 g/L. Results demonstrate that nZVI is selective for Cu, Cd and Al removal (>99.9% removal of all metals within 1 h when nZVI ≥ 1.0 g/L) from unbuffered AMD despite the coexistent of numerous other metals in the AMD, namely: Na, Ca, Mg, K, Mn and Zn. An acidic pH buffer enabled similarly high Cu removal but maximum removal of only <1.5% and <0.5% Cd and Al respectively. HRTEM-EDS confirmed the formation of discrete spherical nanoparticles comprised of up to 68% wt. Cu, with a relatively narrow size distribution (typically 20–100 nm diameter). XPS confirmed such nanoparticles as containing Cu°, with the Cu removal mechanism therefore likely via cementation with Fe°. Overall the results demonstrate nZVI as effective for the one-pot and selective formation of Cu°-bearing nanoparticles from acidic wastewater, with the technique therefore potentially highly useful for the selective upcycling of dissolved Cu in wastewater into high value nanomaterials.

Highlights

Each individual Nanoscale zerovalent iron (nZVI) particle was recorded to contain a discrete outermost layer, which is attributed to be the presence of an oxide shell surrounding the Fe◦ core
In addition dark mottles were recorded within the metallic cores which indicates that individual particles are either polycrystalline or comprised isolated metal crystals in an otherwise amorphous matrix
X-ray photoelectron spectroscopy (XPS) analysis determined the outer surface of the nZVI is comprised of a mixed valent (Fe2+/Fe3+) oxide overlying a Fe◦ core

Summary

Introduction

Whilst it is possible to recover metals from dilute aqueous effluents using existing active treatment technologies e.g. ion exchange [1], the absence of widespread commercial practices for the recovery of metals from AMD indicates that the economic value of the metals rarely offsets the operating costs of recovery. As such a fundamental barrier exists where either the cost of AMD treatment needs to significantly decrease or the economically valuable metals present in such waste needs to be valorised into higher-value products, i.e. products which are worth significantly more than their raw metal value. Such nanomaterials could be directly utilised as high value materials and/or reagents in a range of different processes, and as such provide significantly greater economic return than their equivalent bulk scale metal

Methods

Results

Conclusion