Silver
is a metal widely applied in renewable energy applications
and therefore subject to resource scarcity. The paper presents a new
approach for recovering silver from zinc-containing solutions mimicking
hydrometallurgical base metal process solution. By nature, silver
present in ores or concentrates is more noble than zinc and not effectively
leached into the sulfate media during zinc hydrometallurgical processing.
This paper presents a novel approach for concentrating and recovering
silver present in minor amounts in zinc sulfate media. The electrodeposition–redox
replacement (EDRR) method was investigated in synthetic zinc sulfate
solutions ([Zn] = 60 g/L, [Ag] = 1 ppb–250 ppm, [H2SO4] = 10 g/L) containing silver as low as 1 ppb. The
deposited metal coating was analyzed by electrochemical techniques
and SEM-EDS. As a result, an enrichment of silver as nano- and microparticles
on electrodes was evident. With the application of multiple EDRR steps
(n = 160), the method was shown to result in a high
purity Ag layer (Ag/Zn ratio ≈ 1500 in the product) from solution
with minor Ag content (Ag/Zn ratio ≈ 0.0017 in solution). Moreover,
at the concentration levels studied, the EDRR method was shown to
outperform conventional electrowinning (EW).
Site-specific assembly of gold nanoparticles on a polysaccharide surface was accomplished via a straightforward method exploiting interfacial polymer blends, selective protein adsorption and electrostatic interaction. The method could be useful in further applications due to the universal nature of the utilized phenomena.
In
the current study, platinum—present as a negligible component
(below 1 ppb, the detection limit of the HR-ICP-MS at the dilutions
used) in real industrial hydrometallurgical process solutions—was
recovered by an electrodeposition–redox replacement (EDRR)
method on pyrolyzed carbon (PyC) electrode, a method not earlier applied
to metal recovery. The recovery parameters of the EDRR process were
initially investigated using a synthetic nickel electrolyte solution
([Ni] = 60 g/L, [Ag] = 10 ppm, [Pt] = 20 ppm, [H2SO4] = 10 g/L), and the results demonstrated an extraordinary
increase of 3 × 105 in the [Pt]/[Ni] on the electrode
surface cf. synthetic solution. EDRR recovery of platinum on PyC was
also tested with two real industrial process solutions that contained
a complex multimetal solution matrix: Ni as the major component (>140
g/L) and very low contents of Pt, Pd, and Ag (i.e., <1 ppb, 117
and 4 ppb, respectively). The selectivity of Pt recovery by EDRR on
the PyC electrode was found to be significant—nanoparticles
deposited on the electrode surface comprised on average of 90 wt %
platinum and a [Pt]/[Ni] enrichment ratio of 1011 compared
to the industrial hydrometallurgical solution. Furthermore, other
precious metallic elements like Pd and Ag could also be enriched on
the PyC electrode surface using the same methodology. This paper demonstrates
a remarkable advancement in the recovery of trace amounts of platinum
from real industrial solutions that are not currently considered as
a source of Pt metal.
The electrochemical method for gold extraction from multi-metal industrial solutions in an environmentally benign and energy efficient manner is explained in detail.
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