Ion exchange technology for the efficient recovery of precious metals from waste and low-grade streams
V Yahorava, M Kotze
Efficient recovery of precious metals from process solutions is
essential for improving process economics. Traditionally, precious
metals are relatively effectively recovered from waste streams via
precipitation or cementation. However, these approaches have a
number of drawbacks, including poor water balance, creation of
environmentally unfriendly waste streams, and losses of precious
metals. Ion exchange technology is an alternative for the recovery of
precious metals from waste or low-grade streams. This technology
allows the recovery of the precious metals to extremely low levels
(micrograms per litre) with relatively high upgrade ratios from the
solution onto the resin without major water balance concerns, while
the impact on the environment could be minimized or avoided.
Research was conducted on the recovery of platinum group
metals and gold from different low-grade and waste streams from one
of the precious metals refineries in South Africa by means of ion
exchange. Various functionalities and matrices (granular and
fibrous) of ion exchange materials were evaluated. The results from
these studies indicated that in some cases ion exchange could be very
effective for the recovery of precious metals, and that the PGM
concentration could be reduced to < 1 mg/L. The upgrading ratios of
the various PGMs onto the specific fibres were relatively high for the
specific streams evaluated, which might in some cases justify
incineration of the loaded material instead of stripping and recycling
the adsorbent. The cost of direct incineration for one of the waste
streams tested would be less than 1% of the value of the PGMs
recovered. However, the adsorbent has to be carefully selected and
the process design optimized for each specific stream.
Keywords: PGMs and Au refining, precious metals, waste streams, low-grade
streams, ion exchange, resin, fibre, recovery.