Gc. Lukey et al., The effect of functional group structure on the elution of metal cyanide complexes from ion exchange resins, SEP SCI TEC, 35(15), 2000, pp. 2393-2413
Previous investigations have established that the thiocyanate anion and the
zinc cyanide complex are suitable eluants for the simultaneous recovery of
metal cyanide complexes from ion-exchange resins. However, the effect of t
he ionic density of the resin and the stereochemistry of the functional gro
up on metal recovery has never been systematically studied. The present stu
dy investigated the elution properties of five experimental resins that hav
e the same type of resin matrix but contain different aliphatic amino funct
ional groups. It is shown that ammonium thiocyanate is not a suitable eluan
t because iron and zinc are not completely eluted from any of the resins st
udied. It has been proposed that this is due to the precipitation of Zn-2[F
e(CN)(6)] and possibly Fe-4[Fe(CN)(6)](3) within the resin pores. It has be
en established that potassium thiocyanate at a pH greater than 12 can be us
ed to recover more than 80% of copper, zinc, and iron within the first 10 b
ed volumes of eluant for most resins. The recovery of gold from each resin
using potassium thiocyanate has been shown to be considerably slower than t
hat of other metals, with approximately 60% recovered after 20 bed volumes
of eluant. It has been found that the length of the alkyl chain of the func
tional group does not significantly affect the elution of metal cyanide com
plexes from the resins studied using the thiocyanate eluant. The elution of
metals from all resins has been found to be superior when using a 0.5 M zi
nc cyanide eluant at a temperature of 50 degreesC. More than 90% of copper,
silver and iron were recovered from most resins within 4 bed volumes of el
uant. However, the recovery of gold using a zinc cyanide eluant is dependen
t upon the ionic density of the resin and also the stereochemistry of the a
ttached functional group. The results of this study show that zinc cyanide
is not a suitable eluant for gold-selective ion-exchange resins.