The gold AuIII + 3e(-)-->Au0 reduction and Au0-->AuIII + 3e- oxidation stripping processes in dilute aqua regia electrolyte (0.1 M HCl + 0.32 M HNO3) were examined at platinum, rhodium, iridium, gold and glassy carbon disk electrodes. After ascertaining that the preferred material was platinum, the effect of electrode size was evaluated by using nine different platinum disk electrodes having diameters ranging from 2 to 2000 microns. The optimum analytical response was obtained with a 50 microns diameter platinum disk electrode. With this electrode diameter, a sharp symmetrical gold stripping peak was obtained and the deposition process occurred predominantly under conditions of radial diffusion so that stirring of the solution was not required. In contrast, larger sized platinum electrodes produced a broader, asymmetric stripping response for the gold oxidation peak, whereas electrodes of smaller diameter provided poorer signal-to-noise ratios. The limit of detection and limit of quantification were calculated to be 4.4 x 10(-7) M (86 ppb) and 13.1 x 10(-7) M (258 ppb), respectively, at the 50 microns diameter platinum disk electrode under conditions of linear sweep stripping voltammetry at a scan rate of 200 mV s-1 and a 140 s deposition time. The optimum electrode gave a very well defined gold oxidation signal with negligible background current when applied to the determination of gold in a gold ore sample.
The protonation constant (pKa) of
SO42–(aq) has been
determined at ionic strengths 0.5 M ≤I ≤4.0 M in
NaCl and CsCl media at 25˚C by using Raman spectroscopy. These data were
used to calculate the association constant of the
NaSO4–(aq) ion pair in CsCl
media. The results are in excellent agreement with previous values obtained by
other techniques. The (pKa) was
also measured at I = 4 M in both media at
temperatures up to 85˚C and the associated enthalpy and entropy changes
were calculated. However, reliable thermodynamic data for the ion-pairing
reaction could not be obtained at higher temperatures probably because of
competition from CsSO4–(aq).
The concentration of antimony in copper plant electrolyte needs to be known at the ppm level. Spectroscopic techniques for trace metal determination in this electrolyte, such as atomic absorption and inductively coupled plasma (ICP) spectrometry only enable total antimony to be determined, whereas ideally the concentration of both the antimony(n1) and antimony(v) oxidation states needs to be known. For the determination of antimony(1n) and antimony(v) by differential pulse anodic stripping voltammetry (DPASV), the similar stripping peak potentials of -0.37 V(vs. AglAgC1) for copper and -0.27 V(vs. Ag/AgCl) for antimony in 5 M HCI mean that concentrations of copper greater than 6 times that of antimony cause difficulties in resolving the antimony and copper stripping peaks. In this article, a simple procedure is reported for the determination of antimony(m) and (v) in copper plant electrolyte after separation of antimony from copper by passing an ammoniacal solution of plant electrolyte through a column of Chelex-100 ion-exchange resin. Most of the copper is retained on the column so that the determination of antimony (1n)
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