Electrolytes pure gold

Figure 2 - Cyclic voltammetry (CV) of different electrodes (a) Au (pure gold), (b) RGO (roasted gold ore), (c) Mag (magnetite), (d) Hem (hematite) disc electrodes in 0.04 M NaCN solution at pH 10.5 with scan rate of 10 mV/s, argon bubbling onto the surface of electrolyte at 25 °C...

Figure 1 - Total gold in solution after leaching pure gold samples at the ocp in a solution of either lOOmM Na2S203(blue bars and red bars) or 100 mM CaS203 (green bars). Each electrolyte additionally contained ImM CuSCL,1 mM NaOH and 0, 1, 5, or 15 pM DMSA, in a system that was open to atmosphere, stirred and maintained at 50°C. Solution analysis was performed with ICP-MS for Na2S203 solutions or flame AAS for CaS203 solutions and converted into pg of gold per unit area of the gold sample. The error bars represent the standard deviation on 3 independent trials and the inset represents the ocp measured for the...

The cathode usually consists of pure gold, the anode of a metal less precious than gold silver is very often used. Polyethylene, polypropylene or Teflon are suitable as material for the membrane. A paste-like mass, which has recently replaced the previously common KOH/KCl electrolytes, serves as electrolyte. The remaining parameters for the electrode, such as velocity of approach, polarization DC voltage, zero (residual) current, temperature compensation, settling time for the measured value, gradient or sensitivity and measuring accuracy, should be taken from the... 

The films of pure 26 dispersed in the interior of a polymer matrix [poly(Af-vinyl-carbazole), polyimide] were prepared by casting from solution (method A1). The film thickness varied between 10 and 2600 nm. In contact with a weak acidic electrolyte pure films of 26 are remarkably stable and show reversible electrochromic reduction and oxidation (Eq. (16)) at 200mV vs NHE (AE = 19-38 mV, Fig. 22). Reduction takes place via transport of electrons (about 3 electrons per molecule of 26, Eq. (16)) from the gold carrier and intercalation of protons... 

Wohlwill process An early electrolytic process used to refine gold. It used crude gold as the anode and pure gold as the cathode with a solution of gold chloride in hydrochloric acid as the electrolyte. By applying an electrical current across the electrodes, pure gold... 

Pure Gold Electrolytes Alkaline baths are used exclusively for decorative purposes, for the deposition of thin layers of gold in color finishing of jewelry items and other decorative objects. The composition of typical alkaline cyanide baths used for the electrodeposition of gold is reported in Table 11.4 [2,3,61,62]. 

The base formulation of most snlfite based electrolytes for pure gold electrodeposition comprises the gold sulfite compound at concentration 12-16 g L (about 8-10 g L" as Au) sodium sulfite in the range 50-80 g L", and additional components such as a buffer and a chelating compound. Most commercial formulations are operated at pH 9.5-10.0 and temperature in the range 50-60°C,... 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

Betts Electrolytic Process. The Betts process starts with lead bullion, which may carry tin, silver, gold, bismuth, copper, antimony, arsenic, selenium, teUurium, and other impurities, but should contain at least 90% lead (6,7). If more than 0.01% tin is present, it is usually removed from the bullion first by means of a tin-drossing operation (see Tin AND TIN ALLOYS, detinning). The lead bullion is cast as plates or anodes, and numerous anodes are set in parallel in each electrolytic ceU. Between the anodes, thin sheets of pure lead are hung from conductor bars to form the cathodes. Several ceUs are connected in series. 

The impure copper from either process is refined electrolytically it is made into anodes and plated onto cathodes of pure copper. Other metals may be present in the impure copper and those with highly positive electrode potentials also are reduced. The rare metals—most notably, platinum, silver, and gold—obtained from the anode sludge are sold to recover much of the cost of the electricity used in the electrolysis. 

Vanadium predpitates the metal from solutions of salts of gold, silver, platinum, and iridium, and reduces solutions of mercuric chloride, cupric chloride and ferric chloride to mercurous chloride, cuprous chloride, and ferrous chloride, respectively. In these reactions the vanadium passes into solution as the tetravalent ion. No precipitation or reduction ensues, however, when vanadium is added to solutions of divalent salts of zinc, cadmium, nickel, and lead. From these reactions it has been estimated that the electrolytic potential of the change, vanadium (metal)—>-tetravalent ions, is about —0 3 to —0 4 volt, which is approximately equal to the electrolytic solution pressure of copper. This figure is a little uncertain through the difficulty of securing pure vanadium.5... 

These are very unreactive metals. Silver exists mainly as silver sulfide, Ag2S (silver glance). The extraction involves treatment of the pulverised ore with sodium cyanide. Zinc is then added to displace the silver from solution. The pure metal is obtained by electrolysis. Silver also exists to a small extent native in the Earth s crust. Gold is nearly always found in its native form (Figure 10.17). It is also obtained in significant amounts during both the electrolytic refining of copper and the extraction of lead. 

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