Desorption Of Gold Research Articles

High Field Microscopy Studies of Gallium Arsenide-Metal Interface

ABSTRACTThe Field Emission Microscope has been extensively used in the study of metal and semiconductor surfaces. The process of Field Emission is, itself, of great interest and a considerable amount of both theoretical and experimental work has been carried out in this field. The Field Emission Microscope also yields useful information of a more practical nature, such as the nature of bulk and surface impurity, diffusion, chemisorption and surface potential barriers. It is essential that the surface to be studieg can be prepared in the form of a high curvature tip, with a radius of 10−5cm and can be cleaned sufficiently well for a symmetrical reproducible pattern to be observed.Field Emission technique has been applied to study the behaviour of thin overlayers of gold on GaAs. Using Fowler-Nordheim plots, change in the work function φ, is examined for temperatures, T=77K and T=300K. φ changes slightly for low doses of gold and significantly for larger ones {φ=4.3 − 3.7 eV}. Desorption of gold is also examined and the results indicate two different adsorbed states in Au-overlayers formed at room temperature. Finally, a brief description of sample preparation is also included.

Elution of gold from carbon by the micron solvent distillation procedure

The desorption of gold from activated carbon is promoted by adding organic solvents to aqueous cyanide solutions. At 65–80°C the elution of gold is fast and is not affected by water quality. The Micron procedure involves pretreatment of the loaded carbon with NaCN/NaOH followed by elution with methanol vapour and condensate. Carbon is packed into a column above the distillation pot and acts as a fractionating column. Recovery of the methanol condensate leaves a methanol-free concentrated gold solution and carbon containing less than 200 g t −1 gold suitable for recycling. Aqueous acetonitrile and ethanol are equally effective solvents and desorb gold from carbon slightly faster than methanol. Results of laboratory and pilot testwork using methanol, ethanol and acetonitrile are described. Typically, gold is stripped from the carbon in 4–6 hours in 1 bed volume of solution to give concentrated gold eluates. The carbon retains a high kinetic activity after solvent stripping which is slightly better than that after stripping by the Anglo or Zadra procedures. A cost evaluation indicates that the Micron procedure is cheaper than the Zadra procedure due to significant time and energy savings. It is suited to operations requiring regular and rapid carbon stripping and recycling.

Solvent elution of gold from C.I.P. carbon

The effectiveness of the solvents in promoting gold desorption from activated carbon is in the order acetonitrile > methyl ethyl ketone ⩾ acetone ⪢ dimethylformamide > ethanol. Aqueous acetonitrile and aqueous acetone strip gold in < 8 h using 2–3 bed volumes at temperatures between 25 and 70°C. These organic solvents in particular are strongly adsorbed onto carbon and significantly increase the activity of CN − relative to Au(CN) 2 −. Acetonitrile is quantitatively steam stripped from carbon and has little effect on the kinetic activity of carbon and on the electrowinning or cementation of gold. However, acetone is not so readily recovered from carbon and causes a significant loss of carbon activity. The concentrated gold eluates are readily electrowon in a batch or continuous mode using a simple diaphragm cell to give gold bullion foil. Preliminary cost analysis indicates that this procedure is cheaper than the Zadra elution procedure and comparable to the Anglo elution procedure.

Dynamic sorption and desorption of gold using Spheron DEAE as sorbent

The dynamic sorption and desorption of gold was studied using Spheron DEAE, a macroreticular hydroxyethyl methacrylate-ethylenedimethacrylate copolymer with chemically bonded diethylaminoethyl groups, as the sorbent. Factorial experiments were designed to optimize the composition of the mobile phase (H+ and Cl- ions); as a result, hydrochloric acid was used in a concentration of 0.01 mol l-1. Thiourea solution (0.4 mol l-1) in 0.25M hydrochloric acid served as the eluent: the gold sorbed was eluted completely in seven column volumes. A column of 1 cm3 volume retained gold quantitatively from 0.5 l of solution containing the metal in a concentration of 1 mg l-1 (5 μmol l-1); the recovery of gold by elution was 99% and the degree of concentration of gold with respect to the influent was a hundred. A method is worked out for a direct photometric determination of gold in the thiourea eluates, based on the decomposition of thiourea with hydrogen peroxide.

Recovery of gold from the plating rinse by adsorption with nylon fibers

Taking note of the affinity of some reverse osmosis membranes to Au(CN) - 2 in the citrate buffered gold plating rinse, we accomplished the recovery of gold by the adsorption to some polymers. Among several polymers, tested nylon fibre had the most excellent characteristics of adsorption. The amount of adsorption of gold on nylon fiber increased with a decrease in pH value of the solution, and 7.5 mg of gold was adsorbed on 1 g of nylon fiber at pH 3, 25°C. The rate of adsorption increased with an increase in temperature. In the case of desorption, the solution containing cyanide ions at a pH as high as 10 was desirable to be employed as an eluant. By passing the simulated plating rinse through a column of nylon fiber, the adsorption and desorption of gold was successfully accomplished. The maximum concentration of gold in the eluant was approximately 600 ppm.

Radiotracer studies of gold adsorption and desorption on clean molybdenum surfaces

The adsorption and desorption of gold on heat-cleaned surfaces of polycrystalline molybdenum was studied at a residual gas pressure of 2×10 −9 torr. A radio-tracer method was used in a differential pumping system. The sticking coefficient was measured to be s = 0·99 ± 0·01 at beam densities up to 10 11 particles/cm 2 sec. The desorption probability per unit time was found to obey a relation w = w 0 exp(− E/ kT) with w 0 = 2 · 10 13 sec −1 and E = 4·2 ± 0·2 eV.