Adsorption of Gold(I) and Gold(III) Using Multiwalled Carbon Nanotubes

Abstract

Carbon nanotubes are materials that have been investigated for diverse applications including the adsorption of metals. However, scarce literature has described their behavior in the case of the adsorption of precious metals. Thus, this work reports the efficient adsorption of gold from cyanide or chloride media on multiwalled carbon nanotubes (MWCNTs). In a cyanide medium, gold was adsorbed from alkaline pH values decreasing the adsorption as the pH values were increased to more acidic values. In a chloride medium, the MWCNTs were able to load the precious metal and an increased HCl concentration (0.1–10 M), in the aqueous solution, had no effect on the gold uptake onto the nanotubes. From both aqueous media, the metal adsorption was well represented by the pseudo-second order kinetic model. In the cyanide medium, the film-diffusion controlled process best fitted the rate law governing the adsorption of gold onto the nanotubes, whereas in the chloride medium, the adsorption of the metal onto the nanotubes is best represented, both at 20 °C and 60 °C, by the particle-diffusion controlled process. With respect to the elution step, in cyanide medium gold loaded onto the nanotubes can be eluted with acidic thiourea solutions, whereas in the chloride medium, and due to that the adsorption process involved the precipitation of zero valent gold onto the multiwalled carbon nanotubes, the elution has been considered as a leaching step with aqua regia. From the eluates, dissolved gold can be conveniently precipitated as zero valent gold nanoparticles.

Multi-Walled Carbon Nanotubes

“…Alguacil [11] also characterized the possibility of applying MWCNTs as sorbents, but in this case, for gold(I) and gold(III) cations' adsorption from cyanide and chloride solutions. The reached data suggested that the recovery of the selected metal may be accomplished by subsequent elution with acidic thiourea solutions (for cyanide medium) or with aqua regia (for chloride solutions), with a further possibility of obtaining zero-valent gold nanoparticles.…”

Permeation of AuCl₄^- across a Liquid Membrane Impregnated with A324H⁺Cl^- Ionic Liquid

“…Among these residues, the materials generated from the electronic and communication industries are of importance [1,2], because they contained, among other valuable metals, gold. Thus, there is an interest, from worldwide researchers, to investigate methods for the recovery of this precious metal from these residues or, in general, gold-bearing wastes [3][4][5][6][7][8].…”

Transport of Au(III) from HCl medium across a liquid membrane using R₃NH⁺Cl^-/toluene immobilized on a microporous hydrophobic support: optimization and modelling

“…Very often, the recovery of gold from these wastes is done by leaching of the waste with aqua regia, resulting in a leachate in which gold is present as AuCl4 -or HAuCl4 [5]. The recovery of this precious metal from the HCl solution can be done mainly by activated carbon [6], ion exchange resins [7][8][9][10], liquid-liquid extraction using conventional [11][12][13] and ionic liquid [14][15][16][17] extractants, different adsorbents [18][19][20][21][22] and as mentioned above by liquid membranes [23][24][25][26]; more recently, the use of carbon nanotubes have been also considered in the treatment of dilute Au(III)-bearing HCl solutions [27][28][29].…”