IntroductionWithin the context of gold extraction, the dissolution step of gold-bearing materials is carried out using two main aqueous media: cyanide or chloride solutions, and if the first used the leaching of gold from raw materials, the latter is useful to recover this precious metal from secondary materials and residues, i.e. anode slimes and jewelry scrap. Both dissolution media required both a complexant (cyanide or chloride) and an oxidant (air or nitric acid/chlorine) to achieve acceptable leaching rates and yields.In the particular case of chloride leaching and once gold is dissolved, the metal is presented in the solution as the gold (III)-chloro complex (AuCl4 -) with square planar structure.Very often, and prior to the ultimate gold recovery, a solution purification and/or concentration step is needed in order to produce a higher grade solution. Among the various separation/concentration steps, the use of liquid-liquid extraction, membrane technologies, carbon adsorption and ion exchange has been described [1][2][3][4][5]. In many cases, the adsorption of a solute in a solid support has the advantage over liquid-liquid extraction or even membrane technologies in that no mixing and settling requirements have to be fulfilled and organic phase loss through entrainment is eliminated, also the use of an intermediate step such as filtration is avoided.Due to the anionic nature of the gold (III)-chloro complex, the use of anionic exchangers (and also chelating resins) on the adsorption of this precious metal had been reported in the literature [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In the present work, the adsorption and elution of gold (III) from hydrochloric acid solutions were investigated using the anionic exchange resin Lewatit MP-64. The influence of various parameters affecting the metals adsorption on the resin is studied and a kinetic study to explain the metal uptake is presented, whereas metal elution from the loaded resin is studied using acidic thiourea solutions. The final recovery from the eluates is accomplished by the use of an alkaline borohydride solution.
ExperimentalThe ion exchange resin Lewatit MP-64 (Fluka) was used to adsorb gold (III) from hydrochloric acid solutions. Lewatit MP-64 is a macroporous medium-basic anion exchangecrosslinked polystyrene matrix resin containing tertiary and quaternary ammonium groups (Cl -form-free base). Prior to its use for gold adsorption, the resin was dry until constant weight. Aqueous Au(III) stock solution was prepared from solid HAuCl4 (Fluka), whereas working solutions were prepared by dilution. Other chemicals used in the present investigation were of AR grade.Batch adsorption (elution) experiments were carried out by mixing (750 min The processing of gold (III)-hydrochloric acid solutions by the anionic ion exchange Lewatit MP-64 resin has been investigated. The influence of several variables such as the temperature, the hydrochloric acid and metal concentrations in the aqueous solution and the variation of the amount of resin ...