Processing of residual gold (III) solutions via ion exchange

Abstract

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 ...

Studies of Gold Adsorption from Chloride Media

“…The diminishing availability of mineral resources and the increasing demand for gold metal emphasize the importance of its recovery from waste solutions and scrap materials 2,3 . During the past three decades, many recovery methods have been used, such as cementation 4 , precipitation 5 , ion-exchange 6 and solvent extraction [7][8][9] , and adsorption [10][11][12][13] . Both precipitation and cementation techniques result in higher efficiencies, but they generally do not ensure a complete purification, i.e., further treatment is inevitably necessary.…”

Separation of Ag(I) by Ion Exchange and Cementation from a Raffinate Containing Ag(I), Ni(II) and Zn(II) and Traces of Cu(II) and Sn(II)

“…Less than 5% of silver(I) was adsorbed into Lewaitit MP-64. The adsorption reaction of tin(II) and zinc(II) into Diaion WA21J and Lewaitit MP-64 can be represented as [22]. [Lewaitit MP-64] = 0.5-8 (g/L), time = 6 h, shaking speed = 200 rpm.…”

Simultaneous Coprecipitation of Pd(ii), Rh(iii) and Au(iii) With Mn(oh)2 Without Chelating Agent Prior to Flame Atomic Absorption Spectrometry Determination

“…[7][8][9][10][11] In order to solve these problems, separation-enrichment techniques including solid phase extraction, cloud point extraction, liquid-liquid extraction, coprecipitation, etc. [12][13][14][15][16][17][18] have been used by the researchers around the world. Coprecipitation has also an important place in the preconcentration and separation methods due to its some advantages including simplicity, high preconcentration factors, and low consumption of organic solvent and short analysis time period for the procedures.…”