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Carbon-based nanomaterials for gold (III) recovery: kinetics and loading investigations

AutorGarcía-Díaz, Irene; López Gómez, Félix Antonio ; Rodríguez, O.; Alguacil, Francisco José
Palabras clavecarbon nanomaterials
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Fecha de publicación14-feb-2016
ResumenCurrently, the development of different smart technology to recover or eliminate strategic or toxic metals from liquid effluent is constant. Among the different process developed to the treatment of liquid effluents bearing these types of metallic elements, include chemical or electrochemical precipitation, membrane based technology, ion exchange and adsorption. Adsorption is a high efficiency, cost-effectiveness and easily handing method to recover pollutants or strategic metals. Nowadays a research challenge is the development of new adsorbents. Among nanomaterials, carbon nanomaterials have adequate properties to be used as metal adsorbent. On the other hand gold is one of the most precious elements in the world. The price in 2015 of this strategic metal is 1.376 $/kg. Besides its uses in jewellery it is highly used in different industries, so it is important the gold recovery from liquid effluents generated from these various industries. The adsorption method is a way to treat these types of effluents, characterized for their low gold concentration. The aim of this research was to optimize various operational parameters, and thus obtain efficient carbon nanotubes processing for gold (III)-bearing effluents. The adsorption of gold (III) by carbon nanofibers (CNF), carbon multiwalled (MWCN) and carbon multiwalled with carboxyl group (MWCN_ox) systems were investigated. The experimental parameters which may influence gold adsorption were investigated, i.e. stirring speed of the aqueous solutions, adsorbent dosage, acid concentration, temperature etc. Figure 1 shows the effect of the acid concentration on the Au(III) adsorption to the three adsorbent. It can be seen that the adsorption Au(III) decreases with the increase of HCl concentration. Probalby it is due the existence of other gold species, such as HAuCl4, at the higher hydrochloric solution against the presence of the predominant AuCl4- species in the more dilute HCl solutions which are more adsorbable than the gold-acid form. SEM studies of gold loaded carbon nanomaterials show on the surface dark particles, Figure 2. The EDS of the dark particles show two peaks for Lα(9.7 keV) and Mα (2.1 keV) characteristic of metallic gold. Probably this reduction occurs on the carbon surface, related with the metal reduction. The isotherm and kinetic studies of the carbon nanomaterial-Au(III) system show a different behavior in function of the carbon nanomaterial used as adsorbent. The experimental data obtained using the MWCNT and CNF fit better to a pseudo second order equation and an isotherm Freundlich model. The three carbon nanomaterials, appeared to be a promising material for recovery of Au(III) from this type of acid solutions in the optimal experimental for each one of them condition.
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