Abstract
The effect of the physical properties of an activated carbon such as pore size distribution, specific surface, pore average diameter, in the gold adsorption from cyanide solution with the gold to the Au (CN)–2 form, was studied. To meet the proposed objectives two carbons were studied: carbon A with specific surface of 985 m2 / g, 57 % of micropores and 1.85 nm as average diameter of pores and carbon B with specific surface of 786 m2 / g, 27 % and pores of 2.35 nm as average diameter of pores; both granular carbons made from coconut shell. Batch adsorption tests were performed in a reactor of 500 ml of capacity with mechanical stirring at constant temperature. The effect of cations present in the aqueous solutions such as Ca2+, Na+, K+ and Li+, the effect of pore size distribution, the effect of average pore diameter and surface area were evaluated in function of the rate and amount of gold adsorbed on the activated carbons denominated as A and B. The results to indicate that the physical properties of an activated carbon are an important factor in the gold adsorption process in terms of rate and amount of adsorbed gold. The carbon B with 786 m2 / g of specific surface area reached a higher load per unit area (0.02 mg Au/m2) in relation to the carbon B of 985 m2 / g which had a load of 0.01 mg Au / m2, after 6 h of contact carbon-solution. The rate adsorption of gold in both carbons is controlled by mass transfer in the liquid film surrounding the carbon particles to short times or small loads of gold in the particles, far from equilibrium. Applying a first order kinetic model, it was obtained that the ratio of the kinetic constants for carbons A and B, ie (kB / kA), fluctuates in a value of 3 for the different cations in study. In general it is possible to say that the rate adsorption and the amount of adsorbed gold increased with the increase in macropores and with the increasing pore average diameter. The presence of cations favors the gold adsorption in cyanide media, especially those of higher valence.
Highlights
Se estudió el efecto de las propiedades físicas de un carbón activado, tales como distribución de tamaño de poros, superficie específica, diámetro promedio de poros, en la adsorción de oro desde disoluciones cianuradas, con el oro disuelto a la forma de Au (CN)
The effect of cations present in the aqueous solutions such as Ca2+, Na+, K+ and Li+, the effect of pore size distribution, the effect of average pore diameter and surface area were evaluated in function of the rate and amount of gold adsorbed on the activated carbons denominated as A and B
The carbon B with 786 m2 / g of specific surface area reached a higher load per unit area (0.02 mg Au/m2) in relation to the carbon B of 985 m2 / g which had a load of 0.01 mg Au / m2, after 6 h of contact carbon-solution
Summary
El uso del carbón activado se ha incrementado en el campo de la Hidrometalurgia, especialmente, en la recuperación de oro y plata desde soluciones cianuradas, por ser el más versátil de los adsorbentes sólidos usados en la industria, debido a su elevada área superficial y su distribución de tamaño de poro, bimodal (a veces trimodal), que proporciona el buen acceso de las moléculas del adsorbato al interior de las partículas[1,2,3]. La adsorción bajo condiciones de alta fuerza iónica, como en plantas reales, involucra un mecanismo de par iónico en el cual los pares iónicos del tipo Mn+[Au(CN)–]n son adsorbidos en la superficie del carbón sin cambio. Este trabajo tiene como objetivo estudiar la influencia de las propiedades físicas del carbón activado en el fenómeno de adsorción de oro desde medio cianuro tomando en cuenta, principalmente, las propiedades de superficie específica y distribución de tamaño de poros de los carbones estudiados y su relación con la velocidad de adsorción y cantidad de oro adsorbido
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