Obtención de carbón activado a partir de cáscara de “crescentia cujete” (totumo o mate) para la adsorción de oro por medio de soluciones cianuradas

Abstract

The present research is focused on obtaining activated carbon from the shell of "Crescentia Cujete" (commonly known as totumo or mate) with the objective of evaluating its capacity to adsorb gold in cyanide solutions. This study was carried out in response to the need to develop effective and low-cost adsorbent materials that can be used in the recovery of precious metals in mining. Initially, an analysis of the percentage of organic carbon present in the raw material was carried out using the Walkey Black methodology, obtaining a 50.44% organic carbon content in the peel. This value provided a basis for establishing the calcination conditions necessary for the preparation of the activated carbon. The activated carbon preparation process began with the crushing and sieving of the shell to a particle size between 0.5 and 2 mm, followed by washing with distilled water to remove impurities. Subsequently, chemical activation was carried out by impregnating the peel with 85% phosphoric acid (H3PO4), a process that was repeated to ensure homogeneous activation. The resulting mixture was subjected to continuous agitation for 24 hours and then washed again until a neutral pH was reached. Carbonization was carried out at different temperatures (450°C, 475°C and 500°C) in the absence of oxygen to avoid ash formation, thus determining the optimum treatment. Analysis of the activated carbon yields showed an average of 55.05%, suggesting the presence of a macro- and microporous structure in the activated carbon, in accordance with previous studies. However, the relatively low yield indicates that the activation conditions and the type of chemical used significantly influence the properties of the carbon. To evaluate the gold adsorption capacity, comparative tests were carried out between the activated carbon obtained from "Crescentia Cujete" shell and a commercial coconut shell activated carbon (HAYCARB) using a cyanide solution obtained from canton Camilo Ponce Enríquez with an initial concentration of 2,549 ppm. The tests were carried out in a jacketed glass reactor under normal temperature and pressure conditions. The test was monitored for 12 hours, recording hourly samples to be analyzed using atomic adsorption spectroscopy. These results suggest that, although the activated carbon from "Crescentia Cujete" has a lower initial adsorption capacity compared to commercial carbon, its adsorption capacity improves with time, which could make it suitable for applications where sustained adsorption is required. The difference in physicochemical properties between the two types of activated carbon underlines the importance of adjusting the activation and carbonization conditions to optimize the efficiency of the material in the adsorption of precious metals such as gold.