The growing demand for rare earth elements (REE) driven by their applications in modern technologies has caused the need to search for alternative sources of these elements as their extraction from traditional deposits is limited. A potential source of light rare earth elements (LREE) may be the monazite present in the mining waste generated in the Bagre-Nechí mining district in Colombia due to the processing of sands containing alluvial gold. Consequently, in this research, a systematic evaluation has been carried out for the extraction of Ce, La, and Nd from a leach liquor obtained from monazite present in alluvial gold mining tailings. The leaching process carried out with HCl indicated the recovery of approximately 90% of La and Nd and ∼60% of Ce; the solvent extraction tests of these elements showed that increasing the contact time and pH of the leaching liquor positively affects the extraction of lanthanum, cerium, and neodymium, achieving extractions close to 100% with D2EHPA and to a lesser extent with Cyanex572. McCabe–Thiele diagrams for extraction with D2EHPA indicated the requirement of three stages for the extraction of Ce, La and Nd.

The pyrometallurgical copper extraction process generates 2.2 t of residues for each ton of produced metal. Initially, this paper shows the physical and chemical characterization of a copper processing residue, followed by the procedure to obtain the gold and silver that are contained in the copper residue. The characterization of a white metal oxidized calcine indicates a high content of copper as cupric ferrite, and important values of gold and silver. Gold and silver concentrations were 38.5 g t-1 and 1085 g t-1, respectively. The gold was found scattered in cupric ferrite grains, while the silver was dissolved in a matrix of Cu-S in amounts between 1 % and 50 %. Cyanidation tests showed that 95 % gold recovery could be obtained with a concentration of 0.06 g l-1 KCN, a pH of 10.5, room temperature, and a residence time of 80 h. When the temperature was increased to 75 °C, and the other cyanidation parameters were maintained intact, the same recovery was obtained but with a shorter residence time. Silver recovery was less than 30 % with a concentration of 1.2 g l-1 KCN, pH of 10.5, temperature of 45 °C, and a residence time longer than 72 h.

Polyacrylamides (PAM) are used as flocculants in the copper-molybdenum mining industry to improve the settling rate of flotation tailings. These types of reagents are recirculated to flotation in the water that is recovered from the thickeners, and as a result of this practice they can cause depression of flotation of some important minerals such as molybdenite. The objective of this work was to study the effect of a PAM of 11.9% of degree of anionicity on the flotation of molybdenite. The effect of the anionic PAM on molybdenite flotation was studied under different levels (three) of flocculant mechanical shearing. The flotation data was discussed along with intrinsic viscosity, adsorption, induction time, and electrophoretic mobility measurements. It was found that the non-sheared PAM (NS–PAM) had the strongest depressing effect on molybdenite flotation, followed by the moderately sheared PAM (MS–PAM). The depressing effect of the strongly sheared PAM (SS–PAM) was negligible. The flotation data correlated with the induction time measurements that showed that molybdenite became more hydrophilic in the presence of the NS–PAM. The SS–PAM has no effect on the induction times. Further work is ongoing to understand the effect of PAM on molybdenite flotation in the presence of clay minerals and different aqueous media.

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RESUMENEn este trabajo se presenta la caracterización mineralógica de tres yacimientos auríferos ubicados en el nordeste del departamento de Antioquia, Colombia, que actualmente son beneficiados con mercurio. A tres yacimientos de oro se le realizaron cinco pruebas: determinación de especies minerales y análisis de imágenes en falso color por QEMSCAN®; identificación y cuantificación de oro por FE-SEM; análisis al fuego y pruebas de cianuración. Los resultados por QEMSCAN mostraron que los yacimientos en estudio están formados principalmente por cuarzo, feldespato potásico, moscovita y pirita. Los resultados por FE-SEM arrojaron que el oro se encuentra principalmente como nódulos nanoscópicos esparcidos en la moscovita y el cuarzo. Otra cantidad de oro se encuentra en forma de electrum. El ensayo al fuego entregó que la cantidad de oro estaba entre 1 y 34 g/t y las pruebas de cianuración arrojaron que es posible extraer el oro hasta en un 80% solamente con molienda y cianuración directa sin ningún otro tratamiento. Estos resultados pueden ser la base para una propuesta con métodos metalúrgicos alternativos que permitan la extracción del oro sin la utilización de mercurio.Palabras clave: Caracterización mineralógica; Yacimientos; Oro; Mercurio; QEMSCAN; FE-SEM. ABSTRACTThis work presents the mineralogical characterization of three ore bodies gold located in the northeast of the department of Antioquia, Colombia, which are currently benefited with mercury. Five tests were carried out on three gold deposits: determination of mineral species and analysis of false color images by QEMSCAN®; identification and quantification of gold by FE-SEM; fire analysis and cyanidation tests. The results by QEMSCAN showed that the ore bodies are mainly composed of quartz, potassium feldspar, muscovite and pyrite. The results by FE-SEM showed that gold is mainly found as nanoscopic nodules scattered in muscovite and quartz. Another amount of gold is in the form of electrum. The fire assay showed that the amount of gold was between 1 and 34 g/t and the cyanidation tests showed that it is possible to extract the gold up to 80% only with grinding and direct cyanidation without any other treatment. These results can be the basis for a proposal with alternative metallurgical methods that allow the extraction of gold without the use of mercury.