Concentración de minerales mediante métodos físico-químicos. Aplicación a la obtención de fluorita de alta pureza

Abstract

flotation technique, minimizing the environmental impact. On one hand, it seeks to revalue a residue obtained in the concentration of minerals by physical methods. On the other hand, it is about reducing the amount of waste mineral generated in the extraction and concentration of minerals. With the reduction of the volume of dumps, environmental alterations of the flora and fauna that cause the exploitation of the mineral deposit are being eliminated. This Doctoral Thesis analyzes the flotability of the tailings generated both in the treatment plant of dense media and spirals until reaching grades accepted in the market. Fluorite flotation was already carried out in the Sierra de Lújar deposit in the 1970s by the company Sociedad Minero Metalúrgica de Peñarroya (SMMP). However, they found several problems in the process that were collected in internal reports. Acid grade fluorite (> 97.00% CaF2) was obtained by applying high temperatures, high doses of reagents, and treatment of flotation water, which made the process unprofitable and highly dependent on market prices. In the first chapter of this Doctoral Thesis, a study of the main physical and chemical variables that affect the flotation process is carried out. The reagents used in this chapter were the same used in the 1970s by the SMMP company. First, a design of experiments was performed to determine the optimum reagent concentration in the flotation process for the fluorite residue. The doses of potato starch, quebracho, white dextrin, oleic acid, and sodium silicate were studied. All flotation experiments were carried out on a laboratory scale in a mechanical flotation cell. The results were satisfactorily adjusted to the mathematical model, obtaining correlation coefficients of 91.58% for the metallurgical recovery and 98.51% for the fluorite grade in the concentrate. The optimization of results led to obtaining, for the roughing stage, a metallurgical recovery of 60.45% with a fluorite grade in the concentrate of 68.99%. Later, another design of experiments was carried out with the physical variables; agitation speed, air flow, and time in addition to the pH of the medium. The concentration of flotation reagents was set at the optimal values obtained in the first design. The results of this second design of experiments were adjusted to a polynomial mathematical model, obtaining a fluorite grade of 76.21% and a metallurgical recovery of 70.57%. In the second chapter, new flotation reagents were studied and compared with those used in the first chapter. The studies were carried out under two different flotation equipment (mechanical cell and pneumatic column) to show how the different reagents act under both configurations. First, mixtures of quebracho with other depressants such as white dextrin, potato starch, carboxymethyl cellulose, and sodium hexaphosphate were studied. The best results were obtained with the combination of quebracho and white dextrin, achieving fluorite grade values in the concentrate of 74.00% in pneumatic column and 70.50% in the mechanical cell, both in the stage of roughing. Metallurgical recovery values were also higher when the same depressor mix was used with the pneumatic column configuration. However, the results obtained when only quebracho was used as a depressant are close to those obtained with the quebracho-dextrin mixture. Subsequently, a study was carried out of the different fluorite collectors present in the market, oleic acid, sodium oleate, and potassium oleate, as well as some under development DP-OMC-1033 (DP-I) and DP-OMC-1234 (DP-II). DP collectors are formulated from fatty acids (oleic, linoleic) and resinous acid. DP-II incorporates a sparkling wine in its composition. These collectors were studied under different doses and temperature ranges in a mechanical flotation cell and a pneumatic column, both equipment on a laboratory scale. The results showed that the best values in terms of metallurgical recovery were obtained with the use of the DP-II collector, reaching 87.90% under a concentration of 100 g/ton. However, the best result in terms of fluorite grade in the concentrate was 79.70% for the roughing stage using a dose of 100 g/ton from the DP-I collector. With the increase in temperature, from 25ºC to 55ºC, all the collectors experienced substantial improvements in terms of metallurgical recovery except for the DP-I and DP-II collectors, which only showed slight improvements. Finally, in the third chapter, a pneumatic column flotation scaling was carried out, designing a pilot plant composed of three flotation columns. First configuration consisted in a roughing stage and two cleaners. Based on the results obtained in previous chapters, the DP-II collector and the quebracho depressor were chosen as flotation reagents. Two collector doses were tested: 100 g/ton and 150 g/ton. The results obtained showed a better metallurgical recovery when the high collector concentration was used, reaching a global value of 80.30% with a fluorite grade in the second cleaner of 91.10%. Then, in an attempt to increase the overall metallurgical recovery value, one of the cleaners was removed, making it a scavenging stage. In this new circuit, the overall metallurgical recovery for a collector dose of 150 g/ton, was 92.10% with a fluorite grade in the cleaner stage of 82.10%. Finally, the number of tailings needed to reach acid-grade fluorite in the first circuit was estimated, based on a polynomial fit. Four cleaners were necessary when a high concentration of collector was used and five when a low concentration of collector was used.