Thermodynamic Study of Leaching Conditions of Galena with Citrate Ions and Hydrogen Peroxide as Oxidizing Agent

Galena is the most important mineral for lead production, as it is the main source of lead in the world. Currently, the concentrates of this mineral are mainly treated using pyrometallurgical methods, creating several environmental problems, such as the generation of toxic and greenhouse gases. In addition, these processes involve high energy consumption, which limits their applicability. Hydrometallurgical routes are proposed as alternative processes for obtaining some metals such as silver, copper, gold, etc. The drawback of these processes is that the minerals tend to be passive in aqueous media. To mitigate this issue, researchers have used extreme conditions of pressure and temperature (6 atm. and 155 degrees C) or the use of very corrosive conditions. In this sense, the use of complexing agents that dissolve the metals of interest has been proposed. Citrate ion is one of the most promising complexing agents for galena leaching, obtaining high percentages of dissolution in relatively short times. Unfortunately, there has not been enough investigation about the concentration optimization of the complexing in the pH range from 5 to 9. In this sense, thermodynamic diagrams, such as the Pourbaix diagrams, are very useful for this purpose. Therefore, in this work, the effects of pH and temperature on the leaching of galena in citrate ion solutions are studied thermodynamically and experimentally. The experimental work was carried out with pure galena samples with a particle size of +149 - 74 mu m (-100 + 200 mesh). The results show that higher recoveries were obtained working at a pH of 8 and at temperatures of 30 and 40 degrees C. The thermodynamic and experimental data demonstrated that the existence of an optimal concentration of citrate ion, due the extraction of lead from galena, has a greater reaction rate at a relatively low initial concentration of 0.3 M. This is due the formation of the complex lead citrate 1 (Pb(cit)-).

Automated summary

In the leaching process of galena, the use of citrate ion as a complexing agent can achieve high dissolution rates in a relatively short period of time. The optimal complexing agent concentration for lead extraction shows the highest reaction rate at a pH of 8 and temperatures of 30 and 40 degrees Celsius.