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Rare soil and rare metals identified in Colombian coal

Colombia holds first place in Latin America in coal production and exports, producing Col $2.2B in royalties, it is also used to produce power and coke, a solid fuel formed by distillation. However, currently, other countries are researching it as a source of rare metals and rare soils, as they can have some type of enrichment in their forming processes.

These metals and soils are important as they are used in manufacturing mobile phone parts, computers, nuclear reactors, lasers, rockets, and lithium batteries, among many other technological applications.

According to research on coal formation in several basins around the world, some of the conditions related to the enrichment of these metals in coal are the proximity to magmatic bodies, volcanic material near coal beds, and the presence of mineralizing hydrothermal solutions and leaching of volcanic rocks.

Read more: Without “rare lands” there wouldn’t be any technology (in Spanish).

Rare metals, such as gallium, lithium, and germanium as well as rare soil elements such as lanthanum, cerium, praseodymium, neodymium, samarium, and europium, among others have high magnetic and optical properties, therefore they have great technological applications; producing the need to look for new sources to satisfy the growing demand. Therefore, there are multiple research projects to try to determine important concentrations of some of these elements in coal, turning it into an unusual source.

An example of its use is in China, where they use it for producing power and then they recover the germanium from the ashes to manufacture ingots and make solar panels and optic fiber, which are marketed around the world.

In this scenario, for Universidad Nacional de Colombia (UNal) in Medellín Faculty of Mining, Engineering Ph.D. Olga Patricia Gómez Rojas, this is an opportunity to provide guidelines for future exploitation and use of coal in the center region of Colombia, (Provinces of Boyacá, Cundinamarca, Antioquia, and Caldas, and the inter and intra cordillera of the Colombian Andes.)

The research project hoped to determine the coal forming conditions in said regions that favor metal enrichment, rare soils, and the presence of contaminating metals, taking into account that a greater part of the production in this region is destined to internal consumption and therefore ashes could be recovered.

Discovery of metalliferous coals

Metalliferous coals are those enriched by metals 10 times above the world average (Clarke concentration) and Gomez´s research provides evidence that in the said areas they discovered elements such as lithium and gallium, besides rare soils.

Read more: The most ancient rocks are in the Amazon (in Spanish).

The coals researched correspond to the Guaduas Formation in the Provinces of Boyacá and Cundinamarca, the Amagá formation in the Province of Antioquia, and the volcaniclastic sequence of Aranzazu in the Province of Caldas. These areas were chosen for the geological conditions of their formations, among other factors, ideal for the enrichment of rare metals and soils with environmental and economic impact.

In the areas studied there are coals of different ranges, composition (maceral and mineral content), and paleo-environmental formation conditions. Coal is a sedimentary rock composed of special organic material in different stages of preservation and evolutionized by the increase in temperature and pressure for millions of years, what is known as “coal range”, which passes from peat moss, lignite, sub-bituminous, and anthracite.

The presence of mineral material –including minerals, dissolved salts, and metals– could be present in variable proportions according to the formation environment.

The organic components are recognized through a microscope and known as macerals and have optimal features. There are three groups, vitrinite, liptinite, and inertinite, according to the types of organic material and the paleo-environment.

For instance, the world average concentration of gallium is 5.5 parts per million, while that in some basins analyzed by Gómez, she discovered 93 ppm, much more that could be expected in coal.

For the research project, they took 55 samples from different active mine fronts, except in the Province of Caldas that were made from outcroppings as there aren’t any active mines in this area. After collecting them, they were stored in sealed bags so their properties would not be altered.

To comply with the goals of the research project, they used characterization techniques such as X-ray diffraction, Mössbauer spectroscopy, scanning electron microscope, and petroglyphic and physical-chemistry analysis. Additionally, she used statistical methods or characterization methods that allow mineral, metallic, and maceral qualitative and quantitative analysis in coal. For example, this allows observing forms, sizes, association and distribution, quantification, and establishing uses. They also used a descriptive classification method for the data of the basins analyzed.

According to the researcher, the coals from Caldas have rare soil enrichment, lithium, and gallium in greater concentrations than the world average. These areas are not being currently exploited because the coal has low caloric value and high ash content.

Value-added product

For Earth Sciences Ph.D., Coal Science and Technology M.Sc. Astrid Blandón Montes the most valuable part of Gomez’s research project is the additional benefit acquired by coals and Colombia as one of the main suppliers in Latin America.

“Up to now, Colombia had never approached the topic from the geological standpoint, therefore with this new future methodology and after other research projects; this could have economic significance. Besides producing energy, there could be other important possibilities, such as the use of waste materials, and at this point, the project provides the methodology and the first guidelines. However, it is important to continue researching, as there are areas that need to be researched deeper and obtain more precise information from the data if in the areas there is or are not anomalies of these elements. It is an important base to continue researching the topic, which currently is a priority for some countries such as China which has the greatest source for these elements, managing its reserves and technological applications,” said Blandón.


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