One of the duties of the Geological Survey of Estonia is to investigate the critical raw materials occurring in the Earth's crust of Estonia. The list of critical raw materials is continuously changing as it is influenced by technological developments and global politics. The criticality of raw materials is reviewed regularly on the basis of their importance and supply risks.
Phosphorite is considered a strategic resource of critical importance and the largest deposits of phosphorite in the EU are located in Estonia. Phosphorite in Estonia has so far attracted interest due to its phosphorus content, which is mainly used to produce fertilisers. However, phosphorite also contains a significant quantities of rare-earth elements, such as cerium, praseodymium, neodymium, dysprosium and terbium, which makes phosphorite a potential raw material for rare-earth elements. Rare-earth elements are essential components in the production of semiconductors, liquid-crystal displays (LCDs), and LED lamps, as well as in energy management, including the production of wind turbines and electric vehicles.
One of the main causes of demand for critical raw materials is the so-called battery revolution, which is expected to reduce greenhouse gas emissions and increase renewable energy storage options. Vanadium is an essential element in new-generation batteries; however, it is also a critical raw material. In this regard, Estonian black shale has a great deal of potential as it contains significant amounts of vanadium in addition to other important metals such as molybdenum, uranium, zinc and lead.
Critical raw materials are natural resources which are strategically important for the EU’s economy, but have a high risk associated with their supply.
Phosphorite
Phosphorus is a chemical element of critical importance for life. A rock containing significant amounts of phosphorus is called phosphorite. Phosporus containing fertilisers are widely used in agriculture as they allow food to be produced more sustainably. The main raw material of these fertilisers is phosphorite. Estonian phosphorite contains very low concentration of elements detrimental to health, such as Cd, U and Th, which makes it ideal for the production of fertilisers. Estonian phosphorite also contains a significant amount of rare-earth elements which may have economic potential.
Phosphorite in Estonia was studied in detail from the 1950s up to the end of 1980s. Unfortunately, most of the old rock samples have now been destroyed or are in a poor condition. Moreover, both the drilling methods and analytical capabilities have now further developed. For this reason, the EGT handles both the digitisation and validation of historic data and the collection of new geotechnical and geochemical data.
In our Earth's crust, black shale is positioned directly on top of phosphorite, which is why they are often explored together.
Black shale
Black shale, also known as Tremadocian black shale, is a chocolate-brown claystone of marine origin, containing high amounts of various metals, such as vanadium, molybdenum, zinc and uranium. Organic matter is what gives the rock its dark colour. In the future, black shale may be used as a raw material for technological metals, such as vanadium, but special attention should also be paid to potential dangers arising from its improper handling.
In the geological cross-section of Estonia, black shale is located directly above phosphorite. In Western Estonia, the thickness of reaches seven metres, in the east of the country, the thickness drops down to one to two metres, and in the south, there is no black shal at all.
Guidelines for handling Black shale (in Estonian):
Benefication and volarisation
The benefication of mineral resources is the process of improving the value of the mineral resource without changing its chemical composition. For example, in the case of phosphorite benefication, the separation of phosphorus-rich shells from sand. The objective is also to separate any other useful components such as rare-earth elements.
A number of different technologies are used in the valorisation of phosphate raw materials in the world.
- The most widely used method for the production of P- fertilisers is the wet process in which the phosphorite concentrate that is formed at flotation is decomposed with sulfuric acid.
- JA waste-free alternative would be to use hydrochloric acid (HCl) to decompose phosphorite in the production of phosphate and rare-earth elements.
- The Hard Improve Process allows the production of high-purity phosphoric acid from low-quality phosphorite without the generation of phosphogypsum waste.
One of the objectives of the Geological Survey of Estonia is to research technologies that allow even greater valorisation of phosphorite.
In the light of the phosphate raw material valorisation technologies developed in the world, the Geological Survey of Estonia, together with universities, is seeking the best possible solution for phosphorite valorisation. In order to make the final choice, technical feasibility studies and environmental impact assessments must be carried out.
