Estonia is known for holding some of the largest phosphorite reserves in Europe.

Project manager Lauri Joosu told ERR about the survey: "We are conducting research at the Aru-Lõuna quarry with the aim of understanding, in the event that phosphate mining begins in Estonia, what the economic benefits would be in this specific area, as well as the potential accompanying environmental impacts and risks."

The Geological Survey is primarily looking at surface mining, as phosphorite deposits are generally near the surface. However, deeper reserves in the Rakvere deposit could need different methods.

"There are three major phosphate deposits in Virumaa: Toolse, Rakvere, and Aseri. The Rakvere deposit is located slightly east of Rakvere town, with the phosphate layer situated 60 to 100 meters below the surface. The thickness of the phosphate layer ranges between five and 10 meters," Joosu said.

The Toolse deposit, located north of Rakvere, has a thinner but shallower phosphorite layer. Joosu said since phosphorite forms only a single rock layer, there is little point in digging deeper. Technically, surface mining is the simplest solution.

"The biggest challenge in implementing underground mining is that phosphate rock is very soft and crumbly. It is necessary to consider how to keep the mining tunnels stable to extract the resources. Phosphate cannot be mined in the same way as oil shale, where solid sections are left intact while mining takes place between them," he noted.

The survey is also mining solutions that do not involve lowering the water table, but this research is in its early stages. "This part of the research is still in its very early stages, as such methods are not widely used globally. We are aware of one ongoing trial from which we will learn more about the pros and cons. There may still be unknown factors that, in the Estonian context, could potentially rule out the idea altogether," the project manager added.

What is the best way produce phosphoric acid?

The Geological Survey is also investigating the possibilities that come from mining phosphorite. "Adding value to phosphate rock involves several steps. The first step is the enrichment of the raw material. Simply put, sand is separated from the fossilized shells of once-living organisms, which contain phosphate. This process results in a more concentrated raw material, known as phosphate concentrate," Joosu told ERR.

Phosphorite concentrate is the lowest-grade phosphorite product traded on the world market.

Joosu said the next higher-value step is the production of phosphoric acid. "Phosphoric acid is the next processed material, primarily used in the fertilizer industry. However, with sufficient purification, it can also be used in other industries, such as food production," he cited as an example.

There are various methods for the production of phosphoric acid, which include processing raw materials with sulfuric, hydrochloric and nitric acids and heat treatment. Joosu said treatment based on sulfuric acid is the most common. But there are also a wide range of different subfields.

"Through our analyses, we have concluded that the most feasible processing methods in Estonia are likely those using sulfuric or hydrochloric acid. We are now seeking a partner to conduct the necessary experiments to determine the costs of these processing technologies, as well as the resulting by-products and emissions. Our goal is to understand the potential environmental footprints of these activities," he stressed.

Negotiations are currently taking place with two possible partners, he said. The Geological Survey hopes to reach an agreement before the end of this year and expects the first results in the first half of 2025.

Preparatory work is currently underway at the Aru-Lõuna quarry for test drilling. A larger amount of phosphorite will be collected in November.

One part of the research involves exploring the possibilities for separating rare earth metals. The Geological Survey hopes that during the production of phosphoric acid, it will be possible to extract rare earth elements from shells containing phosphate.

"The concentrations of these rare earth metals are relatively low, and they are found within the shells in a mineral composition along with phosphorus, calcium, and oxygen. Without separating them, the rare earth elements either end up in the phosphoric acid or remain in the waste products," said Joosu.

"We are conducting these studies to obtain numerical indicators for both costs and revenues, considering both financial aspects and environmental impacts," the project manager summarized.

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