How is oil shale ash valorised?

Oil shale ashes are valorised by way of leaching, using the technology developed and patented by the researchers of Ragn-Sells, TalTech and the University of Tartu. The elements contained in oil shale ash are given a new life in the shape of various materials via a carbon neutral production process. 


The share of synthetic calcium carbonate is the biggest among the material produced from ashes. The food and pharmaceutical sectors are the best examples of industries in which calcium carbonate is used. As this material originates from the manufacturing industry, the calcium carbonate produced from the oil shale ash of Ida-Viru County will most probably be used in the paint, plastic and paper industry. 


Professor Andres Trikkel, Institute of Materials and Environmental Technology of TalTech: 
Calcium carbonate (CaCO3)3is the main component of natural limestone. As a mineral, it is known under the name calcite, but also as aragonite or vaterite depending on the differences in the crystal structure. However, the latter two are not very common. Limestone contains at least 50% calcium carbonate. Limestone also contains magnesium carbonate and minor constituents. The carbonate rock with the highest magnesium content is known as dolomitic rock (dolomite as a mineral). The main component of dolomite is the compound3xMgC033Chalk is the soft and porous form of limestone and the decorative material marble has also been developed from limestone or dolomite. Estonian dolomite has often been used as a finishing material (façade and decorative tiles, windowsills, kitchen worktops), and limestone buildings (houses in the Old Town, tombs, walls, churches, manor houses) can be seen everywhere in Estonia. The northern coastline is characterised by steep limestone cliffs.

Synthetic vs organic calcium carbonate 

Andres Trikkel: The difference between natural and synthetic calcium carbonate lies in the content of minor constituents. Minor constituents may comprise up to 25% of natural limestone (clay minerals, quartz, iron compounds, gypsum, organic material, etc.), which affect the colour, strength and other qualities of the material. Construction limestone and technological limestone are differentiated according to these qualities. The first, as the name suggests, is used for construction and as crushed stone, the other is used for the production of cement and lime. Pure limestone is rarely found. The purest of the samples found in Estonia among those kept in the laboratory of inorganic materials of Tallinn University of Technology is Vasalemma ‘marble’ (95.6-97.4% CaCO33, 0,84-1,46% MgCO3, 0.84-1.46% MgCO3 and residue insoluble in hydrochloric acid that characterises a minor constituent content of 0.45-0.76%). High-purity limestone should contain more than 97% CaCO3.3

Why and where is calcium carbonate used? 

Andres Trikkel: Minor constituent content is limited and minimised in synthetic calcium carbonate. Depending on the use (paper, paint, plastic, food and pharmaceutical industries, where limestone is a filler, as well as the cement, glass and ceramic materials industries), calcium carbonate of certain qualities is needed. The content of minor constituents, iron, magnesium, sulphur and other compounds is limited and, depending on use, limits have also been established for the size or colour of the particles of the material. This is achieved by the relevant chemical and technological methods. The Rakke limestone plant of Nordkalk AS offers various limestone products. 


The second result of the valorisation of oil shale ash is a material rich in silicates that can be used, for example, as a backfill material in the construction sector. Ragn-Sells Group is developing a use for this material that best corresponds to its qualities, and it will be released into circulation again. 

In addition to finding uses for waste that was simply deposited until now, the materials made as a result of the technology reduce the pressure on opening new mines for the extraction of the same production materials. The pressure and negative impact on the natural environment will thereby also decrease as a result of the reduction of the CO2 quantities generated by the extraction and valorisation of raw materials.

Innovations implemented by Ragn-Sells in Scandinavia in the valorisation of tailings


Ash2Phos focuses on the separation of the phosphorus found in wastewater mud. This is a complex and unique technology, which helps release the phosphorus that has ended up in wastewater mud via nutrients back into consumption, thereby promoting an agriculture and consumption model that is sustainable and based on circular economy.


Ragn-Sells uses the CleanMap technology to valorise tailings by separating the ammonium phosphates that are used for the production of fertilisers. While the production of fertilisers generally requires very large quantities of energy, the CleanMap technology of Ragn-Sells is unique due to its low energy consumption. This is the major added value of the valorisation and release back into circulation of previously useless tailings.


The newest technology of Ragn-Sells is used for the reprocessing of the ashes left over after incineration of waste.

Until now, these ashes have simply been deposited in landfills, but Rang-Sells reprocesses them into industrial salts.