TALTECH Professor Andres Trikkel explains what is the climate positive calcium carbonate obtained from oil shale ash

Synthetic calcium carbonate represents the biggest share of the materials produced from oil shale ash. The food and pharmaceutical sectors are the best examples of industries in which natural 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 as a filler in the paint, plastic and paper industry. 

What is Calcium Carbonate

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 natural 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% CaCO3,3, 0,84-1,46% MgCO3residue 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 cement, glass and ceramic materials industries), calcium carbonate of certain qualities is needed. The content of minor constituents such as iron, magnesium, sulphur and other compounds is limited and, depending on use, limits have also established for the shape, 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.