Clay raw materials for cement production
General information and occurrence
Lithologically the explored deposits of raw materials for the cement industry represent mainly clays and clayslates, but also loams, loesses and silts.
In the cement industry, clay raw materials are used for the cement clinker baking and for obtaining pozzolana additions for cement (and concrete).
In the clinker production process, clay raw materials (loams, clays, clayey schists, silts, loesses, clayey siderites and others) are natural supplementary additions or additions which adjust the composition of a basic compound: limestones and marls. According to the classification used in the cement industry, clay raw materials are qualified to the so-called “law raw materials”. The law raw materials contain <42% CaO (<75% CaCO3), the normal raw materials contain 42-45% CaO (75-80% CaCO3) and the high raw materials contain >45% CaO (>80% CaCO3). The kiln input should contain 75-80% of CaCO3 (42-45% CaO), be characterized by the relevant proportions of basic compounds CaO, SiO2, Al2O3 and Fe2O3 and by a low content of harmful admixtures. The proportions of basic compounds are as follows: hydraulic modulus MH = CaO/(SiO2 + Al2O3 + Fe2O3), siliceous modulus MK = SiO2/(Al2O3 + Fe2O3) and loamy modulus MG = Al2O3/Fe2O3. In the case of Portland clinker production, the proportions values should be within the following ranges: MH - 1.9-2.9; MK - 2.1-3.5; MG - 1.0-2.8.
For the cement production (from clinker) there can be clay raw materials used after thermal treatment – after milling they are characterized by pozzolana properties and can replaced cement clinker. The materials of this type are: burnt out coal schists or ignited kaolinite loams (meta-kaolinite). The pozzolana admixtures reduce the cement production costs (mainly energy consumption) and optimize cement and concrete properties. Their acceptable content in cement is 55%.
Clayey rocks usable for the cement clinker production occur on the large areas of Poland are easily available. Documented deposits and identified prognostic and prospective areas cover various lithological geological formations: from the Quaternary through to the Cambrian. The usefulness of clayey rocks for the production of pozzolana admixtures has not been the subject of wider explorations in our country. The biggest potential in this respect have the following regions: Upper Silesian, Lower Silesian and the Holly Cross Mts. where clayey sediments reach in kaolinite occur.
The Geological and Mining Law does not define the limit values of the parameters that defines the deposit and its boundaries f a given raw material – it is not listed in the Regulation of the Minister of the Environment of the 1st of July 2015 regarding the geological documentation of a mineral raw material deposit, excluding a hydrocarbons field (number of Polish act: Dz. U. 2015, poz. 987). The decisive factors are needs and requirements of the raw material recipient in terms of the raw material type and composition. The content of: MgO, P2O5 and Mn2O3, high SO3 content and content of NaO and K2O are undesirable factors. Such ingredients can be of the negative impact on the production process and the cement quality. Important factors are: a short distance from a plant and convenient exploitation conditions.
The state of development of documented deposits and current exploitation volumes of the clay raw materials for cement production are relatively low as at the stage of the raw material for the cement industry resources documentation (limestones and marls) and the exploitation planning, the aim is to optimize the raw material composition reducing the necessity of the composition correction. Moreover, there are also the secondary raw materials (wastes, anthropogenic) used (about 4.5 million tonnes/year), including: metallurgical slags, by-products of coal combustion, coal schists and others.
Resources and output
The anticipated economic resources of clay raw materials for the cement production as of the end of 2021 amounted to 279.783 million tonnes (Table 1). They increased by 0.267 million tonnes in comparison with 2020.
In 2021, there was one new deposit documented in Lubelskie Voivodeship – Podgórze. The resources of loams (0.341 million tonnes) for the cement clinker production are the accompanying raw material, whereas the main raw material are sands for building purposes (natural aggregates).
Deposits of clay raw materials for the cement production (together with building ceramics raw materials) are presented on the map.
In the reporting year, there were 2 deposits in Lubelskie Voivodeship exploited: Buśno and Lechówka. The output amounted to 0.087 million tonnes and decreased by 0.005 million tonnes (that is by 5.4%) in comparison with the previous year. The raw material was used by the Chełm cement plant..
In the Kujawy cement plant, as the law raw material, there have been quartz sands from the Barcin-Piechcin-Pakość deposit (Kujawsko-Pomorskie Voivodeship) used for many years. Such sands are recorded in the chapter Quartz sands for production of cellular concrete and lime-sand brick. In 2021 the output was equal 0.020 million tonnes.
The figure below shows changes in resources and output of clay raw materials for cement production in Poland in the years 1989-2021.
The clayey rocks, of the potential to be used for the cement production, occur commonly in Poland and the relatively low quality requirements are not the barrier to the prospecting process. The existing resources base exceeds the current domestic demand of the cement industry. Moreover, for the cement production, there can also be used the clayey raw materials documented for other purposes e.g.: for the building ceramics production, which are not used in line with the intended use*.
Prepared by: Wojciech Szczygielski
* Szczygielski W., Walentek I., 2020 - "Surowce ceramiki budowlanej (building ceramics raw materials), surowce do produkcji kruszyw ceramicznych i cementu (mineral raw materials for production of clay aggregates and cement clinker)". In: "Bilans perspektywicznych zasobów kopalin Polski wg stanu na 31.12.2018 r." (eds. Szamałek K., Szuflicki M., Mizerski W.): 239-257. PIG-PIB, Warszawa [in Polish].