Bentonites and bentonitic clays
Bentonites are clayey rocks originated in the result of the transform (bentonitization) process of a volcanic glass occurring in the pyroclastic rocks such as tuffs and tuffites. The bentonites are built mainly of the smectite minerals group (with the minimum montmorillonite content of 75%) accompanied by other clayey minerals and relicts of a pyroclastic material. Related to the bentonites are bentonitic clays containing, along with smectite minerals, the larger amount of other clayey minerals.
Rocks rich in smectite group minerals have some common features which decide on the rocks usage such as: an ability to swell, their susceptibility to the dispersion of water, a high plasticity, their easy absorption of cations and organic substances from water solutions, their ability to form the thixotropic suspensions. Thanks to these features, there are more than 40 ways of utilization of these rocks, i.a.: in a foundry industry (as a component of foundry mass), in a chemical industry (for the production of fillers, sorbents, catalysts, paints etc.), in a paper industry, a pharmaceutical industry, a cosmetic industry, a ceramic industry, in the engineering and hydro-technical works (a soil stabilization, waterproof screens, sealings), in an agriculture and as a component of drilling fluid. Most of bentonites in Poland are used traditionally in the foundry industry, the drilling and in a new, strongly developing hygienic sorbents market (for animals).
Primary bentonites in Poland (it means almost monomineralic montmorillonitic rocks with a small admixture of other minerlas) occur very seldom. More common are various bentonitic clays with a relatively high content of non-clayey minerlas. The group of bentonitic raw materials contains bentonitic weathering covers of basalts in the Lower Silesia region, bentonitic clays in the Upper Silesia region, bentonitic clays of the southern fringes of the Holy Cross Mts., bentonitic clays in the Carpathian Mts.
In 2018, anticipated economic resources of bentonitic raw materials amounted to 2,883.43 thousand tonnes. There are two deposits with an exploitation concession issued – Jawor-Męcinka and Krzeniów, both located in Dolnośląskie Voivodeship. The output of the bentonites mantle rock of the basalt tuffs has been carried out only from Krzeniów deposit and for more than 10 years it has been maintaining within the range of 0.45-2.80 thousand tonnes per year. In 2018 the output was equal 0.56 thousand tonnes (Table 2).
Table 1 shows the current state of identification and management of resources of bentonites and bentonite clays in Poland.
The figure below shows changes in resources and output of bentonites in Poland in the years 1989-2018.
Prepared by: Dariusz Brzeziński
Table 1. Bentonites - million tonnes