VSK MINING - Ložisko gemerská Poloma

The standards exist and apply to talc in the same matter as for everything else.

• DIN 55924 or DIN 55629
• ASTM D 605 – 82 v 1984
• Anual Book of ASTM Section/6 Paints

Although the standards listed for talc exist, the product itself is being sold mostly with regard to the technique and the fields of application (i.e. upon laboratory tests of the talc producer or supplier) and thus, the field of application determines the specification of the talc products itself. Requirements for talc products can vary in different countries (technological jumps).

The table below shows the stoichiometric values of individual minerals. The content of minerals can be calculated from chemical analyses.

Stoichiometric Values

The important requirements for final products of talc include:

• Chemical compositions
• Mineralogical composition
• Physical attributes as are
  
  • clarity degree (whiteness),
  • hardness,
    
  • abrasiveness,
  • density, bulk density, post-crushing density,
  • oil number,
  • grain size, specific area,
  • lamellarity

As to chemistry, the values expressing the contents of SiO2, MgO, Al2O3, Fe2O3, CaO and the loss by annealing are of importance. In some cases of application (e.g. in the beauty industry) the requirements for trace elements (e.g. As) also have to be checked and guaranteed. In addition to these attributes, the characteristics, as solvability in acids and the way of iron fixation, are also important in relation to the fields of application.

The mineralogical composition is of a special importance e.g. in ceramics, in plastic industry and in the paper industry. As it is impossible to determine the content of minerals only from the chemical analysis, the quality and quantity in mineralogical composition must be specified through the X-ray diffractometer or by the differential thermal analysis.

Signs of accompanying minerals can be distinguished even upon the total chemical analysis. In case of increased loss by annealing, the question immediately arises as to the content of carbonates. The loss by annealing, however, can also be increased by the content of chlorite. The occurrence of aluminum points at presence of pyrophillite or even chlorite. In a sample of talc, it is difficult to define the amount of free silica. The chance to measure the value below 1 % of free silica as required in several regulations, is very small. In such a case the analysis via DTG (differential thermal gravimetry) can be considered, where the silica sample is being cooled down above the jump value of silica at 573 °C. The signs of occurrence of free silica can also be acquired through determination of abrasive values, although other options play their role there too.

Several talc deposits contain Tremolite Ca2Mg5[(OH,F)/Si4O11]2 as the element. The Tremolite belongs to asbestos minerals and thus, these deposits are forbidden to be recovered by the WHO (World Health Organization).

As for physical attributes, in addition to the granulometric composition (granularity), the value of clarity (whiteness) is in the first place too (DIN 53770).

The Values of Clarity (Whiteness) Of Talc Grade Classes

When specifying the granularity, the specification of fineness is set by using the material sedigram, which, due to physical patterns of measurement, always provides the most accurate results as the screening or measuring by the laser granulometer. Sometimes, the specific area is also stated under the flow principle (Blaine) or grindometric values, as standard in e.g. the varnish industry, the fixing of the granularity analysis.

The data on fine grade structure < 30 means that either 80 %, 98 % or 99 % of the material presented (upon the contract) is smaller that the value stated for the grain size.