## 1 Introduction  
Ecological aspects of industrial production are currently paid a great deal of attention. It is extremely important to monitor the carbon footprint at every stage of production processes, including the process of sintering iron ore raw materials within the production of pig iron. In order to avoid excessive releasing of pollutants into the air, there is an ongoing search for different methods of replacing coke dust in the sintering process. Plenty of studies have been carried out with the aim of substituting coke dust by biomass at different substitution degrees of replacement fuel [1; 2; 3; 4; 5]. The advantage of using biomass in the sintering process is its significantly lower ash content and lower proportion of heavy metals in biomass. The results of studies show that the replacement of fossil fuel in the sintering process by biomass is limited to the level of about 10-30%. With such replacement, using certain types of biomass, emissions of oxides of carbon, nitrogen and sulfur would be reduced by 5-40%. The basic criteria of use of biomass for energy purposes are, in particular, the analysis and balance of environmental and economic perspectives. The environmental criterion is connected primarily to the evaluation of the impact of biomass energy use on the environment, the economic criterion is connected on the assessment of the possibilities of economically efficient processing of biomass. The analysis of the costs and competitiveness of using various types of biomass shows that in the area of plant biomass, it appears advantageous to use waste biomass, which is cheaper as fossil fuel [7]. It has been well known that different types of biomass exhibit different properties. These properties must be examined before the sintering is carried out in order to predict how a given material will behave in the process of sinter charge preparation and in the sintering process. The rigidity of micro-pellets charged onto a sintering line is essential for achieving optimal permeability of the sinter charge. Therefore, testing of biomass properties was carried out with a focus on its ability to form compact, firm pellets. Obtaining the valuable information on biomass' ability to absorb liquids is important for further utilisation of biomass in the sintering process, within pre-pelletising of the sinter charge. The wetting of solid materials by liquids is accompanied with marked manifestations of the properties of individual phases that are closely related to the wettability of the surface and the ability of a liquid to wet solid materials. The wetting of a solid material by a liquid medium occurs as a result of forces acting between the solid and liquid phases [8]. The wetting of solid materials is most significantly affected by the surface tension of a liquid, free surface energy, interfacial tension at a phase boundary, chemical structure of the surface of the solid phase, temperature, etc. Figure 1[9] shows the contact angles (\(\delta\)) and surfaces of a liquid. The surface tension is defined on the basis of a kinetic model of a liquid as a result of mutual effects of particles in the liquid. The forces acting on the molecules contained in the surface layer of the liquid are directed towards its volume. These forces try to drag the molecules from the surface into the liquid volume--this is referred to as surface tension. It is the most important parameter, which characterises the surface of liquids [10]. The values of surface tension depend on the composition of the liquid phase, temperature, or pressure and electric charge. Hence, the wetting of a solid material occurs as a result of the effects of forces acting between the solid and liquid phases. In the case of  
Figure 1: Hydrophilic and hydrophobic surfaces [9]. using water as the liquid phase, molecules of water primarily adsorb on surfaces with a negative charge.