ln 1 *B*

*k T* é ù æ ö = - ê ú ç ÷

Table 6 shows the overview of average values of thermodynamic results calculated for

The negative value of entropy (Δ*S*# < 0) indicating formation of more ordered transition state during dehydroxylation is out of the usual findings for thermal decomposition of kaolinite.

Theassessedkinetic tripletof combustionofSOMshows thattheactivationenergyoftheprocess is close tothe activationenergyfordehydroxylationbuttheburningof SOMproceeds fasterdue to the higher *A* and the lower *n*. The gas products of burning of SOM (Fig.15(b)) diffuse through the kaolinite aggregates and increase the pressure of water vapour affecting the thermodynam‐

calculated from the experiment is shown in Fig.18 for both processes. From the kinetic point of view which is given by Eq.10, the rate constant of dehydroxylation with temperature increases more slowly than for the combustion process of SOM. In the other words, increasing pressure

20 It must be pointed that combustion of SOM is strongly affected by the content of individual kind of humic substances and the both processes (combustion of SOM and dehydroxylation) show mutual relationship. For example, intensive origin of water vapor slows down diffusion of oxygen, leads to reducing conditions, changing composition of product and slowing

*h A S R*

activated complex according to Eq. 10 – 13 for interval of Δ*T* according to Fig.17.

Burning of SOM 201 63 183 1.96∙10-17 Dehydroxylation 195 -35 220 2.60∙10-16 Al-Si spinel 844 385 475 8.87∙10-21 Mullite and cristobalite 667 152 486 4.79∙10-18

**Process ΔH># [kJ·mol-1] ΔS># [J·(mol·K)-1] ΔG># [kJ·mol-1]** *K>#*

**Table 6.** Thermodynamics of thermal transformation of kaolin from termite nest.

Since pure well defined sample of kaolin shows mostly Δ*S*#

ics of dehydroxylation via the equilibrium constant (Eq.13; the Δ*G*#

<sup>20</sup>. The temperature dependence of Δ*G*#

phase are responsible for this behaviour.

value of Δ*S*#

)

down the rate of process [74].

) of process were calculated using Eyring equations:
