The main focus in this research is to analyze the way by which the heavy metals (HM) move and transform within the acid forest soils, the distribution of HM in acidic soils, their deposition and cycling in the terrestrial environment. Chemical thermodynamic concepts and laws will be applied for developing the theory of complex chemical equilibria in multicomponent heterogeneous systems and its practical application use under real, non-standard conditions. The buffer action of two-phase soil – soil solution systems, which we intend to study, is based on the shift of complex equilibria, both homogeneous, and heterogeneous in the aqueous phase and between phases, respectively. We will investigate the phenomena which occur by increasing the acidity and alkalinity of soil solution, where simultaneous protolytic reactions with participation of salt ions take place. Computing of global change in Gibbs energy for a set of chemical equilibrium equations in multi-species and multiphase chemical systems will be performed. The criterion of the intensity of buffer action will be applied for the acid soils as the multicomponent systems, containing liquid and solid phases. Determination of soil buffer capacity will be performed by the software computation. The use of the buffer approach will yield our extended knowledge and a deeper understanding of the processes that control the concentrations of components as well as a powerful tool for the assessment and prediction of long-term effects in natural attenuation as a remediation alternative within contaminated environmental systems. The relation of proportionality between the buffer capacities in respect to all ions of the species distributed between phases will be demonstrated for the heterogeneous systems of type “soil mineral-soil solution”, which will serve as a proof of the generality of the proportionality phenomenon for all kinds of homogeneous and heterogeneous buffers, found earlier. Within the context of proposed approach, we intend further to examine the thermodynamics of the coexistence of solid phases, identify the condition under which solids involving common constituents can coexist at equilibrium, the acid-base and mineral equilibria, inorganic and organic complexation. It is expected that applying the methodology outlined above, the buffer capacity approach will provide a suitable method to estimate whether or not the heavy metals content will change appreciable under external influences (perturbations). This thermodynamic study using the developed buffer approach is anticipated to: 1) Extend our mechanistic comprehending of natural processes and accelerate natural processes that may attenuate certain contaminants in acid forest soils via complex formation (chelating) and precipitation reactions; 2) Predict and identify the exact conditions and to what extent these processes are reversible; 3) Improve basic understanding of ecological mechanisms and processes; 4) This approach can be applied for investigating the buffer action in the case of formation of one or several other solid phases in natural waters; 6) The use of results of this research will allow predicting the variations of the composition and response of the acid forest soils at the technogenic loads increasing.