In this diploma thesis, the equilibrium of copper ion sorption from copper (II) chloride solutions of different initial concentrations on two types of cat litter (natural and synthetic bentonite) was examined in a batch reactor at a constant temperature of 300 K, a stirring speed of 200 rpm and an experiment duration of 72 h. The equilibrium amount of sorbed copper ions on natural bentonite increases with the increase of the equilibrium concentration of heavy metal ions in the solution and reaches its maximum value at the highest selected concentration of the heavy metal solution of 29.135 mmol dm-3 with the value of 1.053 mmol g-1. The increase in the initial concentration of the copper ion solution does not significantly affect the equilibrium concentration of sorbed copper ions on the synthetic bentonite, which increases at the very beginning, and then does not significantly change with a further increase in the equilibrium concentration of heavy metal ions in the solution, and is also achieved at the highest selected concentration of the heavy metal solution, with the value of 0.549 mmol g-1. The removal efficiency of copper ions on both types of cat litter continuously decreases with the increase of the initial concentration of copper ions in the solution, which can be attributed to the saturation of the available sites for sorption. The effect of sorption of copper ions is twice as high with the use of natural bentonite. The obtained experimental data were tested with the Langmuir, Freundlich, Toth, Redlich-Peterson and Sips models. Considering the values of the assessment criteria, it can be concluded that the Freundlich isotherm best describes the sorption of copper ions on natural bentonite. A lower value of the parameter describing the surface heterogeneity suggests a stronger interaction between natural bentonite and copper ions. Sorption of copper ions on synthetic bentonite is best described by the Langmuir model, which suggests monolayer sorption on synthetic bentonite, implying that all surface sites have the same affinity for sorbate and that only one atom can be sorbed on them, regardless of the occupancy of neighboring sites.