Peat is an effective sorbent of heavy metals, which is due to its high cation-exchange ability. The use of peat sorbents has many advantages. It is an inexpensive, affordable, and effective sorbent for a wide range of environmental pollutants. Also, it can be used either separately or as a combined sorbent and complex constituents; however, it also has several disadvantages, such as insufficient mechanical strength and low chemical stability of peat particles. To overcome these shortcomings, various methods of peat modification have been developed (e.g., peat modified with chitosan, which is used as a sorbent for heavy metals removal like peat). The ion-exchange sorption properties of sorbents on the base of peat and chitosan - modified peat were evaluated by the method of pH meter. An acid-activated peat sample was also investigated. The experiments were carried out in a static mode using natural peat samples taken from the Lake Sevan (near the city of Vardenis of the Gegharkunik region of the Republic of Armenia). Also, a similar study was conducted on KU-2-8 cation exchange resin. The purpose of this article was the express evaluation of the sorption mechanism of peat sorbents. Cation exchanger was transferred to the H+ form by treatment with HCl (1N). Changes in the pH profile as a function of the exposure time indicate their identity with the pattern of the pH change of the cation exchanger. It was found that acid activation of peat (exposure of a peat sample in HCl 1N for 10-16 hours) increases its adsorption capacity. In this case, the maximum decrease in pH is pH = 2.33, which is 1.44 points lower than for peat (pH = 3.77) and 0.95 points more than for KU-2-8 cationite. This indicates that sorbents based on peat can be regenerated. Chitosan-modified peat exhibits deterioration in sorption capacity. In this case, pHmin = 3.9, which shows that sorption on chitosan is not ion-exchange in nature.