Study the kinetics of adsorption and desorption processes of arsenite-ion by different soil types of Udmurtia

The possible presence of arsenic in natural objects of Udmurtia is associated with the processes of destruction and recycling of chemical weapons. Adsorption and desorption of arsenic in soils control its mobility and bioavailability, which can start or intensify under the influence of anthropogenic factors. The need to study the mechanisms of sorption-desorption process between soils and arsenite ions is due to their high toxicity and mobility. At the laboratory conditions the authors carried out research of the kinetics of adsorption and desorption of sodium arsenite in the most common types of soil Udmurtia. The series of soil suspensions was used in experiments by the kinetics of adsorption and desorption of arsenite. Аt fixed time intervals aliquots of suspensions were taken to determine the ion concentration of arsenic by atomic absorption spectrophotometry. Basic constants of the modified Freundlich equation have been defined and established their influence on the nature of the processes. Freundlich constants of adsorption rate КF are different for each type of soils and do not depend on the amount of inputted arsenite. KF is equal to 1.60 for sod-strongly podzolic sandy loam soil under stirring with solution of arsenite - ion of concentration 7.53 mg/dm$^3$, and under stirring with solution of arsenite - ion of concentration 59.00 mg/dm$^3$ KF is equal 1.65; for sod-carbonate with lightly leached soil under stirring it with solution of arsenite - ion of concentration 7.53 mg/dm$^3$ of arsenic ion KF is equal 1.04. Modified Freundlich equation successfully describes the rate of desorption of arsenite-ion for all types of soils. Freundlich constants of desorption rate КD approximately equal to 1.0 for samples of different types of soils, which were mixed with solution of arsenic with concentration of 7.53 mg/dm$^3$. Under stirring the soils with solution of arsenite-ion with concentration of 58.99 mg/dm$^3$ KD value is approaching 2.0. The intensity of the sorption and desorption is proportional to the quantity of imported arsenic. The extent of arsenite absorption increases with the growth of pH of the soil solution.