Isotherms of Adsorption of Perrhenate-First ash and Slag Waste om Thermal Power Plants

Purpose. The article is devoted to the description of adsorption isotherms of perrhenate ions by ash and slag waste from thermal power plants from the standpoint of the Langmuir and Freundlich models. 

Methods. Sorption was carried out on model solutions in the range of analyte concentrations from 0.10 to 0.40 mg / ml at pH = 2 and pH = 7 under static conditions. The contact time of the phases was 60 min. The content of rhenium (VII) in solutions before and after sorption was monitored photometrically. The values of the constants were determined graphically from linearized adsorption isotherms. 

Results. The shape of the linearized adsorption isotherms indicates the applicability of both models for describing the equilibrium adsorption processes of perrhenate ions. The correlation coefficients calculated by the least squares method for the two adsorption models are comparable with each other. However, the closest closeness to unity of the correlation coefficient is achieved for the Langmuir model (at pH = 7: R² = 0.9748 for the Langmuir model, R² = 0.9275 for the Freundlich model; at pH = 2: R² = 0.9846 for the Langmuir model and R² = 0.9659 for the Freundlich model), which confirms the formation of a monomolecular layer on the surface of the adsorbent. The limiting adsorption capacity of ash and slag waste from thermal power plants in relation to perrhenate ion was 6.211 mg / g at pH = 7 and 5.988 mg / g at pH = 2. 

Conclusion. The results obtained give reason to believe that the adsorption of perrhenate ions by ash and slag wastes from the thermal power plant is complex. At the initial stage, sorption is a physical process; in the region of medium and low analyte concentrations, chemisorption is possible. The adsorption models derived from the analysis of the Langmuir and Freundlich isotherms adequately describe the adsorption equilibria.

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