A New Model of the Chemical Dissolution of Solids
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A New Model of the Chemical Dissolution of Solids A. K. Ryskaliyevaa,* and M. E. Baltabayeva,** a
Kazakh National Agrarian University, Almaty, 050000 Kazakhstan *e-mail: [email protected] **e-mail: [email protected]
Received December 8, 2019; revised March 13, 2020; accepted March 17, 2020
Abstract—M.I. Shakhparonov built a model of the kinetics of the chemical dissolution of solids that was based on L.E. Gurevich’s theory of adsorption and that of the rate constants of chemical reactions. The empirical relation of Kh.K. Ospanov, which is of great practical importance in conducting hydrometallurgical processes, is substantiated theoretically. Keywords: kinetic model of the chemical dissolution of solids, chemisorption, compensatory nature of chemisorption, thermal activation, rate of dissolution of solids in nonideal systems DOI: 10.1134/S0036024420100258
INTRODUCTION An understanding of the essence, mechanism, and sequence of the elementary processes that underlie the dissolution of barely soluble natural compounds is needed to move away from the existing, solely empirical search for the optimum conditions for conducting the industrial hydrochemical nonequilibrium process in polydisperse systems. The problem of devising a theoretical model of the chemical dissolution of solids in the kinetic mode is therefore relevant. PROPOSED SCHEME OF CHEMICAL DISSOLUTION According to the classification of Basolo and Pearson, the reactions of mineral dissolution can be attributed to reactions of the transfer of ion atom A from the surface of the crystal lattice to the volume of the solution:
A+L
AL
AL≠
AL+
ALsolv
(1)
In our model, dissolution proceeds through the formation of surface chemisorption complex AL and its chemical and physical activation, followed by the for≠ mation of surface active complex ALsurf and its subsequent transition to transitional state AL+, which breaks up into reaction products in a solution. The process of chemical activation is the weakening of the bonds between surface chemisorption complex AL and the crystal lattice (marked with dashed semicir-
cle). Physical activation is the subsequent isolation of the surface complex from the crystal lattice, due to its participation in the thermal motion of surrounding particles (marked with solid semicircle). The presence in the model of a separate, chemical stage of activation of the transfer of an ion atom to a solution follows from Hofmann’s concept [1] of the compensatory nature of chemisorption, according to which the chemisorption of ligand L on an active center (ion atom A) on the surface of the lattice weakens the bonds between ion atom A and the crystal lattice. USING GUREVICH’S APPROACH TO DESCRIBE CHEMISORPTION The results obtained by Gurevich in solving the problem of the adsorption of molecules from the gas phase on a solid surface [2] can also be applied to chemisorption from the liquid phase, if we assume that Helmholtz free energies are additive in systems of ligand particles L in the bulk phase and on the surface.
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