Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 4, pp. 535−543.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © N.V. Shul’ga, N.P. Krut’ko, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 4, pp. 513−521.
AND INDUSTRIAL INORGANIC CHEMISTRY
Topochemistry Regularities in Evaluation Technique
of Phosphate Raw Material Reactivity
N. V. Shul’ga and N. P. Krut’ko
Institute of General and Inorganic Chemistry, National Academy of Sciences of Belarus, Minsk, Belarus
Received November 9, 2011
Abstract—Experimental approaches for evaluation of reactivity of phosphate raw material and obtaining additional
information on its phase composition were suggested in view of physicochemical patterns of the phosphate raw
material decomposition in a weakly acidic environment.
The methods recommended by the applicable regula-
tory document  serve for determining the reactivity of
phosphate powder or other phosphate raw materials of
similar chemical nature of the CIS. Earlier we has shown
[2, 3] that, in evaluation of the reactivity (suitability) of
these objects should be taken into account the physi-
cal and chemical patterns of the topochemical process
occurring at the interface between the solid phase and
solution, and some properties of the extraction agent,
weak organic acid.
It is known [4–6] that in studying the mechanism
of heterogeneous reactions on contact of a solid with
gaseous or liquid environment certain rules should be
accounted for. For a speciﬁ c chemical transformation in
the reaction system a condition of its equidistance from
an equilibrium state (ν
= const, where ν is mole frac-
tions of reactants A and B) should be originally ensured.
The validity of this approach was conﬁ rmed by a good
convergence of experimental and calculated values of
an activation energy E for the reactions occurring at the
interface between the solid phase–gas not complicated by
side reactions [4, 6]. There was no reason to neglect the
principle of “equidistance” as the gaseous environment
is replaced by the liquid, the more so from the standpoint
of the kinetics the main differences between them were
reduced to a concentration of one reactant molecules per
unit volume, as well as to conditions and velocity of their
diffusion to a surface of unreacted solid residue. Replace-
ment of the gaseous environment by the liquid in the study
of the mechanism of heterogeneous transformation did not
deny the correctness of the chosen approach, but required
a more careful use of well-known topokinetic equations
 for the mathematical processing of experimental data
and the interpretation of the obtained parameters.
A time required to reach the equilibrium state of the
system is determined by the properties of solid substances
(reactivity, the degree of crystallization, dispersion,
speciﬁ c surface area) and the reaction conditions (tem-
perature, concentration of the active agent in the liquid
phase, conditions of agitation) .
In the case of minerals of natural origin we can ex-
pect that the equilibrium parameters of the system will
deviate from the calculated since together with the main
transformation proceeding of side reactions is possible
with participation of active impurities. When an amount
of reagent in the liquid phase is limited, highly likely, that
in the decomposition of multicomponent solid phase it
is also in deﬁ cit .
The purpose of the study is an analysis and selection of
methodological approaches that allow in view of the main
physical and chemical patterns of this class of reactions
obtaining fairly valid data on the reactivity of phosphate
raw materials using recovery of phosphorus from solid
by a solution of a weak organic acid.