Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 5, pp. 806−810.
Pleiades Publishing, Ltd., 2010.
Original Russian Text
E.E. Bibik, A.V. Semyachkov, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 5, pp. 755−759.
OF SYSTEMS AND PROCESSES
Problems of the Coagulation Kinetics of Suspensions
E. E. Bibik and A. V. Semyachkov
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received December 4, 2009
Abstract—Results obtained in an experimental study of the coagulation kinetics of suspensions by the
sedimentation method, a simulation of the sedimentation of coagulating suspensions, and data following from
the known solutions to equations of coagulation kinetics are compared.
The coagulation kinetics governs the run of a number
of technological processes, e.g., water puriﬁ cation to
remove insoluble impurities. The main physicochemical
parameter describing the coagulation process is
the coagulation rate constant. Another parameter,
coagulation reversibility has no commonly accepted
numerical criterion, but this does not depreciate its
technological signiﬁ cance. Clearly, on-line monitoring
of the coagulation process is technologically important.
However, there are no procedures suitable for these
Coagulation studies devoted to solution of problems
of the theory of dispersed systems are mostly aimed to
elucidate the nature of particle interaction forces 
and, therefore, are limited to methods that can be used
in strongly diluted systems. As a rule, it is only possible
in this case to analyze the initial stage of the process,
while the forming ﬂ occules of the coagulate contain
no more than ten individual particles. As an example
can serve the method in which particles are counted
in the ﬁ eld of an ultramicroscope  or other devices.
However, of technological interest is the coagulation
of rather concentrated suspensions and the full cycle of
coagulation transformations, from formation of pairs
of coupled particles to completion of the process with
some result (stratiﬁ cation, structuring, equilibration
). It seems that a coagulation monitoring procedure
adequate to this task could be based on principles and
devices commonly used in sedimentation analysis. As
is known, this analysis is also made in strongly diluted
suspensions just to eliminate the effect of coagulation
on the analytical results.
A notion of how, and to what extent, can be
changed the primary result of a sedimentation
analysis, dependence of the sediment mass on time t
(sedimentation curve), is provided by simulation the
sedimentation of a coagulating suspension . In the
case of coagulation, the sedimentation curve becomes
S-shaped. The maximum suspension sedimentation rate
(rate of sediment accumulation on a virtual balance pan)
is reached when approximately 50% of the suspension
settles and manyfold exceeds the initial rate of sediment
accumulation. In the case of sedimentation without
coagulation, the maximum sedimentation rate is always
observed in the initial stage. The kinetics of sediment
accumulation on the pan of a sedimentation balance
reﬂ ects the coagulation kinetics.
The interaction of particles, responsible for the
coagulation, is characterized in the model mentioned
above by the hydrodynamically equilibrium ﬂ occule
size dependent on the ratio between the particle cohesion
force in ﬂ occules of the coagulate and the weight force
of the ﬂ occules , rather than by an interaction function
or its parameters (potential barrier and potential well).
This frees the model of the need to be based on some
theoretical concepts of interparticle interaction , to
which real suspensions not necessarily conform.
Figure 1 shows sedimentation curves for Al
suspensions in KCl solutions of various concentrations
(M). The volume fraction of Al
in the suspension is