Volume SLS IX : Part
1 Flocculation and coagulation
The report
provides a comprehensive review of both coagulants and
flocculants. The basic physical chemistry of colloids
is explained. Mechanisms of hydrophilic and hydrophobic
coagulation and factors affecting flocculation are described.
The practical applications of kinetic theories to design
are given. Chemical additives used for particle aggregation
are classified in terms of their properties. Measurement
of characteristics such as molecular weight, ionic content,
polymer configuration, chain length and adsorption are
described. A list of commercially available flocculants
is also given. The section on plant design describes
techniques for the handling, storage and dissolution
of flocculants as well as the metering, mixing and addition
of the solution to the slurry. Problems of handling
thickened sludges and the effects of flocculants on
the environment are described. Laboratory tests to screen
flocculants for sedimentation and filtering applications
are described and examples given of the use of flocculants
in different industries. Novel processes such as selective
flocculation, floccular flotation and pelleting flocculation
are also described.
Volume SLS IX :
Part 2 Instrumentation for solid-liquid separation
Volume SLS IX : Part
3 Discharge and handling of cakes
Part 3
provides practical guidance for discharge of cakes from
the separating surface in filters and centrifuges; for
the discharge of cakes from vessels (eg from the filter
and from storage vessels); for the conveying of cakes
between equipment; for the feeding of cakes at constant
rate; and for pretreatment of cakes before dryers. Typical
problems are listed and it is shown that many of these
arise because binding forces are high. These forces
(eg capillary suction, solid bridging) cause particles
to bind to each other (cohesion) or to surfaces (adhesion).
Methods of measuring cohesion and adhesion are described
but because it is often not possible to utilise such
measurements, the report adopts a more empirical approach.
This empirical
approach classifies cakes by their physical properties
(eg sticky, brittle, matted cakes) which can be done
by visual examination. The cake classifications are
defined in terms of the binding forces and by the state
of the cake (eg desaturated, compressed). Ways of overcoming
problems (eg adhesion to surfaces, lumps too large)
are described and related to the different classes of
cake. The solutions described include; layout of equipment
to avoid storage or handling; modification of cake properties;
modification of surfaces; and correct choice of equipment.
The various types of storage, conveyor and feeder are
described and the applications given.
