Chemical Engineering March 2021 - 14

Veolia
field,
Ill.; www.veoliawatertech.
com). For instance, a major trend
observed in the industry is increased
interest in the use of sulfate of potash
(SOP), a premium fertilizer product
used for high-value, chloridesensitive
crops. Typically produced
via the Mannheim process, which
involves reacting sulfuric acid and
KCl in a high-temperature furnace,
SOP's production costs and energy
consumption can be quite high.
However, Veolia has developed several
crystallization-based
alternatives
to the Mannheim process that
produce a high-purity SOP product
from natural ores, brines, byproduct
streams or low-quality KCl sources.
FIGURE 3. Fertilizer manufacturers are increasingly looking to crystallization technologies to help improve
efficiency and product purity
formed either in agitated vessels or a
draft-tube crystallizer.
Resource recycling and reuse
A small, but emerging, source of
lithium and other battery metals is extraction
from recycled end-of-life batteries.
" With battery recycling, you're
dealing with not only lithium, but also
cobalt, nickel and other metals. The
purification technologies have to
deal with complex mixtures and the
real challenge is how to separate the
components. This could potentially
be done with crystallization, " says
Buchfink. He adds that GEA has several
ongoing battery-recycling studies
and contracts at hand that are looking
at different process routes and
balancing the necessary yield and
purity requirements. While many of
these projects are currently early in
their development, GEA believes that
the demand for battery recycling will
continue to increase.
Another way that crystallization is
contributing to process circularity is
salt recovery in the secondary aluminum
and wastewater-treatment industries.
" In aluminum recycling and
remelting, one normally applies a
cover salt mixture to protect the melt
against oxidation, consisting, for instance,
of sodium chloride and potassium
chloride. Crystallization enables
the continuous re-use of this cover
salt mixture in the process, so that
users don't have to purchase new salt
14
and there is less waste to deal with, "
explains Buchfink.
Similarly, salts contained in wastewaters
can be crystallized out, enabling
easier waste handling and
potentially producing a salable salt
product. " We have several projects
where we look at wastewater and
check for a certain concentration of
valuable components, for instance,
sodium chloride, sodium sulfate or
ammonium sulfate. Then, we crystallize
it out, and it can be sold or more
easily stored, reducing waste-handling
costs, " notes Buchfink. Such
crystallization steps also help move
wastewater-treatment processes
toward zero-liquid-discharge
(ZLD)
status. Wastewater treatment operators
increasingly prefer handling
solid, rather than liquid, waste, and
are also driven to increase their use
of recycled water. Effective crystallization
steps help users to reach
these objectives.
Fertilizers and efficiency
In the fertilizer manufacturing sector,
environmental factors are also shaping
the demands on crystallization
processes (Figure 3). " More emphasis
has been placed on production
of fertilizers that reduce residual soil
salinization and improve application
to reduce runoff, " explains Andrew
Duffy, process designer with Veolia
Water Technologies' HPD Evaporation
& Crystallization group (Plain " The
processes we have developed
facilitate the conversion of KCl to
SOP through solution chemistry
and reaction or evaporative crystallization
at lower temperatures, "
explains Duffy.
Furthermore, he says, because
crystallization is a natural purification
mechanism, these processes
can also enable the utilization of less
pure raw-material inputs while still
resulting in the same or better SOP
product purity as from the Mannheim
process. This means that low-purity
resources, such as natural brines
from evaporated lakes or solution
mining, or even waste streams of
pulp-and-paper mills, could potentially
be used as feedstock for SOP
production. To design such an effective
crystallization solution for a
given combination of feedstock and
product-purity demands, it is clear
that the project's unique chemistry
must be well understood, but Duffy
also points out that there are many
other important considerations.
" We have experienced a significant
increase in demand for highly technical
solutions that often require
laboratory or pilot testing for validation.
These may also require a more
detailed knowledge of materials of
construction, including alternatives
to full-alloy vessels, and more emphasis
on the control systems, operator
training and troubleshooting, "
he adds, also highlighting remote
monitoring and modularization as
trending areas of interest in crystallization
project design.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM MARCH 2021

http://www.veoliawatertech http://WWW.CHEMENGONLINE.COM

Chemical Engineering March 2021

Table of Contents for the Digital Edition of Chemical Engineering March 2021