Surface World October 2019 Surface World October 2019 | Page 58

PRE-TREATMENT, SURFACE PREPARATION, DEGREASING & CLEANING
Cutting the cost of deionised water
Deionised water is a vital
resource for the surface
fi nishing industry but
securing its supply can
require signifi cant capital
expenditure. Here, the Sales
Director of SUEZ Water
Purifi cation Systems Ltd,
Steve Mines, outlines
the options available
to manufacturers.
Water is a vital resource for all sorts of
industrial processes, including surface
preparation, coating, anodising, painting,
laser cutting, ultrasonic baths, the cleaning
of printed circuit boards (PCBs), chrome
plating and electroplating. However, water
from the mains normally contains ions that
have come from the ground, such as sodium
and calcium, and from water pipes, such as
iron and copper. In order to avoid corrosion,
the build-up of minerals and contamination,
water used for these processes must first be
treated or purified to remove these ions.
This process is called deionisation.
Through the process of ion exchange,
deionisation removes all ionised minerals
and salts (both organic and inorganic) from
a solution. Because most non-particulate
water impurities are dissolved salts,
deionisation produces a high-purity water.
Compared with the distillation process,
deionisation is faster, less energy-intensive
and more cost-effective.
There are numerous routes a manufacturer
can take to source deionised water. It can
be bought off-the-shelf, but this is only
economical for those that need negligible
amounts of deionised water for their
operations, and the purity of deionised water
can degrade quickly when exposed to air.
A cheaper and more efficient approach in the
long run is for the manufacturer to produce
deionised water as and when it is required.
This can be achieved using deionisation
cylinders, which feature two ionised resin
beds that are oppositely charged. These
operate by exchanging positive hydrogen
and negative hydroxyl molecules for the
positive and negative contaminant molecules
in the water. The hydrogen and hydroxyl ions
introduced in this process then unite to form
pure water molecules.
Cationic resin is typically made from
styrene- containing negatively charged
sulfonic acid groups, pre-charged with
hydrogen ions, while anionic resin is also
made from styrene and contains positively
charged quaternary ammonium groups.
It is pre-charged with hydroxide ions.
Over time, positive and negative
contaminants in the water displace all the
active hydrogen and hydroxyl molecules
on the ion exchange resin, and the cylinder
loses its ability to remove contaminants.
The lifecycle of a such a filter can vary
greatly with the quality of the feed water,
quantity of water purified, and the type of resins
used. When resin is exhausted, it must be
removed from the cylinder and regenerated.
This is a much more cost effective, and
environmentally friendly process than
disposing and refilling with new resin.
CONTINUED ON PAGE 58
56
OCTOBER 2019
read online: www.surfaceworld.com