Process ECP-2E Specifications 9-13
UL Bleach Formulations
Two UL Bleach formulations are available to fill various
laboratory operating and environmental needs. They are:
• Ammonium UL or “UL House” Bleach. This formulation
contains the highest percentage of ammonium ion which
maximizes bleach activity. Because the least amount of
active ingredients are necessary, this is the least expensive
of the UL bleach varieties to operate. The use of ammonia
in a laboratory may present some handling and odor
considerations and is restricted in some sewer districts.
The “UL House” Bleach formulation was derived to allow
for a common tank and replenisher to be used for both
Processes ECN and ECP. Its advantage is less mixing and
solution handling between the two processes.
• Potassium “UL House” Bleach combines the advantages
of a non-ammonium formulation with a house system
where one replenisher feeds tanks for both Processes ECN
and ECP. Through replenisher rate manipulation, the
tanks for Processes ECN and ECP are maintained at
appropriate levels so bleaching is completed while excess
carryout is avoided.
Selecting a Bleach Formulation
Experimentation has shown that an all-ammonium bleach is
the most active and, therefore, needs the minimum amount
of iron (and the associated amount of PDTA) for adequate
bleaching. When potassium cations are substituted for
ammonium, more iron is needed to complete bleaching for
the same time and temperature. The best formulation for use
in a given lab should be determined based on several
operating factors. Some of the factors to consider are:
• Local chemical cost and availability
• Laboratory ventilation factors
• Restrictions on sewer discharge
Controlling Bleach Tank Concentration
with Replenisher Rate
Since bleach systems are subject to evaporation in the
machine, overflow and replenisher holding tanks, system
evaporation often plays a significant part in striking a
balance between replenisher concentration, replenisher rate,
and tank concentration. The best way to adjust between these
factors, especially in a house system, is to vary the
replenisher rate to maintain the desired tank concentration.
Allowing the tank concentration to run high creates waste
due to carryout. A low tank concentration presents the
danger of inadequate bleaching. A new system should be
started up using the suggested replenisher rates given for
each bleach version. As the process or system seasons, the
rates may be adjusted to give the desired tank concentrations.
Bromide, iron, and pH are the critical parameters and should
stay within limits given. If bromide or iron is too high, no
harm to the process or film will occur, but expensive
chemicals will be wasted due to carryout.
Conversion to UL Bleach
The advantages of converting to the UL bleach, from
ferricyanide bleach (SR-27) are:
• UL bleach maintains a cleaner tank
• UL bleach forms no prussian blue
• UL bleach is easier to regenerate
• UL bleach regenerates into a cleaner replenisher
The advantages of converting to the UL bleach, from
persulfate bleach are:
• UL bleach has more bleaching power
• UL bleach has a longer solution life
• UL bleach is less sensitive to process variations
Mechanical changes are minor; adjust controls to keep the
bleach at 27°C (80°F). Solution times and replenishment
rates do not change.
If using the ferricyanide bleach currently, first remove any
red brass from the system, then clean up the bleach system.
A high pH wash (10 to 12) will help eliminate any prussian
blue in the system. Three cleaning cycles are recommended.
If per sulfa te ble ach is now in your machine, a series of hot
water rinses is needed in the accelerator and bleach tanks.
The bleach and accelerator tanks should be filled with hot
water and the recirculation and replenishment system turned
on. Three to five cleaning cycles are recommended.