Various chemicals are
available for industrial neutralization depending
upon the application and whether you are neutralizing an acid or base
liquid. In most cases, Sulfuric Acid (H2SO4) and Sodium Hydroxide (NaOH)
will be used. The end-user
must consider the concentration to be used, must carefully analyze all
the chemistries involved, must review manufacturers’ warnings and
instructions, and must consider common safety measures for hazardous
liquids. Other chemicals
may be preferred based upon the amount of waste, the pH extremes
expected, operating costs, batch versus continuous considerations,
secondary reactions that might occur with the waste chemicals, storage
issues, and other process design concerns. Wastech Controls OMEGA acid or
caustic neutralization systems and
LabDELTA acid
neutralization systems can be designed for use with all of the
following chemicals.
The
most common neutralizing chemicals are:
Acids:
Sulfuric Acid (H2SO4)
Carbon Dioxide (CO2) - which converts in water to Carbonic Acid
(H2CO3)
Hydrochloric Acid (HCl)
Phosphoric Acid (H3PO4)
Nitric Acid (HNO3)
Bases:
Caustic (NaOH) – also known as Caustic Soda
Calcium Hydroxide (CaOH2)
Calcium Carbonate (CaCO3)
– also known as Lime or Limestone
Ammonium Hydroxide (NH4OH)
The
basic principle of neutralization of a base or acid requires either
hydroxide ions (OH-)
in a base for neutralizing an acid or hydrogen ions (H+) in an acid
for neutralizing a base.
Neutralization
with Acid
Since most chemicals listed above will work to neutralize waste
streams, cost considerations will often determine the selection. Sulfuric Acid (H2SO4)
is by far the most common acid available and is generally less
expensive. Concentration is also an issue. Sulfuric Acid
is available in 98% concentrations and may be the most economical in
this form but storage issues such as the types of tanks and
secondary containment available, familiarity of operators in
handling hazardous liquids, the dangers of refilling storage
containers or procedures for transferring from bulk containers, may
suggest 30% to 50% concentrations regardless of the increased
costs.
Neutralization with Caustic
Liquid
Caustic (NaOH) is most common in 50% concentrations. Because of safety issues, some customers, to avoid a hazardous
liquid, may opt for passive neutralization via Lime or Limestone in its solid, mineral form,
despite its bulk and weight. Sodium
Hydroxide is often preferred because of its solubility. Unfortunately, the neutralization process also forms salts that
are very soluble in water. This
high solids content can affect pump selection and maintenance. Temperature can also be an issue since 50% NaOH will begin to
freeze at temperatures below 60F. This will obviously interfere with the process.
Often 25% NaOH is recommended since this lowers the freezing
point to below that of water.
Neutralization with CO2
In cement pouring operations
large amounts of alkaline wastewater are generated. Discharge
authorities demand that such wastewater be treated on site. Carbon Dioxide (CO2),
which converts to Carbonic Acid (H2CO3)
in water, is an excellent choice for such applications since the
site is temporary, the gas is non-hazardous, can be used in-line
assuming retention and mixing is considered and is self-buffering so
regardless of dosage it will not lower the pH below 7.5-7.0. There are numerous operating considerations for using CO2
which Wastech Controls has mastered and an OMEGA skid mounted
solution can monitor and neutralize on demand saving chemical and
operating costs.
Mixing chemicals is always potentially dangerous. Consider carefully if a hazardous gas may be formed during the
neutralization process. The complexity of most proprietary processes
and the possible changes to a waste stream during operations makes it
impossible for Wastech Controls to recommend or specify a chemical for
a particular process. Wastech
engineers will offer solutions, but final suitability and safety
concerns must be the responsibility of the end-user at the application
site. Problems with
neutralizing chemicals are uncommon but must be anticipated by the
end-user or operator. Many safety features are built into
Wastech's OMEGA
neutralization systems.
