Aqua Ammonia Neutralization of Acid
Effluent from a Deionizer
W. R. GARVIE, Manager
The Carling Breweries Limited
Waterloo, Ontario
D. E. WAITE, Technical Sales Representative
Canadian Industries Limited
Montreal, Quebec
INTRODUCTION
Recent literature concerned with the neutralization of acid waste indicates a
lack of knowledge or at least limited practical experience in utilizing aqua ammonia. This paper is offered in the hope that our experience in this field may
prove beneficial to other industries with similar problems.
A literature survey of methods for treating acid wastes would show that many
chemicals have been used in a variety of processes. Limestone, caustic soda ana
soda ash have won the popularity contest to date but we think aqua ammonia has
merit in many instances.
THEORY
Acidity, alkalinity and neutrality are a function of the hydrogen ion concentration. We can measure this by means of pH. A neutral solution is said to have
a pH of seven, which tells us that the concentration of the hydrogen ion is 10"^
moles/1. For the case of a IN solution of sulphuric acid this can be called a 4.9
per cent solution and has a pH of approximately 0. 3 pH, as a reference value, is
of little significance when the concentration is greater than IN, however, as we
get into more and more dilute solutions pH becomes the logical choice for mea -
surement. ApH change of one unit i. e. from . 3 to 1.3 signifies a dilution factor of
ten so that the solution would now be only 1/10N instead of IN. When an acid or
an alkali or base are mixed a salt is formed. This salt can also impart a pH to a
solution. If the acid is a strong acid such as HC1 or H2SO4 and the base is a weak
base then the salt has an acidic pH and the resulting solution needs a little more
(one or two per cent) of the base to bring it to exact neutrality. The converse is
also true if the acid is weak and the base strong. Aqua ammonia is generally considered a weak base, however it is one of the stronger weak bases. This means
that when used to neutralize a strong acid at .chemical equivalents where only salt
and water exist the pH is slightly lower than seven.
Note in Figure 1 the wide range of chemical neutrality when a strong acid is
neutralized by a strong base. Difficult in controlling to a specific pH is apparent.
The range is somewhat reduced with a strong acid and weak base. Also, with the
latter, chemical neutrality occurs from about 3.3 to 7.5 pH. This becomes the
practical control range and provides a point of interest when considering proposed
control by-laws.
There are quite a few commercially available alkaline materials which can
be used to neutralize acid wastes. Table I gives some of the pertinent facts about
these alkalies. The chemicals are primarily listed according to their costs per
neutralizing equivalent but some of the other points are of vital interest.   For ex-
-  650  -