1070-4272/05/7804-0541 C 2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 4, 2005, pp. 541!545. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005,
Original Russian Text Copyright + 2005 by Sizeneva, Kondrashova, Val’tsifer.
AND INDUSTRIAL INORGANIC CHEMISTRY
Spontaneous Decomposition of Industrially Manufactured
Sodium Hypochlorite Solutions
I. P. Sizeneva, N. B. Kondrashova, and V. A. Val’tsifer
Institute of Technical Chemistry, Ural Division, Russian Academy of Sciences, Perm, Russia
Received December 16, 2004; in final form, November 2004
Abstract-Spontaneous decomposition of industrially manufactured aqueous solutions of sodium hypochlorite
was studied. The rate constants of the decomposition reactions were calculated for different pH values.
In view of the exceedingly high toxicity and
volatility of metallic mercury (MPC for habitats
0.0003 mg m
)  and its wide use, the problem of
efficient salvation in tackling with possible mercury
spillage events remains a matter of current interest.
For this purpose, new demercurization methods are
being developed and the already existing techniques
are being improved. At present, the most widely used
methods are those in which mercury is oxidized with
strong oxidizing agents [2, 3]. In developing a de-
mercurizer, with industrially manufactured sodium
hypochlorite (HC) solutions as an oxidizing agent, it
became necessary to assess the stability of solutions
of this kind in storage and to study the oxidizing
activity of these industrial solutions at various pH
HC solutions are nonequilibrium systems that
undergo spontaneous decomposition. The problem of
spontaneous decomposition of HC solutions has been
extensively studied. The influence exerted by the con-
centration, temperature, and acidity on decomposition
processes has been analyzed and the possible mech-
anisms and kinetic characteristics of decomposition
have been reported . In the known studies, so-
lutions of both calcium and sodium HC were ex-
amined. Model solutions have been mostly studied,
with the HC solutions having low concentrations:
0.0130.20 M in terms of active chlorine.
The aim of this study was to assess the stability of
industrially manufactured concentrated HC solutions
in order to determine the maximum shelf life of so-
lutions of this kind. Another goal was to determine
the kinetic characteristics of real solutions used to
prepare the demercurizing agent.
The choice in developing the demercurizer was
made in favor of sodium HC, taking into account its
availability as a solution, high content of active chlo-
rine, and high stability against decomposition in
an alkaline medium (compared with calcium HC) .
The behavior of the solutions was analyzed at two
temperatures, 25 and 35oC, in view of the regional
climatic conditions (the maximum summer tempera-
ture is not, as a rule, higher than 35oC).
As object of study served industrially manufactured
(Berezniki Soda Plant Open Joint-Stock Company)
sodium HC solution with a concentration of 1803
200 g l
in terms of active chlorine. Model solutions
were prepared by passing at (035oC) Cl
reacting chemically pure hydrochloric acid with
through a NaOH solution containing no car-
bonates. The excess amount of the alkali was about
20 g l
. The reaction vessel was cooled with a mix-
ture of NaCl and ice. The pH values of the solutions
were measured with an EV-74 ionometer with glass
and silver chloride electrodes.
In stability studies, the alkaline (pH 13.5) HC so-
lutions under study were thermostated in hermetically
sealed polyethylene jars for 3 months. The pH value
of the solutions remained virtually constant, irrespec-
tive of the duration and temperature of experiments,
because of the presence of an excess amount of NaOH
in the HC solutions.
The dependence of the degree of HC decomposi-
tion on the pH value was studied at 25 and 30oC.