
The Effects of Aluminum Content, Temperature and
Impurities on the Electrical Conductivity of Synthetic
Bayer Liquors
G. R. BROWNE AND C. W. P. FINN
The electrical conductivity of pure sodium aluminate solutions with compositions in the
range 93 to 128 gl-~ free soda and O to 125 gl-~ alumina was investigated over the
temperature range 40 to 70 ~ Under these conditions, the solution electrical conductivity
was found to vary as a linear function of temperature. For a given free soda content, the
temperature coefficient of conductivity varied as an approximate guadratic function of the
alumina content. A single equation was developed relating solution conductivity to free soda
content in the range 105 to 128 gl-~ alumina, 40 to 100 gl-t over the temperature range 40 to
70 ~ The addition of sodium oxalate and sodium succinate at levels up to 20 gl-~ was
found to have no measurable effect on solution conductivity. However, the addition of
sodium carbonate at levels of 40 gl-~ had a significant effect, generally decreasing the
conductivity. The magnitude of the effect is a complex function of solution composition and
temperature. The technique was used to follow the precipitation of alumina from synthetic
Bayer liquor continuously for 4 h. Possible applications to industrial practice, of the
relationship determined, are briefly discussed.
WITH large amounts of capital tied up in Bayer
process streams and with increasing economic pres-
sures, the viability of the process becomes more depen-
dent on improved efficiency. Maintenance of optimum
process conditions generally requires application of
on-line process control techniques. One parameter of
Bayer liquors which lends itself to continuous monitor-
ing is solution electrical conductivity. Bayer process
liquors are highly conductive and changes in the
conductivity of isothermally decomposing solutions are
related to the stoichiometric release of highly conduct-
ing OH - ions ~ according to the equation
2Na A1 (OH)4a q ~ A1203 9 3H20 $+ Na+OH-aq [1]
This concept is not new 2-9 but published data describing
its quantitative application to solutions of industrial
composition are inherently limited in range due to the
requirement to maintain operating conditions and gen-
erally serve as deviation indicators under conditions of
constant temperature and total soda content.
Laboratory application of this technique is demon-
strated in the literature by the authors ~~ and Kelly I~ over
a limited range of temperature, total soda and alumina
contents.
The aim of this investigation was to extended the
range of electrical conductivity data to cover solution
conditions commonly found during the precipitation
stage of the Bayer process and to investigate the effects
of some significant impurities on conductivity.
G. R. BROWNE, formerly Post-Graduate Student, School of
Mining and Mineral Technology, Kalgoorlie, Western Australia, is
presently Metallurgist, Kambalda Nickel Operations, Western Mining
Corporation. C. W. P. FINN, formerly Alcoa Foundation Lecturer in
Thermodynamics, School of Mining and Mineral Technology, Kal-
goorlie, Western Australia, is presently Associate Professor of
Pyrometallurgy, University of the Witwatersrand, Johannesburg,
Republic of South Africa.
Manuscript submitted February 21, 1980.
METALLURGICAL TRANSACTIONS B
EXPERIMENTAL
Preparation of Solutions
Pure sodium aluminate solutions were prepared by
dissolving electrical grade AI wire in analytical grade
NaOH solution. The dissolution reaction is highly
exothermic and was conducted in covered polypro-
pylene beakers, cooled and diluted to 1 liter. Impurities
were added to the prepared pure solutions as analytical
reagent grade sodium carbonate and sodium oxalate
and technical grade sodium succinate. The prepared
solutions were stable with respect to alumina trihydrate
precipitation indefinitely in the absence of seed mate-
rial.
Composition and Temperature Range
Bayer liquors are described in terms of their free soda
content (expressed as Na20) alumina content (expressed
as A1203) and total soda content (expressed as Na20).
The difference between total soda and free soda is a
measure of impurity content (mainly Na2CO3).
In this study, the range of solution compositions and
temperature used maintained consistency with pub-
lished data 1-8 describing the precipitation stage of the
Bayer Process.
Conductivity Measurements
The conductivity of the solutions was measured using
a Philips PW 9501/01 Conductivity Bridge in earthed
mode with an external reference resistance of 1.000~2
(_+ 0.01). The conductivity cell was a Philips PR
9514/10 immersion probe with a cell constant of 1.00
cm-l (_+ 0.01) at a measuring frequency 200 Hz. Con-
ductivity bridge output was monitored on a Metrohm
Labograph chart recorder.
ISSN 0360-2141/81/0911-0487500.75/0
9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME 12B, SEPTEMBER 1981--487
THE METALLURGICAL SOCIETY OF AIME