Pergamon
MineralsEngineering,Vol. I 1, No. 10, pp. 989-992, 1998
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TECHNICAL NOTE
THE EFFECT OF pH MODIFIER ON THE FLOTATION OF CELESTITE
WITH SODIUM OLEATE AND SODIUM METASILICATE
F.H.B. de CASTRO, M.C. de HOCES and A.G. B O R R E G O
Dep. de Ingenierfa Qufmica, Facultad de Ciencias, Universidad de Granada, Spain
E-mail: agalvez @goliat.ugr.es
(Received 26 March 1998; accepted 9 July 1998)
ABSTRACT
This paper studies the influence of two pH modifiers, namely sodium hydroxide (NaOH)
and sodium carbonate (Na2C03), on the flotation of celestite ore using sodium oleate as
the collector and sodium silicate (Na2SiO 3) as the depressant. The use of Na2CO3
provides the best results for the concentration of celestite, under the same experimental
conditions. © 1998 Elsevier Science Ltd. All rights reserved
Keywords
Industrial minerals; flotation depressants; froth flotation; pH control; mineral processing
INTRODUCTION
Regulating reagents are used in flotation to control alkalinity or acidity and to counteract the interfering
effect of slimes, colloids and soluble salts.
An adjustment of pH by addition of an acid or an alkali [1], affects the the surfaces of solids, the extent
of ionization or solubility of a surfactant, the concentrations of inorganic ions, the level of the
electrochemical potential and the corresponding oxidation-reduction potential. The complexity of all these
effects, particularly the kinetics, and incomplete reversibility involved in the reactions producing these
effects, makes it important to establish the correct sequence of pH adjustment procedures, the optimum
points and the levels of additions.
This paper studies the influence of two pH modifiers, namely NaOH and Na2CO 3, on the flotation of
celestite using sodium oleate as the collector and sodium silicate as the depressant.
EXPERIMENTAL
Mineral species
The experiments were carried out with celestite ore supplied by Kali Chemie Iberia, S.A., from the
company's deposits within the municipal boundaries of Escdzar (Granada).
Flotation agents
*
*
Collecting agent: Seelze-Hannover sodium oleate (93% purity).
Frothing agent: Daksa M-1 pine oil, with a constant concentration of 0.01407 g/L.
989
990
F.H.B. Castro et
al.
pH modifiers: Merck sodium hydroxide and sodium carbonate.
Depressant agent: Merck sodium silicate.
Experimental conditions, apparatus and calculations
The mineral, previously ground to the appropriate size, was added to a 5L glass tank. The density of the
pulp was then adjusted in the proportion ore/water=200g/3000g, and the collector, pH modifier and foaming
agent were added, always at the same time. This mixture was agitated (at 60 r.p.m.) for a 10 minute
conditioning period before being subjected to flotation in a MDL-13 mechanical cell for another 10 minute
period.
The floated mineral was vacuum filtered and the sample was dried by a heating stone at 383K to a constant
weight.
Analysis of the floated mineral was performed by atomic absorption spectrophotometry. Calero [2] has
already provided a detailed description of the analytical method.
RESULTS AND DISCUSSION
NaOH as pH modifier
NaOH was used as the first pH modifier in view of its widespread use in mineral concentration methods
using flotation.
Bearing in mind the results obtained in a previous paper [3] pH in the flotation tub was set at 10.5 and the
concentration of sodium oleate as the collector at 1500 g/T. Experiments were then performed to study the
effect of sodium silicate as depressant when the selected pH modifier (NaOH) was used.
The recovery and the content percentages for celestite and calcite are shown in Table 1 against the
concentration of metasilicate.
TABLE1
pH modifier: NaOH
Na2SiO 3
(M)
Sodium Oleate: 1500 g/T
RECOVERY (%)
CONTENT (%)
Celestite
Calcite
Celestite
Calcite
Others
0.0
41.2
28.7
68.4
21.9
9.7
10-s
39.4
26.4
69.1
22.1
8.8
10-4
38.9
25.3
68.2
23.6
8.2
10-3
29.4
24.1
63.8
26.9
9.3
10-2
11.1
11.6
57.1
30.7
12.2
It should be pointed out that the term calcite in fact represents all calcium minerals present in the sample,
of which calcite is the predominant species (95% in most cases). To avoid complications in the
interpretation of results, all calcium minerals are referred to as calcite.
At low concentrations, sodium silicate exerts a more marked effect on calcite than on celestite, but as
concentration is increased, the difference in recovery percentages for both minerals decreases and levels off
Effect of pH modifieron flotationof celestite
991
at 10 -2 M, giving rise to intense mineral depression. G~ilvez [4], found a similar effect of the depressant
Na2SiO 3 when working in alkaline media on pure minerals.
Likewise, at low depressant concentrations (10-5 M), celestite content is higher, close to 70%, but when
sodium silicate concentration is raised to 10-2M, content lowers to 57%. Calcite content also varies from
22% to 30% for the same range of depressant concentrations. The term "others" represents all minority
minerals (mainly MgCO 3 and SIO2) present in the sample, which barely undergo any alteration throughout
the range of sodium silicate concentrations assayed.
Na2CO 3 as pH modifier
The presence of calcium ions from gypsum (CaSO 4.2H20) may affect the adsorption of the collector on
the celestite mineral surface under study.
Hence, although the solubility of gypsum in water is relatively low (0.223/100 parts, [5]), the presence of
this mineral in the Escuzar deposits at a concentration of between 3 and 5% may give rise to solubilisations
which, in turn, may affect celestite concentration by flotation. Therefore, sodium carbonate (Na2CO3) was
used as a pH regulator in the flotation tub, which acts by precipitating calcium into a corresponding
carbonate form, so that the pH in the tub could then be adjusted accordingly to the appropriate setting.
The pH for the flotation tub was selected at 10.5 with two concentrations of sodium oleate, i.e. 1000 and
1500 g/T, bearing in mind results obtained in a previous paper [2], in order to verify the effect exerted by
sodium silicate on celestite when collector concentration is altered.
The recovery and the content percentages against Na2CO 3 concentration for both sodium oleate
concentrations is shown in Table 2. It is clear that sodium silicate depresses celestite and calcite intensely,
although the recovery percentages do not coincide at any of the depressant concentrations used. It is also
clear, moreover, that the increase in sodium oleate concentration slightly reduces the depressing effect of
Na2SiO 3 which suggests that both agents compete for adsorption on the surface of the floated solids, as
reported by several authors [4, 6-8].
TABLE 2
pH modifier: Na2CO 3
Sodium
Oleate
(g/T)
1000
1500
Na2SiO 3
RECOVERY (%)
CONTENT (%)
(M)
Celestite
Calcite
Celestite
Calcite
Others
0.0
43.7
37.1
67.6
26.4
6.0
10-5
35.3
28.9
63.1
28.1
8.8
10-4
24.6
18.8
66.2
25.9
7.9
10-3
16.2
12.6
66.8
26.2
7.0
0.0
60.4
42.6
69.2
24.5
6.3
10-5
49.5
36.3
65.3
26.4
8.3
10-4
36.9
28.4
66.8
27.1
6.1
10-3
23.6
18.2
67.5
26.7
5.8
992
F . H . B . Castro et al.
If these results are compared with those obtained with NaOH, it is clear that the recovery percentages are
considerably higher, especially at low depressant concentrations.
No alteration is seen in content percentages for either of the minerals under consideration, given that there
is no change with modification of the depressant or collector concentrations. A steady value close to 70%
is maintained for celestite, while calcite remains at 25%.
When these results are compared with those obtained with NaOH, it may be deduced that, although the
celestite content attained under the most favourable conditions is similar, this content does not decrease with
increased sodium metasilicate concentration in the flotation tub.
CONCLUSIONS
It is deduced from the results obtained that Na2CO 3 holds the advantage over NaOH of increasing recovery
percentages for celestite, and maintains the celestite content percentage constantly close to 70%, throughout
the range of depressant concentrations assayed.
REFERENCES
.
2.
3.
4.
5.
6.
7.
8.
Leja, J., Surface Chemistry of Froth Flotation, Ed. Plenum Press, New York (1982).
Calero, M., Aprovechamiento de recursos geol6gicos andaluces. Concentraci6n de celestina, Tesis
Doctoral, Universidad de Granada, Granada (1994).
Hern,Jinz, F.; Calero, M. and G~ilvez, A., The effect of pH modifier on the flotation of celestite
with sodium oleate and quebracho, Chem. Eng. Sci., 51, 4289-4294 (1996).
G,Jlvez, A., Agentes de superficie ani6nicos en la flotaci6n de celestina y calcita, Tesis Doctoral,
Universidad de Granada, Granada (1993).
Perry, R.H. and Chilton, C.H. (Ed.), Manual del ingeniero qufmico, 5'ed., 21-75, Ed. McGrawHill, Mexico (1982).
Dudenhov, S.L.; Shubov, L.Y. and Glazunov, V., Fundamentos de la Teorfa y Prtctica de Empleo
de Reactivos de Flotacitn, Ed. Mir, Moscow (1980).
Hern~iinz, F. and G~ilvez, A., Efecto del Na2SiO 3 en la flotaci6n de celestina y calcita con oleato
s6dico, Afinidad, 425, 36 (1990).
Hern~nz, F. and Calero, M., Influence of quebracho and sodium silicate on flotation of celestite
and calcite with sodium oleate, Int. J. Miner Process. 37, 283-298 (1993).
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