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The influence of temperature during flotation of celestite and calcite with sodium oleate and quebracho
IIITiERnmTofllIL,IOUItllilL OF
mlnsRm. PRO(ENNIU6 ELSEVIER
Int. J. Miner. Process. 46 (1996) 35-52
The influence of temperature during flotation of celestite and calcite with sodium oleate and quebracho F. Hernfiinz Bermddez de Castro, A. G~ilvez Borrego Departamento de lngenierfa Qufmica, Facultad de Ciencias Universidad de Granada, E-18701-Granada, Spain
Received 29 June 1994; accepted 20 June 1995
Abstract A study has been made on the influence of temperature during flotation of the celestite and calcite mineral species, using sodium oleate as the collector and quebracho as the depressant, for a particle size ranging between 80/100 A.S.T.M. mesh (177/149/xm). The experiments were conducted on pure minerals in a thermostatted Hallimond tube with working temperatures between 293 and 323 K. Results indicate that celestite can be depressed during flotation with sodium oleate due to the action of quebracho, although when the temperature in the bath is increased, the depressor action is slightly inhibited, thus increasing recovery of the mineral. The results for calcite show similar findings, although with a less pronounced depressor effect due to quebracho.
1. Introduction
Celeslite, SrSO4, belongs to the commonly denominated salt-type minerals, along with fluorite, barite, scheelite and so on, according to Hanna and Somasundaran (1976). The extractic n and concentration of celestite is of great interest in highly industrialised countries in view of the numerous applications of its derivatives, particularly in carbonate and nitrate forms. Market demands, however, require a celestite concentration of over 90%, by means of separation from other species. This separation can be achieved mainly by leaching, density ,difference or by flotation. This last technique offers the most promising future prospects, since the method is low in cost and easy to operate. Calcite, CaCO3, is also included in the group of salt-type minerals. Calcite is valuable in its own tight as a major raw material used by the cement and conglomerate industry (Witt, 1950; Taylor, 1967; Vian, 1976). However, when found in conjunction with strontium minerals, calcite is the least valuable component and must be separated from the ore. Moreover, calcite usually appears naturally in large deposits with a high degree of purity, 0301-7516/96/$15.00 © 1996Elsevier ScienceB.V. All rights reserved SSDI0301-7516(95)00059-3
36
F. Hernrinz Berm~idez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
thus rendei'ing concentration techniques unnecessary to achieve the mineral to date. It is therefore essential to understand how this mineral responds to techniques which aim to concentrate other species, currently considered as more valuable. It has been proven that an increase in the flotation bath temperature usually enhances the operation of mineral concentration by flotation, (Blazy et al., 1964; Taggart, 1966; Roche, 1973) and (Kulkarni and Somasundaran, 1975). However, for economic reasons, mineral concentration operations are carried out at the mining site using water at ambient temperature. The price of the concentrate on the market, however, may justify the rise in production costs by using higher temperatures. Minerals such as fluorite are usually floated at temperatures even higher than 313 K (Roche, 1973; American Cyanamid Co., 1989). Taking into account the high price of celestite on the international market, it would seem more than logical that the influence of temperature during flotation recovery should be fully examined, though initially on a laboratory scale. Since flotation is based on the capturing of mineral species by means of organic collector agents, the phenomenon must be modulated to achieve selective flotation (Blazy, 1972). In some cases, then, certain agents are used either to allow the collector to adhere on a surface on which it could not normally do so (activators) or to inhibit such fixation (depressants). Within the group of organic depressant agents, quebracho is the most frequently used to avoid flotation of ore, mainly calcareous ore, which is found together with certain other minerals, due to the low selectivity of commonly-used collectors in the separation of the valuable fraction. However, the risk of the depressant agents acting on the mineral to be recovered, especially above certain concentrations of the agent (Hern;iinz and G~ilvez, 1989a, b; Hern~iinz and Calero, 1991a, b), must be taken into account. Quebracho is a vegetable tannin from the wood of the tree of the same name. The most highly appreciated variety of quebracho comes from the Quebrachia lorentzii species, known as coloured quebracho which contains 20-30% extractable tannins. Although the composition may vary, the most representative example (Stubbings, 1972) is given in the following diagram: Quebrachia
I
V CELLULOSE 36.78~
I
TOTAL SOLZDS 28.63~
I
•
AQUEOUS EXTRACT 27.2 IZ
I
f
SOLUBLE SOLZDS 23.77Z
1orentzli
I
I
• RESZNS I . 12~
I
TANNZNS 20.65Z
!
• NON-CELLULOSE 34.89Z
I
OTHER 7.98~
Sodium oleate-celestite and sodium oleate-calcite systems, modulated by quebracho as the depressant at room temperature, have been widely studied. It has been found that quebracho is a strong and unselective depressant for both minerals when a fatty acid is used as the collector. Until now, however, no studies have been undertaken to see how temperature influences these systems. As the temperature variable is of major importance in a mineral such as celestite, it would therefore seem extremely useful to determine if new methods for the separation of celestite and calcite are possible.
F. Herntinz Berm~dezde Castro, A. GdlvezBorrego/Int. J. Miner. Process. 46 (1996) 35-52
37
2. Experimental 2.1. Mineral species
Celestite, SrSO4, and calcite, CaCO3,from two different mines were used for this research study. The celestite was taken from the Cerro de Montevives mine, located in Las Gabias, 12 kilometres southwest of the city of Granada. The mineral was selected, fragmented and selected again by hand to collect only the purest samples, thus guaranteeing a concentration of 97%, as shown by acid leach analysis. The calcite was taken from a deposit near Torredonjimeno (province of Jatn), with a concentration in CaCO3 over 99.6%. Once the minerals had been selected and broken up, they were then ground to the appropriate size using a CULATTI, triple floating hammer micromill. The ground mineral was classified according to size using a high-vibration MECHANICAL-SCIENTIFIC machine with fine A.S.T.M. sieves and sieve base, thus selecting only A.S.T.M. 80/100 mesh size, equivalent to 177/149/xm. 2.2. Flotation agents
The chemical products used in this study are described below. Collector Agent, sodium oleate, supplied by Seelze-Hannover, with a 93% spectrophotometrically determined purity. The solutions were dissolved in distilled water. The solute was then weighed on a SARTORIUS 2442 precision balance, and the desired solution obtained by successive dilutions as the agent concentrations used were very small. In all cases, the solutions were prepared shortly before the experiments were carried out to avoid possible alterations in the collector agent ow,~r time, which could alter its properties. 2.3. Modifying Agents
The modifying agents used were as follows: quebracho, vegetable tannin supplied by the Orgiva (Granada) mineral panning station, Merck sodium hydroxide and Probus hydrochloric acid. These last two were used as pH modifying agents in a 4 N concentration to achieve desired pH easily, and pH measurements were performed with a CRISON 2001 pH-mete:r. 2.4. Experimental methods and conditions, apparatus and calculations
For this research, surface tension measurements were performed using plate method, since no hydrostatic correction is required as in the ring method. Measurements of surface tension were performed with a KRUSS K10 digital tensiometer, with an accuracy of + 0.1 m N / m and a platinum-plate measuring 20 × l0 X 0.1 ram. The solution whose surface tension is to be measured is placed in the duly thermostated flask at 1abe essay temperature, using a thermostat which allows consistent temperature regulation ± 0.1°C. Eleven determinations of surface tension were carded out for each case, the average being taken from the last ten.
38
F. Hern6inz Bermtidez de Castro, A. Gcilvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
L
I
"1
.°
| I
I
Fig. 1. Schematic diagram of experimental setup. 1. Compressor, 2. Regulation valve, 3. Water manometer diaphragm, 4. Thermometer, 5. Thermostat, 6. Magnetic stirrer, 7. Hallimond tube, 7a. Porous plate, 7b. Magnetic stirring bar, 7c. Collector and 7d. Liquid level.
The Hallimond tube was as d as the flotation apparatus, Fig. 1, as conceived originally by Hallimond (1944), modified by Fuerstenau et al. (1957) and again modified by the Flotation Group of the Chemical Engineering Department to acheive a new thermostatted design, enabling studies at different temperatures. The solid-solution suspension was placed in the thermostatted Hallimond tube (7) with a capacity of nearly 400 cm 3, and then subjected to an air current from a compressor ( 1 ). The flow was adjusted by a regulation valve (2) and measured by a water manometer diaphragm (3). Once the air bubbles had been formed and the solid particles dispersed by a magnetic stirrer (6), the floated mineral was collected on the collector (7c). After prior conditioning in a furnace at the appropriate assay temperature (293, 303, 313 and 323 K), 2 g of mineral, either celestite or calcite of A.S.T.M. mesh size 80/100 (177/149/xm) were placed in the Hallimond tube. Then a solution of the agents to be used was added, at the appropriate concentration, i.e. for sodium oleate ( 1.4 × 10 -6, 4.5 × 10 -6, 7.3 X l0 -6 and 1.4 X 10 -5 M) and for quebracho (0.0012, 0.012, 0.12 and 1.2 g / L ) . The pH of these solutions had previously been adjusted with HCI or NaOH at the working temperature. This was then shaken magnetically for three minutes (conditioning time) to ensure adherence to the collector and/or depressant on the solid particle surface. Then the air flow was regulated and the solution placed in the porous plate on the bottom of the tube. The air flow used was reduced to the limit of 8 L / h so as to avoid particles being carded away as far as possible. The particle adhering to the fine gas bubbles rose to the surface where the bubbles burst and were collected in the collecting tube. In all cases, flotation time was equal to conditioning time, i.e. three minutes. The recovery percentage for celestite and calcite is obtained by the difference in weight as both minerals are considered to be pure, although celestite may contain approximately 2% of calcareous impurities. It was decided not to eliminate the presence of carbonate by acid leaching to avoid any possible alteration in the natural surface of the solid, although the results may be affected by a slight degree of error, permissible in assays of this kind. 3. Results and discussion
Tables 1 and 2 show the recovery percentages for celestite and calcite, respectively, under the experimental conditions described above. It may be seen that for the lowest concentra-
F. Herntiinz Bermddez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
39
Table 1 Recovery p,ercentages for celestite [Oleate], M
T, K
Recovery, % pH=6
pH=7
pH=8
pH=9
pH=10
pH=ll
pH=12
1.4 X 10 -6
293 303 313 323
0.89 1.52 1.61 5.90
1.10 1.09 0.98 6.47
0.84 0.85 1.18 3.33
0.84 1.04 0.98 3.29
0.69 0.94 0.91 2.35
0.46 0.62 0.58 2.06
0.24 0.68 0.70 3.57
4.5 × 10 -6
293 303 313 323
16.91 19.85 25.60 30.14
13.35 19.75 29.55 27.45
15.23 18.14 28.00 30.05
11.89 16.62 25.83 24.60
12.27 23.39 29.93 27.96
11.69 17.52 21.67 23.40
13.31 16.52 20.53 21.85
7.3 X 10 - 6
293 303 313 323
15.92 31.66 75.88 95.14
16.78 65.48 92.18 93.93
44.80 93.04 93.36 95.79
28.24 91.76 96.05 95.96
39.23 86.92 93.37 93.04
35.36 78.45 91.21 92.10
30.38 74.44 77.24 90.80
1.4 X 10 -5
293 303 313 323
56.70 70.72 83.35 89.12
91.02 93.49 96.28 98.08
93.10 93.61 97.59 97.23
93.07 96.30 96.87 97.18
78.68 93.46 96.69 96.49
75.49 92.94 94.80 93.39
74.42 84.21 86.73 94.21
Table 2 Recovery l;~rcentages for calcite [Oleate], M
T, K
Recovery, % pH=6
pH=7
pH=8
pH=9
pH=10
pH=ll
pH=12
1.4x 10 -6
293 303 313 323
0.58 2.32 2.00 2.70
0.75 1.10 1.86 2.66
0.25 0.66 1.29 1.51
0.56 0.85 1.53 2.49
0.97 1.25 1.86 2.84
0.91 0.96 1.51 2.75
1.31 0.94 1.35 2.27
4.5 × 10 -6
293 303 313 323
1.27 1.35 2.31 3.02
1.11 1.30 2.57 3.94
0.59 0.82 1.95 2.98
1.11 1.20 2.27 2.57
0.81 1.23 2.10 2.80
0.87 1.62 2.50 4.18
0.85 1.77 3.14 3.27
7.3 × 10 -6
293 303 313 323
1.62 1.35 4.29 8.40
1.19 1.20 3.52 7.78
1.29 1.35 3.55 4.33
1.21 1.43 3.38 3.09
1.00 2.55 3.02 2.89
1.19 2.75 2.84 7.32
!.96 3.71 5.73 6.44
1.4 x 10 -5
293 303 313 323
5.65 98.96 96.65 99.80
6.29 60.83 89.37 97.83
8.08 41.27 97.45 98.98
4.51 23.94 84.04 97.60
4.62 11.14 81.25 96.04
4.78 26.83 85.65 94.05
4.86 90.53 97.85 95.76
40
F. Herntiinz Bermtidez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
tions of sodium oleate used, 1.4 × 10- 6 M, sodium oleate does not float celestite and calcite as proven by the recovery percentages below 10% in all cases, and by the fact that pH variation and temperature modification cause no effect. When the collector agent concentration is increased to 4.5 X 10-6 M, however, the effect of temperature in the bath becomes apparent, considerably improving celestite flttation as temperature rises and in some cases recovery percentages are doubled on raising temperature from 293 to 323 K, although overall percentages are very low. The effect of temperature becomes very clear, however, when the concentration of sodium oleate is 7.3 × 10 - 6 M. At this concentration, the recovery percentages of the mineral rise considerably as the temperature in the bath rises, with the most pronounced and gradual effect occurring at pH 6 and pH 12 with recovery rising from 20% to over 90% at temperatures of 293 to 323 K. However, at the highest sodium oleate concentration tested, 1.4 X 10 -5 M, high recovery percentages are achieved very rapidly, whereas the remaining variables exert less effect than at the preceding concentration. Calcite is not recovered by flotation either by altering pH in the bath nor increasing temperature for the first three concentrations of sodium oleate and recovery rates never exceed 10% recovery in any case. When sodium oleate is used at a concentration of 1.4 × 10 -5 M, the results obtained show that less than a 10% recovery is achieved at 293 K while this rises to over 95% recovery when the temperature is raised to 323 K. On comparing the results obtained for the two mineral species using sodium oleate as the collector and in the absence of a depressant, it may be seen that separation of the two minerals can be achieved in a single flotation operation at 293 K, 1.4 X 10 -5 M and pH between 8 and 10. Experiments performed by Hem~iinz and Calero (1993), however, show that there is no difference in response of celestite and calcite in joint flotation over a wide range of sodium oleate concentrations, including those used in this study. It may be con100 "70 80 iO
v lu
~, u
3
60. ,0 20"
[0 t E AT E] : 1.4x10-5 Id T=293 K "0" CELESTITE "Q'CALCITE 30
0
i 6
i 8
i I11
i 1~'
pH F i g . 2. C o m p a r i s o n o f r e c o v e r y p e r c e n t a g e s o f celestite a n d calcite w i t h a s u r f a c e t e n s i o n o f 1.4 × 1 0 - 5 M s o d i u m oleate s o l u t i o n at 2 9 3 K.
F. Hern6inz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
41
cluded then that there is an interaction between the minerals and sodium oleate, which radically alters the results obtained by flotation of these two minerals separately. The maximum recovery rate achieved for celestite at the pH 8-9 interval, coincides exactly with the minimum values obtained for surface tension in the flotation bath with sodium deate, Fig. 2. This points to a clear dependence in the sodium oleate-celestite system between the minimum surface tension and the maximum flotation of the mineral. This fact has already been pointed out by Pugh and Stenius (1985), although these authors indicate that a decrease in surface tension, may, in certain cases, not be the major efficiency factor in separation by flotation. It does, however, indicate the presence of surfactant species which enhance the hydrophobic quality of the minerals. During their research into fluorite flotation ,with oleic acid and sodium lauryl sulphate, Hern~iinz and G6mez (1986) corroborated that the mineral responds to the technique better at pH values causing a minimum surface tension in the bath. Kulkami and Somasundaran (1975), when using potassium oleate for the flotation of hematite, found a clear dependence between the values for mineral recovery rates and surface pressure and determined that the maximum recovery rate is found at minimam values for surface tension in the bath, in this case at around pH = 8. It is also of outstanding interest that an increase in the temperature in the bath brings about a slight decrease in surface tension in the bath in all cases, and moreover this increase causes a considerable rise in the recovery of celestite by flotation. This has a bearing on the previous comments and fully confirms that a decrease in surface tension raises the recovery percentage for celestite, in some cases quite considerably. The results for calcite, however, contrary to those for celestite, show a low or nil ratio between the minimum surface tension in the bath and the maximum recovery of the mineral, although it is clear that when surface tension is decreased by an increase in temperature, 100
~
'70
80 ~0
6o 3
w U
50 z
3
40'
20' [OL E AT El = l.t*xlO-5Id T=323 K "0" CELESTITE "~CA LCITE 0
! 6
$
i 10
30 i 12
pH
Fig. 3. Comparison o f recovery percentages o f celestit¢ and calcite w i t h a surface tension o f 1.4 × ] 0 - 5 M sodium oleat¢ solution at 323 K .
42
F. Hern6inz Bermtidez de Castro, A. G61vez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
there is an improved recovery rate, especially at 1.4 X 10 -5 M of sodium oleate, Fig. 3. The modification of the pH in almost all cases varies calcite concentration quite noticeably.
3.1. Depressor effect of quebracho The recovery rates of celestite according to pH in the bath are shown in Figs. 4-7 for 293, 303,313 and 323 K respectively, with a concentration of sodium oleate of 7.3 X 1 0 - 6 M and varying concentrations of quebracho. It may be seen that celestite is strongly depressed under such conditions and at 293 K, even at low concentrations of the depressant agent, with a negligeable recovery of celestite in most of the experiments performed. The depressor action of quebracho can clearly be seen when these results are compared with those obtained in the absence of the agent. The depressor effect becomes clearer as temperature rises, since this variable enhances the flotation of celestite. In the absence of quebracho and at 303, 313 and 323 K, this mineral floats well, especially at the pH range between 8 and 10. When quebracho is added, however, its becomes totally depressed for concentrations 0.012 and 0.12 g/L, and quite intensely depressed at 0.0012 g/L. Glembotskii et al. ( 1961 ), when using a temperature 293 K, with oleic acid as the collector, alkaline mediums and a 7 5 c m 3 flotation microcell, found that tannins depress celestite completely at concentrations of 150 g/Tm, and are more efficient as depressant agents than glucose, peptone, gelatine and dextrine. The celestite recovery rates under similar operational conditions to those described, with an increased concentration of sodium oleate of 1.4 X 10 -5 M are shown in Figs. 8-11. Although qualitatively speaking the results obtained are similar to the above, they do reveal that the increase in the sodium oleate concentration considerably decreases the depressor I00'
CELESTITE . [0 L E AT E'] :?.3xI0-~ M
T= 293 K 80 ¸
QUEBRACHO lO glL 0 0,0012 '" O 0.012 " /'. 0.12
>.
o w 4,
8
IO
12
pH
Fig. 4. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 293 K.
F. Hern6inz Bermtidez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
43
100
80
T : 303 K ~60
QUEBRACHO • 0 glL
0
4o
o
o.oo12
-
[] 0.012
20
0 6
8
10
pH
Fig. 5. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 303 K.
effect of quebracho, most markedly at low depressant concentrations. The increase in temperat~Lre also decreases the depressor effect, especially in neutral or mildly alkaline circuits. 100'
CELESTITE _ "~ L EATE] =7,3XI0"GM T=313K
QUEBRACHO e0 glL O0.0012 " O0,012 A 0J2
~> o u w 4C cc
0 8
10
12
pH
Fig. 6. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 313 K.
44
F. Herntiinz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52 100
1 CELESTITE [0 LEATF.,] :7.3x10-6M T=323 K
80
6¢
QUEBRACHO • 0 glL o.o012 " 0 0,012 "
o
o ou la 4~ a:
20 --(3..
8
I0
pH
Fig. 7. Celestite flotation vs. pH, with 7.3 × l 0 -6 M sodium oleate, at various concentrations of quebracho and 323 K.
Although the depressor action mechanism has not been fully determined (Dudenhov et al., 1980), it is clear that the depressant inhibits the adsorption of the collector on the surface of the solid. Therefore, it may be deduced from the results obtained that there is the surfactant and the depressant compete on the mineral covering, or that quebracho somehow blocks I00"
[o LE ATE] :1.4xt05~ \
80
~60
T=293 K
Q
U
-
EBRX:.O • 0
g/L
i!
O U u 40
20
8
pH
10
Fig. 8. Celestite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 293 K.
F. tterntiinz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
45
100" CEUESTITE
80
--
~ 6o
0
A
v
/
\
/
QU E B R ~ H 0
\
\
°
\ \
"°
,,L
o o.oo12 " \
a o.o12
-
o ~c
4c
|
8
10
12
pH
Fig. 9. Cele:~tite flotation vs. pH, with 1.4 × 10 - s M sodium oleate, at various concentrations of quebracho and 303 K.
100'
8C
v
60
o
2¢
8
10
12
pH
Fig. 10. Celestite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 313 K.
46
F. Hern6inz Berm~dez de Castro, A. Gdlvez Borrego lint. J. Miner. Process. 46 (1996) 35-52 100"
QUEBRACHO •
O
o
o.oo12
n
o.o12
g/L " "
" "
• A 0.12
O 1.2 6C
w
g u w 40
20
CELESTITE [OLEATE] :1.4x1(~$M T= 323 K
\ n~
i 8
10
12
pH
Fig. 11. Celestite flotation vs. pH, with 1.4 × 10- s M sodium oleate, at various concentrations of quebracho and 323 K.
the collector agent's action. This action basically depends on the concentration of both agents. Figs. 12-15 show the recovery rates for celestite versus pH for a three-fold sodium oleate concentration, 4.5 × 10 -5 M, and it may be seen how the depressor action of quebracho indeed decreases even farther at the same concentrations. Temperature also attenuates the depressor effect. 10o 0 ,//~"~
w
CELESTITE 5 [OLEATE] =4.5xl6 M
ouEs~~R, o;0,2 c.o
\
Io .
u m!l
\
~,
8
O 0.0012 91L
\
n
10
"
12
pH
Fig. 12. Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 293 K.
F. Herndinz Bermt~dez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
47
I00"
80
6O M
w ~J ~j 40 a:
20
O u 0 6
10
B
pH
Fig. 13. Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 303 K.
In orde,r to check quebracho's depressor effect on calcite, two concentrations of sodium oleate we,re selected, namely 1.4× 10 -5 and 4.5 × 10 -5 M respectively, and the lower concentration, 7.3 × 10 - 6 M was disregarded as the recovery rates for calcite in the absence of this depressant agent were negligeable (see Table 2). The results obtained are shown in 100
O / , ~
//
o
C ELESTITE 5 [OL EAT E] =z~Sxl() M
~
>~ o u wz.,O
Z0
OUEBRACHO A ~ . ~ 0 0,0012g/L D 0.012 "" A 0.12 0 1.2 O O
8
pH
10
12
Fig. 14. Celestite flotation vs. pH, with 4.5 × 10-5 M sodium oleate, at various concentrations of quebracho and 313K.
48
F. Herntiinz Berm~dez de Castro, A. Gdlvez Borrego / int. J. Miner. Process. 46 (1996) 35-52 1oo
00
tel
~o
QUEBRACH9 0 0.0012 g/L n 0,012 " ~.0.12 O 1.2
20 CELESTITE § [ O L E A T E ] :4.5x1() M T = 323 K
0 6
10
8
12
pH
Fig. 15, Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 323 K.
Figs. 16-21. It may be seen that flotation of calcite is negligeable at 293 K for an oleate concentration of 1.4 × 1 0 - 5 M, as was to be expected, both in the absence of the depressant and at any of the concentrations applied. When the temperature is increased, the effectiveness 100" CALCITE [0 LEAT E] : 1.4x10-5M T=293 K $0
QUEBRA~:HQ elL O 0.00tZ " rl 0.012 " A 0.12
• 0
>o
,.o
20
8
p*t
10
12
Fig. 16. Calcite flotation vs. pH, with 1.4 × 10 - s M sodium oleate, at various concentrations of quebracho and 293 K.
F. Herndinz Bermadez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
49
I00" CALCITE [O LEAT E] ~|.4xIO$ M
T=303 K 80 QUEBRACHO 0 glL o 0.oolz o o.0tl
o
2O
0 "'
i
6
8
pH
r
!
10
Fig. 17. C a l c i t e flotation vs. pH, with 1.4 × 10 - 5 M sodium oleate, at various c o n c e n t r a t i o n s o f q u e b r a c h o and 303 K.
of the agent's depressor action is revealed, since at both 303 and at 313 and 323 K, the mineral is completely depressed for all three concentrations of quebracho used, with the most significant effect arising at 323 K since, in the absence of quebracho, recovery rates are over 95% in all cases. The pH effect is of relatively little importance in the depressor IO0-
J
SO
CALCITE $ [ 0 L EAT E'] :l.6x10- M T=313 K
~60
QUEBRACHO e0 91L O 0.0012 " n 0.012 " ,~ 0.12
O
~4o
2O
i
6
8
pH
10
12
Fig. 18. Calcite flotation vs. p H , w i t h 1.4 X 10 - s M s o d i u m olcate, at various concentrations of quebracho and
313K.
50
F. Hern6inz Berm~idez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52 I00
--r-------9~a
~
e-
80 CALCITE -5 tO L E A T E ] =l.4xf0 M T:323 K
6O
v LU
Q~JEBRACHO
• 0
~c
9IL
O 0.0012 " O 0,012 ' Z~ 0.12
z0
0
=
6
i
8
i
i
10
T2
pH
Fig. 19. Calcite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 323 K.
action of quebracho for low collector concentrations, although at 4.5 × 10 -5 M sodium oleate, depression is more effective in clearly alkaline mediums, especially at a quebracho concentration of 1.22 g/L, Figs. 20 and 21. I00
O
O
aO
CALCITE -5 [O L E A T E]=&.5xl0 M T=313 K
60 uJ
o0..o=,,;L
QU EBRACHO
~ o oc
20
0
i
6
i
S
i
pH
i
10
!
t2
Fig. 20. Calcite flotation vs. pH, with 4.5 × 10 -~ M sodium oleate, at various concentrations of quebracho and 313K.
F. lterndinz Bermddez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
51
10G O--
CALCITE 8C
o
t EA rE] =4.~=1o"5 M T=223 K
,QUEBRACHO
o ,o:o;,
lu
=~,,¢
!
6
i
i
8
i
10
i
12
OH
Fig. 21. Ca],cite flotation vs. pH, with 4.5 × 10 - s M sodium oleate, at various concentrations of quebracho and 323 K.
4. C o n c l u s i o n s
When sodium oleate is used as the collector, pH in the medium clearly conditions celestite flotation, with maximum mineral recovery percentages arising at pH between 8 and 9. An increase in temperature considerably improves celestite recovery. For very high sodium oleate concentrations, however, the effect brought about by variations in pH and temperature barely alters recovery of the mineral by flotation. A clear dependence between maximum mineral recovery and minimum surface tension in the bath has been proven for the sodium oleate--celestite system. For most concentrations of sodium oleate used in this research study, calcite was not recovered by flotation, even by modifying pH or by increasing temperature in the bath. At an oleate concentration of 1.4 × 10 -5 M, however, the recovery percentage rises from under 10% to over 95% when temperature is increased from 293 to 323 K. The low recovery rates for calcite at 293 K for all concentrations of sodium oleate studied indicate that the critical concentration of the agent for flotation of the mineral is above or very near to 1.4x 10 -5 M, which agrees with findings by Mishra (1982) and Pugh and Stenius (1985).
References Blazy, P., 1972. La Valorisation des Minerals. Presses Universitaires de France, Nancy, 470 pp. Blazy, P., Cases, J. and Houot, R., 1964. Recovery and selectivity in treatment of fluorite. In: VIIth Int. Miner. Process. Congr., New York, pp. 209-220.
52
F. Hernrinz BermLidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
American Cyanamid Company, 1989. Mining Chemicals Handbook. Mineral dressing notes No. 26-1. The Hibbert Group, Trenton, NJ, 112 pp. Dudenhov, S.L., Shubov, L.Y. and Glazunov, V., 1980. Fundamentos de la teor/a y la pr~ictica de empleo de reactivos de flotaci6n (translated by D. Oktilik). Mir, Moscow, 404 pp. Fuerstenau, D.W., Metzger, P.H. and Seele, G.D., 1957. How to use the modified Hallimond tube. Eng. Min. J., 158: 93-95. Glembotskii, V.A., Uvarov, V.S. and Solozhenkin, P.M., 1961. Some data on celestite flotation. Izvest. Akad. Nauk Tadzh. SSR, 1: 51-56. Hallimond, A.F., 1944. Laboratory apparatus for flotation tests. Min. Mag., 70: 87-90. Hanna, S. and Somasundaran, P., 1976. Flotation of salt-type minerals. In: M.C. Fuerstenau (Editor), Flotation: A.M. Gaudin Memorial Volume. AIME, New York, NY, Vol. 1, pp. 197-272. Hermiinz, F. and G6mez, M., 1986. Effect of particle size on flotation of fluorite. Afinidad, 405: 425-428. Hern~iinz, F. and Calero, M., 1991 a. Depressor effect of quebracho in celestite and calcite flotation in mechanical cell. Afinidad, 431: 35-38. Hern~iinz, F. and Calero, M., 1991b. Effect of Na2SiO3 in the celestite and calcite flotation in mechanical cell. Afinidad, 434: 259-262. Hern,Sinz, F. and Calero, M., 1993. Influence of quebracho and sodium silicate on flotation of celestite and calcite with sodium oleate. Int. J. Miner. Process., 37: 283-298. Hern~nz, F. and G~ilvez, A., 1989a. Celestite and calcite flotation with sodium oleate. Aflnidad, 421: 235-238. Hern~iinz, F. and G~ilvez, A., 1989b. Quebracho as depressant in the celestite and calcite flotation. Afinidad, 422: 355-358. Stubbings, R.L., 1972. In: R.E. Kirk and D.F. Othmer (Editors), Encyclopedia of Chemical Technology, Vol. 11. Interscience, New York, NY, pp. 578-599. Kulkarni, R.D. and Somasundaran, P., 1975. Kinects of oleate adsorption at the liquid/air interface and its role in hematite flotation. AIChE Syrup. Ser., 71: 124-133. Mishra, S.K., 1982. Electrokinetic properties and flotation behaviour of apatite and calcite in the presence of sodium oleate and sodium metasilicate. Int. J. Miner. Process., 9: 59-74. Pugh, R. and Stenius, P., 1985. Solution chemistry studies and flotation behaviour of apatite, calcite and fluorite minerals with sodium oleate collector. Int. J. Miner. Process., 15: 193-218. Roche, M., 1973. Th~se doctoral. Universit6 de Nancy, I, 116 pp. Taggart, F., 1966. Elementos de Preparaci6n de Minerales, 1st ed. Interciencia, Madrid, 648 pp. Taylor, H.F.W., 1967. La QuLrnica de los Cementos. Vol. 1, Eneiclopedia Quimica Industrial. Urmo, Bilbao, 860 PP. Vian, A., 1976. Curso de Introduccirn a la Qutmica Industrial. Alhambra, Madrid, 505 pp. Witt, J.C., 1950. Tecnologla de la Fabricaci6n de Cemento. Mar/n, Barcelona, 621 pp.
mlnsRm. PRO(ENNIU6 ELSEVIER
Int. J. Miner. Process. 46 (1996) 35-52
The influence of temperature during flotation of celestite and calcite with sodium oleate and quebracho F. Hernfiinz Bermddez de Castro, A. G~ilvez Borrego Departamento de lngenierfa Qufmica, Facultad de Ciencias Universidad de Granada, E-18701-Granada, Spain
Received 29 June 1994; accepted 20 June 1995
Abstract A study has been made on the influence of temperature during flotation of the celestite and calcite mineral species, using sodium oleate as the collector and quebracho as the depressant, for a particle size ranging between 80/100 A.S.T.M. mesh (177/149/xm). The experiments were conducted on pure minerals in a thermostatted Hallimond tube with working temperatures between 293 and 323 K. Results indicate that celestite can be depressed during flotation with sodium oleate due to the action of quebracho, although when the temperature in the bath is increased, the depressor action is slightly inhibited, thus increasing recovery of the mineral. The results for calcite show similar findings, although with a less pronounced depressor effect due to quebracho.
1. Introduction
Celeslite, SrSO4, belongs to the commonly denominated salt-type minerals, along with fluorite, barite, scheelite and so on, according to Hanna and Somasundaran (1976). The extractic n and concentration of celestite is of great interest in highly industrialised countries in view of the numerous applications of its derivatives, particularly in carbonate and nitrate forms. Market demands, however, require a celestite concentration of over 90%, by means of separation from other species. This separation can be achieved mainly by leaching, density ,difference or by flotation. This last technique offers the most promising future prospects, since the method is low in cost and easy to operate. Calcite, CaCO3, is also included in the group of salt-type minerals. Calcite is valuable in its own tight as a major raw material used by the cement and conglomerate industry (Witt, 1950; Taylor, 1967; Vian, 1976). However, when found in conjunction with strontium minerals, calcite is the least valuable component and must be separated from the ore. Moreover, calcite usually appears naturally in large deposits with a high degree of purity, 0301-7516/96/$15.00 © 1996Elsevier ScienceB.V. All rights reserved SSDI0301-7516(95)00059-3
36
F. Hernrinz Berm~idez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
thus rendei'ing concentration techniques unnecessary to achieve the mineral to date. It is therefore essential to understand how this mineral responds to techniques which aim to concentrate other species, currently considered as more valuable. It has been proven that an increase in the flotation bath temperature usually enhances the operation of mineral concentration by flotation, (Blazy et al., 1964; Taggart, 1966; Roche, 1973) and (Kulkarni and Somasundaran, 1975). However, for economic reasons, mineral concentration operations are carried out at the mining site using water at ambient temperature. The price of the concentrate on the market, however, may justify the rise in production costs by using higher temperatures. Minerals such as fluorite are usually floated at temperatures even higher than 313 K (Roche, 1973; American Cyanamid Co., 1989). Taking into account the high price of celestite on the international market, it would seem more than logical that the influence of temperature during flotation recovery should be fully examined, though initially on a laboratory scale. Since flotation is based on the capturing of mineral species by means of organic collector agents, the phenomenon must be modulated to achieve selective flotation (Blazy, 1972). In some cases, then, certain agents are used either to allow the collector to adhere on a surface on which it could not normally do so (activators) or to inhibit such fixation (depressants). Within the group of organic depressant agents, quebracho is the most frequently used to avoid flotation of ore, mainly calcareous ore, which is found together with certain other minerals, due to the low selectivity of commonly-used collectors in the separation of the valuable fraction. However, the risk of the depressant agents acting on the mineral to be recovered, especially above certain concentrations of the agent (Hern;iinz and G~ilvez, 1989a, b; Hern~iinz and Calero, 1991a, b), must be taken into account. Quebracho is a vegetable tannin from the wood of the tree of the same name. The most highly appreciated variety of quebracho comes from the Quebrachia lorentzii species, known as coloured quebracho which contains 20-30% extractable tannins. Although the composition may vary, the most representative example (Stubbings, 1972) is given in the following diagram: Quebrachia
I
V CELLULOSE 36.78~
I
TOTAL SOLZDS 28.63~
I
•
AQUEOUS EXTRACT 27.2 IZ
I
f
SOLUBLE SOLZDS 23.77Z
1orentzli
I
I
• RESZNS I . 12~
I
TANNZNS 20.65Z
!
• NON-CELLULOSE 34.89Z
I
OTHER 7.98~
Sodium oleate-celestite and sodium oleate-calcite systems, modulated by quebracho as the depressant at room temperature, have been widely studied. It has been found that quebracho is a strong and unselective depressant for both minerals when a fatty acid is used as the collector. Until now, however, no studies have been undertaken to see how temperature influences these systems. As the temperature variable is of major importance in a mineral such as celestite, it would therefore seem extremely useful to determine if new methods for the separation of celestite and calcite are possible.
F. Herntinz Berm~dezde Castro, A. GdlvezBorrego/Int. J. Miner. Process. 46 (1996) 35-52
37
2. Experimental 2.1. Mineral species
Celestite, SrSO4, and calcite, CaCO3,from two different mines were used for this research study. The celestite was taken from the Cerro de Montevives mine, located in Las Gabias, 12 kilometres southwest of the city of Granada. The mineral was selected, fragmented and selected again by hand to collect only the purest samples, thus guaranteeing a concentration of 97%, as shown by acid leach analysis. The calcite was taken from a deposit near Torredonjimeno (province of Jatn), with a concentration in CaCO3 over 99.6%. Once the minerals had been selected and broken up, they were then ground to the appropriate size using a CULATTI, triple floating hammer micromill. The ground mineral was classified according to size using a high-vibration MECHANICAL-SCIENTIFIC machine with fine A.S.T.M. sieves and sieve base, thus selecting only A.S.T.M. 80/100 mesh size, equivalent to 177/149/xm. 2.2. Flotation agents
The chemical products used in this study are described below. Collector Agent, sodium oleate, supplied by Seelze-Hannover, with a 93% spectrophotometrically determined purity. The solutions were dissolved in distilled water. The solute was then weighed on a SARTORIUS 2442 precision balance, and the desired solution obtained by successive dilutions as the agent concentrations used were very small. In all cases, the solutions were prepared shortly before the experiments were carried out to avoid possible alterations in the collector agent ow,~r time, which could alter its properties. 2.3. Modifying Agents
The modifying agents used were as follows: quebracho, vegetable tannin supplied by the Orgiva (Granada) mineral panning station, Merck sodium hydroxide and Probus hydrochloric acid. These last two were used as pH modifying agents in a 4 N concentration to achieve desired pH easily, and pH measurements were performed with a CRISON 2001 pH-mete:r. 2.4. Experimental methods and conditions, apparatus and calculations
For this research, surface tension measurements were performed using plate method, since no hydrostatic correction is required as in the ring method. Measurements of surface tension were performed with a KRUSS K10 digital tensiometer, with an accuracy of + 0.1 m N / m and a platinum-plate measuring 20 × l0 X 0.1 ram. The solution whose surface tension is to be measured is placed in the duly thermostated flask at 1abe essay temperature, using a thermostat which allows consistent temperature regulation ± 0.1°C. Eleven determinations of surface tension were carded out for each case, the average being taken from the last ten.
38
F. Hern6inz Bermtidez de Castro, A. Gcilvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
L
I
"1
.°
| I
I
Fig. 1. Schematic diagram of experimental setup. 1. Compressor, 2. Regulation valve, 3. Water manometer diaphragm, 4. Thermometer, 5. Thermostat, 6. Magnetic stirrer, 7. Hallimond tube, 7a. Porous plate, 7b. Magnetic stirring bar, 7c. Collector and 7d. Liquid level.
The Hallimond tube was as d as the flotation apparatus, Fig. 1, as conceived originally by Hallimond (1944), modified by Fuerstenau et al. (1957) and again modified by the Flotation Group of the Chemical Engineering Department to acheive a new thermostatted design, enabling studies at different temperatures. The solid-solution suspension was placed in the thermostatted Hallimond tube (7) with a capacity of nearly 400 cm 3, and then subjected to an air current from a compressor ( 1 ). The flow was adjusted by a regulation valve (2) and measured by a water manometer diaphragm (3). Once the air bubbles had been formed and the solid particles dispersed by a magnetic stirrer (6), the floated mineral was collected on the collector (7c). After prior conditioning in a furnace at the appropriate assay temperature (293, 303, 313 and 323 K), 2 g of mineral, either celestite or calcite of A.S.T.M. mesh size 80/100 (177/149/xm) were placed in the Hallimond tube. Then a solution of the agents to be used was added, at the appropriate concentration, i.e. for sodium oleate ( 1.4 × 10 -6, 4.5 × 10 -6, 7.3 X l0 -6 and 1.4 X 10 -5 M) and for quebracho (0.0012, 0.012, 0.12 and 1.2 g / L ) . The pH of these solutions had previously been adjusted with HCI or NaOH at the working temperature. This was then shaken magnetically for three minutes (conditioning time) to ensure adherence to the collector and/or depressant on the solid particle surface. Then the air flow was regulated and the solution placed in the porous plate on the bottom of the tube. The air flow used was reduced to the limit of 8 L / h so as to avoid particles being carded away as far as possible. The particle adhering to the fine gas bubbles rose to the surface where the bubbles burst and were collected in the collecting tube. In all cases, flotation time was equal to conditioning time, i.e. three minutes. The recovery percentage for celestite and calcite is obtained by the difference in weight as both minerals are considered to be pure, although celestite may contain approximately 2% of calcareous impurities. It was decided not to eliminate the presence of carbonate by acid leaching to avoid any possible alteration in the natural surface of the solid, although the results may be affected by a slight degree of error, permissible in assays of this kind. 3. Results and discussion
Tables 1 and 2 show the recovery percentages for celestite and calcite, respectively, under the experimental conditions described above. It may be seen that for the lowest concentra-
F. Herntiinz Bermddez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
39
Table 1 Recovery p,ercentages for celestite [Oleate], M
T, K
Recovery, % pH=6
pH=7
pH=8
pH=9
pH=10
pH=ll
pH=12
1.4 X 10 -6
293 303 313 323
0.89 1.52 1.61 5.90
1.10 1.09 0.98 6.47
0.84 0.85 1.18 3.33
0.84 1.04 0.98 3.29
0.69 0.94 0.91 2.35
0.46 0.62 0.58 2.06
0.24 0.68 0.70 3.57
4.5 × 10 -6
293 303 313 323
16.91 19.85 25.60 30.14
13.35 19.75 29.55 27.45
15.23 18.14 28.00 30.05
11.89 16.62 25.83 24.60
12.27 23.39 29.93 27.96
11.69 17.52 21.67 23.40
13.31 16.52 20.53 21.85
7.3 X 10 - 6
293 303 313 323
15.92 31.66 75.88 95.14
16.78 65.48 92.18 93.93
44.80 93.04 93.36 95.79
28.24 91.76 96.05 95.96
39.23 86.92 93.37 93.04
35.36 78.45 91.21 92.10
30.38 74.44 77.24 90.80
1.4 X 10 -5
293 303 313 323
56.70 70.72 83.35 89.12
91.02 93.49 96.28 98.08
93.10 93.61 97.59 97.23
93.07 96.30 96.87 97.18
78.68 93.46 96.69 96.49
75.49 92.94 94.80 93.39
74.42 84.21 86.73 94.21
Table 2 Recovery l;~rcentages for calcite [Oleate], M
T, K
Recovery, % pH=6
pH=7
pH=8
pH=9
pH=10
pH=ll
pH=12
1.4x 10 -6
293 303 313 323
0.58 2.32 2.00 2.70
0.75 1.10 1.86 2.66
0.25 0.66 1.29 1.51
0.56 0.85 1.53 2.49
0.97 1.25 1.86 2.84
0.91 0.96 1.51 2.75
1.31 0.94 1.35 2.27
4.5 × 10 -6
293 303 313 323
1.27 1.35 2.31 3.02
1.11 1.30 2.57 3.94
0.59 0.82 1.95 2.98
1.11 1.20 2.27 2.57
0.81 1.23 2.10 2.80
0.87 1.62 2.50 4.18
0.85 1.77 3.14 3.27
7.3 × 10 -6
293 303 313 323
1.62 1.35 4.29 8.40
1.19 1.20 3.52 7.78
1.29 1.35 3.55 4.33
1.21 1.43 3.38 3.09
1.00 2.55 3.02 2.89
1.19 2.75 2.84 7.32
!.96 3.71 5.73 6.44
1.4 x 10 -5
293 303 313 323
5.65 98.96 96.65 99.80
6.29 60.83 89.37 97.83
8.08 41.27 97.45 98.98
4.51 23.94 84.04 97.60
4.62 11.14 81.25 96.04
4.78 26.83 85.65 94.05
4.86 90.53 97.85 95.76
40
F. Herntiinz Bermtidez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
tions of sodium oleate used, 1.4 × 10- 6 M, sodium oleate does not float celestite and calcite as proven by the recovery percentages below 10% in all cases, and by the fact that pH variation and temperature modification cause no effect. When the collector agent concentration is increased to 4.5 X 10-6 M, however, the effect of temperature in the bath becomes apparent, considerably improving celestite flttation as temperature rises and in some cases recovery percentages are doubled on raising temperature from 293 to 323 K, although overall percentages are very low. The effect of temperature becomes very clear, however, when the concentration of sodium oleate is 7.3 × 10 - 6 M. At this concentration, the recovery percentages of the mineral rise considerably as the temperature in the bath rises, with the most pronounced and gradual effect occurring at pH 6 and pH 12 with recovery rising from 20% to over 90% at temperatures of 293 to 323 K. However, at the highest sodium oleate concentration tested, 1.4 X 10 -5 M, high recovery percentages are achieved very rapidly, whereas the remaining variables exert less effect than at the preceding concentration. Calcite is not recovered by flotation either by altering pH in the bath nor increasing temperature for the first three concentrations of sodium oleate and recovery rates never exceed 10% recovery in any case. When sodium oleate is used at a concentration of 1.4 × 10 -5 M, the results obtained show that less than a 10% recovery is achieved at 293 K while this rises to over 95% recovery when the temperature is raised to 323 K. On comparing the results obtained for the two mineral species using sodium oleate as the collector and in the absence of a depressant, it may be seen that separation of the two minerals can be achieved in a single flotation operation at 293 K, 1.4 X 10 -5 M and pH between 8 and 10. Experiments performed by Hem~iinz and Calero (1993), however, show that there is no difference in response of celestite and calcite in joint flotation over a wide range of sodium oleate concentrations, including those used in this study. It may be con100 "70 80 iO
v lu
~, u
3
60. ,0 20"
[0 t E AT E] : 1.4x10-5 Id T=293 K "0" CELESTITE "Q'CALCITE 30
0
i 6
i 8
i I11
i 1~'
pH F i g . 2. C o m p a r i s o n o f r e c o v e r y p e r c e n t a g e s o f celestite a n d calcite w i t h a s u r f a c e t e n s i o n o f 1.4 × 1 0 - 5 M s o d i u m oleate s o l u t i o n at 2 9 3 K.
F. Hern6inz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
41
cluded then that there is an interaction between the minerals and sodium oleate, which radically alters the results obtained by flotation of these two minerals separately. The maximum recovery rate achieved for celestite at the pH 8-9 interval, coincides exactly with the minimum values obtained for surface tension in the flotation bath with sodium deate, Fig. 2. This points to a clear dependence in the sodium oleate-celestite system between the minimum surface tension and the maximum flotation of the mineral. This fact has already been pointed out by Pugh and Stenius (1985), although these authors indicate that a decrease in surface tension, may, in certain cases, not be the major efficiency factor in separation by flotation. It does, however, indicate the presence of surfactant species which enhance the hydrophobic quality of the minerals. During their research into fluorite flotation ,with oleic acid and sodium lauryl sulphate, Hern~iinz and G6mez (1986) corroborated that the mineral responds to the technique better at pH values causing a minimum surface tension in the bath. Kulkami and Somasundaran (1975), when using potassium oleate for the flotation of hematite, found a clear dependence between the values for mineral recovery rates and surface pressure and determined that the maximum recovery rate is found at minimam values for surface tension in the bath, in this case at around pH = 8. It is also of outstanding interest that an increase in the temperature in the bath brings about a slight decrease in surface tension in the bath in all cases, and moreover this increase causes a considerable rise in the recovery of celestite by flotation. This has a bearing on the previous comments and fully confirms that a decrease in surface tension raises the recovery percentage for celestite, in some cases quite considerably. The results for calcite, however, contrary to those for celestite, show a low or nil ratio between the minimum surface tension in the bath and the maximum recovery of the mineral, although it is clear that when surface tension is decreased by an increase in temperature, 100
~
'70
80 ~0
6o 3
w U
50 z
3
40'
20' [OL E AT El = l.t*xlO-5Id T=323 K "0" CELESTITE "~CA LCITE 0
! 6
$
i 10
30 i 12
pH
Fig. 3. Comparison o f recovery percentages o f celestit¢ and calcite w i t h a surface tension o f 1.4 × ] 0 - 5 M sodium oleat¢ solution at 323 K .
42
F. Hern6inz Bermtidez de Castro, A. G61vez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
there is an improved recovery rate, especially at 1.4 X 10 -5 M of sodium oleate, Fig. 3. The modification of the pH in almost all cases varies calcite concentration quite noticeably.
3.1. Depressor effect of quebracho The recovery rates of celestite according to pH in the bath are shown in Figs. 4-7 for 293, 303,313 and 323 K respectively, with a concentration of sodium oleate of 7.3 X 1 0 - 6 M and varying concentrations of quebracho. It may be seen that celestite is strongly depressed under such conditions and at 293 K, even at low concentrations of the depressant agent, with a negligeable recovery of celestite in most of the experiments performed. The depressor action of quebracho can clearly be seen when these results are compared with those obtained in the absence of the agent. The depressor effect becomes clearer as temperature rises, since this variable enhances the flotation of celestite. In the absence of quebracho and at 303, 313 and 323 K, this mineral floats well, especially at the pH range between 8 and 10. When quebracho is added, however, its becomes totally depressed for concentrations 0.012 and 0.12 g/L, and quite intensely depressed at 0.0012 g/L. Glembotskii et al. ( 1961 ), when using a temperature 293 K, with oleic acid as the collector, alkaline mediums and a 7 5 c m 3 flotation microcell, found that tannins depress celestite completely at concentrations of 150 g/Tm, and are more efficient as depressant agents than glucose, peptone, gelatine and dextrine. The celestite recovery rates under similar operational conditions to those described, with an increased concentration of sodium oleate of 1.4 X 10 -5 M are shown in Figs. 8-11. Although qualitatively speaking the results obtained are similar to the above, they do reveal that the increase in the sodium oleate concentration considerably decreases the depressor I00'
CELESTITE . [0 L E AT E'] :?.3xI0-~ M
T= 293 K 80 ¸
QUEBRACHO lO glL 0 0,0012 '" O 0.012 " /'. 0.12
>.
o w 4,
8
IO
12
pH
Fig. 4. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 293 K.
F. Hern6inz Bermtidez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
43
100
80
T : 303 K ~60
QUEBRACHO • 0 glL
0
4o
o
o.oo12
-
[] 0.012
20
0 6
8
10
pH
Fig. 5. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 303 K.
effect of quebracho, most markedly at low depressant concentrations. The increase in temperat~Lre also decreases the depressor effect, especially in neutral or mildly alkaline circuits. 100'
CELESTITE _ "~ L EATE] =7,3XI0"GM T=313K
QUEBRACHO e0 glL O0.0012 " O0,012 A 0J2
~> o u w 4C cc
0 8
10
12
pH
Fig. 6. Celestite flotation vs. pH, with 7.3 × 10 - 6 M sodium oleate, at various concentrations of quebracho and 313 K.
44
F. Herntiinz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52 100
1 CELESTITE [0 LEATF.,] :7.3x10-6M T=323 K
80
6¢
QUEBRACHO • 0 glL o.o012 " 0 0,012 "
o
o ou la 4~ a:
20 --(3..
8
I0
pH
Fig. 7. Celestite flotation vs. pH, with 7.3 × l 0 -6 M sodium oleate, at various concentrations of quebracho and 323 K.
Although the depressor action mechanism has not been fully determined (Dudenhov et al., 1980), it is clear that the depressant inhibits the adsorption of the collector on the surface of the solid. Therefore, it may be deduced from the results obtained that there is the surfactant and the depressant compete on the mineral covering, or that quebracho somehow blocks I00"
[o LE ATE] :1.4xt05~ \
80
~60
T=293 K
Q
U
-
EBRX:.O • 0
g/L
i!
O U u 40
20
8
pH
10
Fig. 8. Celestite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 293 K.
F. tterntiinz Bermtidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
45
100" CEUESTITE
80
--
~ 6o
0
A
v
/
\
/
QU E B R ~ H 0
\
\
°
\ \
"°
,,L
o o.oo12 " \
a o.o12
-
o ~c
4c
|
8
10
12
pH
Fig. 9. Cele:~tite flotation vs. pH, with 1.4 × 10 - s M sodium oleate, at various concentrations of quebracho and 303 K.
100'
8C
v
60
o
2¢
8
10
12
pH
Fig. 10. Celestite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 313 K.
46
F. Hern6inz Berm~dez de Castro, A. Gdlvez Borrego lint. J. Miner. Process. 46 (1996) 35-52 100"
QUEBRACHO •
O
o
o.oo12
n
o.o12
g/L " "
" "
• A 0.12
O 1.2 6C
w
g u w 40
20
CELESTITE [OLEATE] :1.4x1(~$M T= 323 K
\ n~
i 8
10
12
pH
Fig. 11. Celestite flotation vs. pH, with 1.4 × 10- s M sodium oleate, at various concentrations of quebracho and 323 K.
the collector agent's action. This action basically depends on the concentration of both agents. Figs. 12-15 show the recovery rates for celestite versus pH for a three-fold sodium oleate concentration, 4.5 × 10 -5 M, and it may be seen how the depressor action of quebracho indeed decreases even farther at the same concentrations. Temperature also attenuates the depressor effect. 10o 0 ,//~"~
w
CELESTITE 5 [OLEATE] =4.5xl6 M
ouEs~~R, o;0,2 c.o
\
Io .
u m!l
\
~,
8
O 0.0012 91L
\
n
10
"
12
pH
Fig. 12. Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 293 K.
F. Herndinz Bermt~dez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
47
I00"
80
6O M
w ~J ~j 40 a:
20
O u 0 6
10
B
pH
Fig. 13. Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 303 K.
In orde,r to check quebracho's depressor effect on calcite, two concentrations of sodium oleate we,re selected, namely 1.4× 10 -5 and 4.5 × 10 -5 M respectively, and the lower concentration, 7.3 × 10 - 6 M was disregarded as the recovery rates for calcite in the absence of this depressant agent were negligeable (see Table 2). The results obtained are shown in 100
O / , ~
//
o
C ELESTITE 5 [OL EAT E] =z~Sxl() M
~
>~ o u wz.,O
Z0
OUEBRACHO A ~ . ~ 0 0,0012g/L D 0.012 "" A 0.12 0 1.2 O O
8
pH
10
12
Fig. 14. Celestite flotation vs. pH, with 4.5 × 10-5 M sodium oleate, at various concentrations of quebracho and 313K.
48
F. Herntiinz Berm~dez de Castro, A. Gdlvez Borrego / int. J. Miner. Process. 46 (1996) 35-52 1oo
00
tel
~o
QUEBRACH9 0 0.0012 g/L n 0,012 " ~.0.12 O 1.2
20 CELESTITE § [ O L E A T E ] :4.5x1() M T = 323 K
0 6
10
8
12
pH
Fig. 15, Celestite flotation vs. pH, with 4.5 × 10 -5 M sodium oleate, at various concentrations of quebracho and 323 K.
Figs. 16-21. It may be seen that flotation of calcite is negligeable at 293 K for an oleate concentration of 1.4 × 1 0 - 5 M, as was to be expected, both in the absence of the depressant and at any of the concentrations applied. When the temperature is increased, the effectiveness 100" CALCITE [0 LEAT E] : 1.4x10-5M T=293 K $0
QUEBRA~:HQ elL O 0.00tZ " rl 0.012 " A 0.12
• 0
>o
,.o
20
8
p*t
10
12
Fig. 16. Calcite flotation vs. pH, with 1.4 × 10 - s M sodium oleate, at various concentrations of quebracho and 293 K.
F. Herndinz Bermadez de Castro, A. Gdlvez Borrego /Int. J. Miner. Process. 46 (1996) 35-52
49
I00" CALCITE [O LEAT E] ~|.4xIO$ M
T=303 K 80 QUEBRACHO 0 glL o 0.oolz o o.0tl
o
2O
0 "'
i
6
8
pH
r
!
10
Fig. 17. C a l c i t e flotation vs. pH, with 1.4 × 10 - 5 M sodium oleate, at various c o n c e n t r a t i o n s o f q u e b r a c h o and 303 K.
of the agent's depressor action is revealed, since at both 303 and at 313 and 323 K, the mineral is completely depressed for all three concentrations of quebracho used, with the most significant effect arising at 323 K since, in the absence of quebracho, recovery rates are over 95% in all cases. The pH effect is of relatively little importance in the depressor IO0-
J
SO
CALCITE $ [ 0 L EAT E'] :l.6x10- M T=313 K
~60
QUEBRACHO e0 91L O 0.0012 " n 0.012 " ,~ 0.12
O
~4o
2O
i
6
8
pH
10
12
Fig. 18. Calcite flotation vs. p H , w i t h 1.4 X 10 - s M s o d i u m olcate, at various concentrations of quebracho and
313K.
50
F. Hern6inz Berm~idez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52 I00
--r-------9~a
~
e-
80 CALCITE -5 tO L E A T E ] =l.4xf0 M T:323 K
6O
v LU
Q~JEBRACHO
• 0
~c
9IL
O 0.0012 " O 0,012 ' Z~ 0.12
z0
0
=
6
i
8
i
i
10
T2
pH
Fig. 19. Calcite flotation vs. pH, with 1.4 × 10 -5 M sodium oleate, at various concentrations of quebracho and 323 K.
action of quebracho for low collector concentrations, although at 4.5 × 10 -5 M sodium oleate, depression is more effective in clearly alkaline mediums, especially at a quebracho concentration of 1.22 g/L, Figs. 20 and 21. I00
O
O
aO
CALCITE -5 [O L E A T E]=&.5xl0 M T=313 K
60 uJ
o0..o=,,;L
QU EBRACHO
~ o oc
20
0
i
6
i
S
i
pH
i
10
!
t2
Fig. 20. Calcite flotation vs. pH, with 4.5 × 10 -~ M sodium oleate, at various concentrations of quebracho and 313K.
F. lterndinz Bermddez de Castro, A. Gdlvez Borrego ~Int. J. Miner. Process. 46 (1996) 35-52
51
10G O--
CALCITE 8C
o
t EA rE] =4.~=1o"5 M T=223 K
,QUEBRACHO
o ,o:o;,
lu
=~,,¢
!
6
i
i
8
i
10
i
12
OH
Fig. 21. Ca],cite flotation vs. pH, with 4.5 × 10 - s M sodium oleate, at various concentrations of quebracho and 323 K.
4. C o n c l u s i o n s
When sodium oleate is used as the collector, pH in the medium clearly conditions celestite flotation, with maximum mineral recovery percentages arising at pH between 8 and 9. An increase in temperature considerably improves celestite recovery. For very high sodium oleate concentrations, however, the effect brought about by variations in pH and temperature barely alters recovery of the mineral by flotation. A clear dependence between maximum mineral recovery and minimum surface tension in the bath has been proven for the sodium oleate--celestite system. For most concentrations of sodium oleate used in this research study, calcite was not recovered by flotation, even by modifying pH or by increasing temperature in the bath. At an oleate concentration of 1.4 × 10 -5 M, however, the recovery percentage rises from under 10% to over 95% when temperature is increased from 293 to 323 K. The low recovery rates for calcite at 293 K for all concentrations of sodium oleate studied indicate that the critical concentration of the agent for flotation of the mineral is above or very near to 1.4x 10 -5 M, which agrees with findings by Mishra (1982) and Pugh and Stenius (1985).
References Blazy, P., 1972. La Valorisation des Minerals. Presses Universitaires de France, Nancy, 470 pp. Blazy, P., Cases, J. and Houot, R., 1964. Recovery and selectivity in treatment of fluorite. In: VIIth Int. Miner. Process. Congr., New York, pp. 209-220.
52
F. Hernrinz BermLidez de Castro, A. Gdlvez Borrego / Int. J. Miner. Process. 46 (1996) 35-52
American Cyanamid Company, 1989. Mining Chemicals Handbook. Mineral dressing notes No. 26-1. The Hibbert Group, Trenton, NJ, 112 pp. Dudenhov, S.L., Shubov, L.Y. and Glazunov, V., 1980. Fundamentos de la teor/a y la pr~ictica de empleo de reactivos de flotaci6n (translated by D. Oktilik). Mir, Moscow, 404 pp. Fuerstenau, D.W., Metzger, P.H. and Seele, G.D., 1957. How to use the modified Hallimond tube. Eng. Min. J., 158: 93-95. Glembotskii, V.A., Uvarov, V.S. and Solozhenkin, P.M., 1961. Some data on celestite flotation. Izvest. Akad. Nauk Tadzh. SSR, 1: 51-56. Hallimond, A.F., 1944. Laboratory apparatus for flotation tests. Min. Mag., 70: 87-90. Hanna, S. and Somasundaran, P., 1976. Flotation of salt-type minerals. In: M.C. Fuerstenau (Editor), Flotation: A.M. Gaudin Memorial Volume. AIME, New York, NY, Vol. 1, pp. 197-272. Hermiinz, F. and G6mez, M., 1986. Effect of particle size on flotation of fluorite. Afinidad, 405: 425-428. Hern~iinz, F. and Calero, M., 1991 a. Depressor effect of quebracho in celestite and calcite flotation in mechanical cell. Afinidad, 431: 35-38. Hern~iinz, F. and Calero, M., 1991b. Effect of Na2SiO3 in the celestite and calcite flotation in mechanical cell. Afinidad, 434: 259-262. Hern,Sinz, F. and Calero, M., 1993. Influence of quebracho and sodium silicate on flotation of celestite and calcite with sodium oleate. Int. J. Miner. Process., 37: 283-298. Hern~nz, F. and G~ilvez, A., 1989a. Celestite and calcite flotation with sodium oleate. Aflnidad, 421: 235-238. Hern~iinz, F. and G~ilvez, A., 1989b. Quebracho as depressant in the celestite and calcite flotation. Afinidad, 422: 355-358. Stubbings, R.L., 1972. In: R.E. Kirk and D.F. Othmer (Editors), Encyclopedia of Chemical Technology, Vol. 11. Interscience, New York, NY, pp. 578-599. Kulkarni, R.D. and Somasundaran, P., 1975. Kinects of oleate adsorption at the liquid/air interface and its role in hematite flotation. AIChE Syrup. Ser., 71: 124-133. Mishra, S.K., 1982. Electrokinetic properties and flotation behaviour of apatite and calcite in the presence of sodium oleate and sodium metasilicate. Int. J. Miner. Process., 9: 59-74. Pugh, R. and Stenius, P., 1985. Solution chemistry studies and flotation behaviour of apatite, calcite and fluorite minerals with sodium oleate collector. Int. J. Miner. Process., 15: 193-218. Roche, M., 1973. Th~se doctoral. Universit6 de Nancy, I, 116 pp. Taggart, F., 1966. Elementos de Preparaci6n de Minerales, 1st ed. Interciencia, Madrid, 648 pp. Taylor, H.F.W., 1967. La QuLrnica de los Cementos. Vol. 1, Eneiclopedia Quimica Industrial. Urmo, Bilbao, 860 PP. Vian, A., 1976. Curso de Introduccirn a la Qutmica Industrial. Alhambra, Madrid, 505 pp. Witt, J.C., 1950. Tecnologla de la Fabricaci6n de Cemento. Mar/n, Barcelona, 621 pp.