- Email: [email protected]
New reagents in sulphide mineral flotation
International Journal o f Mineral Processing, 33 ( 1991 ) 291-306 Elsevier Science Publishers B.V., Amsterdam
291
New reagents in sulphide mineral flotation A.M. Marabini, M. Barbaro and V. Alesse Istituto per il Trattamento dei Minerali, C.N.R., Via Bolognola 7, 00138 Rome, Italy (Received April 25, 1990; accepted after revision May 3, 1991 )
ABSTRACT Marabini A.M., Barbaro, M. and Alesse, V., 1991. New reagents in sulphide mineral flotation. In: K.S.E. Forssberg (Editor), Flotation of Sulphide Minerals 1990. Int. J. Miner. Process., 33: 291306. A review is presented of new reagents for sulphide flotation. These reagents are essentially of the chelating type. Compared with conventional reagents they have a marked selectivity for individual sulphide minerals. The review hinges around: collecting power towards various sulphides and comparison with conventional reagents; influence of molecular structure on collecting power and action mechanism; and criteria for designing and synthesizing chelate-type collectors with optimal structure for a given metallic mineral.
INTRODUCTION
The search for new reagents in sulphide mineral flotation is particularly important for ores containing several commercially useful mineral components finely intergrown with the gangue and with one another, or for ores characterized by a very fine screen analysis. This is the case of the so called complex sulphide ores which have been defined as those ores for which it is difficult to recover one or more selective products of acceptable quality and economic value with minimal losses and at reasonable costs. Complex sulphide ores are fine-grained, intimate associations of chalcopyrite (CuFeS2), sphalerite (ZnS) and galena (PbS), disseminated in dominant pyrite, and which contains valuable amount of silver and, in some cases, gold. Generally, collectors employed for sulphide recovery are of the thiol type, the most commonly used being xanthates. Their mechanism of action has not been completely clarified. (Little et al., 1961; Mielczarski et al., 1981; Giesekke, 1983; Marabini et al., 1983; Kongolo et al., 1984; Mielczarski et al., 1987; Partyka et al., 1987; Laajalehto et at., 1988; Page et al., 1989; Arnaud et al., 1989). Xanthates are active towards the whole class of sulphide minerals, rather than towards one individual mineral. Thus, in order to float a given mineral 0301-7516/91/$03.50 © 1991 Elsevier Science Publishers B.V. All fights reserved.
2tJ2
', M, MARABINI ~ [ . \ [
from a mixture of minerals belonging to the same sulphide class, modifiers always have to be used in order to render the action of the collector more specific, and to improve separation efficiency (Finkelstein et al., 197~ t. However, there are many problems in this procedure and the desired results are not always obtained, especially in the case of minerals of complex composition. Hence the importance of seeking out collectors capable of linking selectively with a given mineral. Selective linkage is possible if the collector structure incorporates active groups having specific affinity for certain cations characteristic of the minera[ surface. Thus, the search for new, more selective reagents for sulphide mineral flotation is mainly concerned with chelate-forming reagents. These reagents are organic compounds endowed with selective action towards certain metallic ions, with which they are capable of linking via two or more functional groups, thus forming one or more rings which render the resulting chelate extremely stable. Different type of chelating reagents have been used for sulphide ore flotation such as binary systems of commercially available chelating reagents plus fuel-oil or conventional collectors and long chain aliphatic and aliphatic aromatic collectors. PRELYMINARY STUDIES: BINARY SYSTEMS
Commercially available chelating reagents are aromatic molecules without a long hydrocarbon chain; thus, altough the chelated mineral particle is fairly hydrophobic, it is not sufficiently aerophilic to ensure flotation. Studies on oxidized minerals (Usoni et al., 1971; Marabini, 1975; Rinelli et al., 1976) were performed by rendering particles hydrophobic by making available longchain organic groups ( such as fuel-oil or oily frother) together with chelating agents commonly used in analytical chemistry. The first application of this conception on sulphide minerals dates back to 1973. A chelating reagent, namely 8-hydroxyquinoline with fuel oil was used to float mixed oxide-sulphide minerals of Zn and Pb (Rinelli and Marabini, 1973). Another example of chelating reagent in sulphide treatment is the flotation of cobaltite with nitroso/~-naphto (N N) (Marabini and Rinelli, 1982 ), which is known to be a reagent for cobalt. Flotation tests on cobaltite-hematite and cobaltite-niccolite indicated good selectivity for cobaltite. Rinelli and Marabini interpreted these results on the basis of greater affinity of Nfl N for cobalt than nickel and copper. The synergistic effect of a chelating reagent and a classical collector has also been investigated. The synergistic effect that glycine and xanthate have on the selective flotation of sulphide minerals was studied first by Wakamatsu et al. (1979) and then by Hanson et al. ( 1988 ). Glycine is a very well known chelating agent for copper minerals. These researchers found that the addition of glycine increases adsorption of ethylxan-
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
293
thate on chalcocite, galena and pyrite minerals, producing an activating effect on flotation. The improved flotation response of chalcocite and partially of galena and pyrite using xanthate collector was explained as follows: ( 1 ) Glycine increases metal cations concentration by the formation of soluble metal-glycinate complexes. (2) It follows that more metal cations are present in solution for xanthate to react and ultimately adsorb onto the mineral surface. ALIPHATIC CHELATE TYPE COLLECTORS
Many researchers have studied the use of chelating agents in metallic mineral flotation. Recently, a review of these studies has been published by Pradip ( 1988 ). However most of the studies concern oxidized minerals, and there are few applications to sulphide. Harris et al. (1988) have patented thiodicarbonates or dithiocarbonates as collectors for non-ferrous metal sulphides. Chalcopyrite was floated at pH 5.0 with excellent recovery and selectivity at this acid pH. The other important studies concern thionocarbamates, thiourea derivatives, phosphinate and phosphate derivatives, glioxalidine, etc. Thionocarbamates were discovered by Harris and Fischback (1954 ). In spite of the considerable industrial acceptance of this class of reagents, surprisingly few fundamental studies on their use have been made. Notable exceptions are the work done by Ryabol et al. ( 1973 ), Bogdanov et al. ( 1976 ), Glembotskii (1978), Bogdanov et al. (1982), and Ackerman et al. (1984). It is known that these reagents form a chelating bond with metals through coordination of sulphur and nitrogen, as shown below: lq'-- O--C
H
Sx
N--R' \
\
/
i
~//,~ MINERAL ~/~/~,
In particular Ackerman et al. ( 1984, 1987a,b,c) studied the collecting power on copper sulphides and pyrite of N-ethyl-O-isopropyl-thionocarbamates (Fig. 1 ) and found that it is comparable to that of xanthate (Fig. 2 ): Ackerman et al. (1987a,b,c) also showed that the flotation of copper sulphides and pyrite is influenced by both the N- and O-alkyl substituents which control hydrophobicity and steric accessibility of the NCS grouping. Ackerman et al. (1987a,b,c) found that for a given number of carbon atoms linked to the nitrogen, an increase in the chain lenght linked to the oxygen increases the collecting power (Fig. 3 ). This is due to the greater hydrophobicity of the surface coating as a result of the greater insolubility of the reagent. This effect is also observed in branched chains.
294
\M.
I
100
T. . . . . . . . . . . . . . .
r
MARABINI
ET,,M
r'--- 7
4
80
60
>or uJ
w ~:
v O A n •
40
20
pyrite chalcocite covellite chalcopyrite bornite
~7--" ". . . . . . . .
XT----
, ~
I
I
I
5
7
9
11
PH
Fig. 1. Flotation recovery of copper sulphides and pyrite using Z-200 (commercial form of Nethyl-O-isopropyl thionocarbamate) (Ackermann et al., 1987)
On the other hand, for the same number of carbon atoms linked to the oxygen, the collecting power increases with an increase in the number of carbon atoms on nitrogen in the case of straight chains, while negative effects occur in the case of branched chains and unsaturated chains (Fig. 4). The increase in collecting power with straight chain length is explained by the lower solubility and hydrophobicity of the surface coating. The effect of the branching and the unsaturation is due respectively to a steric impediment in the reaction of the nitrogen with the metal and to an increase in the hydrophilicity of the molecule containing unsatured bonds. Recently new classes of collectors with chelating properties for copper sulphide minerals have been presented by Nagaraj et al. ( 1989 ). They are alcoxycarbonyl alkyl thionocarbamates and thioureas, dialkyl (or diaryl) monothiophosphates and dialkyl monothiophosphinates. Their structure is reported in Fig. 5. They studied the effect of different substituents on the functional group reactivity on copper sulphides against pyrite. The technique employed (Leppinen et al., 1988 ) for adsorption studies of two differently substituted thionocarbamates was FTIR-ATR. These reagents are the O-IsoPropyl N-EthylThionoCarbamate (IPETC): i- C3H 7 -- O--
C --NH--
II
S
C2H 3
295
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
g-<.-z_--'--_ 80
\.
\
60
\
>rr" LU
> © o
40
LU tr
20 ~7 0 ,~ I~ Ill
pyrite chalcocite covellite chalcopyrite bornite
i
5
7
I
I
9
11
PH
Fig. 2. Recovery for flotation of copper sulphides and pyrite with sodium isopropyl xanthate (Ackermann et al., 1987).
and O-IsoButyl-N-EthoxyCarbonylThionoCarbamate (IBECTC)" i- C4 I"I9 - - O--C - - N H - - C - - O - - C 2 H 3
II
II
S
O
In this case of dialkyl thionocarbamates, such as IPETC, the basic functional group is -O-C ( = S)-NH-, and they offer some advantages over xanthates, dithiophosphates and xanthogen formates in terms of higher selectivity against pyrite and stability in a wide pH range. In the alkoxycarbonyl alkyl thionocarbamates (IBECTC), the basic thionocarbamate functional group is maintained• The use of the strongly electronwithdrawing alkoxycarbonyl substituent, however, introduces an additional active donor, O, in the form of C - O attached to the alkoxy group. Thus the functional group cannot be simply restricted to the thionocarbamate, instead it is the group -O-C-NH-C-O- which has quite different properties from the basic thionocarbamate group. In fact this structure can form with the metal a six-membered ring through the coordination bond of C = O and C = S groups. The possibility of a six-membered chelate formation in the case of alkoxycarbonyl thionocarbamates should increase the stability of the complex formed at the sulphide surface in comparison to IPETC. This added stability may indicate that the copper complex with IBECTC, for example, is favoured over
J
8o i
J a
>- 60 LLI 0 0
# 4o
7 ~7 pyrite O chalcocite Ek covellite C~ chalcopyrite I I bornite
.°
/ .. j~/" ,-
20
.J'"
pH 5
1 O-Et
100
L
T
i O-IP
I
O-IEu
T
I
I
8ol
/S/
n- 60 W > 0 o LU cr 40
./'/
r21goo,t°
Z~covellite / El chalcopyrite ,, • bornite / pH 10.5
20
W'-"-" I
O-Et
I
I
O-IP
I
I
O-IEu
Fig. 3. Flotation o f copper sulfides with N - m e t h y l - O - s u b s t i t u t e d t h i o n o c a r b a m a t e ( A c k e r m a n n
et al., 1984. )
that with IPETC. In the case of modified thioureas the bonding groups were C = S and C = N as in the case of the corresponding thionocarbamates. There are, however, differences between thionocarbamate and thiourea collectors in terms of floatability of the various sulphide minerals. In fact al-
NEW REAGENTSIN SULPHIDEMINERALFLOTATION
297 (a)
100
8O
t'~\ 11..7"..,,~
k..,,
o~ 60 >,,,-tuJ > 0 0 w n," 40
/
V
V pyrite O chalcocite Z~ covellite
20 :
1~ chalcopyrite •
bornite
1
i
N-Me
i
N-Et
i
N-IP
N-BU
i
N-IBe
(b) 100
/.up'--.z.:i
9-,. 80
.,~/
•
o~ >c~ 60 LU
(..) LI.I n.-
/
4O
/
-
"
/ ' ~
~7 pyrite O chalcocite ~ , covellite r'~ chalcopyrite • bornite
20
i
N-Me
N-Et
i
N-IP
1
N-BU
I
N-IBe
Fig. 4. Flotation of copper sulphides and pyrite with N-substituted-O-ethyl thionocarbamates (Ackerman et al., 1984). (a) p H = 5 . 0 ; (b) p H = 10.5.
]t)~
~M
Alkoxycarbony[ Alky Thionocarbamates
i
,
c -.rm~
, -.-q
:, :~
,)
~--
D i a l k y l or diary! Monothiophosphate
MARAP,
3
Alkoxycarbonyl Alkyl Thioureas
il R -- O-
(1 - - - N H - - C - - N H
4 --R'
Dialkyl Monothiophosphinates
~\I
% i! ,i ,P--O
a ~ #
INI|~I
-
R~ii / R~
P-- O-
Fig. 5. New classes of chelating collectors (Nagaraj et al.. 1989 ).
qTH~s--C~.[/CH~ N
L
ROH
Fig. 6. Structure and mechanism of surface attachment of l-hydroxy-ethyl-2-heptadecenyl glyoxalidine (amine 220).
coxycarbonyl thionocarbamate floats copper-rich minerals such as bornite, covellite and chalcocite faster than chalcopyrite, whereas the modified thioureas float chalcopyrite very effectively. Such differences are observed not only with pure minerals but also with natural ores containing the various minerals. As regards the phosphorous acids, Nagaraj et al. (1989) have shown that the monothiophosphates are acid-circuit collectors of sulphides; the monothiophosphinates are effective in neutral and mildly alkaline circuit; the dithiophosphates are effective at pH 9. A mechanism has been proposed for explaining the differences in such collector activity between the phosphorous acids. Ackerman et al. (1987a,b,c) have proposed a new commercial chelating agent for the flotation of sulphide minerals, namely 1-hydroxy-ethyl-2-heptadecenyl glyoxalidine (amine 220) whose structure and mechanism of surface attachment is reported in Fig. 6. Ackerman et al. ( 1987a, b, c ) also found that the collecting power ofglyoxalidine is superior to that of other non-sulphydryl collectors. Two classes of chelating collectors for sulphide mineral flotation have been synthesized by Klimpel et al, (1988); the general molecular formula of the two classes is reported in Fig. 7. They also studied the deflect of substituents and chain length of these reagents on copper recovery (Klimpel and Hansen, 1989). These compounds have been earlier discovered respectively by Gould and Harris ( 1971 ), Taggart ( 1930 ) and Novikova et al. ( 1977 ) and Larribau and Tozzolino (1980). They confirmed that several members of this family have the potential of achieving usage on commercial scale.
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
299
GEERAL FORMULA
R--X--(CH2) n --
N(~
R ~ _ _ S _ _ R II or
S-seHes RI"~ ~'--~C - - RI[ S
EXAMPLES CsH17SC2H5
C6H13S(CH2)2NH O
II
~CC~H=
c6%s(cHP2N\~ H ~ ~
Fig. 7. Chelating collectors for sulphide minerals (Klimpel et al., 1988 ). AROMATIC-ALIPHATIC CHELATE TYPE COLLECTORS
On the basis of the results obtained using binary mixtures of commercial chelating reagents and fuel-oil, Marabini et al. concluded that for practical use as collectors the chelating agents must have a long-chain, be water-soluble and have proper chelating groups endowed with selective action toward a given mineral against others. Subsequently, therefore, they orientated their research towards the design and synthetis of new molecules satisfying these requirements. For the selection of chelating groups theoretically provided with selective collection power towards one given metallic mineral rather than another, a computerized method has been developed, based on the calculation of conditional constants. The method has been applied to the selection of ligands capable of separating Zn and Pb from the cations commonly present in gangue minerals namely Fe, Ca and Mg. Two classes of reagents containing chelating functional groups selected for Zn and Pb and an alkyl or alcoxyl chain linked to the aromatic ring have been synthesized and tested on Zn-Pb oxidized ores. These reagents are of the MercaptoBenzoThiazole (MBT) and AminoThioPhenol (ATP) type. They proved to be effective collectors for Zn-Pb oxidized minerals without any preliminary sulphidization. Reagents having aliphatic chains of various lengths, positions and structures were examined. The results obtained with these two series of reagents, provide interesting pointers on the criteria to be followed in designing mixed aliphatic-aromatic chelate-type collector molecules. Three structural requisites appear essential to ensure collecting power, namely: ( 1 ) the position of the alkyl group on the benzene ring vis-a-vis the chelat-
~,i~(
~ M. MAR~\BiNI 1!1 \ i
ing functional group, with the optimal one having the aliphatic group diametrically opposite the electron donor heteroatom. ( 2 ) the structure of the alkyl group which is the best when it is a straight chain with an ether oxygen atom at the point of attachment to the aromatic ring. (3) the length limit of the chain necessary to ensure adequate hydrophobicity, which ranges between three and six carbon atoms. The results were interpreted on the basis of steric factors and the reactivity of functional groups, namel.v: ( 1 ) the para position in the case of ATP reagents and the 6 position for the MBT reagents are those which permit the chain to position itself most readily perpendicular to the surface, while at the same time ensuring m a x i m u m reactivity for the functional group through the electron releasing effect: (2) linearity is the condition where the lateral forces of attraction can be exerted between the chains in the adsorbed state which are responsible for the hydrophobic effect: ( 3 ) the presence of etheric oxygen where the aliphatic chain joins the aromatic ring guarantees chain fluidity. This favours solubility of the reagent in water and tends to ensure that the chains are arranged on the mineral surface in the position which, from the statistical point of view, is the best for exertion of adequate collateral forces: (4) the limiting number of C atoms needed to achieve mineral flotation (3 to 6 ) is about half that of conventional collectors. This difference stems from the diverse polarity of the polar heads in the two cases. As regards chelatetype collectors with a partially aromatic structure, the hydrocarbon chain is shorter because the overall polarity of the polar head is lower, owing to delocalization of the charges. The ATP compounds discovered by Marabini et al. (1988) are similar to those proposed by Luttinger et al. ( 1961 ). The difference is in the position of aliphatic chain: in the work of Luttinger ( 1961 ) the chain is linked to functional group and this results in good flotation of sulphide minerals but not of oxides. In the work of Marabini (1988) the chain is linked to benzene ring in para position to functional group, and this allowed to float oxide minerals too. Some reagents of each of the two classes have been tried on the flotation of Cu, Pb, and Zn sulphide minerals, namely: Nt-t2 C H~"'~" " v
"~s/~SK
J~SK
C6H13
O
The first two reagents were found to be active on cerussite (the second one giving the best results), while the third is active on smithsonite. Two ore samples were used for the flotation tests. Sample 1, containing chalcopyrite ( 3.2% Cu) and pyrite in a quartz, dolomite and chlorite gangue, was used for the flotation of copper sulphide. Sample 2 containing galena (2.2
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
301
-20 90
80
~e )¢¢ uJ
70
-15
gJ 50
-10 40
30"
2(] MMBT
PMBT
HATP
MBT
EX
Fig. 8. Flotation ofchalcopyrite- Sample 1 Grade ( O ) and recovery ( O ) C u . 20 90
• 80
7O
60 O ILl n-" 50
•
/ol o/
15
/o 10
4O
30 0 20
I
I
i
I
i
MMBT
PMBT
HATP
MBT
EX
Fig. 9. Flotation of galena - Sample 2 Grade ( • ) and recovery (O) Pb. Pb), sphalerite (5.7% Z n ) and pyrite in a quartz, siderite, mica, calcite and dolomite gangue, used for flotation of Pb and Zn sulphides. Flotation tests were performed in a 1.2 1 Denver laboratory cell on 500 g of
M MARABINIE'I a.L
302 20
i
'
i
80With CuSO 4
70-
15
o~
60 >orIll > O O
inn
,< (5 50 ¸ Without CuSO 4
all
10
40
30
20
I
l
I
/
I
MMBT
PMBT
HATP
MBT
EX
Fig. 10. F l o t a t i o n o f s p h a l e r i t e - S a m p l e 2: G r a d e ( 0 )
5
a n d recovery ( O ) Z n
ore ground to - 100 Ftm using 40 g t-~ of Aerofroth 65 for a time of 5 min. The quantity of collector was 40 g t - ~for Cu and Pb flotation and 80 g t- 1for Zn flotation. The pH was 7.3-8 for Cu flotation, 7.7-8.9 for Pb and 9.4-9.5 for Zn (adjusted by CaOH). Sphalerite was floated in the presence and absence of activator (CuSO4200 g/t). Figures 8, 9 and 10 report the results obtained with the three synthesized reagents and, for the sake of comparison, those obtained using known commercial reagents, namely Mercapto-Benzo-Thiazole (MBT) "as-is", EthylXanthate (EX) and Butyl-Xanthate (BX). The chainless MBT is a commercial reagents used in the flotation of sulphides, towards which, as can be observed, it possesses collecting power comparable to that of the xanthates. It is not at all efficient, instead, where oxidized Zn-Pb minerals are concerned for which prior to the studies by Marabini et al. (1988, 1989a,b) no direct-acting collectors capable of producing single-metal concentrates were known. Examination of the results demonstrates that both the reagents of the MBT type have good collecting power vis4t-vis sulphides of Cu, Pb and Zn comparable to, or slightly better, than that of conventional reagents. PMBT is the better of the two, producing concentrates higher in Cu and Pb than the
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
303
commercial reagents. As also observed in the case of oxidized Z n - P b minerals, the HATP has very little effect on the Cu and Pb minerals, while towards sphalerite, its action is comparable to that of the two commercial reagents and branched MBT. Thus, although the two classes of collectors were conceived to float difficult minerals, such as those of the oxidized Zn and Pb type, they can be used to advantage in the flotation of sulphides. The MBTs in particular are good collectors of Cu and Pb sulphides, while the ATPs can be utilized in the flotation of sphalerite. Since these reagents are good collectors of cerussite and smithsonite, respectively, it is evident that the sequential use of MBT and ATP could permit attainment of a succession of two bulk concentrates of Pb and Zn containing the oxide and sulphide forms of both metals. CONCLUSIONS
Use of new reagents of the chelate-type offers the possibility of improving selectivity in the flotation separation of complex sulphide minerals. These reagents were initially utilized in combination with a neutral oil or conventional collector but subsequently they have been designed and synthesized so as to incorporate in a single structure the functional chelating groups and the hydrophobic alkyl chain. The most important reagents synthesized for the flotation of sulphide minerals are: Thionocarbamates, thiourea, derivatives of phosphoric acid, Glyoxalidine, Mercapto-Benzo-Thiazoles, Aminothiophenols. All these reagents appeared to be good collectors for sulphide minerals, their efficiency varying from one sulphide to another. As regards the influence of the structure on the efficiency of the chelating agent, all the studies made concern the effect of the alkyl substituents on the reactivity of the functional chelate group. In all cases the length of the chain necessary to combine hydrophobicity and linearity of the chain itself is important. In the case of chelating agents having a purely aliphatic structure, however, the effects of the substituents are especially of the inductive and steric type. Electrorepulsive substituents activate the chelating groups and vice versa. More complex is the case of chelating agents having an aliphatic-aromatic structure. Here the electronic and steric effects are added to the conjugative or resonance effects with the aromatic ring. In this case, in addition to the length and the structure of the chain, it is also necessary to consider the position of the substituents vis-a-vis the functional chelating group. It has been found that the best position is the one diametrically opposite the active group. It should be noted that in both cases - aliphatic or aliphatic aromatic structures - substituents that contain oxygen improve collecting power. This is
~04
,~1 MAIq:~,BINIt [ A I .
a t t r i b u t a b l e to t h e b e t t e r s o l u b i l i t y o f t h e c o l l e c t o r a n d to an effect o n r e a c t i v ity t h a t m u s t be a n a l y s e d case bv c a s e ,\CKNOWLEDGMENq S p e c i a l T h a n k s m u s t b e e x t e n d e d t o Mr. P. P l e s e i a a n d Mr. D. M a c c a r i for the editing and design work.
REFERENCES Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F., 1984. Effect of alkyl substituents performance on thionocarbarmate as copper sulphide and pyrite collectors. In: M.J. Jones and R. Oblatt (Editors), Reagents in Mineral Industry. IMM, London, pp. 69-78. Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F., 1987a. Evaluation of flotation collectors for copper sulfides and pyrite, 1. Common sulfhydryl collectors. Int. J. Miner. Process., pp, 105-127. Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F,, 1987b. Evaluation of flotation collectors for copper sulfides and pyrite, II. Non-sulfhydryl collectors. Int. J. Miner, Process., pp. 129-140. Ackerman, P.K, Harris, G.H., Klimpel, R. and Aplan, F.F., 1987c. Evaluation of flotation collectors for copper sulfides and pyrite, III. Effect of xanthate chain length and branching. Int. J. Miner. Process., pp. 141-156. Arnaud, M., Partyka, S. and Cases, J.M., 1989. Ethylxanthate adsorption onto galena and sphalerite. Colloid Surfaces, 37: 235-244. Bogdanov, O.S., Vainshenker, 1.A., Podnek, A.K., Ryabol, V.I. and Yanis, N.A., 1976. Trends in the search for effective collectors. Tsvetn. Met./Non Ferrous Metals, 17(4): 79-85. Bogdanov, O.S., Podnek, A.K., Ryabol, V.I. and Yanis, N.A., 1982. Reagents chemisorption on minerals as a process of formation of surface compounds with a coordination bond. XII Mineral Processing Congress Proceedings, Departamento Nacional de Producao Mineral, Brazil. Finkelstein, N.P. and Allison, S.A., 1976. The chemistry of activation, deactivation and depression in the flotation of zinc sulfide: A review, In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial Volume. AIME, New York, NY, pp. 414-457. Giesekke, E.W., 1983. A review of spectroscopic techniques applied to the study of interactions belween minerals and reagents in flotation systems. Int. J. Miner. Process., 11: 19-56. Glembotskii, A.V., 1978. Theoretical principles of forecasting and modifying collector properties. Tsvetn. Met./Non Ferrous Metals, 19 ( 5 ): 69-72. Glembotskii, A.V. and Livshits, A.K., 1968. Determination of the ionization constants of some dialkylthionocarbamates. Tsvetn. Met./Non Ferrous Metals, 11 ( 1 ) 10-12. Gould, W.D. and Harris, M.G., 1971. US Patent, No. 3,590,999. Klimpel, R.R. and Hansen, R.D., 1989. Recent work on developing new sulphide mineral collectors based on chelation chemistry. 118th SME/AIME Annu. Meet., Las Vegas, NV, February 27-March 2. Preprint. Klimpel. R.R., Hansen, R.D. and Fee, B.S., 1988. New collector chemistries for sulphide mineral flotation. SME/AIME Annu. Meet., Phoenix, AZ, Januari 25-28. Kongolo, M., Cases, J.M., Burreau, A. and Predali, J.J., 1984. Spectroscopic study of potassium amylxanthate adsorption on finely ground galena. In: M.J, Jones and R. Oblalt (Editors), Reagents in Mineral Industry. IMM, London, pp. 79-87.
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
305
Hanson, J.S., Barbaro, M., Fuerstenau, D.W., Marabini, M. and Barbucci, R., 1988. Interaction ofglycine and glycine-based polymer with xanthate in relation to the flotation of sulphide minerals. Int. J. Miner. Process., 23: 123-135. Harris, G.H. and Fischback, B.C., 1954. US Patent, No. 2,691,6356. Harris, G.H., Ackerman, P.K. and Aplan, F., 1988. US Patent, No. 4,793,852. Laajalehto, K., Johansson, L.S., Mielczarski, J., Anderson, S. and Suoninen, E., 1988. Electron spectroscopic studies of interaction of xanthate collectors with different substrates. In: E. Forssberg (Editor), Proceedings of the XVIth International Mineral Processing Congres, Stockholm, Sweden, 5-10 June 1988. Dev. Miner. Process., 10: 87-100. Larriban, E. and Tozzolino, P., 1980. French Patent, No. 2,429,617. Leppinen, J.O., Basilio, C.I. and Yoon, R.H., 1988. FTIR study of thionocarbamate adsorption on sulphide minerals. Colloids Surfaces, 32:113-125. Little, L.M., Poling, G.W. and Leja, J., 1961. IR spectra ofxanthate compounds. Can. J. Chem., 39: 745-754. Luttinger, L.L., 1961. US Patent, No. 3,006,471. Mangalam, V., et al., 1983. Zeta potential and flotation studies of chalcopyrite fines with 8hydroxyquinoline. Colloids Surfaces, 7: 209-220. Marabini, A.M., 1975. New collector for cassiterite. Trans. IMM, Sect. C., 84:177-178. Marabini, A. and Cozza, C., 1983. Determination, of lead ethylxanthate on mineral surface by IR spectroscopy. Spectrochimica Acta, 388:215. Marabini, A.M. and Rinelli, G., 1982. Flotation of cobalt minerals with chelating agents as collectors. ATB Metallurgie, XXII, 1:17-22. Marabini, A., Barbaro, M. and Ciriachi, M., 1983. A calculation method for selection of complexing collectors having selective action on a cation. Trans. IMM, Sect. C, 92: 20-26. Marabini, A.M., Alesse, V. and Barbaro, M., 1988. New synthetic collectors for selective flotation of zinc and lead oxidized minerals. In: E. Forssberg (Editor), Proceedings of the XVIth International Mineral Processing Congres, Stockholm, Sweden, 5-10 June 1988. Dev. Miner. Process., 10:1197-1208. Marabini, A., Cases, J. and Barbaro, M., 1989a. Chelating reagents as collectors and their adsorption mechanism. In: K.V. Sastry (Editor), Challenges in Mineral Processing. AIME, Littleton, CO. Marabini, A.M., Barbaro, M. and Passariello, B., 1989b. Flotation of cerussite with a synthetic chelating collector. Int. J. Miner. Process., 25: 29-40. Mielczarski, J. and Leppinen, J., 1987. Infrared reflection-adsorption spectroscopy study of adsorption on xanthates on copper. Surf. Sci., 187: 526-538. Mielczarski, J., Nowak, P., Strojek, J.W. and Pomianowski, A., 1981. Investigation of the products of ethlxanthate sorption on sulphide by IR-ATR spectroscopy. In: J. Laskowski (Editor), Mineral Processing. Proceedings 13th International Mineral Processing Congress, Warsaw, June, 4-9, 1979. Dev. Miner. Process., 2(A): 110-133. Nagaraj, D.R., Basilio, C. and Yoon, R.M., 1989. The chemistry and structure activity relationships for new sulphide collectors. 118th SME/AIME Annu. Meet., Las Vegas, NV, February 27-March 2. Preprint. Novikova, N.T., Dolenko, M.N., Bystrova, L.B., Roshchakovskaya, N.Yu. and Glembotskij, A.V., 1977. USSR Patent, No. 558,908. Page, P.W. and Hazell, L.B., 1989. X-ray photoelectron spectroscopy (XPS) studies of potassium amylxanthate (KAX) adsorption on precipitated PbS related to galena flotation. Int. J. Miner. Process., 25: 87-100. Partyka, S., Arnaud, M. and Lindheimer, M., 1987. Adsorption of ethylxanthate onto galena at low surface coverages. Colloids Surfaces, 26:141-153. Pradip, 1988. Application of chelating agents in mineral processing. Miner. Metall. Process., 80.
3()6
',.M M,~.R~.BINI [ | \ l
Rinelli, G. and Marabini, A.M., 1973, Flotation of zinc and lead oxide-sulphide ores ~v~thchelating agents. 10lh lnl, Miner. Process. Congr., IMM, London. Preprint No. 20, pp. *-20, Rinelli, G., Marabini, A.M. and Alesc, V., 1976. Flotation ofcassiterite with salicylaldheide as a collector. In: M.C. Fuerstenau (Editor I, Flotation, A.M. Gaudin Memorial Volume, AIME, Nc,~' York, NY, 1: 549-560. Ryabol, V.I., Shenerovich, V.A. and Shchukina, N.E., 1973. Acidic properties of a[kylhydroxamic acids and thiocarbamates (flotation agents ). Translated from: Zh. PriM. Khim,, 46(5): 1059-1098, Taggart, A.F., Taylor, T.C. and Ince, C.R., 1930. Experiments with flotation reagents. Trans. Am. Inst. Min. Metall. Eng., 87: 285-369. Usoni, L., Rinelli, G. and Marabini, A.M,, 1971. Chelating agents and fuel oil: a new way to flotation. AIME Centennial Annu. Meet., New York, NY, February 26-March 3. Wakamatsu. T., Numata, Y. and Sugimoto, Y., 1979. The effect of amino acid addition on the flotation of sulphide ore. In: J, Laskowski (Editor), Mineral Processing. Proceedings 13th International Mineral Processing Congress, Warsaw, June, 4-9, 1979. Dev. Miner. Process., 2(A):159-180.
291
New reagents in sulphide mineral flotation A.M. Marabini, M. Barbaro and V. Alesse Istituto per il Trattamento dei Minerali, C.N.R., Via Bolognola 7, 00138 Rome, Italy (Received April 25, 1990; accepted after revision May 3, 1991 )
ABSTRACT Marabini A.M., Barbaro, M. and Alesse, V., 1991. New reagents in sulphide mineral flotation. In: K.S.E. Forssberg (Editor), Flotation of Sulphide Minerals 1990. Int. J. Miner. Process., 33: 291306. A review is presented of new reagents for sulphide flotation. These reagents are essentially of the chelating type. Compared with conventional reagents they have a marked selectivity for individual sulphide minerals. The review hinges around: collecting power towards various sulphides and comparison with conventional reagents; influence of molecular structure on collecting power and action mechanism; and criteria for designing and synthesizing chelate-type collectors with optimal structure for a given metallic mineral.
INTRODUCTION
The search for new reagents in sulphide mineral flotation is particularly important for ores containing several commercially useful mineral components finely intergrown with the gangue and with one another, or for ores characterized by a very fine screen analysis. This is the case of the so called complex sulphide ores which have been defined as those ores for which it is difficult to recover one or more selective products of acceptable quality and economic value with minimal losses and at reasonable costs. Complex sulphide ores are fine-grained, intimate associations of chalcopyrite (CuFeS2), sphalerite (ZnS) and galena (PbS), disseminated in dominant pyrite, and which contains valuable amount of silver and, in some cases, gold. Generally, collectors employed for sulphide recovery are of the thiol type, the most commonly used being xanthates. Their mechanism of action has not been completely clarified. (Little et al., 1961; Mielczarski et al., 1981; Giesekke, 1983; Marabini et al., 1983; Kongolo et al., 1984; Mielczarski et al., 1987; Partyka et al., 1987; Laajalehto et at., 1988; Page et al., 1989; Arnaud et al., 1989). Xanthates are active towards the whole class of sulphide minerals, rather than towards one individual mineral. Thus, in order to float a given mineral 0301-7516/91/$03.50 © 1991 Elsevier Science Publishers B.V. All fights reserved.
2tJ2
', M, MARABINI ~ [ . \ [
from a mixture of minerals belonging to the same sulphide class, modifiers always have to be used in order to render the action of the collector more specific, and to improve separation efficiency (Finkelstein et al., 197~ t. However, there are many problems in this procedure and the desired results are not always obtained, especially in the case of minerals of complex composition. Hence the importance of seeking out collectors capable of linking selectively with a given mineral. Selective linkage is possible if the collector structure incorporates active groups having specific affinity for certain cations characteristic of the minera[ surface. Thus, the search for new, more selective reagents for sulphide mineral flotation is mainly concerned with chelate-forming reagents. These reagents are organic compounds endowed with selective action towards certain metallic ions, with which they are capable of linking via two or more functional groups, thus forming one or more rings which render the resulting chelate extremely stable. Different type of chelating reagents have been used for sulphide ore flotation such as binary systems of commercially available chelating reagents plus fuel-oil or conventional collectors and long chain aliphatic and aliphatic aromatic collectors. PRELYMINARY STUDIES: BINARY SYSTEMS
Commercially available chelating reagents are aromatic molecules without a long hydrocarbon chain; thus, altough the chelated mineral particle is fairly hydrophobic, it is not sufficiently aerophilic to ensure flotation. Studies on oxidized minerals (Usoni et al., 1971; Marabini, 1975; Rinelli et al., 1976) were performed by rendering particles hydrophobic by making available longchain organic groups ( such as fuel-oil or oily frother) together with chelating agents commonly used in analytical chemistry. The first application of this conception on sulphide minerals dates back to 1973. A chelating reagent, namely 8-hydroxyquinoline with fuel oil was used to float mixed oxide-sulphide minerals of Zn and Pb (Rinelli and Marabini, 1973). Another example of chelating reagent in sulphide treatment is the flotation of cobaltite with nitroso/~-naphto (N N) (Marabini and Rinelli, 1982 ), which is known to be a reagent for cobalt. Flotation tests on cobaltite-hematite and cobaltite-niccolite indicated good selectivity for cobaltite. Rinelli and Marabini interpreted these results on the basis of greater affinity of Nfl N for cobalt than nickel and copper. The synergistic effect of a chelating reagent and a classical collector has also been investigated. The synergistic effect that glycine and xanthate have on the selective flotation of sulphide minerals was studied first by Wakamatsu et al. (1979) and then by Hanson et al. ( 1988 ). Glycine is a very well known chelating agent for copper minerals. These researchers found that the addition of glycine increases adsorption of ethylxan-
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
293
thate on chalcocite, galena and pyrite minerals, producing an activating effect on flotation. The improved flotation response of chalcocite and partially of galena and pyrite using xanthate collector was explained as follows: ( 1 ) Glycine increases metal cations concentration by the formation of soluble metal-glycinate complexes. (2) It follows that more metal cations are present in solution for xanthate to react and ultimately adsorb onto the mineral surface. ALIPHATIC CHELATE TYPE COLLECTORS
Many researchers have studied the use of chelating agents in metallic mineral flotation. Recently, a review of these studies has been published by Pradip ( 1988 ). However most of the studies concern oxidized minerals, and there are few applications to sulphide. Harris et al. (1988) have patented thiodicarbonates or dithiocarbonates as collectors for non-ferrous metal sulphides. Chalcopyrite was floated at pH 5.0 with excellent recovery and selectivity at this acid pH. The other important studies concern thionocarbamates, thiourea derivatives, phosphinate and phosphate derivatives, glioxalidine, etc. Thionocarbamates were discovered by Harris and Fischback (1954 ). In spite of the considerable industrial acceptance of this class of reagents, surprisingly few fundamental studies on their use have been made. Notable exceptions are the work done by Ryabol et al. ( 1973 ), Bogdanov et al. ( 1976 ), Glembotskii (1978), Bogdanov et al. (1982), and Ackerman et al. (1984). It is known that these reagents form a chelating bond with metals through coordination of sulphur and nitrogen, as shown below: lq'-- O--C
H
Sx
N--R' \
\
/
i
~//,~ MINERAL ~/~/~,
In particular Ackerman et al. ( 1984, 1987a,b,c) studied the collecting power on copper sulphides and pyrite of N-ethyl-O-isopropyl-thionocarbamates (Fig. 1 ) and found that it is comparable to that of xanthate (Fig. 2 ): Ackerman et al. (1987a,b,c) also showed that the flotation of copper sulphides and pyrite is influenced by both the N- and O-alkyl substituents which control hydrophobicity and steric accessibility of the NCS grouping. Ackerman et al. (1987a,b,c) found that for a given number of carbon atoms linked to the nitrogen, an increase in the chain lenght linked to the oxygen increases the collecting power (Fig. 3 ). This is due to the greater hydrophobicity of the surface coating as a result of the greater insolubility of the reagent. This effect is also observed in branched chains.
294
\M.
I
100
T. . . . . . . . . . . . . . .
r
MARABINI
ET,,M
r'--- 7
4
80
60
>or uJ
w ~:
v O A n •
40
20
pyrite chalcocite covellite chalcopyrite bornite
~7--" ". . . . . . . .
XT----
, ~
I
I
I
5
7
9
11
PH
Fig. 1. Flotation recovery of copper sulphides and pyrite using Z-200 (commercial form of Nethyl-O-isopropyl thionocarbamate) (Ackermann et al., 1987)
On the other hand, for the same number of carbon atoms linked to the oxygen, the collecting power increases with an increase in the number of carbon atoms on nitrogen in the case of straight chains, while negative effects occur in the case of branched chains and unsaturated chains (Fig. 4). The increase in collecting power with straight chain length is explained by the lower solubility and hydrophobicity of the surface coating. The effect of the branching and the unsaturation is due respectively to a steric impediment in the reaction of the nitrogen with the metal and to an increase in the hydrophilicity of the molecule containing unsatured bonds. Recently new classes of collectors with chelating properties for copper sulphide minerals have been presented by Nagaraj et al. ( 1989 ). They are alcoxycarbonyl alkyl thionocarbamates and thioureas, dialkyl (or diaryl) monothiophosphates and dialkyl monothiophosphinates. Their structure is reported in Fig. 5. They studied the effect of different substituents on the functional group reactivity on copper sulphides against pyrite. The technique employed (Leppinen et al., 1988 ) for adsorption studies of two differently substituted thionocarbamates was FTIR-ATR. These reagents are the O-IsoPropyl N-EthylThionoCarbamate (IPETC): i- C3H 7 -- O--
C --NH--
II
S
C2H 3
295
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
g-<.-z_--'--_ 80
\.
\
60
\
>rr" LU
> © o
40
LU tr
20 ~7 0 ,~ I~ Ill
pyrite chalcocite covellite chalcopyrite bornite
i
5
7
I
I
9
11
PH
Fig. 2. Recovery for flotation of copper sulphides and pyrite with sodium isopropyl xanthate (Ackermann et al., 1987).
and O-IsoButyl-N-EthoxyCarbonylThionoCarbamate (IBECTC)" i- C4 I"I9 - - O--C - - N H - - C - - O - - C 2 H 3
II
II
S
O
In this case of dialkyl thionocarbamates, such as IPETC, the basic functional group is -O-C ( = S)-NH-, and they offer some advantages over xanthates, dithiophosphates and xanthogen formates in terms of higher selectivity against pyrite and stability in a wide pH range. In the alkoxycarbonyl alkyl thionocarbamates (IBECTC), the basic thionocarbamate functional group is maintained• The use of the strongly electronwithdrawing alkoxycarbonyl substituent, however, introduces an additional active donor, O, in the form of C - O attached to the alkoxy group. Thus the functional group cannot be simply restricted to the thionocarbamate, instead it is the group -O-C-NH-C-O- which has quite different properties from the basic thionocarbamate group. In fact this structure can form with the metal a six-membered ring through the coordination bond of C = O and C = S groups. The possibility of a six-membered chelate formation in the case of alkoxycarbonyl thionocarbamates should increase the stability of the complex formed at the sulphide surface in comparison to IPETC. This added stability may indicate that the copper complex with IBECTC, for example, is favoured over
J
8o i
J a
>- 60 LLI 0 0
# 4o
7 ~7 pyrite O chalcocite Ek covellite C~ chalcopyrite I I bornite
.°
/ .. j~/" ,-
20
.J'"
pH 5
1 O-Et
100
L
T
i O-IP
I
O-IEu
T
I
I
8ol
/S/
n- 60 W > 0 o LU cr 40
./'/
r21goo,t°
Z~covellite / El chalcopyrite ,, • bornite / pH 10.5
20
W'-"-" I
O-Et
I
I
O-IP
I
I
O-IEu
Fig. 3. Flotation o f copper sulfides with N - m e t h y l - O - s u b s t i t u t e d t h i o n o c a r b a m a t e ( A c k e r m a n n
et al., 1984. )
that with IPETC. In the case of modified thioureas the bonding groups were C = S and C = N as in the case of the corresponding thionocarbamates. There are, however, differences between thionocarbamate and thiourea collectors in terms of floatability of the various sulphide minerals. In fact al-
NEW REAGENTSIN SULPHIDEMINERALFLOTATION
297 (a)
100
8O
t'~\ 11..7"..,,~
k..,,
o~ 60 >,,,-tuJ > 0 0 w n," 40
/
V
V pyrite O chalcocite Z~ covellite
20 :
1~ chalcopyrite •
bornite
1
i
N-Me
i
N-Et
i
N-IP
N-BU
i
N-IBe
(b) 100
/.up'--.z.:i
9-,. 80
.,~/
•
o~ >c~ 60 LU
(..) LI.I n.-
/
4O
/
-
"
/ ' ~
~7 pyrite O chalcocite ~ , covellite r'~ chalcopyrite • bornite
20
i
N-Me
N-Et
i
N-IP
1
N-BU
I
N-IBe
Fig. 4. Flotation of copper sulphides and pyrite with N-substituted-O-ethyl thionocarbamates (Ackerman et al., 1984). (a) p H = 5 . 0 ; (b) p H = 10.5.
]t)~
~M
Alkoxycarbony[ Alky Thionocarbamates
i
,
c -.rm~
, -.-q
:, :~
,)
~--
D i a l k y l or diary! Monothiophosphate
MARAP,
3
Alkoxycarbonyl Alkyl Thioureas
il R -- O-
(1 - - - N H - - C - - N H
4 --R'
Dialkyl Monothiophosphinates
~\I
% i! ,i ,P--O
a ~ #
INI|~I
-
R~ii / R~
P-- O-
Fig. 5. New classes of chelating collectors (Nagaraj et al.. 1989 ).
qTH~s--C~.[/CH~ N
L
ROH
Fig. 6. Structure and mechanism of surface attachment of l-hydroxy-ethyl-2-heptadecenyl glyoxalidine (amine 220).
coxycarbonyl thionocarbamate floats copper-rich minerals such as bornite, covellite and chalcocite faster than chalcopyrite, whereas the modified thioureas float chalcopyrite very effectively. Such differences are observed not only with pure minerals but also with natural ores containing the various minerals. As regards the phosphorous acids, Nagaraj et al. (1989) have shown that the monothiophosphates are acid-circuit collectors of sulphides; the monothiophosphinates are effective in neutral and mildly alkaline circuit; the dithiophosphates are effective at pH 9. A mechanism has been proposed for explaining the differences in such collector activity between the phosphorous acids. Ackerman et al. (1987a,b,c) have proposed a new commercial chelating agent for the flotation of sulphide minerals, namely 1-hydroxy-ethyl-2-heptadecenyl glyoxalidine (amine 220) whose structure and mechanism of surface attachment is reported in Fig. 6. Ackerman et al. ( 1987a, b, c ) also found that the collecting power ofglyoxalidine is superior to that of other non-sulphydryl collectors. Two classes of chelating collectors for sulphide mineral flotation have been synthesized by Klimpel et al, (1988); the general molecular formula of the two classes is reported in Fig. 7. They also studied the deflect of substituents and chain length of these reagents on copper recovery (Klimpel and Hansen, 1989). These compounds have been earlier discovered respectively by Gould and Harris ( 1971 ), Taggart ( 1930 ) and Novikova et al. ( 1977 ) and Larribau and Tozzolino (1980). They confirmed that several members of this family have the potential of achieving usage on commercial scale.
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
299
GEERAL FORMULA
R--X--(CH2) n --
N(~
R ~ _ _ S _ _ R II or
S-seHes RI"~ ~'--~C - - RI[ S
EXAMPLES CsH17SC2H5
C6H13S(CH2)2NH O
II
~CC~H=
c6%s(cHP2N\~ H ~ ~
Fig. 7. Chelating collectors for sulphide minerals (Klimpel et al., 1988 ). AROMATIC-ALIPHATIC CHELATE TYPE COLLECTORS
On the basis of the results obtained using binary mixtures of commercial chelating reagents and fuel-oil, Marabini et al. concluded that for practical use as collectors the chelating agents must have a long-chain, be water-soluble and have proper chelating groups endowed with selective action toward a given mineral against others. Subsequently, therefore, they orientated their research towards the design and synthetis of new molecules satisfying these requirements. For the selection of chelating groups theoretically provided with selective collection power towards one given metallic mineral rather than another, a computerized method has been developed, based on the calculation of conditional constants. The method has been applied to the selection of ligands capable of separating Zn and Pb from the cations commonly present in gangue minerals namely Fe, Ca and Mg. Two classes of reagents containing chelating functional groups selected for Zn and Pb and an alkyl or alcoxyl chain linked to the aromatic ring have been synthesized and tested on Zn-Pb oxidized ores. These reagents are of the MercaptoBenzoThiazole (MBT) and AminoThioPhenol (ATP) type. They proved to be effective collectors for Zn-Pb oxidized minerals without any preliminary sulphidization. Reagents having aliphatic chains of various lengths, positions and structures were examined. The results obtained with these two series of reagents, provide interesting pointers on the criteria to be followed in designing mixed aliphatic-aromatic chelate-type collector molecules. Three structural requisites appear essential to ensure collecting power, namely: ( 1 ) the position of the alkyl group on the benzene ring vis-a-vis the chelat-
~,i~(
~ M. MAR~\BiNI 1!1 \ i
ing functional group, with the optimal one having the aliphatic group diametrically opposite the electron donor heteroatom. ( 2 ) the structure of the alkyl group which is the best when it is a straight chain with an ether oxygen atom at the point of attachment to the aromatic ring. (3) the length limit of the chain necessary to ensure adequate hydrophobicity, which ranges between three and six carbon atoms. The results were interpreted on the basis of steric factors and the reactivity of functional groups, namel.v: ( 1 ) the para position in the case of ATP reagents and the 6 position for the MBT reagents are those which permit the chain to position itself most readily perpendicular to the surface, while at the same time ensuring m a x i m u m reactivity for the functional group through the electron releasing effect: (2) linearity is the condition where the lateral forces of attraction can be exerted between the chains in the adsorbed state which are responsible for the hydrophobic effect: ( 3 ) the presence of etheric oxygen where the aliphatic chain joins the aromatic ring guarantees chain fluidity. This favours solubility of the reagent in water and tends to ensure that the chains are arranged on the mineral surface in the position which, from the statistical point of view, is the best for exertion of adequate collateral forces: (4) the limiting number of C atoms needed to achieve mineral flotation (3 to 6 ) is about half that of conventional collectors. This difference stems from the diverse polarity of the polar heads in the two cases. As regards chelatetype collectors with a partially aromatic structure, the hydrocarbon chain is shorter because the overall polarity of the polar head is lower, owing to delocalization of the charges. The ATP compounds discovered by Marabini et al. (1988) are similar to those proposed by Luttinger et al. ( 1961 ). The difference is in the position of aliphatic chain: in the work of Luttinger ( 1961 ) the chain is linked to functional group and this results in good flotation of sulphide minerals but not of oxides. In the work of Marabini (1988) the chain is linked to benzene ring in para position to functional group, and this allowed to float oxide minerals too. Some reagents of each of the two classes have been tried on the flotation of Cu, Pb, and Zn sulphide minerals, namely: Nt-t2 C H~"'~" " v
"~s/~SK
J~SK
C6H13
O
The first two reagents were found to be active on cerussite (the second one giving the best results), while the third is active on smithsonite. Two ore samples were used for the flotation tests. Sample 1, containing chalcopyrite ( 3.2% Cu) and pyrite in a quartz, dolomite and chlorite gangue, was used for the flotation of copper sulphide. Sample 2 containing galena (2.2
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
301
-20 90
80
~e )¢¢ uJ
70
-15
gJ 50
-10 40
30"
2(] MMBT
PMBT
HATP
MBT
EX
Fig. 8. Flotation ofchalcopyrite- Sample 1 Grade ( O ) and recovery ( O ) C u . 20 90
• 80
7O
60 O ILl n-" 50
•
/ol o/
15
/o 10
4O
30 0 20
I
I
i
I
i
MMBT
PMBT
HATP
MBT
EX
Fig. 9. Flotation of galena - Sample 2 Grade ( • ) and recovery (O) Pb. Pb), sphalerite (5.7% Z n ) and pyrite in a quartz, siderite, mica, calcite and dolomite gangue, used for flotation of Pb and Zn sulphides. Flotation tests were performed in a 1.2 1 Denver laboratory cell on 500 g of
M MARABINIE'I a.L
302 20
i
'
i
80With CuSO 4
70-
15
o~
60 >orIll > O O
inn
,< (5 50 ¸ Without CuSO 4
all
10
40
30
20
I
l
I
/
I
MMBT
PMBT
HATP
MBT
EX
Fig. 10. F l o t a t i o n o f s p h a l e r i t e - S a m p l e 2: G r a d e ( 0 )
5
a n d recovery ( O ) Z n
ore ground to - 100 Ftm using 40 g t-~ of Aerofroth 65 for a time of 5 min. The quantity of collector was 40 g t - ~for Cu and Pb flotation and 80 g t- 1for Zn flotation. The pH was 7.3-8 for Cu flotation, 7.7-8.9 for Pb and 9.4-9.5 for Zn (adjusted by CaOH). Sphalerite was floated in the presence and absence of activator (CuSO4200 g/t). Figures 8, 9 and 10 report the results obtained with the three synthesized reagents and, for the sake of comparison, those obtained using known commercial reagents, namely Mercapto-Benzo-Thiazole (MBT) "as-is", EthylXanthate (EX) and Butyl-Xanthate (BX). The chainless MBT is a commercial reagents used in the flotation of sulphides, towards which, as can be observed, it possesses collecting power comparable to that of the xanthates. It is not at all efficient, instead, where oxidized Zn-Pb minerals are concerned for which prior to the studies by Marabini et al. (1988, 1989a,b) no direct-acting collectors capable of producing single-metal concentrates were known. Examination of the results demonstrates that both the reagents of the MBT type have good collecting power vis4t-vis sulphides of Cu, Pb and Zn comparable to, or slightly better, than that of conventional reagents. PMBT is the better of the two, producing concentrates higher in Cu and Pb than the
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
303
commercial reagents. As also observed in the case of oxidized Z n - P b minerals, the HATP has very little effect on the Cu and Pb minerals, while towards sphalerite, its action is comparable to that of the two commercial reagents and branched MBT. Thus, although the two classes of collectors were conceived to float difficult minerals, such as those of the oxidized Zn and Pb type, they can be used to advantage in the flotation of sulphides. The MBTs in particular are good collectors of Cu and Pb sulphides, while the ATPs can be utilized in the flotation of sphalerite. Since these reagents are good collectors of cerussite and smithsonite, respectively, it is evident that the sequential use of MBT and ATP could permit attainment of a succession of two bulk concentrates of Pb and Zn containing the oxide and sulphide forms of both metals. CONCLUSIONS
Use of new reagents of the chelate-type offers the possibility of improving selectivity in the flotation separation of complex sulphide minerals. These reagents were initially utilized in combination with a neutral oil or conventional collector but subsequently they have been designed and synthesized so as to incorporate in a single structure the functional chelating groups and the hydrophobic alkyl chain. The most important reagents synthesized for the flotation of sulphide minerals are: Thionocarbamates, thiourea, derivatives of phosphoric acid, Glyoxalidine, Mercapto-Benzo-Thiazoles, Aminothiophenols. All these reagents appeared to be good collectors for sulphide minerals, their efficiency varying from one sulphide to another. As regards the influence of the structure on the efficiency of the chelating agent, all the studies made concern the effect of the alkyl substituents on the reactivity of the functional chelate group. In all cases the length of the chain necessary to combine hydrophobicity and linearity of the chain itself is important. In the case of chelating agents having a purely aliphatic structure, however, the effects of the substituents are especially of the inductive and steric type. Electrorepulsive substituents activate the chelating groups and vice versa. More complex is the case of chelating agents having an aliphatic-aromatic structure. Here the electronic and steric effects are added to the conjugative or resonance effects with the aromatic ring. In this case, in addition to the length and the structure of the chain, it is also necessary to consider the position of the substituents vis-a-vis the functional chelating group. It has been found that the best position is the one diametrically opposite the active group. It should be noted that in both cases - aliphatic or aliphatic aromatic structures - substituents that contain oxygen improve collecting power. This is
~04
,~1 MAIq:~,BINIt [ A I .
a t t r i b u t a b l e to t h e b e t t e r s o l u b i l i t y o f t h e c o l l e c t o r a n d to an effect o n r e a c t i v ity t h a t m u s t be a n a l y s e d case bv c a s e ,\CKNOWLEDGMENq S p e c i a l T h a n k s m u s t b e e x t e n d e d t o Mr. P. P l e s e i a a n d Mr. D. M a c c a r i for the editing and design work.
REFERENCES Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F., 1984. Effect of alkyl substituents performance on thionocarbarmate as copper sulphide and pyrite collectors. In: M.J. Jones and R. Oblatt (Editors), Reagents in Mineral Industry. IMM, London, pp. 69-78. Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F., 1987a. Evaluation of flotation collectors for copper sulfides and pyrite, 1. Common sulfhydryl collectors. Int. J. Miner. Process., pp, 105-127. Ackerman, P.K., Harris, G.H., Klimpel, R. and Aplan, F.F,, 1987b. Evaluation of flotation collectors for copper sulfides and pyrite, II. Non-sulfhydryl collectors. Int. J. Miner, Process., pp. 129-140. Ackerman, P.K, Harris, G.H., Klimpel, R. and Aplan, F.F., 1987c. Evaluation of flotation collectors for copper sulfides and pyrite, III. Effect of xanthate chain length and branching. Int. J. Miner. Process., pp. 141-156. Arnaud, M., Partyka, S. and Cases, J.M., 1989. Ethylxanthate adsorption onto galena and sphalerite. Colloid Surfaces, 37: 235-244. Bogdanov, O.S., Vainshenker, 1.A., Podnek, A.K., Ryabol, V.I. and Yanis, N.A., 1976. Trends in the search for effective collectors. Tsvetn. Met./Non Ferrous Metals, 17(4): 79-85. Bogdanov, O.S., Podnek, A.K., Ryabol, V.I. and Yanis, N.A., 1982. Reagents chemisorption on minerals as a process of formation of surface compounds with a coordination bond. XII Mineral Processing Congress Proceedings, Departamento Nacional de Producao Mineral, Brazil. Finkelstein, N.P. and Allison, S.A., 1976. The chemistry of activation, deactivation and depression in the flotation of zinc sulfide: A review, In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial Volume. AIME, New York, NY, pp. 414-457. Giesekke, E.W., 1983. A review of spectroscopic techniques applied to the study of interactions belween minerals and reagents in flotation systems. Int. J. Miner. Process., 11: 19-56. Glembotskii, A.V., 1978. Theoretical principles of forecasting and modifying collector properties. Tsvetn. Met./Non Ferrous Metals, 19 ( 5 ): 69-72. Glembotskii, A.V. and Livshits, A.K., 1968. Determination of the ionization constants of some dialkylthionocarbamates. Tsvetn. Met./Non Ferrous Metals, 11 ( 1 ) 10-12. Gould, W.D. and Harris, M.G., 1971. US Patent, No. 3,590,999. Klimpel, R.R. and Hansen, R.D., 1989. Recent work on developing new sulphide mineral collectors based on chelation chemistry. 118th SME/AIME Annu. Meet., Las Vegas, NV, February 27-March 2. Preprint. Klimpel. R.R., Hansen, R.D. and Fee, B.S., 1988. New collector chemistries for sulphide mineral flotation. SME/AIME Annu. Meet., Phoenix, AZ, Januari 25-28. Kongolo, M., Cases, J.M., Burreau, A. and Predali, J.J., 1984. Spectroscopic study of potassium amylxanthate adsorption on finely ground galena. In: M.J, Jones and R. Oblalt (Editors), Reagents in Mineral Industry. IMM, London, pp. 79-87.
NEW REAGENTS IN SULPHIDE MINERAL FLOTATION
305
Hanson, J.S., Barbaro, M., Fuerstenau, D.W., Marabini, M. and Barbucci, R., 1988. Interaction ofglycine and glycine-based polymer with xanthate in relation to the flotation of sulphide minerals. Int. J. Miner. Process., 23: 123-135. Harris, G.H. and Fischback, B.C., 1954. US Patent, No. 2,691,6356. Harris, G.H., Ackerman, P.K. and Aplan, F., 1988. US Patent, No. 4,793,852. Laajalehto, K., Johansson, L.S., Mielczarski, J., Anderson, S. and Suoninen, E., 1988. Electron spectroscopic studies of interaction of xanthate collectors with different substrates. In: E. Forssberg (Editor), Proceedings of the XVIth International Mineral Processing Congres, Stockholm, Sweden, 5-10 June 1988. Dev. Miner. Process., 10: 87-100. Larriban, E. and Tozzolino, P., 1980. French Patent, No. 2,429,617. Leppinen, J.O., Basilio, C.I. and Yoon, R.H., 1988. FTIR study of thionocarbamate adsorption on sulphide minerals. Colloids Surfaces, 32:113-125. Little, L.M., Poling, G.W. and Leja, J., 1961. IR spectra ofxanthate compounds. Can. J. Chem., 39: 745-754. Luttinger, L.L., 1961. US Patent, No. 3,006,471. Mangalam, V., et al., 1983. Zeta potential and flotation studies of chalcopyrite fines with 8hydroxyquinoline. Colloids Surfaces, 7: 209-220. Marabini, A.M., 1975. New collector for cassiterite. Trans. IMM, Sect. C., 84:177-178. Marabini, A. and Cozza, C., 1983. Determination, of lead ethylxanthate on mineral surface by IR spectroscopy. Spectrochimica Acta, 388:215. Marabini, A.M. and Rinelli, G., 1982. Flotation of cobalt minerals with chelating agents as collectors. ATB Metallurgie, XXII, 1:17-22. Marabini, A., Barbaro, M. and Ciriachi, M., 1983. A calculation method for selection of complexing collectors having selective action on a cation. Trans. IMM, Sect. C, 92: 20-26. Marabini, A.M., Alesse, V. and Barbaro, M., 1988. New synthetic collectors for selective flotation of zinc and lead oxidized minerals. In: E. Forssberg (Editor), Proceedings of the XVIth International Mineral Processing Congres, Stockholm, Sweden, 5-10 June 1988. Dev. Miner. Process., 10:1197-1208. Marabini, A., Cases, J. and Barbaro, M., 1989a. Chelating reagents as collectors and their adsorption mechanism. In: K.V. Sastry (Editor), Challenges in Mineral Processing. AIME, Littleton, CO. Marabini, A.M., Barbaro, M. and Passariello, B., 1989b. Flotation of cerussite with a synthetic chelating collector. Int. J. Miner. Process., 25: 29-40. Mielczarski, J. and Leppinen, J., 1987. Infrared reflection-adsorption spectroscopy study of adsorption on xanthates on copper. Surf. Sci., 187: 526-538. Mielczarski, J., Nowak, P., Strojek, J.W. and Pomianowski, A., 1981. Investigation of the products of ethlxanthate sorption on sulphide by IR-ATR spectroscopy. In: J. Laskowski (Editor), Mineral Processing. Proceedings 13th International Mineral Processing Congress, Warsaw, June, 4-9, 1979. Dev. Miner. Process., 2(A): 110-133. Nagaraj, D.R., Basilio, C. and Yoon, R.M., 1989. The chemistry and structure activity relationships for new sulphide collectors. 118th SME/AIME Annu. Meet., Las Vegas, NV, February 27-March 2. Preprint. Novikova, N.T., Dolenko, M.N., Bystrova, L.B., Roshchakovskaya, N.Yu. and Glembotskij, A.V., 1977. USSR Patent, No. 558,908. Page, P.W. and Hazell, L.B., 1989. X-ray photoelectron spectroscopy (XPS) studies of potassium amylxanthate (KAX) adsorption on precipitated PbS related to galena flotation. Int. J. Miner. Process., 25: 87-100. Partyka, S., Arnaud, M. and Lindheimer, M., 1987. Adsorption of ethylxanthate onto galena at low surface coverages. Colloids Surfaces, 26:141-153. Pradip, 1988. Application of chelating agents in mineral processing. Miner. Metall. Process., 80.
3()6
',.M M,~.R~.BINI [ | \ l
Rinelli, G. and Marabini, A.M., 1973, Flotation of zinc and lead oxide-sulphide ores ~v~thchelating agents. 10lh lnl, Miner. Process. Congr., IMM, London. Preprint No. 20, pp. *-20, Rinelli, G., Marabini, A.M. and Alesc, V., 1976. Flotation ofcassiterite with salicylaldheide as a collector. In: M.C. Fuerstenau (Editor I, Flotation, A.M. Gaudin Memorial Volume, AIME, Nc,~' York, NY, 1: 549-560. Ryabol, V.I., Shenerovich, V.A. and Shchukina, N.E., 1973. Acidic properties of a[kylhydroxamic acids and thiocarbamates (flotation agents ). Translated from: Zh. PriM. Khim,, 46(5): 1059-1098, Taggart, A.F., Taylor, T.C. and Ince, C.R., 1930. Experiments with flotation reagents. Trans. Am. Inst. Min. Metall. Eng., 87: 285-369. Usoni, L., Rinelli, G. and Marabini, A.M,, 1971. Chelating agents and fuel oil: a new way to flotation. AIME Centennial Annu. Meet., New York, NY, February 26-March 3. Wakamatsu. T., Numata, Y. and Sugimoto, Y., 1979. The effect of amino acid addition on the flotation of sulphide ore. In: J, Laskowski (Editor), Mineral Processing. Proceedings 13th International Mineral Processing Congress, Warsaw, June, 4-9, 1979. Dev. Miner. Process., 2(A):159-180.