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The separation of monazite from zircon by flotation
113
Journal o/’ the Less-Common Metals
Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
THE
SEP~TION
OF MONAZITE
FROM
ZIRCON
BY FLOTATrON
A. M. ABEIDU Laboratory of Metallurgy, National Research Centre, Dokki, Cairo (Egypt)
(Received February 29th, 1972)
The conditions for the separation of monazite from zircon in anionic (oleic acid and sodium dodecyl sulphate) and cationic (dodecylaminium chloride) collector systems using sodium sulphide as regulator have been studied by means of electrokinetic measurements, direct flotation tests, and adsorption determination of the collector. The results obtained indicate that sodium sulphide affects the soap flotation of monazite and of zircon differently, hence it is useful in obtaining a high degree of selective separation. On the other hand, sodium sulphide is without selective action in alkyl sulphate and amine flotation. It seems that SH- and S*- ions are adsorbed preferentially onto a monazite surface with subsequent partial displacement of phosphate sites. Since the pll, of oleic acid is relativeiy high and that of SH- is higher than the pK, of HPOZ-, it is likely that the activation of monazite by sodium sulphide takes place by the attachment of oleate ions to the adsorbed activating S2and SH- ions, leading to the successful flotation of monazite. By contrast., sodium sulphide was shown to exert no influence on the adsorptive capacity for oleic acid and floatability of zircon, presumably owing to the extremely low pH of the isoelectric point of silicon sites.
INTRODUCTION
Monazite (Ce, La, Y, Th) PO, is the chief source of thorium which is receiving considerable attention as a source of atomic energy. Monazite is naturally concentrated in sands because of its resistance to chemical attack and its high specific gravity. It is found in association with other resistant and heavy minerals, such as magnetite (Fe,O,), ilmenite (FeTiO,) and zircon (ZrSiO,). It has been reported that monazite and zircon have varying electrostatic properties and even when a combination of electrostatic and magnetic separation is employed, a satisfactory separation may not be possible’. For both technical and economic reasons the flotation process is attractive and has been used by some investigators2*3 in the concentration of monazite ores. The present paper describes a study of the technical feasibility and mechanism of the flotation separation of monazite from zircon using sodium sulphide (Na,S) as regulator. J. Less-Common
Metals, 29 (i 972)
114
A. M. ABEIDU
EXPERIMENTAL
TECHNIQUES
Reagents were of analytical grade. Reasonably pure natural crystals of monazite and zircon from the beach of the Mediterranean Sea on the side of the mouth of the Nile near Rosetta were used. The crystals were crushed in a porcelain mortar to give a - 100, + 150 mesh fraction for flotation tests and a - 150, + 200 mesh fraction for streaming potential studies. The equipment used for measuring streaming potentials basically resembled that used earlier by the author4. The Hallimond tube used has been described previously ‘. A procedure similar to that described by Iwasaki et ~1.~ was used to determine the adsorption of sodium dodecyl sulphate (SDS) and dodecylamine (DA). The method used for adsorption studies with oleic acid (OLH), described elsewhere’**, gives reasonably accurate results (k 10%) and has the advantage of a high sensitivity of detection, viz., 0.02%‘,*. RESULTS
AND DISCUSSION
The basic studies on the surface properties and flotation characteristics of monazite and zircon were made by electrokinetic, adsorption and floatability measurements. The results obtained are represented graphically in Figs. l-6. As seen from Fig. 1 a monazite surface is slightly charged in distilled water and becomes uncharged at a pH of about 5.5. Decreasing the pH by the addition of HCl increases the positive charge on the surface until it reached a maximum at a pH of 2. Further lowering of the pH decreases the positive charge, presumably because of the compression of the double layer. Increasing the pH causes an increase of the negative charge on the monazite surface. At pH values above 10 the negative value of the zeta potential decreases owing to the adsorption of sodium ions. It was found that sodium sulphide, Na,S, increased whereas DA decreased the negative charge of a monazite surface in the pH range 7-10. At pH values below 7, Na,S and DA were without effect on +I0
oo-
,6
> E
3
-lO7
5 ', a 0 % N
-2o-
-30,
I 2
I 3
! 4 j
Hc$ao.,
b
b
;“,,
”
Fig. 1. Zeta potential of monazite as a function of pH. (1) without additions, (2) on addition of 40 mg/l of Na,S, (3) on addition of 150 mg/l of oleic acid, (4) on addition of 150 mg/l of oleic acid to the solution containing 40 mg/l of Na,S, (5) on addition of 175 mg/l of sodium dodecyl sulphate, (6) on addition of 175 rngh of dodecylamine. J. Less-Common
Metals,
29 (1972)
THE SEPARATION
OF MONAZITE FROM ZIRCON BY FLOTATION
115
the zeta potential. On the other hand, SDS decreased the positive charge of a monazite surface and displaced the isoelectric point from pH 5.5 to a pH of about 3.8. OLH increased the negative value of the zeta potential over the pH range 3-9 and displaced the isoelectric point from pH 5.5 to pH 4.5. Pre-addition of 40 mg/l of Na,S increased markedly the effect of OLH on the zeta potential but did not affect the influence of SDS or DA on the zeta potential of monazite.
Fig. 2. Zeta potential of zircon as a function of pH. (1) without additions, (2) on addition of 40 mg/l of sodium sulphide, (3) on addition of 150 mg/l of oleic acid, (4) on addition of 175 mg/l of sodium dodecyl sulphate, (5) on addition of 175 mg/l of dodecylamine.
Figure 2 shows the electrokinetic behaviour of zircon at different pH values and on addition of similar amounts of Na,S and collectors. Zircon has an ionic surface in distilled water. Decreasing the pH value causes the negative charge of a zircon surface to decrease until it reaches zero at a pH of about 3.7. Further decrease of the pH increased the positive charge on a zircon surface. At pH values below 2 the zeta potential decreases owing to the compression of the double layer. The mild effect of Na,S and OLH on the zeta potential of zircon is an indication of the adsorption of Sz-, SH-, OL-, and OLH on zircon but not on silicon sites. This is consistent with the strong differences between the isoelectric points of silicon sites and other cationic sites in a given silicate mineral referred to by the author elsewhere’*“. The effects of Na,S on the adsorptive capacity of the minerals tested for anionic and cationic collectors and on their floatability were investigated. To enable a correlation between flotation and collector adsorption to be attempted when the minerals in both types of test received identical preparative treatment, collector adsorption was determined for a sample which had already been subjected to flotation. The results obtained showed that Na,S possesses selective properties in the soap flotation of monazite and zircon (Figs. 3 and 4). In the absence of Na,S, monazite and zircon have nearly equal adsorptive capacities for OLH at any pH value. There was no clearcut region of selective adsorption of OLH by the minerals tested. Also, there was no marked differences between the flotation recovery of monazite and zircon. Addition of 40 mg/l of Na,S markedly affected the inflection points of both J. Less-Common
Metals, 29 (1972)
116
A. M. ABEIDU
Fig. 3. Recovery of (1) monazite, (2) zircon, (3) uptake of oleic acid from solution by monazite, (4) by zircon.
Fig. 4. Influence of the addition of 40 mg/l of Na,S on the floatability and adsorptive capacity of monazite and zircon in anionic collector system using oleic acid (150 mg/l) as collector on : (1) the recovery of monazite, (2) the recovery of zircon, (3) the uptake of oleic acid from solution by monazite, (4) the uptake by zircon.
the adsorption and flotation curves for monazite and zircon, causing them to become rather widely separated (Fig. 4). The abstraction of OLH by monazite and zircon from sodium sulphide solution is highly selective around pH 8.5, in the vicinity of which zircon hardly adsorbs OLH at all and hence scarcely responds to soap flotation. Zakharov et d3 have suggested that Na,S activates both monazite and zircon at feeds of Na,S up to 10 mg/l and that increasing the feed from 10 to 37.5 mg/l causes severe depression ofzircon, leaving monazite flotation unaffected. They further suggest that the active flotation of the minerals is due to a l.>Zfold increase in the amount of attached collector at Na,S feeds up to 25 mg/l and that on monazite the amount of attached collector in the presence of Na,S is three times that on zircon. They conclude J. Less-Common Metals, 29 (1972)
THE SEPARATION
OF MONAZITE
FROM
ZIRCON
BY FLOTATION
117
that the more extensive attachment of collector to monazite than to zircon, and the absence of attachment of SH- ions to a monazite surface, leads to the successful flotation of the latter. However, these conclusions appear to be at variance with the well-known activating action of Na,S on partially oxidized sulfide minerals using an anionic collector (xanthate). The results of the present investigation suggest that the activation of monazite by sodium sulphide is due to the adsorption of S2- and SH- ions and subsequent partial displacement of phosphate sites. An infrared spectroscopy study” of aqueous solutions of oleic acid and sodium oleate has shown that undissociated OLH molecules and OL- ions exist over the pH range 5.2-11.0. The isoelectric point of monazite occurs at a pH of 5.5 and the pK, of OLH is around pH 5.5. Consequently, the mechanism by which Na,S activates monazite, which contains approximately 70% of cerium, and that by which OLH acts as collector may be schematically represented as follows ; :: :CeOH+SH-
= :: :CeSH+OH-
(pH-8)
(1)
: : :CeSH+OL-
= : : :CeSHOL-
(PH- 8)
(2)
:::CeO-+OLH=
:::CeO.HOL-
(PH ‘v 8)
(3)
(PH N 8)
(4)
(PH-8)
(5)
:::PO,+SH-=
:::SH++PO;-
: : :SH+ + OL- = : : :SH.OL
The symbol : : : represents schematically the lattice surface. The fixation of the oleate ions on the newly created sulfide sites (eqns. 4 and 5) is considered to be the only probable form of attachment. The high negative charge of the surface of zircon and the extremely low pH of isoelectric point of silicon sites coupled with their immunity to the influence of sulfide
Fig. 5. Recovery and adsorptive capacity of monazite and zircon in anionic collector system using sodium dodecyl sulphate (175 mg/l) as collector. (1) recovery of monazite, (2) recovery of zircon, (3) uptake of sodium dodecyl sulphate from solution by monazite, (4) uptake by zircon, N.B. Addition of 40 mg/l of Na,S was almost without effect on both recovery and adsorptive capacity of monazite and zircon. J. Less-Common
Metals, 29 (1972)
118
A. M. ABEIDU
Fig. 6. Influence of Na,S (40 mg/l) on the recovery and uptake of dodecylamine (175 mg/l) from solution by monazite and zircon. (1) recovery of monazite in the absence of Na,S, (2) recovery ofzircon in absence and presence of Na,S, (3) uptake of dodecylamine by monazite, (4) uptake of dodecylamine by zircon in absence and presence of Na,S, (5) recovery of monazite in the presence of Na,S, (6) uptake of dodecylamine by monazite in the presence of Na,S.
ions are believed to be responsible for the insensitivity of zircon to sodium sulfide activation. Monazite can thus be activated by Na,S and responds well to soap flotation, whereas zircon does not. The amenability of monazite and zircon to alkyl sulphate and amine flotation is predictable from Figs. 5 and 6. Comparison of Figs. 3-6 reveals that the adsorption curves for SDS and DA are of a different nature from those for OLH. Na,S is without effect on the alkyl sulphate flotation owing to the relatively high pK, of H,S and SHand the extremely low pK, of alkyl sulphuric acid. As can be seen from Fig. 6, Na,S decreases the adsorptive power of monazite for dodecylaminium ions and is without effect on the adsorption of DA on the surface of zircon. It seems that silicon sites have no affinity for HS or S2- but are suitable for the attachment of the positively charged dodecylaminium ions as follows : : : :SiO- +RNH:
= : : :SiO.H,NR
: : :ZrO-+RNHl
= :: :ZrO.H,NR
(PH 2-9)
(6)
(PH 49) (7) The relatively high pH of the isoelectric point of monazite and the absence of silicon sites make the attachment of dodecylaminium ions to its surface rather improbable. Indeed, the adsorptive capacity of zircon for dodecylaminium ions is higher than that of monazite, for which reason it responds much better to amine flotation. CONCLUSIONS
The data obtained show clearly that Na,S possesses certain selective properties which qualify it for use as a regulator in the differential soap flotation of monazite and zircon. The selective action of Na,S on monazite and zircon is a function of the pH J. Less-Common
Metals,
29 (1972)
THE SEPARATION
OF MONAZITE
FROM
ZIRCON
BY FLOTATION
119
and the collector used. The selectivity increases markedly in the order : alkyl sulphate, amine, soap flotation. The relatively low pH of the isoelectric point of zircon and the extremely low pH of the zero charge of silicon sites impede the adsorption of S2- and SH- ions on the surface of zircon. The feasibility of displacement of some phosphate sites in the monazite mineral crystalline lattice by S2- and SH- ions and the relatively high pK, of SH- help the attachment of oleate ions and oleic acid molecules to a monazite surface in sufficient quantities for flotation to take place. Thus, in the presence of Na,S, monazite is markedly activated and the difference between it and zircon in this respect enables it to be successfully separated by soap flotation. REFERENCES 1 W. K. Finn, Progress in mineral dressing, Trans. Internat. Mineral Dressing Congress, Stockhobn, 1957, Almqvist and Wiksell, Stockholm, 1958, p. 404. 2 S. I. Polkin, P. Illie, V. I. Solnyshkin and A. E. Zakharov, Rev. Metal Lit., 24A (1967) 93. 3 A. E. Zakharov, P. IIIie, S. I. Polkin and V. I. Solnyshkin, Rec. Me&l Lit., 24A (1967) 93. 4 A. M. Abeidu, J. Appl. Chem. Biotechnol., 21 (1971) 19-21. 5 A. M. Abeidu, J. Less-Common Metals, 22 (1970) 355-359. 6 J. Iwasaki, R. S. B. Cook. D. H. Harraway and H. S. Choi, Trans. AIME. 223 (1962) 97-108. 7 A. Ya. Zhavoronkova, E. I. Moiseeva, S. A. Shelkova and N. F. Mishin, Soviet J. Non-Ferrous Metals, (English Transl.) 8 (4) (1967) 28. 8 A. M. Abeidu, Indian J. Technol., 9 (1971) 344-346. 9 A. M. Abeidu, J. Mines, Metals, Fuels, 17 (1969) 8G-86. 10 A. M. Abeidu, Nat. Met. Lab. Tech. J. (Jamshedpur, India), 11 (1969) 25-29. 11 S. I. Polkin, G. S. Berger and I. B. Ribazachibili, Tsvetnaia Metallyrgia Tsuetnikh Ytchibnikh Zauedenia, (3) (1968) 6-l 1 (in Russian). J. Less-Common Metals, 29 (1972)
Journal o/’ the Less-Common Metals
Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
THE
SEP~TION
OF MONAZITE
FROM
ZIRCON
BY FLOTATrON
A. M. ABEIDU Laboratory of Metallurgy, National Research Centre, Dokki, Cairo (Egypt)
(Received February 29th, 1972)
The conditions for the separation of monazite from zircon in anionic (oleic acid and sodium dodecyl sulphate) and cationic (dodecylaminium chloride) collector systems using sodium sulphide as regulator have been studied by means of electrokinetic measurements, direct flotation tests, and adsorption determination of the collector. The results obtained indicate that sodium sulphide affects the soap flotation of monazite and of zircon differently, hence it is useful in obtaining a high degree of selective separation. On the other hand, sodium sulphide is without selective action in alkyl sulphate and amine flotation. It seems that SH- and S*- ions are adsorbed preferentially onto a monazite surface with subsequent partial displacement of phosphate sites. Since the pll, of oleic acid is relativeiy high and that of SH- is higher than the pK, of HPOZ-, it is likely that the activation of monazite by sodium sulphide takes place by the attachment of oleate ions to the adsorbed activating S2and SH- ions, leading to the successful flotation of monazite. By contrast., sodium sulphide was shown to exert no influence on the adsorptive capacity for oleic acid and floatability of zircon, presumably owing to the extremely low pH of the isoelectric point of silicon sites.
INTRODUCTION
Monazite (Ce, La, Y, Th) PO, is the chief source of thorium which is receiving considerable attention as a source of atomic energy. Monazite is naturally concentrated in sands because of its resistance to chemical attack and its high specific gravity. It is found in association with other resistant and heavy minerals, such as magnetite (Fe,O,), ilmenite (FeTiO,) and zircon (ZrSiO,). It has been reported that monazite and zircon have varying electrostatic properties and even when a combination of electrostatic and magnetic separation is employed, a satisfactory separation may not be possible’. For both technical and economic reasons the flotation process is attractive and has been used by some investigators2*3 in the concentration of monazite ores. The present paper describes a study of the technical feasibility and mechanism of the flotation separation of monazite from zircon using sodium sulphide (Na,S) as regulator. J. Less-Common
Metals, 29 (i 972)
114
A. M. ABEIDU
EXPERIMENTAL
TECHNIQUES
Reagents were of analytical grade. Reasonably pure natural crystals of monazite and zircon from the beach of the Mediterranean Sea on the side of the mouth of the Nile near Rosetta were used. The crystals were crushed in a porcelain mortar to give a - 100, + 150 mesh fraction for flotation tests and a - 150, + 200 mesh fraction for streaming potential studies. The equipment used for measuring streaming potentials basically resembled that used earlier by the author4. The Hallimond tube used has been described previously ‘. A procedure similar to that described by Iwasaki et ~1.~ was used to determine the adsorption of sodium dodecyl sulphate (SDS) and dodecylamine (DA). The method used for adsorption studies with oleic acid (OLH), described elsewhere’**, gives reasonably accurate results (k 10%) and has the advantage of a high sensitivity of detection, viz., 0.02%‘,*. RESULTS
AND DISCUSSION
The basic studies on the surface properties and flotation characteristics of monazite and zircon were made by electrokinetic, adsorption and floatability measurements. The results obtained are represented graphically in Figs. l-6. As seen from Fig. 1 a monazite surface is slightly charged in distilled water and becomes uncharged at a pH of about 5.5. Decreasing the pH by the addition of HCl increases the positive charge on the surface until it reached a maximum at a pH of 2. Further lowering of the pH decreases the positive charge, presumably because of the compression of the double layer. Increasing the pH causes an increase of the negative charge on the monazite surface. At pH values above 10 the negative value of the zeta potential decreases owing to the adsorption of sodium ions. It was found that sodium sulphide, Na,S, increased whereas DA decreased the negative charge of a monazite surface in the pH range 7-10. At pH values below 7, Na,S and DA were without effect on +I0
oo-
,6
> E
3
-lO7
5 ', a 0 % N
-2o-
-30,
I 2
I 3
! 4 j
Hc$ao.,
b
b
;“,,
”
Fig. 1. Zeta potential of monazite as a function of pH. (1) without additions, (2) on addition of 40 mg/l of Na,S, (3) on addition of 150 mg/l of oleic acid, (4) on addition of 150 mg/l of oleic acid to the solution containing 40 mg/l of Na,S, (5) on addition of 175 mg/l of sodium dodecyl sulphate, (6) on addition of 175 rngh of dodecylamine. J. Less-Common
Metals,
29 (1972)
THE SEPARATION
OF MONAZITE FROM ZIRCON BY FLOTATION
115
the zeta potential. On the other hand, SDS decreased the positive charge of a monazite surface and displaced the isoelectric point from pH 5.5 to a pH of about 3.8. OLH increased the negative value of the zeta potential over the pH range 3-9 and displaced the isoelectric point from pH 5.5 to pH 4.5. Pre-addition of 40 mg/l of Na,S increased markedly the effect of OLH on the zeta potential but did not affect the influence of SDS or DA on the zeta potential of monazite.
Fig. 2. Zeta potential of zircon as a function of pH. (1) without additions, (2) on addition of 40 mg/l of sodium sulphide, (3) on addition of 150 mg/l of oleic acid, (4) on addition of 175 mg/l of sodium dodecyl sulphate, (5) on addition of 175 mg/l of dodecylamine.
Figure 2 shows the electrokinetic behaviour of zircon at different pH values and on addition of similar amounts of Na,S and collectors. Zircon has an ionic surface in distilled water. Decreasing the pH value causes the negative charge of a zircon surface to decrease until it reaches zero at a pH of about 3.7. Further decrease of the pH increased the positive charge on a zircon surface. At pH values below 2 the zeta potential decreases owing to the compression of the double layer. The mild effect of Na,S and OLH on the zeta potential of zircon is an indication of the adsorption of Sz-, SH-, OL-, and OLH on zircon but not on silicon sites. This is consistent with the strong differences between the isoelectric points of silicon sites and other cationic sites in a given silicate mineral referred to by the author elsewhere’*“. The effects of Na,S on the adsorptive capacity of the minerals tested for anionic and cationic collectors and on their floatability were investigated. To enable a correlation between flotation and collector adsorption to be attempted when the minerals in both types of test received identical preparative treatment, collector adsorption was determined for a sample which had already been subjected to flotation. The results obtained showed that Na,S possesses selective properties in the soap flotation of monazite and zircon (Figs. 3 and 4). In the absence of Na,S, monazite and zircon have nearly equal adsorptive capacities for OLH at any pH value. There was no clearcut region of selective adsorption of OLH by the minerals tested. Also, there was no marked differences between the flotation recovery of monazite and zircon. Addition of 40 mg/l of Na,S markedly affected the inflection points of both J. Less-Common
Metals, 29 (1972)
116
A. M. ABEIDU
Fig. 3. Recovery of (1) monazite, (2) zircon, (3) uptake of oleic acid from solution by monazite, (4) by zircon.
Fig. 4. Influence of the addition of 40 mg/l of Na,S on the floatability and adsorptive capacity of monazite and zircon in anionic collector system using oleic acid (150 mg/l) as collector on : (1) the recovery of monazite, (2) the recovery of zircon, (3) the uptake of oleic acid from solution by monazite, (4) the uptake by zircon.
the adsorption and flotation curves for monazite and zircon, causing them to become rather widely separated (Fig. 4). The abstraction of OLH by monazite and zircon from sodium sulphide solution is highly selective around pH 8.5, in the vicinity of which zircon hardly adsorbs OLH at all and hence scarcely responds to soap flotation. Zakharov et d3 have suggested that Na,S activates both monazite and zircon at feeds of Na,S up to 10 mg/l and that increasing the feed from 10 to 37.5 mg/l causes severe depression ofzircon, leaving monazite flotation unaffected. They further suggest that the active flotation of the minerals is due to a l.>Zfold increase in the amount of attached collector at Na,S feeds up to 25 mg/l and that on monazite the amount of attached collector in the presence of Na,S is three times that on zircon. They conclude J. Less-Common Metals, 29 (1972)
THE SEPARATION
OF MONAZITE
FROM
ZIRCON
BY FLOTATION
117
that the more extensive attachment of collector to monazite than to zircon, and the absence of attachment of SH- ions to a monazite surface, leads to the successful flotation of the latter. However, these conclusions appear to be at variance with the well-known activating action of Na,S on partially oxidized sulfide minerals using an anionic collector (xanthate). The results of the present investigation suggest that the activation of monazite by sodium sulphide is due to the adsorption of S2- and SH- ions and subsequent partial displacement of phosphate sites. An infrared spectroscopy study” of aqueous solutions of oleic acid and sodium oleate has shown that undissociated OLH molecules and OL- ions exist over the pH range 5.2-11.0. The isoelectric point of monazite occurs at a pH of 5.5 and the pK, of OLH is around pH 5.5. Consequently, the mechanism by which Na,S activates monazite, which contains approximately 70% of cerium, and that by which OLH acts as collector may be schematically represented as follows ; :: :CeOH+SH-
= :: :CeSH+OH-
(pH-8)
(1)
: : :CeSH+OL-
= : : :CeSHOL-
(PH- 8)
(2)
:::CeO-+OLH=
:::CeO.HOL-
(PH ‘v 8)
(3)
(PH N 8)
(4)
(PH-8)
(5)
:::PO,+SH-=
:::SH++PO;-
: : :SH+ + OL- = : : :SH.OL
The symbol : : : represents schematically the lattice surface. The fixation of the oleate ions on the newly created sulfide sites (eqns. 4 and 5) is considered to be the only probable form of attachment. The high negative charge of the surface of zircon and the extremely low pH of isoelectric point of silicon sites coupled with their immunity to the influence of sulfide
Fig. 5. Recovery and adsorptive capacity of monazite and zircon in anionic collector system using sodium dodecyl sulphate (175 mg/l) as collector. (1) recovery of monazite, (2) recovery of zircon, (3) uptake of sodium dodecyl sulphate from solution by monazite, (4) uptake by zircon, N.B. Addition of 40 mg/l of Na,S was almost without effect on both recovery and adsorptive capacity of monazite and zircon. J. Less-Common
Metals, 29 (1972)
118
A. M. ABEIDU
Fig. 6. Influence of Na,S (40 mg/l) on the recovery and uptake of dodecylamine (175 mg/l) from solution by monazite and zircon. (1) recovery of monazite in the absence of Na,S, (2) recovery ofzircon in absence and presence of Na,S, (3) uptake of dodecylamine by monazite, (4) uptake of dodecylamine by zircon in absence and presence of Na,S, (5) recovery of monazite in the presence of Na,S, (6) uptake of dodecylamine by monazite in the presence of Na,S.
ions are believed to be responsible for the insensitivity of zircon to sodium sulfide activation. Monazite can thus be activated by Na,S and responds well to soap flotation, whereas zircon does not. The amenability of monazite and zircon to alkyl sulphate and amine flotation is predictable from Figs. 5 and 6. Comparison of Figs. 3-6 reveals that the adsorption curves for SDS and DA are of a different nature from those for OLH. Na,S is without effect on the alkyl sulphate flotation owing to the relatively high pK, of H,S and SHand the extremely low pK, of alkyl sulphuric acid. As can be seen from Fig. 6, Na,S decreases the adsorptive power of monazite for dodecylaminium ions and is without effect on the adsorption of DA on the surface of zircon. It seems that silicon sites have no affinity for HS or S2- but are suitable for the attachment of the positively charged dodecylaminium ions as follows : : : :SiO- +RNH:
= : : :SiO.H,NR
: : :ZrO-+RNHl
= :: :ZrO.H,NR
(PH 2-9)
(6)
(PH 49) (7) The relatively high pH of the isoelectric point of monazite and the absence of silicon sites make the attachment of dodecylaminium ions to its surface rather improbable. Indeed, the adsorptive capacity of zircon for dodecylaminium ions is higher than that of monazite, for which reason it responds much better to amine flotation. CONCLUSIONS
The data obtained show clearly that Na,S possesses certain selective properties which qualify it for use as a regulator in the differential soap flotation of monazite and zircon. The selective action of Na,S on monazite and zircon is a function of the pH J. Less-Common
Metals,
29 (1972)
THE SEPARATION
OF MONAZITE
FROM
ZIRCON
BY FLOTATION
119
and the collector used. The selectivity increases markedly in the order : alkyl sulphate, amine, soap flotation. The relatively low pH of the isoelectric point of zircon and the extremely low pH of the zero charge of silicon sites impede the adsorption of S2- and SH- ions on the surface of zircon. The feasibility of displacement of some phosphate sites in the monazite mineral crystalline lattice by S2- and SH- ions and the relatively high pK, of SH- help the attachment of oleate ions and oleic acid molecules to a monazite surface in sufficient quantities for flotation to take place. Thus, in the presence of Na,S, monazite is markedly activated and the difference between it and zircon in this respect enables it to be successfully separated by soap flotation. REFERENCES 1 W. K. Finn, Progress in mineral dressing, Trans. Internat. Mineral Dressing Congress, Stockhobn, 1957, Almqvist and Wiksell, Stockholm, 1958, p. 404. 2 S. I. Polkin, P. Illie, V. I. Solnyshkin and A. E. Zakharov, Rev. Metal Lit., 24A (1967) 93. 3 A. E. Zakharov, P. IIIie, S. I. Polkin and V. I. Solnyshkin, Rec. Me&l Lit., 24A (1967) 93. 4 A. M. Abeidu, J. Appl. Chem. Biotechnol., 21 (1971) 19-21. 5 A. M. Abeidu, J. Less-Common Metals, 22 (1970) 355-359. 6 J. Iwasaki, R. S. B. Cook. D. H. Harraway and H. S. Choi, Trans. AIME. 223 (1962) 97-108. 7 A. Ya. Zhavoronkova, E. I. Moiseeva, S. A. Shelkova and N. F. Mishin, Soviet J. Non-Ferrous Metals, (English Transl.) 8 (4) (1967) 28. 8 A. M. Abeidu, Indian J. Technol., 9 (1971) 344-346. 9 A. M. Abeidu, J. Mines, Metals, Fuels, 17 (1969) 8G-86. 10 A. M. Abeidu, Nat. Met. Lab. Tech. J. (Jamshedpur, India), 11 (1969) 25-29. 11 S. I. Polkin, G. S. Berger and I. B. Ribazachibili, Tsvetnaia Metallyrgia Tsuetnikh Ytchibnikh Zauedenia, (3) (1968) 6-l 1 (in Russian). J. Less-Common Metals, 29 (1972)