Depressing effect of sodium hexametaphosphate on apatite in flotation of rutile

Journal of University of Science and Technology Beijing Volume 14, Number 3, June 2007, Page 200

Mineral

Depressing effect of sodium hexametaphosphate on apatite in flotation of rutile Ha0 Ding'), Hai L i d ) ,and Yanxi Dengl' 1 ) School of Materials Science and Technology, China University of Geosciences (Beijing), Beijing 100083, China

2) Civil and Environmental Engineering School, University of Science and Technology Beijing, Beijing 100083, China (Received 2006-07-26)

Abstract: The separation of rutile from apatite by flotation and the mechanism of depressing the apatite of sodium hexametaphosphate were studied. The results showed that rutile and apatite could be separated by using alkyl-imino-bismethylenephosphoric acid and sodium hexametaphosphate as a collector and a regulator, respectively. Sodium hexametaphosphate could selectively dissolve calcium ions on the apatite surface, and make calcium ions break away from lattice binding through combining.

Key words: rutile; apatite; sodium hexametaphosphate; flotation; depressing

1. Introduction Rutile is an important mineral in extracting metal titanium and for making titanium white (dioxide) [ 1-21. Natural rutile is an important rutile ore resource in China [3]. Apatite is one of the gangue minerals associated with natural rutile ores, and it has a good deal of influence on raising the grade of rutile concentrate. So it is of remarkable realistic importance to study the mechanism of the separation of rutile from apatite. Flotation is an effective method to separate rutile from the gangue minerals containing apatite. It has been proved that alkyl-imino-bismethylenephosphoric acid (TF,,) is an effective collector for flotation of rutile [4-51, and sodium hexametaphosphate (molecular formula: (NaPO,),) is a common regulator for depressing the minerals containing a calcium cation (such as calcite) [6]. However, the mechanism has not been involved to a great extent up to now. In this article, the separation of rutile by flotation, using TF, and (NaP0,)6 as a collector and a regulator, respectively, was investigated. The emphasis was on the action mechanism of (NaPO,), in the flotation process.

,,

tile was refined. A product with a particle size of 0.043-0.104 mm was obtained by classification in distilled water. They were dried at room temperature and stored as samples. Mineral flotation experiments were carried on in a XFGC-80 type flotation machine, whose volume was 50 mL. A sample of 3.0 g was used each time. Flotation temperature was 25"C, and the flotation time was 2.5 min. The reagents used for experiments were all chemically pure. The water used for flotation was distilled water. The froth products and products remaining in the cell were dewatered, dried, and weighed. The recoveries were directly calculated from the weight of the products. Infrared spectrometry (IR) analysis was done using Fourier infrared spectroscopy, and X-ray photoelectron energy spectroscopy (XPS)analysis was done using KR-ATOS-XSANSOO, more function surface analysis instrument.

3. Results and discussion 3.1. Flotation separation of rutile from apatite

2. Experimental

The influence of TF,,, concentration of on the floatability of rutile and apatite is shown in Fig. 1, and the influence of medium pH is shown in Fig. 2.

Pure rutile minerals were extracted from certain natural rutile ores by using combined gravity and magnetic separation. Apatite originated from China Geological Museum. Then it was crushed, the ironremoved, and then ground in porcelain ball mills. Ru-

It is shown that TF,,, has a strong collecting effect on rutile. Rutile keeps being floated well in acid condition, neutral media and its recovery is greater than 90%. It should be pointed out that TF,,, has a strong collecting effect on apatite also. Although TF,,, has certain

Corresponding author: Hao Ding, E-mail: dinghao@cugb,edu.cn

Also available online at www.sciencedirect.com

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H.Ding et d.,Depressing effect of sodium hexametaphosphateon apatite in flotation of rutile flotation selectivity between rutile and apatite, this selectivity is fairly small. Apparently, TF,,, itself cannot separate rutile from apatite without regulators.

.""

I

&Rutile

--tApatite

6o 50;

t

i

;o

15

1'0

;5

TF,,,/ (mg.L-')

Fig. 1. Effect of TF,,, concentration of on the mineral floatability (pH=6)

Fig. 3. Effect of (NaPO,), concentration of on the minerals floatability (pH=6, TFIl2=15mg/L).

2 min SH 10 mg/L 4 min TF,,, 15 mg/L

O:

4

"

'

6'

'

8'

'

'

10 " 12

PH Fig. 2. Effect of medium pH on the mineral floatability (TF,,,=15 mg/L).

When (NaPO,), is applied in flotation process, the recovery of apatite decreases quickly. It drops to about 20% and keeps constant when the concentration of (NaPO,), is 10 mgL. But the recovery of rutile maintains more than 90%, although, increasing the concentration of (NaPO,),, as shown in Fig. 3. It is (NaPO,), that increases the flotation selectivity between rutile and apatite. So it is concluded that rutile and apatite can be successfully separated by using TFllZas a collector and (NaPO,), as a regulator. The flotation separation of artificial ores, which contain rutile and apatite of 50% respectively, was done following the same experimental conditions and the concentration of reagents as the above experiment. The artificial ores of 1 g were used each time. The experimental procedure and results are shown in Fig. 4 and Table 1, respectively. Table 1 shows that the recovery of TiO, is 76.47% and the concentrate grade of Ti02 increases from 48.32% to 83.27%. Through calculating the quantities of phosphorus in the tailings, the removal efficiency of phosphorus is 85.06% in the flotation process. So it can be seen that the separation results of artificial ores coincide with those of single minerals.

2 min

t

Concentrate

.c

Tailings

Fig. 4. Flotation circuit of artificial ores.

3.2. Mechanism of depressing apatite of sodium hexametaphosphate Sodium hexametaphosphate, that is, (NaPO,),, is a poly-phosphate. Its mechanism of depressing some minerals was traditionally explained from the viewpoint of adsorption, desorption, and deactivation [7-91. Additionally, the research on the depressing effect of other phosphates on the minerals showed that adsorption of reagents is not the key factor, but the influence of reagents on mineral surface [ 101 is.

(1) Infrared spectrum measurement of apatite. The infrared spectra of (NaPO,), and apatite treated with and without (NaP03), are given in Fig. 5 . Polymeric phosphate can be observed from the infrared spectrometry of (NaPo,), (Fig. 5(a)), the characteristic adsorption peak of P-0-P group appears at 1015 cm-' and P=O peak appears at 1290 cm-' [ 11-12]. Although they do not appear in the infrared spectrometry of apatite treated with (NaPO,), (Fig. 5(c)), and the infrared spectrometry of apatite treated with and without (NaPO,), are not obviously different. It is shown that (NaPO,), is not adsorbed on the surface of apatite.

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Therefore, the depression of apatite by (NaPO,), is not

caused by adsorption at the experimental conditions.

Table 1. Flotation experiment results of artificial ores Products Concentrate Tailings Crude ores

Mass fraction / %

Grade (TiO,) / %

44.37

83.27 20.44 48.32

55.63 100

Recovery (TiO,) / % 76.47

23.53 100

anion collector such as TF,,,. Therefore, (NaPO,), depresses apatite through dissolving the cation on the mineral surface.

I

0

I

I

I

I

1

I

3000 2000 1000 Wave numbed cm-I

Fig. 5. Infrared spectra of (NaPO,), and apatite treated with and without ( N m , ) , : (a) (Nm,)(b) ,; apatite; (c) apatite treated with (NaPO,),.

Fig. 6. XPS of apatite treated with and without (NaPO,),: (a) treated without (NaPO,),;(b)treated with (NaPO,),.

(2) XPS measurement of apatite treated with and without (NaPO,),.

(3) Selective dissolving process of (NaPO,), to Ca” on apatite surface.

The XPS results of apatite treated with and without (NaPO,), are given in Fig. 6. The Ca 2p(3/2) binding energy of the apatite surface is 347.30 eV in two cases, and the displacement is zero. This means that the chemical environment of CaZ+on the apatite surface does not change with or without (NaPO,), action, and (NaPO,), does not produce adsorption on the apatite surface through affinity with Ca”.

According to the structure and its complex ability to Ca”, reported by Ref. [6], it is concluded that (NaPO,), can rapidly complex the calcium ion:

The atom concentration of the apatite surface treated with and without (NaPO,), is also measured through XPS (Fig. 6). The change of relative concentration between anion and cation is the following. Not treated: C&,= 46.67/29.62=1.576.

23.72/29.62=O.801, C&,=

Treated with (NaPO,),: C&,= CdCca=47.43/26.28=1.805.

26.30/26.28=1.001,

Because (NaPO,), is not adsorbed on the surface of and C&, mean the apatite, the increases in C&,, decrease of Ca, that is to say, that more cations of surface lattice come into the solution than anions. Obviously, it is the result of selectively dissolving Ca2+by (NaPO,),.The selective dissolution of Caz+lessens active points of surface cations, and lowers the surface electric potential simultaneously, which is the negative

+NazCa2(P0,),+2Na+.

2Ca2++(NaPO3),

Because the stability and water solubility of Na2Ca2(PO3),was very large [6], the calcium ion on the minerals was dissolved in water rapidly. In an apatite solution there exists a dissolving balance (neglecting additional anions of apatite): Ca,(PO,),

+3Ca2++2P0,3-.

Because the dissolving ability of Ca,(P04), is much higher than the dissociation ability of Na,Ca,(PO,),, the stability of NazCaz(PO,), is much higher than that of Ca,(P04),. As a result, not only Ca” in the solution, but also Ca” on the apatite surface has more priority to combination with (NaPO,),. On the other hand, compared with the affinity tendency of PO:-, the surface Ca” is more likely to produce the complex compound with (NaPO,),. This can satisfy Ca-0 pairing of the apatite surface, which is destroyed after PO-: dissolution. (NaPo,), has a very strong complexing ability to Ca2+,and the fixation stability of Ca” on the mineral surface lattice decreases because of producing the complex compound, and it breaks away from the sur-

H.Ding et al., Depressing effect of sodium hexametaphosphate on apatite in flotation of rutile face in the end. Na2Ca2(P03)6,which has high watersolubility, cannot be maintained on the mineral surface. And it comes into solution as soon as it produces. Therefore, the stability of Na2Ca2(P03),affords the conditions to complexing with Ca2+and makes Ca2+ break away from the lattice surface. On the other hand, the water-solubility of the complex compound offers action space and opportunity. The continuous complexing-desorption-dissolving process makes more Ca2*on the surface to be complexed by (NaPO,), and then comes into solution. As the ions from (NaP03), are superior to PO-: during the competition when combining with Ca2+,the dissolving balance (which exists at the same external conditions) of apatite minerals is destroyed. More cations than anions come into the solution because the cations are complexed. Therefore, the depression of apatite is closely related to the selective complexing and dissolution of the calcium ion by (NaPO,),.

4. Conclusions It is shown, by research, that the flotation separation of rutile from apatite can be realized by using TF,,2(alkyl-imino-bismethylene phosphoric acid) as a collector and (NaP03)6 as a regulator, by removing apatite in flotation of rutile. The action mechanism of (NaPO,), studied through infrared spectrometry and XPS showed that (NaPO,), is not adsorbed on the apatite surface, but selectively dissolves Ca2+on the surface. It then lessens the surface cation points and decreases the electric potential. (NaPO,), has a strong selective complexing effect on Ca2+,the complex compound which has very high stability and water solubility is formed in this process. The Ca2+on the apatite surface breaks away from the

203

lattice binding and comes into the solution through complexing. So the depression of apatite is realized by @am),.

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