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Flotation of gold-containing arsenic pyrite

When dealing with arsenic gold ore, gold recovery often depends on the ability to float arsenic pyrite. The main purpose of this test is to determine the optimum conditions for the preparation of arsenic pyrite ore and flotation.
The following gold-containing arsenic ores have been studied:

FeAsS 2.2%; FeS 2 0.6%;

SiQ 71%; (CaO+MgO) 8.2%.

According to the different behaviors of arsenic pyrite in grinding, stirring and flotation, experiments were carried out.
In order to ascertain the degree of oxidation of arsenopyrite during the grinding process, 2 kg of ore was ground to 82%-0.074 mm, using a closed steel and ceramic grinding machine, respectively in an aqueous medium, soda solution and Grinding in a lime solution.
The results show that when grinding with a ceramic grinding machine in a weakly alkaline (pH < 9.0) lime and soda solution, the oxygen consumption does not exceed 50% of its original concentration (9.2 mg / liter). At this time, arsenic in the solution The content is 1~2 mg/L. In a more alkaline (pH > 9.6) solution, the oxygen consumption increased to 85-90%, while the arsenic concentration increased to 10-14 mg/L (see Table 1).

Table 1 is a liquid phase analysis of the slurry after grinding with a steel and ceramic grinding machine.
Drug
pH
Ceramic grinding machine
Steel grinding machine
As
O 2
As
O 2
No added pharmacy
8.00
0.40
6.50
0.25
2.50
CaO
9.50
1.00
4.00
0.50
2.00
10.30
9.00
1.00
0.80
2.00
11.00
10.20
1.00
0.80
2.00
Na 2 CO 3
9.60
2.00
5.00
1.50
2.00
10.10
13.00
2.50
8.00
2.00
10.30
14.00
2.50
8.00
2.00

From the viewpoint of the steel mill, the oxygen requirement is about 80% in all the solutions to be studied. However, the arsenic content in the soda solution was 8 mg/l. At this time, the concentration of arsenic in the lime medium is generally small (about 0.8 mg/liter).
In a flotation machine, a solution of different alkalinity caused by lime or soda oxidizes ore having a fineness of 82% to 0.074 mm. The liquid-solid ratio at this time was 1.5:1, and the temperature was 25 °C. Air was fed into 1 liter of slurry at a rate of 25 liters per minute. This carbon dioxide is pre-purified by the alkali. The arsenic content in the solution was measured with a colorimeter.
The results shown in Figures 1 and 2 show that when the ore is highly neutral and weakly alkaline (pH > 9.5), the concentration of arsenic in the solution is significantly increased, reaching 18 mg / liter in soda medium. And in the lime medium it is 26 mg / liter.

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In the study of the planktonic capacity of arsenic pyrite (using pentyl xanthate 150 g/ton, pine oil 50 g/ton), the test was carried out using a laboratory flotation machine with a volume of 8 liters. Figure 3 shows the results of the test. When lime grinding media mill manufactured with copper, arsenopyrite flotation speed of the slowest. Only when the slurry is inflated for 40 minutes can a better flotation effect be obtained.

If grinding with a ceramic grinder, it only takes 20 minutes to inflate, and the flotation of arsenopyrite can achieve the same effect.
If grinding in soda media, the flotation rate is the fastest.
The results of these tests also prove that arsenic pyrite is not sufficiently oxidized during preparation operations and is also a reason for its low phytoplankability under production conditions. Therefore, the soda solution is the best medium for preparing the ore before the flotation (that is, using a steel mill to grind in this solution, the oxygen concentration is also quite large).
In order to prove this assertion, special experiments were carried out.
The steel mill is equipped with a fixed component solution. The weight ratio of steel ball to solution is 6:1.5. After the mill was rotated for 40 minutes, the oxygen content was measured.
The test results in Table 2 demonstrate that most of the oxygen dissolved in the water is consumed in the oxidation of metallic iron in the mill. In an alkaline lime solution and in a caustic soda solution, the oxygen consumption is 80 to 98% of its original concentration.

Table 2 Effect of carbon and solution pH on the degree of oxygen absorption by iron
Test number (No)
Condition and dosage
Remaining amount of O 2 in the solution after grinding (mg/L)
pH of the solution
Oxygen consumed (%)
1
water
9.20
6.40
-
2
Non-pharmaceutical grinding
1.80
7.90
80.50
3
Grinding in lime medium
1.20
10.80
87.00
4
0.20
11.20
97.80
5
0.20
11.80
97.80
6
0.10
12.20
99.00
7
1.40
12.00
84.80
8
Add NaOH grinding
1.00
12.80
89.10
9
0.60
13.20
93.50
10
0.20
13.60
97.80
11
Add NaHCO 3 grinding
3.50
8.20
62.00
12
4.00
8.40
56.50
13
4.00
8.40
56.50
14
Adding Na 2 CO 3 grinding
6.80
10.10
26.00
15
7.20
10.50
21.70
16
7.00
10.90
23.90
17
6.50
11.40
29.40
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In the soda solution, the amount of oxygen consumed by the oxidation of metallic iron does not exceed 22 to 25%.
Thus, because during the preparation of floating mineral slurry, soda can play a beneficial role in the -, it is that the metallic iron as sodium carbonate inhibitor grinding circuits to ensure there is a higher concentration of dissolved oxygen. This promotes sulfide minerals, including arsenopyrite, which is better oxidized prior to flotation. However, the arsenic concentration in the soda medium is always higher than the arsenic concentration in other solutions, whether during the grinding process (see Table 1) or in the flotation machine (see Figures 1 and 2). When the pH is the same). This - the facts show that carbonate ions can also play a significant role in the surface structure of the oxidized arsenopyrite.
The author of this paper believes that under the conditions of flotation, the sulfide mineral is oxidized and a corresponding thiosulfate complex cation (Me 2 S 2 O 3 ++ ) is formed on the surface. Its two positive charges are neutralized by hydroxide anions. In other words, the following reaction occurs on the surface of the oxidized sulfide mineral:

2MeS+2O 2 +H 2 O ←→Me 2 S 2 O 3 (OH 2 ) (1)

In the presence of the collector (A'), an exchange effect occurs on the surface of the mineral, resulting in the formation of the corresponding compound, which is hydrophobic.

Me 2 S 2 O 3 (OH) 2 +2A'←→Me 2 S 2 O 3 A 2 +2OH' (2)

However, when arsenic pyrite is oxidized, the complex formed on the surface is not neutralized by the hydroxide anion, but is neutralized by the anion of trivalent arsenic.

2FeAsS+3.5O 2 ←→ Fe 2 S 2 O 3 (AsO 2 ) 2 (3)

The anion of arsenic is replaced by hydroxide ions only when the solution alkalinity is continuously increased (see Figure 1).

Fe 2 S 2 O 3 (AsO 2 ) 2 +2OH'←→Fe 2 S 2 O 3 (OH) 2 +2AsO 2 (4)

This means that not only hydroxide anions, but also trivalent arsenic anions can be used as collectors in the flotation of arsenopyrite.

FeS 2 O 3 (AsO 2 ) 2 +2A'←→Fe 2 S 2 O 3 As+2AsO 2 ' (5)

The test results show that when the pre-oxidized arsenopyrite is treated with butyl xanthate, arsenic can be precipitated in the solution.
In soda media, when butyl xanthate is stirred with ore, the arsenic content (mg/L) increases as follows:
Stirring pH: 7.5 pH: 10.5
(neutral medium) (soda medium)
No xanthate 1.2 30
After adding xanthate 1.2 40
Therefore, only use a strong collector (this collector can have both hydrogen hydroxide and arsenic properties), or add arsenic that can be removed from the surface of the oxidized arsenopyrite. In the case of pharmaceuticals, effective flotation of arsenic pyrite can be achieved.
Soda solution has a great practical childlike meaning. If carbonate ions are present in the solution, arsenic can be removed from the surface of the arsenopyrite at a lower pH (see Table 1).
Since the oxidation of arsenopyrite in a closed mill depends on the amount of dissolved oxygen, the higher concentration of arsenic in the soda solution can only be the result of the exchange reaction.

Fe 2 S 2 O 3 (AsO 2 ) 2 +CO 3 ′′→Fe 2 S 2 CO 3 +2AsO 2 ' (6)

The interaction of arsenopyrite with the anion of the collector occurs over a wide pH range.

Fe 2 S 2 O 3 CO 3 +2A'←→ Fe 2 S 2 O 3 A 2 +CO 3 ′′ (7)

Therefore, under these conditions (as indicated by the test), the planktonic capacity of arsenopyrite will be significantly improved (see Figure 3).
Another reason for the good effect of soda is that the carbonate anion can both remove arsenic from the surface of the oxidized arsenopyrite and continue to react with the anion of the collector on the surface of the arsenopyrite.
At present, the process system for preparing flotation pulp has been adopted by a concentrating plant for treating gold arsenic ore by a flotation process. As a result, the recovery rate of arsenite is increased by 13.2%, and the recovery rate of gold is increased by 5.5. %.
Conclusion 1. Soda has a good effect on the flotation of arsenic pyrite. The reason is that sodium carbonate is a resisting agent for metal iron oxidation, which can keep the dissolved oxygen in the grinding circuit at a higher concentration. This is necessary to oxidize the sulfide mineral prior to flotation of the sulfide mineral.
The carbonate anion removes arsenic from the surface of the oxidized arsenopyrite and continues to interact with the anion of the collector.
2. The above-mentioned pharmaceutical conditions for using the soda solution in the grinding circuit have been applied under industrial conditions, so that the process index of the gold selection plant is significantly improved.

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