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3PC flotation column flotation fine gold in low grade tailings

I. Overview

The treatment of flotation tailings is a very interesting topic in the field of mineral processing today. This is because these abandoned resources are both potential resources available and an environmental pollution problem. Thousands of tons of flotation tailings are piled up and discharged today. Complex ore requires flotation to over-grind the ore, so the discharge of flotation tailings is constantly increasing, resulting in substantial loss of useful components. It is recommended that different “in situ” processes be used to recover lost mineral particles from old tailings dams or newly discharged flotation tailings. Valuable metal mineral tailings distributed coarse fraction, but mainly in the fine fraction. The loss of fines is mainly due to the poor effect of flotation of fine-grained minerals of less than 10 μm. The processes for treating these tailings include hydrometallurgical processing and flotation (conventional flotation and flotation columns) for tailings dam stacking tailings and new tailings.

The process of recovering useful components by flotation column flotation continues to grow steadily in many different industrial processes. The main features of the flotation column are low investment, low operating cost, high automatic control and high mineral processing index. However, industrial applications of tailings using flotation columns are not numerous and are not familiar to everyone.

The flotation column is a reactor consisting mainly of a capture zone and a foam zone. The purpose of the trap is to adhere the hydrophobic particles to the bubbles, which primarily serve as transport and foam enrichment. The minerals that have fallen off the foam are returned to the capture zone, and then into the foam zone, in turn, staying at the interface between the slurry and the foam, leaving the flotation column at any time. The flotation column in this paper is a modified flotation column designed to improve mass transfer rate and capture capacity. The flotation column sorts the mineral particles that fall off the foam zone (the third product) and uses a secondary flushing system between the feed zone and the foam zone. This flotation machine and often

Compared to the linear flotation machine, it can produce high-grade concentrates (see Table 1).

Table 1 reported 3PC mineral flotation column
Mineral type
Details and results
Chile's copper industry companies Andina and El Teniente
Concentrator copper sulfide ore flotation
3PC flotation column as flash rough selection; copper concentrate grade is higher than the final concentrate grade of the plant (about 40% copper grade)
Chilean Copper Company Copper Sulfide Mine Andina
Concentrator flotation coarse concentrate (grinded and unground)
3PC flotation column for selection; higher concentrate grade than conventional flotation column (about 30% copper grade)
Zinc- lead sulfide ore
3PC flotation column is used for rough selection of coarse concentrate; higher concentrate grade than conventional flotation column
Fluorite ore
3PC flotation column is used for rough selection and selection; concentrate grade cafe>95%, conventional flotation column can not obtain such high grade
Gold ore
3PC flotation column is used for rough selection and selection; production of gold concentrate; concentrate gold grade is higher than current gold concentrate grade
Calcareous ore
3PC flotation column for rough selection and selection, the effect is obvious

It is well known that energy transfer under high intensity pulping (HIC) conditions can improve flotation recovery, concentrate grade and microparticle dynamics. So far, many theories have been proposed to explain the phenomena occurring in the HIC process, such as carrier or self-supporting flotation through agglomeration between fine particles and medium particles; dispersion of the agent increases the adsorption amount of the collector ; generation of fine bubbles And cleaning the surface.

The purpose of this paper is to demonstrate the results of a modified flotation column (3PC) for recovering gold-bearing minerals from copper-gold flotation tailings under HIC conditions. Whether it is new or stockpiled flotation tailings, the number is very large in many countries, so the recovery of these lost fine minerals has important economic significance. This work provides the results of a continuous test study using a 3PC flotation column.

Second, the test

(1) Materials

The tailings were taken from two different concentrators with similar processes near Copiapo, Chile. A small-scale experimental study was conducted on the sample 1 after the collection, and both samples were subjected to semi-industrial tests and industrial tests.

1. Tailings 1

Tailings 1 is a low-grade copper-gold ore flotation tailings (gold grade 0.15-0.4 g/t), the dissociation of gold is very low, and the copper grade is also very low (<0.2% Cu). Mineralogical studies show that the main minerals are chalcopyrite, bornite, calcite, magnetic iron ore, feldspar and gold. The distribution of gold in different fractions is shown in Figure 1. As expected, gold particles are distributed in coarse and fine fractions.

Figure 1 Distribution of gold in different grain sizes

2, tailings 2

Tailings 2 are taken from the tailings of the flotation of the crudely selected gold plant (gold grade 1 to 1.3 g/t). Most of the gold particles in this ore sample dissociated, partially in contact with pyrite, followed by copper minerals. Particle size analysis showed that 62% of gold was less than 26 μm (50% of gold was less than 10 μm).

(2) Small-scale test method for high-intensity slurry flotation

Tailings 1 was collected within 12 h, with a collector (SF-114, SF-623 and SF-554) of 42 g/t, a mixture of 9g/t of each foaming agent (DF-250, MIBC and pine oil) The syrup is adjusted under the conditions of the pharmacy (selection practice). The sample was filtered, washed, dried, weighed, and the sample was shrunk into a small sample of 908 g. The solids content of the slurry in the flotation cell was approximately 32%.

Before the HIC, the flotation was first placed in a 3L Denver flotation machine for 3 minutes to ensure the adsorption of the collector. The pH was adjusted to 6.5 with lime. Four baffles made of acrylic material were then installed in the same flotation cell to produce HIC in a turbulent state. The energy delivered is controlled by a voltmeter and ammeter.

The 2L slurry was slurried at a stirring speed of 1400 r/min for 25 to 100 s to produce an energy output of 0.5 to 4 kW/h·m 3 .

A concentrate was obtained every 15 s with a flotation time of 10 min, a stirring speed of 1000 r/min and a constant slurry volume. The concentrate and tailings samples are then filtered, dried and weighed, and the gold grade is analyzed by atomic absorption. The standard blank test was carried out in a 2L flotation tank for 1.5 min, with a blade; impeller speed of 1000 r/min (without baffles), pH 7.5, solids content of 32%, and the same amount of medicinal application.

(3) Flotation column

The improved three-product flotation column (3PC) has a diameter of 5 cm and a height of 5.8 m, a foam zone height of approximately 0.5 m (fluctuating between 0.3 m and 0.7 m) and a transition zone height between 30 cm and 90 cm. fluctuation. Details of the operation of the 3PC flotation column and the experimental results obtained from the flotation of different minerals can be found in other papers.

The 3PC flotation column separates the foam zone from the capture zone. Falutsu et al. first applied this flotation column under laboratory conditions to determine flotation recovery and foam flow rate. Rubinstein also described a design similar to the flotation column design, but did not give specific test results.

The differences between the improved flotation column and the conventional flotation column are as follows:

1) There is a secondary enrichment zone or transition zone between the ore supply and the rinse water;

2) The foam sorting zone is located below the foam zone at the top of the flotation column and below the selected zone or foam zone, with the falling off trap and the third product.

The conventional flotation column (CC) used in this work is the same as the 3PC flotation column, except that the upper part is not improved. On-site industrial testing was carried out after a bypass was introduced at the final tailings. Each flotation test lasted 6 h after 30 min of process equilibration.

The flotation efficiency is measured by the sorting parameters of gold (concentrate grade and enrichment ratio). The operating parameters studied were cross-section slurry speed, air flow and flush water volume. A small amount of collector (isopropyl xanthate) and a foaming agent (Dowfroth 1012) were added to enhance the hydrophobicity of the ore and form a thicker and more fluid foam.

(IV) HIC-3PC flotation column flotation test

The HIC pretreatment flotation test was performed only on the ore sample 1. HIC is used in a cylindrical vessel with 4 baffles with an effective volume of 2L and a stirring strength of 1400 r/min, which ensures an amount of 2 kw/h·m 3 during the test residence time. Output (under optimal test conditions). This container is placed in front of the 3PC flotation column to pretreat the ore, as shown in Figure 2.

Figure 2 Schematic diagram of the improved 3PC flotation column

Third, the results and discussion

(1) tailings sample 1

The effect of energy transfer on concentrate recovery in the HIC process is shown in Figure 3. The energy of the recovery peak corresponds to 2kw/h·m 3 , as revealed by the microscopic photograph, when fine gold adheres to the surface of chalcopyrite and porphyrite and medium-sized gold particles in the first minute. Their flotation speed is greatly accelerated (Figure 3).

Figure 3 Effect of HIC strength and flotation time on flotation of metal containing ores
(pH: 6.5, collector 42g/t, foaming agent 27g/t)

Carrier flotation (collection of gold and pyrite) and self-support flotation (aggregate of medium and fine gold) occurred during the sorting process. The authors have reported similar test results for this method.

In high-speed shearing and flotation, the main relevant parameters are slurry turbulence, collector concentration (hydrophobicity) and foaming effect. For particularly low grade gold mines, the foaming effect is very important.

Another factor that affects the selectivity of flotation is the nucleation of bubbles on the ore particles or in the flocculation voids during HIC. When HIC is sucked into the slurry by the air, the bubbles begin to form and adhere to the hydrophobic ore particles, which facilitates the flotation of the minerals.

1. Experimental study on flotation of HIC flotation column

The operating parameters were changed to study the sorting performance of the 3PC flotation column, such as the feed cross-section velocity (Fig. 4), the flush water 2 flow rate (Fig. 5), and the air flow rate (Fig. 6). The test results obtained by feeding the ore under HIC conditions and under conventional agitation were compared.

Figure 4: Feeding slurry cross-section velocity to 3PC flotation column flotation gold mine
The effect of sorting enrichment ratio (gold grade 0.15～0.4g/t)
(Air cross-section flow rate is 1.56 cm / s, cross section of flushing water 1
The flow rate is 0.29 cm/s, and the flushing water 2 has a cross flow rate of 0.20 cm/s.
â– -HIC mixing; â–¡- routine mixing
Figure 5 Washing water 2 cross-sectional flow rate to 3PC flotation column flotation gold mine
Sorting and enrichment ratio (gold grade 0.15～0.4g/t)
(Air cross-section flow rate is 1.56 cm / s cross section of flushing water 1
The flow rate is 0.29 cm/s, and the flow rate of the slurry into the slurry is 0.95 cm/s.
â– -HIC mixing; â–¡- no HIC mixing

As expected, the optimum cross-sectional parameter values ​​for the slurry and air of the flotation column, ie the residence time and turbulence of the slurry in the flotation column, are the determining factors. Washing water 2 can reduce the entrainment of gangue fine mud, which is mainly caused by the bias water flow of the flotation column. Therefore, the transition zone and its length are very important for the 3PC flotation column. The concentration of pulp in this area is less than that of the capture zone suitable for rapid flotation of bubble/hydrophobic minerals.

The comparison of the test results of conventional flotation column and 3PC flotation column flotation gold under HIC as pretreatment conditions is shown in Fig. 6. All the test results show that the grade of the 3PC flotation column flotation concentrate is higher than that of the conventional flotation column flotation concentrate. However, the high recovery rate of conventional flotation is due to the large amount of medium ore.

Figure 6 Air flow rate for CC (conventional) flotation column and 3PC flotation column (mine slurry pretreated by HIC)
The enrichment ratio effect of flotation of low grade metal ore (gold grade 0.15 to 0.2 g/t).
(The cross-section velocity of the mine is 0.95 cm/s, and the cross-flow velocity of the washing water 1 is 0.29 cm/s.
Flushing water 2 cross-sectional flow rate is 0.20cm / s)
â– -HIC mixing; â–¡- no HIC mixing

Compared to conventional flotation columns, 3PC flotation columns can always produce high grade concentrates. As a result, most of the lost gold minerals can be returned using the HIC-3PC flotation column concentrate and then directly into the roughing loop or combined with the final concentrate.

2, tailings 2

The purpose of this test was to confirm the performance of the 3PC flotation column in a more advantageous system where the gold grade is higher and the mineral has been completely dissociated. The test results shown in Figure 7 verify the previous test results and also confirm that in the absence of HIC pretreatment conditions, high grade concentrates can be obtained under higher kinetic conditions. The best test result is a 15% gold recovery with a gold grade above 160 g/t and a gold enrichment ratio of 120.

These results prove that the improved 3PC flotation column is a high enrichment ratio, high selectivity flotation column, even more refined than the conventional flotation column in the flotation plant (gold grade) ~90g/t) is even higher.

Figure 7 Air cross-sectional flow rate for 3PC flotation column flotation metal ore
(gold grade 1 ~ 1.3 g / t) when the enrichment ratio
The 3PC flotation column is the most efficient when the air cross-sectional flow rate is approximately 1.6 cm/s. When the air flow rate is less than 1.6cm/s, the recovery rate is relatively low, and when the flow rate is large, strong turbulence can be seen in the trapping zone, and all the sorting parameters are reduced. For the third product, the gold grade was very low in all tests and could be thrown away with the tailings.
Fourth, some final considerations
(1) HIC
The test results show that HIC pretreatment is very effective for small flotation test and continuous flotation test. The sorting parameters of HIC pretreatment (gold enrichment ratio) are higher than those without HIC pretreatment.
Concentrated microscopy analysis showed that the first is the larger particles of gold, then the single or carry fine-grained gold minerals, and finally the very fine-grained gold that is born on chalcopyrite and porphyrite.
At the highest transfer energy, desorption occurs between the ore particles due to friction, which stabilizes the flotation of the gold particles.
This work and other work results confirm these mechanisms applicable to gold mineral flotation, namely:
1) a high flotation rate (Fig. 3 herein), especially when the fine gold itself is agglomerated or carried by a sulfided mineral;
2) Typical grade-recovery curve;
3) highly realistic flotation parameter values;
4) High concentrate grade (Figure 6 in this article).
The extent of HIC impact depends primarily on the particle size distribution of the precious metal, the hydrophobicity of the mineral, and the amount and manner of total transport energy.
The adhesion process between the particles when the coarse particles and the fine particles collide with sufficient energy may be reversible. Fine-grained ore particles have large specific surface area, shear force and interfacial energy. Therefore, after a short time of HIC, fine particles are easily attached to the surface of coarse particles. This seems to be similar to the phenomenon in which the slime is covered with coarse particles as a carrier.
There are many reports on the effective sorting of minerals when hydrophobic agglomeration or attachment occurs. Examples of this are ultrafine particle shear flocculation flotation, carrier flotation, and emulsification flotation. Hydrophobicization of the ore particles and formation of flocs under strong agitation are the main related issues in this paper. The separation mechanism of these processes is actually the separation of hydrophilic particles and hydrophobic flocs.
(2) 3PC flotation column flotation
The 3PC flotation column can be regarded as a classification column. The performance of the flotation column mainly depends on the hydrophobicity, particle size (dissociation particle size) and washing water action (two-stage washing water) of the ore particles. Therefore, the medium-grained hydrophobic ore particles have a fast flotation rate and will quickly leave the foam and enter the flotation concentrate. Due to the different gold content (contact angle), the medium ore with poor hydrophobicity is not trapped by air bubbles, or is entrained or wrapped with gangue mud as a falling material (third product).
The high efficiency of the 3PC flotation column can be explained by the fact that in the CC flotation column, some materials are always in a circulating state (see Figure 8). Therefore, some of the product that has fallen off the foam stays at the pulp/foam interface, and then a portion of it returns to the foam and a portion is discharged as tailings. The returning foam is again detached from the foam, and a new cycle begins again. This part is mainly composed of medium ore with low grade or medium ore entrained and wrapped with gangue mud. Because this part of the mine must be discharged from one port of the flotation column, it does not enter the concentrate to reduce the concentrate grade, or it is discharged as tailings, thus losing the recovery rate (the tailings amount is large, the loss will be large) . The third product of the 3PC flotation column can be thrown off according to its grade, or it can be recycled to the rough selection, or returned to the grinding closed circuit, or returned to the classification (de-sludge) operation.

Figure 8 Flow characteristics of mineral and gangue mineral particles in CC conventional flotation column
In the conventional flotation column, due to the presence of low-grade detached materials, the enrichment is relatively low, but the recovery rate is high (the middle mine returns to the concentrate). These phenomena indicate that the 3PC flotation column has a higher enrichment ratio than the CC flotation column. The top of the 3PC flotation column capture zone is a foam zone that has not been cleaned by by-products and has not returned (Figure 9). Therefore, the physical properties, solid content and grade of this area remain constant. The flotation column operates under constant slurry concentration, viscosity, water head pressure, and gas content parameters.

Figure 9 Flow characteristics of useful minerals, medium ore and gangue minerals in a 3PC flotation column

Due to the high selectivity of the 3PC flotation column and sorting, it can be used under various conditions. Regardless of the quality of the ore, the enrichment ratio of the 3PC flotation column depends on the number of hydrophobic ore particles dissociated in the system. This allows the 3PC flotation column to handle uneconomical, low grade tailings. For a flotation system, pretreatment of the feed HIC is necessary, which allows very fine useful mineral particles to form flocs that are more conducive to floating.

V. Conclusion

The improved 3PC flotation column has a higher enrichment ratio than the conventional flotation column. The gold thrown away from the tailings can be recovered by flotation using a 3PC flotation column under HIC-assisted conditions. The enrichment ratio fluctuates between 50 and 120 depending on the treatment of the ore processing agent, the gold grade, the dissociation of the gold mineral, the HIC pretreatment of the ore and the cross-sectional flow rate parameters. The selective separation of the product (third product) that has fallen off the foam avoids the return of mineral particles, which often reduce the concentrate grade in conventional flotation columns. In the 3PC flotation column, there is no recycling material, so you can save a selection. The HIC treatment in front of the flotation column is a very effective pretreatment method, which can improve the selectivity of minerals and improve the flotation kinetics. As a result, fine gold can form flocs and be recovered by carrier flotation or self-support flotation. .

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