Application of Pneumatic Flotation Column in Scheelite Flotation

1.       Brief Description of Scheelite Flotation Method

Scheelite flotation is generally divided into two stages: roughing and cleaning.

The molecular formula of scheelite is CaW04. Due to the presence of calcium in the molecular formula, scheelite roughing is usually carried out at room temperature, mainly using the alkaline medium-fatty acid method. The most commonly used adjusting agent and inhibitor combination is sodium carbonate-sodium silicate, followed by sodium hydroxide-sodium silicate, and sodium carbonate-sodium hydroxide-sodium silicate, etc.

Scheelite cleaning mainly includes room temperature method and heated method (also known as Petrov's method). After obtaining low-grade rough concentrate, heating the slurry for desliming can obtain high-grade scheelite concentrate. Heated flotation has strong adaptability to ore with stable selectivity index, and is a common scheelite cleaning method. Currently, some mines also use room temperature flotation in scheelite cleaning section and have achieved good production results, such as Xintianling scheelite mine, etc.

2.       Comparison Test of Flotation Column and Flotation Machine

Today, we take the comprehensive recovery of scheelite from molybdenum tailings of a certain company as an example to explain the reasons why the inflatable flotation column (hereinafter referred to as flotation column) has better application effect in scheelite flotation.

The chemical composition of scheelite in the ore body is WO 76.82%, CaO 19.89%, Mo 2.99%. The disseminated particle size is mainly fine-grained, of which -0.2~+0.1mm accounts for 8.37%, -0.10~+0.074mm accounts for 17.25%, -0.074~+0.020mm accounts for 43.09%, and -0.020mm accounts for 31.29%. The monomer dissociation rate is 82.39%, the symbiotic scheelite-garnet symbiosis accounts for 4.85% in the associated minerals, the symbiotic scheelite-metal ore accounts for 8.21%, and the symbiotic scheelite and other vein minerals account for 4.55%. Most of the above-mentioned symbiotic minerals are intergrowth type, and a small amount is scheelite enclosing molybdenite, calcite, etc. The particle size of the encapsulated minerals is generally less than 0.03 mm, and it is difficult to dissociate by mechanical methods.

The scheelite plant of a certain company processes molybdenum flotation tailings with a concentration of about 30%, and a fineness of -200 mesh accounts for about 65%, with a WO3 content of about 0.14%. The original production process is as follows (all using flotation machines): the molybdenum flotation tailings flow into the scheelite plant for desulfurization, and then enter scheelite roughing. The desulfurization operation is divided into one roughing and one scavenging, and the scheelite roughing operation is divided into one roughing, three scavenging, and three cleaning. After scheelite roughing, rough concentrate is obtained, which is sent for heated desliming and then subjected to scheelite cleaning. The scheelite cleaning operation includes one roughing, three scavenging, and five cleaning. After flotation, the concentrate is subjected to acid leaching, washing, dephosphorization, filtration, and drying to obtain the final concentrate.

Comparison of Flotation Column and Flotation Machine in Production Site

In order to compare the application effects of flotation column and flotation machine in this mine, a flotation column diversion test was conducted. The test pulp was taken from the rough tungsten concentrate stirring tank at the production site, ensuring that the two types of equipment processed the pulp under the same conditions of original ore properties, reagent system, and flotation concentration, so that the test results can serve as data support for industrial transformation. The results of the test are shown in the table below:

From the results of the diversion test, it can be concluded that the concentrate grade and recovery rate of the flotation column test system are superior to those of the flotation machine, especially the recovery rate has increased by about 20 percentage points, indicating a significant improvement in performance.

3.       Industrial Application of Flotation Column

The production process of the flotation column in the white tungsten selection plant is as follows: the molybdenum tailings flow into the white tungsten selection plant for classification and regrinding, desulfurization, and rough tungsten concentrate. The desulfurization operation includes one rough and one scavenging stage, and the rough tungsten concentrate operation includes one rough, one scavenging, and one cleaning stage. The rough and cleaning tungsten concentrates are obtained from the rough tungsten concentrate, and then sent to the heated tungsten selection, where the desulfurization and rough tungsten concentrate are all treated with flotation column, and the heated tungsten selection uses flotation machine. The production indicators are shown in the table below:

4.       Analysis of Reasons

From the results of the diversion test and the production indicators, it can be seen that the use of inflatable flotation column in the recovery of white tungsten in this mine is significantly better than the flotation machine.

Under the same conditions, the concentrate grade of the flotation column is slightly higher than that of the flotation machine, and the recovery rate has increased by nearly 20 percentage points. Especially after industrial application, although the grade of white tungsten in the original ore has decreased significantly, the flotation column still achieves good production indicators, fully demonstrating the strong adaptability of the flotation column to this white tungsten ore.

We analyze the main reasons as follows:

A,The white tungsten in this ore has a fine particle size distribution, with a proportion of -0.074mm (200 mesh) and below accounting for 74.38%, especially -0.020mm (625 mesh) accounting for 31.29%. In the 50-10 micron size range, the recovery effect of the flotation column is significantly better than that of the flotation machine.

B,The processing capacity of the flotation column per unit volume of pulp is much higher than that of the flotation machine, about three times higher, resulting in more complete recovery.

C,The flotation column uses high-pressure gas to burst and generate bubbles, and the instantaneous burst of high-pressure gas releases heat, while a large number of fine bubbles are generated in the mixing zone (bubble generation zone). The increase in temperature and the generation of fine bubbles can enhance the dispersion of flotation reagents, especially fatty acid-type collectors, which are usually sensitive to flotation temperature and have poor dispersion.

D,The number of bubbles in the flotation column is much higher than that of the flotation machine, resulting in a higher probability of contact between the target minerals and the bubbles.

E,The flotation column uses high-pressure gas to burst and generate bubbles, and the instantaneous burst of high-pressure gas also generates a large number of micro-nano bubbles. The continuous action of bubbles and micro-nano bubbles significantly enhances the kinetic flotation rate constant K. The smaller the diameter of the bubbles, the higher the surface energy, and the longer the residence time in the slurry. Fine bubbles are more likely to penetrate the water film on the surface of hydrophobic particles due to their high surface energy and adhere to the surface of hydrophobic particles. The large number of fine bubbles can create a "bubble bridge" effect, which can enhance the aggregation of hydrophobic particles. This is also the reason why the recovery effect of fine-grained minerals in flotation columns is better than that in flotation machines.

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