On the Issue of Deep Beneficiation of Anthracite
Abstract Generated abstract
This study examines the deep beneficiation of fine anthracite intended for electrothermal applications, especially silicon carbide production, where low ash content is required. Using Donets Basin anthracite, the authors compare size classification, density separation, and laboratory flotation with sulfurized kerosene and pine oil across several particle-size fractions. The results indicate that crushing liberates mineral matter and that classification or density separation can substantially reduce ash, while flotation can produce concentrates near 1 percent ash under suitable conditions. However, flotation performance declines sharply with finer grinding because of slime formation, with satisfactory results only when the content of particles below 0.063 mm remains limited.
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On the Issue of Deep Beneficiation of Anthracite
V. M. Vityugin, V. A. Prokhorovich
(Presented by the scientific seminar of the Department of General Chemical Technology)
Fine-grained low-ash anthracite is currently widely used in electrothermal production because of its favorable physical properties and its relative cheapness in comparison with artificial carbon materials. For example, anthracite is widely used for the production of silicon carbide and carbon electrode products.
One of the obstacles to still wider use of finely ground anthracite in these fields is its comparatively high ash content. In terms of chemical composition, electrothermal products must contain a minimum of mineral impurities, which form ash. Thus, in the production of carbon products, according to technical standards, petroleum coke with an ash content of 0,3–0,8%, pitch coke with 0,3–1,0%, and anthracite with 4–8% are used. For the production of silicon carbide, the ash content of anthracite must not exceed 3,5%, and if expensive petroleum coke is eliminated from the process, the ash content of anthracite must not exceed 1,5–2%.
The need to grind anthracite when it is used in electrothermal production opens up possibilities for its preliminary deep beneficiation by the flotation method. However, in the flotation of fine-grained anthracite, certain difficulties are encountered, leading to a sharp deterioration in flotation indices, especially as the depth of beneficiation increases. The present communication gives some results of a study on the flotation of anthracite used for the production of silicon carbide.
For the study, an averaged batch of anthracite from mine No. 67 of the Donets Basin, weighing 3 t and preliminarily ground to 3–0 mm, obtained from the Tashkent Abrasive Plant, was used. Technical analysis of this anthracite sample showed the following results: ash content on dry mass—2,76%, moisture—3,06%, yield of volatile substances on combustible mass—3,05%. Sieve analysis showed the following distribution of ash by size classes:
| Classes, mm | +2 | −2 +1 | −1 +0,5 | −0,5 +0,25 | 0,25 +0,1 | −0,1 |
|---|---|---|---|---|---|---|
| Yield, % | 14,66 | 20,53 | 28,49 | 18,00 | 10,57 | 7,75 |
| Ash content, % | 1,63 | 1,54 | 1,96 | 3,52 | 5,36 | 5,76 |
In the fractional analysis of the initial anthracite it was established:
| Specific gravity fraction | −1,3 | 1,3–1,4 | 1,4–1,5 | 1,5–1,6 | 1,6–1,8 | +1,8 |
|---|---|---|---|---|---|---|
Table 1
Results of flotation of the initial anthracite and of refuse \(1\text{–}0\) mm at various size fractions
| Material | Size, mm | Kerosene consumption, kg/t | Oil consumption, kg/t | Concentrate yield, % | Concentrate ash content, % | Tailings yield, % | Tailings ash content, % | Flotation time, min |
|---|---|---|---|---|---|---|---|---|
| Donetsk initial anthracite | 1–0 | 0.3 | 0.1 | 86.36 | 0.78 | 13.64 | 14.00 | 3 |
| Donetsk initial anthracite | 1–0 | 0.6 | 0.1 | 94.40 | 1.04 | 5.60 | 32.50 | 3 |
| Donetsk initial anthracite | 1–0 | 0.3 | 0.1 | 78.68 | 0.84 | 21.32 | 10.35 | 6 |
| Donetsk initial anthracite | 0.5–0 | 0.6 | 0.1 | 93.00 | 1.03 | 7.00 | 27.60 | 6 |
| Donetsk initial anthracite | 0.25–0 | 0.3 | 0.1 | Flotation does not proceed | — | — | — | — |
| Donetsk initial anthracite | 0.25–0 | 0.6 | 0.1 | 23.80 | 2.09 | 76.20 | 2.98 | 6 |
| Donetsk initial anthracite | 0.25–0 | 3.0 | 0.1 | 49.60 | 1.28 | 40.40 | 6.10 | 6 |
| Donetsk initial anthracite | 0.25–0 | 0.3 | 0.1 | 75.37 | 1.12 | 24.65 | 10.45 | 3 |
| Refuse \(1\text{–}0\) mm | 1–0 | 0.6 | 0.1 | 91.93 | 1.20 | 8.07 | 27.55 | 3 |
| Refuse \(1\text{–}0\) mm | 1–0 | 1.0 | 0.1 | 2.50 | 3.88 | 97.50 | 3.42 | 6 |
| Refuse \(1\text{–}0\) mm | 0.25–0 | 2.0 | 0.1 | 10.20 | 1.50 | 89.80 | 3.75 | 6 |
Yield, % — 7.60 3.20 81.50 5.00 2.70
Ash content, % — 0.45 0.60 0.85 18.35 42.10
From the sieve characteristic of the anthracite it is evident that crushing it to a size of 3–0 mm leads to some liberation of the rock and to its concentration in the fine classes. Even a simple classification of this crushed anthracite, with the aim of removing the most ash-rich fine fractions (less than 0.5 mm), makes it possible to obtain a concentrate with an ash content of not more than 1.75% at a yield of up to 65%. When the anthracite is separated by a specific gravity of 1.6, the yield of light fractions will be 92.3% at an ash content of 0.82%.
A noticeable increase in the ash content of anthracite is observed for classes smaller than 1 mm. It was therefore of interest to test the effect of beneficiation by flotation of this screened class 1–0 mm and of the entire original anthracite after preliminary grinding. Beneficiation was carried out at different material sizes.
The study was conducted in a laboratory flotation machine of the “Mekhanobr” type with a chamber volume of 1 liter. Sulfurized kerosene and an aqueous emulsion of pine oil were used as flotation reagents. The solid-to-liquid ratio in the experiments was taken as 1:4; the air consumption was 0.45 l/min. The flotation results are given in Table 1. As the degree of grinding of the anthracite increases, its floatability deteriorates substantially. Increasing the reagent consumption for the fine classes somewhat improves the flotation results, but the degree of improvement is nevertheless insufficient.
The reason for the low floatability of finely ground anthracite should evidently be sought in the formation of a large amount of fine slime during grinding (1, 2). To confirm this proposition, from a sample of the 1–0 mm class, reground to 0.25–0 mm, before flotation the slime smaller than 0.063 mm was partially or completely removed. Flotation was carried out at a consumption of sulfurized kerosene equal to 1 kg/t and a flotation time of 6 minutes. The remaining flotation conditions were kept the same. It turned out that when the anthracite sample contains up to 5–10% of the slime class, flotation proceeds satisfactorily and ensures the production of a concentrate with an ash content of about 1% at a yield of 90–94%.
When the anthracite contains 15–20% slime particles, the floatability of the anthracite deteriorates and the ash content of the concentrate rises sharply. Even with a high reagent consumption, satisfactory flotation indices are not achieved. An increase in the content of slime particles above 20% leads to the actual cessation of anthracite flotation, even at high reagent consumptions.
LITERATURE
- V. I. Klassen. On the influence of fine slimes on flotation. Mining Journal, No. 10, 1950.
- I. N. Plaksin, V. I. Solnyshkin. Proceedings of Higher Educational Institutions. Mining Journal, No. 11, 1962.