On the Moisture Capacity of Iron Ore Concentrates
Abstract Generated abstract
This study examines how the moisture capacity of iron ore concentrates, a factor affecting agglomeration and pelletizing, depends on concentrate properties and fluxing additions. Capillary and maximum molecular moisture capacities were measured for several magnetite and hematite concentrates, then for a representative magnetite concentrate mixed with varying amounts and particle sizes of calcite or slaked lime. Hematite showed the highest moisture capacity among the tested concentrates, while calcite additions produced only minor increases. Slaked lime, especially when finely ground, substantially increased both capillary and molecular moisture capacity and reduced capillary saturation rate, suggesting that lime additions can help process concentrates with elevated moisture content and may improve pellet or granule strength.
Full Text
V. M. VITYUGIN, V. A. PROKHOROVICH
ON THE QUESTION OF THE MOISTURE CAPACITY OF IRON ORE CONCENTRATES
(Presented by the scientific seminar of the Department of General Chemical Technology)
The moisture content and moisture capacity of iron ore concentrates is an important factor determining the effectiveness of agglomeration and pelletizing of these concentrates. For the satisfactory course of the processes of agglomeration and pelletizing, it is necessary to maintain a definite relationship between the values of moisture content and moisture capacity of the materials being processed. This relationship ultimately determines the indicator of the optimum moisture content of the raw material. As a rule, the optimum moisture content of the raw material before agglomeration and pelletizing should not exceed the indicator of maximum molecular moisture capacity.
The moisture content of iron ore concentrates is a consequence of the adopted scheme of ore beneficiation and the subsequent dewatering of the concentrate. The more deeply wet beneficiation is carried out, the more watered the concentrate will be. Under existing schemes for dewatering the cake, its limiting moisture content usually does not exceed the indicator of capillary moisture capacity.
The molecular and capillary moisture capacities of iron ore concentrates are determined mainly by their particle-size composition and hydrophilicity. The more hydrophilic and more finely ground the concentrate is, the greater its moisture capacity, and vice versa. The preparation of iron ore concentrates for blast-furnace smelting is accompanied by fluxing them with limestone, dolomite, or lime. The moisture capacity of fluxing materials usually exceeds the moisture capacity of iron ore concentrates, while the moisture content of the former, as a rule, is lower than the moisture content of iron ore materials. Hence follows the conclusion that it is possible to regulate the moisture capacity and moisture content of fluxed iron ore concentrates by means of fluxing additions.
Experimental Part
Three different iron ore concentrates, calcite, and technically pure slaked lime were used as the objects of investigation. The characteristics of the iron ore concentrates are given in Table 1. The difference among the concentrates in chemical composition consisted in the fact that sample No. 1 was a low-silica ($\mathrm{SiO_2} = 3.5\%$) magnetite, sample No. 2—a high-silica magnetite ...
\((\mathrm{SiO}_2 = 13.5\%)\) magnetite, and sample No. 3—medium-silica \((\mathrm{SiO}_2 = 9.6\%)\) hematite.
Table 1
| Samples of iron-ore concentrates | Iron content, % | Sieve composition, % | Sieve composition, % | Sieve composition, % | Sieve composition, % |
|---|---|---|---|---|---|
| \(+0.1\) mm | \(-0.1 + 0.074\) mm | \(-0.074 + 0.053\) mm | \(-0.053\) | ||
| No. 1 | 65,5 | 0,3 | 5,2 | 9,2 | 85,3 |
| No. 2 | 61,5 | 6,5 | 12,9 | 32,6 | 48,0 |
| No. 3 | 62,4 | 25,8 | 15,1 | 9,3 | 49,8 |
To determine capillary moisture capacity, the previously dried material under investigation was charged in a layer 100 mm high into glass cylinders 25 mm in diameter with a mesh bottom covered with filter paper. The layer of material in the cylinder was compacted under the action of a load weighing 1 kg. The cylinder was then placed in a cuvette with water so that the water level exceeded the lower boundary of the material layer by 1–2 mm, and this level was maintained throughout the experiment. After complete saturation of the material layer with capillary water, samples for moisture determination were taken from the middle part of the cylinder height.
The maximum molecular moisture capacity of the material was determined by the “moist media” method [1]. To carry out this test, the material was used after saturation with capillary moisture.
In some experiments, simultaneously with determining the values of the capillary moisture capacity of the materials, the rate of their saturation with moisture was measured.
First of all, the values of capillary and maximum molecular moisture capacity were established for pure concentrates. The results of these measurements are given in Table 2. As might have been expected, the hematite concentrate proved to be the most moisture-capacious, i.e., the most hydrophilic material. The least moisture-capacious was the comparatively coarse-grained magnetite concentrate No. 2.
Table 2
| Samples of iron-ore concentrates | Capillary moisture capacity, % | Maximum molecular moisture capacity, % | Saturation rate, mm/min |
|---|---|---|---|
| No. 1 Low-silica magnetite | 14,0 | 6,3 | 4,6 |
| No. 2 High-silica magnetite | 13,6 | 5,2 | — |
| No. 3 Medium-silica hematite | 15,6 | 8,7 | — |
Subsequent experiments were carried out with concentrate No. 1, which had shown an average moisture capacity. Before the experiments this concentrate was mixed with various amounts of lime and calcite additions. In addition, a series of experiments was conducted to determine the effect of the coarseness of lime fines.
The results of the experiments to determine the influence of the amount and coarseness of fluxing additions on the moisture capacity of concentrate No. 1 are shown in Table 3. As can be seen from Table 3, calcite slightly increases the moisture capacity of iron-ore concentrates. Thus, even with an addition of 10%
the moisture capacity of the mixture increases, in terms of the maximum molecular moisture index, by only 0.1%, and in terms of the capillary moisture index by 0.4%. This is no accident, since the capillary moisture capacity of pure calcite does not exceed 25% even with finer grinding.
Table 3
| Amount of additive, % | Coarseness of additive, mm | Capillary moisture capacity, % | Maximum molecular moisture capacity, % | Saturation rate, mm/min |
|---|---|---|---|---|
| Slaked lime, 1% | 0.25 | 14.9 | 7.00 | 3.75 |
| Slaked lime, 2% | " | 16.0 | 7.6 | 3.35 |
| Slaked lime, 3% | " | 16.8 | 7.8 | 3.07 |
| Slaked lime, 5% | " | 17.4 | 8.2 | 2.85 |
| Slaked lime, 8% | " | 19.4 | 8.6 | 2.50 |
| Slaked lime, 5% | 1.0 | 16.2 | 7.6 | 3.15 |
| " | 0.5 | 16.6 | 8.0 | 2.60 |
| " | 0.07 | 16.9 | 8.6 | 2.30 |
| Calcite 5% | 0.1 | 14.2 | 6.3 | 3.55 |
| Calcite 8% | " | 14.3 | 6.35 | 3.50 |
| Calcite 10% | " | 14.4 | 6.4 | 3.50 |
Slaked lime, on the contrary, considerably increases the moisture capacity of iron-ore concentrate, and the finer it is, the greater the increase. Special measurements showed that the capillary moisture capacity of slaked lime reaches 150%. With a slaked-lime particle size of less than 0.25 mm, its addition to the concentrate increases the moisture capacity of the mixture on average by 0.7% for each percent of lime in terms of capillary moisture, and by 0.3% in terms of maximum molecular moisture.
It is interesting to note that fluxing additives substantially reduce the rate at which the material becomes saturated with capillary moisture. This indicates a stronger bond of the moisture with the flux materials. Analyzing the experimental data presented above, the following conclusions may be drawn:
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The addition of slaked lime to iron-ore concentrates significantly increases the capillary and molecular moisture capacities of the mixture. This makes it possible to send iron-ore concentrates with elevated moisture content to pelletizing.
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It is desirable to mix into iron-ore concentrates slaked lime that has first been ground to a particle size of 0.2–0.3 mm, since grinding the lime reduces its consumption.
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Pelletizing iron-ore concentrates with the addition of lime should ensure an increase in the strength of green and dried pellets or granules.
REFERENCES
- A. M. Vasil'ev. Investigation of the Physical Properties of Soil. Gosizdat Moldavii, 1952.