Determination of the Wettability of Fine-Grained Minerals
Abstract Generated abstract
This paper proposes filtration rate as a practical indicator of wettability for fine-grained minerals, where direct contact angle measurement is difficult and capillary impregnation methods may give poorly reproducible results. Treating mineral pores as capillaries, the author argues that changes in contact angle alter capillary counterpressure and therefore the volume of water passing through a mineral layer under fixed conditions. Experiments with ilmenite treated with oleic or humic acid show measurable changes in water filtration rate, suggesting that comparative filtration through a standardized mineral charge can be used to assess reagent-induced changes in mineral wettability relevant to flotation.
Full Text
S. A. BABENKO
DETERMINATION OF THE WETTABILITY OF FINE-GRAINED MINERALS
(Presented by the scientific seminar of the Department of OKhT)
One of the methods that makes it possible to judge the preparedness of a mineral surface for flotation is the measurement of contact angles of wetting. The latter can be measured relatively easily for coarse-grained minerals. In the case of fine mineral grains, as occurs with placers, measurement of the contact angle becomes more difficult.
The method proposed by Z. V. Volkova [1] for determining the wetting angle for powders, based on their impregnation under the action of capillary forces, poorly reproduces the results of measurements in parallel experiments.
As a measure of the wettability of minerals one may take the filtration rate, characterized by the amount of water that has passed through a layer of minerals per unit time.
Taking the pores of minerals to be capillaries, one may write that the height of rise and the depth of lowering of the liquid in them will be equal to
\[ H = \frac{2\sigma \cos \Theta}{qDr}, \tag{1} \]
where \(\sigma\) is the surface tension of the liquid at the interface with air;
\(\Theta\) is the contact angle of wetting of the minerals, measured through the liquid phase;
\(D\) is the density of the liquid;
\(r\) is the capillary radius;
\(q\) is the gravitational constant.
With equality of all the terms entering into formula (1), but with different values of \(\Theta\), determined by the degree of wettability of the minerals, the influence of capillary pressure on the filtration rate will be different.
It is evident that if minerals are well wetted by water, then the angle \(\Theta\) will be small; \(\cos \Theta\) will increase, which will lead to an increase in the height of water rise in the capillary. The pressure exerted in this case will oppose the pressure that ensures filtration of the liquid through the pores of the minerals.
A decrease in the hydrophilicity of minerals will reduce the counterpressure to filtration, and the amount of liquid that has passed through the mineral layer will increase.
By treating one and the same mineral charge with various reagents used in the flotation process, it is possible, from the amount of filtrate that has passed through a specified mineral layer constant for all experiments, to judge wettability.
The procedure for experiments to determine mineral wettability by filtration was as follows.
A mineral charge (30 g), thoroughly washed free of sludge, was placed in the Gintsvetmet apparatus [2] and subjected to filtration with distilled water under a specified head. Under identical conditions the experiment was repeated three times, and each time the amount of filtrate that had passed through the mineral layer was recorded.
Table 1
Rate of filtration of water through a layer of ilmenite treated with various reagents
| Name of reagents | Filtration rate, ml/min | Change in filtration rate relative to pure minerals |
|---|---|---|
| — | 36.9 | 1.0 |
| Oleic acid 300 mg/l | 47.5 | 1.29 |
| Same 600 mg/l | 52.5 | 1.42 |
| Humic acid 330 mg/l | 28.0 | 0.76 |
The interaction of minerals with reagents was carried out by shaking, for 5 minutes, a 30 g charge in a flask with a specified amount of oleic or humic acid.
The experimental data given in Table 1 indicate the possibility of evaluating mineral wettability from the rate of filtration of water through their layer.
LITERATURE
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Z. V. Volkova. Study of the effect of adsorption on particles of an aqueous fluorite suspension on wettability as a method for developing optimal flotation conditions. Mineral Raw Materials, No. 7, 1934.
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E. E. Sergo, B. A. Bun’ko. Testing, control, and automation of technological processes at concentrating plants. Ugletekhizdat, 1957.