Effect of Clays on the Moisture Content of Sand after Filtration
Abstract Generated abstract
This study examines how clay content affects the vacuum filtration and subsequent air drying of fine-grained quartz sand intended for silicate production. Laboratory experiments compared original sand, partially washed sand, and nearly clay-free sand using a Büchner-type filtration setup under constant residual pressure, followed by short periods of room-temperature air drying. The results indicate that clay has little effect on residual moisture immediately after filtration but greatly increases filtration time, while it strongly limits the effectiveness of air drying. For sand beneficiated to about 5% residual clay, satisfactory dewatering to the required moisture level was obtained with a sand layer no thicker than 3 cm, 11 seconds of filtration, and two minutes of air drying.
Full Text
INFLUENCE OF CLAYS ON SAND MOISTURE AFTER FILTRATION
S. A. Babenko, V. M. Vityugin, N. T. Bolotkina
(Presented at the scientific seminar of the Department of General Chemical Technology)
Meeting the needs of silicate plants for high-quality quartz raw material under year-round mining and wet sand beneficiation is complicated by its dewatering. The most acceptable method for dewatering fine-grained sands is filtration. The presence of clay in the sand will have a substantial effect on the filtration process. Since such data are absent from the literature, we carried out the present study. The object of the study was sand, the particle-size composition of which is given in Table 1. The sand washed free of clay (class — 0.02 mm) consists of 95% quartz; a large
Table 1
Particle-size composition of the sand
| Classes, mm | +0.28 | −0.28 +0.20 |
−0.20 +0.14 |
−0.14 +0.071 |
−0.071 +0.02 |
−0.02 +0.0 |
|---|---|---|---|---|---|---|
| Yield, % | 0.40 | 8.66 | 45.88 | 25.27 | 1.70 | 18.39 |
part of it is colored by iron hydroxides. For the filtration experiments we used the original sand, sand partially washed free of clay (clay content 5.10%), and sand practically completely washed free of clay.
The filtration apparatus consisted of a Büchner funnel with built-up walls up to 15 cm high. The funnel was inserted into a thick-walled flask, from which air was pumped out by a vacuum pump. The residual pressure in the flask was maintained at the level of 50 mm of mercury. A cotton-fabric filter was placed in the funnel, onto which sand with water was loaded. The filtration time was counted from the moment the pulp was loaded until the first dry patches appeared on the surface of the sand. The thickness of the water layer above the sand in all experiments was constant and equal to 2 cm; the thickness of the sand layer was 5 and 3 cm.
For a 5 cm layer of sand containing a variable amount of clay, the residual moisture after filtration, as can be seen from Table 2, changes only slightly. The filtration time increases sharply with increasing clay content. For pure sand it is 2 sec, while for sand with 18.39% clay it is almost 70 times greater.
To reduce the moisture content of the sand after filtration, it was additionally dried by drawing room air through it at a temperature of
Table 2
Dependence of sand moisture on clay content during filtration
| Clay content, % | Filtration time, sec | Sand moisture, % |
|---|---|---|
| — | 2 | 24.60 |
| 5.10 | 20 | 26.21 |
| 18.39 | 138 | 27.12 |
Table 3
Dependence of the moisture of sand with a variable amount of clay on the time of air drying
| Drying time, min | Sand moisture, % at clay content | Sand moisture, % at clay content | Sand moisture, % at clay content |
|---|---|---|---|
| — | 5.10% | 18.39% | |
| — | 24.60 | 26.21 | 27.12 |
| 0.5 | 14.34 | 14.86 | 19.76 |
| 1.0 | 10.14 | 14.74 | 18.99 |
| 2.0 | 8.95 | 14.38 | 17.48 |
| 5.0 | 8.11 | 13.21 | 17.27 |
18°C through a layer of sand. The time of air drying of the sand ranged from 0.5 to 5 min. As can be seen from Table 3, only in sand free of clay did the moisture content fall below 10% and amount to 8.95% at a drying time of 2 min. A further increase in the drying time proved to be of little effectiveness.
Under practical conditions of beneficiation, the residual clay content in the sand can be brought to 5%. The moisture content of the sand after dewatering should not exceed 10–11%. To establish an optimal dewatering regime satisfying this requirement, a special series of experiments was carried out. These experiments established that satisfactory dewatering of the beneficiated sand is achieved when it is filtered in a layer no more than 3 cm thick for 11 sec, followed by two-minute air drying.