Activation of Bentonite Clays Used in Pelletizing Iron Ore Concentrates
Abstract Generated abstract
This paper examines the use of bentonite clays as plasticizing additives in pelletizing iron ore concentrates, focusing on how overdrying and surface hydrophobization reduce swelling, structure formation, pellet quality, and pelletizing rate. The authors argue that preliminary hydration, including treatment in water vapor, can activate bentonite without the added cost and technological complexity of chemical activation. Experimental data for Makharadze and Cherkassy bentonites show increased swelling capacity, reduced optimum bentonite consumption, and improved wet pellet strength after hydration. The study recommends drying bentonite only to a residual moisture content of at least 5 percent, with the upper limit determined by maximum hygroscopicity.
Full Text
ACTIVATION OF BENTONITE CLAYS USED IN PELLETIZING IRON ORE CONCENTRATES
V. M. Vityutin, I. N. Lansman, T. N. Somova
(Submitted by the scientific seminar of the Department of General Chemical Technology)
In the granulation of iron ore concentrates, bentonites are most often used as a plasticizing additive. The bentonite introduced into the charge, however, is ballast in subsequent metallurgical processing. The main reasons for the increased consumption of bentonite in pelletizing iron ore concentrates are the low quality of the bentonites and the short contact time of the bentonite with the moist cake. A deterioration in the quality of bentonite clays is often observed when they are dried with hot flue gases in mine drying-and-grinding installations, accompanied by complete dehydration of the clay and hydrophobization of the surface of the clay particles due to adsorption of flue gases and air during cooling of the dry material. This substantially slows the processes of swelling of the bentonite and structure formation in the pore suspension, leads to deterioration of pellet quality and to a decrease in the pelletizing rate. A reduction in the addition of bentonite to the pelletized charges can be achieved by activating the bentonite. At present, both in the Soviet Union and abroad, work is being carried out to improve the quality of bentonites by the action of sodium salts [1, 2] and other additives [3], and also by replacing bentonites with other materials [4]. Chemical activation of bentonites is associated with a considerable increase in the cost of the additive and with complication of the technology for preparing bentonite powders.
Taking into account the positive experience of activating clays by treatment with water vapor in ceramic production [4], it is advisable to use this principle in preparing bentonite powders for pelletizing. Treatment of clay with steam promotes more intensive dispersion and complete hydration of the particles, better processing of the clay, and more uniform—
uniform distribution of moisture in it.
Special experiments on holding dry bentonites in air saturated with water vapor established a 3–4-fold increase in the capillary mobility of water in a layer of powder after such treatment. The effect of hydration of bentonites on their technological properties is clearly illustrated by the data in Table 1.
Table 1
| No. | Bentonites | Activation | Swelling capacity | Swelling moisture, % | Optimum bentonite consumption, % of charge | Strength of wet pellets, kg/pellet |
|---|---|---|---|---|---|---|
| 1. | Makharadze | none | 5,20 | 413 | 0,80 | 1,100 |
| 2. | Same | hydration to \(W = 8,0\%\) | 8,35 | 662 | 0,50 | 1,300 |
| 3. | Cherkassy | none | 3,04 | 220 | 1,50 | 0,900 |
| 4. | Same | hydration to \(W = 6\%\) | 4,34 | 314 | 0,95 | 1,200 |
Thus, it is advisable to dry bentonite to a residual moisture content of no less than 5%. The upper moisture limit for dried bentonite is the value of maximum hygroscopicity. Preliminary hydration of bentonites promotes activation of the clay and substantially reduces bentonite consumption in the pelletizing of magnetite concentrates.