Bentonite
Hydrous aluminium Silicate containing small amounts of alkaline earths. (Mg, Ca)O, Al2O3.5SiO2, nH2O (where n is equal to about 8). Bentonite are very fine grained clays. They vary in colour from cream to olive green. Bentonite shows conchoidal or sub-conchoidal fracture; can be easily cut with knife into thin shavings. It shows waxy lustre on freshly cut surface and are soapy to feel. Bentonite is an important naturally occurring clay of great commercial importance. Based on water absorbing qualities in industry, bentonite are known as swelling and non-swelling types. The swelling types absorbs large quantities of water, swells enormously in the process and remains in suspension for a long time in dilute water dispersions. The non-swelling absorbs water slightly more than ordinary plastic clays. It does not swell much and settles rapidly in dilute suspensions. There are all gradations between two types. The swelling type is highly colloidal and known as sodium montmorillonite bentonite, whereas non-swelling types are calcium montmorillonite bentonite. The swelling property is reversible, i.e. the bentonite can be dried and re swelled again and again.
Key Specifications
| Moisture at 105° | 11.17% |
|---|---|
| Specific gravity | 2.52 |
| Liquid limit | 546 |
| pH30°C | 9.20 |
| Gel value | 60 |
| Swelling index | 28.5 ml |
| Base exchange capacity meg/100 gm | 87.36 |
| Viscosity: (a) 600 rpm | 176 |
| (b) 300 rpm | 166 |
| Filter loss | 20 ml. (max) |
| Exchangeable Ca++ ion | 0.43% |
| Gel formation index | 9.0 to 10.5 |
| Viscosity | Viscometer dial reading 600 RPM 30 min. |
| Yield Point | 16 per 100 (3 x Plastic Viscosity) |
| Filtrate | 13.5 c.c. (max) |
| Wet screen analysis | 40 % (max) residue on U.S. sieve 200 |
| Moisture | 12 % (max) |
| pH | 7.5 to 9.0 |
| (a) 150 micron IS Sieve | 97 minimum |
| (b) 75 micron IS Sieve | 90 % minimum |
| Viscosity at 30° C(in centipoise) | Apparent - 15 minimum |
| Specification | Grade-A |
| Loss on drying % by weight | 5.0 (min) |
| pH 12.00 (max) | 9.0 to 10.5 (max) |
| Fineness (Dry) | 25 (min) |
| a)To pass through 150 micron IS sieve % by weight | 97 (min) |
| b)To pass through 75 micron IS sieve % by weight | 90 (min) |
| c)Fineness wet through 45 micron IS | 95 |
| Calcium Oxide replaceable Ca% by wt. min. | 0.7 |