Bentonite is a naturally occurring clay formed from the weathering of volcanic ash, primarily composed of montmorillonite, a type of smectite mineral. Known for its unique properties such as high water absorption, swelling capacity, and viscosity, bentonite is widely used across various industries, including oil drilling, steel manufacturing, and foundry applications. There are several grades of bentonite tailored for specific industrial needs, including OCMA bentonite, API bentonite, and specialized forms for the steel and foundry industries.
OCMA Bentonite
OCMA bentonite refers to the grade of bentonite that meets the specifications of the Oil Companies Materials Association (OCMA), which is often used in drilling fluids for shallow oil and gas wells or water well drilling. This type of bentonite acts as a viscosifier and filtration control agent in drilling muds, helping to stabilize boreholes, cool and lubricate the drill bit, and transport drill cuttings to the surface. OCMA bentonite is valued for its moderate swelling capacity, good gel formation, and ability to reduce fluid loss.
API Bentonite
API (American Petroleum Institute) bentonite is a higher-grade bentonite that meets stricter requirements, especially for deep well drilling. It is more refined and has a higher yield point and lower fluid loss than OCMA bentonite. API bentonite plays a critical role in high-pressure drilling environments, where maintaining the integrity of the borehole is crucial. It is extensively used in both onshore and offshore drilling operations. The higher quality of API-grade bentonite ensures better performance in complex geological formations.
Bentonite for the Steel Industry
In the steel industry, bentonite is primarily used in the pelletizing of iron ore. Finely ground iron ore particles are mixed with bentonite and rolled into pellets, which are then fired in a furnace to produce hard, spherical pellets used in blast furnaces or direct reduction processes. Bentonite acts as a binder in this process, improving the mechanical strength of the pellets and ensuring they maintain their shape during handling and transport. Its role is critical in achieving the high compressive strength needed for efficient steel production.
Bentonite for Foundry Applications
Foundry-grade bentonite is used as a binding agent in the preparation of moulding sands. When mixed with sand and water, it forms a cohesive and moldable mixture that retains the shape of the mould during the metal casting process. The clay imparts strength and plasticity to the mould, allowing for intricate designs while maintaining thermal stability. Sodium bentonite is often preferred for this purpose due to its superior swelling and bonding capabilities. Foundry bentonite also contributes to improved mould reusability and cleaner casting surfaces, reducing defects in the final product.
The main uses of bentonite are for drilling mud, binder (e.g. foundry-sand bond, iron ore pelletizer), purifier, absorbent (e.e. pet litter), and as a groundwater barrier. As of around 1990, almost half of the US production of bentonite was used for drilling mud.
| Property | Specification |
|---|---|
| Yield point | 16 m3/tone (min) |
| Water loss | 15ml (max) |
| Moisture | 10% (max) |
| Residue on ASTM sieve No: 100 (dry method) | 2 w.t % (max) |
| Residue on ASTM sieve No: 200 (water method) | 2.5 w.t % (max) |
| Property | Specification |
|---|---|
| Viscometer Dial, 600 rpm | 30 (min) |
| Yield Point/ Plastic Viscosity Ratio | 3 (max) |
| Filtrate Volume | 15 ml (max) |
| Residue Greater than 75 µm | 4%w (max) |
| Property | Specification |
|---|---|
| Wate absorption (plate test method) | 600%w (min) |
| Moisture | 6%w (max) |
| Residue on ASTM sieve No:325 | 20%w (max) |
| Property | Value |
|---|---|
| Chemical composition | Sodium bentonite |
| Gelling (after 24 hours) | 26-30%w3 |
| Swelling factor (2g) | 26-34cm3 |
| pH | 11-Aug |
| Methylene blue absorption | 75%w (min) |
| Moisture | 10%w |
| Sinter point | 1100 (0°C) |
| Loss on Ignition (LOI) | 9%w2 |
| Green compressive strength | 750-950 g/cm22 |
| Green Tensile strength | 17-20 g/cm2 |
| Residue on ASTM Sieve No.200 | 7-10%w |
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