Bentonite is essentially a clay with predominance (75-85%) of the clay mineral montmorillonite (a complex hydrate of aluminum, magnesium and silicon) and containing an exchangeable base — sodium or calcium. Depending on whether sodium or calcium is the dominant exchangeable base, Bentonite is called sodium Bentonite or calcium Bentonite. The former is also called swelling type or (sometimes) true Bentonite and the latter non-swelling type or pascalite or (sometimes) sub-Bentonite. But transitional types between these two are also found in nature. Bentonite is believed to have been formed by the alteration of volcanic ash deposits mostly of Upper Cretaceous age.
USES AND SPECIFICATION OF BENTONITE
We are pleased to inform you that Our Company, Asia Mines and Minerals Development Company (AMMD Co)., is the professional producer and supplier in the field of the mineral product like bentonite of IRAN origin. Our bentonite uses and specification categorized as below:
1. Oil well drilling
Sodium bentonite is used as an additive to the drilling mud to the extent of 20-30% depending on the drilling conditions and the quality of bentonite. Drilling mud serves to lubricate and cool the rotary cutting bits and also to bring the chips and powders up from the borehole. The purpose of adding bentonite is threefold:
(i) It should increase the viscosity of the drilling mud.
(ii) It should increase the water suspension of mud.
(iii) It should seal the wall of the hole to prevent fluid loss.
(iv) It should condition the wall rocks to prevent caving.
Approximately 15 tons of bentonite is required for drilling 1000 m. of well.
The whole system of mould-making, melting of metals, casting of the melt in mould, solidifying the cast metal to produce an object in the form of the mould, and final dressing and finishing of the object is called foundry. Moulds may be of two types:
(i) Those made of some metal (e.g., zinc) in which case the mould is called “die” and it is permanent; the casting operation is called “die casting”. (ii) Those made of sand which is called “sand mould” or simply “mould”, and they are generally of the “use-and-throw” kind. The casting operation is called “sand casting”.
A sand mould (hereinafter referred to as mould) for solid cast is made with moist well-bonded sand rammed into the desired pattern by hand or machine, and is suited to casting of metals or alloys. Bentonite is used as a binding agent in casting of both ferrous and nonferrous metals, but more particularly iron. Plasticity when wet, and fusion are the key criteria. High plasticity ensures good binding power, while high fusion point is necessary to ensure that the molten metal/alloy cast does not melt it. Both sodium and calcium types of bentonite can be used.
The purpose is to render a porous surface impermeable with a view to both preventing fluid loss through percolation and preventing caving of wall rock during excavation and drilling. Examples are sealing of water tanks, dams, canals, water wells etc. So, sodium bentonite, being highly impermeable, is preferred. The Indian industries specify some parameters, the important ones of which are: swelling capacity 16-20 ml; gel time instant to 5-7 minutes; gel index 35-45; base-exchange capacity 65-70 milli-equivalents per 100 gm; green compressive strength 8-9.5 psi. However, bentonite is not suitable where the water level is fluctuating. As long as it is submerged under water, it absorbs water, swells and plugs the pores. But as soon as it is out of water, it begins to dry up, shrink and crack.
Bentonite is highly objectionable in the raw material mix for whiteware because due to its high water absorption and high swelling power, it increases the filter pressing time for the raw material mix during mould preparation, and only a very small quantity (less than 1%) is sometimes added to the raw material mix for whiteware, mainly with a view to improving plasticity. But, sodium bentonite is used in the glazing mixture. The semi-finished ceramic bodies are dipped in the glaze and fired at 100-13000C. The glaze should be deposited on the surface of the body uniformly, and for this purpose, it is necessary that the ingredients of the mixture do not settle down but remain in suspension for a long time. The role of bentonite is to help in this by virtue of its high dispersion.
5. Refractories and abrasive wheels
In alumina refractories which are otherwise not plastic, bentonite is used as a binder for imparting green strength. For the same reason, it is also used in crucibles and abrasive wheels. Fe2O3 and TiO2 are objectionable because, when exposed to high operational temperatures to which the refractories are exposed, they may combine to form low-melting iron-titanate glass causing blisters on the refractory body and consequent increase in porosity. High green strength of bentonite is a necessary criterion for use in both refractories and abrasive wheels.
6. Pelletizing of iron ore
Loose fines of very small particle size (less than 325 mesh) of iron ore that cannot be sintered are formed into pellets. To the iron ore fines, 0.5-3.0% bentonite is added as a binder. Coke breeze and some flux (limestone) may also be added. The mixture is placed in cones, drums or discs, out of which discs are relatively more flexible with regard to types of ore and they can be controlled better. A disc pelletizer is a rotating inclined flat plate table. The particles gradually coalesce first, into very small pellets, which go on taking more and more particles and keep enlarging in size till they attain specified sizes. Water is sprayed as required. These are called green pellets, and the operation is called balling. The control is effected by changing the angle (20-800) and the rpm. of the disc (+8) of the disc. The green pellets are then heat treated at a temperature of above 12000 C – generally around 13150C – in grate kilns, followed by air cooling with a view to obtaining necessary strength.
7. Cosmetics and pharmaceuticals
In both applications, the purpose is to make a paste. Bentonite increases viscosity and also, it is non-toxic and harmless. It is especially suitable for use in the therapeutic intestinal absorbent preparation. Liquid bentonite (1-2% concentration) containing its minerals absorbs toxins and bacteria responsible for various types of intestinal infections and, being inert, it passes through the body undigested after delivering mineral nutrients. In naturopathy, it is used in mud packs. Due to its non-toxicity and high absorption, it is can be applied for a smoothening effect in skin diseases. The therapeutic use of a type of clay believed to be bentonite was in vogue amongst the aboriginal people in many countries since centuries.
8. Detergents and soaps
Sodium bentonite is the constituent of many detergents used in UK, USA, and Germany for scouring textiles. The role of bentonite is to absorb the dirt particles through the exchange of cations. Besides the type of bentonite, swelling capacity, fineness of size, pH and content of grit particles are important criteria. The industries specify 10 ml swelling capacity, (-) 240 mesh size, neutral to a slightly alkaline solution (pH 8-9) and freedom from grit. The sodium type of bentonite and the swelling capacity ensure good cation-exchanging and adsorptive capacities. Fine size means the longer duration of the suspension and larger availability of surface area for adsorption. Acidic or strongly alkaline solution may corrode the textile and grit will tend to damage the threads while scouring. Bentonite is used in certain soaps to the extent of 25 percent. Bentonite is effective in a purification of sewage and turbid water. Here again, the criteria are its base-exchanging capacity, fine particle size with large available surface area and ability to remain in suspension for a long time.