Bentonite deposits are normally exploited by quarrying. Extracted bentonite is distinctly solid, even with a high moisture content of approximately 30%. The material is initially crushed and, if necessary, activated with the addition of soda ash (Na2CO3). Bentonite is subsequently dried (air and/or forced drying) to reach the moisture content of approximately 15%.

According to the final application, bentonite is either sieved (granular form) or milled (into powder and superfine powder form). For special applications, bentonite is purified by removing the associated gangue minerals, or treated with acids to produce acid activated bentonite (bleaching earths), or treated with organics to produce organoclays.

Mining sequences

Pre-operational monitoring
Prior to mining vegetation and hydrology studies are conducted. Stockpond designs are developed in order to transform excavated areas into ponds.

Drilling and sampling
Before the actual mining of Bentonite begins, the quality is tested by drilling shallow holes into the deposit and sampling the cuttings for important characteristic.

Soil profiling
A soil profile is developed to aid in reclamation. During reclamation soils are replaced in a similar order to which they were stripped to enhance revegetation efforts. The profile shown above is a typical soil profile found around Wyomimg bentonite deposit.

Topsoil removal
Topsoil and subsoil are removed from the mining area and stockpiled for future reclamation.

Overburden removal
Bentonite is mined on the surface using open pit methods. Overburden is removed in order to gain access to the Bentonite deposits.

Stripping with scrapers
Machines called scrapers carefully remove the layers down to the Bentonite. If the scrapers are not careful, the underlying Bentonite can be contaminated. The overburden layers are usually loosely consolidated, so there is no need for explosives and blasting.

Exposed bentonite
The Bentonite is mined and stockpiled at the mine site. Then, at the mine site, the Bentonite is "field dried." Field drying removes approximately 50% of the moisture, and reduces hauling and final drying costs.

Loading bentonite
Front end loaders then load the Bentonite into trucks, which transport the mineral to stockpiles at processing plants. The stockpiles are separated into several different types and qualities of Bentonite.

Feeding the Bentonite Mill
First, the stockpiled Bentonite is run through a crusher to break the material into small chunks.

Bentonite Mill
Next, the Bentonite is processed through coal or gas fired rotary dryers, in addition to calciners to reduce the moisture content. Control of the temperature in the dryer is important because many of the Bentonite properties can be destroyed if too much heat is applied. As a result of the drying, the Bentonite is only 5-20 percent moisture. The Bentonite product is then pulverized and manufactured into customer specifications. After the processing, the Bentonite is either bagged or shipped in bulk by rail or truck.

Product and qualities

Calcium-Bentonite (non-activated Bentonite): Bentonite that is predominantly occupied by Ca2+ or Mg2+-ions in the intermediate layers.

Activated Bentonite: Bentonite whose initial composition of Ca2+ -ions in the intermediate layer has been replaced with Na+-ions in a technical process (alkali-activation).

Natural Sodium-Bentonite (usually Wyoming-Bentonite, but also found in other locations): Bentonite predominantly occupied by Na2+-ions in the intermediate layers. Ca2+ or Mg2+ -ions can also occur commonly in Na-bentonite in varying concentrations.

Organophilic Bentonite (organoclays): Bentonite whose cations in the intermediate layers have been replaced by polar organic molecules (e.g. alkylammoniumions). They are hydrophobic and can swell in organic solvents.

Acid Activated Bentonite: Bentonite whose structure has been partially dissolved by treatment with acids. Depending on degree of activation, original Ca2+, Mg2+, and Na+ cations are mostly removed, and part of Al, Fe, Mg, Si from the lattice are dissolved. Acid activated bentonite exhibits high surface area > 200 m2/g and large micropore volume.