Bentonite is a sedimentary deposit containing greater than 50% montmorillonite and is volcanic in origin.Bentonite is subject to the federal laws of the 1872 Mining Act. From a commercial standpoint, there are two primary types of natural bentonite, sodium and calcium. Sodium-Bentonite is characterized by its ability to absorb large amounts of water and form viscous, thixotropic suspensions. Calcium-Bentonite, in contrast, is characterized by its low water absorption and swelling capabilities and its inability to stay suspended in water. Each type of bentonite has its own unique applications and is known as the clay of thousand uses.
Zenith has Bentonite applications in metalcasting, cat litter, laundry care, animal health, geosynthetic clay liners for landfills, environmental remediation, industrial wastewater, greenroofs, water treatment and well testing among many others.
Compared to conventional mining operations for coal and other minerals, the mining of bentonite is performed at the surface. Typically the topsoil/subsoil layer is 30 inches in depth. The overburden layer consists of shaley type rock located above the mineral reserve and ranges from 0-50 feet in depth. The bentonite reserves are located below the overburden and range sfrom 2-7 feet thick.
Zenith uses a mining process known as backcasting where reclamation is concurrently done with the mining by using the overburden and soils from subsequent pits to fill in the ones before them. Using this approach, the mine is reclaimed as quickly as possible and “livespreading” the topsoil provides the best seed-bed possible.
Once the bentonite is exposed and cleaned, further testing is done to confirm the grade. In order to reduce the energy usage for drying the bentonite, it is often field dried before it is taken to the plant for processing. Once grade is confirmed the bentonite can be stockpiled on site or transported to a processing facility so that the reclamation process can begin.
The reclamation process begins by replacing the overburden and blending it into the surrounding landscape. After the appropriate grade is achieved, the subsoil and topsoil are replaced in a timely manner, as to maintain the health of the soils. A hybrid tillage system is then used to plant a variety of native seeds into the soil to begin the establishment of native habitat. In this step, our reclamation team is able to create improved seed mixes so that the reclaimed land is a more productive environment for both livestock and wildlife species. In as little as three years, perennial grasses may be established.
Shrubs will often take a greater amount of time to establish themselves. In addition to the seed mixes, our reclamation team can establish water features to benefit livestock and wildlife in subsequent years.
When the vegetation is self-sustaining and can withstand grazing, the reclamation is considered successful. On average reclamation can be achieved in a time-span of five years or less. An addtional 5-10 years needed to allow the native habitat to fully reestablish itself prior to bond release. Through years of experience and study to determine the optimal process for reclaiming land, our reclamation team is able to produce land conditions that are as good or better than the pre-mined environment and are more conducive to the native species needs.