BentoniteEnhancedSoils

_{The Natural Solution to Waste Disposal Environmental Problems}

Bentonite in the Environment: A tremendous amount of waste is now produced, both domestic and industrial, much of it harmful to the environment. Thanks to modern methods of waste separation, recycling and incineration, etc., the remainder can be contained to a certain extent.



Due to recent legislation more attention is now being paid to the installation of waste tips. The main problems associated with waste tipping are the generation of methane gas (a greenhouse gas) and leachate, making it necessary to line and cap the landfill. Rainwater percolates through the waste thus leaching into the groundwater and rivers, whilst gas migrates uncontrolled. Large surrounding areas can become polluted and dangerous as a result.



One sollution offered to prevent uncontrolled gas migration and leachate from coming into contact with ground water and rivers is the installation of a "Controlled Waste Tip". By providing a bentonite seal covering the complete waste tip, i.e. top, sides and base, leachate can then be pumped off for purification and gas can be vented or extracted at controlled points. After capping the "controlled" tip, leachate will no longer occur.

 

B.E.S. (Bentonite Enhanced Soils) as a Seal: In conjunction with the Institute for Land and Water Management Research (ICW) in Wageningen, Netherlands and the waste disposal company V.A.M. at Wijster, an investigation into the feasability of top-sealing of waste tips commenced in 1982. From this study B.E.S. sealing, in comparison with other methods, has emerged very favourably.

 

Principle: Bentonite can, due to its swelling capacity, absorb ten to fifteen times its own volume of water. With a good mixture of soil and bentonite, the voids between the soil particles are filled with bentonite. By means of compression the pore volume is reduced greatly and when water is added, the bentonite will absorb it and fill up the pore volume still remaining. In this way a 100 % water-proof barrier is formed.

The capacity to swell (absorbent capacity) of bentonite is specified with the Enslin test. The Enslin value of Cebogel bentonite is 800 % after only 16 hours and will continue to absorb/swell for at least a further 60 days.

 

Why B.E.S. as a Seal ? :

1. Bentonite is a natural clay. Thus with B.E.S. as a sealant, a material that is environmentally friendly is being used.

2. The natural property of montmorillonite, in absorbing water and releasing it again, is a self-generating, non-decreasing process which has been occuring naturally for thousands of years.

3. Used in a minimum layer thickness of 200mm is capable of following almost all lay-outs above and below ground. The B.E.S. does not harden but remains in a plastic state.

4. The natural property mentioned above shows that B.E.S. is capable of self-sealing. Thus any damage caused as a result of penetration occuring from waste working its way up, roots growing through or rodent holes etc. will be "self repaired".

5. Depending on the soil to be used and the percentage of bentonite addition, a high degree of impermeability, measured in "K values" (Darcy), can be attained. Resulting in multiples of 10^-10 m/s and reaching as low as 10^-12 m/s.

6. A B.E.S. seal is also an economical product.

 

How B.E.S. is Applied: The production of B.E.S. begins with the analysis of the soil to be used (classification and chemical analysis). Following laboratory trial mixes, optimum moisture, maximum dry density and permeability results are obtained.

For top sealing (capping), whereby only rainwater and gas must be impeded, we advise a seal thickness of 200mm.

For basal sealing (liner) we recommend a seal thickness of 300mm. However the percentage of bentonite and seal thickness are both determined by the nature of material to be tipped and the type of leachate expected.

Method of mixing: The bentonite and soil are mixed in a computerised batching plant and transported to the required location for laying and compaction. The batched B.E.S. can be stockpiled and sealed for future use. The quality of the material does not deteriorate during storage.

 



 

On site Q.A. facilities: The mobile batching plant is supported by a Mobile Laboratory with facilities for the sampling and analysis of the host materials and mixed B.E.S. throughout production. Once the B.E.S. is placed and compacted the laboratory can test for relative compaction.