Processing these waters entails a considerable environmental improvement

Bentonite slurry is used in construction and civil engineering works during the trench shoring (provisional containment structure) process, for its containment properties in foundation walls before the concrete sets. To this end, the slurry (bentonite suspension in water) must maintain certain rheological properties, which help support the walls during the excavating or drilling process. They also provide cooling functions in the hydrofraise cutting head. 

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The slurry can be used several times, usually three cycles, after which they are renewed. 

Used slurry is diverted to the treatment line, where with the help of a filter press, water is separated from the bentonite cake.

The problem arises once the slurry is used and subjected to the separation process by applying a filter press, in order to reuse the water to generate new slurry. The water, due to the loss of quality it suffers during the construction process, interferes with the proper functioning of bentonite, forming an unstable slurry, which tends to flocculate, and thus loses the necessary properties for application.

Water from bentonite slurry is characterised by high conductivity, usually greater than 8000 μS/cm and a very high pH, Around 12 or more due to the high concentration of Na+ and Ca2+ ions, with values around 400 ppm, respectively. The presence of these ions is primarily responsible for the flocculation of slurry when reusing the filtered water.

Processing these waters entails a considerable environmental improvement, in addition to cutting operating costs by reducing water consumption and the dumping of effluent which, due to the physicochemical characteristics acquired, is not suitable for discharge under current legislation.

The bentonite slurry water treatment process patented by IMDEA Agua comprises the following stages:

• Removal of carbonates by aeration/bubbling with CO2
• Calcium carbonate sedimentation
• Each of these stages is designed and adapted to each situation based on the patented process.

The granting of the patent Process for the treatment of water from bentonite slurry has just been published in the Bulletin of Industrial Property in July 2016.

This technology can be implemented by construction and civil engineering companies, mining sector and engineering companies.