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[ Lime Softening ]

Lime softening is a precipitation technology to remove water hardness (calcium and magnesium salts) applied mainly in large brackish water plants but not limited to that.

The process is usually carried out in up-flow clarifiers where are implemented:

  • pH increasing to shift the carbonates equilibrium to carbonate ions
  • Calcium hydroxide Ca(OH)2

The resulting reactions lead to Calcium Carbonate and Magnesium Hydroxide oversaturation and its subsequent precipitation. In addition, the implementation of coagulant and flocculant dosage can enhance the reduction of suspended solids, barium, strontium and organic substances content.

Unidro developed a dedicated design for clarifier turbine and reaction cone. Our design permits recirculating part of the sludge collected on the clarifier’s bottom to improve flocculation and decrease overall chemical consumption. The turbine also assures an optimal mixing between feed water and all chemical dosage, thus optimizing reaction cone design. All the chemical reactions are completed in the reaction cone before passing into the sedimentation zone for final solid-liquid separation.

Special Applications

Unidro successfully applies this technology also on ZLD plants as a pre-treatment for ZLD reverse osmosis.

In particular, this technology also finds application for Silica removal. Hydrated lime dosage together with Soda ash and coagulant promotes the Silicates precipitation. Very high removal rate can be achieved in warm/hot water condition.