Recycling of double filtration residues

RECYCLING OF RESIDUAL SODIUM CHEMICALS IN THE PRODUCTION OF SODIUM CARBONATE: NEUTREC^® PROCESS

In the case of municipal and hospital waste incineration and where double filtration is used for flue gas cleaning, the RSCs collected at the second filter consist mainly of sodium chloride, sodium sulphate and sodium carbonate. They also contain impurities such as part of fly ash, activated carbon and heavy metals.

As part of the NEUTREC^® process, SOLVAY has developed, patented and industrialised an original technology which makes it possible to produce a brine with a level of purity that allows it to be recycled as a raw material substitute in sodium carbonate production units.

The RSCs are dissolved with a controlled pH and with certain additives. The suspension formed in this way is passed through a filter press which separates out the insolubles: heavy metal hydroxides, activated carbon and fly ash. In this way a raw brine and a filtration cake are obtained.

The raw brine is then passed over activated carbon in order to adsorb any remaining organic components. Final traces of heavy metals are eliminated by passing over ion exchange resins. The perfectly purified brine is now ready to be injected into the sodium carbonate manufacturing process.

The filtration cake, which is the olny ultimate waste, is tipped on an approved landfill site. The total amount is no more than 1 to 3 kg per ton of incinerated municipal waste.

Internal recycling of all the washing and regeneration fluid from the ion exchange resins means that no aqueous effluent is produced, only recyclable brine and the filtration cake.

This technology is implemented industrially at the Rosignano unit operated by SOLVAL^®, a SOLVAY subsidiary.

Other possibilities:

Direct recycling of flue gas cleaning residues (single filtration). 

Recycling of Residual Sodium Chemicals in the manufacturing of sodium carbonate (single filtration).

Valorisation of all the flue gas cleaning residues: REVASOL pilot.