ZLD in pickling waste treatment

A Life Dime plant integrates 3 technologies that have been successfully tested for small and large scales: extraction, crystallization and membrane distillation.

Extraction

The organic solvent is used to separate the Zn during the extraction process.

Crystallization

Fe is recovered through crystallization by separation it from the liquid solution that contains it. It is then transferred to the solid phase in the form of crystals.

Distillation

Membrane Distillation is a thermal separation process, in which only vapour molecules are transferred through a microporous hydrophobic membrane (HCl recovery).

Extraction

An organic phase is used to remove the Zn from the SSL.

The aqueous phase will contain a high concentration of ZnCl2 that will be fully reused by the galvanizing industry itself (fluxing process).

Nonetheless, this solution needs to be occasionally purged producing a small amount of sludge. This should be collected by an authorized waste manager in order to recycle through distillation.

The recycled solvent is reused by the Life Dime process.

Crystallization

A crystallization process generates FeSO4 salts.

These salts are separated from the liquid phase with micron filter bags made of polypropylene.

There is much interest in FeSO4 salts within horticulture and viticulture sectors, for example, and they can be commercialized as a fertilizer.

Distillation

A distillation process undertaken with membrane distillation produces a concentrate composed of water, H2SO4 and FeSO4 that can be reused by the Life Dime solution for its crystallization process.

However, the concentrate must be regularly purged since it will accumulate unwanted compounds (such as metal salts) and the H2SO4 will be increasingly diluted.

The sludge produced once the concentrate is purged must be collected by an authorized waste manager.

Process Diagram

Hydrochloric acid recovery

Results and output

A Life Dime plant allows the regeneration of 99% of HCl (both free and combined) and also 99% of metal salts (mainly Fe and Zn) contained in SPL and SSL, with no additional liquid effluents (ZLD).

 

Nonetheless, occasional purges need to be performed in order to ensure the correct functioning of the overall process. The amount of waste derived from such purges represent 1% of the total flow in the form of strange salts and solvents.

 

The integration of a multiple effect system using distillation membranes for HCl distillation, the first of its kind in the world, offers the following benefits to the overall treatment process:

 

  • · The material used is PVDF film
  • ·  Fully corrosion resistant and has a low cost compared to superalloy
  • ·  Easy to clean with a compact system
  • ·  A multi-effect system that can reduce by 3 times or more the thermal energy involved compared to a normal single distillation unit