BENEFITS

     ▪ Recycles 80-95% of used or spent acid, resulting in reduced
       acid consumption and treatment
     ▪ Rejects metals at 95%, allowing baths to be used without
       need for dumping
     ▪ Eliminates need for concentrated acid waste treatment and
       disposal
     ▪ Lowers by half the energy requirements in anodizing baths


KEY FEATURE

     ▪Patent pending "one-piece spacer technology allows for rapid
      and efficient mass transfer

     ▪Use of natural gravity flow to achieve separation of acid and
      contaminants and constant flow rates to membrane stack


OTHER FEATURES

     ▪ Uses (5.4% in volume) water to remove contaminants to
       central waste treatment or metal recovery
     ▪ Fully automatic and continuous operation
     ▪ Chemical resistant membranes that last up to five years for  typical applications
     ▪ Acid feed filtration


APPLICATIONS

Diffusion dialysis technology is used in the following industrial applications:
     ▪ Maintenance and recycling of HNO₃/HF for etching baths
       used in stainless steel processing
     ▪ Reclamation of H₂SO₄ and HCl for etching steel
     ▪ Reclamation of H₂SO₄ for anodizing processes
     ▪ Regeneration of battery acids
     ▪ Recovery of H₂SO₄/HNO₃ and H₂SO₄/HCl for etching non-
       ferrous

The technology is not suitable to handle acids in concentrations higher than 40%. In some instances, due to formation of metal complexes (such as zinc chloride), the separation of acid and metal ions are not possible. In addition, the technology is not designed to handle feed acid temperatures above 130ºF (40ºC).

The membranes require occasional replacement every three to five years, depending on the applications, and process requirements.

Exergy’s Diffusion Dialysis (DD) is a state-of-the-art technology that uses ion exchange membranes to recycle used or spent industrial acids. The membranes are installed in single or multiple stacks that is supported in a plate and frame structure. Exergy’s patent pending “one-piece” membrane spacers creates compartments with appropriate cell distances for optimum diffusion. Counter-current streams of spent acid and deionized water alternate through the cells. Free acid is transported from the spent acid stream into the deionized water stream. This stream (diffusate) is recovered acid for reuse in the process. The metals in the feed spent acid are rejected, and are carried as the dialysate, creating a waste stream for metal recovery or treatment.


SYSTEM COMPONENTS AND OPTIONS

Exergy’s DD systems are modular; skid- mounted, and may be fully automated. The system includes high-quality, heavy-duty components:
     ▪ Automated level controls for storage tanks
     ▪ Automated flow meters for feed streams
     ▪ Acid pre-filtration
     ▪ Membrane stack

Exergy’s DD skids can be customized with optional components, and custom DD systems can be provided to meet special plant requirements. Typical options include:
     ▪ Materials of construction
     ▪ Heat exchangers
     ▪ Ion exchange system to produce deionized water for the DD process
     ▪ Additional feed and discharge storage tanks

Simple System configuration illustrates passage of acid through ion selective membrane material and rejection of metal salts. Diffusate is the recovered acid product that is recycled. Dialysate is the water carrying metals salts to wastewater treatment or recycling.