Provide process engineering services and a due diligence review for a vendor-supplied HCl purification system, as well as provide insight and recommendations on incorporating the system into existing facility operations at an Australian mining site.
The client, a specialty engineering company based in Australia that specializes in ion exchange systems, contracted Process Engineering Associates, LLC (PROCESS) to provide process engineering services and a due diligence review for a vendor-supplied HCl purification system, as well as provide insight and recommendations on incorporating the system into existing facility operations. The client is considering use of a commercial recovery system to purify hydrochloric acid (HCl) that has been used to regenerate an ion exchange system. The system is to be applied to an Australian mineral mine site currently undergoing infrastructure upgrades. The scope of the evaluation by PROCESS included a review of the chemistry and thermodynamics of the process, review of the heat and material balance, an evaluation of the proposed process equipment and materials of construction, and providing a professional opinion of the process design.
The incoming aqueous HCl solution is a waste acid stream that will contain various metals including antimony, bismuth, and arsenic. The system is being designed to recover as much of the metals as possible in a separate stream while recovering an aqueous solution of HCl. A distillate stream of slightly acidic water will also be produced. The waste acid stream is produced during regeneration of the resin in an ion-exchange system (proposed, supplied by others). The composition of the waste acid stream is approximately 15 weight percent HCl in water, with smaller amounts of chlorinated metals, of which Bismuth Chloride (BiCl3) is the greatest in concentration.
The ion-exchange system is proposed to be comprised of a single batch-operated bed. Waste acid from the regeneration process is periodically rejected and routed to a storage/surge tank. The tank is sized for two full regeneration cycles. The tank is expected to dampen waste acid flow fluctuations and allow for a consistent aqueous HCl feed rate into the acid recovery process. The recovered acid stream produced by the process is returned to the ion-exchange system, along with fresh acid make-up, for reuse. The processes are intended to support a mining operation that does not allow for the release of wastewater.
The recovery process is a bulk separation process based on forced-circulation flash separation (high volume, high pressure flash). Flash overheads are routed to a multi-trayed distillation unit that produces a slightly acidic aqueous distillate and an aqueous HCl stream. Acid purity is constrained by the azeotrope corresponding to the process conditions. Flash bottoms are forced circulated back through the flash system along with the fresh feed. A metals-rich purge stream is removed to control solids buildup.
PROCESS performed technical due diligence on the process design and provided the client with a list of recommendations for future work. PROCESS also developed a Risk Assessment that profiled the inherent process, environmental, and operational risks associated with pursing the project. The client is now considering the next steps to take.
- Independent process design review
- Process validation due diligence.