HCl Recovery Process – Independent Third-Party Review

Posted in News on May 03, 2023

A specialty engineering company based in Australia contracted Process Engineering International, LLC (PROCESS) to provide process engineering services and a due diligence review of a vendor-supplied HCl purification system. PROCESS was also asked to provide insight and recommendations on incorporating the vendor-provided system into existing facility operations.

The client was considering the use of a commercial recovery system to purify hydrochloric acid (HCl) via ion exchange. The system is expected to be installed in an Australian mineral mine site undergoing an infrastructure upgrade. The scope of the evaluation by PROCESS included a review of the chemistry and thermodynamics of the process, a 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 system is designed to recover as much of the metals as possible in a separate stream while recovering an aqueous solution of HCl.

The incoming aqueous HCl solution is a waste acid stream that will contain various metals including antimony, bismuth, and arsenic. A distillate stream of slightly acidic water is also produced. The waste acid stream is produced during the regeneration of the resin in an ion-exchange system. The composition of the waste acid stream is mainly water and HCl, 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 higher purity and 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 to circulate back through the flash system along with the fresh feed. A metals-rich purge stream is removed to control solids buildup.

PROCESS performed due diligence on the process 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 pursuing the project. The client used the project deliverables to consider the next steps to take.