DESIGN ENGINEERING: A FILTRATION SYSTEM FOR THE REMOVAL OF MERCURY FROM A WEAK ACID LINE (LA4)

ISSUE

A lead foundry had sustained a mercury contamination in one of its weak acid lines. STS was assigned a contract to handle this situation by designing a proper filtration system. STS participated in all steps of the project, from the establishment of the design criteria to selecting the right technology and to sizing the selected equipment.

TECHNOLOGICAL CHALLENGE

Owing to the effluents' physico-chemical properties (ageing of the suspension after 24h), the laboratory testing and analyses had to be done on location. The laboratory testing not only contributed to the equipment selection process but also validated the necessity of a mercury precipitation step upstream. Also, throughout the whole operation, health and safety control measures (IPE's) were ensured for personnel safety towards all chemical products used.

RECOMMENDED SOLUTIONS

The selection method developped by STS led to the identification of:

1. The best technology to facilitate thickening (the addition of a coagulant)
2. The best suited dewatering equipment for the process.

This selection process included gathering the System Considerations, an internal identification tool, and using the laboratory testing for specific analyses. Then, lab filtration trials made it possible to determine the right operating parameters. With the results, STS was also able to validate what impact the addition of a coagulant product would have on equipment sizing.

RESULTS

Laboratory testing demonstrated that the recommended solution makes the removal of 99% of mercury elements possible. Moreover, disposal costs are greatly reduced because the cake's residual moisture is cut down significantly. The selection process was carried out with the help of the plant's staff. Indeed, the client was involved at every step, especially at the validation stage. This made the recommended solution the best match for the client's issue.