Fluoride reduction system for the reduction of fluorides from wastewaters

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Courtesy of Digital Analysis Corp.

Client: Major semiconductor fab; Santa Clara, CA.

Industry: Semiconductor Manufacturing.

Installation Date: May 2001.

Objective: To reduce total fluorides and neutralize rinse waters and concentrated bath dumps from the fab area.

Criteria and Limitations: Influent flow varies from 5,000 gpd to 40,000 gpd and can contain up to 2% HF and BOE as fluoride source. Combined plant flow requires a total fluoride level of less than 10 ppm.

Overview:

As with all semiconductor fabs fluorides in the wastewater is a problem due to the extensive use of Hydrofluoric Acid (HF) and Buffered Oxides Etches (BOE). Fluorides discharge levels across the country range from 50ppm to as low 2ppm.

Fluorine, an anion, is unique and behaves much differently than the cations, or heavy metals, that industry is experienced in removing. Ion exchange does not work economically because the very low affinity that anion exchange resins have for fluorides (abv. F-). Membrane technology is normally not economical because of low flux and membrane fouling. Fluoride bearing waste streams are normally high in silica, the bane of crossflow membranes.

Fluorides can be precipitated as Calcium Fluoride (CaF2), however, due to the solubility of this salt, and due to the difficulty in separating this salt from solution, this can be very problematic also.

The Process:

Digital Analysis Corp. has developed a unique process for reducing fluorides in semiconductor fab operations. This process allows for the totally automated reduction in total fluorides. Fluoride levels as low as 2ppm can be reliably attained.

Conclusion:

The project, as with many wastewater treatment systems, was constrained by time, space, and money. The use of a standard packaged system at the center of the treatment process allowed us to offer the customer a very capable system with a good delivery time, very competitive price, and minimal installation since the entire treatment system was fabricated in our shop prior to shipping.

The system performance has exceeded all specified and published requirements. In the first 2 years of operation there has not been a single discharge contravention and the total plant fluoride has averaged 2ppm. The system has been fully functional 24/7 for the first 2 years with no downtime, other than routine calibrations (weekly) and routine, scheduled maintenance. The influent fluoride levels are routinely in excess of 1,500 ppm.

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