Client: Major semiconductor manufacturer in the southwest United States.
Industry: Semiconductor Manufacturing.
Installation Date: June 2008.
Objective: To remove fluoride and neutralize hydrofluoric acid and fluoride laden wastewater.
Criteria and Limitations: Influent flow is relatively constant and ranges from 150 to 175 GPM with fluoride levels ranging from 0 - 5000 ppm. Fluoride influent limit is 17ppm of total fluoride and effluent pH range is 6.0 < pH < 9.0
Overview: The extensive use of hydrofluoric acid (HF) and buffered oxide etches (BOE) for the use of silica substrate etching requires the use of fluoride reduction system throughout the industry to remove fluorides from the wastewater stream. Free fluorides in industrial wastewater can be very corrosive and very toxic to both aquatic and terrestrial life, therefore fluorides must be removed.
In a typical application fluorides are removed from wastewater via Calcium Fluoride (CaF2) precipitation and subsequent pH neutralization. The fluorides, once properly treated, are handled as a completely inert, non-hazardous, dry sludge cake with resale / recycle value.
In this example we examine a 200 GPM fluoride reduction and pH neutralization system designed to remove fluorides from levels as high as 5,000 ppm to less than 17 ppm of total fluoride. The system is installed outdoors in a hurricane prone region in the vicinity of a chemical production classified as hazardous (Class 1, Division 1, group C&D).
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.
Solution: A modular continuous flow through fluoride reduction system was developed and installed by DAC to handle flows up to 200 GPM of acidic fluoride laden wastewaters. The major stages of this system include:
- Influent Equalization.
- First stage pretreatment and co-precipitant addition.
- Second stage treatment and fluoride precipitation.
- Third stage treatment and fluoride precipitation (identical to the 2nd stage providing process assurance and redundancy).
- Flocculant addition.
- Clarification via an inclined plate clarifier.
- Sludge holding and dewatering (via a filter press).
- SCADA system monitoring and continuous data logging.
- Continuous online total fluoride analyzer for monitoring total fluoride in the effluent stream.
- Continuous effluent pH and flow monitoring.
- Chemical (calcium chloride) bulk offload and storage.
Conclusion: Digital Analysis was contracted to design, build, install, and commission a fluoride reduction and pH neutralization system as outlined above. This system, as with many industrial wastewater treatment systems, was constrained by time, space, and money with special emphasis on space. This fluoride removal system was installed outdoors in a hurricane prone region near a chemical process that was classified as hazardous necessitating an explosion proof design and installation.
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 facility prior to shipping.
The fluoride system performance has exceeded all specified and published requirements and has run continuously for over three years and has been very well maintained by the end user.
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