Fluoride Removal 




Measure and control fluoride at low pH



What It Does For You

The Foxcroft FX-300-F-AS analyzer measures free fluoride ion activity in low pH solutions with high HF concentrations used in cleaning and etching operations as well as in semiconductor waste treatment. Measurements over 10,000 ppm are possible with our high range model.

The sensors are engineered to survive the corrosive nature of the solution as well as the aggressive cleaning required to keep them functional, resulting in more reliable readings with less down time and longer sensor life.


Hydrofluoric acid (HF) is a corrosive chemical that is extremely toxic to human tissue that will dissolve glass.

Industrial process streams must be treated to reduce fluoride concentrations to meet mandated waste discharge limits.

HF Uses

HF is used in many industrial processes including: to make refrigerants, as a metal cleaner and stainless steel pickling agent, aluminum can etching, to remove silicon dioxide in semiconductor wafer production, to etch glass, chrome and enamel products.

Problems for Electrodes

Low pH in the presence of high HF levels destroys general purpose fluoride and pH sensors.

HF dissolves the glass in most commercial pH sensors. Etching solutions drain the sensor's reference  of its internal salts, which causes drifting.

In treatment, fluoride is converted to calcium fluoride salt for removal, but also precipitates onto the sensing element and reference surface, reducing sensor response.

Most fluoride ion selective electrode sensing elements and reference junctions are destroyed by the low pH solution being measured.

A Better Fluoride Electrode

The fluoride electrode's sensing element is protected from acidic solutions by a special seal.

The solid state polymer reference junction is engineered to resist acid, fluoride and shifting that can occur in high ionic strength solutions.

The reference surface surrounding the sensor tip can withstand cleaning with concentrated or dilute hydrochloric acid as well as abrasive removal, even scraping with a razor knife, of hardened deposits.

The sensor is fully submersible due to chemical resistant materials used for waterproofing.


A Better pH Sensor

pH sensors feature specially formulated, true HF resistant, thick wall low profile parabolic break resistant glass.

Deposits can be removed from the solid state reference surface with concentrated or dilute hydrchloric acid and by abrasive scrubbing or scraping to produce a clean "new" surface.

Thicker pH glass used with some sensors doesn't offer true HF resistance, it only slows the rate of degradation.

ISFET and antimony based pH sensors have HF resistance but lack the stability and accuracy of a glass element sensor.

Cable and sensor waterproofing is provided with chemical resistant flexible tubing and sealant to allow full submersion into the process fluid.

System Summary

Concentration range: 0.019 - 19,000 ppm, possibly to saturation in select applications

pH range: 0 - 9.5 pH continuous

Standard System Results: free fluoride, pH, pH compensated total free fluoride

Available with analog or smart digital pH sensors


Product Features

The standard system includes Din rail mounted transmitters each with 3-digit LED display and 0/4-20mA output for free fluoride, pH, and pH compensated total free fluoride.

Each module can also display temperature and the absolute millivolt reading.

The total fluoride module also includes RS485 Modbus RTU output of all inputs including temperature.

The standard 7" wide IP65 wall mount enclosure with lift up clear lid features a 6A fused power entry module with 2-meter power cord for AC input from standard US grounded outlets.

The modular system can be supplied in a 10" wide enclosure  for two additional functions that can include temperature output, additional fluoride, pH or other measurements, or data logging.

Download  FX-300-F-AS Brochure


Fluoride High Range

The Foxcroft FX-300-F-AS-HR allows you to monitor high range fluoride waste treatment processes.

Our KILO PPM transmitter can be ranged in the field to 0-10,000 ppm, 0-100,000 ppm, or 0-999,000 ppm.

The analyzer is controlled as usual from the transmitters, while the measurement values are sent via 0/4-20mA output to external LED displays to show operators the ion activity in actual ppm units.

A bridge terminal relays the 0/4 mA output to your control or monitoring system.

Available with one or two displays, the model shown includes displays for both free and total pH compensated unbound fluoride.

The standard system includes one each free fluoride and pH measurement module, as well as a pH compensation module housed in a water proof IP67 / NEMA 4X polycarbonate enclosure with clear door.

The system uses our standard acid service fluoride sensor and either smart digital or analog high HF resistant pH sensor.

Download  FX-300-F-AS Brochure


pH Compensation

The FX-300-TOT module computes the total free fluoride concentration when the process is below 6pH. It's based on the free fluoride activity at a given temperature and pH;  and the extent of ionization of HF.

The extent of ionization defines the percentage of fluoride that is converted into the unbound form the sensor can detect: the free ionized fluoride species.

The total ISE displayed is the value computed as if all fluoride present is the ionic form.



The Fluoride Sensor

Sensors can only be submerged into a tank or basin, or inserted through a tank wall using stainless steel hot tap insertion fittings.

Inline mounting into a pipe is not recommended because the special sealing gasket tends to trap bubbles at the sensing tip, preventing a measurement.

Chemical resistant waterproofing sealing protects both the back of the sensor and cable.

For cable lengths over 20 feet sensors are provided with either an integral or external analog preamplifier. Digital electronics are not available for fluoride.

Cable extensions with water resistant snap connectors make handling easier and minimize replacement sensor cost. You replace only the cable integral to the sensor, not the entire length.

Get sensor specifications here


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The pH Sensor

One of the few pH sensors available with true high HF resistant reference that can function at low pH in the presence of high concentrations of fluoride.

The industrial duty design includes thick wall break resistant pH glass, formed into a hemispherical shape which is inherently stronger than round or flat glass. A 4-tine tip guard protects the glass against accidental damage during handling.

The solid state reference prevents intrusion of gas or liquids into the double junction and can withstand acid cleaning as well as scraping to remove deposits on the sensor.

Chemical resistant flexible tubing seal protects the back of the sensor and sensor cable against chemical and mechanical damage.

Digital sensors with auto calibration and calibration data storage for reporting are also available.

Get sensor specifications here

Contact us  for more info

Our customer, a supplier to the semiconductor industry, was replacing fluoride and pH sensors weekly due to precipitate buildup and the harsh conditions of their HF waste reduction treatment. After installing the FX-300-F-AS in January 2018, the first replacement sensors were installed 16 months later in May 2019.

A Confidential US Supplier to Semiconductor Manufacturers