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Gold Processing: Refractory Sulfide Ores (pH/ORP)

Gold Processing Refractory

Refractory gold ores are defined as containing minerals or carbon compounds that trap encapsulated gold and make leaching extraction diffi cult. These types of ores require pretreatment prior to cyanidation.

Measurement Challenges
The pH measurements in the scrubber are typically used to control the process. The SO2 will convert to sulfuric acid in the scrubber causing low pH and corrosion issues. A setpoint around 6.0 to 6.5pH will be used to control the lime addition. The application of the sensor is often difficult. The combination of solids from the roasting process and gypsum formation create a slurry. The high solids content of the slurry (up to 15% solids) can coat the pH sensor and plug the porous reference junction. Heavy metals and sulfi de compounds will be present in the roaster gas. These contaminants are well known to poison the Ag/AgCl element used in pH sensors causing instability in the measurement.

Barben Analytical recommends using our Performance series pH sensors in scrubber applications. The Axial Ion Path® reference design of the Barben sensors is well suited to prevent poisoning of the sensor by chemical attack. The 547 retractable pH sensors is most commonly specified for scrubber applications. These sensors can easily be isolated from the process for cleaning, calibration and eventual replacement. Ideal mounting would be in a recirculation pipeline on the scrubber with 1/2 inch insertion depth. The flowrate in the pipeline will help prevent buildup from forming on the sensor thus reducing maintenance intervals.