It is important to check the pH of metallurgical tests (e.g. flotation, leaching) grinding, flotation or cyanidation circuits. Basically, the gold mill operator must periodically check the pH of the various circuit slurries and/or solutions to verify that the correct amount of reagent is being added to the circuit. For example the addition of lime has an impact on the pH. Also, by checking the pH we can know if the readings of the instruments in field are ok. The pH of a solution expresses its relative acidity or alkalinity on a scale from 0 to 14. The pH expresses the concentration of the hydrogen ion (H+). Pure distilled water has a pH value of 7, and is regarded as neutral (neither acidic nor alkaline). pH values decreasing from 7 to 0 indicate increasing acidity, and pH values increasing from 7 to 14 indicate increasing alkalinity.
Each unit on a pH scale represents a ten-fold change in concentration of H+ or OH‑. For example, a solution with a pH of 1 is ten times more acidic than a solution with a pH of 2. The pH of various circuit slurries or solutions is measured using an installed pH probe. To verify that the installed pH meter is functioning correctly, the pH is periodically measured using a portable pH meter. The following procedure lists the steps required to calibrate the pH probe and measure the pH. The equipment required includes a Portable pH meter, Wash bottle with deionized water, 250-milliliter beakers, 250-milliliter beaker with deionized water, Buffer solution (pH 7.0), Buffer solution (pH 10.0), Paper tissue, Acidic solution.
Checking pH during leaching tests Basic scheme of pH measurements