MONITORING THE REDUCING END-POINT IN GOLD RECOVERY-SYSTEM USING REACTION HEAT AS CHEMICAL PROBE

Monitoring system for detecting the reducing end point in gold recover ing system is presented by using the reaction heat measurement as chem ical probe. Sodium hydrogen sulfite was selected as reducing agent for gold(III) among the various agents examined, which yielded gold preci pitation quantitatively. The reducing solution was pumped at a flow ra te of 36 ml/min to the reaction vessel containing gold(III) solution a nd the increase in temperature was measured using thermistor detector. A linear relationship was observed between the gold(III) concentratio n up to 135 gAu/I and the increase in temperature. The relative standa rd deviation of recovered gold was 0. 13 % (n = 4) for 60 g gold. The results of recovered gold mass from industrial waste in accessary fact ories agreed well with the one calculated from the increase of tempera ture.