REDUCTION OF GRAPHITE IN LEAD CONCENTRATE DURING FLOTATION OF A COMPLEX LEAD-ZINC ORE FROM RAJPURA - DARIBA, INDIA

摘要

The quality of lead concentrates produced from Rajpura-Dariba ore of Hindustan Zinc Limited, India is adversely affected due to the flotation of graphitic carbon in the lead circuit. Fluctuations in the quality of the ore obtained from two different sources also contributed to the worsening of the plant performance. A comprehensive investigation was carried out on ore feeds consisting of the two constituent ore types, namely, Graphite-Mica-Schist (GMS) ore and Calcareous-Silicate (CS) ore. The study involved bench scale laboratory flotation experiments and locked cycle tests, which were followed by plant trials. The flotation performance deteriorated when GMS content in the ore feed exceeded 40%. This is attributed to the higher contents of pyrite and graphite in GMS ore. Excessive fineness of flotation feed significantly increased the build-up of graphitic impurities in the final lead concentrate. A coarser grind size of 62/66% minus 200 mesh was found to be best for the plant. Variation in pH was found to affect flotation kinetics of pyrite vis-a-vis galena. The preferred pH condition, from the points of view of lead metallurgy, as well as the lowering of graphite content, was found to be ～7. Locked cycle tests confirmed the findings of the batch scale flotation experiments. Subsequent plant trials yielded the envisaged improvement in plant performance.