Case study
Bulk Concentrate
The conventional technology for flotation of lead-zinc ores is differential flotation to produce separate concentrates of lead and zinc. The separate concentrates are then fed to respective smelters of lead and zinc for recovery of metals. In this process, misplaced metals (Zinc in Lead concentrates and Lead in Zinc concentrates) are lost and conventionally not accounted for in recovery, either at mines or at smelters. These losses range between 2% to 10%, depending upon concentration and tonnages of different concentrates for different mines.
The Imperial Smelting Process (ISP) existing at CLZS, enjoys the advantages of being able to use ‘Dirty’ feed i.e. both lead and zinc in the feed to the furnace without affecting its performance. Historically, bulk concentrates (concentrates containing both lead and zinc produced by bulk flotation at mines) should be fed to the furnace giving advantages of correspondingly higher recovery at mines and without affecting performance of ISF.
Two underground mines – namely Rajpura Dariba (RDM) & Zawar Mines (ZM) – earlier produced separate (zinc and lead) concentrates. The recoveries of zinc, lead and silver were relatively lower from RDM. Bulk flotation was carried out after a lot of R&D and plant trials at both the mines and after modifying the flow sheets to suit the requirements of the smelter and significant better overall recoveries were achieved at both the mines for all the metals. Zawar now produces all its output in the form of bulk concentrate while RDM produces bulk concentrate for a portion of its output depending on the grade mix and requirement of the ISF smelter. The innovativeness of this project lies in the use of Zawar bulk concentrate to blend with RDM bulk concentrate to make it acceptable to the smelter. In this process, zinc, lead and silver recoveries have improved by 0.5%, 2% and 1% respectively in ZM and by 2.5%, 6% and 4% respectively in RDM. Besides helping in better management of mineral resources, substantial financial savings are generated through this effort.
