Strategic reforms in hydro-refining units for handling manganese rich zinc concentrates at HZL

Sundar S. Sombhatla, Kiran Kr. Rokkam, Ashish Kumar, Sheeba Mashruwala, Akhilesh Shukla

Manganese is frequently found, as a naturally associated element with lead-zinc ores. During the processing of Zinc concentrates with high manganese content, the selective sulphate leaching of zinc from concentrate is not possible and eventually ends up with extraction of manganese along with other minor impurities in to the zinc leachate. The manganese and magnesium levels in zinc hydrorefineries of Hindustan Zinc have increased above acceptable limits and resulting in an adverse impact on cell house performance. Due to limited capacity of continuously operated Magnesium Removal (MR) bleeding section alternative routes for reducing Mn in the zinc sulphate solution have been explored. The focus is mainly laid on using selective oxidants to oxidize and precipitate manganese from zinc leach solution. In this regard, KMnO4 has been selectively preferred for Mn reduction, by taking account of reagent consumption as well as operational lenience. Consumption of MnO2 for oxidizing ferrous to ferric ions in leaching circuit was identified as another source of manganese increase. This problem was related to the roaster calcine with high sulphide sulphur content. Therefore, the usage of MnO2 slurry was unavoidable in leaching circuit along with air and oxygen sparging. “Sodium persulphate (SPS)”, a powerful oxidizing agent, was explored to replace MnO2 slurry in leaching; SPS has additional advantages in oxidizing ferrous ions to ferric along with “sodium sulphate” generation, a prime reagent used for iron precipitation in the form of Jarosite. Above improvements, together with additional operational disciplines, have led to an appreciable control over manganese levels in purified solution and an improvement in cell house performance.