Thermodynamics and Viscosity Aspects in Manganese Nodule Residue Smelting for Silicomanganese Production

Among several under trial processes for extraction of base metals (Cu, Co and Ni) from manganese nodules (MN), the reduction-roast ammoniacal leaching {NH4OH/(NH4)2CO3} process is considered very attractive. After the leaching of base metals from roast-reduced MN, a substantial quantity of residue left behind (about 70 wt. %, by mass) as wastes for disposal or further use. Smelting studies showed that leached manganese nodules residue (WMNR) can be successfully utilized as raw material for silicomanganese production after maintaining proper metallurgical aspects like thermodynamics, viscosity etc. Literature survey on slag liquidus and viscosity aspects of silicomanganese smelting has been done. The slag liquidus has been found to be closely associated to slag basicity i.e. (CaO+MgO/SiO2) showing significant increase above 0.7 slag basicity. Charge mix basicity of 0.2 was found to give maximum Mn and Si recoveries. Increasing or decreasing charge basicty from 0.2 resulted in lower metallic yield and Mn and Si recoveries. This has been explained with liquidus calculations of final slags obtained at those charge mix basicities. Addition of CaF2 during holding time i.e. time given after complete melting of charge mix was found to be beneficial. The optimum amount of CaF2 was 4% of WMNR+Mn ore blend, which gave rise to maximum Mn and Si recoveries and metallic yield. Further addition of CaF2 (>4%) produced a high basicity slag (basicity =0.83) having very high liquidus leading to decrease in metallic yield and Mn and Si recoveries.