Role of Mineralogy, Mineral Chemistry and Geochemistry in Mineral Processing : A case study for High Phosphorous manganese ores of Nishikhal, South Orissa, India

Abstract

Conformable manganese ore bands are present in the khond-alite suite of rocks belonging to the Eastern Ghats Complex of South Orissa,India. The ores cart be classified as high-grade, siliceous and ferruginous. Cryptomelane, romanechite, pyrolusite, jacobsite, hausmannite, braunite, lithiophorite, birnessite and pyrophanite represent the manganese minerals. Goethite, limonite, graphite, hematite, magnetite are the associated opaque gangue minerals while quartz,orthoclase, hyalophane, garnet, kaolinite, apatite, collophane,. fibrolite,zircon, biotite and muscovite are the silicate gangue minerals recorded in these ores. Optical microscopic and Electron Probe Microanalysis studies revealed that the phosphorous, in these ores, present in the form of (i) apatite inclusions within qua-rtz, orthoclase and garnet, (ii) amorphous calcium phos-phate (collophane) within the voids of garnet, (iii) ads-orbed component within the manganese oxide and silicate phases as well as in the iron oxide phase (goethite) Geochemical studies indicated that high amount of phos-phorous is linked with ferruginous manganese ores. Regression analysis of the geochemical data suggests a strong positive correlation between P-Fe and P-Mn. Magnetic separation studies on low- and off- grade bulk manganese samples, indicated that the phosphorous contributed by apatite is relatively low (4.44 to 17.76%) compared to the phosphorous held in adsorption(82.24 to 95.56%), while the contribution of phosphorous by collophane is insignificant.The above studies confirm that the association of phosphorous in Nishikhal ores is very complex. Since most of the phosphorous is in adsorption, these low and off grade ores are expected to respond well to dephosphorisation by reduction roasting followed by magnetic separation or roast alkali leaching method.