Search

Slime briquettes as a coolant to replace iron ore lump as 8 wt% of charge in basic oxygen furnaces are produced by hydraulic compaction using 10 wt% ordinary Portland cement (OPC) as binder. An investigation was carried out to find an economically viable alternative that would make utilisation of washery slimes more technically feasible while reducing the volume of CO2 emitted in cement manufacture. A range of organic, inorganic, hydraulic and non-hydraulic such as lime, sodium silicate, bentonite, molasses and sodium lignosulphonate were tested singly and in combination on slimes from the Noamundi mine in India with 10% of particles smaller than 8.6 micrometres, 50% smaller than 28.2 micrometres and 90% smaller than 85.9 micrometres. A combination of lime with smaller amounts of Portland cement was observed to produce briquettes whose properties were comparable to those made with cement alone., Slime briquettes as a coolant to replace iron ore lump as 8 wt% of charge in basic oxygen furnaces are produced by hydraulic compaction using 10 wt% ordinary Portland cement (OPC) as binder. An investigation was carried out to find an economically viable alternative that would make utilisation of washery slimes more technically feasible while reducing the volume of CO2 emitted in cement manufacture. A range of organic, inorganic, hydraulic and non-hydraulic such as lime, sodium silicate, bentonite, molasses and sodium lignosulphonate were tested singly and in combination on slimes from the Noamundi mine in India with 10% of particles smaller than 8.6 micrometres, 50% smaller than 28.2 micrometres and 90% smaller than 85.9 micrometres. A combination of lime with smaller amounts of Portland cement was observed to produce briquettes whose properties were comparable to those made with cement alone.

Mechanical activation of industrially prepared gibbsite (with a mono modal size distribution with a median size of 110 microns) has been carried out in a planetary mill at ambient conditions. The samples were described in terms of particulate characteristics, structural characteristics and reactivity. The mono modal size distribution of the unmilled gibbsite was found to change to a broad multimodal distribution as a result of milling. Size reduction was sharp in the initial stages, with median size reducing to around 7 microns during 15 minutes of milling. The size then increased gradually with increased milling time, indicating particle aggregation. Morphological studies of milled gibbsite showed that the platelets forming the agglomerate are separated first; the separated platelets then undergo breakage. Aggregation of particles occurs in the later stages of milling as a result of increased surface area and surface energy. XRD data showed that the crystallite size of gibbsite decreases as the milling time progresses whereas its microstrain increases. TEM micrographs show signs of defects, leading to disordering of gibbsite structure. Reactivity of milled gibbsite and alkali dissolution were found to increase with mechanical activation, while dehydroxylation temperature decreased, Mechanical activation of industrially prepared gibbsite (with a mono modal size distribution with a median size of 110 microns) has been carried out in a planetary mill at ambient conditions. The samples were described in terms of particulate characteristics, structural characteristics and reactivity. The mono modal size distribution of the unmilled gibbsite was found to change to a broad multimodal distribution as a result of milling. Size reduction was sharp in the initial stages, with median size reducing to around 7 microns during 15 minutes of milling. The size then increased gradually with increased milling time, indicating particle aggregation. Morphological studies of milled gibbsite showed that the platelets forming the agglomerate are separated first; the separated platelets then undergo breakage. Aggregation of particles occurs in the later stages of milling as a result of increased surface area and surface energy. XRD data showed that the crystallite size of gibbsite decreases as the milling time progresses whereas its microstrain increases. TEM micrographs show signs of defects, leading to disordering of gibbsite structure. Reactivity of milled gibbsite and alkali dissolution were found to increase with mechanical activation, while dehydroxylation temperature decreased

Although Cu and Ni recovery at the Indian National Metallurgical Laboratory, Jamshedpur, was more than 90%, Co recovery was only 50-60%. Dissolution studies using pure metal powders showed that the presence of metallic Fe and Mn in the leaching stage was detrimental to Co recovery. Tests were carried out on various additives, some of which improved Co recovery without affecting the Cu and Ni recovery rates. Electrochemical studies were carried out on the Fe-Co alloy which is likely to form during the reduction roasting stage and is difficult to leach in an ammoniacal system. Potentiodynamic polarisation studies of the alloy in ammonia solution showed that the alloy system was pre-passivated at open circuit potentials. Addition of some additives caused increased dissolution of the Fe-Co alloy. The leaching of roasted sea nodules in the presence of these additives resulted in an improvement in Co recovery to about 80%., Although Cu and Ni recovery at the Indian National Metallurgical Laboratory, Jamshedpur, was more than 90%, Co recovery was only 50-60%. Dissolution studies using pure metal powders showed that the presence of metallic Fe and Mn in the leaching stage was detrimental to Co recovery. Tests were carried out on various additives, some of which improved Co recovery without affecting the Cu and Ni recovery rates. Electrochemical studies were carried out on the Fe-Co alloy which is likely to form during the reduction roasting stage and is difficult to leach in an ammoniacal system. Potentiodynamic polarisation studies of the alloy in ammonia solution showed that the alloy system was pre-passivated at open circuit potentials. Addition of some additives caused increased dissolution of the Fe-Co alloy. The leaching of roasted sea nodules in the presence of these additives resulted in an improvement in Co recovery to about 80%.

It has been suggested that reduction of the iron and manganese phases as far as FeO and MnO is preferred for the complete liberation and selective reduction of the copper, nickel and cobalt oxides in manganese nodules. The oxygen partial pressure/temperature regime suitable for this purpose has been delineated. Free-energy minimisation and thermogravimetric results indicate that the requisite conditions can be achieved if more than 10% of neutral oil is used at temperatures greater than 923 degrees C. Neutral oil content, temperature and roasting time have been optimised to maximise leaching recoveries of Cu, Ni and Co: up to 96% of Cu and Ni and up to 85% of Co can be recovered if 15% of neutral oil is used as a reductant at 973 K for 90 min., It has been suggested that reduction of the iron and manganese phases as far as FeO and MnO is preferred for the complete liberation and selective reduction of the copper, nickel and cobalt oxides in manganese nodules. The oxygen partial pressure/temperature regime suitable for this purpose has been delineated. Free-energy minimisation and thermogravimetric results indicate that the requisite conditions can be achieved if more than 10% of neutral oil is used at temperatures greater than 923 degrees C. Neutral oil content, temperature and roasting time have been optimised to maximise leaching recoveries of Cu, Ni and Co: up to 96% of Cu and Ni and up to 85% of Co can be recovered if 15% of neutral oil is used as a reductant at 973 K for 90 min.

Advances in the field of mechanical activation of Al-oxyhydroxide minerals (synthetic as well as in natural bauxites) over the years around the globe are described in this review. An overview of fundamental aspects of mechanical activation with select examples of applications/examples in extractive metallurgy preludes the theme, mechanical activation of Al-oxyhydroxides. The focus is primarily on mechanically induced reactivity of largely used (and most commonly available too) Al-oxyhydroxides viz. gibbsite and boehmite. Reactivity, considered in the context of dissolution in alkali solution and transformations during thermal treatment, is reported to increase with mechanical activation. Available information is pieced together to answer the question why/how the observed effects happen. Gaps in the existing knowledge and prospects in the Bayer process are also discussed. (Authors.), Advances in the field of mechanical activation of Al-oxyhydroxide minerals (synthetic as well as in natural bauxites) over the years around the globe are described in this review. An overview of fundamental aspects of mechanical activation with select examples of applications/examples in extractive metallurgy preludes the theme, mechanical activation of Al-oxyhydroxides. The focus is primarily on mechanically induced reactivity of largely used (and most commonly available too) Al-oxyhydroxides viz. gibbsite and boehmite. Reactivity, considered in the context of dissolution in alkali solution and transformations during thermal treatment, is reported to increase with mechanical activation. Available information is pieced together to answer the question why/how the observed effects happen. Gaps in the existing knowledge and prospects in the Bayer process are also discussed. (Authors.)

Almost the entire metallurgical grade alumina is produced from bauxite using the Bayer process. The leaching conditions in the Bayer process depend on various Al-oxyhydroxide minerals/phases present in the bauxite. Among the various bauxite types, gibbsitic (trihydrate) bauxite is easiest to digest. Monohydrate (boehmitic and diasporic) bauxites need more stringent digestion conditions in terms of temperature, pressure and alkali concentration. Mechanical activation during milling, especially high energy milling, results in enhanced reactivity of solids due to physicochemical changes induced by milling. This paper is an overview of our recent research on mechanical activation of bauxite and its constituent phases, gibbsite and boehmite, and focuses on the leaching of mechanically activated bauxite ores. Complementary results on mechanical activation of gibbsite and boehmite phases are included for a deeper understanding. Implications of these results are highlighted in the context of the Bayer process., Almost the entire metallurgical grade alumina is produced from bauxite using the Bayer process. The leaching conditions in the Bayer process depend on various Al-oxyhydroxide minerals/phases present in the bauxite. Among the various bauxite types, gibbsitic (trihydrate) bauxite is easiest to digest. Monohydrate (boehmitic and diasporic) bauxites need more stringent digestion conditions in terms of temperature, pressure and alkali concentration. Mechanical activation during milling, especially high energy milling, results in enhanced reactivity of solids due to physicochemical changes induced by milling. This paper is an overview of our recent research on mechanical activation of bauxite and its constituent phases, gibbsite and boehmite, and focuses on the leaching of mechanically activated bauxite ores. Complementary results on mechanical activation of gibbsite and boehmite phases are included for a deeper understanding. Implications of these results are highlighted in the context of the Bayer process.