Alumina Separation And Environmental Control In Iron Ore

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Amos Matthews
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1 Lecture 32 Alumina Separation And Environmental Control In Iron Ore Beneficiation Keywords: Iron Ore, Alumina Separation, Environmental Control As illustrated in tables 32.1, 32.2 and 32.3, efficient separation of alumina (corundum) from hematite requires prior adaptation of bacterial cells in the presence of corundum. Such preadapted cells were found to secrete alumina-specific bioproteins. Corundum-adapted bacterial cells and their metabolic products were efficient in the separation of hematite from corundum through bioflocculation. Proteins separated from adapted cell metabolites could also be used to separate alumina from hematite. [202] Table 32.1: selective bioflocculation of corundum-hematite (1:1) mixture using corundum-adapted cells Percent hematite removal Table 32.2: separation of corundum-hematite through selective flocculation using corundumadapted bacterial metabolite Percent hematite removal

2 Table 32.3: selective flocculation of corundum-hematite mixture using corundum-adapted bacterial protein Percent hematite separation Selective separation of hematite and silica from their mixtures containing corundum can also be brought about using corundum adapted P.polymyxa. (table 32.4). Table 32.4: Separation of corundum-hematite-quartz mixture through selective flocculation using corundum-adapted cells Percent hematite removal Percent silica removal ph ph It should be however noted that the adapted cells need be preserved and frequently subcultured in the presence of alumina to maintain their adapted properties. Subculturing of adapted cells in the absence of the adapted mineral (corundum) will lead to deadaptation. As shown in table 32.5, deadapted cells lose their aquired mineral specificity. 2

3 Table 32.5: Separation of corundum-hematite mixture through selective flocculation using cells deadapted through serial subculturing in mineral-free medium Number of subculture in mineral-free medium Percent hematite removal Metabolite from Deadapted cells deadapted cells Applicability of bioflotation and bioflocculation was demonstrated using real iron ore samples. From an alumina rich iron ore containing upto 15% aluminium oxides and silicates, very significant reduction in alumina and silica could be brought about through bioflotation or bioflocculation as illustrated in table.32.6 and Table 32.6: Alumina removal from iron ores through bioflotation and bioflocculation Conditions Bioflotation after interaction with hematiteadapted cells. Selective flocculation, 6 deslimings, hematiteadapted cells Percent concentrate analysis Fe(T) 69.5 Al 2 O SiO Recovery ~ 82 Fe Reduction in alumina to 0.5% from the flocculated iron concentrate Similarly, significant removal of silica could be obtained through bioflotation and bioflocculation from another silica rich iron ore, containing upto 32% silica and 45% iron. Typical results are illustrated in table

4 Table 32.7: Silica removal from iron ores through bioflotation and bioflocculation Experimental conditions 1. Flotation without biotreatment using 0.15 kg/ton of amine collector at ph After 5min bacterial interaction followed by collector-less floatation 3. After bacterial treatment as above followed by flotation in the presence of 0.15 kg/t of amine collector 4. Selective bioflocculation (in presence of cells) at ph 7.0 with 6 desliming stages Concentrate Percent Fe Percent SiO 2 Percent Fe-Recovery No significant silica removal Bio-environmental control in mineral beneficiation [200] Microbially-induced iron ore beneficiation would be more cost effective, energy-efficient and environment-friendly compared to other chemical alternatives. Native microorganisms inhabiting iron ore deposits are preferred since such organisms are already acclimatized to the mining environment and are known to be involved in biomineralization. For example, FeOOH sheaths formed by Leptothrix incorporates exopolysaccharides which protect the organisms against metal toxicity. Magnetotactic bacteria synthesize magnetic minerals such as magnetite. Since phosphorous is an essential micronutrient promoting microbial growth, phosphorousspecific organisms colonize phosphorous-enriched zones of iron ore deposits. An anaerobe, Shewanella oneidensis can recognize goethite which it prefers to colonise on, and not alumina or gibbsite! Such organisms may prove to be critical in the separation of a desired impurity mineral such as alumina or apatite from iron oxides. 4

5 Many mining organisms are also found to be capable of bioremediation of toxic effluents. For example, Bacillus spp, Pseudomonas spp, yeasts and algae are capable of metal accumulation, biosorption and biodegradation. The use of Paenibacillus polymyxa in the biodegradation of several toxic flotation collectors commonly used in iron ore and sulfide mineral flotation has been reported. For example, active cultures of P.polymyxa could efficiently degrade and remove dodecylamine within about 8 hours. Similar biodegradation and efficient removal of oleate and xanthate collectors could also be achieved. Typical results are presented in Table Table 32.8: Biodegradation of different collector reagents under various conditions of treatment Percent degradation Reagents Cells alone Cells in fully grown culture Cell-free metabolite DAA (Dodecylamine) 100% (6h) 100% (2 h) 45% DA-16 (Silica collector) 100% (8h) 100% (2 h) 45% Sodium oleate 75% (5h) 80% (8h) 30% Isopropyl xanthate 40%(5h) 100% (5h) 100% (10 h) Cationic collectors such as amines exhibited pronounced biosorption onto bacterial cell surfaces and the surface-adsorbed amines were also utilized and degraded by bacterial metabolism. Adsorbed amine and oleate collectors from the floated iron ore surfaces could also be effectively stripped through biological conditioning using P.polymyxa. Such biological surface stripping of reagents from floated concentrates is of practical significance in subsequent pelletization process. Improved pellet quality requires moisture control and mineral surface hydrophobicity plays a determinative role. Biotreatment of ore tailings would enhance settling rates of fines and would enable iron recovery from wastes as well as water harvesting. 5

6 Restoration of ore mined sites requires functional microbial community for soil remediation and fertility. Many mining microorganisms serve as biological indicators for ore mineralization and also serve as pointers to disturbed mine sites. Abandoned mine rehabilitation Biorestoration of ore mined areas can be efficiently used. Native functional microbial community will be useful in soil development, biogeochemical activity and for successful plant community establishment. Abandoned mine rehabilitation can be achieved through beneficial microorganisms such as Rhizobia and Mycorrhizal fungi(amf) Biological indicators of disturbed mine sites will serve as monitors to identify polluted soils and waters.. Soil phosphate solubilizing microorganisms and cellulolytic population are used as biological indicators of iron mined lands Brazil. Restoration of tailing dams Processed ore tailings containing moderate amounts of heavy metals such as iron, copper, manganese, lead and zinc can be readily bioremediated. Microorganisms colonise such manmade habitat. Soil bioremediation and phytoremediation are practiced. Biological restoration of tailing contaminated soils will be cost effective and environment - friendly. Metabolic activity of iron reducing bacteria will enhance natural or engineered bioremediation of contaminated sites Increasing surface hydrophobicity of iron ore fines through microbial treatment. Dewatering of concentrates and tailings through microbes. Microbially-induced flocculation/sedimentation of iron ore fines in tailing ponds. Water harvesting and recirculation. Microbial dephosphatisation of iron ores, slags and furnace dusts. 6

Biogenesis Of Metals And Minerals

Lecture 2 Biogenesis Of Metals And Minerals Keywords: Biomineralization, Metal-bacteria Cycles, Biogenesis Many types of bacteria (autotrophic, heterotrophic, aerobic-anaerobic, mesophile-thermophile,