Iron Grain

Not all iron oxides are available for reduction. Some iron minerals are solid crystals or even entire iron grains, which makes them resistant to microbial reduction (Lovley, 1991 Postma, 1993 Heron et al., 1994b). Other iron oxides or hydroxides are amorphous and readily reducible. Over time, even some crystalline minerals such as goethite and hematite may be reduced in the complex environment in leachate (Heron and Christensen, 1995). This indicates that the importance of iron as a redox buffer controlling the size of plumes is not given just by the amount of iron oxides present. The composition and microbial availability of iron for reduction are key parameters. Methods for the actual quantification of the microbial iron reduction capacity have, however, not been developed. 

Nuth 111 JA, Wilkinson GM (1995) Magnetically enhanced eoagulation of very small iron grains A correction of the enhaneement faetor due to dipole-dipole interaetions. learus 117 431-434 O Reilly W (1984) Rock and Mineral Magnetism. Blackie, Glasgow and London... 

Figure F.5.1. AC susceptibility at different frequencies for a granular film consisting of iron grains dispersed in an alumina matrix (Fe-Al Oj). The out-of-phase component x" is reported for v = l Hz. (Reproduced with permission from Ref. 181.)...

The enrichment of salt with iodine, the fortification of milk with vitamin D, and the start of the thiamin, riboflavin, niacin, and iron, grain enrichment program in 1941, have played a significant role in the practical elimination of the following deficiency diseases simple goiter, rickets, beriberi, ariboflavi-nosis, pellagra and simple iron-deficiency anemia. The average American receives approximately 40% of his thiamin, 25% of his iron, 20% of his niacin and 15% of his riboflavin from enriched foods. 

As seen from Figure 5, when the reduction extent is 90%, most of the iron oxides at the periphery of pellets have transformed into metal iron, whieh have joined together and appear in the shape of large laminar. And the interconnected iron grains oan hamper the diffusion of reduction gas. 

With the increasing of reduction temperature and reduction time, the reduction extent obviously increases. The reduction rate decreases accompany with the increasing of reduction time. At the final stage, the reduction rate is distinctly tardiness because of the formation of large, laminar and interconnected iron grains. 

Enlarged picture shown in Figure 9 and Figure 10 illustrated that average iron grain size increased from smaller than 7 rm at the 60th minute to over 30 rm at the 140th minute, when iron particles were associated with each other. 

A fracture of particles was found not only in thermal decomposition of siderite, but also in the transformation of magnetite to wustite, and iron grain size grew along with roasting time. 

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