Nodulizing elements

The role of the nodulizing elements can, therefore, be speculated as two-fold. They cleanse the melt of elements such as oxygen or sulfur which prohibit spheroidal graphite growth. The... 

The rare earths play three roles in the production of nodular iron. These roles are as a nodulizing element (or as the growth modifier) as a means of enhancing the nodule count (or nucleation) and, finally as controllers of deleterious elements. The use of the rare earths for each of these purposes will be described in detail in the following sections. 

The modern foundry process for producing nodular iron can be oversimplified by describing it as the treatment of a base iron (3% to 4% carbon, 1% to 2% silicon) having low (0,005% to 0.05%) sulfur levels and containing little (<0,05%) phosphorus. The treatment is carried out by means of the introduction of the appropriate nodulizer into this base iron. Inadequate addition of nodulizer results in incomplete spheroidization. Excessive concentrations of nodulizers promote the formation of unwanted iron carbides. The nodulizing elements include the rare earths, magnesium, yttrium and calcium. The latter two elements find little or no use today because of economical and technical problems. 

One of today s basic requirements for economical nodular iron production is a base (or untreated) iron having between 0,004% and 0,05% sulfur. In most practices, the sulfur level is held at approximately 0,01% in order to minimize the necessary addition of nodulizing elements. On the other hand, a minimal sulfur level is evidently required in order to facilitate adequate nucleation (12). 

No causes were established for the variation in behavior of the rare earths. Unfortunately, no further work exploring the properties of the individual rare earths as nodulizing elements has been reported since that time. 

Manganese minerals are widely distributed oxides, silicates, and carbonates are the most common. The discovery of large quantities of manganese nodules on the floor of the oceans may become a source of manganese. These nodules contain about 24% manganese together with many other elements in lesser abundance. 

Partk/es (nodules) are the primary stmcture element. They are roughly spherical elements that are joiaed ia the aggregate stmctures. 

A rich supply of manganese lies in nodules of ore that litter the ocean floors (Fig. 16.9). These nodules range in diameter from millimeters to meters and are lumps of the oxides of iron, manganese, and other elements. However, because this source is technically difficult to exploit, manganese is currently obtained by the thermite process from pyrolusite, a mineral form of manganese dioxide ... 

Courtois, C. and Clauer, N. (1980) Rare earth elements and strontium isotopes of polymetallic nodules from southeastern Pacific Ocean. Sedimentology, 27, 687-695. 

Identification of sources of analytical bias in method development and method validation is another very important application of reference materials in geochemical laboratories. USGS applied simplex optimization in establishing the best measurement conditions when the ICP-AES method was introduced as a substitute for AAS in the rapid rock procedure for major oxide determinations (Leary et al. 1982). The optimized measurement parameters were then validated by analyzing a number of USGS rock reference samples for which reference values had been established first by classical analyses. Similar optimization of an ICP-AES procedure for a number of trace elements was validated by the analysis of U S G S manganese nodule P-i (Montaser et al. 1984). 

The bulk Fe and Mn composition of the nodules is variable and, they contain a variety of trace elements, including significant amounts of P, Ba and As (Table 2). 

Figure 5 shows the analytical results for Fe, Mn, As and P along a transect across a nodule from LG1. This nodule is enriched in Fe, As and P at the centre. The As and P enrichment are spatially correlated with the Fe-rich areas of the nodule, indicating co-precipitation of these trace elements with the Fe oxyhydroxide minerals. This compositional variation isassumed to reflect changes in the groundwater chemistry over time, potentially since the lake formed. 

Elemental x-ray maps (EDS) indicate the nodules are mainly Ca and S (i.e. gypsum) whereas surrounding rims mainly consist of As, Fe, and Ni (Fig. 5). 

Manganese is an important element in the aquatic environment. It is an essential micronutrient U 2) and is the subject of much interest because its oxides scavenge other heavy metals (3). Of particular interest are ferromanganese nodules, which are abundant in the aquatic environment. These nodules contain high concentrations of cobalt, nickel, copper and other heavy metals (4). 

Occurrence. In order of abundance in the earth s crustal rocks, it is the third within the transition elements (after Fe and Ti) and the 12th in the general order of all the elements. It occurs in several minerals such as primary deposits of silicates and as secondary deposits (commercially more important) of oxides and carbonates as pyrolusite, Mn02, hausmannite, Mn304, rhodochrosite, MnC03, etc. Large amounts of manganese are present in the deep sea nodules located over certain areas of the ocean floor. 

Sediments formed by the abiogenic precipitation of solutes from seawater are termed hydrogenous. Unequivocal examples of hydrogenous sediments are ones formed from the evaporation of seawater. The minerals deposited are collectively called evaporites and are the subject of Chapter 17. Others form with the assistance, to varying degrees, of marine microbes. For example, bacteria seem to play a role in the formation of Fe-Mn nodules and crusts. Some hydrogenous minerals, such as barite, celestite, glauconite, and francolite, are produced from the precipitation of elements... 

Two types of metal-rich hydrogenous deposits are formed on the seafloor iron-manganese oxides and polymetallic sulfides. The iron-manganese oxides have been deposited as nodules, sediments, and crusts. They are enriched in various trace elements, such as manganese, iron, copper, cobalt, nickel, and zinc, making them a significant repository for some of these metals. Most of the metals in the polymetallic sulfides are of hydrothermal origin. These sulfides have been deposited as metalliferous sediments aroimd hydrothermal systems and as rocks that infill cracks within former... 

Element Z (atomic ) Upper Crust Shale Pelagic Clay Phosphorite Fe-Mn Nodule Fe-Mn Crust MOR Basal Sediment MOR Ridge Sediment Seawater Hydro- thermal Fluid... 

It is apparent from our pXRF analyses that at the scale of the analytical window, there are regular, reproducible, variations in element enrichments between sulfide accumulations (nodules, concretions, crusts) and shale matrix. Some of the largest base metal and associated element contents measured in the field (e.g. Zn = 1.4 wt% Cu = 600 ppm Mn = 1 wt% Cd = 90 ppm Hg = 50 ppm) are in apparently (to the naked eye) sulfide-free shale. The majority of such enrichments appear to be due to the incorporation of disseminated, very fine-grained, Fe-rich sphalerite. In many instances this is not evident even when using a hand lens, and care must be taken not to overlook these cryptic enrichments. 

Variability of U and some trace elements in ferromanganese nodules of the Clarion-Clipperton zone (Pacific Ocean) and mechanism of their formation... 

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