Refractory or difficult to treat ores, ie, those containing excessive amounts of sulfur as pyrites or pyrrhotites, arsenic, teUurides, or carbonaceous material, are pretreated prior to extraction. Pretreatment may include fine grinding, roasting, or pressure oxidation (autoclaving) (18—27), as well as biological preoxidation. Roasting achieves oxidation of sulfides, teUurides, and carbon, and creates porosity (17). The roasting temperature must be carefuUy controUed. The economics of processing refractory ores have been reviewed (28).  [c.379]

Magnetic susceptibiUty, a bulk property, is the ratio of the intensity of magnetization (M) produced in the mineral to the magnetic field (H) which produces the magnetization. In addition to field intensity, field gradient, ie, the rate at which field intensity increases toward the magnet surface, is also important (2). Minerals may be divided into ferromagnetic, paramagnetic, and diamagnetic depending on how strongly they interact with an appHed magnetic field. Iron and magnetite are ferromagnetic hematite, ilmenite, pyrrhotite, wolframite, and chromite are paramagnetic quartz and feldspar are diamagnetic. Magnetic susceptibiUty is ca —0.001 for quartz and ca 0.01 for hematite (2). It is much higher for ferromagnetic materials and is a function of the magnetic field.  [c.408]

The SRC-II process, shown in Figure 2, was developed in order to minimise the production of soHds from the SRC-I coal processing scheme. The principal variation of the SRC-II process relative to SRC-I was incorporation of a recycle loop for the heavy ends of the primary Hquefaction process. It was quickly realized that minerals which were concentrated in this recycle stream served as heterogeneous hydrogenation catalysts which aided in the distillate production reactions. In particular, pyrrhotites, non stoichiometric iron sulfides, produced by reduction of iron pyrite were identified as being  [c.281]

Strom, m. magnetizing eurrent. Magnet-kern, m. magnet core, -kies, m. magnetic pyrites (pyrrhotite). -kraft,/. magnetic force, -messer, m. magnetometer, -nadel, /. magnetic needle.  [c.286]

Figure 4-469 shows the effect on corrosion rates of 1020 steel in different water systems with dissolved hydrogen sulfide. The difference in corrosion rates is due to different corrosion products formed in different solutions. In solution I, kansite forms. Kansite is widely protective as the pyrrhotite coats the surface giving slightly more protection until a very protective pyrite scale is formed. In solution II, only kansite scale forms, resulting in continued increase in the corrosion rate. Finally, in solution 111, pyrite scale is formed as in solution I however, continued corrosion may be due to the presence of carbon dioxide.  [c.1308]

Nickel is found as a constitutent in most meteorites and often serves as one of the criteria for distinguishing a meteorite from other minerals. Iron meteorites, or siderites, may contain iron alloyed with from 5 percent to nearly 20 percent nickel. Nickel is obtained commercially from pentlandite and pyrrhotite of the Sudbury region of Ontario, a district that produces about 30 percent of the world s supply of nicke.  [c.67]

Some of the most important metal sulfides are pyrite [1309-36-0] EeS2 chalcopyrite [1308-56-1J, CuEeS2 pyrrhotite [1310-50-5] Ee sphalerite [12169-28-7] ZnS galena [12179-39-4] PbS arsenopyrite [1303-18-0] 2 pentlandite [53809-86-2] (Fe,Ni)2Sg. Sulfide deposits often occur in  [c.119]

Heterogeneous reactions. This categoiy covers the greatest commercial use of fluidized beds other than petroleum cracldug. The roasting of sulfide, arsenical, and/or autimouial ores to facilitate the release of gold or silver values the roasting of pyrite, pyrrhotite, or naturally occurring sulfur ores to provide SO9 for sulfuric acid manufacture and the roasting of copper, cobalt, and zinc sulfide ores to solubilize the metal values are the major metallurgical uses. Figure 17-26 shows basic items in the system.  [c.1573]

A Dorr-Oliver fluidized bed roaster 5.5 m (18 ft) in diameter, 7.6 m (25 ft) high, with a bed height of 1.2 to 1.5 m (3.9 to 4.9 ft) has a capacity of 154,000 to 200,000 kg/d (340,000 40,000 IbiTi/d) at 650 to 700°C (1,200 to 1,300°F) (Kunii and Levenspiel, Fluidization Engineering, Butterworth, 1991). Two modes of operation can be used tor a fluidized bed unit hke that shown in Fig. 23-43. In one operation, a stable bed level is maintained at a superficial gas velocity of 0.48 iti/s (1.6 ft/s) a unit 4.8 m (16 ft) in diameter, 1.5 m (4.9 ft) bed depth, 3 m (9.8 ft) freeboard, has a capacity of 82,000 kg/d (180,000 Ibm/d) pyrrhotite, 200 mesh, 53 percent entrained sohds, 875°C (1,600°F). In the other mode, the superficial gas velocity is 1.1 m/s (3.6 ft/s) and 100 percent entrainment occurs. This is called transfer line or pneumatic transport reaction a unit 6.6 m (22 ft) diameter by 1.8 m (5.9 ft) handles 545,000 kg/d (1.2 X 10" IbiTi/d), 200 mesh, 780°C (1,436°F).  [c.2126]

The coiTesponding reaction for die oxidation of pyrrhotite has a somewhat different behaviour. There is an initial reaction leading to the formation of SO2, but no formation of the oxide layer. After a period of oxidation in dris mode, die reaction shown by pyrite occurs, with the formation of a cracked oxide product. During the initial quiet period it is found that die sulphur/hon ratio in the sample increases and iron is removed to the surface as magnetite, until a critical state is reached where oxidation of sulphur occurs. PyiThotite is known to show a range of composition, and it is dris range which is traversed before the oxidation of sulphur occurs. Clearly, the iron is initially removed from the interior of the solid to the gas-solid interface where it has a lower chemical potential in combination with oxygen. This phenomenon is common among sulphides, and when these are complex, i.e. drey contain more than  [c.282]

See pages that mention the term Pyrrhotite : [c.832]    [c.832]    [c.438]    [c.2]    [c.419]    [c.120]    [c.383]    [c.60]    [c.1832]    [c.125]   
The Nalco Guide to Cooling Water System Failure Analysis (1993) -- [ c.74 ]