Haematite deposition

The ilmenite-haematite deposits usually contain these minerals in intimate intergrowths, and hemo-ilmenite concentrates can be produced from these ores. 

Fig. 7.9 shows the effect ofpH on the measured haematite deposit mass per unit area with time. In these experiments the particulate concentration was 100 mg/kg and the Reynolds number 11,000. The high levels of deposit mass per unit area at a pH of around 6 may also be compared to the data on Fig. 7.10. The pH controls the magnitude and sign of charges on particles and substrate, as shown in the work of Matijevic [1982]. It may be possible with systems having these characteristics that particle deposition could be limited by suitable pH control. It is also interesting that the work of Newson et al [1988] with turbulent flow conditions gave similar results to Kuo and Matijevic [1980] for laminar flow through a packed bed.

Williamson [1990] has presented data that show the dependence of the haematite deposition (i.e. 0.2 pm particles) on velocity. Fig. 7.12 illustrates the rapid fall in asymptotic deposit mass mg/m ) as velocity is increased. Fig. 7.12 also records the corresponding values of friction velocity u and Reynolds number. The data suggest that employing velocities > 2 m/s would minimise the fouling due to particle deposition. 

A laboratory system to study the removal of particulate haematite deposits is shown on Fig. 17.3 [Williamson 1990]. The similarities to the equipment shown in Fig. 17.1 are apparent. In this particular experiment radioactivity is used to measure changes in the deposit thickness. 

Anorthositic deposits - nearly all of the known commercially important rock deposits of titanium minerals are associated with anorthositic or gabbroic rocks. There are three main types (a) ilmenite-magnetite (titanoferous magnetite), (b) ilmenite-haematite, and (c) ilmenite-rutile. 

Fe203.H20, is a common ore which contains about 5 per cent, of water. It occurs as an earthy deposit frequently known as red haematite and as red ochre it is also found in a compact, fibrous condition, and in botryoidal and stalactitic forms, similar to limonite, for which ore it has frequently been mistaken. It may usually be distinguished by its redder colour, its red streak, and its greater hardness. Hardness 5 to 6 density 3-56 to 4 7. When heated in a tube it splinters in a characteristic manner, which serves to distinguish it from limonite and other ores of analogous composition. 

Large deposits of brown haematite occur in Northamptonshire, the beds extending into Lincolnshire and Oxfordshire. The ore is abundant in the U.S.A. 

Beneath the brown haematite ores of Northamptonshire, an impure unaltered ferrous carbonate deposit occurs which is bluish or greenish-grey in appearance. The depth at which it lies represents the depth to which weathering or oxidation of the upper layers has occurred. 

Figure 3.8 Examples from the ferricrete alteration profile observed at outcrop at Palika Ba (13°28 N, 15°14 W), near the Gambia River, Gambia, West Africa. (A) Nodules of ferricrete developing within Quaternary alluvial sands and silts deposited by the Gambia River. Nodules consist of predominantly goethite with minor haematite (sample PG4 in Table 3.3). (B) Massive iron-cemented ferricrete horizon displaying characteristic tubes (i.e vermiform structure sample PG2 in Table 3.3). Importantly, the iron cement is entirely due to the introduction of allochthonous iron into the pore spaces of the sediment.

In Fig. 4, some data on the deposition of the corrosion product haematite from water flowing through 316 stainless steel tubes at different pH values is provided. 4 Conditions under which these data were obtained include particle size of approximately 0.2 pm, particle concentration of lOOmg/kg, and a Reynolds number of 11,000. 

Newson, I.H. Miller, G.A. Haynes, J.W. Bott, T.R. Williamson, R.D. Particulate fouling studies of deposition, removal and sticking mechanism in a haematite/water system. Proceedings of the Second U.K. National Conference on Heat Transfer, Glasgow, U.K., Sept 14—16, 1988 Int. Mech. Eng., London, U.K., 1988 137-160. 

One clue to oxygen levels during this period is to be found in the very same iron formations that overlie the shales of the Hamersley Range. Massive sedimentary iron formations were deposited here and around the world in alternating bands of red or black ironstone (haematite and magnetite, respectively), and sediment, typically flint or quartz. The individual bands range in depth from millimetres to metres, while the formations themselves can be up to 600 metres [approximately 2000 feet] thick. Most of these formations were deposited between 2.6 and 1.8 billion years ago, but sporadic outcrops range in age from 3.8 billion to 800 million years. 

Newson et al [1988] have studied the deposition of small diameter particles (-0.2 fjm) of haematite (Fef) ) from a water system onto aluminium and 316 stainless steel tubes. Particle concentrations up to 210 mg/Jcg and Reynolds numbers in the range 11,000 - 140,000 were employed. These authors found a significant effect of pH on the extent of the deposition and also that it would appear that agglomeration of particles in suspension could also be significant. 

The initial deposition rate was determined for a series of experiments and divided by the particulate concentration, i.e. representing the driving force (see Equation 7.2) to give a deposition Kp. The mass transfer coefficient is a maximum at a pH of about 6.2. It would also appear that there is little difference between "fresh" and "used" haematite particles that may have experienced agglomeration. 

In their comprehensive studies of the haematite particle deposition Newson et al... 

FIGURE 17.4. Data obtained on haematite particle deposition... 

Migration of dissolved substances from a fault into the body of the limestone can result in mineralisation of the rock in the immediate vicinity of the fault. For routine limestone production, such rock is generally tipped. However, commercially important metal ore deposits are found in certain types of limestone. They include galena (PbS), sphalerite (ZnS), barite (BaCO ), haematite (Fe203) and fluorite (CaF2). A few deposits contain commercially viable concentrations of trace metals, the more important of which are silver and mercury. 

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