Need for Processing

Any ore in general, seldom occurs in purity and form required by the industry iron ore is no exception to it. In many cases, presence of deleterious impurities like silica, alumina, sulphur and phosphorous beyond desired limits render the ore unsuitability for use in iron-making or adversely effects its productivity and quality both.

Efficient and economic production of pig iron in blast furnace depends to a very large extent on the input of appropriate quality of raw materials. Some of the common methods/techniques applicable for iron ore processing are discussed below:

Washing and wet scrubbing

This process is widely in lumpy iron ore processing to dislodge soft and friable lateritic masses, fine sand and limonitic clay particles adhering to lumps. The scrubbing practice is also helpful in hard and porous hematite lumps, which invariably have cavities filled with clayed material, and that needs substantial elimination.

Gravity concentration

This technique is deployed if valuable and heavy iron minerals are free from associated light gangue minerals or waste rock. It is the simplest method of ore dressing and depends on the fact that in general the metallic compounds have a higher specific gravity than the gangue, and hence settle faster in a steam of water. Gold panning is the simplest illustration of the procedure. On a larger scale, it is carried on in jibs where ore is placed on a screen and a pulsating stream of water forced through the screen, causing the lighter gangue to be washed out. Another form of gravity concentrator is the table, consisting of a surface with longitudinal ridges, which is given a jerking end-to-end motion (возвратно-поступательное движение) while a stream of water flows across it laterally.

As it was mentioned above, the common iron ore minerals have usually high specific gravity (hematite: 5.1, magnetite: 5.2 and siderite: 3.8) as compared to the most common associated gangue minerals like, quartz (2.65), limestone (2.75), and clay (2.63).

Effectiveness of gravity concentration depends on proper feed preparation, which includes crushing, screening and grinding to ensure feed of proper size to a particular unit operation, which affects the separation efficiency of the machine, as it enhances the viscosity of the pulp before subsequent treatment.

Модуль 2 заняття 2-3 Elements and their Classification

If we pass an electric current through the water using platinum or gold electrodes to introduce the current into the water, we find that two gases are give off at the electrodes and the water is used up. If we collect the gas given off at the negative electrode, we find that it is very light, that the soap bubbles filled with it rise like balloons and that it will burn in air with a faintly luminous very hot flame. This gas is hydrogen. The other gas, given off the positive electrode, will not burn in air, but burning substances thrust into it will continue to burn with greatly increased vigour and brilliancy. We know this gas to be oxygen, also one of the constituents of air.

From this analysis of water we may conclude that water is a compound of hydrogen and oxygen. The analysis might be made in many other ways. We might also synthesize water by allowing hydrogen and oxygen to combine, which they do very rapidly.

It was never possible to resolve lead, oxygen, and hydrogen into simpler substances. These substances and all others, which have never by ordinary chemical reactions been resolved into simpler substances, were given the name of elements. About one hundred elements are known at the present time. They are found to form almost endless combinations with each other.

The elements were classified in various ways, any of which might be useful for certain purposes. Some of them are solids, some liquids, and some gases at ordinary temperature and pressure. This is, however, not fundamental distinction, as each element may be made to exist in any of these states by suitable alterations in temperature and pressure. One of the most useful divisions was that into metals and non-metals. Several characteristics of metals and non-metals are familiar to all.

Metals are characterized by an appearance called metallic lustre, by malleability and ductility and by relatively high conductivity for heat and electricity. These physical differences are accompanied by fundamental differences in their chemical behaviour.