Screening of Materials and Types of Screens...

Screening of Materials and Types of Screens Size control is done (i) to prevent undersize in the feed from blocking the next size reduction stage (scalping), (ii) to prevent oversize from moving into the next size reduction or operation stage (circuit sizing), and (iii) to prepare a sized product (product sizing). There are two methods dominating size control processes. They are (i) screening using a geometrical pattern for size control, and (ii) classification using particle motion for size control. Screening using geometrical patterns for size control (Fig 1) makes use of screening media made of bars, wires, and panels with holes usually rounds, squares, rectangle aligned to length and rectangle aligned to width. Fig 1 Geometrical patterns for the size control Screening is the process of separating solids into two or more products on basis of their size. The objective of screening is size control. The purpose of screening is to separate from a granular substance particles that are smaller than the screen opening from those that are larger. This is not as simple as it sounds, and the difficulties compound as the opening becomes smaller. This can be done dry or wet. Action of screening is aided when screen is subjected to some kind of motion, reciprocating or gyratory in the horizontal plane, or shaken with a reciprocating motion having both vertical and horizontal components. The minus particles pass through the screen at a diminishing rate until all but the particles closest to the opening size have been separated out. The time duration of the shaking to reach this stage is roughly proportional to the amount of the material on the screen. The performance of screens falls back on three main parameters namely (i) motion, (ii) inclination, and (iii) screening media. It is...

Understanding Iron Ores and Mining of Iron Ore Apr03

Understanding Iron Ores and Mining of Iron Ore...

Understanding Iron Ores and Mining of Iron Ore Iron (Fe) is an abundant and a widely distributed element in the in the crust of the earth, constituting on anĀ  average ranging from 2 % to 3 % in sedimentary rocks to 8.5 % in basalt and gabbro. Its supply is essentially limitless in almost all regions of the world. However, most of this iron is not in a form which can be used in current iron making practices. Hence only that part of the total iron in the crust of the earth which is available to the steel industry both economically and spatially, may correctly be termed iron ore. However, what constitutes iron ore varies widely from place to place and time to time. There are many factors which determine whether iron bearing mineral can be classified as an iron ore, but basically it is a question of economics. Keeping this concept in mind, a logical definition of iron ore for commercial purposes is ‘iron bearing material that can be economically used at a particular place and time under then current cost and market price conditions.’ Because iron is present in many areas, it is of relatively of low value and thus a deposit must have a high percentage of Fe to be considered ore grade. With the advent of improved methods of beneficiation, concentration and agglomeration, the variety of iron bearing materials that can now be used has been broadened and many low grade material types which were once considered uneconomic, are now being considered as iron ore. Typically, a deposit must contain at least 25 % Fe to be considered economically recoverable. Over 300 minerals contain iron but five minerals are the primary sources of iron ore. They are (i) magnetite (Fe3O4),...