Mineral processing is a complex of technological measures directed to increasing concentration of useful components in minerals mined from subsoil. Process of preparation takes intermediate place between mining and subsequent processing of useful components. It is stipulated by technology of further processing of natural resources.
Necessity of processing , as a rule, is connected with low content of useful component in mined ore. For example, content of molybdenum in ore makes up 0.06% , while for concentration of metallurgical conversion content of molybdenum should be not less than 45 %. With small concentration of useful component in process of metallurgical conversion the loss of metal takes place, besides it requires a great number of heat carriers. Thus, preparation is operation caused by technology and process economics of treatment.
Kinds of natural resources
All natural resources which are subjected to preparation can be divided into the following types :
1.Metallic : containing copper, lead, zinc, molybdenum , etc.
2.Coal containing : graphite, coal, anthracite.
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Types of preparation plants
Depending on processed raw material the preparation plants are classified into the following types :
•Plants for dressing ores of ferrous and non-ferrous metals - mining preparation plants, central mining preparation plants, ore mining and smelting works
•Plants for preparation coals, anthracites - mining preparation plants, Central preparation plant
•Plants attached to coke chemical works – preparation plant.
Products of preparation
As a result of preparation the following products are obtained:
•Concentrate : product containing maximum amount of useful component
•Intermediate product : product of intermediate position in quality between concentrate and wastes
• wastes – product containing minimum amount of useful component.
Technological factors of preparation processes
There are two groups of factors :
1.Characterizing amount of material under preparation
2.Characterizing quality of material under preparation and products of preparation.
To quantitative indexes include loading and yield.
Loading (Q,t/h) – it is amount of material expressed in t/h coming into operation.
Yield (y, %) – it is amount of product in relation to raw material, expressed in percents.
Y=Qproduct* 100/Qin, %
Quality of preparation products is evaluated with the following factors :
-Ash content (Ad, %), characterizes content of noncombustible residue after burning unit of product mass
-Humidity (Wr, % ), characterizes content of moisture in unit mass of product
-Sulfur content (Sd,%) , characterizes content of sulfur in coals or in products of preparation
-Volatiles content (Vd, %) - characterizes content of hydrocarbons in coal
For ores the following factors are used :
•Content of metal in base ore ……a, %
•Content of metal in concentrate …….b, %
•Content of metal in wastes …………Q, %
Efficiency of process is evaluated by factor called recovery (E, % )
E=y*b/a, %
Kinds of preparation procedures
Process of preparation includes the following operations:
1.Preparatory. They include: crushing, grinding, screening. They are used to prepare material for preparation
2.Major. They are as follows : gravity processes, flotation processes, magnetic separation, electrical separation, special methods of preparation. They are intended for direct separation of material for useful components and wastes.
3.Final. They include : dewatering, classification for commercial grades.
They are used for bringing preparation products to quality standards.
Sequence of operations of preparation is called process flowsheet.
Properties of minerals and methods of preparation
Into process of preparation are laid difference of minerals in different properties. The more contrast these differences , the higher efficiency of mineral separation. To the properties of minerals accepted as a basis of separation are referred the following :
•Density
•Wetting by water
•Magnetic susceptibility
•Electric conductivity
•Group of properties laid into basis of special methods of preparation
Density is laid into basis of gravity processes , which include the following : heavy media separation, jigging, table concentration, sluicing, spiraling, washing in heavy medium cyclones .
Difference in wetting ability is laid into basis of flotation process. Difference in magnetic properties is laid into basis of magnetic separation. Difference in colour, shine, hardness, coefficient of friction, radiation, etc., is laid into basis of special methods of preparation.