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metallurgy notes,mineral dressing,mod 1 Lecture 2






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    metallurgy notes,mineral dressing,mod 1 Lecture 2 metallurgy notes,mineral dressing,mod 1 Lecture 2 Presentation Transcript

    • MINERAL DRESSING METALLURGY , SEM 3 MODULE 1 LECTURE2 Ref: Chapters 1-3 , “ Mineral processing”, S.K.JAIN, CBS PUBLISHERS & DISTRIBUTORS P Ltd, N. Delhi, 2012. Chapter 1, “Principles of Mineral Dressing” , A. M. GAUDIN, TATA McGRAW HILL,1993. 1
    • PHYSICAL PROPERTIES OF MINERALS 5. TENACITY, BRITTLENESS , FRIABILITY – This refers to the breaking strength of a mineral – ability of a mineral to withstand shock, crushing, cutting, bending actions. Eg:- Gold is soft but difficult to break. Terms used to describe tenacity of minerals:- 1. Malleable - These minerals are very soft and can be beaten to thin sheets without breaking( Native metals of Cu, Au, Ag). 2. Brittle - These minerals are very hard but crumble to pieces under shock load - Diamond, quartz. 3. Elastic - This type of minerals can be bent , but they spring back on removal of the bending force – Muscovite- common mica KAl2(AlSi3O10)(F,OH)2 , 4. Flexible - They can be bent but remains distorted on removing the bending force- Gypsum CaSO4·2H2O, flakes of molybdate. 2 Muscovite gypsum
    • PHYSICAL PROPERTIES OF MINERALS 5. TENACITY, BRITTLENESS , FRIABILITY – Hardness and toughness of a mineral determine how it can be ground / crushed. Hardness affects brittleness and friability(Readily crumbled), Toughness affects Resilience (elasticity ). Valuables in ores are liberated from the gangue by Comminution ( Crushing & Grinding). Comminution is an expensive process. Hardness and toughness of the ore body affect this treatment. These two are the most important parameters to decide the compressive and abrasive forces needed in comminuition. They are assessed by grindability tests and suitable methods are used. Finer the grains , tougher the mineral- more force needed in comminution. 3
    • 4 PHYSICAL PROPERTIES OF MINERALS 5. TENACITY, BRITTLENESS , FRIABILITY – Toughness is influenced by the crystal structure and grain size. The smaller the grains, the tougher the material- more force needed in comminution. Many ores have valuable sulphide minerals and unwanted silicate gangue. The sulphides are friable and the silicates are tough. Normally , on breaking, finer particles ( powder) will be richer in sulphide- they shouldnot be thrown out after comminution.
    • PHYSICAL PROPERTIES OF MINERALS 5.CLEAVAGE- property of a mineral to break evenly along one or more special directions. It leaves a smooth plane. It is the tendency of crystalline materials to split along definite crystallographic structural planes. As the crystal structure is regular & repetitive, cleavage planes are also regular. These planes are of relative weakness. Eg:- Mica – breaking along very closely spaced flat planes that yield thin "sheets”. IT IS AN IMPORTANT PORPERTY TO DISTINGUISH MINERALS. 5 Green fluorite with prominent cleavage. Definition of cleavage- Cleavage is the tendency of a mineral to break along smooth planes parallel to zones of weak bonding.
    • 5.CLEAVAGE- Cleavages are described in terms of their quality - how smoothly the mineral breaks and their difficulty - how easy or how hard, it is to produce the cleavage. The quality of cleavages are perfect, imperfect, distinct, good, fair, and poor. The difficulty is described as easy, hard, and difficult to produce. Mica has a perfect cleavage in one direction that is easy to produce. Calcite has a perfect cleavage in three directions that is also easy to produce. Feldspars have a perfect cleavage in one direction that is easy to produce and a good cleavage in another direction that is hard to produce. Diamond has a perfect cleavage in four directions that is easy to produce etc. PHYSICAL PROPERTIES OF MINERALS 6
    • PHYSICAL PROPERTIES OF MINERALS 5.CLEAVAGE- Cleavage describes how a crystal breaks when subjected to stress on a particular plane. If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has cleavage. A mineral that doesnot produce any crystallised fragments when broken off - has no cleavage. Cleavage is often measured by three factors: 1) Quality of Cleavage (Perfect,Good,Poor, distinct, none etc) 2) Number of Sides Exhibiting Cleavage ( 1,2,3 all) 3) Cleavage Habit ( basal, cubic, octahedral ..) 7
    • PHYSICAL PROPERTIES OF MINERALS 5.FRACTURE- Refers to the appearance of the surface of minerals when broken Fracture is the shape and texture of the surface formed when a mineral is broken. Minerals often have a highly distinctive fracture. This property can be used in their identification. Fracture is different from cleavage. Cleavage involves clean splitting along the cleavage planes of the mineral's crystal structure. The mineral cleaves along the plane of atoms. Fracture is general breakage. It doesnot have special direction within a crystal structure. The mineral fractures across the planes of atoms. 8 Fractured surface
    • CONCHOIDAL FRACTURE- has concentric sets of cracks – looks like the concentric ripples of a mussel shell – Eg:- glass, quartz, olivine etc. EARTHY FRACTURE - looks like freshly broken soil. It is frequently seen in relatively soft, loosely bound minerals, such as limonite, kaolinite, aluminite .. HACKLY FRACTURE (JAGGED FRACTURE) - jagged, sharp and not even. It occurs when metals are torn, and so is often en countered in native copper, and silver. PHYSICAL PROPERTIES OF MINERALS 5.FRACTURE- 9
    • PHYSICAL PROPERTIES OF MINERALS 5.FRACTURE- The shape into which the mineral breaks depends on its crystalline nature. Eg:- Galena breaks into cubes Feldspar breaks into elongated fragments. Mica breaks into flat scales. Magnetite breaks into rounded grains. Chalacopyrate breaks into conchoidal fragments. Galena PbS Feldspar Mica Chalacopyrate ( Cu Fe Sulphide) 10
    • PHYSICAL PROPERTIES OF MINERALS 6. MAGNETIC PROPERTIES- Some minerals arte strongly attracted by magnets than others. This property is extremely useful in separating minerals. Diamagnetic ( slightly repelled) - Magnetic minerals result from properties that are specific to a number of elements. Minerals that do not have these elements, and thus have no magnetism are called diamagnetic Eg:-quartz, calcite, apatite. Paramagnetic ( weakly magnetic)- Elements like Ti, Cr, V, Mn, Fe, Co, Ni, and Cu can sometimes result in magnetism. Minerals that contain these elements may be weakly magnetic and can be separated from each other by their various degrees of magnetic susceptibility. These are called paramagnetic minerals. Paramagnetic minerals only show magnetic properties when subjected to an external magnetic field. When the magnetic field is removed, the minerals have no magnetism- heamatite, beryl. 11
    • PHYSICAL PROPERTIES OF MINERALS 6. MAGNETIC PROPERTIES- Ferromagnetic ( permanently magnetic- parallel spins)- minerals having permanent magnetism if the temperature is below the Curie Temperature.(the temperature above which a ferromagnetic substance loses its ferromagnetism and becomes paramagnetic ). These materials will become magnetized when placed in a magnetic field, and will remain magnetic after the external field is removed. Eg:- magnetite, hematite, pyrrhotite. Antiferromagnetic ( antiparallel spins)- Minerals with no permanent magnetic moment. Ferrimagnetic - minerals have antiparallel elements where components in opposite directions are unequal. It results in permanent magnetic moment. MAGNETS ARE USED TO SEPARATE MINERALS. MINERALS ATTRACTED BY MAGNETS ARE FERROMAGNETIC. MINERALS NOT ATTRACTED- PARA OR DIAMAGNETIC. 12
    • PHYSICAL PROPERTIES OF MINERALS 7. ELECTRICAL PROPERTIES- Refer to 1)the behaviour of the minerals when affected by electricity or 2) the ways in which minerals may produce electric currents. Minerals can be conductors or non conductors of electricity. Some non conducting minerals produce electricity when subjected to temperature changes – PYROELECTRICITY- Eg:- Tourmaline. Some minerals ( like Quartz) produce electric current when the crystal is subjected to mechanical cycling- PIEZOELECTRICITY. ELECTRICAL CONDUCTIVITIES OF MINERAL ARE USED TO SEPARATE THEM EFFECTIVELY. 13 Piezoelectric property
    • PHYSICAL PROPERTIES OF MINERALS 15 Isotopes - variants of a particular element. All isotopes of a given element share the same number of protons andelectrons. Each isotope has different number of neutrons 8. RADIACTIVE PROPERTIES- Radioactive minerals emit high energy radiations – alpha α, beta β, gamma γ . Radioactive minerals contain radioactive elements- U Uraninite, Th in Thorite. U and Th decay spontaneously by emitting a helium nucleus ( α particle ) (2 protons and 2 neutrons ) from the parent isotope. This is followed by loosing an electron ( β particle ) . There is a simultaneous emission of γ rays too. This is followed by successive emissions of α and β particles till a stable isotope of lead is formed. The emitted radiation is measured ( Scintillation Counter)
    • PHYSICAL PROPERTIES OF MINERALS 9. OPTICAL PROPERTIES - Depend on atomic arrangement in the mineral. Refractive index- measure of the bending of a ray of light when passing from one medium into another. The differences in optical properties are used to identify and separate them. 10. FRICTION – Ability of mineral particles to move or slide on a surface. It is affected by the size, shape and coefficient of friction of the particles. 16
    • PHYSICO - CHEMICAL PROPERTIES OF MINERALS The chemical properties used should affect only the physical behaviour of the mineral, no chemical change should take place ( It may affect the mechanical operations that follow) , may be used to effect chemical changes, if chemical beneficiation is used. 17
    • PHYSICO - CHEMICAL PROPERTIES OF MINERALS 18 1. CHANGE IN POROSITY ON HEATING- Certain minerals loose volatile constituents on heating. They become spongy. The pores get filled with air. This lowers apparent specific gravity . This helps in separation of minerals. 2. DECREPITATION- Decrepitation is the act of heating up a mineral to the point that it crackles or fly to pieces until the crackling stops. This is due to unequal expansion within the mineral molecules on heating. Eg Calcite, Flourite, Barite. This property is used to separate minerals that decripitate.
    • PHYSICO - CHEMICAL PROPERTIES OF MINERALS 19 3. CHANGE IN MAGNETISM ON HEATING- Slightly magnetic / non magnetic Minerals of iron loose oxygen, carbonic acid, sulphur etc and become strongly magnetic .Certain minerals loose volatile constituents on heating. They can be separated out now with the aid of a magnet. 4. SURFACE PROPERTIES- Surface properties like greasiness, adhesion, wettability, surface tension etc are used for separating minerals ( flotation, amalgamation, selective adhesion etc) Surface properties may be modified using chemical reagents. 5. SELECTIVE DISSOLUTION- Dissolve either the valuables or the gangue selectively using chemicals. Eg: in Gold Cyanidation , Au is dissolved in cyanide and removed from the impurities. It is later Recovered.
    • 21 THANK YOU