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Mineral processing; Beneficiation (or Mineral Dressing); Extractive Metallurgy; Beneficiation Steps: Comminution; Classification; Separation; Physical; Techniques; Chemical Techniques; Smelting; ...

Mineral processing; Beneficiation (or Mineral Dressing); Extractive Metallurgy; Beneficiation Steps: Comminution; Classification; Separation; Physical; Techniques; Chemical Techniques; Smelting; Electrochemical Refining of pure metal; Dewatering; Product Handling; China Clay processing; Limestone Cycle; Lime; Soda Ash; Processing Silica Sand Sand into Silicon; Silicon carbide ; Heavy Mineral Sand; Separation of zircon from the heavy sand raw material; Zirconium Extraction
Titania; Alumina: Bayer process; Magnesium oxide; Feldspar

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  • 1. Topic 2: Mineral Processing Prof. Dr. H.Z. Harraz Presentation Mineral Processing A short series of lectures prepared for the Third year of Geology, Tanta University 2013- 2014 by Hassan Z. Harraz hharraz2006@yahoo.com
  • 2. OUTLINE OF TOPIC 2: Defination Mineral processing Beneficiation (or Mineral Dressing) Extractive Metallurgy Beneficiation Steps: 1) Comminution 2) Classification 3) Separation i) Physical Techniques ii) Chemical Techniques iii) Smelting iv) Electrochemical Refining of pure metal 4) Dewatering 5) Product Handling Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 2 Examples:  Kaolinite  China Clay processing  Limestone  Limestone Cycle  Lime  Soda Ash  Silica Sand  Processing Silica Sand  Sand into Silicon  Silicon carbide  Heavy Mineral Sand  Separation of zircon from the heavy sand raw material  Zirconium Extraction  Titania  Alumina: Bayer process  Magnesium oxide  Feldspar
  • 3. Figure Disciplines related to mineral processing Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 3
  • 4. Mineral Processing Mining Mineral Processing Refining Comminution Manufacture Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 4
  • 5. What is mineral processing? Processing:–  Is the recovery of valuable minerals from ore  Extraction of metal from rock/mineral  Extract values, reject waste Conversion of mined ore into usable product:  More expensive/challenging with lower grade ores  Numerous processing methods Mineral Processing Methods = Beneficiation + Extractive Metallurgy Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 5
  • 6. Fields of Metallurgical Engineering Methods Field Description Steps Mineral Processing Beneficiation or Mineral Dressing Theory and practice of liberation of minerals from ores and their separation by physical methods at ambient conditions i) Crushing and Grinding, ii) Magnetic and Electrical methods, iii) Flotation, …etc. Extractive Metallurgy Chemical methods sometimes at high temperature and pressure for treating ores to recover their metal values in a pure form i) Leaching, ii) Precipitation, iii) Electrolysis, iv) Oxidation, v) Reduction, …etc. Metal Processing Physical metallurgy Study of physical properties of metals and alloys, preparation of alloys Crystal structure, effect of impurities, metallography, heat treatment, etc. Engineering metallurgy Processing of metals in the molten state Casting, welding, etc. Mechanical metallurgy Processing of metals in the solid state Forging, rolling, extrusion, piercing Powder metallurgy Processing of metal powders into finished products Preparation of metals in powder form, hot pressing, etc.
  • 7. 1) Beneficiation (or Mineral Dressing):  Theory and practice of liberation of minerals from ores and their separation by physical methods at ambient conditions  Overlap of physical and chemical methods, depending on product,  Enrichment of ores and separation of unwanted gangue minerals  Subsequent metals extraction more efficient.  Can be divided into two distinct steps: i) Liberation: the rock is broken down by mechanical means, mineral components become independent of each other, detached. ii) Separation: valuable minerals are separated by means of physical and physico- chemical methods making use of differences in specific gravity, magnetic properties, ..etc. 2) Extractive Metallurgy:  Chemical methods sometimes at high temperature and pressure for treating ores to recover their metal values in a pure form.  Leaves off, metal processing begins .  Chemical reactions of the processes.  Equipment where reactions take place.  Flowsheets – combinations of processes. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 7
  • 8. 1) Comminution 2) Classification 3) Separation: i) Physical Techniques ii) Chemical Techniques iii) Smelting iv) Electrochemical Refining of pure metal 4) Dewatering 5) Product Handling Beneficiation (or Mineral Dressing) Steps: Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 8
  • 9. 1) Comminution:  Reduction of particle size  Size reduction by crushing and milling.  Starts at mine with blasting  Two basic types of equipment used: Crushing : breakage by compression Grinding : breakage by abrasion and impact 2) Classification:  Size separation by differential gravitational settling.  Separation based mainly on particle size  Behavior affected by size, shape, and density of the particles  Two common types of classifiers:  Screens : size separation by sieves-dry method, coarser particles  Hydrocyclones : wet method, finer particles Beneficiation (or Mineral Dressing) Steps: Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 9
  • 10. Shaft Comminution Equipment
  • 11. Shaft Comminution Equipment
  • 12. Classification Equipment
  • 13. 3) Separation :  take advantage of the differences in characteristics between minerals..  Depending on the ore, the number and sequence of the processes will be different.  Particle size distribution has large influence on results  separation of different phases in the feed: i) Physical Techniques:-  Gravity: differences in specific gravity of materials  Gold from quartz  Diamonds  Tantalum  Dense medium separation  Flotation: Attachment of minerals to air bubbles - hydrophibicity  Sulphides from silicates  Cu and Ni sulphides  NaCl from KCl  Magnetic Separation: Apply magnetic field  Electrostatic Separation: Apply electrostatic polarity Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 13
  • 14. Separation Equipment  Flotation cell
  • 15. Separation Equipment  Magnetic separator
  • 16. Separation Equipment  Electrostatic separator
  • 17. Separation Equipment  Gravity separation - jig
  • 18. 3) Separation Techniques (cont.) : ii) Chemical Techniques:  CN leaching  Roaster oxidizes: sulphide to SO2 Example: 2ZnS + 3O2  2ZnO + 2SO2 iii) Smelting:  Separates remaining silicates from metals  Slag (molten silicates) pored off  Metal pores into bars or sent for final electochemical refining iv) Electrochemical Refining of pure metal Consider the waste generated at each stage Smelting Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 18
  • 19. 4) Dewatering: To remove water from a substance. Also refers to the circuit where this takes place.  Dewatering Techniques: Thickener: Allow gravity settling Filter: Apply air pressure to draw water out Centrifuge: Apply centrifugal force Dryer: Apply heat to evaporate  Slurry Density: The amount of solids in a slurry, expressed as a percentage by weight. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 19
  • 20. Dewatering Equipment  Disc filter  Rotary kiln dryer  Thickener
  • 21. Examples
  • 22. Clay Grades Clays are categorized into six groups: 1) Kaolin or China clay: white, claylike material composed mainly of kaolinite industrial applications: paper coating and filling, refractories, fiberglass and insulation, rubber, paint, ceramics, and chemicals 2)Ball clay: kaolin with small amount of impurities industrial application: dinnerware, floor tile, pottery, sanitary ware. 3)Fire clays: kaolin with substantial impurities (diaspore, flint) industrial applications: refractories 4)Bentonite: clay composed of smectite minerals, usually montmorillonite industrial applications: drilling muds, foundry sands 5)Fuller’s earth: nonplastic clay high in magnesia, a similar to bentonite industrial applications: absorbents 6)Shale: laminated sedimentary rock consisting mainly of clay minerals mud industrial application: raw material in cement and brick manufacturing Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 22 CLAY
  • 23. Blunging :The kaolin is mixed with water and chemical dispersants, which puts the clay particles in suspension (slurry). De-gritting: The slurried kaolin is usually transported through pipelines to degritting facilities (rakes), where sand, mica and other impurities are extracted with the help of gravity. Centrifuging: The centrifuge separates the fine kaolin particles from coarse particles.Fine particles, still in the form of a slurry, move on for further processing. China Clay processing De-gritting (rake) tables Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 23
  • 24. Brightness enhancement: Undesirable colors are removed through one or more processes including bleaching, magnetic separation, flocculation, ozonation, flotation, and oxidation, which will remove iron oxides, titanium oxides, organic, and other undesirable materials. Delamination :For customers who want a delaminated clay product suited for lightweight coating applications, coarse kaolinite particles are used as starting material. Delamination occurs as the coarse particles of kaolin which when magnified appear as "booklets" are broken into thin platelets by mechanical milling. China Clay processing (cont.) Filtering and drying :Large rotary vacuum filters remove water from the slurried kaolin. Large gas-fired spray dryers remove and evaporate the remaining moisture. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 24
  • 25.  Kaolin is a relatively pure, white firing clay composed principally of the mineral kaolinite Al2Si2O5(OH)4 but containing other clay minerals, as indicated in Table 3.2, and a minor amount of impurity minerals such as quartz (SiO2), ilmenite (FeTiO3), rutile (TiO2), and hematite (Fe2O3).  Ball clay is a sedimentary clay of fine particle size containing complex organic matter ranging down to a submicron size.  Bentonite is a high proportion of the clay mineral monllonite.  Clays are used in whiteware formulations and aluminosilicate refractories to produce plasticity in forming and resistance to deformation when partial fusion occurs during firing.  Crushed and milled quartz (SiO2), derived from relatively pure deposits of sandstone granular silicate mineral used extensively in whitewares refractory and glaze compositions.  A typical flow diagram for beneficiation and refining kaolin is shown in Fig. 3.3.  Concentrated solids are usually dried using a rotary or belt dryer or by spray drying.  Some materials are calcined, and a hard aggregate is formed Dried cake or calcined materials may be pulverized or ground and then sized or air elutriated before bagging or loading in hopper cars.  Many fine materials are loaded and unloaded using pneumatic fluidization and are stored at the plant site m large silos. Examples: Beneficiation of Kaolin
  • 26. Figure shows Processing flow diagram for the beneficiation of kaolin Spray Drying Centrifugal classification Wet Screening Apron Drying Rotary Vacuum Filtration Chemical Leaching or Magnetic Separation Dragline Shovel Slurry Tank Car Hopper Car Box Car or Truck Bagging Pulverizing Slurry Blending and Storage Slurry from Other Deposits Water Portable Blunger Surface Modification Grit Grit Pump Calcined
  • 27. LIMESTONE BASIC DEFINITION  Limestone is a highly porous rock formed over thousands of years from the compression of shells and the bones of sea animals.  These carbonate rocks or fossils, comprises primarily of Calcium Carbonate (CaCO3 ) or combinations of Calcium (Ca) and Magnesium Carbonate (MgCO3) with varying amounts of impurities (silica and alumina)  High quality deposits exist – 98% CaCO3 high purity grade.  Limestone, the source material for all lime based value added products – calcined, hydrated, precipitated.  Limestone is widely used as a building construction material – concrete, blocks.  Limestone is used in the manufacture - cement and glass.  Limestone is used to strengthen and stabilize the sub-grade in road construction.  Limestone is an alkali and is used extensively to neutralize acids – PH control . USES of LIMESTONE Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 27
  • 28. Limestone Deposits in Egyptian • Egyptian’s most abundant mineral is limestone 50 - 60 billion tonnes. • High quality deposits exist – 98% CaCO3 high purity grade. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 28
  • 29. Limestone Cycle Limestone Lime Hydrated Lime Milk of Lime Heat CO2 H2OH2O CO2 H2O Slurry Calcium oxide (CaO) Calcium hydroxide (Ca(OH)2 - DRY Calcium Hydroxide Ca(OH)2 - WET Quicklime Slaked lime Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 29 CaCO3
  • 30. Vertical Lime Kiln Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 30
  • 31. Lime (CaO)  Include hydrated lime & quicklime  Only quicklime can use to make glass Extraction of Lime  Quarry of limestone  Transported to crush plants  Undergo Calcination process:  heating limestone or chalk (CaCO3) in kiln till 900oC  CO2 is emitted in this process and calcium oxide (lime) is produced. Calcination Process • Calcined lime  Quicklime/Burnt lime/White wash is obtained by heating limestone at temperatures above 900oC in a Kiln: CaCO3  heat CaO + 2CO2 • Hydrated lime  Calcium Hydroxide/Slaked Lime is a dry powder, resulting from the controlled slaking of Calcined Lime with water in a Hydrator: CaO + H2O  Ca(OH)2 • Precipitated Calcium Carbonate  Carbonation of Hydrated lime, also known as purified, refined or synthetic Calcium carbonate: CaO + H2O + CO2  CaCO3 + H2O LIME Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 31
  • 32. Purposes for the Utilize of Lime Historical Use: Ancient Egyptian civilization used lime to make plaster and mortar. Nowadays: Use extensively for: glass making, the pulp & paper industry & steel mills Other uses: municipal & industrial water / wastewater treatment, as an addictive for road stabilization & construction projects More than 90 % of lime production is for chemical and industrial uses MAJOR USES of LIME Flux – Alumina, Steel Lubricant – Wire drawings, Oil Wells Neutralisation –Water Treatment, Agricultural soils Solvent – Leather, Paints Absorption – Bleaches, Sulphur Dioxide removal Raw Material – Rubber, Cement, Concrete, Glass, Tooth-paste Bonding Agent – Mortars, Plasters, Road & Soil stabilization Causticization – Caustic soda, Alkali scrubbing Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 32
  • 33. SODA ASH (NaHCO3)  Anhydrous sodium carbonate  Texture: soft  Color: grayish & white  Appearance: lump / powder in nature Naturally:  Erosion of igneous rock form sodium deposits  Transport by waters as runoffs & collect in basins  When sodium comes in contact water/ CO2, precipitates out sodium carbonate. Synthetically:  Extraction of Soda Ash(NaHCO3),  Manufactured synthetically through Solvary process by using salt, ammonia & limestone Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 33
  • 34. Purposes for the Utilize of Soda Ash History:  Early Egypt: make glass & soap  Early Roman: make glass, bread & pharmaceuticals (medicine) purpose to cure choric & skin rashes  Glass manufacture (49%)  Chemical production (27%)  Pulp & Paper manufacturing  Sodium compounds manufacturing  Soap & detergents (11%)  Water treatment (2%)  Textile processing  Cleaning preparations  Petroleum refining  Metallurgical refining (Mineral processing in mining)  Metal refining  Removal of sulfur from smokestack emissions (3%) (5%) Nowaday: 1 April 2014 Prof. Dr. H.Z. Harraz Presentation Mineral Processing 34 Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 34
  • 35. The Solvay process for the manufacture of Soda Ash (NaHCO3). cwx.prenhall.com/petrucci/medialib/ media_portfolio/22.html Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 35
  • 36. 4) SILICA SAND Silicon is the 2nd most abundant element in earth’s crust. Commonly found in its oxidized form (SiO2). SiO2 The production of pure silicon usually begins with SiO2 and results in pure electronic-grade silicon. To work as an effective semi-conductor for electronics, silicon has to be in its purest, elemental form. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 36
  • 37. HEAVY MINERAL SANDS Sand is a naturally occurring granular material comprised of finely divided rock and mineral particles. • Sand is transported by wind and water and deposited in the form of beaches, dunes, sand spits, sand bars (placer deposits) etc. • The most common constituents of sands are silica (SiO2), usually in the form of quartz, iron oxides, zircon, rutile, ilmenite, monazite, garnet. Heavy mineral sands  A class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones.  Zircon is a coproduct or byproduct of the mining and processing of heavy-mineral sands.  Primarily worked for titanium minerals, ilmenite and tin minerals. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 37
  • 38. 1 April 2014 Prof. Dr. H.Z. Harraz Presentation Mineral Processing Fig.2: Processing Silica Sand:- (a) Stripping and extracting Silica sand; (b)Transportation system; (c )Screening silica sand; (d) Classified and grading; (e ) Silica sand washing Machines; (f) Spirals for removing heavy minerals, (g) Magnetic Separation (a) (b) (c) (d) (e) (f) (g) The glass sand requires processing as follows: (a) Stripping and extracting Silica sand; (b)Transportation system; (c )Screening silica sand; (d) Classified and Grading; sizing, using hydrocyclones, attrition scrubbing, ……etc (e ) Washing Machines; (f) Flotation and/or chemical/acid leaching to remove Fe minerals and stained quartz (g) Gravity (sluices, spirals, shaking tables, Reichert cones), Spiralling and/or tabling to remove heavy minerals. (h) Magnetic (low/high intensity dry/wet) and high tension separation methods (i) Dewatering. 38 4.1) Processing Silica Sand
  • 39. Glass Sands Beneficiation Concentration of Heavy Minerals  Gravity (sluices, spirals, shaking tables, Reichert cones),  Magnetic (low/high intensity dry/wet) and high tension separation methods can be used together to treat/upgrade the heavy content of the beach sands. Glass Sand Flotation for Iron Impurity Removal  After removal of the Fe-bearing impurities, some plants separate feldspar from quartz by floating feldspar with amines at pH 3 using HF. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 39
  • 40. 4.4) Silica Sand into Silicon Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 40 Carbon reacts with oxygen in the molten silica to produce carbon dioxide and silicon: SiO2 + C → Si + CO2 Product = metallurgical-grade silicon (99% pure). Fine powdered metallurgical-grade Si is reacted with gaseous HCl at 300°C in fluidised bed reactor: Si + 3HCl → SiHCl3 (trichlorosilane)+ H2 Product = liquid compound of silicon (trichlorosilane). Trichlorosilane is vaporized and reacted with hydrogen gas at 1100°C: SiHCl3 + H2 → Si + 3HCl Product = electronic-grade elemental silicon (99.99999% pure) Basic Process
  • 41. 4.5) Silicon carbide (SiC) • Silicon carbide SiC is produced in large tonnages using the Acheson process by reacting a batch consisting principally of high-purity sand and low-sulfur coke at 2200-2500 °C in an electric arc furnace. SiO2 + 3C → SiC + 2CO(gas) • The crystalline product is crushed, washed in acid and alkali, and then dried after iron has been removed magnetically. • Granular material is used in refractories and bonded abrasives. • Milled material chemically treated to remove impurities introduced in milling is used industrially for structural ceramics introduced in milling is used industrially for structural ceramics.
  • 42. Raw materials extraction The heavy mineral bearing sands are extracted within artifical ponds (above) by dredgers (left) and pumped to the separation and concentration plant. HEAVY MINERAL Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 42
  • 43. 4.6) Zircon containing raw materials  The principal economic source of zirconium is the zirconium silicate mineral, zircon (ZrSiO4).  Zircon is also the primary source of all hafnium.  Zirconium and hafnium are contained in zircon at a ratio of about 50 to 1.  Zircon is a coproduct or byproduct of the mining and processing of heavy-mineral sands Hawks Nest, a beach sand deposit within Murray Bay (Australia) operated by Mineral Deposits Ltd. They extract 21,147 t of concentrate from about 20’000’000 t of sand. This deposit has a very low grade (0.2 -0.3wt% heavy minerals), but large reserves. The sand is extracted by a dredge. Murray Bay heavy mineral concentrate dominated by zircon (colorless, rounded grains) and rutile (deep yellow grains) (Image length 20mm) http://www.mineraldeposits.com.au/ Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 43
  • 44. http://www.outokumpu.com http://www.tiomin.com/ Separation of zircon from the heavy sand raw material The main separation method for heavy mineral sand is based on the difference in gravity Mineral sand slurry moving down the spiral gravity separator with increased concentration of the heavy minerals in the center of the spiral. ZIRCONIUM RAW MATERIALS Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 44
  • 45.  Zirconia (ZrO2) of 99% purity is obtained by the caustic fusion of zircon (ZrSiO4).  The first step is to convert zircon to zirconyl chloride : ZrSiO4 (Zircon) + 4NaOH Na2ZrO3 + Na2SiO3 + 2H2O Na2ZrO3 + HCl ZrOCl2 8H2O (Zirconyl chloride)  There are two methods to make zirconia from the zirconyl chloride: thermal decomposition and precipitation.  The precipitation method, however, gives the better end-product: ZrOCl2 8H2O in solution + NH4OH Precipitated intermediate Zr(OH) 4 i) Chemical extraction of zirconia (ZrO2) from zircon (ZrSiO4) ore Zirconia Powder (ZrO2) http://www.zrchem.com/ ZIRCONIUM EXTRACTION Melting Wash Cl-free precipitate, wet Zr(OH) 4 Freeze Drying (Liquid N2) Dried powdered Zr(OH)4 Calcination Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 45
  • 46.  The Kroll method is used for zirconium and involves the action of chlorine and carbon .  The resultant zirconium tetrachloride (ZrCl4) is separated from the iron trichloride (FeCl3), by fractional distillation.  Finally, zirconium tetrachloride (ZrCl4) is reduced to metallic zirconium by reduction with magnesium (Mg).  Air is excluded so as to prevent contamination of the product with oxygen or nitrogen. ZrO2 + 2Cl2 + 2C (900°C)  ZrCl4 + 2CO ZrCl4 + 2Mg (1100°C)  2MgCl2 + Zr  Excess magnesium and magnesium dichloride is removed from the product by treatment with water and hydrochloric acid to leave a zirconium "sponge".  This can be melted under helium by electrical heating. ii) Chemical extraction of zirconium from zirconia Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 46
  • 47. • Titania (TiO2) is produced by the sulfate or chloride process. • In the sulfate process ilmenite FeTiO3 is treat with sulfuric acid at 150- 180°C to from the soluble titanyl sulfate TiOSO4 FeTiO3+ 2H2SO4+ 5H2O→ FeSO4.7H2O +TiOSO4 • After removing undissolved solids and then the iron sulfate precipitate the titanyl sulfate is hydrolyzed at 90°C to precipitate the hydroxide TiO(OH)2 TiOSO4 + 2H2O → TiO(OH)2 + H2 • The titanyl hydroxide is calcined at about 1000oC to produce titania (TiO2). • In the chloride process, a high-grade titania ore is chlorinate in the presence of carbon at 900-1000°C and the chloride TiCl4 formed is subsequently oxidized to TiO2. • As indicated by the nominal solid-state reaction for the formation of barium titanate at a temperature above 1250°C BaCO3 + TiO2 → BaTiO3 + CO2  the partial pressure of CO2 in the pores of the product influences the reaction kinetics. • Also the nonequilibrium phase Ba2TiO4 initially forms between BaTiO3 and unreacted BaCO3 and is undesirable in the calcined product;  this phase is minimized by dispersing agglomerates of titania and mixing thoroughly to maximize the particle contacts and reduce the diffusion path between BaCO3 and TiO2. 4.7) Titania (TiO2) Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 47
  • 48. • Magnesium oxide (MgO) of greater than 98% purity is prepared by precipitating magnesium hydroxide in a basic mixture of treated dolomite and natural brines or seawater containing MgCl4 and MgSO4, followed by washing, filtration, drying, and calcination. 5) MAGNESIUM OXIDE (MgO) Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 48
  • 49.  Bauxite forms most commonly in deeply weathered rocks as a hydrated aluminum oxide ore.  In some locations, the parent material is basalt or other volcanic rocks.  Depending on the main aluminum bearing phase, 3 types of bauxite are distinguished: gibbsitic, boehmitic and diasporic bauxite.  The composition range of bauxites are given below. http://www.alcoa.com/australia/en/info_page/mining_homepage.asp Average composition of bauxites Main bauxite producing regions in the world : Australia 35%, Guinea 11%, China 10%, Brasil 10%, Jamaica 10%, India 8%, others 16% Jarrahdale bauxite mine (Australia, Alcoa) Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 49 6) ALUMINA (Al2O3)
  • 50.  Alumina (Al2O3) is the most widely used inorganic chemical for ceramics and is produced worldwide in tonnage quantities for the aluminum and ceramics industries using the Bayer process.  The principal operations in the Bayer process are the physical beneficiation of the bauxite, digestion (in the presence of caustic soda NaOH at an elevated temperature and pressure), clarification, precipitation, and calcinations, followed by crushing, milling, and sizing (see Fig. 3.4).  During the digestion, most of the hydrated alumina goes into solution as sodium aluminate: Impurity + Al(OH)3(solid) + NaOH(sol) → Na+ + Al(OH)4 -(sol) + Impurity and insoluble compounds of iron, silicon, and titanium are removed by settling and filtration  After cooling, the filtered sodium aluminate (AlO2Na) solution is seeded with very fine gibbsite (Al(OH)3), and at the lower temperature the aluminum hydroxide reforms as the stable phase.  The agitation time and temperature are carefully controlled to obtain a consistent gibbsite precipitate.  The slurry from the precipitation thanks is filtered to extract the fines (recycled as seed crystals).  The gibbsite is continuously classified, washed to reduce the sodium content, and then calcined.  The filter cake is than calcined at 1100oC (rotary kiln, or fluidized bed calciner) resulting in sandy alumina with more than 90% of the particles >45µm.  Material calcined at 1100-1200°C is crushed and ground to obtain a range of sizes (Fig. 3.5).  Tabular aluminas are obtained by calcining to a higher temperature, about 1650°C. 6) ALUMINA (Al2O3) Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 50
  • 51. Unsoluble residues, mainly iron and titanium oxides, are separated from the aluminum containing solution by gravitational settling. The recovered mud is washed. http://www.qal.com.au/ • The cooled pregnant liquor flows to rows of precipitation tanks which are seeded with crystalline trihydrate alumina,to promote crystal growth. • Cooling and depressurizing reverses reactions (1) and (2) above. Holding time: about 3 hours. Alumina: Bayer process (Cont.) Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 51
  • 52. Bayer Process chart Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 53 Most of the refined alumina is further processed by electrolysis to obtain aluminum.
  • 53. 7) FELDSPAR Generally, feldspar is used in the manufacture of glass products (70%), in ceramics and other products (30%). Feldspar is also used Filler (in paint, in mild abrasives, urethane, latex foam, and as a welding rod coating). In the manufacture of ceramics, feldspar is the second most important ingredient after clay. Feldspars are an important glaze raw material used as the main flux in ceramic industries. Feldspar is a source for the simultaneous introduction of SiO2, Al2O3, Na2O, K2O and CaO and is the most suitable material for introducing alkaline oxides into glazes. Feldspars are used as fluxing agents to form a glassy phase at low temperatures and as a source of alkalis and alumina in glazes. Feldspars play an important role as fluxing agents in ceramics and glass applications, and also are used as functional fillers in the paint, plastic, rubber and adhesive industries. Because of their low melting point, feldspars are used as a melting agent in ceramic mixtures, glass batches, glazes, enamels and also as casting powders in the last years. Feldspar does not have a strict melting point, since it melts gradually over a range of temperatures. This greatly facilitates the melting of quartz and clays and, through appropriate mixing, allows modulations of this important step of ceramic making. Feldspars melt at ~1150oC. The feldspathic glass they produce surrounds the refractory clay particles and fills up the pores between them. Due to the free fluxes they contain, feldspathic glasses will also bind to the surfaces of the refractory particles thus helping to bind the ceramic body together. The more feldspathic glass a ceramic body contains, the denser the fired body will be. They improve the strength, toughness, and durability of the ceramic body, and cement the crystalline phase of other ingredients, softening, melting and wetting other batch constituents. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 54
  • 54. In the feldspar process, one may distinguish three different flotation steps, namely the micas flotation, the oxides flotation, and the feldspar flotation. Each of these requires a different reagent regime. The following flow sheet shows the steps involved in the recovery of feldspar.
  • 55. Feldspar (Naturally occurring forms of devitrified glass) Potassium Feldspar (Orthoclase or microcline) K2O Al2O3 6SiO2 Sodium Feldspar (Albite) Na2O Al2O3 6SiO2 Lime Feldspar (Anorthite) CaO Al2O3 2SiO2 Flux Stabilizer Glass Former Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 56
  • 56. i) Feldspar in Glass Manufacture  Feldspar is an important ingredient in the manufacture of glass , because it acts as a fluxing agent, reducing the melting temperature of quartz and helping to control the viscosity of glass.  The Raw material for Glass consists of:  Silica sand (quartz), Soda ash (sodium carbonate) and Limestone (calcium carbonate).  Feldspar adds certain qualities to the process.  Alumina in feldspar acts as a stabiliser  improves the finished product by increasing resistance to impact, bending, and thermal shock,  increases viscosity during glass formation and inhibits devitrification.  provides hardness, workability, strength, and makes glass more resistant to chemicals.  Alkali content (Na2O + K2O) in feldspar acts as flux:  lowering the glass batch melting temperature,  reduce the melting temperature of quartz so less energy is used  decrease the amount of soda ash needed  helping to control the viscosity of glass,  thus reducing production costs. Prof. Dr. H.Z. Harraz Presentation Mineral Processing1 April 2014 57
  • 57. ii) Feldspar in Ceramic Manufacture • In the manufacture of ceramics, feldspar is the second most important ingredient after clay. • Feldspar does not have a strict melting point, since it melts gradually over a range of temperatures. This greatly facilitates the melting of quartz and clays and, through appropriate mixing, allows modulations of this important step of ceramic making. • In the fabrication of ceramic material, feldspars are used as fluxing agents to form a glassy phase at low temperatures, and as a source of alkalies and alumina in glazes. • They improve the strength, toughness, and durability of the ceramic body and cements the crystalline phase of other ingredients, softening, melting and wetting other batch constituents. • Fluxing temperature is depend on free silica content, body composition and the ratio of the alkali oxides (Na2O, K2O, and Li2O). • Different ceramic bodies require difference degree of vitrification, and hence different types and amounts of flux. •In the flooring sector, feldspar is the main constituent in the body composition. It is used as a flux, lowering the vitrifying temperature of a ceramic body during firing and forming a glassy phase. Surface tensions pull the remaining solid particles together, giving a densification of the ceramic body. With rising temperatures the alkalis become more active and first dissolve the clay particles and then the free silica. Ceramic products Feldspar (%) Soft porcelains 25 - 40 Tableware 18-30 Sanitaryware 30-60 Whiteware, pottery, and tile 15-35 Note: In ceramic, K-spar is prepared over Na-spar, since it form a highly viscous melt even at very high temperatures and thus prevents distortion during firing.