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University of Saskatchewan Geological Engineering GEOE 498.3 Introduction to Mineral Engineering Lecture 11 Mineral

Mineral Processing Overview. Mineral Processing Terms, EconomicsComminution and ClassificationPhysical processing methodsChemical processing methodsWaste products treatment and disposalProcess plant flow sheets: uranium and potash. These course notes are a compilation of work conducted by many people.Notes have been taken from the following Edumine courses:The Mill Operating Resource 1

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University of Saskatchewan Geological Engineering GEOE 498.3 Introduction to Mineral Engineering Lecture 11 Mineral

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    2. Mineral Processing Overview Mineral Processing Terms, Economics Comminution and Classification Physical processing methods Chemical processing methods Waste products treatment and disposal Process plant flow sheets: uranium and potash

    4. Lecture 11 Chemical Processing Hydrometallurgy Basic Circuits Leaching Solvent Extraction Precipitation Drying Pyrometallurgy Smelting Electrometallurgy Electrowinning

    5. Chemical Processing

    6. Hydrometallurgy Terminology Hydrometallurgy: aqueous methods of extracting metals from their ores hydrometallurgical plant: large amounts of water are needed, and a water balance must be maintained Generally involves two distinct steps: leaching = Selective dissolution of the metal values from an ore precipitation = Selective recovery of the metal values from the solution Sometimes includes purification/concentration

    7. Hydrometallurgy

    8. Leaching

    9. Leaching

    10. Leaching - Solubility

    11. Leaching

    12. Leaching

    13. Leaching

    14. Leaching

    15. Leaching

    16. Leaching

    17. Agitated Leaching

    18. Leaching

    19. Leaching

    20. Leaching

    21. Leaching

    22. In-Situ Uranium Leaching

    23. In Situ Leaching

    24. Heap/Dump Leaching

    25. Heap/Dump Leaching

    26. Bio-Heap Leaching example – Talvivaara, Finland

    27. Hydrometallurgy Terminology purification/concentration operation: After leaching. Prior to precipitation. Goals: 1) purification and 2) increase solution concentration, from which the metal values can subsequently be precipitated effectively. methods used are: adsorption on activated charcoal, sorption on ion exchange resins extraction by organic solvents. Common operation scheme: loading, washing, and unloading (elution or stripping) is used in all three operations. After the elution step, the material is ready for another cycle.

    28. Purification and Concentration

    29. Purification and Concentration

    30. Purification and Concentration

    31. Granular Activated Carbon

    32. Example - Gold

    33. Gold Cyanidation

    34. Gold Leaching

    35. Gold Cyanidation

    36. Ion Exchange (IX) Natural (zeolite) or synthetic (polymer resin) material Uranium was the first metal to be recovered commercially using IX – paved the way for other metals Especially useful in the treatment of very dilute solutions with metal ion concentration of the order of 10 ppm or less An ion exchanger is a framework or a matrix (sponge) which carries a positive or a negative electric charge. Counter-ions (holes) can be replaced by other ions of the same sign, while the fixed ions (matrix) are not mobile.

    37. Ion Exchange Types of IX systems: Columns – fixed resin bed. Batchwise, carousel operation

    38. Ion Exchange Equipment Types of IX systems: Resin-in-pulp - unfiltered leach liquor fed through tanks with wire-mesh baskets containing coarse-grade resin Continuous – pump the resin between loading and elution

    39. Ion Exchange Types of IX resins: Strong acid: cation exchangers, containing -SO3H groups Weak acid: cation exchangers, containing -COOH groups Strong base: anion exchangers. Strength of the resin can be increased by using substituted amines Weak base: anion exchangers, containing amino groups Anion exchange.. The extracted species is a negatively charged ion and the extractant is a base, e.g., an amine:

    40. Solvent Extraction

    41. Solvent Extraction Pregnant – loaded with the metal of interest Barren – metal of interest has been removed Pregnant aqueous – the feed solution to SX that contains the components to be separated. Solutes – minor components in the feed (or other) solutions = dissolved metals. Solvent – the immiscible liquid added to a process for the purpose of extracting a solute or solutes from the feed. Organic – the “light” phase, used for extraction from feed. Raffinate – the liquid phase left from the feed after extraction = barren aqueous. Strip solution – acts as the solvent to remove metal of interest from the organic phase

    43. Hydrometallurgy Equipment Solvent extraction mixer-settlers mixing chamber: aqueous and organic phases are mixed together by a rotating impeller settling chamber: mixed phases are given enough time to separate

    44. Solvent Extraction

    45. Solvent Extraction Equipment Krebs mixer-settler: Interphase regulator Mixer and conical pump Top launder for initial phase disengagement

    46. Solvent Extraction Equipment Column cell: Discs and doughnuts No exposure to air Gentle mixing

    47. Solvent Extraction Equipment Outotec Spirok mixers Low shear

    48. Solvent Extraction Organic typically has the following components: Carrier – main volume of organic, eg. kerosene Extractant – active in collecting metal. Eg. amine Diluent – Reduces surface tension, aids phase separation, eg. Isodecanol (alcohol)

    49. Example: Uranium

    50. Solvent Extraction

    51. Uranium Solvent Extraction and Precipitation

    52. Uranium Solvent Extraction Key Lake SX circuit

    53. Hydrometallurgy Precipitation is the final step in many hydrometallurgical processes. It is also used as a purification step to separate impurities Can be physical or chemical

    54. Precipitation Equipment Solar Crystallizers: Used for evaporating sea water or brines from wells for the bulk recovery of sodium chloride or other salts (magnesium chloride, lithium chloride) Large evaporation ponds are constructed adjacent to the source. Climate in the region must show high yearly evaporation and low rainfall.

    55. Precipitation Equipment Vacuum crystallizer: no reagents are added, but the concentration and temperature adjusted concentrate a solution such that crystallize solids by evaporation Evaporation is conducted under vacuum to decrease the boiling point of the solution and thus economize in heat requirement common procedure for obtaining pure salts, e.g., sodium chloride, ammonium sulphate However, cooling will also effectively lead to crystallization of a salt provided its solubility is largely dependent on temperature.

    56. Precipitation Equipment multiple effect evaporators - steam generated in the first evaporator is used to heat the charge in the second evaporator, and that from the second is used to heat the charge in the third.

    57. Hydrometallurgy Equipment Chemical precipitation methods: hydrolysis – just add water! Precipitation of oxides, hydrated oxides, hydroxides, or hydrated salts Ionic - ions formed are neutralized by a base, example: Reduction - a reducing agent is added which results in the precipitation of a metal and the agent is oxidized: An important sub-group is hydrogen reduction Substitution – precipitate metal ions from organic solvents

    58. Precipitation Particle size Particle size and form of a precipitate depend upon the conditions of formation. Freshly formed precipitate is sometimes described as amorphous or gelatinous and is difficult to separate by filtration. Precipitates undergo continuous recrystallization as they age ... accelerated by heating

    59. Precipitation Precipitation involves two steps: nucleation crystal growth Rate of nucleation is influenced by: concentration agitation nucleating agents Change in valency by adding an oxidizing or reducing agent may be used to effect selective precipitations.

    60. Extractive Metallurgy Terminology Electrometallurgy – use of electrical energy to induce a chemical transformation Electrowinning – to precipitate a metal from solution using electric potential Electrorefining – to purify a metal by dissolving it, then re-precipitating it

    61. Electrometallurgy Equipment Electrolytic process: precipitation of a metal from its aqueous solution is affected by imposing an outside electromotive force from a direct current source. This can be represented by:

    62. Electrometallurgy Equipment Alternating anodes and cathodes in a tankhouse for electrowinning For example, copper, zinc, cadmium, and nickel are recovered industrially from leach solutions by electrolytic methods Example: Gold and silver are recovered from the eluate by electrolysis using steel wool cathodes The aqueous solutions are electrolyzed using inert electrodes; the pure metal is deposited on the cathode.

    63. Extractive Metallurgy Terminology Pyrometallurgy – use of heat to induce a chemical transformation Roasting – convert to oxide form. Often first step preceding smelting for Cu, Ni, Pb Example: 2 CuS2 + 5 O2 ? 2 CuO + 4 SO2 Equipment – fluidized bed roaster

    64. Extractive Metallurgy Terminology Smelting - uses reducing substances that will combine with those oxidized elements to free the metal. Example: 2 Fe2O3 + 3 C ? 4 Fe + 3 CO2 Converter – add back a bit of oxygen to purify, example: blister copper

    65. Pyrometallurgy Equipment Smelter: Add flux (silica or lime) to remove impurities - waste becomes slag Dust and off gas control are big issues

    66. Pyrometallurgy The molten components coalesce, each forming an individual molten layer Slag: top layer with specific gravity 3.6, and is composed of silicates. Matte: next layer with specific gravity 5.2, and is composed of sulfides. Speiss: next layer with specific gravity 6.0, and is composed of arsenides. Bullion: bottom layer with specific gravity > 6, and is composed of metals.

    67. Pyrometallurgy Calcination – Chemical decomposition – but not oxidation or reduction. Example: CaCO3 = CaO + CO2(g)

    68. Pyrometallurgy Multi-hearth calciner/roaster:

    73. Assignment / Tutorial #11 Tutorial / Assignment Complete selected EduMine sections: Hydrometallurgy 1: Review #3 Extractive Metallurgy 2: Review #2

    74. Flowsheet examples Aluminum: from bauxite Copper: from chalcopyrite Iron: from hematite Gold – Placer, sulphide and oxide Dead Sea – Israel

    75. Aluminum

    76. Copper

    77. Iron

    78. Gold

    79. Dead Sea brine

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