Applied Mineralogy and Non-Metallic Resources I. Aluminum. Aluminum. Current head lines: Toxic flood in Hungary

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Elvin Goodwin
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1 Current head lines: Toxic flood in Hungary 1

2 Current head lines: Walls of a red mud reservoir broken Current head lines: Toxic flood high ph 2

3 from Latin: alumen Alaun (ge), alum (e) = KAl(SO 4 ) 2 12 H 2 O Humphry Davy, English chemist describes aluminum for the first time in 1808; tried its production 1825: aluminum was produced in metallic form for the first time by Hans Christian Østed (Danish chemist/physicist) 1827: the same process was applied by Friedrich Wöhler, a German chemist, using pure K aluminum of higher purity Does generally not occur as native metal strong affinity to oxygen Can very seldom be found as a minor phase in certain volcanoes in low oxygen fugacity environment Was once considered to be more precious than gold ( S/C story of Napoleon III ( ) most honored guests were give aluminum utensils) 3

4 Cap stone of the Washington Monument put in place 1884: 100 ounce (2.8 kg) aluminum, largest piece cast at that time as expensive as silver 4

5 from from the French village Les Baux, the most important aluminum ore, was first discovered in 1821 by the geologist Pierre Berthier 1846: Henri Etienne Saint-Claire Deville refined the Wöhler process (with financial support of Napoleon III); he published it in 1859 caused a drastic price drop for aluminum 1855: Paris Exhibition showed a bar of aluminum alongside the Crown Jewels 1886: Charles Martin Hall and Paul Héroult developed the electrolysis of aluminum independently from 1888: Carl Joseph Bayer developed and patented a process to extract alumina from bauxite The Bayer process caused together with the Hall-Héroult process to drop the price for aluminum by about 80% in 1890 with respect to the price of 1854 These two processes are still used today for aluminum production 5

6 is the source of 99% of metallic aluminum is a rock - a mixture of minerals. It consists of: Gibbsite g-alo(oh) 3 Boehmite g-alo(oh) Diaspore a-alo(oh) further: quartz, kaolinite, goethite, hematite, rutile, anatas 6

7 7

8 Formation of bauxite is a product of weathering and transport processes Al is concentrated from source rocks with about 15% of Al 2 O 3 to exploitable bauxite with % of Al 2 O 3 Solution and transport of low soluble of SiO 2 and Fe only possible under seasonal changing ph/eh conditions Tropical climate: soil water in dry season has high ph solution of SiO 2, then transported during rainy season Fe is dissolved and transported under low ph/eh-conditions Two types of bauxite deposits: Lateritic bauxites (silicate bauxites) were formed by weathering of various silicate rocks including granite, gneiss, basalt, syenite, shale (Australia, India, Guinea, Brazil, Guyana, Venezuela) mainly gibbsite Karst bauxites (carbonate bauxites) were formed by lateritic weathering and residual accumulation of clays. Rather small deposits. (Greece, France, Montenegro, Hungary, Jamaica) mainly boehmite, diaspore 90% of reserves are lateritic bauxites 8

9 Exploration Poços de Caldas, 1940 Exploration Guinea 9

10 Exploration Exploration is mainly based on: Macroscopic identification of bauxite is difficult as color, texture and structure are variable deposits cannot be traced by geochemical methods Geoelectric methods can be used due to difference in conductivity between bauxite and carbonates Example Weipa: the red cliff were already described by the discoverers of Australia; - the bauxite deposits were recognized in 1955 during an oil exploration campaign - mining started only in 1963 Exploitation Selective open pit mining using scrapers, bulldozers; front-end loaders feeding trucks and conveyor belts to a blending pile Underground mines are rare: Croatia, Greece, France Initial processing: crushing to ca. 5 cm and washing to remove silica and iron Metallurgical grade: dried and rod milled Chemical grade: dried and shipped as a commercial product Abrasive and refractory grades: calcined to a mixture of corundum and mullite 10

11 Mining Guinea Transport Guinea 11

12 Drying before shipping Guinea Shipping Guinea 12

13 of Alumina Bayer alumina refining process: Ground metallurgical-grade bauxite is digested in caustic soda solution at C in pressure tanks; red mud is filtered off Al 2 O 3. 3H 2 O + 2NaOH Na 2 O. Al 2 O 3 + 4H 2 O + red mud bauxite caustic soda sodium aluminate filtered Remaining sodium aluminate filtrate is cooled to C, diluted stirred, seeded with aluminum hydroxide and agitated in crystallizers for hrs Na. 2 O Al 2 O 3 +4H 2 O Al 2 O 3. 3H 2 O + 2NaOH Calcining in rotary kilns or fluid bed calciners Al 2 O 3. 3H 2 O Al 2 O 3 +3H 2 O calcined 2.2 t bauxite 1 t alumina of Alumina 13

14 of Alumina Why these differences? 14

15 Hall-Héroult Process Power requirement: ca. 13 kwh/kg aluminum Pure alumina melts at C Alumina (2 9%) is mixed with 75% cryolite and various additives including aluminium fluoride (5-15%), fluorspar (2 6%), lithium carbonate (2 5%) to reduce the melting point and to curtail fluorine emissions Melting temperature cryolite-alumina-mixture 950 C The mixture (up to 90 t) are placed in a graphite lined electrolytic reduction cell ( pot ) = cathode Carbon anodes are inserted from the top Direct current is applied: 4 5 V, up to A Hall-Héroult Process Cathode: 4Al e - Al (liquid) positive charged Al-ions move to the cathode, take electrons up and are reduced to Al-atoms Anode: 6O 2-3O 2 (gas) + 12e - negative charged O-ions move to the anode, dispose of the electrodes and are oxidized to O- molecules Net: 4Al 3+ Al (liquid) + 3O 2 (gas) Oxygen reacts with the carbon of the anode to carbon dioxide and carbon monoxide exhaust The liquid aluminum has a higher density than the cryolite-mixture is collected at the bottom of the pot from where it is removed by a siphon and vacuum 15

16 Hall-Héroult Process Cryolite Na 3 AlF 6 16

Synthetic cryolite is used for aluminum production Synthesized from fluorosilic acid and sodium aluminate

17 Cryolite Cryolite: Na 3 AlF 6 Used as flux for aluminum production An natural deposit of cryolit exists in Greenland, Ivigtut, where it was mined This deposit is depleted. Synthetic cryolite is used for aluminum production Synthesized from fluorosilic acid and sodium aluminate Fluorspar is the source for fluorine In future, hexa-fluoro silicic acid from phosphate production will increasingly be used Hall-Héroult Process Brazil 17

pots Plant was designed for a production

anodes Every cell has 18 anodes Lifetime

18 Hall-Héroult Process Voerde, Germany 2 halls of 560 m length with a total of 188 pots Plant was designed for a production of t/y With computerization and improvements: t/y Hall-Héroult Process Voerde, Germany Placing the anodes Every cell has 18 anodes Lifetime of an anode: 1 month 120 anodes are replaced per day 18

19 Hall-Héroult Process Voerde, Germany Anode manufacturing Raw material: petrol coke, black coal tar pitch, remains of old anodes Fired at 1270 C Integrated Brazil 19

20 Environmental Concerns Very high energy demand (10 x higher than for the same amount of sheet metal) Toxic fumes (flourine) are produced filter system? of 1 t aluminum requires: - ca. 5 t bauxite - cryolite (flux) - carbon (anode) - aluminum fluoride (to start reaction) of 1 t aluminum produces 1.5 t red mud landfill disposal Comparison of prices for Gold and aluminum What is the ratio gold/aluminum today? attention: 1 ounce (oz.) = gr. 1 troy ounce (oz. tr.) = gr. (precious metal only) 20

21 Political/Social Problems Guinea mining in Guinea Country s main export goods; highest quality bauxite Military dictatorship for 50 years; a government with ministers does not exist at the moment Corruption: nobody knows what happens to the income from mining Mining companies are owned by foreign owners/ multinational companies added value does rarely stay in the country Guinea could be the second richest country of western Africa after Nigeria but is no. 170 of 182 listed countries 21

GENARAL INTRODUCTION TO METALLURGY :Std: XI-CHEMISTRY

GENARAL INTRODUCTION TO METALLURGY :Std: XI-CHEMISTRY 1. What is matrix? The ore is generally associated with rock impurities like clay, sand etc. called gangue or matrix 2. What is mineral? The natural