Mineral Processing Industry (DDJ) PDF

Chemical Process Technology (CPT150X) Mineral Processing Lecturer: Dr Debbie De Jager  Introduction to Mineralogy Mining and downstream minerals processing remains keystones of the economy of the Republic of South Africa. The minerals industry contributes ~8% of th...

Chemical Process Technology (CPT150X) Mineral Processing Lecturer: Dr Debbie De Jager  Introduction to Mineralogy Mining and downstream minerals processing remains keystones of the economy of the Republic of South Africa. The minerals industry contributes ~8% of the GDP and provides direct employment to about 500 000 people. In 2023, the total revenue of South Africa's mining industry was 654-billion rand. The most important mineral commodities produced in South Africa, in terms of value, are gold, coal, platinum-group metals (PGM), ferroalloys (ferrochromium, ferromanganese, ferrosilicon, and ferrovanadium), aluminum, steel, iron ore, diamond, vanadium and copper.  Introduction to Mineralogy South Africa has the world's largest resources of PGMs (87,7% of the world total), manganese (80%), chromium (72,4%), gold (29,7%) and alumino-silicates. South Africa accounts for over 40% of global production of ferrochromium, PGMs (platinum, palladium, rhodium, iridium, osmium and ruthenium). These metals are extremely resistant to corrosion hence they are used in a number of industrial processes, technologies and commercial applications. World's largest producer of chrome, manganese, platinum, vanadium and vermiculite. Second largest producer of ilmenite, palladium, rutile and zirconium. World's third largest coal exporter. Additionally, significant output of metallic commodities included antimony, chromite, cobalt, lead, manganese, nickel, silver, titanium, uranium, zinc and zirconium. Introduction to Mineralogy  MINERALS INDUSTRY CHALCOPYRITE (CuFe)S2 DOLOMITE (MgCO3.CaCo3) GALENA (PbS) GYPSUM PENTLANDITE (NiFe)9S8  MINERALS INDUSTRY File:Covellite-USA.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/4/42/ChromiteUSGOV.jpg/240px-ChromiteUSGOV.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Hematite.jpg/240px-Hematite.jpg COVELLITE (CuS) CHROMITE (FeCr2O4) HEMATITE (Fe2O3) http://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Sphalerite-221270.jpg/220px-Sphalerite-221270.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/Sphalerite-Dolomite-Chalcopyrite-165227.jpg/240px-Sphalerite-Dolomite-Chalcopyrite-165227.jpg Complex minerals Sphalerite crystals with minor Sphalerite on dolomite associated chalcopyrite  MINERALS INDUSTRY Sometimes, some metals occur in nature in their native form. Examples of these metals are copper, silver, mercury, gold and platinum File:Platinum-nugget.jpg GOLD PLATINUM SILVER Terminologies Many metals occur naturally in compounds known as minerals. When a mineral deposit in the crust of the earth has a sufficiently high concentration of mineral present and the mineral can be profitably recovered, the mineral deposit becomes known as an ore. Complex ores contain more than one extractable mineral. The ore consists of the extractable minerals and the gangue material. Mineralogy prior to Mineral processing Exploration & identification of minerals present in a deposit Size & depth of the ore body Orientation relative to the surface Geographical location Characterisation of the ore: Macro (determines mining method) & micro (determines ore processing) bases Open and underground mines Ores mined from open mine Ores mined from underground mine  MINERAL PROCESSING Beneficiation is a variety of processes whereby extracted ore from mining is separated into mineral and gangue, the former suitable for further processing or direct use. The cost of extraction increases with increasing gangue content. Gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. The process of separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing. It can be a complicated process, depending on the nature of the minerals involved.  STEPS OF BENEFICIATION ORE COMMINUTION SEPARATION beneficiation CLASSIFICATION FLOTATION ELECTROSTATIC CONCEN. MAGNETIC CONCEN. DEWATERING REDUCTION & REFINING PYROMETALLURGY HYDROMETALLURGY ELECTROMETALLURGY FINAL PRODUCT  MINERAL PROCESSING ORE Mineral processing, also LIBERATION known as ore dressing, COMMINUTION mineral dressing Comes after mining and SEPARATION prepares ores for extraction. The aim of mineral CLASSIFICATION FLOTATION ELECTROSTATIC CONCEN. MAGNETIC CONCEN. processing is to produce a CONCENTRATION concentrate containing the DEWATERING valuable minerals and a tailing containing the gangue REDUCTION & REFINING minerals. PYROMETALLURGY HYDROMETALLURGY ELECTROMETALLURGY Mineral processing is a combination of liberation and concentration. FINAL PRODUCT  COMMINUTION ORE LIBERATION Generic name for particle size reduction COMMINUTION of ore using crushing and grinding. SEPARATION CLASSIFICATION FLOTATION ELECTROSTATIC CONCEN. MAGNETIC CONCEN. DEWATERING REDUCTION & REFINING PYROMETALLURGY HYDROMETALLURGY ELECTROMETALLURGY FINAL PRODUCT  COMMINUTION REJECTED REJECTED CRUSHING SIZING DEVICE GRINDING SIZING DEVICE crushing grinding primary stage secondary stage intermediate size reduction fine grinding dry basis wet basis Crushing is an operation that ensures a small enough particle size to provide optimum surface area for the required reactions to occur. In open circuit grinding, the material passes though the crusher once. In closed circuit grinding, the oversized material is separated and returned to the crusher. reasons for comminution = mineral recovery increases with decrease in particle size excessive comminution = high cost (need more energy) loss of mineral as slime  COMMINUTION: Crushing Class of Crusher Example of Crusher Product Size Coarse crushers Stag jaw crusher, dodge jaw 50 – 5 mm crusher, gyratory crusher Intermediate crushers Crushing rolls, edge runner 5 – 0.1 mm mill, hammer mill Fine crushers Roller mill, ball mill, Babcock 0.1 mm mill Colloid mills Down to 0.01 m The choice of crusher for a particular duty depends on the nature of the feed material and the product size. Additional factors needing consideration are: hardness, structure, moisture content, crushing strength, friability, stickiness, soapiness, and explosiveness. In addition, materials that produce large amounts of dust should be treated under conditions where the dust is not allowed to escape. Crushing: Jaw crusher Crushing: Cone Crusher Crushing: Rock crusher  COMMINUTION: Grinding Grinding is a combination of impact and abrasion. It normally takes place in tumbling mills. The correct degree of grinding is essential for optimum mineral recovery and energy consumption. Grinding uses the most energy at a mill. Grinding can be done wet or dry (Coulson & Richardson, 1991). Wet grinding is generally used in low-speed mills and its advantages are: Power consumption is reduced by 20 – 30%. Increased plant capacity. Product removal is easier and the amount of fines is reduced. No dust is formed. The solids are more easily handled. The disadvantages of wet grinding are: The product may need drying. The wear on the grinding medium is 20 % greater than in dry grinding.  GRINDING: Ball mill The grinding medium may be steel rods, steel balls, hard rock or the ore itself. Examples of tumbling mills are rod mills, centre peripheral discharge mills, end peripheral discharge mills, overflow mills, ball mills and autogenous mills.  SEPARATION ORE COMMINUTION SEPARATION Purpose is to separate valuable mineral from gangue CLASSIFICATION FLOTATION ELECTROSTATIC CONCEN. MAGNETIC CONCEN. DEWATERING REDUCTION & REFINING PYROMETALLURGY HYDROMETALLURGY ELECTROMETALLURGY FINAL PRODUCT  SEPARATION Physical methods used to concentrate the valuable minerals. These methods make use of differences in physical properties of the valuable minerals and the gangue minerals. One or a combination of the following physical methods achieves concentration of the valuable minerals: – Separation based on differences in density (Dense Medium Separation). – Separation based on surface tension (froth flotation). – Separation dependent on electrical conductivity (electrostatic concentration). – Separation dependent on magnetic properties (magnetic concentration).  SEPARATION: Classification Classification: – The velocity of a particle falling through a fluid depends upon the shape of the particle, its size, and its density. Classification is a method based on this principle and it is used to separate minerals from one another. – Perry (1988) lists the following three “fundamental laws” of classification: 1. Considering particles of the same density, coarse particles have a higher settling velocity than fine particles. 2. High-density particles have a higher settling velocity than lower density particles of the same size. 3. The increased density or viscosity of the carrier fluid reduces the settling rates of particles. Free settling and Hindered settling  SEPARATION: Classification Free settling occurs when particles fall through a stationary fluid and are sufficiently far from each other that they do not influence each other’s rate of fall through the fluid. This happens when the percentage of solids is less than approximately 15%. The forces acting on the particle are: gravitational force, buoyancy and viscous drag. Equations for the terminal settling velocities of particles in a fluid. gd2 (D s − D f ) Stokes’s Law (particles less than 50m in diameter ): v= 18 1/ 2 Newton’s Law (particles greater than 0.5 cm in diameter ):  3gd(D s − D f )  v=   D f   SEPARATION: Classification Hindered settling Occurs when the percentage of solids is greater than approximately 15% and crowding causes the falling rate of the particles to decrease. There are two reasons for this decrease in falling rate. Firstly, when there is a high percentage of solids, the system behaves as if the particles are falling through a fluid with the density of the pulp instead of the density of the carrier fluid. The pulp density is generally higher than the carrier fluid density. Secondly, the pulp generally has a higher viscosity than the carrier fluid and this also slows the particles down. A modified Newton’s law gives an estimate of the terminal velocity of a particle during hindered settling: v = kd(D s − D p  1/ 2  SEPARATION: Classification Particles travel downward Example of classifier is the sorting column. Those particles with a settling velocity higher Sorting column than the upward velocity of the fluid will move fast enough to reach the bottom of the sorting column. They will be removed in the underflow product. Those particles with a settling velocity lower than the upward velocity of the fluid will be carried into the overflow product. Water travels upward  SEPARATION: Dense Medium Separation (DMS) A mixture of minerals with different densities are placed in a liquid with an intermediate density. The grains with densities less than that of the liquid will float and grains with densities greater than the liquid will sink. SEPARATION: Dense Medium Separation (DMS) (cont.)  SEPARATION: Flotation A modern froth flotation process involves the interaction of three phases: solid, liquid and gas. The solid phase is the ore, commonly the liquid is water, while the gas is air. Successful flotation separations depend on the interrelation among the various physical, chemical and mechanical factors involved in the system. The success of this process depends on the appropriate use of a variety of flotation reagents that upon their adsorption at the solid/liquid, solid/gas and liquid/gas interfaces, modify the physical-chemical characteristics of the system.  SEPARATION: Flotation (cont.) Substance with greater affinity for water are called ‘hydrophilic’ (water-friendly or wettable) whereas those with greater affinity for air are hydrophobic. Only few minerals are naturally hydrophobic, but many minerals (as well as many synthetic compounds) can be made hydrophobic by the adsorption of certain surface active reagents (i.e. collectors or frothers). The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical; the particular chemical depends on the mineral being refined Example: pine oil is used to extract copper. Sulphide minerals are easily floated with anionic collectors. The most commonly used collectors for sulphide flotation are xanthates.  SEPARATION: Flotation (cont.) Uses modification of surface tension of particles, which affects settling in liquid Ore is hydrophilic (i.e. wetted easily) Flotation agent is hydrophobic 1. therefore the flotation agent attaches to ore surface, ore is less easily wetted Air flow 2. air bubble from bottom, attaches to the solid 3. solid floated to top (apparent density Froth drop) phase 4. froth & solid scrapped off Air Hydrophilic bubbles Comes from Greek words meaning water and friend. A hydrophilic material is a friend of water and can be easily Pulp wetted. A hydrophilic material can bond with water through phase hydrogen bonding. Tailings Hydrophobic Come from the Greek words meaning water and fear. The material repels the water and the contact angle between the surface and the droplet is more than 90°.  SEPARATION: Electrostatic concentration Uses difference in electrical properties of ore constituents. Surface of the mineral particles are charged. Mixture consisting of readily-conducting and poorly-conducting minerals (e.g. grains of copper and grains of sand). conducting material loses charge quickly, while non-conducting material does not Mixture is dropped onto an electrified (i.e. charged) roll with a high potential. Immediately upon contact with the electrified roll the better-conducting minerals become charged to the potential of the roll and are thrown vigorously from it. The poorer conductors require a much longer time to reach the electrical condition of the roll, and they are not given time to reach this condition; due to being removed from the roll a separation is obtained. Capital cost high, capacity low, recycling usually necessary.  SEPARATION: Magnetic concentration Involves separation using a magnetic force. Any susceptible magnetic substance attracts the magnet (e.g. iron mining). These magnets can either be: 1. ferromagnetic 2. diamagnetic 3. paramagnetic Ferromagnetic substances are already magnets (i.e. natural magnets). Paramagnetic substances are weakly attracted towards the magnetic field. Diamagnetic substances strongly attract towards any magnetic field. The size of the magnetic field determines the feed size. Dry or wet basis. Capital cost high, capacity low, recycling necessary.  DEWATERING Drying is usually last step of beneficiation process Most mineral separation processes use large amounts of water and the concentrates obtained have to be dewatered to facilitate subsequent processing and transport. The methods of dewatering are: 1. Sedimentation 2. Filtration 3. Thermal drying Sedimentation produces a thickened pulp of 55 to 65% solids. This is then filtered to produce a wet filter cake. This cake is then dried by thermal drying Stages: thickeners, centrifuges, vacuum/pressure filtration The extent of dewatering is determined by the refining processes Flocculants or flocculating agents are chemicals that promote flocculation by causing colloids and other suspended particles in liquids to aggregate, forming a floc. Used in water treatment processes to improve sedimentation or filterability of small particles.  METALLURGY (EXTRACTION) Once a concentrate of the ORE valuable minerals has been obtained, the metals are COMMINUTION extracted by pyrometallurgy, hydrometallurgy, or electrometallurgy. SEPARATION These chemical techniques use the addition of heat, solvents, CLASSIFICATION FLOTATION ELECTROSTATIC CONCEN. MAGNETIC CONCEN. or electricity, respectively, and use large amounts of energy. DEWATERING Pyrometallurgy, the most widely used chemical REDUCTION & REFINING technique, takes place in a modified furnace called a PYROMETALLURGY HYDROMETALLURGY ELECTROMETALLURGY smelter. To minimise energy usage in the smelter, only the necessary material should enter FINAL PRODUCT it. MINERALS INDUSTRY The grade of the ore is the mass % of the valuable METAL AVERAGE MINIMUM metal. CONTENT WORKABLE (WT %) GRADE (WT %) Al 8.0 30 Economic exploitation of a gold Fe 5.7 25 ore having a grade of 0,0005% is Mn 0.1 15 possible, while exploitation of an Cr 0.0096 15 Zn 0.0075 3 iron ore with a grade of 10% may Ni 0.007 1 not be profitable. Cu 0.0055 0.45 Pb 0.001 3 Thus, profitability cannot simply Sn 0.00015 0.4 Ag 0.0000007 0.01 be assessed from the grade of the Pt 0.0000004 0.0001 ore. Profitability depends on, Au 0.0000002 0.0008 among other factors, the mining cost and the cost of the metal in its final form.  PFD for the Minerals Industry Sampling/Analysis (i.e. Mineralogy) Comminution Liberation (i.e. Crushing and Grinding) Separation Beneficiation (i.e. Classification, Dense Medium Separation, Concentration Froth Flotation, Electrostatic concentration, Magnetic concentration) Dewatering Extraction (i.e. Pyrometallurgy, Hydrometallurgy, Electrometallurgy)  NEWS Oct 2010 33 Miners trapped underground for 69 days in San José Mine in Chile Rescued on 13 October 2010