Prof. Dr. Zafir Ekmekçi Assoc. Prof. Dr. Özlem BIÇAK Flotation Prof. Dr. Zafir Ekmekçi Assoc. Prof. Dr. Özlem BIÇAK Add picture of the flotation machines. Update the metal prices.

REFERENCES Kelly, E.G. and Sprottiswood, D.J., Introduction to Mineral Processing, John Wiley and Sons, 1982. King, R.P. (Ed.), Principles of Flotation, South African Institude of Mining and Metallurgy, 1982. Fuerstenau, M.C., Miller, J.D. and Khun, M.C., Chemistry of Flotation, AIME, 1985. Fuerstenau, D.W. (Ed), Froth Flotation 50th Anniversary Volume, AIME, 1962. Gaudin, A.M., Flotation, 1957. Wills, B.A., Mineral Processing Technology, Pergamon Press. Mular, A.L., Halbe, D.N., Barrat, D.J., Mineral Processing Plant Design, SME, 2002.

I MID TERM: 26 OCTOBER 2015 MONDAY II MID TERM: 14 DECEMBER 2015 MONDAY For the Lecture Notes & Presentations: http://yunus.hacettepe.edu.tr/~obicak/MAD_459

Flotation Course Outline Introduction and Principles of Flotation General Concepts of Flotation Properties and Structures of Minerals Surface chemistry Physical Aspects of Flotation Flotation Chemicals Flotation of Sulphide minerals Flotation of Non-sulphide minerals Effects of Particle Size Flotation machines

Overall Scope of Course (1) Definition of flotation Basic principles Aim to present basic principles for practical application Complexity of flotation Importance of chemistry & physics Industrial practice

Overall Scope of Course (2) Chemistry determines if mineral will float Hydrophobic or hydrophilic Physics determines the process efficiency Particle & bubble size, equipment design The chemical and physical principles will be developed Applications to industrial practice will be discussed

1. Introduction to Flotation Definition of flotation Importance of flotation to industry Brief history of process development Flotation in mineral circuits Liberation & concentration Mineral texture Complexity of flotation Scale of operations Equipment Applications

The stages required turning a mineral into metal: The goal of mineral processing is to separate the valuable minerals from each other and from gangue. The stages required turning a mineral into metal: Mining Mineral Processing Extraction Refining Manufacturing

Scope of Mineral Processing Heterogenous mixtures of finely divided solid phases frequently require an efficient technique for separation of components. Separation of solids can be achieved, for appropriate particle sizes denoted by diameter (d), by techniques exploiting the following physical and physicochemical characteristics: Colour :In sorting of lump coal or other distinct minerals (d> 50 mm). Specific Gravity :In wet or dry gravity concentration techniques (d>0.1 mm) Shape and Size :In screening and classification (d>0.04 mm) Electrical Charge :In electrostatic separation of well-dried materials (0.05<d<5 mm) Magnetic In wet or dry magnetic concentration devices Susceptibility : (0.1<d<5 mm) Surface Properties: In froth flotation, spherical agglomeration, selective flocculation (d<0.2 mm).

Scope of Froth Flotation Flotation is undoubtedly the most widely employed, the most important and versatile mineral processing technique. Flotation utilises the differences in physicochemical surface properties of particles of various minerals. By using some chemicals mineral surfaces are either made water repellent (HYDROPHOBIC) or water loving (HYDROPHILIC). A hydrophobic surface always tends to stick (adhere) air bubbles as hydrophilic surface does not. When a small air bubble sticks to a hydrophobic mineral surface in water, density of the mineral becomes much less than that of waters so, the couple (mineral+air bubble) floats.

Weight of galena = 0.008 mm3 * 7.5 mg/mm3 = 0.06 mg To understand the physics of flotation let us consider a cubic galena particle having 0.2 mm (200 m) dimension and an air bubble of 1 mm3 sticking together. 1 mm3 Air Galena Water Volume of galena = 0.2*0.2*0.2=0.008 mm3 Weight of galena = 0.008 mm3 * 7.5 mg/mm3 = 0.06 mg Volume of air = 1 mm3 Weight of air = 0.0002 mg (negligible) Volume of galena+air = 1.008 mm3 Weight of galena+air = 0.06 mg (0.0602 mg) Density of galena+air = 0.06mg / 1.008 mm3 = 0.0595 mg/m3 Density of water = 1 mg/mm3 Ratio = 1/0.0595 = 16.80  17 An air bubble and a galena particle couple are approximately 17 times lighter than water so, the couple naturally floats to the surface.

In pulps (mineral - water mixtures) air bubbles are generated by a machine called flotation machine. Air (self-aeration or forced) Mineral Air Minerals or Pulp Non-float (sink) product Float (froth products)

Importance of Flotation (1) Very important in industry Pb, Zn, Ag all produced by flotation Most Cu still floated (leaching also) Other metals Mn, Cr, Ni, Co, etc, etc Phosphate, fluorite, feldspar, mica, etc Coal floated on large scale Used widely outside minerals industry

Importance of Flotation (2) Flotation shapes modern industry Enables more difficult ores to be treated 1935 average Cu ore in USA was 1.57% 1960 dropped to 0.72 % And price of copper fell! Economic reserves in the world have been greatly increased by flotation

Brief History of Flotation (1) Year Contributor Contribution 1860 Haynes Bulk-oil process 1877 Bessel Boiling process for graphite 1885 Chemical-generation gas process for graphite 1886 Everson Acidulated pulps desirable 1902 Froment, Potter and Delprat Gas as a buoyant medium for sulphide ores 1905 Schwarz Na2S to recover oxidized base metal minerals 1913 Sulphur dioxide to depress sphalerite 1921 Perkins and Sayre Specific organic collectors - Alkaline circuits 1922 Sheridan, Griswold Cyanides to depress sphalerite and pyrite 1924 Sulman and Edser Soaps for flotation of oxides 1925 Keller Xanthates as collectors 1929 Gaudin pH control Jeanprost Flotation of highly soluble salines 1933 Nessler Flotation of water-soluble chemical salt mixtures 1934 Chapman and Littleford Agglomeration Alkyl sulphates as collectors 1935 Cationic collectors

Brief History of Flotation (1) First industrial use about 100 years ago 1860 – oil added to trap grains which then floated with oil 1877 – flotation process for graphite using oil and boiling mixture 1901 – first large scale development for Zn 6 million tonnes recovered from dumps Dry feed to hot acid solution produced gas bubbles

Brief History of Flotation (2) Intense industrial research followed aimed at improving the basic process Bubble generation A “vacuum” process tried for bubble generation Air bubbles generated by violent agitation – true froth flotation as we know it Sub aeration introduced 1913

Brief History of Flotation (3) Selective flotation was an important step as there was galena in the zinc dumps 1912 galena floated in alkaline solution 1912 lead “depressed” with dichromate 1913 zinc depressed with sulphur dioxide Zinc “activated” by copper sulphate

Brief History of Flotation (4) A major advance was modern collectors Soluble organics with tri-valent N or bi-valent S were substituted for oils 1925 – discovery and use of xanthate – this is still used as the basic sulphide collector For non-sulphides – soaps, alcohols and amines were used, but good results needed effective depressants

Brief History of Flotation (5) Selective flotation was difficult – easy to float all minerals, but hard to float just one from ores with several minerals Alkalis used to depress pyrite and float sphalerite 1922 - Sodium cyanide proved very valuable At high pH pyrite & sphalerite depressed, galena floats Then activate sphalerite with CuSO4 to float sphalerite Finally neutralise to float pyrite

Brief History of Flotation (6) 1924 – systematic study of frothers Needed to maintain a stable froth zone and small bubbles Provided a large bubble area for particle capture

Brief History of Flotation (7) Basic cell geometry established early Many patents claimed improved operation Some with induced air – some air sparged Incremental changes to agitation, bubble generation, froth removal, etc. Massive changes in scale from a few m3 to a few hundred m3

Brief History of Flotation (8) Control systems and on-line instrumentation developed During 70s continuous assay measurements At the same time computer control systems were introduced These gave operators great assistance Still mainly stabilising control, but steadily improving

Brief History of Flotation (9) Recently new flotation devices introduced Columns the major change Other special application units, eg for fine particles Also new collectors and frothers introduced

Float demonstration

Flotation in a Mineral Circuit (1) Mineral processing involves Size reduction (crushing, grinding) Separation (flotation, gravity, magnetic, etc) Flotation is part of overall circuit Optimisation must be of the overall circuit Feed preparation must suit flotation Flotation must be optimised for best overall performance of the circuit

Flotation in a Mineral Circuit (2) Feed ores are always complex mixtures of minerals Size reduction breaks the grains apart so that they may be floated separately If the feed preparation is not satisfactory then flotation cannot solve the problem

Liberation and Concentration (1) Feed preparation for flotation involves Liberation of the mineral grains Adjusting particle size to suit flotation May not be able to do both at the same time: Pure mineral particles may be too large to float Fine grinding to liberate fine grained ores may produce particles too small to float well

Liberation and Concentration (2) Liberation is achieved by size reduction Breakage is generally random – not along grain boundaries Thus particles must be much smaller than the grain “size” for good liberation Liberation refers to a particular mineral Galena grains generally smaller than sphalerite The lead mineral is the first to liberate If possible liberate one mineral, separate, then grind again to liberate second mineral (save grinding energy and limit overgrinding)

Liberation and Concentration (3) “Locked” particles are not fully liberated and contain more than one mineral phase Flotation is basically a physical separation “Locked particles must go to con or tail They dilute the purity of concentrate They contribute to losses in tails Overall strategy determines best destination

Liberation and Concentration (4) Liberation effects on flotation and leaching Flotation: Surface process so controlled by surface exposure of mineral The more exposure the faster the flotation Locked particles can float Leaching: Surface exposure also needed Also the more exposure the faster the leaching Connectivity of the mineral phase determines extraction

Fully liberated particle - can be floated or leached Gangue Mineral Simple locked particle – can be fully leached but goes either to flotation concentrate (dilutes purity) or tailings (losses) Rimmed particle (1) – can be fully leached but will float to concentrate and dilute the purity Mineral is only partly recovered by leaching, flotation, etc. Rimmed particle (2) – cannot be recovered by leaching or flotation

Mineral and Particle Texture The “texture” of an ore is the geometric arrangement of the mineral phases, e.g. Mineral proportions Mineral grain sizes Mineral associations The “texture” determines how the minerals will liberate and the types of particles The structure of the particles determines how efficiently flotation or other separation processes will operate

30 microns

Complexity of Flotation (1) Flotation is very complex Many chemical engineering processes are only one or two phases Flotation - gas, liquid & many solid phases Particle shapes and structures are complex Fluid flows in cells poorly defined Interfacial phenomena

Complexity of Flotation (2) Only a general understanding is possible Predictions still difficult Early developments mainly empirical Research work has been to try and explain what is happening It is amazing that so complex a process can operate so effectively on so large a scale

Complexity of Flotation (3) Some of the physical complexities are: Relative movement of the phases – geometry & phase properties Dynamics of the movement – collision of bubbles & particles, froth drainage Recycle of the streams and circuit arrangements

Complexity of Flotation (4) Some of the chemical complexities are: Hydrolysis reactions & pH effects in water Oxidation/reduction reactions due to flotation with air Water composition defined by solubilities of the mineral species, pH, Eh Surface conditions – hydrophobicity Added chemical reagents

Complexity of Flotation (5) Aim of lectures is to give a framework General understanding of major factors Look at simplified systems Single mineral behaviour Simple flotation equipment Eliminate some of the complexities to get basic principles

Pulp Zone

Scale of Operations (1) One of the early challenges was the development of large scale equipment Early circuits expanded by duplication in parallel “lines” Partly capacity but also thought to give flexibility of operation Now trend to single lines & large equipment Maintenance & control expensive with replicated equipment

Scale of Operations (2) Now huge AG and SAG mills (10m diameter) Flotation cells up to about 200m3 volume This makes massive plant capacities possible Escondida – about 1M tonnes/y Cu produced Chuquicamata – 65 M tonnes/y ore El Teniente – 35 M tonnes/y ore Ok Tedi – 29 M tonnes/y ore

Equipment (1) Basic flotation cells are tanks with An aeration system – induced or sparged Feed and exit pulp flow arrangements Launder to collect the froth Control systems

Equipment (2) Cells are connected into banks Promotes plug flow of pulp Minimises short circuiting Banks are connected into stages & circuits Roughing Cleaning Scavenging

Equipment (3) Many attempts to design better equipment Major advance in recent years is the flotation column Follows chemical engineering practice of counter-current processing Now used widely in cleaning circuits

Equipment (4) Other recent developments Jameson cell – short column induced air coal, metals, waste Microcell – fine bubbles for small particles Coal TurboFloat – development aimed to optimise aeration, mixing, separation coal

Non-Sulphide Minerals Applications Sulphide Minerals Copper Zinc Lead Silver Non-Sulphide Minerals Feldspar Phosphates Mica Quartz

History of Metal Prices