Descirpcion De Unidad Fab
Páginas: 10 (2436 palabras)
Publicado: 12 de diciembre de 2012
Flotation
1.0 Introduction
Today, flotation is the dominant method of mineral concentration. It is used for almost all sulphide minerals and is widely used for non-sulphide metallic minerals, industrial minerals and coal.
Flotation can be applied to low grade ores and ores that require fine grinding to achieve liberation. It is a relatively selective process and is an importantapplication in the separation and concentration of minerals in complex ores (ie. sulphide ores containing copper, lead and zinc).
Since most minerals are naturally hydrophilic, the surface of one mineral must be selectively rendered hydrophobic to achieve a separation by flotation. This is achieved by the regulation of the solution chemistry followed by the addition of a collector. The particlesrendered hydrophobic must contact and adhere to air bubbles, allowing them to rise to the surface and form a froth. The waste material (gangue) settles to the bottom. The froth is skimmed off and the water and chemicals are distilled or otherwise removed, leaving a clean concentrate.
A typical froth flotation cell is shown in Fig. 1.
2.0 Minerals
Non-polar minerals such asmolybdenite, sulphur, graphite, coal, diamond and talc are naturally hydrophobic because of their covalent, non-polar molecular bonds. They therefore require minimal conditioning prior to flotation and will float easily with hydrocarbon oil collectors.
The majority of minerals, however, are polar and can be classified by their varying degrees of polar bonding as indicated below:
Group 1 –sulphide minerals and native metals
Group 2 – sulphate minerals
Group 3 – carbonates, phosphate and halide minerals
Group 4 – oxide and hydroxide minerals
Group 5 – silicate minerals
Mineral polarity increases from Group 1 to Group 5. Group 3 minerals can be rendered more hydrophobic by sulphidisation prior to flotation.
As the mineral polarity increases, polarised water molecules have anincreased affinity for the mineral surface and so render it more hydrophilic. In such cases, the mineral must be conditioned with a collector to repel the water molecules in favour of an air bubble.
3.0 Collectors
Collectors are the most critical of the flotation reagents. They are organic molecules or ions that selectively adsorb on to mineral surfaces and render them hydrophobic so that atequilibrium (indicated by contact angle), there is bubble/particle collision attachment. They must also reduce the induction time to ensure attachment occurs on bubble/particle collision.
Most collectors are weak acids, bases or their salts. They are heteropolar and may be considered to have two functional “ends”, one ionic (which can be adsorbed at the mineral surface either by chemicalreaction with ions of the mineral surface – chemisorption, or by electrostatic attraction to the mineral surface - physisorption), the other an organic chain or group (which provides the hydrophobic surface to the mineral).
Hydrocarbon chain length in thiol collectors is quite short. Most of these collectors have chain lengths to about six carbon atoms due to decreasing solubility with increasingchain length. In general, longer chain length results in stronger adsorption of the collector but reduced selectivity between sulphides. For maximum selectivity, it is normal practice to use a short chain collector.
Oxyhydryl, carboxylate, organic sulphate and sulphonate anionic collectors are used for the flotation of non-sulphide minerals. Carboxylates (fatty acids and their Na+ salts) are themost widely used, with the most frequently used being marketed as “tall oil”, a by-product of the wood pulp industry. “Tall oil” is approximately 50% oleic acid, with smaller amounts of linoleic, linolenic and resin acids. Sodium salts are often used since they are more soluble than the associated acids. The solubility of fatty acids used as collectors is limited to the eighteen carbon chain of...
1.0 Introduction
Today, flotation is the dominant method of mineral concentration. It is used for almost all sulphide minerals and is widely used for non-sulphide metallic minerals, industrial minerals and coal.
Flotation can be applied to low grade ores and ores that require fine grinding to achieve liberation. It is a relatively selective process and is an importantapplication in the separation and concentration of minerals in complex ores (ie. sulphide ores containing copper, lead and zinc).
Since most minerals are naturally hydrophilic, the surface of one mineral must be selectively rendered hydrophobic to achieve a separation by flotation. This is achieved by the regulation of the solution chemistry followed by the addition of a collector. The particlesrendered hydrophobic must contact and adhere to air bubbles, allowing them to rise to the surface and form a froth. The waste material (gangue) settles to the bottom. The froth is skimmed off and the water and chemicals are distilled or otherwise removed, leaving a clean concentrate.
A typical froth flotation cell is shown in Fig. 1.
2.0 Minerals
Non-polar minerals such asmolybdenite, sulphur, graphite, coal, diamond and talc are naturally hydrophobic because of their covalent, non-polar molecular bonds. They therefore require minimal conditioning prior to flotation and will float easily with hydrocarbon oil collectors.
The majority of minerals, however, are polar and can be classified by their varying degrees of polar bonding as indicated below:
Group 1 –sulphide minerals and native metals
Group 2 – sulphate minerals
Group 3 – carbonates, phosphate and halide minerals
Group 4 – oxide and hydroxide minerals
Group 5 – silicate minerals
Mineral polarity increases from Group 1 to Group 5. Group 3 minerals can be rendered more hydrophobic by sulphidisation prior to flotation.
As the mineral polarity increases, polarised water molecules have anincreased affinity for the mineral surface and so render it more hydrophilic. In such cases, the mineral must be conditioned with a collector to repel the water molecules in favour of an air bubble.
3.0 Collectors
Collectors are the most critical of the flotation reagents. They are organic molecules or ions that selectively adsorb on to mineral surfaces and render them hydrophobic so that atequilibrium (indicated by contact angle), there is bubble/particle collision attachment. They must also reduce the induction time to ensure attachment occurs on bubble/particle collision.
Most collectors are weak acids, bases or their salts. They are heteropolar and may be considered to have two functional “ends”, one ionic (which can be adsorbed at the mineral surface either by chemicalreaction with ions of the mineral surface – chemisorption, or by electrostatic attraction to the mineral surface - physisorption), the other an organic chain or group (which provides the hydrophobic surface to the mineral).
Hydrocarbon chain length in thiol collectors is quite short. Most of these collectors have chain lengths to about six carbon atoms due to decreasing solubility with increasingchain length. In general, longer chain length results in stronger adsorption of the collector but reduced selectivity between sulphides. For maximum selectivity, it is normal practice to use a short chain collector.
Oxyhydryl, carboxylate, organic sulphate and sulphonate anionic collectors are used for the flotation of non-sulphide minerals. Carboxylates (fatty acids and their Na+ salts) are themost widely used, with the most frequently used being marketed as “tall oil”, a by-product of the wood pulp industry. “Tall oil” is approximately 50% oleic acid, with smaller amounts of linoleic, linolenic and resin acids. Sodium salts are often used since they are more soluble than the associated acids. The solubility of fatty acids used as collectors is limited to the eighteen carbon chain of...
Leer documento completo
Regístrate para leer el documento completo.