Froth Floatation

Presented By:

Gulfam Hussain

Introduction

Floatation is an extractive process where various minerals can be selectively extracted.

Flotation is a selective process and can be used to achieve specific separations from complex ores.

For example, in poly-metal ores such as Pb-Zn-Cu, floatation allows separate extraction of Pb, Cu and Zn.

Principal of froth floatation Flotation is a physico-chemical separation process that utilises the difference in surface properties of the valuable minerals and the unwanted gangue minerals.

1. Selective attachment to air bubbles (or "true flotation").

2. Entrainment in the water which passes through the froth.

3. Physical entrapment between particles in the froth attached to air bubbles (often referred to as "aggregation").

Steps involved mineral recovery through floatation 1. Liberation 2. Establish hydrophobic film on minerals that are not naturally hydrophobic. 3. Promote bubble formation.

Classification of mineralso Polaro Non-polarAll minerals are classified into polar or non-polar types according to their surface characteristics. Since water is a polar molecule, polar mineral

surfaces tend to be hydrophyllic Whereas, nonpolar mineral surfaces tend to be

hydrophobic.

The goal is to make the mineral surface hydrophobic so the minerals will attach to the bubbles in the froth.

Classification of polar mineralsGroup 1 Group 2 Group 3(a) Group 4 Group 5

GalenaCovelliteBorniteChalcociteChalcopyriteStibniteArgentiteBismuthiniteMilleriteCobaltiteArsenopyritePyriteSphaleriteOrpimentPentlanditeRealgarNative Au, Pt, Ag, Cu

BariteAnhydritGypsumAnglesit

CerrusiteMalachitAzuriteWulfenit

Group 3(b)FluoriteCalciteWitheriteMagnesiteDolomiteApatite Scheelite Smithsonite RhodochrositeSideriteMonazite

HematiteMagnetiteGothiteChromiteIlmeniteCorundumPyrolusiteLimoniteBorax WolframiteColumbiteTantalite Rutile Cassiterite

ZirconWillemiteHemimorphiteBerylFeldsparSillimaniteGarnetQuartz

Degree of polarity of mineral types: Sulfides < sulfates < carbonates < phosphates < oxides < hydroxides < silicates.

The surfaces of non-polar minerals are characterised by relatively weak molecular bonds. The minerals are composed of covalent molecules held together by van der Waals forces, and the non-polar surfaces do not readily attach to the water dipoles, and in consequence are hydrophobic.

Types of non-polar mineral include: Coal, oil, molybdenite, diamond, talc, gold

Collectors Render minerals hydrophobic by attaching to

the surface of mineral particles. A collector’s polar head will attach to a polar

mineral surface, leaving the nonpolar tails toward the surrounding water molecules, rendering the mineral hydrophobic,

Fig 2: interaction of collector with mineral surface

Frothers Produces stable bubbles for hydrophobic

particles to attach. When the mineral surfaces have been

rendered hydrophobic by the collector, the frother is meant to produce a stable bubble. Frothers also act as collectors, which can lead to decreased selectivity.

Some collectors are such good frothers as well that they stabilize the froth so much as to reduce their transportability.

Example frothers include pine oil and MIBC (methyl isobutyl carbinol).

Regulators Regulators, or modifiers, are used

extensively in flotation to modify the action of the collector, either by intensifying or by reducing its water-repellent effect on the mineral surface.

Regulators can be classed as activators, depressants, or pH modifiers.

Activators These reagents alter the chemical nature

of mineral surfaces so that they become hydrophobic due to the action of the collector.

Activators are generally soluble salts which ionise in solution, the ions then reacting with the mineral surface.

A classical example is the activation of sphalerite by copper in solution

ZnS + Cu 2 CuS + Zn 2+

Depressants Depression is used to increase the

selectivity of flotation by rendering certain minerals hydrophilic (water-avid), thus preventing their flotation.

They are key to the economic flotation of certain ores such as platinum and nickel sulphides.

There are many types of depressants and their actions are complex and varied, and in most cases not fully understood, making depression more difficult to control than the application of other types of reagent, particularly when the froth phase is also affected by their action.