Day A. Mining chemicals hand book

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• The use of a more selective reagent or reagent combination in the

rougher-scavenger circuit usually enables operation of that circuit

at a lower pH, thus reducing the amount of lime or other depres-

sant required.

• The use of a selective collector may produce a sufficiently high-

grade concentrate in the early stages of the rougher circuit, that

this product can bypass the regrinding stage and be sent directly

to the feed to the first or second cleaner. This not only further

reduces the load on the regrind circuit, but also minimizes the

risk of overgrinding already liberated value minerals. Such over-

grinding can lead to "sliming" and subsequent loss of overall

recovery. Flowsheets 1 and 2 are traditional, simple flotation cir-

cuits. Flowsheet 3 indicates the kind of circuit which may be pos-

sible when using more selective reagents.

Effect of selective reagents on flotation circuit design and operation

Flowsheet 1 – Conventional

Flowsheet 1 is typical of early base-metal flotation flowsheets. The

cleaning circuit is totally "closed" with the 1st. cleaner tails being

returned to the head of rougher-scavenger flotation. In some cases,

the scavenger concentrate was also returned to the head of rougher

flotation. Such a flowsheet is typified by high circulating loads in

both the rougher-scavenger and cleaner stages.

Mining Chemicals Handbook

Flowsheet 2 – Modified Conventional

Flowsheet 2 is probably the most typical of current base-metal flota-

tion circuits. The 1st. cleaner tailing is sent to a cleaner-scavenger

stage, the concentrate of which is returned to the regrind mill. The

cleaner-scavenger tailing joins the rougher-scavenger tailing to form

the final plant tailings. This design reduces the circulating loads in

both the rougher-scavenger and cleaner stages, thereby reducing the

flotation capacity required for a given mill tonnage.

Effect of selective reagents on flotation circuit design and operation

Flowsheet 3 – Selective Rougher

Flowsheet 3 represents the type of design which may be made pos-

sible by the use of more selective collectors in the rougher-scavenger

stage. Samples of the concentrate are taken from successive cells

down the rougher bank for both chemical assay and mineralogical

examination. In most cases, it will be found that the concentrate

from the early stages of rougher flotation will be of high enough

grade and sufficiently liberated to bypass the regrind mill. Whether

this concentrate is sent to the first, second, or final cleaner stage will

depend upon its grade and mineralogical characteristics. This flow-

sheet design further reduces the circulating load in the cleaners as

well as minimizing overgrinding of already-liberated value mineral.

The advantages described above for simple ores are even more

important when treating complex ores containing two or more

value minerals. With these ores, separation efficiency between the

individual value minerals is often more critical than the selectivity

between the value minerals and the gangue minerals.

Mining Chemicals Handbook

by-passing regrind and depending on product grade may go into 1st, 2nd, or 3rd cleaner

Effect of selective reagents on flotation circuit design and operation

In the case of already existing flotation circuits, many of the

described advantages could still be obtained if suitable circuit and

piping changes were made. Furthermore, since many plants are

already operating at or above design tonnages, greater selectivity in

the rougher circuit and the consequent reduction of the load on the

regrind and cleaning circuit, can have major benefits, such as elimi-

nating circuit bottlenecks.

To summarize, the selection of collector and other reagents should

not be based on rougher-scavenger evaluation only, and certainly

not solely on reagents that give the highest recovery therein. Rather,

reagents should be evaluated on the grade-recovery relationships

they produce throughout the whole process, including regrinding

and cleaning. This will inevitably entail at least locked-cycle testing

in the laboratory, preferably followed by pilot-scale testing.

4.1 Bibliography and references

1. Crozier, R. D., 1992. Flotation, Theory, Reagents and Testing. Oxford:

Pergamon Press.

2. Booth, R. B., 1954. “Flotation”. Ind. Eng. Chem. (1954), 46, 105-11.

3. Fuerstenau, D.W. ed. 1962. “Froth Flotation” – 50th anniversary

volume, New York: AIME.

4. Gaudin, A. M., 1939. Principles of Mineral Dressing. New York:

McGraw-Hill.

5. Glembotskii, V.A., V. I. Klassen and I. N. Plaksin, 1963. Flotation.

New York: Primary Sources.

6. Hartman, H. L., 1992. SME Mining Engineering Handbook.

2nd ed. 2 vols. Littleton: SME.

7. Mular, A. L. and R. B. Bhappu. 1980. “Mineral Processing Plant

Design”. 2nd ed. New York: AIME. Chapters 2 and 3.

8. Nagaraj, D. R. and A. Gorken, 1991. “Potential controlled flotation

and depression of copper sulfides and oxides using hydrosulfide

in non-xanthate systems”. Canadian Metallurgical Quarterly vol. 30,

No. 2, pp. 79-86.

9. Nagaraj, D.R. and F. Bruey, 2002. “Reagent Optimization:

Pitfalls of Standard Practice”. Workshop/Conference on Flotation

and Flocculation, Hawaii, USA.

10. Perry, J. H., 1963 Chemical Engineers Handbook. New York:

McGraw-Hill.

11. Sutherland, K. L. and I.W. Wark. 1955. “Principles of flotation”.

Melbourne: AIMM.

12. Taggart, A. F., 1945, Handbook of Mineral Dressing. New York:

McGraw-Hill.

13. Trahar, W. J., 1981. “A rational interpretation of the role of

particle size in flotation”. Int. J. Min. Proc., 8, 289.

14. Weiss, N. L., 1985, SME Mineral Processing Handbook. 2 Vols. New

York: AIME. Vol. 2, Section 30.

15. Wills, B. A., ed. 1997. Mineral Processing Technology. 6th ed.

Oxford: Butterworth-Heinemann.

Mining Chemicals Handbook

FLOTATION REAGENT

FUNDAMENTALS

Mining Chemicals Handbook

Section 5 Flotation reagent fundamentals

Flotation is a physico-chemical process. This statement clearly indi-

cates that both physical and chemical factors are equally important

in flotation. In other words, it would be naïve to proclaim that one

set of factors is more important than the other set, which is some-

times done in research or practice. Chemical factors include the

interfacial chemistry involved in the three phases that exist in a

flotation system, viz. solid, liquid and gas. Interfacial chemistry is

dictated by all the flotation reagents – such as collectors, depres-

sants, frothers, activators, and pH modifiers – used in the process,

water chemistry, and the chemistry of the minerals. Physical (or

more accurately, physical-mechanical and operational) factors

comprise equipment components (cell design, hydrodynamics,

bank configuration, and bank control) and operational components

(feed rate, mineralogy, particle size, and pulp density). Thus

flotation, while simple in concept, is an extremely complex process

in practice involving many scientific and engineering phenomena.

In most flotation systems, physical and chemical factors are not

independent, i.e. there are significant interactions among the many

variables. In theory, when all physical factors are optimized, a

change in a chemical factor should clearly record a measurable

change in flotation efficiency (either recovery or grade or both), and

vice versa. In practice, however, this may not be immediately obvious

because of certain operational restrictions, and metallurgists have

to revert to statistical tools to demonstrate significant changes.

A further complication is that neither physical nor chemical factors

can always be fully or satisfactorily optimized since there can be

significant changes occurring routinely in mineralogy, feed rates and

particle size distribution. Nevertheless, flotation plant operators still

achieve impressive separations and performance by managing

controllable factors.

In general, in a fully commissioned plant it is more difficult to

change physical-mechanical factors than operational or chemical

factors. Indeed, in most plants considerable attention is, therefore,

focused on changing or optimizing chemical and operational variables.

The importance of chemical factors in achieving target performance

has been widely recognized. In many circuits, a mere change in pH

of the pulp can cause dramatic differences in flotation efficiency.

This is true of flotation reagents as well.

In this section an attempt is made to highlight how changes in the

chemistry of flotation reagents can have marked influence on

flotation efficiency. The chemistry of collectors is used to illustrate

Flotation reagent fundamentals

structure-activity aspects, though the principles are applicable to

depressants as well.

A brief, simplified description of terminology will be necessary to

appreciate the structure-activity aspects of flotation reagents. Donor

Atoms or donors or ligand atoms are those atoms in the reagent mole-

cule that bond directly with the metal atom on the mineral surface.

Ligands are the functional groups containing the donor atom(s) on

the reagent molecule that participate in bond formation with metal

atoms on the mineral; donor atoms are also often referred to as

ligands. Functional Groups are a well-recognized group of atoms

containing the donor atoms in the reagent molecule. Acceptors are

atoms or groups of atoms that accept electrons from donors. A

metal atom on the mineral surface is the acceptor in most instances.

Acceptors are generally positively charged, while donors or ligands

or functional groups are often negatively charged. Note, however,

that in cationic flotation reagents, the functional group of the mole-

cule carries a positive charge, and this can interact with a mineral

surface that has negative sites. Functional groups are generally polar

(i.e. carrying a charge, partially or fully). Non-polar moieties of a

flotation reagent molecule are generally a hydrocarbon chain (linear

or branched, aliphatic or aromatic or a combination).

For a vast number of flotation reagents, adsorption at the solid-

liquid interface is of critical importance. Frothers, which adsorb

significantly at the liquid-air interface and alter its properties, can also

adsorb at the solid-liquid interface and influence flotation outcome.

However, interfacial chemistry of frothers is largely characterized by

non-specific adsorption processes. Most commonly used frothers

belong to the classes of short-chain alcohols and polyglycols (and

their monoethers). Consequently, the scope of structure-activity

relationships is rather limited.

The driving force for, and the mechanism of, adsorption of

flotation reagents on minerals comprises chemical (chemisorption,

surface reaction or complexation, and chemical adsorption), electro-

static (physisorption or physical adsorption), and non-specific forces

(such as Van der Waal’s forces, hydrogen bonding, and the so-called

hydrophobic force). Chemical interactions have the highest adsorp-

tion energies followed by electrostatic and non-specific interactions.

In many cases, more than one driving force is in operation. Overall

adsorption energy is, therefore, a sum of all energies associated with

various adsorption processes.

In the case of non-specific adsorption processes, structural aspects

of the reagent molecule that can be changed include the nature and

type of the hydrocarbon chain, moieties capable of hydrogen bond-

ing etc. In general, such changes in the molecule can only cause

Mining Chemicals Handbook