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Mineral Processing Applications
Mineral processing, minerals beneficiation, ore dressing, are all names used for the step following the mine where an ore is processed. In general mineral processing is used on:
(1) Metallic Sulphide ores;
(2) Metallic Oxides ores;
(3) Nonsulphide or non-metallic ores,
(4) Free metal ores
Metallic Sulphide Ores
The primary method of processing sulphide
ores is by froth flotation (following a multistage crushing and
grinding). The best example of this is copper, where low grade
sulphide deposits predominate and flotation is extensively used for
producing a high-grade copper-sulphide concentrate low in iron. Much
of the ore is of a finely disseminated nature, requiring carefully
comminution to achieve liberation. There are often several different
mineral forms and other metallics.
Molybdenum is often found with copper and is a common by-product
that requires multi-stage processing usually by flotation to produce
the necessary high-grade concentrate required. A considerable
proportion of "Moly" production is acquired as a byproduct from
copper concentration plants.
In the production of lead, zinc, and tin concentrates the important
factor is the rejection of iron in the form of iron sulphides
(pyrites). Flotation is the commonest process. As selectivity is
important in the production of lead concentrates, it is usually
necessary to have two or more cleaning stages in a lead circuit.
Complex cobalt sulphides and arsenides are recovered with flotation.
The main problem in satisfactory recovery is close operating
control. Controlled aeration of the pulp is very important when
floating this mineral for it is usually associated with other
sulphides.
The precious metals, silver, gold and platinum are frequently found
associated with sulphides, arsenides and other complex ores.
Flotation of these sulphides and arsenides is extensively used,
particularly for silver ores. Gold tellurides are frequently found
present in these complex mixtures and are also recovered in the
flotation concentrates.
Metallic Oxide Ores
Iron is one of the main oxides and the
concentration of iron ores has received widespread attention.
Although magnetic separation, classification, and gravity methods
have been used (and still are) in this field, flotation is widely
used. Not only can a higher grade concentrate be produced by
flotation but heretofore unworkable deposits are amenable to this
process. Fine grinding is required to liberate the silica from the
iron oxide and consequently the importance flotation.
The general application of titanium compounds in alloys, pigments,
welding rod, and chemical warfare has created quite a demand for
such minerals as rutile and ilmenite, the chief sources of this
important element. Gravity, magnetic and electrostatic methods have
been employed, principally from deposits in which the minerals occur
in granular size. The necessity of working lower grade, more complex
deposits, has expanded the use of flotation.
Processing of copper oxide ores presents both mechanical and
metallurgical problems which, by careful analysis can been overcome
primarily by hydrometallurgical processes in both heap leach and in
full milling operations.
Non-Metallics
Non-metallics are processed to a large extent
by froth flotation. By far the greatest present application of
flotation in the non-metallic field is in the recovery of phosphate.
Washing, screening, and classification are the common methods for
recovering the coarse and pebble phosphate, but it remained for
flotation to provide a satisfactory and low-cost means to reclaim
and beneficiate phosphate formerly rejected as tailing.
The great demand for high-grade fluorspar, in particular that
meeting the specifications for ceramic and acid grade, has been met,
in part at least, by flotation, the most important recovery method.
Recovery of manganese minerals, because of their generally high
gravity, is for the most part accomplished by gravity methods
employing coarse and fine jigs and tables. Practically all manganese
minerals are soft and therefore, losses by gravity methods leave
considerable to be desired insofar as recovery is concerned. Then,
too, some manganese ores are not amenable to gravity methods due to
close association with impurities. This, of course, necessitates
grinding, in some instances quite fine. Manganese flotation has been
successfully employed for several years, although only on certain
specific ores.
Coal is one the biggest users of gravity separation, featuring large
(1,000 t/hr and larger) plants using multi-stage heavy media, and
other gravity processes. The fines are often processed by flotation.
Graphite is perhaps one of the easiest non-metallic minerals to
recover by flotation because of its natural floatability and water
repellent action. It has been successfully floated as coarse as 10
mesh, which contributes much to the market value. Flake graphites
are sold according to size with the coarser sizes commanding the
highest prices.
The most important present-day commercial source of aluminum is from
the mineral bauxite, a hydrous aluminum silicate, which usually has
a variable composition and is associated with such impurities as
clay, silica, iron oxide and titanium oxide. Present day production
is generally from high-grade deposits and concentration depends to a
large extent on washing plants to remove clay and other impurities.
Free Metal Ores
When people think of free metal ores they
generally refer to gold and silver and the main processing is by
gravity separation for small operations or by cyanidation for large.
While in most operations recovery and extraction of free gold and
silver is by means of cyanidation or gravity or a combination of
these methods. However, flotation is sometimes necessary where
certain physical conditions preclude the use of other processes.
Notable examples are in extremely slow settling ores, as well as
ores containing excessive cyanicides, soluble salts, or containing
carbonaceous material. Direct flotation of gold and silver has been
done, and is possible.
Diamonds, while not a metal, or processed mostly by gravity
processes similar to small scale precious metal operations.
More information on specific processes is available at:
A Mining Engineers Notebook:
Mineral processing.
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40+ years’ experience in the mining industry with strong mineral
processing experience in precious metals, copper, industrial
minerals, coal, and phosphate
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Operational experience in precious metals, coal, and phosphate plus
in petrochemicals.
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Extensive experience performing studies and determining feasibility
in the US and international (United States, Canada, Mexico, Ecuador,
Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).
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E-mail:
info@smartdogmining.com
