Ores
Ores
A crude is any mixture of minerals in the form in which it occurs as a part of the
earth's crust. An ore is solid crude containing a tillable constituent in such amounts as to
constitute a promise of possible profit in extraction, treatment and sale.
The valuable constituent of an ore is ordinarily called valuable mineral or often just
mineral: the associated worthless material is called gangue. In some ores the mineral is
in the chemical state in which it is desired by primary consumers, e.g. graphite, sulphur,
asbestos, talc, garnet; in tact this is true of the majority of nonmetallic minerals. In
metallic ores however, the valuable mineral is rarely the product desired by the
consumer, and chemical treatment of such mineral is a necessary step in the process of
benefication. In such cases the sale product is usually the result of concentration by the
method of ore-dressing, followed by further concentration by the chemical methods of
metallurgy. The valuable product of the ore-dressing treatment is called concentrate, the
discarded waste is tailing.
Concentrate is, in most cases, the feed to the metallurgical plant. If the metallurgical
process is one in which separation is effected in a melt, the process is called smelting; if
the separation is effected by differential or selective solution, the process is leaching or
lixiviation; where the process is one of selective vaporization, it is called retorting.
The valuable metal product of smelting is usually differently named according to the
metal involved, e.g. blister (copper), base bullion (lead), pig (iron), etc.; the waste is
slag.
Metals occur in ores either in the native state (e.g., Au, Ag, Pt, Cu) or as salts or
oxides (CuS, Fe2O3, PbCo3), etc. But no matter what chemical form, the metal or mineral
is invariably associated with more or less — usually more — barren rock. The form in
which the metal is required by the primary customers is a relatively pure substance.
Hence a more or less extended process of purification, usually involving, in order, oredressing, metallurgical extraction, and chemical refining, intervenes between delivery of
ore at the mine exit and delivery of the metal to the customers.
One way in which the non-ferrous metals differ from iron is in the manner of their
occurrence. Iron oxide occurs in large and comparatively pure deposits; the other metals
and compounds from which metals are derived are scattered through large volumes of
rock, such as limestone or quartz. Since it would be difficult and costly to smelt these
large amounts of barren rock, metallurgists have recourse to concentration* or "ore
dressing" by which the metals or metallic compounds are partially separated from the
"gangue," or worthless material, before smelting.
Gravity Methods of Ore Dressing. — The simplest method of ore dressing depends
on the fact that in general the metallic compounds have a higher specific gravity than the
gangue, and hence settle faster in a stream of water. Gold panning is the simplest
illustration of the procedure. On a lager scale, it is carried on in jigs where the ore is
placed on a screen and a pulsating stream of water forced through the screen, causing the
lighter gangue to be washed out. Another form of gravity concentrator is the "table",
consisting of a surface with longitudinal ridges, which is given a jerking end-to-end
motion while a stream of water flows across, it laterally. By this means the heavy ore is
shaken over the end while the gangue washes off the front.
A crude is any mixture of minerals in the form in which it occurs as a part of the
earth's crust. An ore is solid crude containing a tillable constituent in such amounts as to
constitute a promise of possible profit in extraction, treatment and sale.
The valuable constituent of an ore is ordinarily called valuable mineral or often just
mineral: the associated worthless material is called gangue. In some ores the mineral is
in the chemical state in which it is desired by primary consumers, e.g. graphite, sulphur,
asbestos, talc, garnet; in tact this is true of the majority of nonmetallic minerals. In
metallic ores however, the valuable mineral is rarely the product desired by the
consumer, and chemical treatment of such mineral is a necessary step in the process of
benefication. In such cases the sale product is usually the result of concentration by the
method of ore-dressing, followed by further concentration by the chemical methods of
metallurgy. The valuable product of the ore-dressing treatment is called concentrate, the
discarded waste is tailing.
Concentrate is, in most cases, the feed to the metallurgical plant. If the metallurgical
process is one in which separation is effected in a melt, the process is called smelting; if
the separation is effected by differential or selective solution, the process is leaching or
lixiviation; where the process is one of selective vaporization, it is called retorting.
The valuable metal product of smelting is usually differently named according to the
metal involved, e.g. blister (copper), base bullion (lead), pig (iron), etc.; the waste is
slag.
Metals occur in ores either in the native state (e.g., Au, Ag, Pt, Cu) or as salts or
oxides (CuS, Fe2O3, PbCo3), etc. But no matter what chemical form, the metal or mineral
is invariably associated with more or less — usually more — barren rock. The form in
which the metal is required by the primary customers is a relatively pure substance.
Hence a more or less extended process of purification, usually involving, in order, oredressing, metallurgical extraction, and chemical refining, intervenes between delivery of
ore at the mine exit and delivery of the metal to the customers.
One way in which the non-ferrous metals differ from iron is in the manner of their
occurrence. Iron oxide occurs in large and comparatively pure deposits; the other metals
and compounds from which metals are derived are scattered through large volumes of
rock, such as limestone or quartz. Since it would be difficult and costly to smelt these
large amounts of barren rock, metallurgists have recourse to concentration* or "ore
dressing" by which the metals or metallic compounds are partially separated from the
"gangue," or worthless material, before smelting.
Gravity Methods of Ore Dressing. — The simplest method of ore dressing depends
on the fact that in general the metallic compounds have a higher specific gravity than the
gangue, and hence settle faster in a stream of water. Gold panning is the simplest
illustration of the procedure. On a lager scale, it is carried on in jigs where the ore is
placed on a screen and a pulsating stream of water forced through the screen, causing the
lighter gangue to be washed out. Another form of gravity concentrator is the "table",
consisting of a surface with longitudinal ridges, which is given a jerking end-to-end
motion while a stream of water flows across, it laterally. By this means the heavy ore is
shaken over the end while the gangue washes off the front.