New SAT Reading Practice Test 5

Tin is a metal often found in nature in its
oxidized form, as the mineral called cassiterite.
Cassiterite has been the primary source of tin
throughout history, and remains the primary
Line 5 Source of tin today. Small amounts of tin are
also recovered from sulphide minerals such
as stannite. Cassiterite is found in alluvial
deposits and can also be found in lode deposits
in association with other metallic minerals.
10 Cassiterite is mined by the dredging of alluvial
deposits, where the ore is broken up by either
high-pressure water or an excavator, or hard-rock
mining methods, usually from underground
mines. Crushed ore is concentrated, usually
15 in co-location with the mine, through a
combination of flotation, gravity, and magnetic
processes to produce a cassiterite concentrate
containing 70-77 percent tin. Tin concentrate
is then smelted by heating it in the presence of
20 carbon to 1,200-1,300 degrees Celsius, reducing
the cassiterite to tin metal, and releasing carbon
dioxide. Following the smelting process to
produce tin metal, the remaining impurities are
removed through a refining process, usually at a
25 facility co-located with the smelter. Refining tin
involves heating it to temperatures just past the
tin melting point, allowing impurities to drop out
as solids, and then skimming off the pure liquid
tin. Refining is done by either heat treatment
30 or electrolytic processes. Heat treatment uses
carbon-based fuel as a main heat source, usually
in a reverberatory furnace. Heat treatment is
more widely used than electrolytic processes,
but produces only 99.85 percent tin. Electrolytic
35 processing involves inserting the smelted tin in an
ionic solution and running an electrical current
through it. The smelted tin is the anode, and the
cathode collects the pure tin metal. Electrolytic
processing is more expensive, but provides up to
40 99.9999 percent tin.
Tin is often found in everyday life. It is the
primary component of solder. Solder is used
to combine two pieces of metal, allowing an
electrical charge to flow across the connection.
45 Solder is used on every electronic circuit board,
and it is difficult or expensive to replace. There
are some substitutes available for tin, with lead
being the most viable alternative. Solder has
been made from lead and tin, but since the Safe
50 Drinking Water Act, tin has become the primary
metal in solder. Tin is also a primary component
in food grade tin cans manufactured from
tinplate. Tinplate is made by annealing molten
tin onto a steel sheet. The resulting metal, formed
55 into cans, is then used in canning food, where the
tin prevents corrosion and leaching of steel into
the food product. Tinplate accounts for about 25
percent of domestic tin consumption. Because
tin is not harmful to humans, it is a preferred
60 method of canning and preserving food for
long-term storage. Substitutes for tinplate include
aluminum, plastic, and organic-coated steel. Tin
is also used in chemicals and accounts for 35
percent of domestic consumption.

65 The tin supply chain is complex and, often,
opaque. Companies usually report products that
they supply to the marketplace; however, they
may not describe which of their plants use which
starting materials or processes. As a result, plants
70 reported for some multi-plant corporations may
or may not consume or produce all of the tin
materials reported. Some large companies have
multiple plants, which may or may not have been
described in sufficient detail to identify their
75 location or the tin material that was processed.
For example, information was not available on all
tin producing companies, and many companies
that were reported to have been tin suppliers
could not be confirmed as such. Companies
80 changed names, were referred to imprecisely,
changed ownership, or went out of business.