The Preparation of Metals and metal oxides—Extractive Metallurgy
Katie Ames
Department of Chemistry and Biochemistry, Kennesaw State University, Kennesaw, GA 30144
Abstract:
Metals cannot just be picked from the ground in a pure state and they are typically mixed
and bonded with other substances. Some of these metals have to go through a series of reactions
so that the metal can be extracted. Antimony was extracted from its original state Antimony (III)
oxide (Sb2O3 (s)). This processes yield a pure form of Antimony that was extracted and cleaned
after several reactions occurred. Chromium was also extracted in a similar way with its starting
material of ammonium dichromate that underwent several reactions and an ignition to form pure
chromium solid.
Introduction:
Most of the metals that one uses on a day to day basis did not start out as the pure form of that
metal. For many metals, a process called metallurgy is used in which a series of reactions causes
the metal to become its pure solid form and become easily extractable. Metallurgy has been used
for centuries by the ancient Egyptians, ancient Romans, the Middle Ages alchemists, and all the
way up to the modern day (1). The extraction of antimony and chromium were completed in the
lab as a way to introduce students into the idea of metallurgy and ways to extract a pure
substance from an original form.
Antimony was extracted by the ancient Middle East in areas such as Egypt and Rome. It
was originally used as an alloy to make lead tools harder so the tools could stand up to more use
and wear (2). Antimony is still being used to harden lead but it is also being used as a semiconductor, in batteries, and when it is combined with other elements, like oxygen and chlorine, it
can be used as a flame retardant as well as many other uses (3). Metallurgy is one of the main
ways to extract this metal, so it can be used in these ancient and modern applications.
Chromium was extracted in the late 16th century by similar methods that are used today.
Its main use in the modern day is to make metals harder like stainless steel and is used on some
metals to make the surface have a glossy, polished finish. Chromium has many other uses that
include leather tanning and dying materials (4). Its same extraction methods are still used to this
day though they have been modified with today’s technology and knowledge.
Experimental:
The metals chromium and antimony were extracted using two different techniques and
methods. Both methods were carried out simultaneously but they did not interact or interfere
with each other.
The extraction of chromium was the first reaction started since it was the reaction that
should take the longest to react. 5.065 grams of ammonium dichromate was mixed in an
evaporating dish that was covered and then heated. Once the dish was heated it was allowed to
cool and then heated again to remove any impurities. What was left was a sage green powderlike material. This green powder was chromium (III) oxide which was used in the next step of
the experiment.
2.5 752 grams of the resulting chromium (III) oxide was then mixed with 4.9695 grams
of a powder form of solid aluminum and 7.0078 grams of potassium dichromate in a large
crucible that was lined with calcium fluoride. A small hole was then made in the center of this
mixture where 2.4893 grams of barium dioxide and .9925 grams of magnesium were placed as
an ignition mixture. A fuse of solid magnesium was made and placed standing up in the center of
the ignition mixture which was then lighted and placed under the hood. After the reaction, which
created a large amount of light briefly as the mixture burned, the reaction had to be cooled before
any metal could be manually extracted from the burned material. After letting the crucible cool
for several minutes, the chromium metal could be extracted by breaking up the charred remains
of the mixture. This process took some time because the metal was coated with the burnt on
original mixture so the metal was not distinguishable by its shiny surface. Thankfully, a wrench,
though a little unorthodox, was brought into the lab and helped to break up the remains easier so
the metals exterior could be exposed and removed from the remains. About .6254 grams of
chromium metal was extracted from this experiment, though 4.232 grams were expected to be
extracted.
The Antimony underwent a similar process though no ignition was needed in this case.
Antimony (V) oxide was the starting material; .9958 grams of antimony (V) oxide and 1.9730
grams of urea were mixed in a small crucible. The crucible was coved and then placed over a
Fischer Burner for about thirty minutes. The crucible was then allowed to cool until it was at
room temperature. At this point, the metal had not quite been solidified so another .9914 grams
of urea was added to the mixture and it was placed on the Burner again for about fifteen minutes.
After the crucible was allowed to cool the second time, the metal was easily noticeable and could
be extracted. The small metal spheres were placed in water to be cleans and then weighed out to
be about .5195 grams though the amount expected was about .8318 grams.
Results and Discussion:
Table 1. Expected and actual amounts of metal products and the calculated percent yield
Antimony
Chromium
Expected amount
.8318 g
4.232 g
Actual amount
.5195 g
.6254 g
Percent Yield
62.45%
14.78%
The expected amounts for both products were simply found by stoichiometry. The
chromium expected amount came from two separate sources: the original chromium (III) oxide
as well as the potassium dichromate. Both of these compounds were taken into account when
calculating the percent yield for the chromium. For the antimony, only one source was present in
the mixture, the antimony (V) oxide, and only it was taken into account when calculating the
expected amount for antimony.
The results were all but expected. Both of these reactions were supposed to have fairly
high yields but as one can see by Table 1 the yield for antimony was somewhat moderate
whereas the yield for chromium was under moderate. There are a few possible reasons for this
occurrence.
The first reason that these reactions might not have produced a more acceptable yield
might have been because some of the material was lost in the reaction. Both the antimony and
the chromium involved an explosive or violent reaction that could have caused some of the
starting material to have escaped the crucibles and losing some of the possible metal product.
Another possible reason for the antimony’s low yield might have been because the reaction was
never completed. The reaction had to be heated twice and it is possible that during the second
time some of the metal still did not come out as the solid. As for the Chromium, probably the
main reason why the reaction did not yield as much chromium as expected was probably because
the charred remains of the reaction were not gone through thoroughly enough and much of the
product was thrown away as remains. It is also possible that this reaction was not carried out
completely when it was ignited and some of the starting material was never reacted. Finally, for
both reactions, it is possible that one or more of the starting materials were not measured out
properly so the reaction could not be taken to completion due to a lake of starting material
therefore causing fewer products to be formed.
Conclusion:
Metallurgy is the main way to extract metals from its natural existing alloys, such as
chromium (III) oxide and antimony (V) oxide. These methods, or similar ones, have been used
for centuries and have been rather successful in producing a desired metal. For these reactions
more caution and more preciseness would have allowed these reactions to be more effective and
would have allowed one to see how well these methods truly work to extract metal solid. Further
experiments, or a repeat of these, could be performed with more attention being paid to detail so
that these reactions could react to their fullest. Otherwise, one can assume that these reactions
obviously are usually successful since they are used in modern labs and facilities to extract the
metals we use on a daily bases.
References:
1. O’Klatner, B. L.; Rabinovich, H. G. J. Chem. Educ. Metallurgy in the Laboratory:
Preparation of pure antimony. 2000, 77 is. 2, 2, 251.
2. Cramb, A. W. A Short History of Metals.
http://neon.mems.cmu.edu/cramb/Processing/history.html (accessed 1/25/2009), part of
The Department of Materials Science and Engineering at Carnegie Mellow University.
http://www.materials.cmu.edu/ (accessed 1/25/2009).
3. Antimony. http://periodic.lanl.gov/elements/51.html (accessed 1/26/2009), part of A
Periodic Table of the Elements at Los Alamos National Laboratory.
http://periodic.lanl.gov/default.htm (accessed 1/26/2009).
4. It’s Elemental: The Element Chromium.
http://education.jlab.org/itselemental/ele024.html (accessed 1/26/2009), part of Thomas
Jefferson Lab National Accelerator Facility. http://www.jlab.org/ (accessed 1/26/2009).