The Iwami-Ginzan Silver Mine in Japan produced a large volume of silver from the sixteenth to the se — Physical Chemistry — Thermodynamics Chemistry Question
Silver smelting and refining
The Iwami-Ginzan Silver Mine in Japan produced a large volume of silver from the sixteenth to the seventeenth centuries. The ores included natural silver and argentite (silver sulfide). To obtain pure silver from the ores, galena (lead sulfide) was used for the smelting. In the method, the silver ore was mixed with lead sulfide and then melted in a container. During the heating process, an alloy of silver and lead was formed and pooled at the bottom of the container due to the high density of the alloy. The obtained alloy was put on an unglazed porous ceramic sheet and heated under an air flow. The alloy was melted and formed a droplet on the sheet. Lead in the alloy reacted chemically with the air and was removed from the alloy. The other impurities were also removed simultaneously and silver metal could be obtained.
Write the 2-step chemical reactions from lead sulfide to lead metal. Lead sulfide is heated under an air flow in the first step of the process, and then heated while blocking the air in the second step. You should provide the possible two routes with the different intermediate compounds in your answer.
Model Answer
Route 1
PbS + 2 O2 → PbSO4
PbS + PbSO4 → 2 Pb + 2 SO2
Route 2
2 PbS + 3 O2 → 2 PbO + 2 SO2
PbS + 2 PbO → 3 Pb + SO2
If the same procedure is carried out with the presence of silver sulfide, an alloy of silver and lead is obtained. Write the chemical reactions between silver sulfide and the intermediate compounds of question 1. In general, the composition of the alloy can be changed continuously and the chemical formula of the alloy cannot be written stoichiometrically. Answer the question assuming the chemical formula of the obtained alloy to be AgPb2.
Model Answer
Route 1
AgS + 2 PbSO4 → AgPb2 + 2 SO2
Route 2
Ag2S + 4 PbO → 2 AgPb2 + SO2
Write the chemical reaction for lead in the alloy during the heating process of the alloy in the air at about 800 ºC.
Model Answer
2 Pb + O2 → 2 PbO
Which is the reason that best describes why the lead compound obtained in question 3 can be removed from the alloy. Choose one from the following choices:
A: The lead compound reacts chemically with the ceramic sheet and is removed from the alloy.
B: The lead compound wets the ceramic sheet and is sponged into the porous ceramics due to a capillary action.
C: The lead compound evaporates and is removed from the alloy.
D: The lead compound is separated from the silver due to the low density of the compound.
E: The lead compound is separated from the silver due to the high density of the compound.
Model Answer
B
What happens, if gold is included in the ores? Choose one from the following choices.
A: Silver is oxidized when gold is precipitated.
B: Gold is precipitated at the bottom of the alloy and can be separated from silver.
C: Gold covers the surface of the alloy and can be separated from silver.
D: Gold is precipitated at the center of the alloy and can be separated from silver.
E: Gold remains in the silver metal as a uniform alloy and cannot be separated from silver.
Model Answer
E