Lead
... but today does not mine it much. The USA is the worlds leading producer. Lead makes up 2 x 10-4% of the Earth’s crust. On top of the sources already mentioned, lead sometimes can be found in its elemental state. Often, lead is present in some minerals such as carbonate-phosphate, chromate, molybdate or tungsten. Galena is one of the only ores processed. Currently, there are two methods used to convert this ore to elemental Pb. The first method is the roasting reduction process. In this process, the PbS is roasted to lead (II) oxide and then reduced in a blast furnace by carbon monoxide formed by burning coke. This reaction can be shown in the following equation: PbO + CO à Pb + CO2. The second method, or the roasting reaction method, roasts the sulfide only until the lead oxide is formed in the correct proportion to react the remaining sulfide to lead and sulfur dioxide. The equation for this method is as follows: 2PbO + PbS à 3Pb + SO2. Each of these processes produces crude lead and there are usually significant amounts of other elements present as impurities. Elements that are present as impurities include: copper, tin, arsenic, antimony, gold, and silver. First, in the process to refine the lead ore, the copper is removed from the molten bullion by skimming off the copper as dross. After the removal of the copper, the temperature of the bullion is increased with or without a stream of air. With this temperature increase, the arsenic, antimony, and tin rise to the surface along with some lead oxide. These impurities are then skimmed from the top as well. The removal of the gold and silver is accomplished by adding small amounts of zinc to the molten bullion. The zinc alloys with the gold then the silver. After these alloys cool, they float to the top and are skimmed off. The sequence of steps to the metallurgy of lead is extremely varied and depends on the impurities present in the ore, the location the ore was mined, etc. Lead occurs only in a metallic form with a packed structure. When lead is freshly cut, it has a bright silvery luster with a bluish cast. As an oxide coating forms, a dull gray appearance is seen. Lead is a soft ductile metal. Pb has 29 isotopes with masses ranging from 194 to 214. Lead has an atomic number of 82, and an atomic mass of 207.2. Its crystalline structure is described as a face-centered cubic. Lead has a melting point of 327.3° C and a boiling point of 1744° C. Pb also is not a very good conductor of electricity and is heavy. It is also the most corrosive-resistant of the common metals. Lead is in Group IVA, Period 6 of the Periodic Table. At room temperature these elements are relatively unreactive, especially if they are in crystalline form. All of these elements will burn if the temperature is raised. Lead usually gives lead (II) oxide, PbO, unless the temperature is kept below 500° C. If the temperature is kept at this mark, the lead will form red oxide, Pb3O4 with lead in +2 and +4 oxidation states. Lead in the +2 oxidation state is the most stable. These IVA elements are also relatively unreactive with water. Lead does react with dilute acids, which is not common with the IVA elements. Only tin and lead react with acids. Lead is relatively insoluble in sulfuric and hydrochloric acid, but it dissolves slowly in nitric acid. Lead is also slowly oxidized in moist air. Pb will also combine with halogens at high temperatures. When lead combines with a halogen, lead (II) haldide is usually formed. Once again, the stability of the +2 oxidation state is observed. Lead is used for many various things. It is very important and is usually used in the form of alloys. However, pure lead is used in lead-storage batteries. Pure lead is also used for radiation protection because it absorbs such things as x-ray...