Lead is a metal element with atomic number 82 and is presented on the periodic table by the symbol “Pb”. In solid form, lead has a dullish grey colour and in liquid form it gets a shiny chrome-silver colour. It melts at 327.5 °C and boils at 1740.0 °C, has a high resistance to corrosion and a high density. This makes lead very suitable in containing highly corrosive elements such as sulphuric acid. Pure lead is rarely found in the nature, it is more commonly found in combination with
Zinc,
Silver and most notably
Copper.
The largest geographical deposits of lead are located in USA, Peru, Argentina, Bolivia, Australia, Zambia, South Africa, Germany, Spain, Sweden, Italy and Serbia. At the current rate of consumption, it is estimated that the remaining lead deposits will be depleted in 42 years.
Lead
History
Lead is one the earliest metals discovered by mankind and is being used as far back as 6500 B.C., when the first manmade lead object, a small lead covered statue, was found in Turkey. The Egyptians and Chinese used lead in many different forms around 4000 B.C.
Lead was widely used by the Romans in many different functions and played a significant role in various parts of roman society. They used lead for all their water pipes and their famous baths. The modern word of plumbing is derived from the Latin word for lead: “Plumbum”, because lead was so widely used in water pipes. Aside from the technical usage of lead the Romans also used it extensively in a number of recipes. Roman winemakers exclusively used lead pots to crush grapes, because the overtones of lead would add a favourable flavour to the wine.
In the middle ages lead was widely used in the coating of rooftops, creation of gutters and tanks and in different forms of decorations such as statues and the joining of the huge colored glass decorations in the numerous churches across Europe.
During the industrial revolution, there was a huge increase in the demand for lead. Both used in the newly developed equipment as well as the various products created during the industrial revolution. It was also during this period, that scientist began discovering the connection between some diseases and the toxic effects of lead. This would eventually lead to regulations that would limit the use of lead in a number of applications and protect workers in lead industries.
The making of Lead
Mining
Lead is extracted out of different ores which are mined from underground mines. There are various ores containing some percentage of lead. However only three ores are usually mined in order to produce lead. The most common ore is Galena and this ore generally contains only lead and sulphur. The other two types of ore, mined for lead production, are Cerussite and Anglesite. These three ores combine for 95% of the total lead mining production. However these deposit commonly contain other ores more prominently, such as silver and zinc. Lead is therefore usually a by-product of silver and zinc mining. Only half of the worldwide lead production is derived from mining activities. The other half is obtained from recycling, most notably of car batteries.
Lead is extracted from underground mines by drilling the rock with heavy machinery of blasting it with dynamite. When the ore is extracted from the rocks it is transported to the surface for further processing.
When the lead ore is extracted to the surface, the process of extracting the actual lead from the ore, starts. The first step in processing lead ore is concentration. In a concentration mill, the ore is separated from the waste rock and ground into small particles.
Floatation
The next step involves flotation. The small particles of lead ore still consist of multiple types of chemicals such as sulphur. In order to remove the sulphur from the lead, the ore is poured into a tank or flotation cell which is filled with water. After this one percent pine oil or similar chemical is added to mixture in the tank and the tank will then mix all the different components with each other. The pine oil will bind to the sulphur and air is bubbled through the mixture, which causes the pine oil and sulphur combination to become an oily substance which will float atop the water in the tank. The waste rock will sink to the bottom and the lead will be separated from all other minerals.
The waste rock will sink to the bottom and the lead will be separated from all other minerals. The water with the lead components is pushed through a filter which removes up to 90% of the water and leaves a concentrate that is comprised of about 40 to 80 % lead.
Roasting
The next step is called roasting. This takes the concentrate from the filtering process and pours it in a moving grate and limestone and sand are added to the concentrate. Air that is heated to 1400 °C is blown through the moving grate. This results in the sulphur in the ore combusting to sulphur oxide, removing it from the concentrate. This can be used to create the by-product sulphuric acid. The remaining concentrate turns into a bristle material called sinter. This sinter is broken into lumps and moved on to the next step in the manufacturing process.
Blasting
The final step in manufacturing lead is called blasting. During this step, the lumps of sinter are dropped into a blast furnace and coke fuel is added. The coke fuel is heated up to 1200 °C, which produces carbon monoxide. The carbon monoxide generates a reaction with the lead and produces molten lead. This molten lead is poured drossing kettles or moulds. This lead now has a purity of 95% and needs to be refined in order to be sold on the market.
Refining
The molten lead is kept in the drossing kettle and is kept at a temperature of 330°C, just above melting point. The liquid form and temperature causes the remaining copper and other minerals to float to the surface of the drossing kettle. At this point the other minerals can be skimmed of the top and what remains is commercially accepted pure lead. This lead is cast into blocks and once cooled is a finished product that can be sold on markets.
Applications
Lead is still a common metal used in a number of functions. Due to its hazardous elements and consequently negative effects on the environment, scientists are looking for replacement materials in several applications.
Automobile industry
The automobile industry is the biggest consumer of lead. Half of the world lead consumption is due to the automobile industry. In this industry the most common application is the use in car batteries where it function as electrodes.
Construction
Lead is a very common material used in the construction of buildings. It is used for a number of specific tasks. Most notably is it used in the coating of rooftops and construction of gutters. The high resistance against corrosion makes it an ideal component for this function. High density combined with a favourable weight-to-volume ratio also makes it very desirable in the use of ballast keels for sailboats. Due to it’s high density, lead is also very effective as a radiation shield, for example in x-ray rooms. The high density is also very useful for the sound insulation of constructions.
Alloys
The best known alloy comprised of lead is solder. This is an alloy of lead and tin and in commercial use the balance of metals consists of 40% lead and 60% tin. This alloy is used to join metal pieces and is very useful because it has a lower melting point than most common metals. Solder is commonly used in electronica, plumbing and jewellery.