uses and misues of lead compounds ?
Answers
the 1900s, lead arsenate was used as a pesticide against leaf-eating insects, although not permitted on crops destined for human or animal consumption. It was regarded as safe when dusted on tobacco crops, but the result was that smokers has more lead in their bodies than non-smokers. That misuse of lead has now ceased and at least smokers need no longer worry about their exposure to these two toxic elements.
More lead today is mined, recycled, and used than in any previous time in history. Production in 2003 was around 6.5 million tonnes of which 60% was recycled lead. The popularity of the motor car and the production of lead went hand in hand throughout most of the 1900s. Lead production doubled and doubled again as it was used in many ways: lead undercoats, lead in tyres, lead batteries, and lead in the petrol. The last use has since almost ended but not the love affair between car-makers and lead producers. Car batteries still account for more than three-quarters of all lead consumed in the USA. In lead batteries the anode is spongy lead, the cathode a paste of lead oxide on a lead alloy metal grid, and all of this can be recycled.
What cannot be recycled was the leaded glass used for the cathode ray tubes of television sets and PCs. These contained a lot of lead, maybe up to a kilogram or more. However, though it can't be reclaimed, it poses no threat, not even when it is disposed into a landfill site because the lead is bonded to the glass and does not dissolve when it comes in contact with groundwater.
Mined lead is still refined to remove the silver it contains (as much as 1.2 kg/tonne). This is done by adding zinc to the molten metal and allowing it to cool slowly until the zinc settles out as a separate layer on top of the lead carrying the silver with it and this is separated off to reclaim the silver. The molten lead is then heated under vacuum to drive off any remaining zinc, giving a product that is 99.99% pure.
Other uses for lead are in sheeting, cables, solders, lead crystal glassware, ammunition, bearings, and in sports equipment, for weight-lifting and to balance golf clubs. It is used as a stabilizer for PVC although this is to be banned in the EU from 2015 onwards. Lead is very poor at transmitting sound and vibrations, so that it is added to plastic sheeting and tiling designed to block out noise. Lead is still used in architecture as roof cladding and for stained glass windows. It provides protection that will last for centuries, even in industrial and coastal regions, nor does it cause discoloration of surrounding stone or brickwork. In urban or industrial environments the protective surface layer slowly changes over the centuries from lead oxide to lead carbonate, and finally to lead sulphate. In all cases the lead compound that is formed is insoluble and, unlike rust, does not flake from the surface, and it forms a protective coating.
Some uses of lead that were no threat to humans have been phased out because of their threat to wildlife. Unfortunately lead shot is still widely used, but lead sinkers are a thing of the past in countries where swans are to be found. Fishermen used lead sinkers and these were often lost to the bottom of rivers and lakes where swans could scoop them up as they fed in the mud along the bottom of rivers. The sinker would then reside in the bird's stomach, slowly weakening it over many months until it died of lead poisoning.
Curiously, as one form of lead pollution is ended, there seems always to be another way in which it can be exploited to the detriment of some. In 1994 there was an outbreak of lead poisoning in Hungary, due to red lead being used to colour paprika, the spicy flavouring made from dried red peppers. Eighteen people were arrested but the extent of the damage it caused is hard to assess because Hungarians used the paprika to colour many foods, such as goulash, sausages, and salami. Thankfully, the deceit was not practised for so long that it put lives at risk, although one wonders if this was really a new way to adulterate food, or a rediscovery of an ancient food colouring additive.
Lead is still a useful metal, but only for a few products, and none of which should release its lead so that it could find its way into the human body. At the start of this chapter I quoted the words written on the lead casket in Merchant of Venice and commented on how prescient the phrase was: 'Who chooseth me must give and hazard all he hath.' At the end of this chapter I hope you agree. When we expose ourselves, our society, and our environment, to lead then we do indeed hazard all we have. Thankfully that lesson has now been learned.
In the 1900s, lead arsenate was used as a pesticide against leaf-eating insects, although not permitted on crops destined for human or animal consumption. It was regarded as safe when dusted on tobacco crops, but the result was that smokers has more lead in their bodies than non-smokers. That misuse of lead has now ceased and at least smokers need no longer worry about their exposure to these two toxic elements.
More lead today is mined, recycled, and used than in any previous time in history. Production in 2003 was around 6.5 million tonnes of which 60% was recycled lead. The popularity of the motor car and the production of lead went hand in hand throughout most of the 1900s. Lead production doubled and doubled again as it was used in many ways: lead undercoats, lead in tyres, lead batteries, and lead in the petrol. The last use has since almost ended but not the love affair between car-makers and lead producers. Car batteries still account for more than three-quarters of all lead consumed in the USA. In lead batteries the anode is spongy lead, the cathode a paste of lead oxide on a lead alloy metal grid, and all of this can be recycled.
What cannot be recycled was the leaded glass used for the cathode ray tubes of television sets and PCs. These contained a lot of lead, maybe up to a kilogram or more. However, though it can't be reclaimed, it poses no threat, not even when it is disposed into a landfill site because the lead is bonded to the glass and does not dissolve when it comes in contact with groundwater.
Mined lead is still refined to remove the silver it contains (as much as 1.2 kg/tonne). This is done by adding zinc to the molten metal and allowing it to cool slowly until the zinc settles out as a separate layer on top of the lead carrying the silver with it and this is separated off to reclaim the silver. The molten lead is then heated under vacuum to drive off any remaining zinc, giving a product that is 99.99% pure.
Other uses for lead are in sheeting, cables, solders, lead crystal glassware, ammunition, bearings, and in sports equipment, for weight-lifting and to balance golf clubs. It is used as a stabilizer for PVC although this is to be banned in the EU from 2015 onwards. Lead is very poor at transmitting sound and vibrations, so that it is added to plastic sheeting and tiling designed to block out noise. Lead is still used in architecture as roof cladding and for stained glass windows. It provides protection that will last for centuries, even in industrial and coastal regions, nor does it cause discoloration of surrounding stone or brickwork. In urban or industrial environments the protective surface layer slowly changes over the centuries from lead oxide to lead carbonate, and finally to lead sulphate. In all cases the lead compound that is formed is insoluble and, unlike rust, does not flake from the surface, and it forms a protective coating.