Lead is a toxic metal that can harm nervous connections (in particular with young children) and root blood and brain disorders. Long term experience to lead or its salts (in particular soluble salts or the physically powerful oxidant PbO₂) can reason nephropathy, and colic-like abdominal trouble. The anxiety about lead's responsibility in cognitive deficits in children has brought about extensive decrease in its usage (lead disclosure has been associated to schizophrenia). Most issues of adult eminent blood lead levels are workplace-related. High blood levels are connected with belated puberty in girls.

MINING AND PROCESSING :

Lead is known to naturally occur in free form in nature, but is generally obtained from the ores galena(PbS), anglesite (PbSO₄), cerussite (PbCO₃) and minum (Pb₃O₄). It is never considered to be a rare element even though it makes up only about 0.0013% of the earth's crust since it is easily mined and refined.

Lead is extracted from ores dug from under-ground mines. Lead is also found in conjunction with other metals such as silver and zinc. Lead materials are mined as a by- product of these other more valuable metals.

Extracting the lead materials from the ore is a tedious process. First the lead ore is ground into small salt-like particles. Following this, the flotation process takes place which involves mixing the powdered lead ore with water, the addition of pine oil and the introduction of air bubbles and agitation forms a froth of oil containing the lead ore, on the surface.

HOW IS LEAD OBTAINED?

The froth is skimmed and then filtered to remove the water. The powder is then sintered at over 2500?F to oxidize impurities such as sulphur and the resulting powder is further heated in a blast furnace, with carbon producing molten lead which is drawn off into lead molds.

At this stage, about 95% pure lead is obtained and is further refined to reach greater than 99% purity by melting and skimming impurities. Once the lead materials reach a sufficient level of purity it is cast into lead blocks as the finished product. Sometimes small quantities of impurities such as copper, antimony, tin & zinc are added to form lead alloys with various properties.

THE MANUFACTURING PROCESS OF LEAD:

Mining the ore :

The first step requires the lead ore to be mined from the grounds. Heavy machinery is used to drill the rocks from deep tunnels or blast it with dynamite, breaking the ore into pieces. The ore is then shoveled onto loaders and trucks and hauled to a shaft. The miners dump the ore down the shaft, and from there it is hoisted to the surface.

Concentrating the ore :

After the ore is removed from the mine, it is treated at a concentrating mill. Concentrating is generally removing the waste rock from the lead. The ore is crushed and grounded at the mill making it particles of diameters of 0.1 millimeter or less which appear to be finer than table salt, giving it granulated sugar like texture.

Flotation process :

Sulfur makes up a substantial portion of the mineral in the lead ore galena which is called lead sulfide. The flotation process helps in bringing out the sulfur-bearing portions of the ore, since it also contains the valuable metal. The finely crushed ore is diluted with water and then poured into a tank. The mixture of water and ground ore together is called slurry to which a small amount of pine oil is added. This pine oil shall attract the sulfide particles allowing the air to be bubbled through the mixture. This makes the sulfide particles to form an oily froth at the top while the gangue settles at the bottom. The X-ray analyzers play a major role in the floatation process. Using x-ray analysis, the metal content of the slurry can be checked with the floatation monitor and through this the proportion of the chemical additives to optimize the recovery of the metal can be adjusted. Hence, other chemicals like alum and lime which aggregate the metal are added to the tank to help concentrate the minerals. The salt xanthate is also added to the slurry which helps the metal particles float to the surface. As a result of this process, the lead is separated from the rock as well as from minerals such as zinc and copper.

Filtering process :

The concentrated ore is then filtered through which 90% of water is removed. This concentrate contains about 40-80% lead with greater amounts of other impurities. At this stage it is shipped to the smelter. The gangue which is waste rock is simply of no use as it is not mineral bearing and is forced out of the tank and then disposed into a pond or a natural lake from which the land gets replanted once it is filled.

Roasting the ore :

The filtered lead concentrate needs to be refined in order to remove the sulfur and other impurities. Thus, it is mixed with other lead-bearing materials along with sand and limestone. The entire mixture is spread on a moving grate. The air being heated to 2,550?F is blown through the grate. The sulfur in the concentrate combusts to sulfur dioxide gas after coke is added as a fuel. This sulfur dioxide is an important byproduct of the lead refining process and is captured at a separate acid plant and converted to sulfuric acid for several uses. Once the ore has been roasted, it is known to fuse into a brittle material called sinter which is mostly lead oxide, but can also contain oxides of zinc, iron, and silicon, some lime and sulfur. When the sinter is taken off the moving grate, it is broken into lumps which are loaded into the blast furnace.

Blasting process :

With coke as fuel, the sinter is added to the top of the blast furnace. Through the lower part of the furnace a blast of air comes out burning the coke. This burnt coke generates a temperature of about 2,200?F and produces carbon monoxide. The produced carbon monoxide reacts with lead and other metal oxides to give molten lead along with waste slag and carbon dioxide. The molten metal is then drawn off to dross kettles or molds.

Refining process :

The molten lead produced from the blast furnace is about 95-99% pure and is known as base bullion because of the purity attained. Again,it must be further refined to remove impurities since commercial lead must be about 99-99.999% pure. This base bullion is kept at a

drossing kettle at a temperature just above its melting point which is about 626?F in order to be refined. At this temperature, any copper left in the bullion rises to the top of the kettle and forms a scum or dross which can be skimmed off. The presence of gold and silver can be removed from the bullion by a small quantity of zinc added to it since both gold and silver dissolve more easily in zinc than in lead. When the bullion is slightly cooled, zinc dross rises to the top carrying the other metals along.

Casting process :

At last when the lead has been refined adequately, it is cooled and then cast into blocks as a finished product and may weigh in tons. Alloys of lead may also be produced at the smelter plant. Metals added to the molten lead in precise proportions produce a lead material for specific industrial uses. Examples of lead being employed in car batteries, making pipes, sheets, cable sheathing, and ammunition is blended with antimony as this increases the strength of the metal.

TOP LEAD PRODUCING COUNTRIES :

 

 

 

ANNUAL LEAD USAGE :

 

LEAD PRODUCTION IN THE WORLD :

The largest producer of lead materials in the world is Australia followed by the USA, China and Canada. Lead is extracted from ores dug from under-ground mines. Even though more than 60 minerals contain lead, only galena, cerussite and anglesite are commercially viable. The U.S. is the world's largest producer and consumer of refined lead metal. Major mine producers other than the U.S. include Australia, Canada, China, Peru, and Kazakhstan. In the U.S., six lead mines in Missouri, along with lead-producing mines in Alaska and Idaho, accounted for domestic mine production. Significant amounts of lead are recovered as a by-product or co-product from zinc mines, and silver-copper deposits. The top seven lead producing countries are as follows:

 

Rank	Country/Region	Lead production (thousands of tonnes)
1	China	2,400
2	Australia	450
3	United States	313
4	Peru	300
5	Russia	250
6	Mexico	230
7	India	150