Lead and zinc

By: Peter Russell and Tharsika Tharmanathan

Lead

Lead is a very soft, bluish-gray, metallic element. Since it is so soft, lead is usually alloyed with other elements. Water pipes in ancient Rome, some of which still carry water, were made of lead. The English word plumber and pluming are derived from the Latin word for lead, plumbum. The properties of lead which make it an excellent material for many applications are its density, high level of stability, and it has high degree of flexibility, which makes it easy to work.

It is rare to have lead alone in nature. Lead combines with other elements to form a variety of interesting minerals. The most common lead mineral is lead sulphide, (galena). 

Uses of Lead

The main three forms of compounds of lead are white lead, red lead and litharge. White lead was mainly used to make paints because of its opacity and it was preserved for a longer period of time. Red lead is used as a protective coating and Litharge, an oxide of lead, is utilized for making glass, ceramics and varnishes.

Lead is poisonous if exposed to large amounts. Major radioactive elements (such as uranium) break down and create lead as one of their end products. However, it is also interesting to note that lead is not only poisonous, but also offers protection. Metallic lead is used to safely store radioactive materials due to its capability to absorb radiation from the radioactive isotopes. As well, x-ray protection such as aprons and gloves are made of lead, which traps dangerous x-rays and gamma radiation. In nuclear power reactors, glass containing lead monoxide is used to protect against radioactive radiation. 

Exposure to even small amounts of lead can be harmful since lead has no use in the body. Elevated levels and long term exposure of lead is linked to blood and kidney problems, as well as neurological disorders. As a result, its use in some applications has been discontinued. At one time, the fuel industry was among the major users of lead. Before gasoline is ignited in the engine, it is compressed, but under heavy compression the gasoline detonates without having been ignited. Tetraethyl (anti-knock) lead was added to gasoline to prevent detonations and ensured that the fuel burned evenly. However, tetraethyl lead has been eliminated from gasoline products because of the tremendous amounts of lead discharged by engines into the atmosphere. 

Three thousand years ago people used lead to make paint. Pieces of lead were placed on top of a cask containing a solution of vinegar with branches of shrubs arranged over the solution and the cask was covered tight. After a while, white substance (white lead) would emerge on the surface and this was scraped off the metal and used as paint. Most old buildings dating back 100 years or more, used lead. In Britain, people would use white lead paint, on window frames and doors. After one week of exposure to the sulphur in the air (from coal fires and industry) the paint turned completely black due to the white lead altering the into galena (lead sulphide). Paint was washed regularly, and turned black again within a few days. Non-toxic titanium compounds have replaced lead used in paints. 

Lead mines in Missouri, Alaska, Colorado, Idaho and Montana produce the majority of lead recovered in the U.S. followed by Canada, which is the second largest producer of lead. Lead and zinc are formed in the same types of ore deposits.

More than seventy six percent of the lead consumed annually is used to make batteries for cars, trucks and other vehicles. Another twenty percent of the lead is used in electronics and communications (cell phone batteries, for example), ammunition, television glass, construction and protective coatings. A small amount is used to make protective aprons for patients having x-rays to shield the body from excess radiation exposure. Lead has the highest recycling rate of all industrial metals in the world because lead is easily re-melted and refined. More than 95% of the batteries used in the automotive industry are recycled. 

Uses of Lead

• Alloying
• Ammunition
• Batteries
• Bearing plates
• Cable covering
• Ceramics
• Corrosion resistant tank linings for chemical processing,
• storage and transport equipment
• Electrical filters
• Gaskets
• Glass
• Gramophone pick-ups
• Insecticides
• Lead crystal glass
• Lead solder used in electronic circuitry
• Leveling shims
• Non-spark flooring
• Paints (lead was used in paints in the past)
• Plumbing
• Radiation shield protects against X-rays, CAT scans, nuclear reactors and TV and Computer screens
• Roofing
• Sound absorber
• Sensors
• Seat belt pendulum
• Shower pans
• Spark generators
• Weights
• Toys (in the past and occasionally we receive consumer warnings about toys containing lead today, mainly inexpensive jewellery).
• Wine bottles - metal foil capsule

Lead plays a vital role in electronic industry, in space exploration and telecommunications. Without the use of lead solders and leaded glass you would not be able to safely sit in front of your computer. Lead alloy solders enable your computer to send electronic data and lead is the glue that binds our electronic world together. 

NASA's space shuttle uses lead-alloy solder of connecting transistors, relays and other electronic components because it is the most reliable way of soldering materials together. In addition, lead glazes are used to encapsulate and protect the electronic microcircuits from atmospheric corrosion.

Lead Crystal

Lead crystal glass was developed in the 17th century by combining molten quartz with lead. The final product usually contains 24 to 36 percent lead oxide. It is widely used today for serving beverages such as wine and alcohol. Lead crystal is known for its brilliance and clarity. However, there are some health risks associated with using lead crystal. When lead crystal comes in contact with acidic beverages, some lead dissolves into the liquid. As well, any container you drink from that has an exterior decorative pattern around the rim, such as a coating or glaze, may also release lead. The amount of lead dissolved into the liquid depends on the type of beverage and length of time they are in contact. Alcoholic beverages such as wine and non-alcoholic beverages such as fruit juices and soft drinks also absorb lead. However, the actual amount of lead released from crystal glasses over the course of a normal meal tends to be very low. 

Beverages stored in crystal decanters for weeks and months can accumulate very high levels of lead. Lead concentrations of up to 20 parts per million - 100 times higher than the Canadian limit have been found in wines kept for weeks or months in crystal containers. Manufactures are now coating the interior of some lead crystal containers to prevent lead from leaching in the beverage. It is also evident that washing crystal in harsh detergents such as dishwasher detergents can increase lead release into beverages. New lead crystal glasses, should be cleaned by soaking in vinegar for more than 24 hours to prevent any lead contamination. Lead foil capsules were used to cover wine bottles, this has been discontinued due to the hazardous oxide remaining on the lip and neck of the bottle. 

Lead Batteries

Lead-acid batteries represent sixty percent of batteries sold worldwide. Lead-acid batteries date back to 1860 when Raymond Gaston Plantz first invented them. Lead-acid batteries provide power for everything from forklifts to backup systems used in hospitals. All lead batteries work on the same set of reactions and use the same active materials. At the positive electrode, lead dioxide is converted to lead sulfate and at the negative electrode, sponge metallic lead is also converted to lead sulfate. The electrolyte is a dilute mixture of sulfuric acid that provides the sulfate ion for the discharge reactions. 

Lead Paint

In the 1920's, children became the primary target of company's advertising campaign. Lead paint companies used children in their marketing strategy, to promote the use of lead paint in general public places and for interior wall uses. In the late 1920's, National Lead published a book called "The Dutch Boy's Lead Party" which also promoted the use of lead paint in schoolrooms and suggested that summer was the best time to get school officials to have the school rooms repainted. Advertising lead paint using children even became more important after information about lead paint's danger to children started to accumulate. The rigorous lead pigment campaign overshadowed the medical evidence concerning the dangers of lead to children, painters and manufactures of paint in the 1930's. One advertisement showed a child in a bathtub scrubbing himself with a brush. Another promotion depicted a crawling infant touching a painted wall. The clear message proclaimed by the advertisement was that it was safe for toddlers to touch walls and woodwork covered with lead paint. Until the mid 1950's, National Lead used the Dutch Boy image as a clever way of countering negative publicity by developing a campaign focusing on children.

Zinc

Zinc (Zn) is a bluish-white shiny metal that is fragile at room temperature, but becomes malleable at 100 degrees Celsius. Zinc is one of the most common elements in the Earths crust. It is found in soil, air, and water and is present in food. Zinc was used in Rome and China more than 2000 years ago as a component of brass (see What on Earth winter 2003 issue, zinc-copper alloy). Commercial production of zinc did not start in Europe until the middle of the 18th century and in the United States until 1860. Zinc metal has never been found naturally. The great majority of zinc deposits contain the lead mineral, galena, and both the lead and zinc minerals are mined together. Other metals that are found with zinc are silver and copper. Zinc-Copper ores could be smelted into brass. Zinc also exists as a variety of salts and combines with other elements, such as chlorine, oxygen, and sulphur, to form zinc compounds.

Zinc is mined in over 50 countries with Canada being the leading producer, followed by Russia, Australia, Peru, United States and China. Deposits of zinc-bearing ores are found in most provinces of Canada, as well as in the Yukon and North West Territories. Zinc sulphide (ZnS), sphalerite, is the commonest mineral containing zinc.

Pine Point Mine

In 1898, galena was shown by natives to prospectors travelling to the Klondike gold fields. By 1930, Northern Lead Zinc Limited started work on lead - zinc sinkholes. The Great Depression halted this work. Company reports indicated over 500,000 tons of reserves. In 1951 a company called Pine Point Mines was established. A much larger company, the Consolidated Mining and Smelting company, (now called Cominco) then began construction of a large mill and 50 homes in the early 1960s. The Pine Point townsite soon had all the amenities of a modern community. In 1981, the population was 1861. About 10,000 tons-per-day of ore were produced at that time. Over $2 billion worth of zinc and lead (at today's prices) was recovered by Cominco during 25 years. Low base metal prices and high recovery costs forced Cominco to shut down operations in 1988, and the mine and townsite have been rehabilitated.

Red Dog Mine, Alaska

Pine Point was closed at the same time Cominco was developing the Red Dog Mine in Alaska. The Red Dog Mine combined lead-zinc averages 24% with a credit of around 90 grams of silver per ton. Cominco decided to focus its resources on developing the Red Dog Mine which has the largest annual production and is the most profitable zinc mine in the world.

Kidd Creek Mine (Falconbridge)

Kidd Creek Mine (Falconbridge) at Timmins, Ontario, produces ore containing zinc, copper, lead, silver and cadmium.

Uses of Zinc

Zinc is essential to a healthy life for humans and animal. It is necessary for the function of different enzymes. It is necessary for skin and bone growth. Above all, the body uses zinc to process food and nutrients. 
When zinc is alloyed with other metals, it becomes a good electrical conductor. Zinc-bromide and zinc-nickel power cells are amongst the newest types of batteries.

Minerals, which occur naturally in the Earth's crust perform vital roles in our everyday lives. But few of us ever make the connection between these objects, appliances and materials we use and which help us make our life easier. The following is a list of few materials and appliances where Zinc is used.

To protect from rusting, Zinc is applied in thin layers to iron and steel products. This process is called galvanizing. More than half of the zinc consumed is used for galvanizing. Galvanizing is done in a number of ways. Usually, the metal is dipped in molten zinc. It can also be done by electroplating or by painting on a layer of zinc compound. More than half of the zinc consumed is used for galvanizing.Zinc makes the average vehicle last longer. About 7.7 kilograms of zinc is used to protect average automobile from rust. Another 9 kilograms are used to make zinc die cast parts like door handles and locks, and each tire contains about quarter of a kilogram of zinc, which is needed to cure the rubber.

Recently zinc metal is being applied to buildings due to its long, maintenance-free life and its ability to adapt to various design styles. Zinc's subtle colour is being praised by architects who say its colour gets richer as the material adapts to specific atmospheric conditions and blends beautifully with other building materials such as concrete and wood. It is also easy to work with to form complex shapes.

In the United States, zinc is mined in several states. Alaska produces the most, followed by Tennessee, and Missouri.

Mississippi Valley Lead-Zinc Deposits

Mississippi Valley Lead-Zinc deposits are a family of ore deposits formed by sea water flowing through sedimentary rocks including limestone, dolostone, salt and shale. The brines (seawater) flows through these recently deposited sediments reacting with the limestone and changing it with addition of magnesium from the water. Calcium in calcite is replaced by magnesium forming the mineral dolomite. This reaction usually destroys fossils in the limestone and forms holes in the rocks, which are then good places where lead-zinc minerals may form. Brines flowing through other sediments such as shale may pick up lead and zinc from them. The water then flows through dolostones which are now at a depth where oil migrates through the rock. The oil migrates upwards bringing sulphur with it. The sulphur from the oil interacts with the brines containing lead and zinc sulphide in the holes in the dolostone depositing galena and sphalerite. Bacterial action assists this process. Other minerals form later such as calcite.

Mississippi valley deposits are found in mid-west United States. They are also found at Navisivik on Baffin Island. Alaska produces the most, followed by Tennessee, and Missouri.

Lead-zinc deposits are found in dolostones of southern Ontario. The only reason we haven't got mine is that holes formed in the dolostone before mineralization were not large enough to host economic deposits. These types of deposits are common worldwide.

Volcanigenic Massive Sulphide Deposits

Volcanogenic massive sulphide deposits are a major source of copper, zinc, lead, silver and gold. These deposits have been found actively forming at a temperature of 350 degrees Celsius. Hydrothermal vents on spreading ocean bottom ridges, such as those found in the eastern Pacific Ocean are actively precipitating metal sulphides. These deposits are formed by the discharge of solution into the seafloor.

Oxidized Zone Minerals

Zinc sulphide is oxidized and enriched by interaction with the atmosphere, naturally acidic rainwater and nearby rocks and minerals (see "Copper the Red Metal", What on Earth, winter issue 2003). Zinc sulphide is changed to zinc sulphate. This solution trickles down through the deposits. Oxidized minerals form, such as Hemimorphite and lower down in the deposits the sulphate reacts with limestone and other rocks containing calcium forming zinc carbonate (Smithsonite). 

Copper into Gold

A copper penny is placed in an evaporating dish and heated with a mixture of sodium hydroxide solution and zinc. It turns silver. The penny is then heated in a burner flame and it suddenly turns gold!

Procedure

1. Place about 5 grams of zinc dust in an evaporating dish.
2. And enough NaOH solution to cover the zinc and fill the dish about one-third.
3. Place the dish over a burner, or hot plate until the solution is near boiling.
4. Prepare a copper penny by cleaning it thoroughly with a light abrasive (Brillo pads work well).
5. Using crucible tongs, or tweezers, place the cleaned penny in the mixture in the dish.
6. Hold the penny in the dish for 3-4 minutes. You will be able to tell when the coating is complete.
7. Remove the penny, wash it, and blot dry with paper towels. (Do not rub.)
8. Using tweezers, hold the coated penny in the flame of a burner. The production of the gold colour is immediate.
9. After 3-5 seconds, remove the coin, wash it, and dry it.

Reactions

1. The first reaction is the plating of the copper with zinc: Zinc reacts with sodium hydroxide to form sodium zincate, Na2ZnO2. This product is then reduced by the copper penny to metallic zinc. This reaction gives the silver colour to the penny.
2. The second reaction is the formation of the brass alloy. This alloy gives the penny the gold colour. Heat causes a fusion of the zinc and copper.

Solution
The sodium hydroxide solution is 6 M: Dissolve 240 g of NaOH per liter.

This experiment was taken from Chemical Demonstration by Lee R. Summerlin and James L. Ealy, Jr., 1985, American Chemical Society, Washington, DC.