Lead
Lead is a chemical element with the symbol Pb and atomic number 82. It is a heavy metal and is one of the common densest metal in the periodic table.[citation needed] Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull gray color when exposed to air. It also has the highest atomic number of any stable element and three of its isotopes are endpoints of major nuclear decay chains of heavier elements (e.g. Uranium).
Lead is a neurotoxin that accumulates in soft tissues and bones; it damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders ranging from behavioral problems to brain damage, and also affects general health, cardiovascular, and renal systems. It is commonly associated with heavy metal poisoning and can also cause insanity.
Uses
Lead is an option as projectiles for ranged weapons, including the sling and the slingshot.[1] Lead is also commonly used as Solder for pipes and Electronic circuits due to its low melting point and electrical conductivity.
Other uses of lead for more advanced purposes/technologies also include radiation shielding, ceramic and glass production, cheap batteries, creation of specific chemical compounds and more.
Production
Lead production can be divided into Primary processes and Secondary processes. Primary from mined ores, and secondary from scrap and debris.
Lead can be obtained with scrap lead. Given adequate techniques, lead obtained via secondary processes is indistinguishable from lead obtained via primary processes. Scrap lead from the building trade is usually fairly clean and is re-melted without the need for smelting, though refining is sometimes needed. Secondary lead production is usually cheaper depending on the process, in terms of energy requirements, than is primary production, often by 50% or more but may need refinement.
Primary
Most lead ores contain a low percentage of lead which must be concentrated for extraction. During initial processing, ores undergo crushing, dense-medium separation, grinding, froth flotation, drying. The resulting concentrate, which has a lead content is then turned into (impure) lead metal.[citation needed]
There are two main ways of doing this: a two-stage process involving roasting followed by Blast furnace extraction, carried out in separate vessels; or a direct process in which the extraction of the concentrate occurs in a single vessel.
Secondary
Smelting, which is an essential part of the primary production but can be often skipped during secondary production. It is only performed when metallic lead has undergone significant oxidation. The process is similar to that of primary production in either a blast furnace or a Rotary furnace used to melt and cast lead.
Common sources of lead for secondary production are lead–acid batteries, lead pipe, sheet, and cable sheathing.
Refinement
Lead refining involves several steps to remove impurities from crude lead ore or lead-containing materials. This is a list of some of the possible refinement techniques:
Smelting: Crude lead ore (galena) is heated in a furnace with coal or natural gas to produce a lead-bismuth alloy.
Flotation: The lead-bismuth alloy is then separated from impurities using flotation, a process that uses air bubbles to separate particles based on their density.
Roasting: The lead ore is roasted to convert lead sulfide into lead oxide, which is then heated to produce lead monoxide.
Leaching: The lead monoxide is then leached with acid to dissolve the lead, leaving impurities behind.
These are some of the more primitive methods of refinement. It is also important to note that some processes may create toxic lead fumes that may lead to lead poisoning
Some of the more advance refinement technique includes:
Crystallization: The purified lead is then crystallized into a solid, high-purity lead product.
Anode electrolysis: This method uses an anode made of lead to remove impurities from the lead solution.
Cathode electrolysis: This method uses a cathode made of lead to deposit pure lead onto the surface.
Vacuum distillation: This method uses a vacuum to distill impurities from the lead solution, resulting in high-purity lead.
Some of the impurities removed in the process may include:
Arsenic: removed through roasting and leaching
Bismuth: removed through flotation and electrolysis
Copper: removed through electrolysis
Silver: removed through electrolysis
Gold: removed through electrolysis
Application
Elemental lead
Lead metal has several useful mechanical properties, including high density, low melting-point, ductility, and relative inertness compared to other common metals.[citation needed] Although many metals are superior to lead in some of these aspects but are generally less common and more difficult to extract from parent ores. Due to lead's toxic properties, it is recommended to phased out the use of lead when possible; although, this may only be possible in advance stages of civilization, due to the abundance of lead and its cheap cost of production, as well as the rarity of other viable replacement metals for lead.
Batteries
Lead can also be used to create lead–acid batteries. The lead in batteries undergoes no direct contact with humans, so there are fewer toxicity concerns. Although caution is required in the production of lead battery or recycling plants due to the exposure to lead fumes. The reactions in the battery between lead, lead dioxide, and sulfuric acid provide a reliable source of voltage compared to other cheap alternatives. [citation needed] These batteries have lower energy density and charge-discharge efficiency than lithium-ion batteries, but are significantly cheaper.
Radioactive shielding
Lead's high density and ability to absorb radiation make it a cheap and effective material for shielding against X-rays, gamma rays, and other forms of ionizing radiation.
Soldering
Lead can be used in soldering due to its low melting-point and cheap cost of production. But due to the toxicity of lead, it is recommended to use safer alternatives. Examples of lead-free solders that can be use are Tin, Copper, Silver, Bismuth, Indium, Zinc, Antimony, and alloys including these metals.
Ceramics and glass
Lead oxide can also be used in the production of ceramic glazes and glass, imparting a bright, shiny appearance. It may also be used as non-food-grade pigments in paints. Although it is important to note that due to its toxicity, it is recommended to avoid its use when possible.
Health hazards and biological effects
Lead has no confirmed biological role, and there is no confirmed safe level of lead exposure. Pure lead is tasteless and odorless, it is also one of the main metals that causes heavy metal poisoning (along side with Mercury, Arsenic, Cadmium, Thallium, and Copper).
Lead salts are very efficiently absorbed by the body. A small amount of lead (~1%) is stored in bones; the rest is excreted in urine and feces within a few weeks of exposure (Note - Only about a third of lead is excreted by a child). Continual exposure may result in the accumulation of lead in the body.[citation needed]
Toxicity
Lead is a highly poisonous metal when inhaled or consumed, affecting almost every organ and system in the human body. Most ingested lead is absorbed into the bloodstream. The primary cause of its toxicity is interfering with the proper functioning of essential enzymes. It does so by binding to the sulfhydryl groups found on many enzymes, or mimicking and displacing other metals which are essential for normal function. The essential metals that lead interacts with include calcium, iron, and zinc. High levels of calcium and iron in the body provides some protection from lead poisoning however low levels cause increased susceptibility.[citation needed]
Symptoms and effects
Lead will cause severe damage to the brain and kidneys, and can cause death. By mimicking calcium, lead can cross the blood–brain barrier. It also interferes with neurotransmission routes, and decreases brain growth which can lead to insanity.
Here is a list of symptoms ranging from mild to severe, it also includes symptoms in children:[citation needed]
Mild Symptoms:
- Abdominal pain or cramps
- Constipation
- Headaches or dizziness
- Fatigue or weakness
- Irritability or mood changes
- Loss of appetite
- Nausea or vomiting
Moderate Symptoms:
- Numbness or tingling in the hands and feet
- Muscle weakness or tremors
- Confusion or difficulty concentrating
- Memory problems or learning disabilities
- Hearing loss or ringing in the ears
- Vision problems or blurred vision
Severe Symptoms:
- Seizures or convulsions
- Coma or loss of consciousness
- Organ failure (kidney, liver, or heart)
- Respiratory problems or difficulty breathing
- Cardiovascular problems or high blood pressure
- Reproductive problems or infertility
Symptoms in Children:
- Delayed development or learning disabilities
- Behavioral problems or hyperactivity
- Speech or language delays
- Vision problems or eye damage
- Hearing loss or ear damage
- Developmental delays or growth problems
Sources of exposure
Here is a list of common causes of lead poisoning:
- Lead-based paint and contaminated dust in older buildings.
- Contaminated air, water, and soil.
- Lead pipes and fixtures in homes.
- Occupational exposure, such as in mining, construction, and manufacturing.
- Used firearm ammunition and gunsmoke.
- Contaminated food and water.
- Lead fumes (note - Lead vapors are tasteless, odorless, and colorless).
Dependencies
See also
References
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