Lecture Eight

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Lecture Eight
Human exposure to toxic metals
1- Distribution of trace metals in the environment

• The atmosphere over land contains significant
  amounts of silicon,
• aluminum, and iron from soil dust.
• -Air over the oceans contains high levels of
  sodium.
• -Groundwater contain metals from the soil.
• -water draining from mines may contain high
  concentration of
• metals.

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2- Trace metals in the air
Trace metal can be in the form of gases or
particles. The size distribution depends on how
the particles were formed

• - Particles in the nuclei mode are not stable due
  to high rates
• Of diffusion for small particle size.
• Particles at high concentration (airborne) will
  collide with each
• other to form larger particles. They will grow
  rapidly to reach stable
• size. This is known as accumulation mode.
• -Some metals will be emitted from the combustion
  zone as particles, these
• Particles are in the coarse particle mode.

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3- Trace metals in the water
Surface waters and ground water are used for
drinking water Supplies. Trace metals may be
dissolved in water or un-dissolved In the form
of suspended particles. Groundwater at many
locations Contains a high concentration of
iron. Human activities can contribute metals to
drinking water
- Runoff from agriculture lands containing
fertilizers may add metals To drinking
water. -Metals from industries may reach the
water through effluent streams. -most people
living in urban areas receive their drinking
water through a distribution system from a
water treatment plant, some pipes made of Lead
are used in the distribution and can add amounts
of lead to the Drinking water.
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4- Trace metals in Food
-airborne particles containing metals can deposit
onto food grown Outdoors, such as fruits,
vegetables. -metals-containing dust can be added
to the food during processing. -storage
containers may contain metals.
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Case study
Batteries and the Environment
Cellular hones, laptop computers etc, require
Energy to operate, and this energy is
provided By batteries.
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There are two basic categories of batteries

• Non-rechargeable zinc-carbon and alkaline
  (primary)
• Rechargeable nickel-cadmium (secondary)

The concept of the battery is a portable energy
source that can be Manufactured in the range of
sizes.
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• Primary Consumer Batteries
• In general, primary consumer batteries are
  dominated by cylindrical and button cell
  batteries (both dry cell). The most common
  primary dry cell batteries used by Canadian
  consumers include
• 1- Cylindrical
• Zinc carbon (ZnC) - Zinc carbon batteries are
  cheaper than alkaline batteries but have a
  shorter life span and are used in low drain
  applications. Zinc carbon batteries are commonly
  used for flashlights, toys, clocks and radios
• Alkaline (ZnMnO2)- Alkaline batteries are often
  called "general purpose" batteries and although
  they are more expensive than zinc carbon
  batteries they last longer and are considered
  leak- proof. Alkaline batteries are commonly used
  in toys, radios, flashlights, clocks, etc.
• Lithium Primary - Lithium primary batteries
  provide a constant voltage until they are fully
  discharged they are commonly used for cameras,
  watches and games.

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• 2- Button Cell
• Zinc air (ZnO2)- Zinc air batteries are longer
  lasting than other button cell batteries and they
  provide a medium power drain they are used
  primarily in hearing aids.
• Silver Oxide (ZnAgO2) - Silver oxide button cell
  batteries provide a medium power drain they are
  commonly used for watches, toys and calculators.

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• Secondary Consumer Batteries
• 1- Dry Cells
• The most common secondary consumer batteries used
  by Canadian consumers include
• Nickel Cadmium (NiCd) - Nickel cadmium batteries
  comprise the largest segment of the secondary
  battery market and are good for equipment
  requiring high power but frequent charging. NiCd
  batteries are not good in applications requiring
  long storage times. They are commonly used for
  rechargeable appliances such as portable power
  tools, hand held vacuums, and cordless phones
  that need high power and frequent charging.
• Nickel Metal Hydride (NiMH) - Nickel metal
  hydride batteries are longer lasting than nickel
  cadmium batteries but are more expensive they
  are commonly used for cellular phones, video
  camera, and in some applications as a
  rechargeable replacement to alkaline batteries.
• Lithium Ion (Li-ion) - Lithium ion batteries are
  lighter in weight and have a greater energy
  storage capacity than NiCd or NiMH batteries but
  are more expensive. These are commonly used for
  cellular phones, laptop computers and video
  cameras.

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2- Wet Cells Small sealed lead acid batteries
(SSLA) are also referred to as Gel cell
batteries. These batteries (gel cells and sealed
lead-acid batteries) are commonly used to power
industrial equipment, emergency lighting, and
alarm systems.
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Wet and Dry Cells Wet and dry cells are
classified by the type of electrolyte the
battery uses. The electrolyte of a cell may be
a liquid or a paste. If the electrolyte is a
paste, the cell is referred to as a dry cell. If
the electrolyte is a solution, the cell is called
a wet cell.
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Example How much were mercury discharges
reduced for a simple size AA alkaline
battery By the design change to no added
mercury? A typical size AA alkaline battery
has a mass of 22.6 g. approximately 1 was
added mercury. With no added mercury, the amount
of naturally occurring mercury is 0.001.
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Battery basics
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Lead Acid Battery cells
Lead Acid Battery cells consist of a Lead (Pb)
electrode and a Lead oxide (PbO2) electrode
immersed in a solution of water and sulphuric
acid (H2SO4). When the battery is connected to a
load, the Lead combines with the sulphuric acid
to create Lead sulfate (PbSO4), and the Lead
oxide combines with hydrogen and sulphuric acid
to create Lead sulfate and water (H2O). As the
battery discharges, the Lead sulfate builds up
on the electrodes, and the water builds up in the
sulphuric acid solution. When the battery is
charged, the process reverses, with the Lead
sulfate combining with water to build up Lead
and Lead oxide on the electrodes. Common
examples of Lead acid batteries are car
batteries, alarm system backup batteries, and
camcorder batteries.
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Zinc-Carbon Batteries or dry cell
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The components of the zinc-carbon battery are
housed within a solid zinc can, which also serves
as the battery's anode (Figure 1). The cathode
mix is usually a moist substance of manganese
dioxide powder, special carbon black, an
electrolyte, and solution blended together. A
carbon electrode rod runs down the middle, and
the positive top cover and negative bottom cover
are both metal. Zinc-carbon batteries usually
provide 1.4 to 1.7 volts of D.C. electric power
that gradually declines to .9 volts during use.
The cells arent affected by the many impurities
their ingredients contain, and remain inexpensive
whether used on heavy or light electrical loads.
Despite their low cost, the cells have excellent
shelf life, and have very low leakage when unused
for long periods of time. - carbon-zinc cell
used in flash lights and small appliances.
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Theoretical capacity of cell
The capacity of a cell is expressed as the total
quantity Of current flow over time from an
electrochemical reaction (ampere-hours, Ah).
The theoretical specific capacity
The capacity per unit mass of material, Ah/g,
(active materials participating in the reaction)
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The capacity of batteries can also be expressed
on an energy (watt-hour) Energy (Wh) voltage
(V) X capacity (Ah) The energy density Energy
density (Wh/g) voltage (v) X specific capacity
(Ah/g) Energy density is the amount of energy
stored in a given system per unit mass
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Example Determine the theoretical energy
density of a carbon-zinc cell in Wh/g, where The
theoretical voltage 1.99 V Theoretical specific
capacity 1.13 Ah/g. The actual energy density
of a carbon-zinc cell has been observed to
be About 30 of the theoretical value, Calculate
the actual energy density?
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Battery Life Versus Temperature 
One of the factors affecting battery life is
ambient temperature.
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Voltage measures the potential energy of an
electric fields to cause an Electric current.
Capacity is The amount of electricity that can
safely flow through a wire without the wire
overheating.
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• The main environmental concerns of batteries are
• the harmful materials they contain, such as
  Mercury (Hg), Cadmium (Cd) and Lead (Pb).
  Batteries containing these materials need to be
  carefully disposed of to avoid the harmful
  effects on human health and environment.

How we can make the batteries more
environmentally friendly?

• - Manufacturers of lead-acid car batteries are
  required to accept
• and recycle spent batteries.
• Elimination of mercury from alkaline batteries
  (mercury was added to retard
• corrosion of the zinc anode). now,
  anticorrosive techniques are available.
• - Photovoltaic PV batteries

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Example A device has a load of 10 O and uses
one 1.5 V size C alkaline battery. The device
becomes inoperable at 95 mA. Determine the number
of Service hours, assuming the device is used
continuously at room temperature.
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Example Assume that 90 of depleted household
batteries are thrown away as municipal solid
waste. Determine the total mass of cadmium
disposed of each year?
annuals sales in millions
Average Weight in grams