Assurance of
safe drinking water is essential. Ignoring lead
contaminated drinking water can eventually cause
irreversible health effects and even death. It
has been postulated that the decline of the
Roman Empire may have been causally related to
the presence of excess lead in the water supply
secondary to leakage from piping. One will never
know. However, modern science has helped to
establish guidelines for acceptable tolerated
levels of lead in the water supply, and in the
United States these levels are monitored by the
Environmental Protection Agency. Lead is a
cumulative toxin remaining in the body and
concentrating over time. Long term exposure to
lead can lead to damage to the gastrointestinal,
hematologic and nervous systems and as noted may
cause death. Lead contamination in drinking
water is usually due to plumbing corrosion in
service lines, lead solder and brass fixtures.
There are over 40 million miles of water
pipeline infrastructure in the North American
aquifier system (United States and Canada).
Within this extensive water delivery system more
than 34 billion gallons of water daily are
purified using industrial scale water
purification systems. Over 3 billion of glasses
of water are consumed daily in the United
States. Within this setting there are more than
170,000 public water authorities. Lead pipes
used by older municipal systems are well known
to leach lead over time. However, and not
recognized by many, even unplasticized poly
(vinyl chloride) now used for the transportation
and distribution of potable water leaches lead.
In the making of PVC piping lead compounds are
used as stabilizers and the pipes are produced
by extrusion at a temperature of 180 C. The
finished pipes contain a lead content of about
1% by weight. This lead may leach out when the
pipes are in contact with water. The rate of
leaching of UPVC pipe is based on the
temperature and the nature of extractants. A
report from Virginia Tech illustrated that they
may be more susceptible to leaching of lead and
copper into drinking water than other types of
piping, especially when the PVC systems include
brass fixtures and pipe fittings. Brass is
composed of copper, zinc and lead.
A particular problem is that water purification
plants are using chloramine rather than chloride
to disinfect water. At the same time many new
homes are constructed using plastic pipe rather
than copper in order to cut construction costs.
Ammonia formed in chloramine treated water leads
to a series of events that corrode brass faucet
components and connectors which are commonly
used in PVC plumbing systems. Corrosion of brass
releases copper, zinc and lead into water pipes.
There is a spectrum of treatment methods
employed for removal of heavy metals from water.
Commercially available techniques include
chemical precipitation, ultrafiltration,
membrane separation, solvent extraction,
adsorption and ion exchange, reverse osmosis,
electrodialysis and alternative biological
treatments. One way to minimize the risk of lead
being dissolved from lead pipes and lead solder
in pipe fittings is to make water slightly
alkaline. Treatment methods such as chemical
precipitation and ion exchange do not yield
sufficient removal of lead and are expensive due
to the high cost of chemicals. The two “point of
use” technologies which are successful at
removing lead from water are reverse osmosis and
activated alumina.
Metal oxides such as activated alumina may be an
ideal sorbent for the removal of heavy metals.
Whether in bulk media or as nanoparticles
alumina oxide is cost effective and with a
demonstrated safety record.
Adsorption results show pH dependency with a
Freundlich isotherm fit, which is determined as
the percentage of lead removed versus mass of
alumina.
Activated alumina is able to sorb lead from
aqueous solutions by concentrating lead at the
particle surface. Sorption of lead by activated
alumina is effected by factors such as pH,
alumina surface area (particle size), and
presence of background matrices. Particle size
and pH plays significant roles in lead sorption.
Activated alumina is a porous granular form of
aluminum oxide possessing a large surface area.
It is able to sorb lead from aqueous solutions
by concentrating lead at the particle surface.
Sorption processes can be used effectively when
the lead concentration is extremely low.
Furthermore activated alumina can be efficiently
regenerated, which significantly reduces
treatment costs. Lead adsorption using activated
alumina is best explained by the Freundlich
isotherm in which q = KFCl/n
Where q is the adsorbate mass per adsorbent unit
mass at equilibrium; KF is the adsorbent
capacity meaure; C is the aqueous concentration;
and n is a measure of how adsorbate affinity
changes with adsorption density changes
Experimental data indicates that lead adsorbs
to metal oxides in a heterogenous absorbed
fashion. While lead is adsorb in a pH dependent
fashion, the amphoteric property of activated
alumina oxide makes it an excellent agent for
the adsorption of heavy metals regardless of the
pH. Activated alumina possesses both Lewis and
Bronsted acidic and basic sites. While being
amphoteric, alumina for lead removal works best
under acidic conditions, as in the pH range of
5.5 to 6.0. The surface of compositionally pure
activated alumina oxide becomes negatively
charged between pH 8 and 10. Because of its
acidic pH and low dissolved solid content such
as calcium and magnesium soft water tends to be
more corrosive than hard water.
Water characteristics promoting the corrosion of
water include low pH, low total dissolved
solids, high water temperature and high
concentrations of dissolved gases such as oxygen
or carbon dioxide.
Smaller particles have greater surface area.
Surface area as defined by particle size impacts
on sorption capacity and rate of lead removal.
For this reason it has been suggested that
nanoparticles may provide a more cost efficient
method for the sorption of lead from the water
supply than more bulky conventional media.
One method for using activated alumina for the
removal of lead is to add powdered alumina oxide
to a batch tank reactor in order to remove lead
from solution. The alumina particles with lead
ions sorbed to their surface can then be
captured by an ultra membrane filtration system.
Another method is to house (contain) the
activated alumina inside a cartridge, with a
selectively permeable membrane at the end of the
cartridge assuring that the alumina and sorbed
lead complex remain within the cartridge which
can then be easily regenerated.
DAI offers AL 2000, a large particle activate
alumina (+200 microns) specifically designed,
modified and chemically treated in order to
enhance the removal of metal ions from a water
stream. It is ideal for point of use
applications. This product is specifically
designed to remove dissolved lead and other
cations from water. It provides a cost
efficient, simple and reliable solution for
municipal, industrial and home use needs.
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