Arsenic Purification And Information

Arsenic Exposure And its Effect on Health

noreply@blogger.com (rajj) — Mon, 24 Dec 2007 03:32:00 +0000

Arsenic is known as a poison and human carcinogen. Arsenic trioxide (As2O3), a water-soluble powder that produces a colorless, tasteless, and odorless solution, was a favorite homicidal agent during the Middle Ages and its use continues today, although not to the same extent. There is much debate on Napoleon's death, whether he was poisoned by arsenic-tainted wine during his exile on the island of St. Helena.

Arsenic is the 20'th most abundant element in the earth's crust, and is present in the natural environment. The current problem of arsenic is devastating in history as the cause of the largest mass poisoning ever. In Bangladesh and India, millions of people are affected by high levels of arsenic in drinking water. Millions of wells have been installed since the 1970''s with the aim of providing clean water, free of microbial pathogens. However, the rock containing naturally high levels of arsenic releases of arsenic in water, arsenic in water higher than concentration several hundred micrograms per liter (µg/L) or even milligrams per liter (mg/L) in some wells. Ingestion of such high levels of arsenic in drinking water over several years can lead to a variety of adverse health effects including cancers of the skin, bladder, and lung as well as possible neurological and cardiovascular effects.

The magnitude of the arsenic problem and the seriousness of the adverse health outcomes resulting from exposure to arsenic make arsenic the single most important environmental contaminant. As a consequence, regulations on arsenic have become more stringent. Arsenic is also abundant in seafood at concentrations as high as several hundred micrograms per gram (µg/g). Arsenobetaine is the major arsenic species in most seafood (crustaceans). It is excreted into urine without metabolism, and is essentially non-toxic.

Arsenic-induced hyperkeratosis of the hands

More than 20 arsenic compounds (species) are present in the natural environment and biological systems. The following Table lists some of the common arsenic species. Although the trivalent arsenic species, such as inorganic arsenite (AsIII), monomethylarsonous acid (MMAIII), and dimethylarsinous acid (DMAIII) are highly toxic (8-13), arsenobetaine (AsB), the predominant arsenic species present in most crustaceans, is essentially non-toxic.

History Of Arsenic: Toxic Element

noreply@blogger.com (rajj) — Tue, 18 Dec 2007 01:25:00 +0000

Arsenic has been found in Nature since Antiquity. Aristotle makes reference to sandarach (arsenic trisulfide) in the 4th century B.C. In the 1st century A.D., Pliny stated that sandarach is found in gold and silver mines and arsenic (arsenic trioxide) is composed of the same matter as sandarach. By the 11th century three species of arsenic were known, the white, yellow and red - since then recognized as arsenic trioxide, arsenic trisulfide (orpiment) and arsenic disulfide (realgar), respectively. (reference)

The Picture below you can see is Eye Disease caused by Arsenic

Albertus Magnus is reputed in the 13th century to be the discoverer of metallic arsenic. However, his documentation is considered vague. It was not until 1649 that J. Schroder clearly reported the preparation of metallic arsenic by reducing arsenic trioxide with charcoal. Thirty-four years later, N. Lemery also observed that metallic arsenic was produced by heating arsenic trioxide with soap and potash. By the 18th century the properties of metallic arsenic were sufficiently known to classify it as semimetal.

Safe Water Technology for Arsenic Removal

noreply@blogger.com (rajj) — Fri, 14 Dec 2007 03:38:00 +0000

Arsenic removal efficiency is excellent (typically > 95%), for both arsenate
and arsenate, but arsenic capacity varies significantly, and is controlled primarily by pH and influent arsenic concentration and speciation. Arsenate removal capacity is best in the narrow range from pH 5.5 to 6.0, where the alumina surfaces are protonated, but acid anions are not yet concentrated enough to compete with arsenic for sorption sites (Trussell et al., 1980; Rosenblum and Clifford, 1984; Clifford, 1999). Typically, activated alumina has a point of zero charge (PZC), below which the surface is positively charged, and above which the surface bears a negative charge, at pH 8.2. Arsenic removal capacity drops sharply as the PZC is approached, and above pH 8.5, is reduced to only 2-5% of
capacity at optimal pH (Clifford, 1999). For neutral and basic waters, therefore,pH adjustment may be necessary for effective arsenic removal.

Fine (28-48 mesh) particles of activated alumina are typically used for
arsenic removal, with an Empty Bed Contact Time of five to eight minutes
(Rubel and Woosely, 1979). When operated in the optimal pH range, activated
alumina beds have much longer run times than ion exchange resins. The number
of bed volumes that can be treated at optimal pH before arsenate breaks through
is mainly controlled by the influent arsenic concentration.

Frank and Clifford reported an arsenate capacity (at pH 6) of about 1.6 g/L of
activated alumina, consistent with an earlier reported capacity of 4 mg/g,
assuming a bulk density of 0.5 kg/L (Gupta and Chen, 1978). Fox reported a
somewhat lower capacity of 1 mg/g, but this is likely due to the elevated pH (7.4-
8.0) of the influent water (Fox, 1989).
The sorption sites on the activated alumina surface are also attractive to a
number of anions other than arsenate: Clifford reports the selectivity sequence of
activated alumina in the pH range of 5.5 to 8.5 as (Clifford, 1999):

OH-> H2AsO4-> Si(OH)3O-> HSeO3-> F-> SO42-> CrO42->> HCO3->Cl-> NO3-> Br->I

Trussell and others reported a similar selectivity sequence, but included
phosphate as the second most preferred anion, after hydroxyl, and placed fluoride
above arsenate in the sequence (Trussell et al., 1980). Because of activated
alumina’s strong selectivity for arsenate, competing anions pose less of a
problem than with ion exchange resins. Sulfate, and to a lesser extent, chloride,have been shown to reduce capacity, but the competition effect is not as dramatic as with ion exchange resins (Rosenblum and Clifford, 1984). Phosphate and
fluoride are also sorbed onto activated alumina, producing improvements in
drinking water quality, but at the same time reducing arsenic removal potential.
Activated alumina can be regenerated by flushing with a solution of 4%
sodium hydroxide, which displaces arsenic from the alumina surface, followed
by flushing with acid, to re-establish a positive charge on the grain surfaces.

Technologies related to Arsenic Removal

noreply@blogger.com (rajj) — Thu, 13 Dec 2007 03:54:00 +0000

Sorry for my bad english, i am not a native english speaker.
In some areas, water contaminated by arsenic will be abundant, and arsenic-free sources scarce or polluted with other compounds. In these areas, it may be more efficient to remove arsenic from contaminated water, at least in the short term Measure. Many technologies have been developed for the removal of arsenic.
Most of the experience has been documented with large municipal treatment plants, but some of these same technologies can be applied to the community or households.
All technologies arsenic removal rely on a small number of basic chemicals processes, which are summarized below:

• Oxidation/reduction: reactions that reduce (add electrons to) or oxidize
(remove electrons from) chemicals, altering their chemical form. These
reactions do not remove arsenic from solution, but are often used to
optimize other processes.

• Precipitation: Causing dissolved arsenic to form a low-solubility solid
mineral, such as calcium arsenate. This solid can then be removed
through sedimentation and filtration. When coagulants are added and
form flocs, other dissolved compounds such as arsenic can become
insoluble and form solids, this is known as coprecipitation. The solids
formed may remain suspended, and require removal through solid/liquid
separation processes, typically coagulation and filtration.

• Adsorption and ion exchange: various solid materials, including iron and
aluminum hydroxide flocs, have a strong affinity for dissolved arsenic.
Arsenic is strongly attracted to sorption sites on the surfaces of these
solids, and is effectively removed from solution. Ion exchange can be
considered as a special form of adsorption, though it is often considered
separately. Ion exchange involves the reversible displacement of an ion
adsorbed onto a solid surface by a dissolved ion. Other forms of
adsorption involve stronger bonds, and are less easily reversed.

• Solid/liquid separation: precipitation, co-precipitation, adsorption, and
ion exchange all transfer the contaminant from the dissolved to a solid
phase. In some cases the solid is large and fixed (e.g. grains of ion
exchange resin), and no solid/liquid separation is required. If the solids
are formed in situ (through precipitation or coagulation) they must be separated from the water. Gravity settling (also called sedimentation) can
accomplish some of this, but filtration is more effective. Most
commonly, sand filters are used for this purpose.

• Physical exclusion: some synthetic membranes are permeable to certain
dissolved compounds but exclude others. These membranes can act as a
molecular filter to remove dissolved arsenic, along with many other
dissolved and particulate compounds.

• Biological removal processes: bacteria can play an important role in
catalyzing many of the above processes. Relatively little is known about
the potential for biological removal of arsenic from water.

• Boiling does not remove arsenic from water.

Risk of Arsenic

noreply@blogger.com (rajj) — Mon, 10 Dec 2007 08:02:00 +0000

If you live in an area with a high level of arsenic in the water or soil, substituting cleaner sources of water through water treatment devices that are certified for the removal of arsenic, and limiting contact with soil (for example, through use of a dense groundcover or thick lawn) would reduce family exposure to arsenic.

Exposure to arsenic?

You normally take in small amounts of arsenic in the air you breathe, the water you drink, and the food you eat. Children may also be exposed to arsenic by eating dirt. The concentration of arsenic in soil varies widely, generally ranging from about 1 to 40 parts of arsenic to a million parts of soil (ppm) with an average level of 5 ppm.

The concentration of arsenic in natural surface and groundwater is generally about 1 part in a billion parts of water (1 ppb) but may exceed 1,000 ppb in mining areas or where arsenic levels in soil are high. Groundwater is far more likely to contain high levels of arsenic than surface water. Surveys of U.S. drinking water indicate that about 80% of water supplies have less than 2 ppb of arsenic, but 2% of supplies exceed 20 ppb of arsenic. Some areas of the United States contain unusually high natural levels of arsenic in rock, and this can lead to unusually high levels of arsenic in soil or water. If you live in an area like this, you could take in elevated amounts of arsenic in drinking water. Some hazardous waste sites contain large quantities of arsenic. If the material is not properly disposed of, it can get into surrounding water.

How can arsenic enter and leave human body?

If you swallow arsenic in water, soil, or food, most of the arsenic may quickly enter into your body. If you breathe air that contains arsenic dusts, many of the dust particles settle onto the lining of the lungs.

If you are exposed to arsenic, your liver changes some of this to a less harmful organic form. Most of the arsenic will be gone within several days, although some will remain in your body for several months or even longer.

Facts about Arsenic

noreply@blogger.com (rajj) — Mon, 10 Dec 2007 03:43:00 +0000

What is Arsenic ?

Arsenic is an element that is widely distributed in the earth's crust. Inorganic arsenic occurs naturally in soil and in many kinds of rock, especially in minerals and ores that contain copper or lead.

Here is the picture of periodic-tables of elements and Arsenic's place in the periodic-table.

Arsenic occurs naturally in soil and minerals and therefore it may enter the air, water, and land from wind-blown dust and may get into water from runoff and leaching. Arsenic is associated with ores mined for metals, such as copper and lead, and may enter the environment during the mining and smelting of these ores.

Arsenic cannot be destroyed in the environment. It can only change its form, or become attached or separated, from particles. Many common arsenic compounds can dissolve in water. Thus, arsenic can get into lakes, rivers, or underground water by dissolving in rain or snow or through the discharge of industrial wastes. Ultimately most arsenic ends up in the water, soil or sediment.

How can arsenic affect our health?

Inorganic arsenic has been recognized as a human poison since ancient times, and large oral doses (above 60,000 ppb in food or water) can produce death. If you swallow lower levels of inorganic arsenic (ranging from about 300 to 30,000 ppb in food or water), you may experience irritation of your stomach and intestines, with symptoms such as stomach ache, nausea, vomiting, and diarrhea. Other effects you might experience from swallowing inorganic arsenic include decreased production of red and white blood cells which may cause fatigue, abnormal heart rhythm, blood-vessel damage resulting in bruising, and impaired nerve function causing a "pins and needles" sensation in your hands and feet.

Arsenic has also been reported to increase the risk of cancer in the liver, bladder, kidneys, prostate, and lungs. The Department of Health and Human Services (DHHS) has determined that inorganic arsenic is a known carcinogen.

Perhaps the single most characteristic effect of long-term oral exposure to inorganic arsenic is a pattern of skin changes. These include a darkening of the skin and the appearance of small "corns" or "warts" on the palms, soles, and torso.

Affect of Arsenic on Children
Children who are exposed to arsenic may have many of the same effects as adults, including irritation of the stomach and intestines, blood vessel damage, skin changes, and reduced nerve function, making them look older than their age. Thus, all health effects observed in adults are of potential concern in children. We do not know if absorption of arsenic from the gut in children differs from adults.