Abstract
Cr (VI) is a well-known highly toxic metal. This project focuses on the removal of Cr
(VI) from contaminated water using activated carbon entrapped in calcium alginate beads.
Activated carbon used for this work was prepared from an organic waste material called walnut
shell by carbonization using phosphoric acid as an activating agent. 0.5g of activated carbon was
added to 10mL of 4% sodium alginate solution.The mixture was promptly dropped into 3.5%
aqueous solution of calcium chloride (CaCl2) using a pump.It was then continuously stirred until
homogenous mixture was obtained.Finally the calcium alginate beads formed were hardened and
rinsed. Batch experiments were carried out in the laboratory to evaluate the efficacy of activated
carbon entrapped in calcium alginate beads for the removal of Cr (VI) from contaminated water.
Different masses of entrapped calcium alginate beads (0.5g, 1.0g, & 1.5g) were mixed with
contaminated water containing Cr (VI). It was observed that w
1.1 BACKGROUND
Hexavalent chromium Cr (VI) is a potential carcinogen, teratogen, and mutagen and is on
the top priority list of toxic pollutants defined by USEPA (USEPA, 1998). Contamination of
water with Cr (VI) is a worldwide problem and the remediation of contaminated site has become
environmental challenge.Chromium is one of the key contaminants in the wastewaters of
industrial dyes and pigments, film and photography, galvanometry and electric, metal cleaning,
plating and electroplating, leather and mining (Anwar et al., 1961). While hexavalent and
trivalent species of chromium are prevalent in industrial waste solutions, the hexavalent form has
been considered more hazardous to public health due to its mutagenic and carcinogenic
properties.
Chromium occurs in the environment primarily in two valence states, trivalent chromium
Cr (III) and hexavalent chromium Cr (VI). Exposure may occur from natural or industrial
sources of chromium. Chromium (III) is much less toxic than chromium (VI). The respiratory
tract is also the major target organ for chromium (III) toxicity, similar to chromium (VI).
Chromium (III) is an essential element in humans. The body can detoxify some amount of
Cr(VI) to Cr (III). The respiratory tract is the major target organ for chromium (VI) toxicity, for
acute (short-term) and chronic (long-term) inhalation exposures. Shortness of breath, coughing,
and wheezing were reported from a case of acute exposure to chromium (VI), while perforations
and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and other
respiratory effects have been noted from chronic exposure (Danielsson et al., 1982). Human
studies have clearly established that inhaled chromium (VI) is a human carcinogen, resulting in
an increased risk of lung cancer. Animal studies have shown chromium (VI) to cause lung
tumors via inhalation exposure (Danielsson et al., 1982).
1.2 ACUTE EFFECTS OF CHROMIUM (VI)
Chromium (VI) is much more toxic than chromium (III), for both acute and chronic exposures.
The respiratory tract is the major target organ for chromium (VI) following inhalation exposure
in humans (Bloomfield and Blum, 1928). Shortness of breath, coughing, and wheezing were
reported in cases where an individual inhaled very high concentrations of chromium trioxide.
Other effects noted from acute inhalation exposure to very high concentrations of chromium (VI)
include gastrointestinal and neurological effects, while dermal exposure causes skin burns in
humans. Ingestion of high amounts of chromium (VI) causes gastrointestinal effects in humans
and animals, including abdominal pain, vomiting, and hemorrhage. Acute animal tests have
shown chromium (VI) to have extreme toxicity from inhalation and oral exposure (Davies,
1978).
1.3 CHRONIC EFFECTS OF CHROMIUM (VI)
Chronic inhalation exposure to chromium (VI) in humans results in effects on the respiratory
tract, with perforations and ulcerations of the septum, bronchitis, decreased pulmonary function,
pneumonia, asthma, and nasal itching and soreness reported (Davies, 1978). Chronic human
exposure to high levels of chromium (VI) by inhalation or oral exposure may produce effects on
the liver, kidney, gastrointestinal and immune systems, and possibly the blood (Frentzel-Beyme,
1983). Rat studies have shown that, following inhalation exposure, the lung and kidney have the
highest tissue levels of chromium. Dermal exposure to chromium (VI) may cause contact
dermatitis, sensitivity, and ulceration of the skin.
1.4STATEMENT OF PROBLEM
The presence of hexavalent chromium in water resulting from rapid industrialization and high
anthropogenic activities has posted treat to man. It is therefore essential to find a cheaper way of
removing Cr (VI) from waste water.
1.5 AIM AND OBJECTIVES OF THE PROJECT WORK
1) To prepare activated carbon from walnut shell by carbonization using phosphoric acid as an
activating agent.
2)To entrap activated carbon into calcium alginate beads.
3) To remove Cr (VI) from contaminated water using activated carbon entrapped in calcium
alginate beads.