Adsorption of Hexavalent Chromium from Aqueous Solution by Rice Husk-Based Adsorbent

Chromium exists in two stable oxidation states apart from its metal form that are the
trivalent state and hexavalent state. Hexavalent chromium has been identified by
academicians worldwide to be hazardous towards the human health in general as a
result of ingestion, direct or indirect. Existing methods of treating Cr(VI)-
contaminated water proves to be sophisticated and may be out of reach for
developing countries until the near future. Hence the employment of a simple yet
effective method of treatment is vital to counter this kind of contamination in places
with limited capital and capabilities where it can be mobilized easily without the
need for sophisticated machineries and equipment. Adsorption promises an effective
way of removing hexavalent chromium from aqueous solutions based on researches
done throughout the globe while still maintaining feasibility. Efforts are being made
to come up with new materials to be used as adsorbent, preferably from low-cost
materials produced as a waste product from other industries to further cut down the
cost of treatment by studying the adsorptive capability of said materials. This project
studied the adsorptive capabilities of rice husk-based adsorbent for use in
decontaminating purposes. Preliminary experiment showed an adsorption percentage
as high as 99.9% of 20 mg/L chromium solution using acid-treated rice husk-based
adsorbent. Tests for other parameters such as pH value, contact time and adsorbent
dosage resulted in positive results and pH 2 is found to be the optimum pH value for
adsorption tests, two hours of shaking was the equilibrium time and adsorbent dosage
of 8 g/L was the equilibrium dosage for testing purposes. In addition to that,
adsorption of chromium(VI) by acid-treated rice husk-based adsorbent fitted well
into pseudo first-order and pseudo second-order kinetic models, and it demonstrates
a high adsorptive capacity of 47.62 mg/g in isotherm studies. The acid-treated RHA
as well as exhausted acid-treated RHA were characterized by means of FTIR and
SEM