Sawdust scrounger

To remove toxic dye

Published: Saturday 30 April 2005

indian scientists have developed a simple and cheap technique to remove crystal violet (cv), a toxic dye used in lab experiments, from waste water. The researchers from the Indian Institute of Technology in Kharagpur used hardwood sawdust to trap (adsorb) the cv molecules. "We found 1 gramme (g) of sawdust removes 341 milligramme (mg) of cv at 25 c," says Jayanta K Basu, the lead author of the study.

"Rise in temperature speeds up the adsorption process, removing more cv," says co-author Sunando DasGupta, adding, "This may be due to enlargement of pores of sawdust particles." The study appeared in C hemosphere (Vol 58, No 8).

cv causes skin and eye irritation, and if ingested, may even cause cancer. To devise an indigenous method to dispose cv, the scientists took hardwood sawdust from a local sawmill. After sieving and washing with water, the material bathed in phosphoric acid was charred in a furnace at 500 c. It was finally dried at 120 c for 8 hours. It was then used with 1 litre of dye solution at different concentrations of cv .

The study found that for a fixed temperature, the adsorption capacity of sawdust increased with a decrease in the particle size. At 25 c, 1 g of sawdust having a particle size of 0.23 millimetre (mm) adsorbed 195 mg cv, which increased to 341 mg for particles measuring 0.04 mm. "Smaller particles provide more surface area per unit mass, resulting in more adsorption," claims DasGupta. An increase in the amount (from 0.5 g to 1 g) of sawdust added to dye solution also accelerated the adsorption process considerably.

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