Ironing out pollution

30/07/1994
Down To Earth

SCIENTISTS at the University of California at Berkeley in the US have developed a method that cuts to 1/10th the cost of cleaning up nitrogen oxides produced when fossil fuels are burned (Nature, Vol 369, No 6476). The new technology is also environmentally less harmful than the techniques currently used by power plants and fossil fuel-intensive industries.

The burning of coal pollutes the atmosphere with the oxides of sulphur and nitrogen, which create acid rain and urban smog. Sulphur dioxide is removed by using wet limestone to absorb it, and nitric oxide, which is insoluble in water, uses catalysts to be converted to less harmful ammonia. The catalysts, however, are poisoned by arsenic and alkalis present in the fly ash, making their disposal difficult.

But Berkeley's Eric K Pham and Shih-Ger Chang have developed a water-soluble iron compound that enhances the solubility of nitric oxide in water. This then allows the removal of both nitric oxide and sulphur dioxide with wet limestone. The iron catalyst can be regenerated, and the nitric oxide is liberated as ammonia.

Pham and Chang have simulated this effluent treatment on a small scale. A gas containing 300-600 parts per million of nitric oxide was bubbled over a solution of the iron-compound. About 75 per cent of the nitric oxide was absorbed, compared to only 26 per cent of this gas absorbed using traditional methods.

Scientists reckon that removing one tonne of nitrogen oxides using the new technology would cost about $390, whereas traditional technologies costs as much as $2,000-4,000.

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