| 摘要 |
<p>The procedure consists of phosphatising the sludge, preferably with phosphoric acid at a rate of under 15 per cent, depending on the heavy metal content, and then causing it to foam by the addition of chemical reagents or mechanical agitation to reduce its density to less than 90 per cent of its original density. The foam is dried by existing composting techniques, e.g. in a tunnel with a bed of sand on an impermeable membrane, and the dried sludge is calcined at a temperature of 550 - 750 deg C. After calcination it is slaked with water and left to set and harden.</p> |
