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Microbially induced CaCO 3 precipitation (MICP) is a natural process which has recently been applied as a technique for soil solidification and hydraulic conductivity reduction. In the present study, laboratory-based MICP tests were carried out in four columns containing sand with different particle sizes together with cultures of Sporosarcina pasteurii. A calcium solution was supplied continuously to the columns at a speed of 0.97 ml/min to mimic underground seepage. Hydraulic conductivities in the columns were monitored by hydraulic tests before and during MICP. Results showed that the reduction in conductivity values could be as high as 97% after 24 h of MICP. Columns clogged with calcite precipitates were examined by environmental scanning electron microscopy and energy dispersive X-ray spectroscopy. Calcite precipitation was shown to be the reason for hydraulic conductivity reduction. The calcium precipitation rates and amounts were quantified and verified.

Synthesis of ultrafine Al2 O 3 is considered. An X-ray phase analysis indicates that ultrafine γ-Al 2 O 3 , (θ + α)-Al 2 O 3 , and α-Al 2 O 3 are synthesized by explosion of water-gel explosives with a zero oxygen balance, prepared by mixing aluminum nitrate, RDX, and carbamide. All granules of ultrafine Al 2 O 3 are spherical and homogeneous, and the granule size varies from 10 to 30 nm. The average crystal sizes of ultrafine Al 2 O 3 are calculated by the Scherrer equation. The temperatures of explosion of water-gel explosives are found by a simplified approach. A comparison indicates that the higher the temperature of explosion, the greater the average nanocrystal size.