Effect of nano-silica on microbiologically induced calcium carbonate precipitation

Microbiologically induced calcium carbonate precipitation (MICP) is a new technique in environmental geotechnical engineering. Ultrafine particles including nanoparticles consisting of clay particles and organic matter present in the nanometer size range are ubiquitous in sand due to the erosion or chemical reactions of earth minerals. In this paper, nano-SiO2 (NS) was used to represent nanoparticles and investigate the influence of nanoparticles in soil on MICP. Both MICP in a solution environment and MICP on the surface of quartz sand were investigated. Then, a series of macroscopic and microscopic tests were conducted to investigate the effect mechanism of NS on MICP. It was found that the NS could inhibit the MICP reaction process and promote calcite formation in a solution environment. Conversely, NS could inhibit calcite formation on the quartz sand surface. Besides, the main products of these two cases are quite different: the former is vaterite, while the latter is calcite. In general, the nanoscale silica particles are detrimental to MICP.