Enzyme-induced carbonate precipitation utilizing synthetic Ca2+-zeolite for low ammonium

Abstract

In this study, a low-ammonium enzyme-induced carbonate precipitation (LA-EICP) technique is proposed that utilizes the cation exchange capability of zeolite to remove ammonium, an environmentally harmful by-product of urea hydrolysis. The LA-EICP process is a modified enzyme-induced carbonate precipitation (EICP) suitable for soil stabilization, by mixing zeolite and resulting solution of urea hydrolysis. The amounts of calcium carbonate precipitated and ammonium ions removed by the synthetic calcium-modified zeolite were analyzed through tube precipitation tests. In addition, the unconfined compressive strengths of the soil specimens were measured and compared to investigate the reinforcing effect of LA-EICP. The precipitation of calcium carbonate within the soil specimen was also confirmed by scanning electron microscope and energy dispersive spectrometry analyses. The results showed LA-EICP can precipitate the same amount of calcium carbonate as conventional EICP, while removing almost all ammonium ions. In addition, the LA-EICP-treated specimen showed a higher strength improvement than the conventional EICP-treated specimen, due to the combined effect of the calcium carbonate and the zeolite.