Effect of acid type on biomineralization of soil using crude soybean urease solution

The one-phase-low-pH method is a simple, efficient, and user-friendly biogrouting technique that can effectively improve the biomineralization of enzyme-induced carbonate precipitation (EICP) using free urease enzyme. One of the most significant advantages of this method is its capacity to effectively delay calcium carbonate (CaCO 3 ) precipitation by reducing the pH of the solution through the addition of acid. This prevents bioclogging during the biogrouting process and improves the biomineralization effect. However, the biomineralization of the one-phase-low-pH based EICP method may be influenced by the specific acid used. To investigate the impact of acid type on the one-phase-low-pH EICP method using crude soybean urease solution (CSUS), four types of acids, including hydrochloric acid (HCl), nitric acid (HNO 3 ), acetic acid (CH 3 COOH), and lactic acid (C 3 H 6 O 3 ), were used to adjust the pH of CSUS. A series of macroscopic and microscopic experiments were conducted to evaluate the effect of acid type on the one-phase-low-pH EICP method. The results indicate that the acid has an inhibition on the urease activity (UA) of CSUS. Among the acids tested, HNO 3 exhibits the most pronounced inhibitory effect on the UA of CSUS, followed by HCl, and the least pronounced inhibitory effect for CH 3 COOH and C 3 H 6 O 3 under the same pH conditions. Meanwhile, CH 3 COOH and C 3 H 6 O 3 could provide a longer delay duration of CaCO 3 precipitation than HNO 3 and HCl. Therefore, the one-phase-low-pH EICP method based on CH 3 COOH and C 3 H 6 O 3 can significantly improve the effective biocementation depth compared to that based on HNO 3 and HCl. Nevertheless, the different types of acids appear to have no obvious effect on the polymorph and crystalline of the precipitated CaCO 3 crystals.