Heavy metal contamination is one of the most prominent environmental issues worldwide, and heavy metal tailings are one of the main sources of such contamination. Biomineralization based on enzyme-induced carbonate precipitation (EICP), as a promising technique for the remediation of heavy metals, has many advantages such as high efficiency, greenness and environmental friendliness. In this study, soybean urease solution self-extracted from soybean powder was used to treat lead-zinc tailings. Heavy metal tolerance test, contaminated solution remediation test and lead-zinc tailings biomineralization test, as well as ICP, XRD and SEM-EDS analyses, were conducted to study the prevention of heavy metal contamination of lead-zinc tailings through soybean urease-based biomineralization. The test results showed that both Pb²⁺ and Zn²⁺ reduced the activity of soybean urease, and the effect of Pb²⁺ on urease activity was time-dependent, whereas the effect of Zn²⁺ was immediate. Soybean urease could effectively remove more than 99% of Pb²⁺ and Zn²⁺ in solution by forming protein complexes and inducing calcium carbonate precipitation. Meanwhile, the calcium carbonate precipitated by the soybean urease could encapsulate the tailings, reducing the amount of heavy metals leached by 70%.

Enzyme induced carbonate precipitation (EICP) technique for soil improvement using self-extracted soybean urease solution to induce calcium carbonate precipitation has various advantages such as economic, ecological and environmental considerations. However, the high turbidity of the self-extracted soybean urease solution easily leads to bioclogging during the biogrouting process, resulting in poor biocementation. In this study, an alum-containing solvent was used for the extraction of soybean urease solution to reduce its turbidity. Incorporating soybean urease extraction, solution tests, and sand column solidification with macro- and micro-scale tests were carried out to investigate the effects of alum content on turbidity and biocementation of the extracted soybean urease solution. The results indicate that the addition of an appropriate amount of alum (e.g., 3.0 g/L for 100 g/L soybean powder content) can effectively reduce the turbidity of the self-extracted soybean urease solution without affecting its urease activity. However, excessive amount of alum may lead to a reduction or even loss of urease activity. The use of a low-turbidity soybean urease solution is beneficial in improving the uniformity of its biocementation, without an apparent effect on the morphology and crystallinity of the precipitated calcium carbonate crystals.