## 1 Introduction  
With the rapid development of industry, the problem of heavy metal contamination caused by electroplating and non-ferrous metal smelting enterprises, mining activities, solid waste management, and the combustion of fuels is becoming increasingly serious [1; 2; 3]. Toxic heavy metals, including zinc, nickel, chromium, lead, and cadmium, in water or soil can not only induce plant poisoning and soil degradation but also pose considerable health threats to human beings. For instance, contamination by Zn\({}^{2+}\) may result in symptoms such as vomiting, shock, and convulsions [4]. Ni\({}^{2+}\) pollution has been associated with lung and nasal cancers [5; 6]. Cr(VI) tends to damage the liver and kidneys, potentially leading to carcinogenesis [7]. Furthermore, lead pollution seriously threatens human health by causing substantial damage to vital organs. Hence, it is imperative to ensure the effective remediation of heavy metal contaminated water before disposal or emission. At present, there are several conventional methods for heavy metal remediation, such as the chemical precipitation method and the ion exchange method [8]. In the chemical precipitation method, a flocculant is used to precipitate heavy metal ions. In the ion exchange method, heavy metal ions can be absorbed by ion exchange resin. Despite their widespread usage, traditional methods suffer from some limitations, including high costs, low treatment efficiency, and the propensity for secondary pollution, thus significantly constraining their practical application. Consequently, other scholars have embarked on exploring novel and environmentally friendly techniques characterized by low costs, the absence of secondary pollution, and the ease of operation. The bioremediation of heavy metals has been widely explored, among which MICP ( microbial-induced carbonate precipitation) has attracted great attention. MICP uses microorganisms isolated from contaminated water or soil, such as _Pseudomonas steinii_, _Baillus cereus_, _Bacillus pasterennsis_, and _Geobacillus tumens_, to induce heavy metal carbonate precipitation and thus remove heavy metals [9; 10; 11; 12; 13]. However, studies have also shown that the activity of microorganisms is easily influenced by heavy metals, with bacterial proteins losing their remedial capacity due to denaturation under high concentrations of heavy metal ions. Hence, separating and cultivating bacteria from contaminated water requires significant cost and time investments. Moreover, identifying a specific bacterium suitable for remediating multiple heavy metals poses a considerable challenge [14; 15]. Recently, it was found that enzyme-induced carbonate precipitation (EICP), a more convenient and cheaper method, could be used to remediate heavy metal contamination as an alternative method. [PERSON] et al. [16] reported that the immobilization of Cd\({}^{2+}\) using the EICP method can be achieved via three predominant mechanisms: the chemisorption/co-precipitation of calcite; the generation of pure CdCO\({}_{3}\); and the generation of CdCO\({}_{3}\) as a nuclei site for CaCO\({}_{3}\). [PERSON] et al. [17] explored the potential of immobilizing Pb and Cu by the chitosan-assisted EICP method. They found that added chitosan would protect enzyme activity and improve Cu\({}^{2+}\) immobilization efficiency. At present, the enzymes used are highly purified urease, with crude urease extracted from plants hardly being used to remediate heavy metals. Compared with highly purified urease, crude urease extracts are much cheaper and abundant in organic molecules [18; 19; 20]. Although previous studies have demonstrated specific individual heavy metal immobilization efficiency by EICP using highly purified commercial urease, the potential for heavy metal immobilization by using crude urease extracts, particularly for multiple heavy metals, remains unexplored. Research on the process and mechanism of multiple heavy metal immobilization using the crude urease-based EICP method is still limited.