Urease-producing bacteria (UPB) have great potential for the bioremediation of heavy-metal pollution through biomineralization and adsorption. In this study, a strain of UPB, C7-12, was isolated from heavy-metal-contaminated soil in a lead–zinc mining area and identified as Serratia marcescens. The heavy-metal removal ability, influencing factors, and precipitation mode of this UPB strain in solution were investigated. The cadmium (Cd) removal rate in a Cd (1 mg/L) solution from C7-12 reached 85%, and pH was the main influencing factor. With urea mediation, S. marcescens C7-12 biomineralizes the Cd²⁺ in solution to form CdCO₃ and removes it through extracellular precipitation and surface adsorption. Furthermore, the removal rates of Cd²⁺, Pb²⁺, Zn²⁺ and Cu²⁺ in solution by S. marcescens C7-12 were 33–65%, 28–32%, 22–49%, and 38–44%, respectively. The precipitation mode involves coprecipitation of multiple heavy metals to form a mineral. These heavy metals are adsorbed on the surface of bacteria through the participation of carboxyl, amino, and phosphate functional groups and extracellular polymeric substances. Therefore, S. marcescens C7-12 has strong biomineralization and adsorption capacity for heavy-metal ions in solution, which can provide potential resources for the bioremediation of heavy-metal-contaminated soil and water.

Soils in alpine mining areas suffer from severe heavy metal contamination and infertility, yet little is known about the effects of different materials on soil improvement in such regions. In this study, a field experiment was conducted in farmlands contaminated by the Lanping lead–zinc mine in Yunnan, China, to compare the effects of four materials (biochar, organic fertilizer, lime, and sepiolite) on soil properties, heavy metal (lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) fractions and their availability, and the growth of Phaseolus coccineus L. Results showed that biochar and organic fertilizer significantly enhanced soil nutrient content and enzyme activities. Lime, biochar, and sepiolite effectively reduced heavy metal bioavailability by promoting their transition to residual fractions. Notably, biochar outperformed other materials by substantially increasing grain yield (by 82%), improving nutritional quality (sugars, protein, and starch contents raised by 20–88%), and reducing heavy metal accumulation in grains (by 36–50%). A comprehensive evaluation based on subordinate function values confirmed biochar as the most effective amendment. Structural equation modeling further revealed that biochar promoted plant growth and grain quality primarily by enhancing soil available nutrients and immobilizing heavy metals. These findings demonstrate the strong potential of biochar for remediating heavy metal-contaminated farmlands in alpine lead–zinc mining regions.