Lead and copper ions from wastewater induced by metallurgical processes are accumulated in soils, threatening plant and human health. The bioinspired calcium carbonate precipitation is proven effective in improving the cementation between soil particles. However, studies on capsulizing heavy metal ions using the bioinspired calcium carbonate precipitation are remarkably limited. The present study conducted a series of test tube experiments to investigate the effects of bacterial culture and calcium source addition on the remediation efficiency against lead and copper ions. The calcium carbonate precipitation was reproduced using the Visual MINTEQ software package to reveal the mechanism affecting the remediation efficiency. The degradation in the remediation efficiency against lead ions relies mainly upon the degree of urea hydrolysis. However, higher degrees of urea hydrolysis cause remediation efficiency against copper ions to reduce to zero. Such high degree of urea hydrolysis turns pH surrounding conditions into highly alkaline environments. Therefore, pursuing higher degrees of urea hydrolysis might not be the most crucial factor while remedying copper ions. The findings shed light on the importance of modifying pH surrounding conditions in capsulizing copper ions using the bioinspired calcium carbonate precipitation.
Heavy metal contamination has caused serious threats to surrounding fragile environments and human health. While the novel microbial-induced carbonate precipitation (MICP) technology in the recent years has been proven effective in improving material mechanical and durability properties, the mechanisms remedying heavy metal contamination still remain unclear. In this study, the potential of applying the MICP technology to the lead remediation under the effects of urease activity and calcium source was explored. The values of OD 600 corresponding to the ureolytic bacterial activity , electrical conductivity (EC), urease activity (UA) and pH were applied to monitor the degree of urea hydrolysis. Further, the carbonate precipitations that possess different speciations and cannot be distinguished through test tube experiments were reproduced using the Visual MINTEQ software package towards verifying the validity of the proposed simulations, and revealing the mechanisms affecting the lead remediation efficiency. The findings summarised in this work give deep insights into lead-contaminated site remediation engineering.
Rulong Ban,Bo Kang,Fusheng Zha,Qiao Wang,Weilong Song
The resource utilization of phosphogypsum (PG), a calcium-rich solid waste, still requires urgent attention. Identifying alternative calcium sources to replace traditional ones remains a critical challenge for MICP. This study proposes a novel approach to activate PG as an alternative calcium source for MICP. It systematically analyzes various activators for Ca²⁺ extraction, assesses the feasibility and environmental benefits, and investigates the underlying mechanisms of Ca²⁺ release. The results indicate that the optimal conditions for extracting Ca²⁺ from PG are a 1 mol/L sodium gluconate solution with a solid-to-liquid ratio of 1:20, reacting at 30°C for 30 min. Ammonium acetate and sodium gluconate activators can convert CaSO₄·2H₂O into more easily soluble CaSO₄·0.5H₂O and structurally stable CaSO₄, respectively. The concentrations of heavy metals in the MICP solutions with activated PG calcium sources all comply with the concentration limits. All activators facilitate the formation of calcite precipitates in the bio-mineralization process, with the MICP efficiency of sodium gluconate-extracted PG calcium sources approaching 100 %. The activation mechanisms of PG can be categorized as ion exchange (chloride salts), complexation and ion exchange (ammonium acetate), and chelation and ion exchange (sodium gluconate). This study provides new insights into the application of PG in MICP.
危险品化学品经营许可证（带存储）