School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, China; Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering (XAUAT), Xi'an, 710055, China.
Environ Pollut. 2023 Feb 15;319:120947. doi: 10.1016/j.envpol.2022.120947. Epub 2022 Dec 26.
Enzyme-induced carbonate precipitation (EICP) is considered as an environmentally friendly method for immobilizing heavy metals (HMs). The fundamental of the EICP method is to catalyze urea hydrolysis using the urease, discharging CO and NH. CO helps to form carbonates that immobilize HMs afterwards. However, HMs can depress urease activity and reduce the degree of urea hydrolysis. Herein, the potential of applying the chitosan-assisted EICP method to Pb and Cu immobilization was explored. The chitosan addition elevated the degree of urea hydrolysis when subjected to the effect of Cu toxicity where the protective effect, flocculation and adsorption, and the formation of precipitation, play parts in improving the Cu immobilization efficiency. The use of chitosan addition, however, also causes the side effect (copper-ammonia complex formation). Two calcium source additions, CaCl and Ca(CHCOO), intervened in the test tube experiments not only to prevent pH from raising to values where Cu complexes with NH but also to separate the urease enzyme and Cu from each other with the repulsion of charges. The FTIR spectra indicate that the chitosan addition adsorbs Cu through its surface hydroxyl and carboxyl groups, while the SEM images distinguish who the mineral are nucleating with. The findings shed light on the potential of applying the chitosan-assisted EICP method to remedy lead- and copper-rich water bodies.
酶促碳酸沉淀（EICP）被认为是一种固定重金属（HM）的环保方法。EICP 方法的基础是使用脲酶催化尿素水解，释放 CO 和 NH。CO 有助于形成碳酸盐，随后固定 HM。然而，HM 会抑制脲酶活性并降低尿素水解的程度。本文探索了壳聚糖辅助 EICP 方法在 Pb 和 Cu 固定中的应用潜力。壳聚糖的添加提高了 Cu 毒性作用下尿素水解的程度，其中保护作用、絮凝和吸附以及沉淀的形成在提高 Cu 固定效率方面发挥了作用。然而，壳聚糖的添加也会产生副作用（铜氨络合物的形成）。两种钙源添加（CaCl 和 Ca（CHCOO））在试管实验中进行干预，不仅可以防止 pH 值升高到 Cu 与 NH 络合的程度，还可以通过电荷排斥将脲酶和 Cu 彼此分离。FTIR 光谱表明，壳聚糖通过其表面的羟基和羧基基团吸附 Cu，而 SEM 图像则可以区分出矿物的成核情况。这些发现为壳聚糖辅助 EICP 方法在修复富含铅和铜的水体中的应用提供了思路。
