Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu, 611756, China.
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
J Environ Manage. 2023 Dec 15;348:119365. doi: 10.1016/j.jenvman.2023.119365. Epub 2023 Oct 18.
Supercritical water gasification (SCWG) is an advanced and highly efficient method for treating oily sludge. However, it is crucial to consider the transformation characteristics of heavy metals (HMs) during the SCWG process to prevent potential secondary pollution. This work studied the transformation and distribution characteristics of Cu, Cr and Zn after SCWG of oily sludge in a batch reactor at temperatures ranging from 550 to 700 °C. Additionally, thermodynamic equilibrium analysis was conducted to assess the distribution of HMs based on the minimization of Gibbs free energy. Experimental results indicated that higher temperatures led to the conversion of HMs into more stable forms, effectively immobilizing them within solid products. Furthermore, the addition of NaCO enhanced this process and contributed to a reduction in HMs pollution in the effluent. Thermodynamic equilibrium results were consistent with our experimental data, indicating that the molar fraction of stable HMs forms followed the order: Cr > Cu > Zn. Besides, it is worth noting that NaCO had a limited impact on the distribution of Cu and Cr. However, it played a significant role in inhibiting the formation of silicate Zn at lower temperatures, promoting the decomposition of ZnO*AlO into unstable Zn. This may explain the higher presence of unstable Zn when NaCO was introduced. In summary, this study offers valuable insights into the transformation characteristics of heavy metals and strategies for pollution control during SCWG of oily sludge.
超临界水气化（SCWG）是一种处理含油污泥的先进且高效的方法。然而，在 SCWG 过程中考虑重金属（HM）的转化特性至关重要，以防止潜在的二次污染。本工作在间歇式反应器中研究了温度范围为 550 至 700°C 时含油污泥的 SCWG 过程中 Cu、Cr 和 Zn 的转化和分布特性。此外，还进行了热力学平衡分析，根据吉布斯自由能最小化来评估 HM 的分布。实验结果表明，较高的温度导致 HM 转化为更稳定的形式，有效地将其固定在固体产物中。此外，添加 NaCO 增强了这一过程，有助于减少废水中的 HM 污染。热力学平衡结果与我们的实验数据一致，表明稳定 HM 形态的摩尔分数顺序为：Cr>Cu>Zn。此外，值得注意的是，NaCO 对 Cu 和 Cr 的分布影响有限。然而，它在较低温度下抑制硅酸盐 Zn 的形成方面发挥了重要作用，促进了 ZnO*AlO 分解为不稳定的 Zn。这可以解释引入 NaCO 时不稳定 Zn 含量较高的原因。总之，本研究为 SCWG 处理含油污泥过程中重金属的转化特性和污染控制策略提供了有价值的见解。
