School of Environment, Tsinghua University, Beijing 100084, China.
School of Environment, Tsinghua University, Beijing 100084, China.
Sci Total Environ. 2023 Jul 10;881:163267. doi: 10.1016/j.scitotenv.2023.163267. Epub 2023 Apr 5.
Recycling into lightweight aggregate (LWA) by sintering is a promising technology for disposal of municipal solid waste incineration fly ash (FA). In this study, FA and washed FA (WFA) were combined with bentonite and SiC (bloating agent) to make LWA. The performance was comprehensively studied by hot-stage microscopy and laboratory preparation experiments. Water washing and increased FA/WFA improved LWA bloating extent, while shorten the bloating temperature range. Water washing also increased the 1 h-water absorption rate of LWA, making it harder to meet the standard. Excessive FA /WFA usage (70 wt%) will prevent LWA from bloating. For the goal of recycling more FA, mixture with 50 wt% WFA could prepare LWA that meet standard GB/T 17431 at 1140-1160 °C. After water washing, the ratio of Pb, Cd, Zn, and Cu stabilized in LWA increased by 279 %, 410 %, 458 %, and 109 % for 30 wt% FA/WFA addition, and 364 %, 554 %, 717 %, and 697 % for 50 wt% FA/WFA addition, respectively. The change of liquid phase content and viscosity at high temperature were determined using the thermodynamic calculations and chemical compositions. The bloating mechanism was further investigated by integrating these two properties. To obtain accurate results of the bloat viscosity range (2.75-4.44 log Pa·s) for high CaO systems, the composition of the liquid phase should be taken into account. The liquid phase viscosity required for bloating start was proportional to the liquid phase content. With temperature increasing, bloating would end when viscosity drops to 2.75 log Pa·s or liquid phase content reach 95 %. These findings provided further understanding of the heavy metal stabilization during LWA production and the bloating mechanism of high CaO content systems, and could contribute to the feasibility and sustainability of recycling FA and other CaO-rich solid wastes into LWA.
通过烧结将城市固体废物焚烧飞灰（FA）回收成轻骨料（LWA）是一种很有前途的处理技术。在这项研究中，将 FA 和水洗 FA（WFA）与膨润土和 SiC（发泡剂）结合制成 LWA。通过热台显微镜和实验室制备实验综合研究了其性能。水洗和增加 FA/WFA 提高了 LWA 的发泡程度，同时缩短了发泡温度范围。水洗还增加了 LWA 的 1h 吸水率，使其更难达到标准。过量的 FA/WFA（70wt%）的使用会阻止 LWA 发泡。为了回收更多的 FA，添加 50wt%的 WFA 可以制备出在 1140-1160°C 下符合 GB/T 17431 标准的 LWA。水洗后，对于 30wt% FA/WFA 添加量，Pb、Cd、Zn 和 Cu 在 LWA 中的稳定比增加了 279%、410%、458%和 109%，对于 50wt% FA/WFA 添加量，增加了 364%、554%、717%和 697%。通过热力学计算和化学成分确定了高温下液相含量和粘度的变化。通过整合这两个性质，进一步研究了发泡机制。为了获得高 CaO 体系准确的发泡粘度范围（2.75-4.44 log Pa·s），应考虑液相的组成。发泡开始所需的液相粘度与液相含量成正比。随着温度的升高，当粘度降至 2.75 log Pa·s 或液相含量达到 95%时，发泡结束。这些发现为 LWA 生产过程中重金属的稳定以及高 CaO 含量体系的发泡机制提供了进一步的认识，并有助于提高回收 FA 和其他富 CaO 固体废料制成 LWA 的可行性和可持续性。
