Transformation of Cr under sintering of Ca-rich solid waste with kaolin: Analysis of multi-element coupled interactions. (January 2022)

• Record Type: Journal Article
• Authors: Zhu, Zhicheng; Huang, Yaji; Zha, Jianrui; Yu, Mengzhu; Cheng, Haoqiang; Zhang, Zhenrong; Dong, Lu; Li, Zhiyuan; Fan, Conghui
• Is Part Of: Chemosphere. Volume 287:Part 3(2022)
• Publication Date: 2022-01
• Subjects: River sludge -- Heavy metals -- Cr solidification -- Kaolin -- Cr2O3/CaO co-Existence; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2021.132181
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The high toxicity of Cr–Ca compounds generated during the heat treatment of solid waste will heavily threat the environment. In this work, a kind of Ca-rich river sludge which is bound with Ca and heavy metals was combusted with kaolin under 900 °C for 3 h in a muffle to study the transformation of Cr. The effects of kaolin on Cr transformation were investigated through sequential extraction, the risk assessment of heavy metals, and constant pH leaching test, also combined with crystal phase analysis of Ca–Al–Si minerals. The experimental results showed that the formation of Ca10 (SiO4 )3 (SO4 )3 Cl2 was inhibited by the addition of 10% (mass fraction) kaolin and the released Cl promoted the evaporation of target elements in priority while 30% kaolin addition further inhibited the solidification of Cr. Furthermore, the effect of NaCl and CaCO3 on the Cr solidification by kaolin were also explored by leaching procedure or XRD analysis of calcination products of their mixtures. It should be noticed that the addition of kaolin in Cr2 O3 –CaCO3 mixture will directly react with CaCrO4 and fixed the generated Cr2 O3 into internal layered structure, preventing its re-oxidization by the free CaO. This work aims to help illustrate the Cr transformation with existence of Ca during sintering of Ca-rich solid wastes and reduce the Cr contamination in future. Highlights: Sintering of river sludge enhanced the leaching toxicity of heavy metals. Solidification of Cr was highly affected by during sintering with kaolin. Complex reactions among Ca–Si–Al–Zn–Cu compositions will affect the Cr solidification. CaCrO4 reacted with excess CaCO3 at 900 °C and generated Ca10 Cr6 O24 CO3 . Cr2 O3 can co-exist with CaO after kaolin was added in CaCO3 –Cr2 O3 sintering system.