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Environ Sci Pollut Res Int. 2019 May 11. doi: 10.1007/s11356-019-05161-7. [Epub ahead of print]

Formation of high crystalline LDH sludge for removing Cu and Zn from wastewater by controlled double-jet precipitation.

Wu L1,2, Peng B1,3,4, Li Q5,6,7, Wang Q1,3,4, Yan X1,3, Lin Q1, Ji C1.

Author information

1
School of Metallurgy and Environment, Central South University, Changsha, 410083, China.
2
Institute of Material and Chemical Engineering, Tongren University, Tongren, 554300, China.
3
Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution, Changsha, 410083, China.
4
Water Pollution Control Technology Key Lab of Hunan Province, Changsha, 410004, China.
5
School of Metallurgy and Environment, Central South University, Changsha, 410083, China. qingzhuli@csu.edu.cn.
6
Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution, Changsha, 410083, China. qingzhuli@csu.edu.cn.
7
Water Pollution Control Technology Key Lab of Hunan Province, Changsha, 410004, China. qingzhuli@csu.edu.cn.

Abstract

In order to improve the heavy metal wastewater treatment by avoiding formation of amorphous sludge phase, we develop a faster formation of high crystalline layered double hydroxide (LDH) sludge to remove Cu and Zn from wastewater by controlled double-jet precipitation (CDJP) without hydrothermal or heat aging post-treatment. A series of experimental procedures are conducted to determine the optimal parameters. Results show that the optimal adding rate, pH value, and stirring rate is 0.5 mL min-1, 9.0, and 500 rpm, respectively. The CuZnAl-LDH phase sludge is formed in a well-crystallized hexagonal platelet, which assembled into a flower-like architecture. Comparative studies show that the formation of amorphous LDH sludge in conventional precipitation (CP) could be divided roughly into two stages-from the mixed copper hydroxide, zinc hydroxide, and scarbroite to the mixed low crystallinity CuAl-LDH and ZnAl-LDH. However, in CDJP method, the high crystalline LDH sludge evolved from a new four-step evolution process that is the formation of an amorphous (quasi-)multinary metastable ternary CuZnAl-LDH phase, followed by the indiffusion of cations and substitution of anions to fabricate crystalline LDH, the integrated LDH hexagonal platelets assembled into a flower-like architecture by the screw dislocation growth mechanism, the coarsening growth of each ternary LDH platelet, respectively. Thereinto, the formation of (quasi-)multinary metastable LDH phase instead of metal hydroxide in initial stage would be an obvious advantage of the CDJP method compared to CP method due to the former skipping the sequential precipitation.

KEYWORDS:

Controlled double-jet precipitation; Formation mechanism; Heavy metal wastewater; Layered double hydroxide

PMID:
31079305
DOI:
10.1007/s11356-019-05161-7

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