Formation of high crystalline LDH sludge for removing Cu and Zn from wastewater by controlled double-jet precipitation
- 97 Downloads
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.
KeywordsHeavy metal wastewater Layered double hydroxide Controlled double-jet precipitation Formation mechanism
Financial support by National Key R&D Program of China (2017YFC0210401), National Natural Science Foundation of China (51504299), and the Key Project of Guizhou Provincial Education Department (KY288).
- Behrens M, Brennecke D, Girgsdies F, Kißner S, Trunschke A, Nasrudin N, Zakaria S, Idris NF, Hamid SBA, Kniep B, Fischer R, Busser W, Muhler M, Schlögl R (2011) Understanding the complexity of a catalyst synthesis: co-precipitation of mixed Cu, Zn, Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments. Appl Catal A Gen 392:93–102CrossRefGoogle Scholar
- Brown ID (2002) The chemical bond in inorganic chemistry. The bond valence model. Oxford University Press, Oxford, p 374Google Scholar
- Cavani F, Trifirò F, Vaccari A (1991) Hydrotalcite-type anionic clays: preparation, properties and applications. Catal Today 2:172–301Google Scholar
- Sideris PJ, Nielsen UG, Gan Z, Grey CP (2008) Mg/Al ordering in layered double hydroxides revealed by multinuclear NMR spectroscopy. Science 321:113–117Google Scholar
- Ye L, Chai L, Li Q, Yan X, Wang Q, Liu H (2016) Chemical precipitation granular sludge (CPGS) formation for copper removal from wastewater. RSC Adv 6:11445–114411Google Scholar