Effective self-purification of polynary metal electroplating wastewaters through formation of layered double hydroxides.
Heavy metal ions (Ni(2+), Zn(2+), and Cr(3+)) can be effectively removed from real polynary metal ions-bearing electroplating wastewaters by a carbonation process, with ∼99% of metal ions removed in most cases. The synchronous formation of layered double hydroxide (LDH) precipitates containing these metal ions was responsible for the self-purification of wastewaters. The constituents of formed polynary metals-LDHs mainly depended on the Ni(2+):Zn(2+):Cr(3+) molar ratio in wastewaters. LDH was formed at pH of 6.0-8.0 when the Ni(2+)/Zn(2+) molar ratio ≥ 1 where molar fraction of trivalent metal in the wastewaters was 0.2-0.4, otherwise ZnO, hydrozincite, or amorphous precipitate was observed. In the case of LDH formation, the residual concentration of Ni(2+), Zn(2+), and Cr(3+) in the treated wastewaters was very low, about 2-3, ∼2, and ∼1 mg/L, respectively, at 20-80 °C and pH of 6.0-8.0, indicating the effective incorporation of heavy metal ions into the LDH matrix. Furthermore, the obtained LDH materials were used to adsorb azoic dye GR, with the maximum adsorption amount of 129-134 mg/g. We also found that the obtained LDHs catalyzed more than 65% toluene to decompose at 350 °C under ambient pressure. Thus the current research has not only shown effective recovery of heavy metal ions from the electroplating wastewaters in an environmentally friendly process but also demonstrated the potential utilization of recovered materials.
School of Environmental and Chemical Engineering, Shanghai University, No. 333, Nanchen Road, Shanghai 200444, PR China.
Ji Zhi
JZ
Zhou
Yue Ying
YY
Wu
Chong
C
Liu
Ajay
A
Orpe
Qiang
Q
Liu
Zhi Ping
ZP
Xu
Guang Ren
GR
Qian
Shi Zhang
SZ
Qiao
D002245:Carbon Dioxide / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D004595:Electroplating; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry*; D007220:Industrial Waste / Q000032:analysis; D008669:Metallurgy; D019216:Metals, Heavy / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods; D014961:X-Ray Diffraction
D002412:Cations; D006878:Hydroxides; D007220:Industrial Waste; D019216:Metals, Heavy; D014874:Water Pollutants, Chemical; D002245:Carbon Dioxide