Ni removal from aqueous solutions by chemical reduction: Impact of pH and pe in the presence of citrate.
The chemical precipitation of Ni ions from industrial wastewater at alkaline pH values creates waste chemical sludge (e.g., Ni(OH)2). We herein focused on Ni removal via chemical reduction using dithionite, by converting Ni(II) to its elemental or other valuable forms. Without the presence of a chelator (e.g., citrate), the nickel reduction efficiency increased with increasing dithionite:Ni molar ratio, reaching ∼99% at ratios above 3:1. The effect of pH on Ni reduction was in agreement with the standard redox potentials (pe0) of dithionite, which became more negative with an increase in pH leading to greater Ni reduction efficiencies. With the formation of Ni-citrate chelates, however, the Ni reduction deteriorated. Elevated pH and temperature improved nickel reduction, due to the greater reducing power of dithionite. The optimal pH value for Ni(II) reduction was found to be ∼8. Injecting Cu seed particles enhanced the rate and amount of Ni reduced. NiS and Ni3S2were identified in the crystal of the resulting solids by X-ray crystallography, and the presence of elemental Ni was explained by X-ray photoelectron spectroscopy. The chemical reduction of actual printed circuit board wastewater with the dithionite:Ni(II) molar ratio dose of 12:1 retrieved ∼99% nickel after 30-min reaction at 40°C.
Department of Water Resources and Environmental Engineering, Tamkang University, No. 151 Yingzhuan Road, Tamsui District, New Taipei City, 25137, Taiwan. Electronic address: chiwang@mail.tku.edu.tw.
Chi-Wang
CW
Li
Department of Water Resources and Environmental Engineering, Tamkang University, No. 151 Yingzhuan Road, Tamsui District, New Taipei City, 25137, Taiwan; Department of Marine Leisure and Tourism, Taipei College of Maritime Technology, No. 150, Sec. 3, Binhai Road, Tamsui District, New Taipei City, 251, Taiwan.
Jui-Hsuan
JH
Yu
Department of Water Resources and Environmental Engineering, Tamkang University, No. 151 Yingzhuan Road, Tamsui District, New Taipei City, 25137, Taiwan.
Yang-Min
YM
Liang
Department of Water Resources and Environmental Engineering, Tamkang University, No. 151 Yingzhuan Road, Tamsui District, New Taipei City, 25137, Taiwan.
Yi-Hsuan
YH
Chou
Department of Environmental Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea.
Hyung-June
HJ
Park
Department of Environmental Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea. Electronic address: chookh@knu.ac.kr.
Kwang-Ho
KH
Choo
Institute of Environmental Engineering and Management, National Taipei University of Technology, No. 1, Sec. 3, Chung-Hsiao E. Road, Taipei, 106, Taiwan.
Shiao-Shing
SS
Chen
Chemical reduction; Citric acid; Complex; Dithionite; Nickel