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Yan X.,Central South University | Chai L.,Central South University | Chai L.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Li Q.,Central South University | Li Q.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution
Separation Science and Technology (Philadelphia) | Year: 2013

The purpose of this study is to investigate the impact of precipitant additives, i.e., calcium hydroxide (Ca(OH)2), calcium carbonate (CaCO3) and recycled sludge (RS), on the settling and compacting performance of sludge formed in the process of heavy metal wastewater treatment using bio-polymer ferric sulfate (BPFS). The results show that CaCO3 is the most suitable additive since heavy metal removal, sludge settling performance, and compacting performance is improved by 20%, 83.3%, 23.5%, respectively. In addition, scanning electron microscopy and X-ray diffraction were measured for contrasting the sludge morphology and crystallinity. The results suggest that CaCO3 acted as seeding material produces the largest flocs. Moreover, the flocculation theory combined with zeta potential measurement was used to explain the sludge formation mechanism, which is proposed as charge neutralization by BPFS, sweep flocculation by amorphous precipitate, and bridging flocculation by polyacrylamide (PAM) in sequence. The improvement of sludge properties by adding CaCO3 benefits from the enhancement of sweep flocculation. In summary, the interaction mechanism between precipitant additives and sludge performance is well understood, thus providing useful information about adding precipitant additives to improve both the sludge settling properties and the quality of the treated water during the heavy metal wastewater treatment. © 2013 Copyright Taylor and Francis Group, LLC.


Li Q.,Central South University | Li Q.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Chai L.,Central South University | Chai L.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Qin W.,Central South University
Chemical Engineering Journal | Year: 2012

A novel adsorbent-esterified spent grain (ESG) was used to remove Cadmium(II) from aqueous solution. Cd(II) adsorption behavior and mechanisms were investigated in this paper. The sorption process was very fast and the equilibrium was established in 15min. The maximum Cd(II) adsorption capacity of ESG calculated from Langmuir isotherm was 473.93mgg-1 that was higher than other adsorbents reported. The sorption kinetics was well described by the pseudo-second order kinetic model. The calculated activation energy (Ea) implied that adsorption of Cd(II) on ESG was a chemical adsorption. The thermodynamic parameters of sorption systems indicated a spontaneous and endothermic process. More importantly, Cd(II) binding mechanisms on ESG were discussed by FT-IR and XPS studies. The results showed that the carbon-oxygen (CO) in carboxyl group of ESG directly attached to the cadmium ion that led to most of the adsorption. © 2012 Elsevier B.V.


Li M.,Central South University | Peng B.,Central South University | Peng B.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Chai L.,Central South University | And 4 more authors.
Journal of Hazardous Materials | Year: 2012

The recovery of iron from zinc leaching residue by selective reduction roasting with carbon was studied. The effects of roasting temperature, duration time and mass ratio of carbon to residue on decomposition of ZnFe2O4, iron recovery and iron grade were investigated based on thermodynamic calculation and phase composition analysis of zinc leaching residue. 58.6% of iron grade in magnetic concentrate and 68.4% of iron recovery were achieved after the residue roasted at 750°C for 1h under carbon to residue mass ratio of 4%. The phase composition of roasted residue indicated that the ZnFe2O4 decomposed in four stages: reduction of ZnFe2O4 to ZnO and Fe3O4, reduction of Fe3O4 to FeO, formation of Fe0.85-xZnxO and reduction of FeO to Fe. A technological process for simultaneously recovering iron and zinc from zinc leaching residue is proposed. © 2012 Elsevier B.V.


Min X.-B.,Central South University | Min X.-B.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Xie X.-D.,Central South University | Chai L.-Y.,Central South University | And 4 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2013

Four different methods, namely mineralogical analysis, three-stage BCR sequential extraction procedure, dynamic leaching test and Hakanson Potential Ecological Risk Index Method were used to access the environmental activity and potential ecological risks of heavy metals in zinc leaching residue. The results demonstrate that the environmental activity of heavy metals declines in the following order: Cd>Zn>Cu>As>Pb. Potential ecological risk indices for single heavy metal are Cd>Zn>Cu>As>Pb. Cd has serious potential ecological risk to the ecological environment and contributes most to the potential toxicity response indices for various heavy metals in the residue. © 2013 The Nonferrous Metals Society of China.


Yan H.,Central South University | Chai L.-Y.,Central South University | Chai L.-Y.,Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution | Peng B.,Central South University | And 4 more authors.
Minerals Engineering | Year: 2014

A novel method to recover zinc and iron from zinc leaching residue (ZLR) by the combination of reduction roasting, acid leaching and magnetic separation was proposed. Zinc ferrite in the ZLR was selectively transformed to ZnO and Fe3O4 under CO, CO2 and Ar atmosphere. Subsequently, acid leaching was carried out to dissolve zinc from reduced ZLR while iron was left in the residue and recovered by magnetic separation. The mineralogical changes of ZLR during the processes were characterized by XRF, TG, XRD, SEM-EDS and VSM. The effects of roasting and leaching conditions were investigated with the optimum conditions obtained as follows: roasted at 750 C for 90 min with 8% CO and CO/CO + CO2 ratio at 30%; leached at 35 C for 60 min with 90 g/l sulfuric acid and liquid to solid ratio at 10:1. The iron was recovered by magnetic separation with magnetic intensity at 1160 G for 20 min. Under the optimum operation, 61.38% of zinc was recovered and 80.9% of iron recovery was achieved. This novel method not only realized the simultaneous recovery of zinc and iron but also solved the environmental problem caused by the storage of massive ZLR. © 2013 Elsevier Ltd. All rights reserved.

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