Sha Liang

A novel hollow sphere bismuth oxide doped mesoporous carbon nanocomposite material derived from sustainable biomass for picomolar electrochemical detection of lead and cadmium

A novel ultrasensitive, selective and low cost electrochemical sensor based on a hollow sphere bismuth oxide doped mesoporous carbon aerogel nanocomposite derived from a sustainable biomass material was successfully fabricated for simultaneous Pb2+ and Cd2+ detection at picomolar levels. In this nanocomposite material, we successfully brought together the advantages of an extraordinarily large surface area biomass derived carbon matrix with mesopores for analyte pre-enrichment and the excellent electroanalytical activity of the bismuth oxide hollow sphere structure for highly sensitive heavy metal sensing. Under optimized conditions, this electrode material exhibited a very low detection limit of 1.72 pM for Pb2+ and 1.58 pM for Cd2+ under ambient conditions, the lowest ever limit of detection recorded for the detection of both Pb2+ and Cd2+ using activated carbon. Furthermore, two wide linear ranges from 0.5 pM to 10 pM and from 10 pM to100 pM were observed due to the differences of adsorption dynamics at different metal ion concentration ranges. The nanocomposite sensor material demonstrated excellent reproducibility and great resistance to interference. Furthermore, the application for real water analysis was demonstrated and the result was highly consistent with the measurement from inductively coupled plasma optical emission spectroscopy (ICP-OES).

Co-disposal of MSWI fly ash and Bayer red mud using an one-part geopolymeric system

In this research, Bayer red mud (RM) was pretreated through alkali-thermal activation process, and prepared as an one-part geopolymer precursor, which could be used as geopolymeric solidification/stabilization (S/S) reagent for municipal solid waste incineration fly ash (MSWI FA). Compressive strength test, modified TCLP leaching test and sequential extraction test were conducted to evaluate the effectiveness of the RM-based geopolymeric S/S reagent. The results show that the S/S effects for heavy metals of RM-based geopolymer exhibit the following order: Pb>Cu>Zn>Cr. Most of the Zn, Pb and Cu in the MSWI FA transform from the leachable fractions into the inactive fractions difficult or unavailable to leach out. In the geopolymeric S/S solid, the active aluminosilicates in MSWI FA are dissolved in the alkaline environment formed by pretreated RM and then participate in the geopolymerization, which increases the SiO2/Al2O3 ratio and enhances the structural stability of geopolymeric S/S solid. MSWI FA offsets the strength deterioration of RM based one-part geopolymer and improves the immobilization efficiency for heavy metals in the geopolymer structure.

Enhanced Cr(VI) removal from acidic solutions using biochar modified by Fe 3 O 4 @SiO 2 -NH 2 particles

Fe3O4@SiO2-NH2 magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the Fe3O4@SiO2-NH2 magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g-1, surpassing original carboxylated biochar (18.2mg·g-1). VSM and XPS characterizations demonstrated that the attached Fe3O4@SiO2-NH2 magnetic particles not only endowed biochar with perfect magnetic property (23emu·g-1) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L-1. The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater.

Distribution and speciation of heavy metals in two different sludge composite conditioning and deep dewatering processes

Pilot-scale sewage sludge dewatering experiments were conducted using two composite conditioners: FeCl3 + lime (Fe-lime) and Fentons reagents + red mud (Fenton-RM). Mass balance analysis was performed on Cu, Zn, Pb, Cd, and Cr during the conditioning and dewatering processes to investigate their transformation and distribution. Speciation of heavy metals was also investigated by the Tessier sequential extraction method. Results show that (1) most of the heavy metals were retained in the solid cake during the dewatering process, especially Cu and Cr; (2) in the sludge cakes, more than 87 wt% of Cu and Cr existed in organic bound and residual forms, and the contents of the bioavailable fractions (exchangeable, carbonate bound and Fe–Mn oxides bound form) for Zn, Pb, and Cd were larger in the Fenton-RM system than those in the Fe-lime system; (3) the main factors affecting the distributions of these heavy metals are pH and chemical speciation in two conditioning processes. Generally, heavy metal concentrations in filtrate and dewatered sludge cakes in both systems were below the corresponding standards, and heavy metals in the dewatered sludge cake could be more effectively immobilized in the Fe-lime system than in that of the Fenton-RM system.

The effect of barium sulfate-doped lead oxide as a positive active material on the performance of lead acid batteries

Barium sulfate (BaSO4) is a common impurity in recycled lead paste that is challenging to eliminate completely during hydrometallurgical recycling of spent lead acid batteries, so the effect of this impurity in positive active materials on the performance of recycled lead acid batteries was investigated. The BaSO4 doped lead oxide composite was used as a positive active material in positive plates of lead acid batteries with theoretical capacities of 2.0 A h. BaSO4 was retained in the solid phase throughout the battery fabrication process. Different BaSO4 dosages affected the phase of the positive plates during the curing process, with the highest content of metallic lead obtained at a BaSO4 dosage of 0.06 wt%. Morphology analysis indicated that aggregates were formed in the positive plates and the particles became rougher with increasing addition of BaSO4 during the formation process. BaSO4 also demonstrated a large impact on charge/discharge cycles with 100% DOD in battery testing. Analysis of disassembled failed batteries indicated that the expansion and shedding-off of the positive active material were mainly responsible for the failure of these batteries, and this could be attributed to the non-uniform growth of lead oxide on the BaSO4 nucleus, and the accumulation of internal stress.

Citric acid assisted Fenton-like process for enhanced dewaterability of waste activated sludge with in-situ generation of hydrogen peroxide

Fentons reagent has been widely used to enhance sludge dewaterability. However, drawbacks associated with hydrogen peroxide (H2O2) in Fentons reagents exist, since it is a hazardous chemical and shows carcinogenicity, explosivity, instability, and corrosivity. Moreover, initial acidification and subsequent neutralization are needed as optimal conditions for homogeneous Fenton conditioning and final filtrate discharge. In this study, a Fenton-like process for the enhanced dewaterability of waste activated sludge with in-situ generation of H2O2 and without extra pH adjustment was firstly proposed, namely citric acid (CA)-assisted oxygen activation in an air/nano zero-valent iron (nZVI) system and chemical re-coagulation with polydiallyldimethylammonium chloride (PDMDAAC). Using the response surface methodology (RSM), the optimal doses of CA, nZVI, and PDMDAAC were determined to be 13, 33, and 9 mg g-1 dry solids (DS), respectively. This composite conditioner showed a good dewatering capability compared with the raw sludge, e.g. the capillary suction time decreased from 130.0 to 9.5 s. The enhanced sludge dewaterability was further confirmed by laboratory-scale diaphragm filter press dewatering tests, which produced a lower cake moisture content compared with the raw sludge, and the final pH of the filtrate was close to neutrality. The citric acid promoted the production of H2O2 and Fe(II)/Fe(III) species, the degradation of protein in tightly-bound extracellular polymeric substances, and the decomposition of protein-N in the solid phase of sludge, resulting a greater conversion of bound water to free water. The results of electron spin resonance indicated that the hydroxyl radicals were mainly responsible for the decomposition of proteinaceous compounds. The subsequent chemical re-coagulation with PDMDAAC can make the zeta potential of sludge samples less negative, reduce the repulsive electrostatic interactions, and agglomerate the smaller particles into larger aggregates, thus enhancing sludge dewaterability.

An Emission-Free Vacuum Chlorinating Process for Simultaneous Sulfur Fixation and Lead Recovery from Spent Lead-Acid Batteries

Spent lead-acid battery recycling by using conventional technologies is usually accompanied by releases of lead-containing wastewater as well as emissions of sulfur oxides and lead particulates that may potentially cause secondary pollution. This study developed a vacuum chlorinating process for simultaneous sulfur fixation and high-purity lead chloride (PbCl2) recovery from spent lead paste by using calcium chloride (CaCl2) and silicon dioxide (SiO2) as reagents. The process train includes pretreatment, simultaneous PbCl2 production and sulfur fixation, and PbCl2 volatilization. The pretreatment eliminated chlorine emission from direct chlorinating reaction of PbO2 in the initial S-paste (PbSO4/PbO2/PbO/Pb). During the subsequent PbCl2 production and sulfur fixation step, lead compounds in the P-paste (PbSO4/PbO) was converted to volatile PbCl2, and sulfur was simultaneously fixed to the solid residues in the form of CaSO4 to eliminate the emission of sulfur oxides. The final step, PbCl2 volatilization under vacuum, is a physical phase-transformation process of ionic crystals, following a zeroth-order kinetic model. A cost estimate indicates a profit of USD

Direct reuse of two deep-dewatered sludge cakes without a solidifying agent as landfill cover: geotechnical properties and heavy metal leaching characteristics

8.50/kg PbCl2. This process offers a novel green lead recovery alternative for spent lead-acid batteries with environmental and economic benefits.

Lead adsorption from aqueous solutions by a granular adsorbent prepared from phoenix tree leaves

Two types of deep-dewatered sewage sludge cakes were produced from pilot-scale experiments by using two composite conditioners: FeCl3 + quick lime (Fe–Lime) and Fentons reagent + red mud (Fenton–RM). The feasibility of direct reuse without any solidifying agents of these two deep-dewatered cakes, with water content of about 60 wt%, as landfill cover materials was investigated. Geotechnical properties of these two sludge cakes were found appropriate for reuse as landfill covers. Their plasticity index values increased significantly from 11.6 (raw sludge) to 23.8 (Fe–Lime) and 35.4 (Fenton–RM). The unconfined compressive strength and direct shear strength of the two deep-dewatered sludge cakes could meet or exceed the requirement of landfill cover materials after a certain curing time. Microstructural analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that their microstructures were more porous than that of raw sludge since the skeleton builders played a role in building the rigorous framework. There was negligible leaching of Cu, Zn, Pb, Cd and Cr from the deep-dewatered sludge cake from the toxicity characteristic leaching procedure and column leaching test. Both deep-dewatered sludge cakes could be reused as effective landfill cover materials with a suitable curing time.

A bio-electro-Fenton system with a facile anti-biofouling air cathode for efficient degradation of landfill leachate

In this study, a granular adsorbent was prepared from phoenix tree leaf powder with bentonite as the binder. The granular adsorbent was characterized by TG, BET and SEM analyses. The maximum specific surface area and pore volume were 166.3 m2 g−1 and 0.276 cm3 g−1, respectively, after the granular adsorbent was calcined at 500 °C. Effects of pH, adsorption time and initial metal ion concentration on the adsorption of Pb2+ by 500 °C calcined granular adsorbent were investigated in batch experiments. Higher pH was favorable for the adsorption process and significant release of Na+, K+ and Mg2+ were observed, assuming the predominant Pb2+ adsorption mechanism was ion exchange. The adsorption could attain equilibrium within 24 h with a gradual increase of the solution pH. The kinetics data were analyzed using three adsorption kinetic models: the pseudo-first-order, pseudo-second-order and intraparticle diffusion equations. Results show that intraparticle diffusion or chemical adsorption is the rate-limiting step depending on the adsorption time. The adsorption isotherms best fitted the Langmuir–Freundlich model and the maximum Langmuir adsorption capacity was found to be 71 mg g−1. This novel granular adsorbent has proven to be a potential inexpensive adsorbent for Pb2+ removal from aqueous solutions.