Changzhong Liao

Quantitative X-ray Diffraction (QXRD) analysis for revealing thermal transformations of red mud.

Red mud is a worldwide environmental problem, and many authorities are trying to find an economic solution for its beneficial application or/and safe disposal. Ceramic production is one of the potential waste-to-resource strategies for using red mud as a raw material. Before implementing such a strategy, an unambiguous understanding of the reaction behavior of red mud under thermal conditions is essential. In this study, the phase compositions and transformation processes were revealed for the Pingguo red mud (PRM) heat-treated at different sintering temperatures. Hematite, perovskite, andradite, cancrinite, kaolinite, diaspore, gibbsite and calcite phases were observed in the samples. However, unlike those red mud samples from the other regions, no TiO2 (rutile or anatase) or quartz were observed. Titanium was found to exist mainly in perovskite and andradite while the iron mainly existed in hematite and andradite. A new silico-ferrite of calcium and aluminum (SFCA) phase was found in samples treated at temperatures above 1100°C, and two possible formation pathways for SFCA were suggested. This is the first SFCA phase to be reported in thermally treated red mud, and this finding may turn PRM waste into a material resource for the iron-making industry. Titanium was found to be enriched in the perovskite phase after 1200°C thermal treatment, and this observation indicated a potential strategy for the recovery of titanium from PRM. In addition to noting these various resource recovery opportunities, this is also the first study to quantitatively summarize the reaction details of PRM phase transformations at various temperatures.

Hydrothermally synthesized CuxO as a catalyst for CO oxidation

Hydrothermally synthesized CuxO exhibited improved performance for CO oxidation compared to the hydrothermally synthesized Cu2O, as well as commercial CuO nanoparticles. Hydrothermally synthesized CuxO predominantly consists of CuO, but it also contains a small contribution from Cu2O, as well as Cu2(OH)3(NO3) (before annealing). After annealing, only CuO and Cu2O phases are present, and the T50 value is significantly improved from 179 °C to 149 °C, and the T50 value of annealed hydrothermal CuxO remains practically unchanged for 3 catalytic cycles. The improved performance of hydrothermal CuxO can be attributed to its composition and surface properties. The ratio of lattice oxygen to surface oxygen (oxygen in surface adsorbates, surface states, and defects) increases after the first CO oxidation reaction for all samples except commercial CuO nanoparticles, which exhibit steady decrease with increased cycling. In addition, pure Cu2O irreversibly changes to CuO after CO oxidation reaction, but its catalytic performance after the first cycle is significantly improved compared to commercial CuO nanoparticles.

In Situ Synthesis of CuxO/SnOx@CNT and CuxO/SnOx@SnO2/CNT Nanocomposite Anodes for Lithium Ion Batteries by a Simple Chemical Treatment Process

SnO2-based electrodes for lithium ion batteries (LIBs) typically exhibit high initial specific capacity but poor cycling performance. A possible strategy to improve the cycling performance is to prepare nanocomposites containing SnO2. Here we demonstrate a straightforward method to prepare composites containing SnOx and CuxO by a simple chemical treatment of the LIB electrode on copper foil. The in situ formation of a multiphase composite results in a dramatic improvement in the cycling performance, so that specific capacities exceeding 580 and 800 mA·h/g can be obtained after 70 charge/discharge cycles for CuxO/SnOx@CNT and CuxO/SnOx@SnO2/CNT electrodes, respectively (compared to <100 mA·h/g for pure SnO2). The capacity retention achieved at the 70th cycle compared to the 2nd cycle was 96% for the CuxO/SnOx@CNT electrode. The mechanisms responsible for the formation of a composite material and the improvement in the performance are discussed.

An alumina stabilized graphene oxide wrapped SnO2 hollow sphere LIB anode with improved lithium storage

SnO2 hollow spheres were stabilized by graphene oxide wrapping, by alumina coating deposited via atomic layer deposition (ALD), or the combination of the two methods and used in lithium ion battery anodes. We found that graphene oxide wrapping provides a better buffering of volume changes and results in reduced electrode pulverization and better preservation of the electrode morphology compared to bare SnO2 hollow spheres. On the other hand, ALD coating provides a significant improvement in the rate performance of the anodes, and it could also improve the adhesion of the metal oxide to the conductive additive since the coating is applied to the entire electrode. The combination of the two techniques results in anodes with superior cycling and rate performance, with specific capacity of 1176 mA h g−1 after 60 cycles at 0.1 A g−1 (compared to 115 mA h g−1 for bare hollow SnO2 nanospheres) and specific capacity of 329 mA h g−1 at 2 A g−1 charge/discharge rate (compared to 7 mA h g−1 for bare SnO2 hollow spheres). The improvement in the performance was attributed to the superior preservation of anode morphology after cycling.

Double-Barrier mechanism for chromium immobilization: A quantitative study of crystallization and leachability.

Glass-ceramics are well known for the excellent combination properties provided by their components, a glassy matrix and crystalline phases, and have promising applications in the immobilization and detoxification of solid waste containing toxic metals. Glass-ceramic products were successfully synthesized in CaO-MgO-SiO2-Al2O3 -Cr2O3 system. Two key measures--partitioning ratio of Cr in the spinel and Cr leaching ratio--were used to investigate the mechanism of Cr immobilization in the glass-ceramic products. The results of powder X-ray diffraction revealed that both spinel and diopside were major crystalline phases in the products. The value of x in the MgCr(x)Al(2-x)O4 spinel was highly related to the amount of Cr2O3 added to the glass-ceramic system. As Cr2O3 content increased, the proportion of spinel phase increased, while that of glass phase decreased. The partitioning ratio of Cr in spinel phase was about 70% for 2 wt.% Cr2O3, and increased to 90% when loaded with 10 wt.% of Cr2O3. According to the results of the prolonged toxicity characteristic leaching procedure, the Cr leaching ratio decreased with the increase of Cr partitioning ratio into the spinel phase. The findings of this study clearly indicate that glass-ceramic formed by spinel structure and residual glass successfully immobilized Cr.

Cadmium Stabilization Efficiency and Leachability by CdAl4O7 Monoclinic Structure.

This study investigated the stabilization efficiencies of using an aluminum-rich precursor to incorporate simulated cadmium-bearing waste sludge and evaluated the leaching performance of the product phase. Cadmium oxide and γ-alumina mixtures with various Cd/Al molar ratios were fired at 800-1000 °C for 3 h. Cadmium could be crystallochemically incorporated by γ-alumina into CdAl4O7 monoclinic phase and the reaction was strongly controlled by the treatment temperature. The crystal structure details of CdAl4O7 were solved and refined with the Rietveld refinement method. According to the structural refinement results, the stabilization efficiencies were quantified and expressed as a transformation ratio (TR) with optimized processing parameters. The preferred treatment temperature was found to be 950 °C for mixtures with a Cd/Al molar ratio of 1/4, as its TR value indicated the cadmium incorporation was nearly completed after a 3 h treatment scheme. Constant-pH leaching tests (CPLT) were conducted by comparing the leachability of the CdO and CdAl4O7 phases in a pH 4.0 environment. A remarkable reduction in cadmium leachability could be achieved via monoclinic CdAl4O7 structure formation to effectively stabilize hazardous cadmium in the waste stream. The CPLT and X-ray photoelectron spectroscopy (XPS) results suggested incongruent dissolution behavior during the leaching of the CdAl4O7 phase.

Detoxification and immobilization of chromite ore processing residue in spinel-based glass-ceramic

A promising strategy for the detoxification and immobilization of chromite ore processing residue (COPR) in a spinel-based glass-ceramic matrix is reported in this study. In the search for a more chemically durable matrix for COPR, the most critical crystalline phase for Cr immobilization was found to be a spinel solid solution with a chemical composition of MgCr1.32Fe0.19Al0.49O4. Using Rietveld quantitative X-ray diffraction analysis, we identified this final product is with the phases of spinel (3.5wt.%), diopside (5.2wt.%), and some amorphous contents (91.2wt.%). The partitioning ratio of Cr reveals that about 77% of the Cr was incorporated into the more chemically durable spinel phase. The results of Cr K-edge X-ray absorption near-edge spectroscopy show that no Cr(VI) was observed after conversion of COPR into a glass-ceramic, which indicates successful detoxification of Cr(VI) into Cr(III) in the COPR-incorporated glass-ceramic. The leaching performances of Cr2O3 and COPR-incorporated glass-ceramic were compared with a prolonged acid-leaching test, and the results demonstrate the superiority of the COPR-incorporated glass-ceramic matrix in the immobilization of Cr. The overall results suggest that the use of affordable additives has potential in more reliably immobilizing COPR with a spinel-based glass-ceramic for safer disposal of this hazardous waste.

Cubic and tetragonal ferrite crystal structures for copper ion immobilization in an iron-rich ceramic matrix

This study proposes a strategy by reusing the incineration ash of municipal wastewater sludge as a ceramic material to immobilize copper. After sintering the mixture of CuO and sludge ash, hematite (α-Fe2O3, one major component) incorporated copper into cubic CuFe2O4. To observe copper incorporation mechanisms, mixtures of CuO + α-Fe2O3 were sintered from 650 to 1050 °C, and different copper incorporation behavior was detected. A low-temperature CuFe2O4 phase with a tetragonal structure was detected at 750 °C, and the cubic CuFe2O4 developed at 1000 °C. The incorporation efficiencies were first quantitatively determined by Rietveld refinement analysis of the X-ray diffraction data. The maximum copper incorporation into tetragonal and cubic CuFe2O4 reached around 80% and 73%, respectively. The leachability analysis pointed to the superiority of both copper ferrites in stabilizing copper, suggesting a promising technique for incorporating copper into the iron-rich ceramic matrix. Both tetragonal and cubic CuFe2O4 were observed with incongruent leaching behavior, but the lower copper concentrations and higher [Cu]/[Fe] ratio in tetragonal CuFe2O4 leachates indicates its higher capacity for copper stabilization. With a high transformation ratio into CuFe2O4 phases and dramatic reduction in metal leachability, the beneficial use of sludge ash to immobilize hazardous metal contaminated soil may be potentially successful.

Cu2O-promoted degradation of sulfamethoxazole by α-Fe2O3-catalyzed peroxymonosulfate under circumneutral conditions: synergistic effect, Cu/Fe ratios, and mechanisms

ABSTRACT To promote the application of iron oxides in sulfate radical-based advanced oxidation processes, a convenient approach using Cu2O as a catalyst additive was proposed. Composite catalysts based on α-Fe2O3 (CTX%Cu2O, X = 1, 2.5, 5, and 10) were prepared for peroxymonosulfate (PMS) activation, and sulfamethoxazole was used as a model pollutant to probe the catalytic reactivity. The results show that a synergistic catalytic effect exists between Cu2O and α-Fe2O3, which was explained by the promoted reduction of Fe(III) by Cu(I). Iron K-edge X-ray absorption spectroscopy investigations indicated that the promoted reduction probably occurred with PMS acting as a ligand that bridges the redox centers of Cu(I) and Fe(III). The weight ratio between Cu2O and α-Fe2O3 influenced the degradation of sulfamethoxazole, and the optimal ratio depended on the dosage of PMS and catalysts. With 40 mg L–1 PMS and 0.6 g L–1 catalyst, a pseudo-first-order constant of ∼0.019 min–1 was achieved for CT2.5%Cu2O, whereas only 0.004 min–1 was realized for α-Fe2O3. Nearly complete degradation of the sulfamethoxazole was achieved within 180 min under the conditions of 40 mg L–1 PMS, 0.4 g L–1 CT2.5%Cu2O, and pH 6.8. In contrast, less than 20% degradation was realized with α-Fe2O3 under similar conditions. The CT2.5%Cu2O catalyst had the best stoichiometric efficiency of PMS (0.317), which was 4.5 and 5.8 times higher than those of Cu2O (0.070) and α-Fe2O3 (0.054), respectively. On the basis of the products identified, the cleavage of the S–N bond was proposed as a major pathway for the degradation of sulfamethoxazole.

Incorporation of Cadmium and Nickel into Ferrite Spinel Solid Solution: X-ray Diffraction and X-ray Absorption Fine Structure Analyses

The feasibility of incorporating Cd and Ni in hematite was studied by investigating the interaction mechanism for the formation of CdxNi1-xFe2O4 solid solutions (CNFs) from CdO, NiO, and α-Fe2O3. X-ray diffraction results showed that the CNFs crystallized into spinel structures with increasing lattice parameters as the Cd content in the precursors was increased. Cd2+ ions were found to occupy the tetrahedral sites, as evidenced by Rietveld refinement and extended X-ray absorption fine structure analyses. The incorporation of Cd and Ni into ferrite spinel solid solution strongly relied on the processing parameters. The incorporation of Cd and Ni into the CNFs was greater at high x values (0.7 < x ≤ 1.0) than at low x values (0.0 ≤ x ≤ 0.7). A feasible treatment technique based on the investigated mechanism of CNF formation was developed, involving thermal treatment of waste sludge containing Cd and Ni. Both of these metals in the waste sludge were successfully incorporated into a ferrite spinel solid solution, and the concentrations of leached Cd and Ni from this solid solution were substantially reduced, stabilizing at low levels. This research offers a highly promising approach for treating the Cd and Ni content frequently encountered in electronic waste and its treatment residues.