Yanjie Liang

Stabilization of arsenic sludge with mechanochemically modified zero valent iron

Modified zero valent iron (ZVI) is obtained from commercial iron powder co-ground with manganese dioxide (MnO2) in intensive mechanical stress. The result indicates that the modified ZVI is very effective in arsenic sludge stabilization with a declination of arsenic leaching contraction from 72.50xa0mg/L to 0.62xa0mg/L, much lower than that of ordinary ZVI (10.48xa0mg/L). The involved process, including mechanochemical activation, corrosion and arsenic adsorption, is characterized explicitly to verify the improved arsenic stabilization mechanism. It shows that the mechanically formed Fe-Mn binary oxides layer results in an intensive corrosion extent, generating a mass of corrosion products. Moreover, as the emergence of Mn will restrain the process of iron (hydr)oxides crystallization, the ultimate corrosion products of the modified ZVI predominates in amorphous iron (hydr)oxides, performing much better in arsenic absorption. According to the BCR analysis, unstable arsenic in sludge is easily transformed to residual fraction by the help of amorphous iron (hydr)oxides, resulting in a restrained environmental availability of arsenic sludge after the modified ZVI stabilization.

Co-treatment of flotation waste, neutralization sludge, and arsenic-containing gypsum sludge from copper smelting: solidification/stabilization of arsenic and heavy metals with minimal cement clinker

Flotation waste of copper slag (FWCS), neutralization sludge (NS), and arsenic-containing gypsum sludge (GS), both of which are difficult to dispose of, are major solid wastes produced by the copper smelting. This study focused on the co-treatment of FWCS, NS, and GS for solidification/stabilization of arsenic and heavy metals with minimal cement clinker. Firstly, the preparation parameters of binder composed of FWCS, NS, and cement clinker were optimized to be FWCS dosage of 40%, NS dosage of 10%, cement clinker dosage of 50%, mill time of 1.5xa0h, and water-to-binder ratio of 0.25. On these conditions, the unconfined compressive strength (UCS) of the binder reached 43.24xa0MPa after hydration of 28xa0days. Then, the binder was used to solidify/stabilize the As-containing GS. When the mass ratio of binder-to-GS was 5:5, the UCS of matrix can reach 11.06xa0MPa after hydration of 28xa0days, meeting the required UCS level of MU10 brick in China. Moreover, arsenic and other heavy metals in FWCS, NS, and GS were effectively solidified or stabilized. The heavy metal concentrations in leachate were much lower than those in the limits of China standard leaching test (CSLT). Therefore, the matrices were potential to be used as bricks in some constructions. XRD analysis shows that the main hydration products of the matrix were portlandite and calcium silicate hydrate. These hydration products may play a significant role in the stabilization/solidification of arsenic and heavy metals.

Utilization of red mud and Pb/Zn smelter waste for the synthesis of a red mud-based cementitious material

A new method in which Pb/Zn smelter waste containing arsenic and heavy metals (arsenic sludge), red mud and lime are utilized to prepare red mud-based cementitious material (RCM) is proposed in this study. XRD, SEM, FTIR and unconfined compressive strength (UCS) tests were employed to assess the physicochemical properties of RCM. In addition, ettringite and iron oxide-containing ettringite were used to study the hydration mechanism of RCM. The results show that the UCS of the RCM (red mud+arsenic sludge+lime) was higher than that of the binder (red mud+arsenic sludge). When the mass ratio of m (binder): m (lime) was 94:6 and then maintained 28days at ambient temperature, the UCS reached 12.05MPa. The red mud has potential cementitious characteristics, and the major source of those characteristics was the aluminium oxide. In the red mud-arsenic sludge-lime system, aluminium oxide was effectively activated by lime and gypsum to form complex hydration products. Some of the aluminium in ettringite was replaced by iron to form calcium sulfoferrite hydrate. The BCR and leaching toxicity results show that the leaching concentration was strongly dependent on the chemical speciation of arsenic and the hydration products. Therefore, the investigated red mud and arsenic sludge can be successfully utilized in cement composites to create a red mud-based cementitious material.

The non-isothermal kinetics of zinc ferrite reduction with carbon monoxide

This study aims to reduce zinc ferrite using carbon monoxide in the temperature range of 25–1000xa0°C using temperature-programmed reduction. The kinetic parameters were evaluated using the Friedman isoconversional method, and multi-step reaction models were determined by nonlinear regression methods. The reduction of zinc ferrite is a stepwise process according to the thermodynamic calculation and the variation of the activation energy Ea. Ea generally remained between 100 and 120xa0kJxa0mol−1 during the reduction process. The mechanism was determined based on an F-test of the fit quality. The corresponding kinetic parameters were obtained and employed to predict the isothermal reduction of zinc ferrite. The experimental data were found to be consistent with the predicted data, suggesting that the reduction can be satisfactorily described by the presented mechanism.

Uranium bioleaching from low-grade carbonaceous-siliceous-argillaceous type uranium ore using an indigenous Acidithiobacillus ferrooxidans

We evaluated the effectiveness of bioleaching uranium from a low-grade carbonaceous-siliceous-argillaceous type uranium ore using an indigenous iron-oxidizing bacteria, Acidithiobacillus ferrooxidans, isolated from local uranium ore. The effects of initial acidity, pulp density and ferrous ion concentration of the feed solution were investigated. The uranium (U3O8) content was 0.036% by weight. Using uranium ore acidified leachate as medium with initial ferrous ion concentrations of 3xa0g/L, pH 1.7 and pulp density of 20% as optimal conditions, the maximum rate of dissolved uranium recovery was 85.14%. This approach is thus, suitable for recovering uranium from low-grade CSA ore using bacterial leaching.

Formation mechanism of Zinc-doped fayalite (Fe2-xZnxSiO4) slag during copper smelting

The interactions between Fe2SiO4 and ZnO play an essential role in the recovery of zinc from copper slag. The dissolution and substitution mechanism of ZnO in fayalite were investigated by using TG-DSC, XRD, PPMS DynaCool, XPS, Mossbauer and SEM-EDS analyses and compared with MS calculation results. The results indicate that the dissolution and substitution are actually processes of the penetrating dissolution of Zn(II) ions that can be divided into three steps: 1) ZnO dissociates into Zn1-yO and Zn(II) ions; 2) Zn(II) penetrates the gap of the octahedron outer layer to substitute Fe(II) sites in the internal structure of SiOFe(II) (M2) to form (Fe2-x, Znx)SiO4; 3) Fe(II) is forced to migrate to the surface of (Fe2-x, Znx)SiO4 to form (Zn1-y, Fe(II)y)O. These findings can be derived the occurrence state and distribution of zinc in copper slag theoretically.

Hydrothermal Treatment of Arsenic Sulfide Residues from Arsenic-Bearing Acid Wastewater

Arsenic sulfide residue (ASR), a by-product from the treatment of arsenic-bearing acidic wastewater, is abundantly generated but not properly disposed of in China. The utilization of such high-content arsenic waste residue is limited by the market. The traditional methods of stabilization/solidification (S/S) by lime cement or iron salt have a large mass/volume addition, high dumping cost and secondary pollution risk. In this paper, hydrothermal technology was used to treat three kinds of ASRs obtained from different smelters to minimize waste. The leaching toxicity and chemical speciation of the generated products was also evaluated by TCLP and BCR analyses. It was found that the hydrothermal treatment could greatly reduce the volume and moisture content of the ASRs. TCLP tests showed that the leachability of arsenic and heavy metals significantly decreased after the treatment. According to the BCR analysis, most of the unstable As, Cd and Cr transformed into a residual fraction. Finally, XRD, SEM, Raman and XPS techniques were carried out to reveal the mechanism. As a result, hydrothermal treatment can efficiently achieve the dehydration, volume reduction and stabilization/solidification of ASRs.