Cu/Cr co-stabilization mechanisms in a simulated Al2O3-Fe2O3-Cr2O3-CuO waste system

• Cu and Cr can be mostly incorporated into CuFe_xAl_yCr_2−x−yO₄ with a spinel structure. • Spinel phase is the most crucial structure for Cu and Cr co-stabilization. • Compared to Al, Fe and Cr are easier to be incorporated into the spinel structure. • ‘Waste-to-resource’ by thermal process at attainable temperatures can be achieved. Chromium slag usually contains various heavy metals, making its safe treatment difficult. Glass-ceramic sintering has been applied to resolve this issue and emerged as an effective method for metal immobilization by incorporating heavy metals into stable crystal structures. Currently, there is limited knowledge about the reaction pathways adopted by multiple heavy metals and the co-stabilization functions of the crystal structure. To study the Cu/Cr co-stabilization mechanisms during thermal treatment, a simulated system was prepared using a mixture with a molar ratio of Al₂O₃:Fe₂O₃:Cr₂O₃:CuO= 1:1:1:3. The samples were sintered at temperatures 600–1300°C followed by intensive analysis of phase constitutions and microstructure development. A spinel phase (CuFe_xAl_yCr_2−x−yO₄) started to generate at 700°C and the incorporation of Cu/Cr into the spinel largely complete at 900°C, although the spinel peak intensity continued increasing slightly at temperatures above 900°C. Fe₂O₃/Cr₂O₃ was more easily incorporated into the spinel at lower temperatures, while more Al₂O₃ was gradually incorporated into the spinel at higher temperatures. Additionally, sintered sample microstructures became more condensed and smoother with increased sintering temperature. Cu / Cr leachability substantially decreased after Cu/Cr incorporation into the spinel phase at elevated temperatures. At 600°C, the leached ratios for Cu and Cr were 6.28% and 0.65%, respectively. When sintering temperature was increased to 1300°C, the leached ratios for all metal components in the system were below 0.2%. This study proposes a sustainable method for managing Cu/Cr co-exist slag at reasonable temperatures.     

Model reactions of chromium compounds with mammalian and bacterial cells†

Chromate uptake, reduction, cytotoxicity and mutagenicity were studied with human red blood cells, Chinese hamster ovary (CHO) cells and/or Salmonella typhimurium mutant cells. All cell types rapidly took up chromates whereas chromium(III) salts were excluded under the experimental conditions. Red blood cells reduced and accumulated chromium from chromate. At concentrations above 0.1 mM, chromate inactivated the red cell chromate carrier. Chromate above 0.01 mM inhibited CHO cell proliferation irrespective of the cations present. Chromate and two chromium(III) complexes were mutagenic with Salmonella mutants in the Ames’ assay. A model for chromate metabolism and genotoxicity is proposed.     

Electrochemical reduction of Cr(VI) in the presence of sodium alginate and its application in water purification

Chromium (Cr) is used in many manufacturing processes, and its release into natural waters is a major environmental problem today. Low concentrations of Cr(VI) are toxic to human health and living organisms due to the carcinogenic and mutagenic nature of this mineral. This work examined the conversion of Cr(VI) to Cr(III) via electrochemical reduction using gold electrode in an acidic sodium alginate (SA) solution and subsequent removal of the produced Cr(III)-SA by the polymer-enhanced ultrafiltration (PEUF) technique. A solution of SA in nitric acid was used both as an electrolytic medium during the voltammetric measurements and bulk electrolysis and as an extracting agent during the PEUF technique. The electroanalysis of Cr(VI) was performed by linear sweep voltammetry in the presence of acidic SA solution to study its voltammetric behavior as a function of the Cr(VI) concentration, pH, presence of Cr(III), SA concentration and scan rate. In addition, the quantitative reduction of Cr(VI) to Cr(III) was studied through the bulk electrolysis technique.The results showed efficient reduction with well-defined peaks at approximately 0.3 V vs. Ag/AgCl, using a gold working electrode. As the pH increased, the reduction signal strongly decreased until its disappearance. The optimum SA concentration was 10 mmol/L, and it was observed that the presence of Cr(III) did not interfere in the Cr(VI) electroanalysis. Through the quantitative reduction by bulk electrolysis in the presence of acidic SA solution, it was possible to reduce all Cr(VI) to Cr(III) followed by its removal via PEUF.     

Enhanced the photoelectrochemical performance of Bi2XO6 (X = W, Mo) for detecting hexavalent chromium by modification of CuS

In this work, Bi₂XO₆ (X = W, Mo) are synthesized at different temperatures. The results of tests find the optimal temperatures of Bi₂WO₆ and Bi₂MoO₆ are 180 and 160°C (BW-180, BM-160). Then, BW-180 and BM-160 are further compounded with different contents of CuS. The results of photoelectrochemical (PEC) tests show that CuS can improve the PEC performance of semiconductor materials, and it has better performance when CuS mass fraction is 5%. These maybe the photoelectron potentials generated by CuS/Bi₂XO₆ (X = Mo, W) heterojunction reduce the combination of photogenerated electrons and holes. When the PEC sensor based on 5%-CuS/BW-180 detects Cr(VI), it has a linear range of 1–80 μmol/L with detection limit of 0.95 μmol/L, while the PEC sensor based on 5%-CuS/BM-160 detects Cr(VI) has a linear range of 0.5–230 μmol/L and a detection limit of 0.12 μmol/L. Thus, 5%-CuS/Bi₂XO₆ has potential application in hexavalent chromium detection.     

Chromium transport, oxidation, and adsorption in manganese-coated sand

We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (beta-MnO2)-coated sand. We find that beta-MnO2 effectively oxidizes Cr(III) to Cr(VI) and that the extent of oxidation is sensitive to changes in pH, pore water velocity, and influent concentrations of Cr(III). Cr(III) oxidation rates, although initially high, decline well before the supply of beta-MnO2 is depleted, suggesting that a reaction product inhibits the conversion of Cr(III) to Cr(VI). Rate-limited reactions govern the weak adsorption of each chromium species, with Cr(III) adsorption varying directly with pH and Cr(VI) adsorption varying inversely with pH. The breakthrough data on chromium transport can be matched closely by calculations of a simple model that accounts for (1) advective-dispersive transport of Cr(III), Cr(VI), and dissolved oxygen, (2) first-order kinetics adsorption of the reduced and oxidized chromium species, and (3) nonlinear rate-limited oxidation of Cr(III) to Cr(VI). Our work supplements the limited database on the transport of redox-sensitive metals in porous media and provides a means for quantifying the coupled processes that contribute to this transport.     

用铬渣作水泥矿化剂

介绍了铬渣作水泥矿化剂的原理和生产控制条件,通过经济和环境效益分析证明,铬渣作水泥矿化剂确实是一种处理和利用铬渣的好方法。     

铬的浸出毒性试验方法研究

以铬为分析指标,探讨了钻井废充泥浆在不同的提取剂、没的提取时间、不同的固液比以及不同的提取方式下铬的浸出毒性大小,提出了适合评价钻井废充泥浆中铬的浸出毒性的试验方法。     

利用废铁屑处理含铬废水试验研究

通过研究在酸性条件下利用废铁屑处理剧毒的六价铬电镀废水的工艺条件 ,在最佳条件下废水中六价铬去除率达99 %以上 ,出水总铬含量为0.040mg/l,六价铬含量为0.002mg/l,大大低于国家排放标准0.500mg/l。     

Changes of organic acid exudation and rhizosphere pH in rice plants under chromium stress.

The effect of chromium (Cr) stress on the changes of rhizosphere pH, organic acid exudation, and Cr accumulation in plants was studied using two rice genotypes differing in grain Cr accumulation. The results showed that rhizosphere pH increased with increasing level of Cr in the culture solution and with an extended time of Cr exposure. Among the six organic acids examined in this experiment, oxalic and malic acid contents were relatively higher, and had a significant positive correlation with the rhizosphere pH, indicating that they play an important role in changing rhizosphere pH. The Cr content in roots was significantly higher than that in stems and leaves. Cr accumulation in plants was significantly and positively correlated with rhizosphere pH, and the exudation of oxalic, malic and citric acids, suggesting that an increase in rhizosphere pH, and exudation of oxalic, malic and citric acid enhances Cr accumulation in rice plants.     

生物法处理含铬废水的研究进展

随着人类对环境保护的重视和环境法规的日益严格，国内外研究人员纷纷将注意力转向生物法处理含铬废水。文章介绍了惰性生物吸附法和纯种微生物法处理含铬废水近年来的研究进展。