The characterization of a novel magnetic biochar derived from sulfate-reducing sludge and its application for aqueous Cr(â ¥) removal through synergistic effects of adsorption and chemical reduction.

Removal of heavy metals from the aqueous environment via physiochemical adsorption always remains a great challenge owing to the slow kinetics and low removal capacity for the conventional adsorbent. In this study, the sulfate-reducing bacteria (SRB)-rich anaerobic sludge was pyrolyzed for the preparation of magnetic biochar, i.e. SBC-20-500 (SBC: sulfate-reducing sludge-based biochar; 20 denotes the biochar dosage, namely 8 g dried sludge in 400 mL iron solution which is equal to 20 g/L; 500 represents the pyrolysis temperature, i.e. at 500 °C) with tunable pore structure and surface properties towards efficient removal of chromium (Cr (Ⅵ)). The characterization revealed that magnetic biochar SBC-20-500 exhibited higher surface area and larger pore volume compared to non-magnetic SBC-500. Batch experiments on Cr (Ⅵ) removal were performed under different biochar dosages, pH values, initial Cr (Ⅵ) concentrations and temperatures. The results illustrated that magnetic biochar demonstrated much larger Cr (Ⅵ) adsorption capacity with qe of 5.3585 mg/g as compared to non-modified one (qe = 0.7206 mg/g). The maximum Cr (Ⅵ) removal efficiency of SBC-20-500 reached approximately 93.7% within 24 h under the conditions of pH = 3.0, biochar dosage = 0.8 g and initial Cr (Ⅵ) concentration = 50 mg/L. The kinetic and isotherm fitting results suggested that the pseudo-second-order kinetic and Langmuir isotherm model were more suitable for describing the adsorption behavior of Cr (Ⅵ) by SBC-20-500. The XPS and FTIR results confirmed that chemical reduction of Cr (Ⅵ) to Cr (Ⅲ) also played a role in Cr (Ⅵ) removal in the presence of SBC-20-500. Moreover, the Cr (Ⅵ) removal capacity could still achieve 3.50 mg/g even after five adsorption-desorption cycles, indicating the satisfactory reusability of the as-prepared biochar. The results of this study may provide a win-win approach for simultaneous resource recovery from the wasted sulfate-reducing sludge (SRS) and highly-efficient remediation of Cr (Ⅵ)-contaminated environment.

Experimental Study on Thermal Runaway Process of 18650 Lithium-Ion Battery under Different Discharge Currents.

Lithium-ion batteries (LIBs) subjected to external heat may be prone to failure and cause catastrophic safety issues. In this work, experiments were conducted to investigate the influence of discharge current on the thermal runaway process under thermal abuse. The calibrated external heat source (20 W) and discharge currents from 1 to 6 A were employed to match the thermal abuse conditions in an operational state. The results indicated that the key parameters during the failure process, such as the total mass loss, the onset temperatures of safety venting and thermal runaway, and the peak temperature, are ultimately determined by the capacity inside the battery, and the discharge current can hardly change it. However, discharge currents can produce extra energy to accelerate the thermal runaway process. Compared with the battery in an open circuit, the onset time of thermal runaway was reduced by 7.4% at 6 A discharge. To quantify the effect of discharge current, the total heat generation by discharge current was calculated. The results show that a heat generation of 1.6 kJ was produced when the battery was discharged at 6 A, which could heat the cell to 34 °C (neglect of heat loss). This study simulates the failure process of the LIB in the operational state, which is expected to help the safety application of LIB and improve the reliability of the battery management system.

A comprehensive investigation on the thermal and toxic hazards of large format lithium-ion batteries with LiFePO4 cathode.

Toxic gases released from lithium-ion battery (LIB) fires pose a very large threat to human health, yet they are poorly studied, and the knowledge of LIB fire toxicity is limited. In this paper, the thermal and toxic hazards resulting from the thermally-induced failure of a 68 Ah pouch LIB are systematically investigated by means of the Fourier transform infrared spectroscopy (FTIR) and 1/2 ISO full scale test room. The LIBs with higher state of charge (SOC) are found to have greater fire risks in terms of their burning behavior, normalized heat release rate, and fire radiation, as well as the concentration of toxic gases. Specifically, the thermal hazards are evaluated by combining the effects of convective and radiative heat. The major toxic gases detected from the online analysis are CO, HF, SO2, NO2, NO and HCl. Furthermore, Fractional Effective Dose (FED) and Fractional Effective Concentration (FEC) models are used to quantitatively assess the overall gas toxicity. Results show that the effects of irritant gases are much more significant than those of asphyxiant gases. HF and SO2 have much greater toxicity than the other fire gases. The maximum FEC value is approaching the critical threshold in such fire scenarios.

Prediction of Three-Dimensional Downward Flame Spread Characteristics over Poly(methyl methacrylate) Slabs in Different Pressure Environments.

The present study is aimed at predicting downward flame spread characteristics over poly(methyl methacrylate) (PMMA) with different sample dimensions in different pressure environments. Three-dimensional (3-D) downward flame spread experiments on free PMMA slabs were conducted at five locations with different altitudes, which provide different pressures. Pressure effects on the flame spread rate, profile of pyrolysis front and flame height were analyzed at all altitudes. The flame spread rate in the steady-state stage was calculated based on the balance on the fuel surface and fuel properties. Results show that flame spread rate increases exponentially with pressure, and the exponent of pressure further shows an increasing trend with the thickness of the sample. The angle of the pyrolysis front emerged on sample residue in the width direction, which indicates a steady-burning stage, varies clearly with sample thicknesses and ambient pressures. A global non-dimensional equation was proposed to predict the variation tendency of the angle of the pyrolysis front with pressure and was found to fit well with the measured results. In addition, the dependence of average flame height on mass burning rate, sample dimension and pressure was proposed based on laminar diffusion flame theory. The fitted exponent of experimental data is 1.11, which is close to the theoretical value.