Aqueous stability and mobility of C 60 complexed by sodium dodecyl benzene sulfonate surfactant

Surfactant complexation may have significant effects on the environmental behavior of nano-particles. In order to understand the ecological exposure of nano-materials, it is important to determine the stability and mobility of surfactant-complexed nano-materials in aqueous systems. In this study, the aggregation and transport of C-60 complexed by the surfactant sodium dodecyl benzene sulfonate (SDBS) were investigated. It was found that SDBS-complexed C-60 had a.-potential of -49.5 mV under near-neutral pH conditions and remained stable during an aging period of 15 days. It had a critical coagulation concentration of 550 mmol/L for NaCl, which was higher than common natural colloids and many kinds of raw nano-materials, and was comparable to those of many kinds of surface-modified nano-materials. SDBS enhanced the stability of C-60 colloid; however, at the same time, it also enhanced the colloidal particle aggregation rate. Much higher mobility was found for SDBS-complexed C-60 than C-60 colloid. Increase in ionic strength, Ca2+ concentration or Al3+ concentration decreased the mobility. In general, SDBS-complexed C-60 had high stability and mobility. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V

The Recycling of Acid Wastewater with High Concentrations of Organic Matter: Recovery of H₂SO₄ and Preparation of Activated Carbon

Little work has been focused on the recycling of hazardous acid waste with high concentrations of organic matter from petroleum refining. This study developed an innovative, effective, and simple method for the recycling of acid waste that can successfully resolve this significant problem in industry. After parameter optimization, the optimal process is as follows. (1) Through heat treatment at 170 °C, liquid acid waste was transformed into solid; (2) by washing the solids, 70% by weight of sulfuric acid was recycled; and (3) the solid residue after washing was activated by alkali (NaOH or KOH) at an alkali and organic carbon ratio of 2:1, at a temperature of 650 °C for 60 min, producing superior-grade activated carbon with a specific surface area of 1378 m2/g, a pore volume of 0.5107 cm2/g, an iodine number of 1800 mg/g, and a methylene blue adsorption capacity of 240 mg/g. Thus, in this way, both waste sulfuric acid and organic impurities are turned into valuable resources, and no hazardous waste gypsum residues are generated. This method both reduces carbon emissions and recycles valuable resources, which is of important environmental and economic significance

Mechanisms of UV-Light Promoted Removal of As(V) by Sulfide from Strongly Acidic Wastewater

Strongly acidic wastewater with a high arsenic concentration is produced by a number of industries. The removal of As­(V) (H₃AsO₄) by sulfide from strongly acidic wastewater remains a difficult issue. This study proposed a UV-assisted method to efficiently remove As­(V) by sulfide, and the involved mechanisms were systematically investigated. In the dark, the low removal efficiency of As­(V) by sulfide was attributed to the slow formation and transformation of an intermediate species, i.e., monothioarsenate (H₃AsO₃S), in the As­(V) sulfuration reaction, which were the rate-controlling steps in this process. However, UV irradiation significantly promoted the removal efficiency of As­(V) not only by promoting the formation of H₃AsO₃S through light-induced HS^• and •H radicals but also by enhancing the transformation of H₃AsO₃S through a charge-transfer process between S­(-II) and As­(V) in the H₃AsO₃S complex, leading to the reduction of As­(V) to As­(III) and the oxidation of S­(-II) to S(0). The formed As­(III) species immediately precipitated as As₂S₃ under excess S­(-II). Kinetic modeling offered a quantitative explanation of the results and verified the proposed mechanisms. This study provides a theoretical foundation for the application of light-promoted As­(V) sulfuration removal, which may facilitate the recycling and reuse of arsenic and acid in strongly acidic wastewater

Adsorption of -Nitrophenol onto PDMDAAC-Modified Bentonites

A novel organobentonite was prepared by modifying bentonite with poly(dimethyldiallylammonium chloride) (PDMDAAC), a harmless and cost-effective type of polycation. Zeta potential and X-ray diffraction measurements suggest that PDMDAAC was intercalated into the bentonite interlayer space. PDMDAAC—bentonite has been found to be effective for the removal of p -nitrophenol with a removal rate of 81.4% being achieved. The adsorption process was pH-dependent and was slightly decreased by the Ca 2+ and Mg 2+ ions co-existing in the solution. A dual-phase adsorption mechanism was suggested for the process. The adsorbents obtained from the regeneration of PDMDAAC—bentonite still exhibit good adsorption capacities

Mechanism for Photopromoted Release of Vanadium from Vanadium Titano-Magnetite

The release of V from vanadium titano-magnetite, a predominant natural source of V, was studied under light irradiation. The release rate of V from vanadium titano-magnetite was accelerated by light irradiation, and the oxidation of V was detected. The essence of the photopromoted release of V is that the immobile low valence V is transformed to the mobile V­(V) by photoinduced active species generated from the photocatalysis process of magnetite. Among the photoinduced active species, •OH and H₂O₂ were recognized as the most important oxidizing agents. Not only can they directly convert the immobile low-valence V to the mobile V­(V) but also initiate the Fenton reaction, which produces more •OH and then further promotes the oxidation of low-valence V. In addition, a conceptual model of the photo promoted release of V was proposed. This study, as part of a broader study of the release behavior of V, can improve the understanding of the pollution problem about V, as well as the fate and environmental geochemistry cycling of V in the natural environment

A modified zone model on vertical cable tray fire in a confined compartment in the nuclear power plant

Room fire with vertical cable tray involves upward flame spread along the cable. Assessing the vertical cable tray fire hazard in confined spaces has been challenging because of the strong coupling between flame spread and heat transfer. Long computing time is required in using sophisticated field model with computational fluid dynamics. Therefore, developing an appropriate zone model in a cable room fire with experimental validation is required for engineering applications. In this study, a vertical cable tray fire in a confined compartment was simulated using a modified zone model along three new areas on having temporal variations of the fire position, upward-spreading cable flame considered as a burning source moving at a constant speed, and validated through full-scale experiments on vertical cable tray fire with two typical cable-line spacing. The modified zone model can predict accurately the upper-layer temperature in the compartment. The accuracy is at least 25% higher than the model with fixed fire position. The measured temperature at different heights started to decrease at different times, which was due to the vertical spreading of the cable flame. For interface height, the relative error and normalized Euclidean distance in the time-varying fire position model can be improved by 50%

Removal of Arsenic from Strongly Acidic Wastewater Using Phosphorus Pentasulfide As Precipitant: UV-Light Promoted Sulfuration Reaction and Particle Aggregation

Strongly acidic wastewater (H₂SO₄) with a high arsenic concentration is produced by many industries. The removal of arsenic by traditional sulfide (e.g., Na₂S, FeS) from strongly acidic wastewater introduces cations (Na⁺ and Fe²⁺) to the solution, which may prevent the recycle of acid. In this study, a new sulfuration agent, phosphorus pentasulfide (P₂S₅) was employed, and its feasibility in arsenic removal from strongly acidic wastewater was investigated. In the dark, As­(III) was efficiently removed, but the removal rate of As­(V) was rather slow, which was the crucial defect for this method. We found that this defect can be efficiently overcome by UV irradiation through accelerating the formation and transformation of an intermediate species, monothioarsenate (H₃AsO₃S) in the As­(V) removal process. In addition, the hydrolysis of P₂S₅ was enhanced under UV irradiation, which resulted in the increase of the arsenic removal efficiencies. Besides, the aggregation of the formed particles was also promoted. Different from FeS and Na₂S, P₂S₅ introduces H₃PO₄ instead of cations to the solution, which can facilitate the recycle and reuse of arsenic and acid in strongly acidic wastewater