Arsenate immobilization associated with microbial oxidation of ferrous ion in complex acid sulfate water

Chemical, XRD, SEM, RS, FTIR and XPS techniques were used to investigate arsenate immobilization associated with microbial Fe 2+ oxidation in a complex acid sulfate water system consisting of a modified 9K solution (pH 2.0) plus As, Cu, Cd, Pb, Zn and Mn. At a 1:12.5:70 molar ratio of As:Fe:S, schweretmannite formation was impeded. This was in contrast with the predominant presence of schwertmannite when the heavy metals were absent, suggesting that a schwertmannite binding model is not valid for explaining arsenate immobilization in the complex system. In this study, arsenate was initially immobilized through co-precipitation with non-Fe metals and phosphate. Subsequently when sufficient Fe 3+ was produced from Fe 2+ oxidation, formation of a mixed iron, arsenate and phosphate phase predominated. The last stage involved surface complexation of arsenate species. Pb appeared to play an insignificant role in arsenate immobilization due to its strong affinity for sulfate to form anglesite. Phosphate strongly competed with arsenate for the available binding sites. However, As exhibited an increased capacity to compete with P and S for available binding sites from the co-precipitation to surface complexation stage. Adsorbed As tended to be in HAsO 42- form. The scavenged arsenate species was relatively stable after 2464-h aging. © 2012 Elsevier B.V.

The role of rainwater-borne hydrogen peroxide in the release of arsenic from arsenopyrite

A microcosm experiment was conducted to examine the effects of hydrogen peroxide (at a concentration range of 5-50μM) on the release of arsenic from the dissolution of arsenopyrite, a dominant arsenic-bearing mineral occurring in natural environments. This was to simulate the reaction between rainwater-borne hydrogen peroxide and arsenopyrite grains exposed on the land surfaces during rainfall events. The results showed that the release of arsenic from arsenopyrite was enhanced by the H2O2 at this concentration range. It was also evident that H2O2 played an indirect role in the transformation of arsenite into arsenate in the solutions, which might affect the fate of the liberated arsenic species due to the formation of FeAsO4 precipitates. The preliminary study sheds some light on the possible role of rainwater-borne H2O2 in the weathering of arsenopyrite, which could complicate the geochemical processes governing the release, transport and fate of arsenopyrite-derived arsenic in natural environments. This provides a rationale for conducting additional laboratory-based investigations to obtain further insights into the chemical mechanisms and kinetics, and the subsequent field-scale study to validate the research findings. © 2013 Elsevier Ltd

Comparison of copper scavenging capacity between two different red mud types

A batch experiment was conducted to compare the Cu scavenging capacity between two different red mud types: the first one was a highly basic red mud derived from a combined sintering and Bayer process, and the second one was a seawater-neutralized red mud derived from the Bayer process. The first red mud contained substantial amounts of CaCO3, which, in combination with the high OH- activity, favored the immobilization of water-borne Cu through massive formation of atacamite. In comparison, the seawater-neutralized red mud had a lower pH and was dominated by boehmite, which was likely to play a significant role in Cu adsorption. Overall, it appears that Cu was more tightly retained by the CaCO3-dominated red mud than the boehmite-dominated red mud. It is concluded that the heterogeneity of red mud has marked influences on its capacity to immobilize water-borne Cu and maintain the long-term stability of the immobilized Cu species. The research findings obtained from this study have implications for the development of Cu immobilization technology by using appropriate waste materials generated from the aluminium industry. © 2012 by the authors

Capping hazardous red mud using acidic soil with an embedded layer of zeolite for plant growth

A nearly three-year microcosm experiment was conducted to test the effectiveness of capping red mud using acidic soil with an embedded layer of zeolite in sustaining the growth of a grass species. This sandwich-structured design allowed self-sustaining growth of the plants under rain-fed conditions no matter whether the underlying red mud was neutralized or not. During the initial stage, the plants grew better when the red mud was not neutralized with MgCl2 probably due to pH rise in the root zone. Neutralization of red mud led to salinization and pH decrease in the root zone. However, the difference in plant growth performance between these scenarios became less remarkable over time due to gradual improvement of soil conditions in the neutralized scenarios. Continuous leaching of soluble salts and alkali by rainwater extended the root zone to the red mud layer. As a result of vegetative production, soil organic matter rapidly accumulated. This, combined with increase in pH and decrease in salinity, markedly facilitated microbial activities and consequently improved the supply of nutrients. This study provides a basis for field-scale experimental design that will have implications for effectively establishing vegetative cover in red mud disposal sites to control dust hazards. © 2014 Taylor & Francis

Spatial Variation and Fractionation of Bed Sediment-Borne Copper, Zinc, Lead, and Cadmium in a Stream System Affected by Acid Mine Drainage

An investigation was conducted to examine the spatial variation and fractionation of bed sediment-borne Cu, Zn, Pb, and Cd in a stream system affected by acid mine drainage. The pH had a major control on the spatial variation pattern of soluble, exchangeable, and carbonate-bound Cu, Zn, and Cd. There was a prominent concentration peak of carbonate-bound, oxide-bound, and organic-bound metals at the 29 km station, as controlled by the abundance of organic C, carbonate C, and oxides of manganese and iron. In general, the residual fraction was the dominant form for all four investigated metals. It was likely that oxide-Mn played a more important role in binding Zn and Cd than oxide-Fe did. In contrast, Cu had a higher affinity for iron hydrous oxides than for manganese oxide. Pb had a higher affinity for oxides of iron and manganese than for carbonates and organic matter. The presence of organic-bound metals in both the acidic upstream reach and non-acidic downstream reach suggests that the binding of these metals by organic matter was not markedly affected by pH, while the correspondence of organic C peak and organic-bound metal peaks at the 29 km station indicates a strong control by organic matter abundance on the quantity of organic-complexed metals. © 2012 Copyright Taylor and Francis Group, LLC

Peer performance and the asymmetric timeliness of earnings recognition

This paper investigates the impact of peer performance on the asymmetric timeliness of earnings recognition. We find a positive relationship between peers' weak performance and timely bad news disclosure. Our results are robust to a variety of tests, including instrument variable approach, difference-in-differences analysis, alternative measures and subsample analysis. Consistent with the notion that weak peer performance increases investors' demand for information, the relationship is more profound for firms suffering from high information externality, with weak governance and high information asymmetry. Furthermore, we find that the relationship is difficult to reconcile with the explanation of managers' herding behaviour. In addition, we show that conservative accounting information disclosure due to weak peer performance alleviates managerial bad news hoarding and information asymmetry for underperforming firms, but distorts investment decisions for outperforming firms. We highlight the spillover effect of peer performance on conservative accounting information and the related heterogeneous outcomes

Recent advancements in N-ligated group 4 molecular catalysts for the (co)polymerization of ethylene

Group 4 metal (Zr, Ti, Hf) catalysts for olefin polymerization and specifically those based on non-metallocene complexes have continued to be a subject of intense study in homogeneous catalysis. With a view to forming new or improved polyolefinic materials, complexes bearing N-donor anionic ligands such as β-diketiminate, amidinate, guanidinate, amido, imido as well as mixed N-donor ligands including N,C,C-azaallyl and N,O-phenoxy-imine, have been central to many key developments; high catalytic activities for homo- and copolymerization of ethylene have been a highlight of their catalysis. The fine tuning of these nitrogen-containing ligands significantly controls the catalytic performances of their metal catalysts as well as the structural properties of the resulting polymers with high molecular weight or even ultra-high molecular weight materials accessible. In this review the focus is on more recent publications in the field, in which we correlate the influence of ligand structure with the catalytic performance and microstructure of the polyethylenes. Furthermore, we examine the effects of co-catalyst on activity and thermostability of the precatalyst while efforts directed towards the copolymerization of ethylene with 1-hexene are also summarized. Overall, this work presents an overview of current knowledge pertaining to catalyst design and especially with regard to how the modulation of steric and electronic properties impact on the (co)polymerization process

Unimodal polyethylenes of high linearity and narrow dispersity by using ortho-4,4′-dichlorobenzhydryl-modified bis(imino)pyridyl-iron catalysts

Six different examples of 4,4′-dichlorobenzhydryl-substituted 2,6-bis(arylimino)pyridyl-iron(ii) chloride complex, [2-{{2,6-((p-ClPh)2CH)2-4-MeC6H2}N = CMe}-6-(ArN CMe)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-iPr2C6H3Fe3, 2,4,6-Me3C6H2Fe4, 2,6-Et2-4-MeC6H2Fe5, 2,6-((p-ClPh)2CH)2-4-MeC6H2Fe6), have been synthesized in good yield and characterized by various spectroscopic and analytical techniques. The molecular structures of Fe2 and Fe5 emphasize the uneven steric protection of the ferrous center imposed by the unsymmetrical N,N,N′-chelate. When treated with either MAO or MMAO (modified-MAO) as activators, Fe1-Fe5 exhibited very high productivities at elevated temperature with peak performance of 21.59 × 106 g PE mol−1(Fe) h−1 for Fe5/MMAO at 50 °C and 15.65 × 106 g PE mol−1(Fe) h−1 for Fe1/MAO at 60 °C. By contrast, the most sterically hindered Fe6 was either inactive (using MAO) or displayed very low activity (using MMAO). As a further feature, this class of iron catalyst was capable of displaying long lifetimes with catalytic activities up to 10.77 × 106 g PE mol−1(Fe) h−1 observed after 1 h. In all cases, strictly linear and unimodal polyethylene was formed with narrow dispersity, while the polymer molecular weight was strongly influenced by the aluminoxane co-catalyst (Mw using MAO > MMAO) and also by the steric properties of the second N-aryl group (up to 32.9 kg mol−1 for Fe3/MAO)

Plastomeric-like polyethylenes achievable using thermally robust N,N'-nickel catalysts appended with electron withdrawing difluorobenzhydryl and nitro groups

A new set of five unsymmetrical N,N'-diiminoacenaphthenes, 1-[2,6-{(4-FC6H4)2CH}2-4-NO2C6H4N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2C6H3L1, 2,6-Et2C6H3L2, 2,6-iPr2C6H3L3, 2,4,6-Me3C6H2L4, 2,6-Et2-4-MeC6H2L5), have been synthesized and used to prepare their corresponding nickel(ii) halide complexes, LNiBr2 (Ni1-Ni5) and LNiCl2 (Ni6-Ni10). The molecular structures of Ni3(OH2) and Ni4 reveal distorted square pyramidal and tetrahedral geometries, respectively, while the 1H NMR spectra of all the nickel(ii) (S = 1) complexes show broad paramagnetically shifted peaks. Upon activation with either methylaluminoxane (MAO) or ethylaluminum sesquichloride (Et3Al2Cl2, EASC), Ni1-Ni10 displayed very high activities for ethylene polymerization with the optimal performance being observed using 2,6-dimethyl-containing Ni1 in combination with EASC (1.66 × 107 g PE mol-1 (Ni) h-1 at 50 °C) which produced high molecular weight plastomeric polyethylene (Mw = 3.93 × 105 g mol-1, Tm = 70.6 °C) with narrow dispersity (Mw/Mn = 2.97). Moreover, Ni1/EASC showed good thermal stability by operating effectively at an industrially relevant 80 °C with a level of activity (6.01 × 106 g of PE mol-1 (Ni) h-1) that exceeds previously disclosed N,N'-nickel catalysts under comparable reaction conditions. This improved thermal stability and activity has been ascribed to the combined effects imparted by the para-nitro and fluoride-substituted benzhydryl ortho-substituents

Exceptionally high molecular weight linear polyethylene by using N,N,N′-Co catalysts appended with a N′-2,6-bis{di(4-fluorophenyl)methyl}-4-nitrophenyl group

The bis(arylimino)pyridines, 2-[CMeN{2,6-{(4-FC6H4)2CH}2–4-NO2}]-6-(CMeNAr)C5H3N (Ar = 2,6-Me2C6H3 L1, 2,6-Et2C6H3 L2, 2,6-i-Pr2C6H3 L3, 2,4,6-Me3C6H2 L4, 2,6-Et2–4-MeC6H2 L5), each containing one N′-2,6-bis{di(4-fluorophenyl)methyl}-4-nitrophenyl group, have been synthesized by two successive condensation reactions from 2,6-diacetylpyridine. Their subsequent treatment with anhydrous cobalt (II) chloride gave the corresponding N,N,N′-CoCl2 chelates, Co1 – Co5, in excellent yield. All five complexes have been characterized by 1H/19F NMR and IR spectroscopy as well as by elemental analysis. In addition, the molecular structures of Co1 and Co3 have been determined and help to emphasize the differences in steric properties imposed by the inequivalent N-aryl groups; distorted square pyramidal geometries are adopted by each complex. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), precatalyts Co1 – Co5 collectively exhibited very high activities for ethylene polymerization with 2,6-dimethyl-substituted Co1 the most active (up to 1.1 × 107 g (PE) mol−1 (Co) h−1); the MAO systems were generally more productive. Linear polyethylenes of exceptionally high molecular weight (Mw up to 1.3 × 106 g mol−1) were obtained in all cases with the range in dispersities exhibited using MAO as co-catalyst noticeably narrower than with MMAO [Mw/Mn: 3.55–4.77 (Co1 – Co5/MAO) vs. 2.85–12.85 (Co1 – Co5/MMAO)]. Significantly, the molecular weights of the polymers generated using this class of cobalt catalyst are higher than any literature values reported to date using related N,N,N-bis (arylimino)pyridine-cobalt catalysts