Review on heterogeneous oxidation and adsorption for arsenic removal from drinking water

The long term exposure of arsenic via drinking water has resulted in wide occurrence of arsenisim globally, and the oxidation of the non-ionic arsenite (As(III)) to negatively-charged arsenate (As(V)) is of crucial importance for the promising removal of arsenic. The chemical oxidants of ozone, chlorine, chlorine dioxide, and potassium permanganate may achieve this goal; however, their application in developing countries is sometimes restricted by the complicate operation and high cost. This review paper focuses on the heterogeneous oxidation of As(III) by solid oxidants such as manganese oxide, and the adsorption of As(V) accordingly. Manganese oxide may be prepared by both chemical and biological methods to achieve good oxidation performance towards As(III). Additionally, manganese oxide may be combined with other metal oxides, e.g., iron oxide, to improve the adsorption capability towards As(V). Furthermore, manganese oxide may be coated onto porous materials of metal organic frameworks to develop novel adsorbents for arsenic removal. To achieve the application in engineering works, the adsorbents granulation may be achieved by drying and calcination, agglomeration, and the active components may also be in situ coated onto the porous materials to maintain the oxidation and adsorption activities as much as possible. The novel adsorbents with heterogeneous oxidation and adsorption capability may be carefully designed for the removal of arsenic in household purifiers, community-level decentralized small systems, and the large-scale drinking water treatment plants (DWTPs). This review provides insight into the fundamental studies on novel adsorbents, the development of innovative technologies, and the demonstration engineering works involved in the heterogeneous oxidation and adsorption, and may be practically valuable for the arsenic pollution control globally.     

Highly inhibited transport of dissolved thallium(I) in manganese oxide-coated sand: Chemical condition effects and retention mechanisms

Thallium contamination in water can cause great danger to the environment. In this study, we synthesized manganese oxide-coated sand (MOCS) and investigated the transport and retention behaviors of Tl(I) in MOCS under different conditions. Characterization methods combined with a two-site nonequilibrium transport model were applied to explore the retention mechanisms. The results showed that Tl(I) mobility was strongly inhibited in MOCS media, and the retention capacity calculated from the fitted model was 510.41 mg/g under neutral conditions. The retention process included adsorption and oxidative precipitation by the manganese oxides coated on the sand surface. Cotransport with the same concentration of Mn(II) led to halving Tl(I) retention due to competition for reactive sites. Enhanced Tl(I) retention was observed under alkaline conditions, as increasing pH promoted electronegativity on the media surface. Moreover, the competitive cation Ca²⁺ significantly weakened Tl(I) retention by occupying adsorption sites. These findings provide new insights into understanding Tl(I) transport behavior in water-saturated porous media and suggest that manganese oxide-coated sand can be a cost-effective filter media for treating Tl-contaminated water.     

Oxidation of bisphenol F (BPF) by manganese dioxide

Bisphenol F (BPF), an environmental estrogen, is used as a monomer in plastic industry and its environmental fate and decontamination are emerging concern. This study focused on the kinetics, influencing factors and pathways of its oxidation by MnO₂. At pH 5.5, about 90% of BPF was oxidized in 20 min in a solution containing 100 μM MnO₂ and 4.4 μM BPF. The reaction was pH-dependent, following an order of pH 4.5 > pH 5.5 > pH 8.6 > pH 7.5 > pH 6.5 > pH 9.6. Humic acids inhibited the reaction at low (≤pH 5.5) and high pH (≥pH 8.6) at high concentrations. In addition, metal ions and anions also suppressed the reaction, following the order Mn²⁺ > Ca²⁺ > Mg²⁺ > Na⁺ and HPO₄²⁻ > Cl⁻ > NO₃⁻ ≈ SO₄²⁻, respectively. A total of 5 products were identified, from which a tentative pathway was proposed.     

Effects of cadmium,zinc, copper and manganese on hepatic parenchymal cell gluconeogenesis

Abstract

The effects of divalent cations on gluconeogenesis in enzy‐matically isolated rat hepatic parenchymal cells were examined. Cadmium, zinc and copper decreased glucose production from lactate (10 mM). However, manganese at 0.05 to 1.0 mM levels stimulated gluconeogenesis by the cells and reduced the effects of the Cd⁺², Zn⁺² and Cu⁺² on gluconeogenesis. The results indicate that under these in vitro conditions the cations altered an aspect of hepatic function—gluconeogenesis from lactate.     

Arsenic and Mn levels in Isaza (Gymnogobius isaza) during the mass mortality event in Lake Biwa, Japan

The present study measured the concentrations of 25 elements (Li, Mg, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Hg, Tl, Pb and Bi) in the whole body of Isaza which is an endemic fish species to Lake Biwa, Japan, and compared the values in the specimens from the mass mortality Isaza (MMI) and normal fresh Isaza (NFI). The mean levels of Mn and total As (T-As) were relatively higher in MMI than in NFI. In the T-As, highly toxic inorganic As was detected in MMI. Moreover we found Mn and As concentrations in surface sediment were extremely high and temporally increased. From all these results, we could infer that the dissolution of Mn and As from surface sediment of Lake Biwa might have been one of the cause for the mass mortality of Isaza.     

Synthesis of a highly recoverable 3D MnO2/rGO hybrid aerogel for efficient adsorptive separation of pharmaceutical residue

Water contamination by non-steroidal anti-inflammatory drugs, such as acetaminophen, is an emerging ecological concern. In this study, a new three-dimensional manganese dioxide-engrafted reduced graphene oxide (3D MnO₂/rGO) hybrid aerogel was developed for acetaminophen sequestration. The synthesis involved firstly the self-assembly of GO aerogel, followed by thermal reduction and in-situ MnO₂ growth by redox-reaction. The aerogel demonstrated interlinked planes with smooth surfaces deposited with MnO₂ nanospheres and pores of 138.4 – 235.3 µm width. The influences of adsorbent dosage, initial pH, acetaminophen concentration, temperature and contact time were investigated. It was determined that the adsorption of acetaminophen occurred on uniform sorption sites in the aerogel, as suggested by the best fit of data to the Langmuir isotherm, yielding a maximum adsorption capacity of 252.87 mg/g. This highest adsorption performance of the 3D MnO₂/rGO aerogel was attained at a dosage of 0.6 g/L, initial pH of 6.2 and temperature of 40°C. The process kinetics were in-line with the pseudo-first-order and pseudo-second-order kinetics at 10 and 20 – 500 mg/L concentrations, respectively. Thermodynamic assay showed the spontaneity and endothermicity features of the 3D MnO₂/rGO-acetaminophen system. The acetaminophen adsorption mechanisms were mainly hydrogen bonding and pore entrapment. Moreover, the as-synthesised aerogel was effectively regenerated using acetone and re-utilised in four adsorption-desorption cycles. Overall, the results highly recommend the implementation of the 3D MnO₂/rGO hybrid aerogel for purification of wastewater polluted by acetaminophen residue.     

Development of LnMnO3+σ perovskite on low temperature Hg0 removal

LnMnO_3+σ (Ln = La, Pr, Nd, Sm, Eu, Gd or Dy) perovskites synthesized by sol-gel method were employed for gaseous elemental mercury (Hg⁰) removal from coal-fired flue gas. Characterization results revealed the structure of the perovskites presented a phase transition process from rhombohedral system to O- and O'-orthorhombic structure with the change of A-site rare earth elements. The perovskites showed satisfactory Hg⁰ removal capacity in a narrow temperature range of 100–150°C. NdMnO_3+σ with an O-O’ orthorhombic structure presented the best Hg⁰ removal performance, which markedly depends on four factors: crystal structure, oxygen vacancy density, Mn⁴⁺/Mn³⁺ ratio and surface element segregation. The Hg⁰ removal mechanism was illustrated based on the mercury temperature programmed desorption experiment and X-ray photoelectron spectroscopy characterization. Both chemisorption and catalytic oxidation played a role in the Hg⁰ removal process. Chemisorption dominated the Hg⁰ removal, due to the slow catalytic oxidation rate at low temperature. This work preliminarily established the relation between the structure of rare earth manganese perovskite and Hg⁰ removal performance.     

Marine mineral resources: Effect of the low of the sea convention

The degree of security of investment afforded by the applicable legal regime is one of the most important factors affecting minerals projects. This article outlines the deep-sea mining regime contained in the recently adopted Law of the Sea Convention. A history of subsea mining, including petroleum mining, is presented and the events leading to adoption of the Convention are described. Those parts of the Convention relating to deep-sea mining are analysed, and the International Sea-Bed Authority is examined. It is concluded that deep-sea mining on a commercial scale is unlikely before the end of the decade.     

地热水除铁除锰工艺研究

通过对地热水的特点及其用途的分析 ,阐述了地热水除铁除锰机理 ,采用曝气充氧、天然锰砂接触氧化的除铁除锰工艺 ,并适当控制反冲洗强度和时间 ,使处理后地热水含铁、锰浓度达到标准 ,且不增加有害成分或减少有益成分。设备投资省、运行成本低 ,热损失小 ,是一种理想的地热水除铁工艺。