Mobility of arsenic and environmentally significant elements in mine tailings following liming

Remediation of a legacy tin-tailings site in northeast Tasmania, Australia was carried out by statutory authorities. This study evaluated the fate of As and other deleterious trace metals Cd, Cu, Fe and Zn (among others) following the application of lime and fertiliser. Arsenic concentrations in the tailings ranged from 86 mg/kg to 0.26 wt%. Surface application of lime resulted in a 100-fold reduction in dissolved As concentrations in on-site surface waters; from an average of 196 µg/L prior to lime addition, to between 2.0 and 7.4 µg/L post-amendment. The concentration of other deleterious elements, however, varied between dry and wet cycles. The concentrations of Cd, Cu and Zn in surface waters were high and similar to pre-remediation levels during dry conditions (0.4, 13.5 and 6.1 mg/L, respectively), and only below freshwater ecosystem protection values during wet conditions. Bioaccumulation of Cd was observed in the naturally occurring coloniser, Juncus pallidus, with 4–5 times more Cd in the above-ground biomass relative to the tailings. Ferric arsenate (scorodite) was the dominant source of As identified in the tailings mineralogy. Hydrous ferric oxides and Fe-bearing cassiterite were also identified as hosting As. The pH increase in the surface lime-amended tailings was inferred to result in precipitation of observed hydrous ferric oxides, hematite and goethite, providing high-surface area for adsorption of arsenate onto positively charged surfaces. Jarosite was observed in both the surface lime-amended and subsurface non-amended tailings and suggests a continued supply of acidity to the pore waters despite the application of lime. Leaching experiments showed that As was more mobile in the lime-dosed tailings than in subsurface non-amended tailings, likely owing to desorption in alkaline pH conditions. By contrast, the mobility of Cd, Cu and Zn in the surface lime-amended tailings was reduced by at least two orders of magnitude compared with subsurface non-amended tailings. Evaluation of the applied rehabilitation strategy highlights the limits of a single chemical remediation approach to a polymetallic (including metalloids) waste with complex mineralogy and large seasonal fluctuations. Rehabilitation of metalliferous mine sites requires a complete understanding of all environmentally significant elements and their pathways into local receptors.     

Carbonate precipitation in the alkaline lake Specchio di Venere (Pantelleria Island,Italy) and the possible role of microbial mats

Alkaline lakes like the hydrothermally affected lake Specchio di Venere (Pantelleria Island, Central Mediterranean) are typical geological settings harbouring calcified microbial mats. The present work is focused on the discrimination between biotic and abiotic processes driving carbonate precipitation in this lake, using hydrochemical, mineralogical and isotopic data. Hydrochemical analyses demonstrate that the lake is nearly 10−fold supersaturated with regard to aragonite and seasonally reaches hydromagnesite supersaturation. Microscopic observations depict organosedimentary laminated structures consisting of microbial communities and aragonitic precipitates, which are rather disseminated in pores than directly linked to microorganisms. Oxygen isotopic data indicate that authigenic carbonate crystallisation from evaporating water is the dominant precipitation process, further suggested by the absence of textural evidence of diagenetic processes. Conversely, the observed δ¹³C values reflect an influence of extracellular polymeric substances (EPS) on carbon fractionation during the precipitation process, due to the selective sequestration of ¹²C in the biomass. The above considerations suggest that at lake Specchio di Venere the carbonate precipitation is mainly of inorganic nature, but a minor role played by biologically influenced processes in microbial mats is not excluded.     

Gem corundum deposits of Madagascar: A review

Madagascar is one of the most important gem-producing countries in the world, including ruby and sapphires. Gem corundum deposits formed at different stages in the geological evolution of the island and in contrasting environments. Four main settings are identified: (1) Gem corundum formed in the Precambrian basement within the Neoproterozoic terranes of southern Madagascar, and in the volcano-sedimentary series of Beforona, north of Antananarivo. In the south, high-temperature (700 to 800 °C) and low-pressure (4 to 5 kbar) granulites contain deposits formed during the Pan-African orogenesis between 565 and 490 Ma. They accompany mafic and ultramafic complexes (ruby deposits of the Vohibory group), skarns at the contact between Anosyan granites and the Proterozoic Tranomaro group (sapphire deposits of the Tranomaro–Andranondambo district), and shear-zone corridors cross-cutting feldspathic gneisses, cordieritites and clinopyroxenites in the Tranomaro, Vohimena and Androyan metamorphic series (biotite schist deposits of Sahambano and Zazafotsy, cordieritites of Iankaroka and Ambatomena). The circulation of fluids, especially along discontinuities, allowed in-situ alkaline metasomatism, forming corundum host rocks related to desilicified granites, biotitites, “sakenites” and “corundumites”. (2) Gem corundum also occurs in the Triassic detrital formations of the Isalo group, as giant palaeoplacers in the Ilakaka–Sakaraha area. Here, sapphires and rubies may come from the metamorphic granulitic terranes of southern Madagascar. (3) Gem corundum deposits occur within the Neogene-Quaternary alkali basalts from Ankaratra (Antsirabe–Antanifotsy area) and in the Ambohitra Province (Nosy Be, Ambato and Ambondromifehy districts). Primary deposits are rare, except at Soamiakatra where ruby in gabbroic and clinopyroxenite xenoliths within alkali-basalts probably derive from mantle garnet peridotites. The blue-green-yellow sapphires typical of basaltic fields are always recovered in palaeoplacer (in karst formed upon Jurassic limestones from the Montagne d'Ambre, Antsiranana Province) and alluvial and soil placers (Ankaratra volcanic massif). (4) Deposits occur within Quaternary eluvial, colluvial and alluvial concentrations, such as high-quality rubies from the Andilamena and Vatomandry deposits.     

Leaching of rock-concrete interfaces

Summary  It has been shown that contacts between host rock and engineered barriers may be critical in the design of deep radioactive waste repositories. Water is expected to reach the interface zone after the resaturation of the geological massive and its presence may lead to concrete leaching. Such a phenomenon could increase the interface transmissivity and compromise the confinement of radioactive waste. This paper intends to investigate the influence of concrete leaching on the hydromechanical behaviour of host rock-concrete interfaces. Some concrete specimens have been subjected to an accelerated leaching process using ammonium nitrate. The hydromechanical response of degraded concrete-rock interfaces has been studied under shearing and compared to that of sound interfaces. Consistent with the results available in the literature on bulk concrete, a loss of mechanical strength has been observed for the degraded interface. Unlike the sound specimens, the degraded interfaces do not dilate when sheared and they tend to be closed, thereby preventing water from flowing. Correspondence: O. Buzzi, Centre for Geotechnical and Materials Modelling, School of Engineering, University of Newcastle, 2308 Callaghan NSW, Australia     

微生物氧化脱砷浸取金的方法

选用了耐砷能力强、具有分解硫化矿能力的氧化亚铁硫杆菌1s、1号和马兰3种菌株作为实验用菌,对DBF矿样做氧化浸出实验,就其氧化过程中砷含量、pH变化和金的最佳浸出条件均做了详细的研究。给出细菌氧化金矿过程随时间变化的规律及金的最佳浸出条件。     

Effects of poor quality irrigation waters on the nutrient leaching and groundwater quality from sandy soil

Sodium (Na⁺) in poor quality irrigation water participate in ion-exchange processes results in the displacement of base cations into solution and a raised concentration in groundwater. Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) of irrigation water on nutrients leaching and groundwater quality in columns of sandy soil. Three types of irrigation waters at three NaCl–CaCl₂ solutions with the following levels of SAR (5, 15, and 30) were synthesized in laboratory. With the application of solutions, exchange occurred between solution Na⁺ and exchangeable cations (Ca²⁺, Mg²⁺, and K⁺), resulting in the displacement of these cations and anions into solution. Increasing the level of SAR from 5 to 15 and 30 resulted in increase in the average exchangeable sodium percentage (ESP) of the soil from 10.4 to 20.3, and 32.5, respectively. Adverse effect of high Na⁺ concentration in the solutions on raising ESP was less pronounced in solution having low SAR. Leaching of Ca²⁺, Mg²⁺, K⁺, and P from soil with the application of solutions represents a significant loss of valuable nutrients. This sandy soil showed the high risk for nutrients transfer into groundwater in concentrations exceeding the groundwater quality standard. Irrigation with poor quality water, which is generally more sodic and saline than regional groundwater, increases the rate of sodification and salinization of shallow groundwater.     

A Comparative Study of the Use of Organoclay‐Based Formulations and Organic Amendment to Reduce the Leaching of the Herbicide MCPA in Soil

MCPA (4‐chloro‐2‐methylphenoxyacetic acid) is an acidic herbicide widely used on olive crops in Spain. Due to its anionic form at natural soil pH, there is high risk of leaching and groundwater contamination by the use of this herbicide. The aim of this work was to study the effects of organoclay‐based formulations of MCPA and olive oil waste amendment on MCPA leaching in a sandy loam soil. For this purpose, batch adsorption and column leaching studies were performed. The organoclays used to prepare the clay‐based formulations of MCPA were obtained by treating Wyoming montmorillonite (SWy‐2) and Arizona montmorillonite (SAz‐1) with an amount of hexadecyltrimethylammonium (HDTMA) cation equal to 100% of the CEC of the montmorillonites. The organic residue used in this study was a solid waste from olive oil production (olive oil waste, OOW). The soil was amended with the organic residue at the rate of 10% (w/w). Batch release and column leaching studies indicated that organoclay‐based formulations of MCPA reduced the release rate and the leaching of the herbicide as compared to the use of a conventional formulation containing the herbicide in an immediately available form. The increase in soil organic matter of the soil upon amendment with the organic residue also resulted in greater adsorption and reduced leaching of MCPA in the soil. Accordingly, both the use of organoclay‐based formulations and the amendment of soil with OOW are proposed as efficient strategies to reduce extensive leaching losses associated with the application of MCPA in high‐risk scenarios, such as Mediterranean olive groves.     

不同岩溶生态系统中元素的地球化学迁移特征比较——以广西弄拉和弄岗自然保护区为例

研究了广西弄拉和弄岗自然保护区两种不同岩溶生态系统的元素地球化学循环特点,结果表明,弄拉、弄岗的成土过程都表现为Si和Fe相对累积,而其它化学元素则表现为相对淋失。弄岗与弄拉相比,其元素的淋失程度更为强烈,但在植物中两者表现出比较相似的元素地球化学特点。弄岗泉水p H比弄拉的低,水的溶蚀能力增大,水中可溶物增多,元素循环也比弄拉的快。      

SHRIMP Zircon U‐Pb Dating of Alkaline Dykes in the Pobei Area,Beishan Rift,Xinjiang Autonomous Region,China: Implications for Tectonic Setting and Mantle Plume Events

In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270–290 Ma mafic-ultramafic intrusions associated with Ni-Cu sulphide mineralization. These mafic-ultramafic intrusions are typically found along E-W major faults in the Tianshan orogenic belts. We report SHRIMP U-Pb dating of zircons from a dyke of alkaline composition, which yielded a mean age of 252±9 Ma. Alkaline dykes of the same age are found in the Altay region of Siberia. This age is younger than the 270–290 Ma intraplate magmatic events that produced the mafic-ultramafic intrusions in the region, but in general agreement with the 250–260 Ma Permian plume event that gave rise to the Siberian traps and the Emeishan flood basalts in SW China. We suggest that there is a link between the Emeishan event and the dyke swarm in the Beishan rift and that the intraplate magmatism at 270–290 Ma reflects an early stage of mantle plume activity. The N-S trending dyke swarm in the Beishan rift may represent a later stage in the evolution of mantle plume activity in the NW and SW of China. We also speculate that in Beishan rift and possibly elsewhere in the Tianshan region, the dykes fed basaltic volcanism, whose products have since been eroded due to the strong uplift of the Tianshan orogen as a result of the India-Eurasia collision in the Cenozoic.     

冀北水泉沟岩体西段锆石U-Pb年代学及Hf同位素研究

冀北水泉沟碱性正长杂岩体位于华北克拉通北缘中段,主要岩性为正长岩、石英正长岩、碱性正长岩、角闪正长岩、角闪二长岩和碱长花岗岩等.为了避开后期热液蚀变作用的影响,作者采集了远离东坪-后沟金矿田的水泉沟岩体西段无蚀变的角闪二长岩、角闪正长岩样品,并对这些代表性岩石进行了锆石U-Pb年代学和锆石Hf同位素研究.LA-ICP-MS锆石U-Pb年龄表明,角闪二长岩结晶年龄为372.7±2.5Ma,角闪正长岩结晶年龄为372.7±2.4Ma,二者年龄结果一致,表明水泉沟碱性杂岩体西段形成于晚泥盆世.角闪二长岩的锆石ε_Hf(t)＝-12.4~-8.9,两阶段Hf模式年龄为1.93~2.16Ga,平均2.05Ga.角闪正长岩的锆石ε_Hf(t)＝-13.2~-11.1,两阶段Hf模式年龄为2.07~2.21Ga,平均2.13Ga.考虑到两种岩石的模式年龄与华北基底变质岩的形成年龄相近,我们初步认为水泉沟碱性杂岩体西段角闪二长岩和角闪正长岩可能主要来源于富集岩石圈地幔部分熔融形成的镁铁质岩浆与古老的中下地壳变质岩部分熔融形成的长英质岩浆混合的结果.野外地质和地球化学数据表明,水泉沟碱性杂岩体形成于晚造山阶段的张性构造环境.