Occurrence,distribution and source of arsenic in deep groundwater wells in Maydavood area,southwestern Iran

Groundwater in some deep wells of Maydavood aquifer, southwestern Iran, contains relatively high concentrations of arsenic. Detailed hydrochemical analysis of these groundwaters (with ICP-OES instrument) showed that concentrations of iron, manganese, nickel, and vanadium are also high in them and concentrations of total arsenic in 81% of deep wells are greater than World Health Organization’s permissible value (10 ppb). XRF analysis of surrounding geological formations and aquifer sediments proposed that original source of arsenic in aquifer material can be attributed to minerals from Asmari Formation. It appears that a key mechanism for arsenic mobilizing to deep wells is microbial biodegradation of petroleum related organic matters (PROMs), which exist in aquifer sediments and originates from the bedrock of the aquifer (Gachsaran Formation). This process is followed by microbially mediated reductive dissolution of arsenic-bearing iron/manganese oxyhydroxides/oxides and further by nickel and vanadium mobilizing to groundwater. According to hydrogeochemical conditions and cluster analysis, water wells in Maydavood aquifer are divided to four subgroups: the wells with mildly reducing condition (subgroup I), moderately reducing condition (subgroup II), reducing condition (subgroup III), and high reducing condition (subgroup IV). Affected wells to arsenic are belonged to subgroups III and IV.     

Groundwater contamination with arsenic in Sherajdikhan,Bangladesh: geochemical and hydrological implications

An integrated study has been carried out to elucidate the distribution and occurrence of arsenic in selected groundwater samples in the area of Sherajdikhan, Bangladesh. Arsenic and other parameters (T, pH, EC, Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, PO₄ ³⁻, Fe, Mn and DOC) have been measured in groundwater samples collected from shallow/deep tube wells at different depths. Hydrogeochemical data suggest that the groundwaters are generally Ca–Mg–HCO₃ and Mg–Ca–HCO₃ types with bicarbonate (HCO₃ ⁻) as the dominant anion, though the other type of water has also been observed. Dissolved arsenic in groundwater ranged from 0.006 to 0.461 mg/l, with 69% groundwater samples exceeded the Bangladesh limit for safe drinking water (0.05 mg/l). Correlation and principal component analysis have been performed to find out possible relationships among the examined parameters in groundwater. Low concentrations of NO₃ ⁻ and SO₄ ²⁻, and high concentrations of DOC, HCO₃ ⁻ and PO₄ ³⁻ indicate the reducing condition of subsurface aquifer where sediments are deposited with abundant organic matter. Distinct relationship of As with Fe and Mn, and strong correlation with DOC suggests that the biodegradation of organic matter along with reductive dissolution of Fe–Mn oxyhydroxides has being considered the dominant process to release As in the aquifers studied herein.     

Experimental study of the stability of metals associated with iron oxyhydroxides precipitated in acid mine drainage

Iron oxyhydroxide precipitates associated with acid mine drainage (AMD) from the Stearns Coal Zone in southeastern Kentucky were analyzed for their metal (Al, Cu, Pb, Mn, Ni, and Zn) content. The most concentrated metals within these sediments are nickel (27–32×10³μmol/kg), manganese (16–29×10³μmol/kg), and aluminum (13–22×10³μmol/kg) as determined by HCl-HNO₃ digestion. Metal concentrations associated with the organic fraction as determined by H₂O₂ digestion were generally far lower, with the exception of aluminum. "Batch" experiments (at initial pH=2.0) were used to analyze the stability of these metals associated with a contaminated soil. Aluminum was the most mobile of the metals, presumably the result of the formation of aluminum-sulfate aqueous complexes. The solubilization rates for nickel and iron were very similar, suggesting that nickel, unlike the other metals, coprecipitated with iron in these sulfatic oxyhydroxides. Received: 9 October 1997 · Accepted: 15 December 1997     

Pb on groundwater particles,Door County,Wisconsin

Pb was detected on groundwater particles larger than 0.45m. Pb concentration (micrograms per liter) showed positive correlations with particle concentration (milligrams per liter) at five sampled wells, although the slopes of the best-fit lines were different. X-ray fluorescence scans suggested that the particles primarily consist of K-Al silicate minerals, and that Pb is absorbed onto Fe oxyhydroxide coatings on Mg-rich silicates. Particle compositions varied at wells, but remained consistent at each well through the sampling period of a month. The particulate nature of Pb in groundwater could cause the spatial and temporal variations due to: (1) the unique composition of particles at wells, (2) the irregular pathways for groundwater particles, (3) the unpredictable amount of Pb-carrying particles entering the groundwater system during recharge events, and (4) the irregular sampling of groundwater particles subsequently dispersed along the advective flow path.     

Rare earth element studies of surficial sediments from the southwestern Carlsberg Ridge,Indian Ocean

The rare earth element (REE) contents of sixteen surficial calcareous sediments from the southwestern Carlsberg Ridge, Indian Ocean, have been determined. The total REE vary from 35 ppm to 126 ppm and are inversely related to the calcium carbonate content. REEs show a strong positive correlation with Al + Fe + K + Mg + Na (r ²= 0.98) and Mn + Fe + Cu + Ni (r ²= 0.86) suggesting that the REE is associated with a combined phase of clays (mainly illite) and Mn-Fe oxyhydroxides. The aeolian input into these sediments is suggested from the weak positive Eu/Eu* anomaly. Shale-normalized (NASC) pattern along with La_(n)/Yb_(n) ratio suggest enrichment of heavy REE (HREE) relative to the light REE (LREE) with a negative Ce/Ce* anomaly implying retention of a bottom water REE pattern. An erratum to this article is available at .     

Cl-/SO42-铁盐对含可溶性胞外多聚物Acidithiobacillus ferrooxidans溶液中铁矿物形成的影响

铁细菌胞外多聚物作用下聚集的铁可通过氧化或者沉淀作用使铁稳定或沉积,从而形成铁矿物。本文基于铁细菌胞外多聚物(extracellular polymeric substances,EPS)对铁矿物形成的调控作用,介绍了Cl-/SO_4~(2-)的Fe(Ⅲ)或Fe(Ⅱ)盐作用下,含可溶性EPS的氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)溶液中铁矿物的形成,观察了溶液pH值变化及形成铁矿物的矿相与结构,并采用XRD、FTIR和FESEM对其进行表征。结果发现反应溶液中OH-离子可与Fe3+形成微米级"针垫"聚集球状或纳米级小球形施威特曼石和微米级"菱形"块状黄钾铁矾铁矿物沉淀。反应溶液中的可溶性EPS可调控和促进铁矿物的形成,但对Fe2+的氧化未产生影响;外源Fe盐可促进施威特曼石向黄钾铁矾转化。随着Cl-/SO_4~(2-)摩尔比例的增加(即Cl-含量的不断增加),两矿相间的转化明显受到抑制,且铁矿物颗粒之间的集聚作用明显减弱;反之,SO_4~(2-)含量升高时,有利于铁矿物间的转化和聚集球状颗粒形貌结构的形成。     

The role of biogeochemical processes in minimising uranium dispersion from a mine site

The Ranger Uranium Mine located in the Alligator Rivers Region of the Northern Territory lies in the tropical zone and has an annual wet-dry monsoonal climate. Following the commencement of the wet season, runoff from the waste rock dump accumulates in a retention pond (RP4). This water is permitted to discharge to the nearby Magela Creek once minimum flow of 5 m³/sec is reached and following filling of the pond. The discharge proceeds via a channel, experimental wetland and a backflow billabong (Djalkmarra Billabong) which acts as a natural wetland filter and flows out to Magela Creek.This study examines monitoring data for water releases over 3 wet seasons. I wet season with no release and 4 dry seasons. The monitoring data comprised electrical conductivity (EC). pH, Na, K. Ca, Mg. HCO⁻₃ SO²⁻₄, Cl⁻ and U (total or filtered, < 0.45 μm). Some ICP-MS scans of trace elements were also undertaken with particular reference being made to Re and U.Specific features of the sequence of water accumulation, release and reconstitution of Djalkmarra Billabong are able to show that U is effectively removed from solution, from about 50 ppb down to < 1 ppb. Soluble salts may remain in the water column and are removed by dilution following discharge to Magela Creek. Sediment levels show no increase in U concentration with time.The pH of the billabong water during releases (6.0–6.6) suggests that cationic forms of U, such as (UO₂)₃ (OH)⁵, predominate, favouring adsorption on to the humic-rich sediments of the natural wetland. The application of this principle enables U to be removed efficiently from waste water and to be contained within the mine lease.     

自然光下羟基氧化铁处理水溶液中甲基橙的研究

自然界广泛存在羟基氧化铁,研究其在地质中的光催化作用对环境的污染防治有着重要意义。在自然光照下,用针铁矿和四方纤铁矿处理甲基橙溶液,不同反应时间取样经高速离心后,用紫外/可见分光光度计和傅立叶变换显微红外光谱仪(FTIR)进行分析。结果表明,FeOOH/Visible light体系能使甲基橙溶液脱色率达83%,四方纤铁矿比针铁矿有更好的光催化降解效果;FeOOH/Visible light体系能将甲基橙分子中的偶氮键打开,从而使溶液脱色,FeOOH/Visible lihgt/H2O2则能进一步降解甲基橙,使其分子中的苯环部分打开。     

铁细菌胞外多聚物对铁矿物的调控形成及其环境意义

环境介质溶液中铁的水解作用和稳定化作用主要受铁细菌及其代谢有机物质的影响。铁细菌普遍存在于自然环境中,可利用低价铁源为自身生长所需能量。铁细菌胞外有机物的主要组分如多糖和蛋白质等可与铁结合,并通过氧化或沉淀作用使铁稳定、沉积而形成铁矿物;此外铁细菌胞外多聚物可催化铁的氧化或促进铁的聚集。这些生物成因铁矿物因具有良好的表面吸附与氧化还原等化学活性,及有效固定环境中的重金属、放射性核素和催化降解有机污染物的良好环境属性,在环境生物矿物材料和环境治理研究领域被日益重视。故本文基于铁细菌及其胞外多聚物对铁矿物矿化形成的重要调控作用,介绍了环境中存在的铁细菌及其生物矿化特征,重点阐述了铁细菌胞外多聚物(组分、结构及特性)及其在铁矿物矿化过程中的作用,同时对铁细菌胞外多聚物及生物成因铁矿物的环境意义进行了概述。     

Effects of tides and weather on sedimentation of iron‐oxyhydroxides in a shallow‐marine hydrothermal environment at Nagahama Bay,Satsuma Iwo‐Jima Island,Kagoshima, southwest Japan

Nagahama Bay of Satsuma Iwo‐Jima Island, southwest Japan, is an excellent place for studying sedimentation of iron‐oxyhydroxides by shallow‐marine low‐temperature hydrothermal activity. Its fishing port has a narrow entrance that limits exchange of seawater between the bay and open ocean, allowing the accumulation of fine‐grained precipitates of iron‐bearing materials (Fe‐oxyhydroxides) on the seafloor. The fishing port is usually filled with orange‐ to brown‐colored Fe‐rich water, and deposits >1.5 m thick Fe‐rich sediments. To elucidate the movement and depositional processes of the Fe‐rich precipitates in the bay, we conducted continuous profiling of turbidity throughout the tidal cycle and monitoring of surface water. The results showed that clear seawater entered the bay during the rising tide, and turbid colored water flowed into the ocean during the ebb tide. Neap tide was found to be an optimal condition for sedimentation of Fe‐oxyhydroxides due to weak tidal currents. Storms and heavy rains were also found to have influenced precipitation of Fe‐oxyhydroxides. Storm waves disturbed the bottom sediments, resulting in increased turbidity and rapid re‐deposition of Fe‐oxyhydroxides with an upward‐fining sequence. Heavy rain carried Fe‐oxyhydroxides originally accumulated in nearby beach sands to the bay. Our findings provide information on optimal conditions for the accumulation of Fe‐rich sediments in shallow‐marine hydrothermal settings.