Geochemical characteristics of dissolved rare earth elements in acid mine drainage from abandoned high-As coal mining area,southwestern China

Acid mine drainage (AMD) represents a major source of water pollution in the small watershed of Xingren coalfield in southwestern Guizhou Province. A detailed geochemical study was performed to investigate the origin, distribution, and migration of REEs by determining the concentrations of REEs and major solutes in AMD samples, concentrations of REEs in coal, bedrocks, and sediment samples, and modeling REEs aqueous species. The results highlighted that all water samples collected in the mining area are identified as low pH, high concentrations of Fe, Al, SO₄ ^2? and distinctive As and REEs. The spatial distributions of REEs showed a peak in where it is nearby the location of discharging of AMD, and then decrease significantly with distance away from the mining areas. Lots of labile REEs have an origin of coal and bedrocks, whereas the acid produced by the oxidation of pyrite is a prerequisite to cause the dissolution of coal and bedrocks, and then promoting REEs release in AMD. The North American Shale Composite (NASC)-normalized REE patterns of coal and bedrocks are enriched in light REEs (LREEs) and middle REEs (MREEs) relative to heavy REEs (HREEs). Contrary to these solid samples, AMD samples showed slightly enrichment of MREEs compared with LREEs and HREEs. This behavior implied that REEs probably fractionate during acid leaching, dissolution of bedrocks, and subsequent transport, so that the MREEs is primarily enriched in AMD samples. Calculation of REEs inorganic species for AMD demonstrated that sulfate complexes (Ln(SO₄)⁺and Ln(SO₄)₂ ^?) predominate in these species, accounting for most of proportions for the total REEs species. The high concentrations of dissolved SO₄ ^2? and low pH play a decisive role in controlling the presence of REEs in AMD, as these conditions are necessary for formation of stable REEs-sulfate complexes in current study. The migration and transportation of REEs in AMD are more likely constrained by adsorption and co-precipitation of Fe-Al hydroxides/hydroxysulfate. In addition, the MREEs is preferentially captured by poorly crystalline Fe-Al hydroxides/hydroxysulfate, which favors that sediments also preserve NASC-normalized patterns with MREEs enrichment in the stream.

     

Distribution of rare earth elements in an alluvial aquifer affected by acid mine drainage: the Guadiamar aquifer (SW Spain)

This work analyses the spatial distribution, the origin, and the shale-normalised fractionation patterns of the rare earth elements (REE) in the alluvial aquifer of the Guadiamar River (south-western Spain). This river received notoriety in April 1998 for a spill that spread a great amount of slurry (mainly pyrites) and acid waters in a narrow strip along the river course. Groundwaters and surface waters were sampled to analyse, among other elements, the REEs. Their spatial distribution shows a peak close to the mining region, in an area with low values of pH and high concentrations of sulphates and other metals such as Zn, Cu, Co, Ni, Pb, and Cd. The patterns of shale-normalised fractionation at the most-contaminated points show an enrichment in the middle rare earth elements (MREE) with respect to the light (LREE) and heavy (HREE) ones, typical of acid waters. The Ce-anomaly becomes more negative as pH increases, due to the preferential fractionation of Ce in oxyhydroxides of Fe.     

稀土冶炼过程草酸沉淀废水资源化处理技术

为了实现稀土生产草沉废水的资源回用,对稀土草酸沉淀废水建立资源回收工艺,回收废水中的草酸和盐酸。研究包括草沉废水水质分析、草沉废水蒸馏分离工艺研究、蒸馏盐酸的回收利用、盐酸蒸发过程中的浓度变化趋势分析、草沉废水草酸回收研究以及工艺经济性分析。结果表明:草沉母液中TOC含量为4 661 mg/L,金属离子总体含量不高;通过常压实沸点蒸馏发现,草沉母液可回收5 mol/L盐酸330 mL/L或1 mol/L盐酸600 mL;蒸发后草酸产率超过16 g/L草沉废水;并且结晶草酸纯度≥99.5%,硫酸根未检出,灼烧残渣≤0.16%,重金属(以Pb计)≤0.000 01%,铁离子≤0.004 5%,氯化物≤0.08%。通过上述研究,为草沉废水资源化处理技术的工业化应用提供了理论依据。     

Speciation of rare earth elements in soil and accumulation by wheat with rare earth fertilizer application

A greenhouse study was conducted to investigate the accumulation of rare earth elements (REEs), La, Ce, Pr and Nd, in winter wheat (Triticum aestivum L.), and the speciation of these elements in soil following the application of REE-based fertilizers. Improved crop yield was confirmed by the experiment. The accumulation behavior of La, Ce, Pr and Nd in wheat varied depending on the concentration of REE fertilizer application, i.e. increased with increasing REE concentration at low fertilization application, constant over the medium REE range, and decreased with increasing REE concentration at high fertilizer application. Significant negative correlation was obtained between REE contents in roots and soil pH (r = -0.5787 to -0.8442 for La). REEs in both the fertilized and unfertilized soils were fractionated by a three-stage sequential extraction procedure into three chemically distinct fractions: water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3). REEs in fertilized soils were found mainly in the B2 and B3 fractions, with only a small amount in the B1 fraction. REEs in B1 and B2 fractions were negatively correlated with soil pH (r = -0.6892 to -0.8927 and -0.7462 to -0.9482). Significant correlation was obtained between REEs in B1 fraction and REE contents in root. The correlation coefficients ranged from 0.6159 to 0.7410 when fertilizer application was lower than 20.0 mg/kg soil. No acceptable relationship was observed between REE contents in shoot and any of the extractable fractions in soils.     

Uptake and distribution of rare earth elements in rice seeds cultured in fertilizer solution of rare earth elements

The uptake behavior of rare earth elements (REEs) under pot conditions using deionized water and a REE fertilizer solution as the culture media as well as the distribution of REEs in rice proteins were studied. The uptake of REEs in rice seeds increased dramatically after a lag period of approximately three days. Roots can accumulate a much higher content of REEs than germs and the resting seeds. The REE content in each water-soluble (albumin) and salt-soluble (globulin) component of the rice seeds accounted for 5-8% and 4-6% of the total REEs, respectively. However, there are less than 1.5% of the total REEs were found in the alcohol-soluble (prolamin) and acetic acid-soluble (glutelin) components. The high performance liquid chromatography (HPLC) in the gel permeation and the reserved-phase were used to monitor changes in the molecular weight distribution changes of the soluble proteins of rice seeds during germination after having been cultured in the same solution for seven days. No changes occurred in the prolamin, while a slight change occurred in the albumin, globulin and glutelin. Fractionation of the albumin of rice seeds cultured in a REE fertilizer solution on the Sephadex G-100 column indicated that REEs, especially Ce, La, Pr and Nd, were associated mainly with biological compounds of a molecular weight between 10,000 and 12,000.     

浓硫酸低温分解废弃稀土抛光粉工艺研究

采用浓硫酸低温分解回收废弃稀土抛光粉,考察了硫酸用量、分解温度和反应时间对分解效果的影响,结果显示,较佳实验条件下,稀土收率可达95%以上。通过热重-差热与红外光谱联用技术实时在线监测技术,表明分解过程分为2个阶段,分别在270℃和300℃温度范围附近,稀土氧化物和稀土氟氧化物与硫酸发生反应。     

Application of an integrated biomarker response index to assess ground water contamination in the vicinity of a rare earth mine tailings site

We utilized a multi-biomarker approach (Integrated Biomarker Response version 2, IBRv2) to investigate the scope and dispersion of groundwater contamination surrounding a rare earth mine tailings impoundment. Parameters of SD rat included in our IBRv2 analyses were glutathione levels, superoxide dismutase, catalase, and glutathione peroxidase activities, total anti-oxidative capacity, chromosome aberration, and micronucleus formation. The concentration of 20 pollutants including Cl^?, SO₄ ^2?, Na⁺, K⁺, Mg²⁺, Ca²⁺, TH, COD_Mn, As, Se, TDS, Be, Mn, Co, Ni, Cu, Zn, Mo, Cd, and Pb in the groundwater were also analyzed. The results of this study indicated that groundwater polluted by tailings impoundment leakage exhibited significant ecotoxicological effects. The selected biomarkers responded sensitively to groundwater pollution. Analyses showed a significant relationship between IBRv2 values and the Nemerow composite index. IBRv2 could serve as a sensitive ecotoxicological diagnosis method for assessing groundwater contamination in the vicinity of rare earth mine tailings. According to the trend of IBRv2 value and Nemerow composite index, the maximum diffusion distance of groundwater pollutants from rare earth mine tailings was approximately 5.7 km.

     

Kinetic analysis of constructed systems for the recovery of contaminated areas by acid mine drainage

INTRODUCTION: Flowing of the acid mine drainage may contaminate the adjacent water bodies causing substantial changes in the aquatic ecosystem. This aspect is the most relevant problem in the southern of Santa Catarina once the contaminated areas are inserted in the watershed of the Araranguá, Urussanga, and Tubar?o rivers, increasing the need for recovery studies. These areas are between Criciúma, I?ara, Urussanga, Siderópolis, Lauro Müller, Orleans, and Alfredo Wagner towns where a conservation unit exist called the Environmental Preservation Area of Baleia Franca. Aiming to compare the kinetics of the ash derived from burning coal and to neutralize acid mine drainage, different neutralizer, limestone, fly, and bottom ash, was mounted on a pilot scale experiment. DISCUSSION: The transport parameters showed the same order of infiltration and dispersion: fly ash < bottom ash < limestone. The order of measured alkalinity was: limestone < fly ash < bottom ash, with pH values of 9.34, 12.07, and 12.25, respectively. The limestone kinetics of acidic drainage neutralization was first order with reaction rate constant k?=?0.0963 min(-1), bottom ash was 3/4 with k?=?0.0723 mol(1/4) L(-1/4) min(-1), and the fly ash had higher order kinetics, 4/3, with reaction rate constant k?=?27.122 L(1/3) mol(-1/3) min(-1). However, by mathematical modeling, it was found that due to a combination of transport and kinetics, only limestone treatment reached a pH above 6 within 5 years, corresponding to the ideal as planned.     

稀土元素对生物塔烟气同时脱硫脱氮的强化作用

依据对9组持续20 d/组的正交实验(L_9(3~4))结果直观分析的极差值R变化情况考察,对稀土元素强化生物膜填料塔烟气同时脱硫脱氮性能(重点对脱氮性能)的作用进行了分析研究。分析及实验验证的结果表明,在启动阶段及实验的全过程中,添加稀土元素对生物塔烟气脱氮效率的影响均远大于同时添加的镁盐和碳源,而且其对脱氮菌生长的强化刺激作用存在于生物净化操作的全过程。     

离子型稀土尾矿除铵效果对比

离子型稀土尾矿存在氨氮残留污染问题,分析尾矿中氨氮的赋存形式能更有效地处理尾矿中的氨氮。通过室内柱浸实验、浸泡除铵实验和淋洗除铵实验,分析稀土尾矿中氨氮残留的赋存形式,并根据色层塔板理论计算和比较2种除铵方式下的除铵效率。结果表明,尾矿中氨氮残留赋存形式包括离子交换态氨氮、不可流动溶液残留氨氮、物理吸附氨氮和化学吸附氨氮。其中主要以化学吸附氨氮为主,占尾矿氨氮残留量的30.47%~40.73%;物理吸附氨氮含量最少,占尾矿氨氮残留量的4.86%~5.34%。3种硫酸铵单耗下淋洗方式的单位体积清水除铵效率为53.84%、54.05%和75.77%;浸泡方式的单位体积清水除铵效率为14.4%、20.66%和23.10%;淋洗方式效率相比浸泡方式更有效。在处理尾矿氨氮中使用淋洗方式能有效地解决尾矿残留氨氮污染。     

微生物对煤矿固体废弃物的脱硫效应

煤矸石是煤矿特有的一种固体废弃物,应用本实验室筛选出的氧化亚铁硫杆菌Thiobacillus ferrooxidans和嗜酸氧化硫硫杆菌Thiobacillus thiooxidans对宁夏大武口高硫煤矸石进行微生物脱硫技术及应用条件的研究,如不同煤矸石粒径、不同接种浓度和不同煤矸石浓度。2种脱硫细菌对煤矸石的脱硫效果显著,小粒径煤矸石的微生物脱硫效果更好。考虑脱硫成本及脱硫效率,Thiobacillus ferrooxidans菌最佳的接种浓度为25%,在Thiobacillus Thiobacillus thiooxidans菌悬液中,能脱出最大量硫酸根的煤矸石最佳比例是10%。2种菌混合较单菌株脱硫效果更好,以Thiobacillus ferrooxidans∶Thiobacillus thiooxidans=2∶3的比例混合后对煤矸石的脱硫效果最佳,该结果为煤矿废弃物煤矸石的污染防治提供技术依据。     

Effects of fulvic acid on the bioavailability of rare earth elements and GOT enzyme activity in wheat (Triticum aestivum)

Fulvic acid (FA) was extracted and purified from natural soil and the effects of such FA on the bioaccumulation of rare earth elements (REEs, La3+, Gd3+ and Y3+) in wheat seedling were investigated. The results indicated that low concentration of FA (<0.4 mg C/l to root, <0.7 mg C/l to tops (stem and leaves)) could increase the bioaccumulation values of REEs in wheat, but when the concentration of FA was high (>0.4 mg C/l to root, >1.5 mg C/l to tops) the bioaccumulation values were decreased. Kinetic experimental results suggested that bioaccumulation values of REEs in roots for 30 days were correlated with the kinetic linear growth equation, and correlation coefficients were higher than 0.861. The kinetic bioaccumulation pattern of REEs in tops was different from that in root. The bioaccumulation values of REEs in wheat root were much higher than in wheat tops. Variations of glutamic oxaloacetic transaminase (GOT) enzyme activities in wheat root and tops were determined. A good correlation existed between the bioaccumulation values of REEs and GOT enzyme activities, and the correlation coefficients were higher than 0.922. GOT is an important parameter influencing the bioavailability of REEs.     

室内模拟地表PRB处理离子型稀土矿区尾水

采用室内模拟PRB装置,以粒径2~4、0.6~1 mm沸石为填料,研究了地表PRB主要构造因子对渗流量的影响,并考察了地表PRB对稀土矿区尾水氨氮削减和泥沙拦截的效果。结果表明,细粒沸石级配为10%~15%时,渗流量变化平缓,有利于PRB系统稳定运行;渗流量与PRB厚度成线性负相关,与水位差成线性正相关;当进水口位置为1/3 PRB高度时,在较宽的水位差范围内水流均以渗流方式经过PRB,因而提高了PRB填料的利用率。优化设计PRB装置对稀土尾水的氨氮平均去除率为14.2%,泥沙平均去除率为58.2%,出水pH在运行前期有明显提高,其处理容量放大60倍后相当于尾水日处理能力354 t·d⁻¹,可满足矿区一般小流域支流的实际需要。以上研究结果可对南方离子型稀土矿区治理提供参考。     

Phytoextraction of rare earth elements in herbaceous plant species growing close to roads

The aim of study was to determine the phytoextraction of rare earth elements (REEs) to roots, stems and leaves of five herbaceous plant species (Achillea millefolium L., Artemisia vulgaris L., Papaver rhoeas L., Taraxacum officinale and Tripleurospermum inodorum), growing in four areas located in close proximity to a road with varied traffic intensity. Additionally, the relationship between road traffic intensity, REE concentration in soil and the content of these elements in plant organs was estimated. A. vulgaris and P. rhoeas were able to effectively transport REEs in their leaves, independently of area collection. The highest content of REEs was observed in P. rhoeas leaves and T. inodorum roots. Generally, HREEs were accumulated in P. rhoeas roots and leaves and also in the stems of T. inodorum and T. officinale, whereas LREEs were accumulated in T. inodorum roots and T. officinale stems. It is worth underlining that there was a clear relationship between road traffic intensity and REE, HREE and LREE concentration in soil. No positive correlation was found between the concentration of these elements in soil and their content in plants, with the exception of T. officinale. An effective transport of REEs from the root system to leaves was observed, what points to the possible ability of some of the tested plant species to remove REEs from soils near roads.     

Use of rare earth tracers for the study of diesel emissions in the atmosphere

The emissions of diesel vehicles mainly contain soot, which is difficult to distinguish from soot originating from other sources. The use of a tracer which can be detected in extremely low mass concentrations and does not occur normally in the atmospheric aerosol can help to differentiate between aerosols from different sources. The rare earth element Dysprosium has proven useful for this purpose. It can be detected by neutron activation analysis in quantities of nanograms and does not occur naturally.An organic, diesel soluble Dysprosium compound was added to the fuel. During the combustion process the Dysprosium is oxidized and attaches to the formed soot particles. For the atmospheric filter samples an extraction technique was used.This marking method has been successfully applied for an extended field experiment.     

Effect of organic acids on adsorption and desorption of rare earth elements

Effect of citric, malic, tartaric and acetic acids on adsorption of La, Ce, Pr and Nd by and desorption from four typical Chinese soils was studied. Generally, adsorption capacities of rare earth elements (REEs) were significantly correlated with the cation exchange capacity (CEC) of soils. In the presence of acetic acids adsorption of REEs was similar to that in the presence of Ca(NO3)2. However, in the presence of citric, malic and tartaric acids adsorption of REEs by Heilongjiang, Zhejiang and Guangdong soils decreased to varying extents if compared with that in the presence of nitrate and acetic acid. The significance of suppression followed the order of citric acid > malic acid > tartaric acid > acetic acid, which was consistent with the order of stability of complexes of REEs with these organic acids. However, the adsorption increased with increasing equilibrium solution pH. For Jiangxi soil with low soil pH, CEC and organic matter these organic acids exerted an even more serious suppression effect on the adsorption of REEs. Another feature of the relationship between the adsorption of REEs and equilibrium solution pH was that the adsorption of REEs decreased with increase of pH from 2 to 4.5 and then slightly increased with further increase of pH. Desorption of REEs varied with soils and with organic acids as well. REEs were released easily from Heilongjiang, Zhejiang and Guangdong soils in the presence of organic acid. Generally, desorption of REEs decreased with increasing equilibrium solution pH. Effect of organic acids on desorption of REEs from Jiangxi soil was more complicated. In the presence of citric and malic acids no decrement and/or slight increase in desorption of REEs were observed over the equilibrium solution pH from 3 to 6.5. The reasons for this were ascribed to the strong complexing capacity of citric and malic acids and low soil pH, CEC and organic matter of Jiangxi soil.