Efficient uranium immobilization on red clay with phosphates

Uranium is a very toxic and radioactive element. Removal of uranium from wastewaters requires remediation technologies. Actual methods are costly and ineffective when uranium concentration is very low. Little is known about the enhancement of sorption of uranyl ions by phosphate ions on aluminosilicates. Here, we studied sorption of uranyl acetate on red clay in the presence of phosphates. The concentration of U(VI) ranged 0.0001–0.001 mol/L, whereas the concentration of PO₄ ^3? was constant at 0.0001 mol/L. We designed a new method for the analysis of ternary surface complexes. We observed for the first time a remarkable improvement of U(VI) sorption on red clay under the influence of phosphates. We also found that at least two different ternary surface complexes U(VI)–phosphate–clay are formed in the sorbent phase. The complexation of UO₂ ²⁺ cations by phosphate ligands in the sorbent phase was confirmed by the X-ray photoelectron spectra of U 4f electrons.     

The effects of application of agricultural wastes to firing range soil on metal accumulation in Ipomoea aquatica and soil metal bioavailability

The immobilisation of heavy metals in the soil of a 25-year-old active firing range using durian (Durio zibethinus L.) tree sawdust (DTS), coconut coir (CC) and oil palm empty fruit bunch (EFB) was investigated. The immobilisation effects were evaluated in terms of metal accumulation in water spinach (Ipomoea aquatica) and soil metal bioavailability. A pot experiment was conducted by amending the firing range soil with DTS, CC and EFB at application rates of 0%, 1% and 3% (w/w), respectively. All amendments increased the biomass yield and reduced the uptake of heavy metals in the plant tissue. Zn had the highest values of Bioconcentration Factor (BCF: 0.301–0.865) and Translocation Factor (TF: 1.056–1.883). Pb was the least-accumulated and transported metal in the plant tissues, with the BCF and TF values of 0.019–0.048 and 0.038–0.116, respectively. The bioavailable fraction of heavy metals in the firing range soil decreased following the application of the three agricultural wastes studied. DTS, CC and EFB did not cause toxicity symptoms in the water spinach over the pot experiment. Therefore, DTS, CC and EFB are considered promising immobilising agents for the remediation of metal-contaminated land.     

Efficacy of woody biomass and biochar for alleviating heavy metal bioavailability in serpentine soil

Crops grown in metal-rich serpentine soils are vulnerable to phytotoxicity. In this study, Gliricidia sepium (Jacq.) biomass and woody biochar were examined as amendments on heavy metal immobilization in a serpentine soil. Woody biochar was produced by slow pyrolysis of Gliricidia sepium (Jacq.) biomass at 300 and 500 °C. A pot experiment was conducted for 6 weeks with tomato (Lycopersicon esculentum L.) at biochar application rates of 0, 22, 55 and 110 t ha^?1. The CaCl₂ and sequential extractions were adopted to assess metal bioavailability and fractionation. Six weeks after germination, plants cultivated on the control could not survive, while all the plants were grown normally on the soils amended with biochars. The most effective treatment for metal immobilization was BC500-110 as indicated by the immobilization efficiencies for Ni, Mn and Cr that were 68, 92 and 42 %, respectively, compared to the control. Biochar produced at 500 °C and at high application rates immobilized heavy metals significantly. Improvements in plant growth in biochar-amended soil were related to decreasing in metal toxicity as a consequence of metal immobilization through strong sorption due to high surface area and functional groups.     

High adsorption of ethylene by alkali-treated halloysite nanotubes for food-packaging applications

Environmental Chemistry Letters - Fresh food products such as fruits and vegetables are usually degrading fast after harvest, notably due to the production of ethylene, an aging hormone, by the...     

Release of Cd immobilized by soil constituents and its bioavailability

Release of Cd immobilized by soil constituents (clay, humic acids, bacterial cells) in vitro and under soil conditions and its bioavailability to lettuce were studied. The most resistant to extraction with 0.02 M EDTA in vitro as well as under soil conditions was cadmium immobilized by humic acids during decomposition of contaminated plant residues but Cd‐dead cells when 0.1 M NaNO₃ was the extractant.

Cadmium addition (3 mg kg^‐1) to soil and its form were without effect on plant growth and amount of metal accumulated in roots. Tops of plants grown in soil supplemented with Cd‐resting cells contained significantly less metal then other ones.     

土壤重金属化学形态的生物可利用性评价

重金属化学形态是近年来土壤化学、植物营养和环境科学研究领域的一个热点和难点,利用重金属的化学形态分布和含量变化来评价重金属的生物可利用性,有利于全面研究重金属的危害性和治理重金属污染土壤。结果表明,水溶态和交换态的重金属易被生物吸收利用,而残留态重金属一般不被生物利用,其它形态如碳酸盐结合态、铁锰氧化物结合态和有机物结合态的生物可利用性主要取决于外界环境的变化。     

电池企业铅污染土壤稳定化修复实验研究

采用电池企业的场地土壤进行实验,研究了铅污染土壤中混合施加过磷酸钙(C)、膨润土(B)和腐殖酸(H)后对土壤中铅形态及浸出毒性的影响,同时研究了在相同固定剂组合中改变单一固定剂投加量对土壤修复效果的影响。结果表明,(1)经不同配比的C+B、B+H、和H+C组合方式处理后,土壤中铅的有效态质量分数明显降低,而有机结合态和残渣态质量分数增加。固定时间为40 d时,其修复效果优于25 d。修复后土壤的有效态铅大部分转化为有机结合态,其中经过20%B+20%H和10%H+6%C处理后,有效态铅质量分数降低幅度较大,分别从331.3 mg·kg-1降至91.8 mg·kg-1和96.57 mg·kg-1;相应地,有机结合态铅质量分数增加幅度也较大,分别从57.19 mg·kg-1升至264.28 mg·kg-1和267.99 mg·kg-1;(2)C+B组合投加处理中,土壤修复效果随膨润土投加量增加而降低,B+H组合投加处理中,土壤修复效果随着腐殖酸投加量的增加而增加,H+C组合投加处理中,随过磷酸钙投加量增加,土壤修复效果也呈增加趋势。(3)经不同处理固定修复后,土壤浸出液中铅的质量浓度大幅降低,对周周水环境的风险降低。     

改性天然磷灰石促进Pb/Zn复合污染土壤的稳定化修复

采用草酸和柠檬酸分别与天然磷灰石共培养以对其改性,并将改性磷灰石用于Pb/Zn复合污染土壤的稳定化修复,借助XRD、FTIR等仪器方法表征改性磷灰石的物相组成及其P结合形态的转变,采用TCLP方法评价改性天然磷灰石对土壤重金属的修复效果.研究表明,草酸改性磷灰石诱导了草酸钙生成,并且32.4%的P由稳定形态转化为水溶态,而柠檬酸改性未能使磷灰石主要成分发生显著变化,仅有0.28%的P转化为水溶态P.与天然磷灰石相比,改性磷灰石提高了对Pb和Zn的稳定性.草酸改性磷灰石可同时有效地稳定土壤中的Pb和Zn,稳定化效率分别为68%—100%和64%—73%,其固定机制主要是形成难溶的磷酸盐沉淀;柠檬酸改性磷灰石对Pb和Zn的稳定化效率分别为20%和62%—69%,对Pb和Zn的稳定性主要是通过吸附作用.总之,草酸改性磷灰石对Pb和Zn的稳定化优于柠檬酸改性磷灰石,是一种高效经济的土壤重金属稳定化修复材料.     

Desorption characteristics of kaolin clay contaminated with zinc from electrokinetic soil processing

A number of bench scale laboratory column tests were carried out using a newly designed and developed electrokinetic cell to investigate the fundamental behavior of zinc-spiked kaolin clay subjected to an electric field. Laboratory investigations focused on (i) zinc migration by the combined effects of electromigration and electro-osmosis and (ii) the electrically induced desorption characteristics of zinc-contaminated kaolin that occurred during processing. The correlations of the applied voltage gradient, electro-osmotic flow rate, and the development of a pH gradient were examined and evaluated. The results showed that the removal efficiency was high during the early stage of processing due to rapid desorption by electrokinetic effects in the cathode region. However, the majority of zinc migrating from the anode was precipitated due to the high pH environment in the cathode region.     

脱硫石膏对重金属污染沉积物中Cd的稳定固定化作用

研究了掺杂不同比例脱硫石膏的沉积物中Cd的吸附热力学特征及其稳定固定化效果。实验将脱硫石膏掺杂比例不同的沉积物与不同初始质量浓度的Cd溶液混合、振荡、离心后测定上清液中Cd的质量浓度,结果表明,脱硫石膏掺杂量不同的沉积物吸附Cd的热力学过程均符合Langmuir吸附等温线;脱硫石膏掺杂比例的提高增强了沉积物对溶液中Cd的吸持能力,二者显著正相关;脱硫石膏的掺杂还削弱了溶液中Cd初始质量浓度对其固定率的影响,使研究中8个初始质量浓度下沉积物对Cd的固定率均维持在较高水平。通过16个时间点对连续搅拌下的沉积物样品溶液中Cd质量浓度的测定,研究了模拟重金属污染沉积物和自然沉积物掺杂脱硫石膏前后对照了其中Cd的稳定性,结果表明,脱硫石膏的掺杂降低了沉积物中Cd的释放量,并将实验条件下两种沉积物中Cd的固定率均保持在99.2%以上且保持相对平稳状态。同时,脱硫石膏的掺杂可导致吸附体系pH的升高,促进了Cd与固相介质之间由吸附向沉淀作用的转化,从而提高了沉积物中Cd的稳定性,有利于重金属污染沉积物中Cd的稳定固定化。     

Heavy metal bioavailability and chelate mobilization efficiency in an assisted phytoextraction process

The heavy metal bioavailable fraction of a soil is a core parameter to verify the potential risks of contaminant exposure to organisms or plants. The purpose of the present work is to identify the bioavailable metal fraction in soils treated with chelates. This fraction was evaluated directly by analyzing metal concentrations in soil solution and indirectly using sequential extraction procedures. The metal bioavailable fraction was compared with metal accumulated in plant leaves, grown in both untreated and chelate-treated reactors. In order to verify the effect of the readily and slowly biodegradable chelates [S,S]-ethylenediaminedisuccinic acid (EDDS), methylglycine diacetic acid (MGDA), and ethylenediaminetetraacetic acid (EDTA) on metal speciation in soils, a simulation of chelate treatment was made and metal concentrations in different soil compartments before and after the simulation were compared. Lead concentration in the soil solution was positively correlated with metal concentration in the test plants. The soluble fraction showed the best correlation with metal concentration in soil solution. The simulation of the chelate treatment demonstrated that EDTA and EDDS were able to extract part of the organic- and sulfide-bound fraction, which are less available to plants.     

Reliability of solid phase microextraction in estimating bioavailability of pyrene in soil

Solid phase microextraction (SPME) coupled with gas chromatography was employed to estimate bioavailability of pyrene in soils with different properties of textures, organic matter contents (SOM) and aging periods. Experimental results indicated that biodegradation rates increased from 0.10 (sandy loam) to 0.15 (silty loam) microg g-1 hr1. By contrast, biodegradation rate decreased from 0.10(1.3% SOM) to 0.04 (7.6% SOM) microg g-1hr1. The amounts of pyrene biodegraded decreased 27% when SOM was modified from 1.3 to 7.6%, indicating that distributions of pyrene in soils at biodegradation end points were affected by the SOM. Sequestration as measured by sonication extraction had evidently occurred in aged soil samples. SPME measurements slightly overestimated the amount of pyrene degraded by indigenous and seeded microorganisms, in soils with the different properties (correlation coefficient, R2= 0.74). The present study demonstrates that the SPME method can not replace biodegradation tests commonly used for predicting bioremediation efficacy.     

Total immobilization of soil heavy metals with nano-Fe/Ca/CaO dispersion mixtures

This report shows that soil heavy metals can be totally immobilized by grinding with nano-Fe/Ca/CaO. Remediation of soils contaminated by heavy metals is a critical issue in Japan. Indeed, contaminated soils are notoriously difficult to remediate using available technologies. Major setbacks in typical immobilization techniques for heavy metals are wet conditions, forming secondary effluents and further treatment for effluents. Solidification with nano-Fe/Ca/CaO dispersion mixture is a promising treatment for the total immobilization of soil heavy metals As, Cd, Cr, Pb, and separation in dry conditions. Here, we studied the heavy metal immobilization by simple grinding with the addition of three mixtures: nano-Fe/CaO, nano-Fe/Ca/CaO, and nano-Fe/Ca/CaO/PO₄. Samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) and scanning electron microscopy combined with electron dispersive spectroscopy (SEM–EDS). Results show that the addition of nano-Fe/Ca/CaO immobilized 95–99 % of heavy metals, versus 65–80 % by simple grinding. After treatment, 36–45 wt% of magnetic and 64–55 wt% of nonmagnetic fractions of soil were separated. Their condensed heavy metal concentration was 85–95 % and 10–20 %, respectively. Nano-Fe/Ca/CaO treatment reduced the concentration of leachates heavy metals to values lower than the Japan soil elution standard regulatory threshold of 0.01 mg/l for As, Cd, and Pb; and 0.05 mg/l for Cr. This technology can therefore immobilize totally soil heavy metals and reduce heavy metal by separation.     

施用磷肥对南方酸性红壤镉生物有效性及土壤酶活性影响

采用盆栽试验,研究了普钙和钙镁磷肥对油菜生物量和Cd含量、土壤p H值和Cd有效态含量以及土壤酶活性的影响.结果表明,施加普钙和钙镁磷肥后,油菜生物量分别比对照处理增加41.8%—60.5%和90.2%—171.6%,油菜地上部Cd含量分别降低达54.3%—86.7%和74.4%—79.6%,其中当普钙和钙镁磷肥施加量为中高剂量时,油菜地上部Cd含量降低至0.18 mg·kg-1和0.10 mg·kg-1,符合国家食品安全标准《食品中污染物限量》(GB 2762—2012)规定的叶菜蔬菜中Cd的最大限量值.施加普钙和钙镁磷肥均降低了土壤中Cd有效态,与对照相比,土壤中HCl提取态Cd含量分别降低0.9%—21.2%和33.8%—43.9%,CMP处理下TCLP(Toxicity characteristic leaching procedure,TCLP)提取态Cd含量降低33.0%—43.0%.施加高剂量普钙和中剂量钙镁磷肥时,土壤过氧化氢酶活性与对照相比分别增加了202.5%和52.6%,施加不同剂量的普钙均显著降低土壤脲酶活性,降低率达28.2%—65.9%,而添加普钙和钙镁磷肥对蔗糖酶活性均无显著性影响.土壤p H与油菜生物量以及土壤脲酶成极显著正相关关系,与TCLP-Cd成显著负相关关系.油菜生物量与土壤有效态Cd含量和油菜体内Cd含量存在负相关关系,其中与HCl提取态Cd及地上部Cd含量存在显著负相关关系.     

石灰氮对镉污染土壤中镉生物有效性的影响

以石灰作对比,在大田条件下研究了不同石灰氮用量对镉污染土壤中镉生物有效性的影响。结果表明,一定量石灰或石灰氮处理均能显著提高酸性土壤的pH值,降低污染土壤中有效态镉质量分数及水稻茎叶和糙米中的镉质量分数。与不施改良剂的对照相比,石灰施用量达到1 200 kg.hm-2时土壤pH值显著提高,土壤有效态镉质量分数降低12.6%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低25.5%（P〈0.05）和28.3%（P〈0.05）;石灰氮施用量达到600 kg.hm-2时,土壤pH值显著高于对照,土壤有效态镉质量分数较对照降低10.9%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低36.8%（P〈0.05）和33.0%（P〈0.05）。等量条件下（600 kg.hm-2）石灰氮对降低土壤镉有效性及水稻累积镉的效果相对优于石灰处理。因此,石灰氮与石灰一样可用于酸性重金属污染土壤的修复与改良,是一种极具潜力的土壤改良剂。     

根际环境的调节与重金属污染土壤的修复

根际环境的pH和Eh会产生影响土壤中重金属的化学过程。pH的变化影响到重金属的固定和活化，根际的酸化能够活化大多数重金属，使其毒性增强；反之，则固定大多数重金属，减轻其毒性。Eh的变化可改变重金属的价态和存在形态，使其毒性减弱或增强。根分泌物可从多方面影响金属的毒性和有效性，如改变根际环境的pH值和Eh来改变金属的存在形态和活度；与金属络合或者吸附、包埋金属污染物；通过影响根际微生物特征来改变金属的毒性。根际环境中微生物能改变金属离子存在形态，其代谢产物能对金属离子产生沉淀、螯合等作用。土壤脲酶对重金属污染最敏感，可以用于监测土壤重金属污染。调控根际环境，可以有效地调节土壤中重金属污染物的活度、毒性及其转移，对重金属污染土壤起到修复作用。     

污泥农用后土壤中重金属形态的转化

污泥农用后,土壤中重金属的形态会发生转化.用土柱模拟实际土壤,采用棕壤和褐土两种土壤类型,分别施人生活污泥和工业污泥.混合后,对土柱进行淋洗,经过7次淋洗后,测定土柱中0～10 cm均匀混合层中重金属各形态的含量,然后再与污泥和土壤混合后重金属形态不发生变化时重金属的总量相比较,得出污泥农用后土壤中重金属形态的转化规律.结果表明:Cu主要向碳酸盐结合态和残渣态转化,Pb向铁锰氧化物结合态转化,Zn向碳酸盐结合态转化.     

重金属离子存在下黏土矿物表面蒽的光化学降解性能

探讨了蒽在Cu、Pb、Zn、Cd、Ni等重金属离子饱和的黏土矿物表面的光降解行为,研究了重金属离子种类,黏土矿物种类、p H、自由基捕获剂和氧气对黏土表面蒽降解速率的影响.研究表明,不同种类金属离子饱和的蒙脱石表面蒽的降解速率Cu2+Pb2+Zn2+Cd3+Ni2+Na+,其中Cu-蒙脱石表面蒽的光降解速率达78.8%;黏土矿物CEC值越高,可交换的铜离子含量越大,对蒽的光降解速率的促进作用越明显;Cu-蒙脱石表面蒽的光降解速率随p H值增大而逐渐减小,p H≥8.71时,蒽的降解率为0,其变化规律与Cu2+随p H值的存在形态的变化趋势相吻合.此外,蒽在Cu-蒙脱石表面的光降解速率随加入的对苯醌增多而减小,对苯醌含量达2.0 mg·g-1时蒽的降解率为0,无氧条件下蒽的降解率为0,推测该反应体系中有氧化活性自由基(O-2·)的产生,可能为光催化氧化降解起始因素之一.     

Relationship between plant biodiversity and heavy metal bioavailability in grasslands overlying an abandoned mine

Abandoned metal mines in the Sierra de Guadarrama, Madrid, Spain, are often located in areas of high ecological value. This is true of an abandoned barium mine situated in the heart of a bird sanctuary. Today the area sustains grasslands, interspersed with oakwood formations of Quercus ilex and heywood scrub (Retama sphaerocarpa L.), used by cattle, sheep and wild animals. Our study was designed to establish a relationship between the plant biodiversity of these grasslands and the bioavailability of heavy metals in the topsoil layer of this abandoned mine. We conducted soil chemical analyses and performed a greenhouse evaluation of the effects of different soil heavy metal concentrations on biodiversity. The greenhouse bioassays were run for 6 months using soil samples obtained from the mine polluted with heavy metals (Cu, Zn, Pb and Cd) and from a control pasture. Soil heavy metal and Na concentrations, along with the pH, had intense negative effects on plant biodiversity, as determined through changes in the Shannon index and species richness. Numbers of grasses, legumes, and composites were reduced, whilst other species (including ruderals) were affected to a lesser extent. Zinc had the greatest effect on biodiversity, followed by Cd and Cu. When we compared the sensitivity of the biodiversity indicators to the different metal content variables, pseudototal metal concentrations determined by X-ray fluorescence (XRF) were the most sensitive, followed by available and soluble metal contents. Worse correlations between biodiversity variables and metal variables were shown by pseudototal contents obtained by plasma emission spectroscopy (ICP-OES). Our results highlight the importance of using as many different indicators as possible to reliably assess the response shown by plants to heavy metal soil pollution.     

High immobilization of soil cesium using ball milling with nano-metallic Ca/CaO/NaH2PO4: implications for the remediation of radioactive soils

This report shows that cesium can be immobilized in soils with an efficiency of 96.4% by ball milling with nano-metallic Ca/PO₄. In Japan, the major concern on ¹³⁷Cs deposition and soil contamination due to the emission from the Fukushima Daiichi nuclear power plant showed up after a massive quake on March 11, 2011. The accident rated 7, the highest possible on the international nuclear event scale, released 160 petabecquerels (PBq) of iodine ¹³¹I and 15 PBq of ¹³⁷Cs according to the Japanese Nuclear and Industrial Safety Agency. Both ¹³⁷Cs and ¹³¹I radioactive nuclides are increasing cancer risk. Nonetheless, ¹³⁷Cs, with a half-life of about 30 years compared with 8 days for ¹³¹I, is a major threat for agriculture and stock farming and, in turn, human life for decades. Therefore, in Japan, the ¹³⁷Cs fixation and immobilization in contaminated soil is the most important problem, which should be solved by suitable technologies. Ball milling treatment is a promising treatment for the remediation of cesium-contaminated soil in dry conditions. Here, we studied the effect, factors and mechanisms of soil Cs immobilization by ball milling with the addition of nano-metallic Ca/CaO/NaH₂PO₄, termed “nano-metallic Ca/PO₄.” We used scanning electron microscopy combined with electron dispersive spectroscopy (SEM/EDS) and X-ray diffraction. Results show that immobilization efficiency increases from 56.4% in the absence of treatment to 89.9, 91.5, and 97.7 when the soil is ball-milled for 30, 60 and 120 min, respectively. The addition of nano-metallic Ca/PO₄ increased the immobilization efficiency to about 96.4% and decreased the ball milling time. SEM/EDS analysis allows us to observe that the amount of Cs decreased on soil particle surface. Use of nano-metallic Ca/PO₄ over a short milling time also decreases Cs leaching. Therefore, ball milling with nano-metallic Ca/PO₄ treatment may be potentially applicable for the remediation of radioactive Cs-contaminated soil in dry conditions.