Aluminium contamination from fluoride assisted dissolution of metallic aluminium

Trace amounts (microg g(-1) quantities) of fluoride ion are found to catalyse the dissolution of metallic aluminium in very slightly acidic or alkaline aqueous media. Possibly hazardous levels of aluminium could get leached from cooking utensils if fluoridated water or fluoride rich foodstuffs are used. The fluoride assisted corrosion of aluminium is most dramatic in oxalic, tartaric acids or sodium bicarbonate. Carbon dioxide also corrodes aluminium in the presence of the fluoride ion, generating colloidal hydrated aluminium oxide which is readily soluble in dilute organic and mineral acids.     

Effect of short-chain organic acids and pH on the behaviors of pyrene in soil-water system

The effects of five short-chain organic acids (SCOAs) on the behaviors of pyrene in soil-water system were investigated. The influences of the quantity and species of organic acids, pH, and soil dissolved organic matter were considered. The results showed the presence of SCOAs inhibited the adsorption and promoted the desorption of pyrene in the following order: citric acid>oxalic acid>tartaric acid>lactic acid>acetic acid. The decreased extents of pyrene adsorption performance enhanced with increasing SCOA concentrations, while the decreasing rate became less pronounced at high SCOA concentrations. In the presence of organic acids, the adsorption ability of pyrene decreased with increasing pH. However, there was a slight increase of pyrene adsorption with the addition of oxalic acid, tartaric acid and citric acid above pH 8. The capacity for pyrene retention differentiated significantly between the soils with and without dissolved organic matter. The presence of SCOAs was also favorable for the decrease of pyrene adsorption on soil without dissolved organic matter. The results of this study have important implications for the remediation of persistent organic pollutants in soil and groundwater.     

Influence of organic acids on the transport of heavy metals in soil

Vegetation historically has been an important part of reclamation of sites contaminated with metals, whether the objective was to stabilize the metals or remove them through phytoremediation. Understanding the impact of organic acids typically found in the rhizosphere would contribute to our knowledge of the impact of plants in contaminated environments. Heavy metal transport in soils in the presence of simple organic acids was assessed in two laboratory studies. In the first study, thin layer chromatography (TLC) was used to investigate Zn, Cd, and Pb movement in a sandy loam soil as affected by soluble organic acids in the rhizosphere. Many of these organic acids enhanced heavy metal movement. For organic acid concentrations of 10mM, citric acid had the highest R(f) values (frontal distance moved by metal divided by frontal distance moved by the solution) for Zn, followed by malic, tartaric, fumaric, and glutaric acids. Citric acid also has the highest R(f) value for Cd movement followed by fumaric acid. Citric acid and tartaric acid enhanced Pb transport to the greatest degree. For most organic acids studied, R(f) values followed the trend Zn>Cd>Pb. Citric acid (10mM) increased R(f) values of Zn and Cd by approximately three times relative to water. In the second study, small soil columns were used to test the impact of simple organic acids on Zn, Cd, and Pb leaching in soils. Citric acid greatly enhanced Zn and Cd movement in soils but had little influence on Pb movement. The Zn and Cd in the effluents from columns treated with 10mM citric acid attained influent metal concentrations by the end of the experiment, but effluent metal concentrations were much less than influent concentrations for citrate <10mM. Exchangeable Zn in the soil columns was about 40% of total Zn, and approximately 80% total Cd was in exchangeable form. Nearly all of the Pb retained by the soil columns was exchangeable.     

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.     

Effect of short-chain organic acids and pH on the behaviors of pyrene in soil–water system

The effects of five short-chain organic acids (SCOAs) on the behaviors of pyrene in soil–water system were investigated. The influences of the quantity and species of organic acids, pH, and soil dissolved organic matter were considered. The results showed the presence of SCOAs inhibited the adsorption and promoted the desorption of pyrene in the following order: citric acid > oxalic acid > tartaric acid > lactic acid > acetic acid. The decreased extents of pyrene adsorption performance enhanced with increasing SCOA concentrations, while the decreasing rate became less pronounced at high SCOA concentrations. In the presence of organic acids, the adsorption ability of pyrene decreased with increasing pH. However, there was a slight increase of pyrene adsorption with the addition of oxalic acid, tartaric acid and citric acid above pH 8. The capacity for pyrene retention differentiated significantly between the soils with and without dissolved organic matter. The presence of SCOAs was also favorable for the decrease of pyrene adsorption on soil without dissolved organic matter. The results of this study have important implications for the remediation of persistent organic pollutants in soil and groundwater.     

Effect of transpiration on Pb uptake by lettuce and on water soluble low molecular weight organic acids in rhizosphere

The effect of transpiration (high and low) on Pb uptake by leaf lettuce and on water soluble low molecular weight organic acids (LMWOAs) in rhizosphere has been studied. After two weeks of growth the plants were cultured in greenhouse for more four weeks and two days. Pb(NO(3))(2) solutions of different concentrations (100, 200, and 300 mg l(-1) of Pb) were then added to the quartz sand pots of different plants and studies were initiated. Blank experiments (without treating the quartz sand pots with Pb(NO(3))(2) solutions) were also run in parallel. No significant differences in the growth of the plants with the concentrations of added Pb(NO(3))(2) solutions were observed by both low and high transpirations at the end of the 0, 3rd, and 10th days of studies. The total evaporation of the volatiles during 10 days did not depend on the concentration of Pb(2+) but with high transpiration the rate of evaporation was significantly higher than with low transpiration. Uptake of Pb by shoots and roots of the plants was found to be proportional to the concentration of various Pb(NO(3))(2) solutions added and more accumulation was observed in roots than in shoots at the end of 3rd and 10th days. High transpiration created more Pb uptake than low transpiration did. One volatile acid, propionic acid and nine non-volatile acids, lactic, glycolic, oxalic, succinic, fumaric, oxalacetic, D-tartaric, trans-aconitic, and citric acids in rhizosphere quartz sands were identified and quantified by gas chromatography (GC) analysis. D-Tartaric and citric acids were major among the non-volatile acids. The amount of LMWOAs in rhizosphere quartz sands increased with the higher amount of Pb uptake and also with the duration of studies. The total quantities of the LMWOAs in the rhizosphere quartz sands were significantly higher under high transpiration with 300 mg l(-1) Pb solution addition at the end of 10th day. The present study shows prominent correlation between transpiration and uptake of heavy metal and interesting correlation between Pb contaminated level and quantity of water soluble LMWOAs in rhizosphere quartz sands. The latter thus deserves of further studies.     

Phytoextraction of metals from a multiply contaminated soil by Indian mustard

The effects of nitrilotriacetate (NTA) and citric acid applications on metal extractability from a multiply metal-contaminated soil, as well as on their uptake and accumulation by Indian mustard (Brassica juncea) were investigated. Desorption of metals from the soil increased with chelate concentration, NTA being more effective than citric acid in solubilising the metals. Plants were grown in a sandy soil collected from a contaminated field site and polluted by Cd, Cr, Cu, Pb and Zn. After 43 days of plant growth, pots were amended with NTA or citric acid at 5 mmol kg-1 soil. Control pots were not treated with any chelate. Harvest of plants was performed 1 week after chelate addition. Soil water-, NH4NO3- and DTPA-extractable Cd, Cu, Pb and Zn fractions were enhanced only in the presence of NTA. In comparison to unamended plants, Indian mustard shoot dry weights suffered significant reductions following NTA application. NTA treatment increased shoot metal concentrations by a factor of 2-3, whereas citric acid did not induce any difference compared to the control. Chromium was detected in the above-ground tissues only after NTA amendment. Due to differences in dry matter yield, a significant enhancement of metal uptake was observed in NTA-treated plants for Cu and Zn.     

Desorption of copper and cadmium from soils enhanced by organic acids

The adsorption/desorption behavior of copper and cadmium on soils was investigated in this study. The adsorption isotherm of copper and cadmium conformed to Langmuir equation better than Freundlich equation. The effect of ionic strength, pH, and organic acid, including ethylenediamine tetraacetic disodium acid salt (EDTA), citric acid, oxalic acid and tartaric acid, on the desorption of copper and cadmium was studied. The desorption of copper and cadmium increased with the increase of ionic strength, while the desorption decreased with the rise of pH. The desorption of copper and cadmium enhanced by organic acids was influenced by pH. EDTA showed excellent enhancement on the desorption of both copper and cadmium; citric acid demonstrated great enhancement on the desorption of copper but negligible enhancement on the desorption of cadmium; oxalic acid enhanced the desorption of copper only at pH around 6.4 and enhanced the desorption of cadmium in the pH range from 6.4 to 10.7; tartaric acid slightly enhanced the desorption of copper but negligibly enhanced the desorption of cadmium. The desorption mechanism in the presence of organic acids were explained as the competition of complexation, adsorption and precipitation. The net effect determined the desorption efficiency. This study provided guidance for the selection of organic acids to enhance the electrokinetic (EK) remediation of copper and cadmium from contaminated soils.     

有机酸对成都平原镉污染土壤的淋洗效果

以成都平原某化工厂附近受Cd污染的2种土壤为对象,采用振荡淋洗技术,研究了有机酸在不同浓度、固液比、振荡时间和复合淋洗条件下对重金属Cd的去除效果。实验结果表明：柠檬酸和酒石酸对Cd含量为22.78 mg·kg-1的SLT-01土壤具有更好的去除效果,分别达到73%和62%,而乙酸和草酸的去除能力较低;随着固液比的降低,有机酸对Cd的去除率逐步提高;随着时间的增加,Cd的去除率波动增加;柠檬酸和酒石酸复合淋洗并没有提高Cd的去除率;振荡淋洗前后土壤结构未发生明显变化。综合考虑土壤中Cd的去除效果和成本,选择柠檬酸作为最佳淋洗剂;最佳实验条件：溶液浓度为0.10 mol·L-1,固液比为1∶20,淋洗时间为8 h。     

6种低分子有机酸对针铁矿、蒙脱石和生物炭中结合态Cd活化效果的对比

选择3种常用的土壤重金属稳定介质针铁矿、蒙脱石和生物炭,首先通过吸附实验使其对Cd达到吸附平衡（8、16和4 h）,并通过氯化镁洗脱获得稳定结合的Cd（2.52、0.93和1.04 mg·g-1）。随后分别用柠檬酸、苹果酸、马来酸、酒石酸、草酸、琥珀酸6种常见的植物根际低分子有机酸进行结合态Cd活化实验,测定活化率和活化量,对比活化效果。结果表明,6种低分子有机酸对针铁矿、蒙脱石、生物炭中结合态Cd的活化效果随浓度的增加而增加,其中柠檬酸的活化作用最大,其次为草酸,其余4种酸的活化效果差异不显著。柠檬酸随浓度增加,其对Cd活化率的线性增长率最高,在针铁矿、蒙脱石、生物炭中分别为1.74%、4.71%、2.12%。在250 μmol·L-1时,柠檬酸对针铁矿、蒙脱石、生物炭3种材料中Cd的活化率分别达到4.2%、11.0%、5.6%。对比研究表明,针铁矿吸附Cd效率高且稳定,蒙脱石吸附Cd效率低且易于被低分子有机酸活化。     

3种纳米材料对低分子质量有机酸淋洗铅、锌和镉效率的影响

新型高效淋洗剂的筛选是土壤重金属淋洗修复技术的基础之一。通过振荡淋洗法研究了纳米二氧化钛（TiO2）、碳纳米管（C）和纳米二氧化硅（SiO2）与柠檬酸和酒石酸组合改性后对2种铅锌矿区土壤的淋洗效率。结果表明,单一柠檬酸对土壤Pb、Zn和Cd去除率最高为71.28%、61.09%、57.40%,而单一纳米材料对3种重金属去除率均小于2%;2种有机酸与纳米材料改性后的重金属淋洗率与单独淋洗差异显著（P2浓度升高,2种有机酸对2种土壤中Pb的去除率显著降低（P2能够明显提升2种有机酸对土壤Pb、Zn和Cd的去除率（P2分别在0.04 mol·L-1和0.10 mol·L-1时提高柠檬酸对3种金属的去除率达13.1%~25.1%和13.5%~26.8%。     

Role of organic acids in enhancing the desorption and uptake of weathered p,p'-DDE by Cucurbita pepo

Experiments were conducted to assess the effect of seven organic acids [succinic, tartaric, malic, malonic, oxalic, citric, ethylene-diaminetetraacetic (EDTA)] over a concentration range of two orders of magnitude (0.001-0.10 M) on the abiotic desorption of weathered p,p'-DDE and the extraction of polyvalent inorganic ions from soil. At 0.05 M all organic acids significantly increased contaminant desorption by 19-80%. Organic acids also increased the aqueous concentration of eight inorganic constituents extracted from soil, with at least a six-fold increase in the release of Al, Fe, Mn, and P at 0.001 M. Zucchini seedlings grown for 28 d in soil containing weathered p,p'-DDE (300 ng/g, dry weight) were periodically amended with distilled water, citric or oxalic acids (0.01 M). Plants receiving water removed 1.7% of the p,p'-DDE from the soil. Seedlings amended with citric or oxalic acids removed 2.1 and 1.9% of the contaminant, respectively, and contained up to 66% more contaminant in the shoot system than unamended vegetation. A second crop of untreated (distilled water) zucchini in the same soil removed more contaminant than the first crop (2.5%), although the addition of organic acids did not further enhance contaminant uptake. The data indicate that the addition of low molecular weight organic acids causes the partial dissolution of the soil structure through the chelation of inorganic structural ions, potentially enhancing bioavailability and having implications for the phytoremediation of persistent organic pollutants in soil.     

鸡粪堆肥水溶性有机物转化特性研究

采用离子色谱和三维荧光光谱,分别对鸡粪堆肥不同阶段水溶性有机物(DOM)中典型小分子有机酸、磷酸和荧光有机物进行了研究。分析显示,所研究的7种酸(乙酸、琥珀酸、苹果酸、草酸、柠檬酸、酒石酸及磷酸)中,苹果酸的含量最高(1 000 mg/L),草酸的浓度最低(3 mg/L),琥珀酸和柠檬酸未检测到。随着堆肥的进行,各种酸的含量先上升而后下降,堆肥结束降至最低;堆肥过程样品所有荧光峰强度之和与COD达到显著相关(R=0.917,P0.05),类蛋白荧光峰强度与总荧光峰强度的比值不断降低,而类富里酸荧光峰强度与总荧光峰强度的比值不断上升。结果表明,堆肥过程小分子有机酸主要出现在堆肥中期;类蛋白荧光强度或类富里酸荧光强度与总荧光强度之比可以有效表征堆肥腐熟过程。     

Influence of sodium nitrilotriacetate (NTA) and citric acid on phenolic and organic acids in Brassica juncea grown in excess of cadmium

Brassica juncea cv. 426308 was grown in soils containing 150 mg Cd(2+)kg(-1) soil. After 38 days, the soil was amended with two rates of citric acid or NTA (10 and 20 mmol kg(-1) soil). Control soil was not amended with chelates. Plants were harvested during growth, immediately before and seven days after chelate addition. Shoot composition of organic and phenolic acids and shoot Cd(2+) concentration were determined. Cadmium concentration remained constant during the growth and increased following NTA and citric acid amendments depending on chelate type and concentration. The highest increments in Cd(2+) were measured after the addition of NTA. Compared to the control, 10 and 20 NTA-treated plants showed two- and three-fold increases, respectively. At 150 mg Cd(2+)kg(-1) soil the amount of organic and phenolic acids in the leaves of B. juncea was always higher than that detected in the control. A direct correlation between organic acid concentration and cadmium content was detected both during growth and after chelate addition. On the contrary, the amount of phenols seemed to be correlated with the metal content only in non-amended and NTA-treated plants. The 10 and 20 citric acid additions caused 45% and 90% increases in shoot phenolic acids although cadmium content rose to a smaller extent. The inhibition of citrate synthase and the entrance of phosphoenolpyruvate in shikimate pathway leading to the formation of aromatic compounds might come into play. The increase in phenylalanine ammonialyase activity following citric acid amendments suggested this metabolic response.     

典型进口再生塑料颗粒中重金属溶出特性及其影响因素

为了解我国进口再生塑料颗粒中重金属溶出特性,以某检测机构的5种再生塑料颗粒PP、PE、PS、PET和ABS为研究对象,研究不同温度、不同接触时间和不同模拟液等条件下,再生塑料颗粒中重金属溶出特性。结果表明,在25、40、70 ℃这3种温度下,PP、PE、PET和ABS再生塑料颗粒中重金属铬、铅、锰、镉、汞和铜的溶出量随着温度的升高而增加,PS中重金属浓度随温度升高变化不大;随着接触时间的增长,样品中的6种重金属Cr、Pb、Mn、Cu、Cd、Hg溶出量增长趋势由快至慢,5种再生塑料颗粒中重金属Cr的溶出浓度最高;PE、PS、PET和ABS再生塑料颗粒在4种模拟液中重金属溶出量大小整体呈现出：50%乙酸>3%乙酸>10%乙醇>95%乙醇,但PP再生塑料颗粒中重金属Cu在3%乙酸中的溶出量比10%乙醇中的多。本研究结果可为建立塑料接触材料及制品中重金属溶出量的标准方法提供依据。     

Nitrilotriacetate- and citric acid-assisted phytoextraction of cadmium by Indian mustard (Brassica juncea (L.) Czernj, Brassicaceae)

In a pot experiment the effects of nitrilotriacetate (NTA) and citric acid applications on Cd extractibility from soil as well as on its uptake and accumulation by Indian mustard (Brassica juncea) were investigated. Plants were grown in a sandy soil with added CdS at four levels ranging from 50 to 200 mg Cd kg(-1) soil. After 30 days of growth, pots were amended with NTA or citric acid at 10 and 20 mmol kg(-1). Control pots were not treated with chelates. Harvest of plants was performed immediately before and one week after chelate addition. Soil water-, NH(4)NO(3)- and EDTA-extractable Cd fractions increased constantly with both increasing soil metal application and chelate concentration. Shoot dry weights did not suffer significant reductions with increasing Cd addition to the soil except for both NTA treatments in which at 200 mg Cd kg(-1) a 30% decrease in dry matter was observed. Generally, following NTA and citric acid amendments, Cd concentration in shoots increased with soil Cd level. However, due to Cd toxicity, at the highest metal application rate both NTA treatments lowered Cd concentration in the above-ground parts. Compared to the control, at 10 mmol kg(-1) citric acid did not change Cd concentration in shoots, whereas NTA-treated plants showed an about 2-fold increase. The addition of chelates at 20 mmol kg(-1) further enhanced Cd concentration in shoots up to 718 and 560 microg g(-1) dry weight in the NTA and citrate treatments, respectively.     

Light-induced degradation of perfluorocarboxylic acids in the presence of titanium dioxide

The UV-photon-induced degradation of heptafluorobutanoic acid was investigated in acidic aqueous solutions in the presence of titanium dioxide. Heptafluorobutanoic acid could be degraded with this photocatalyst in a light-induced reaction generating carbon dioxide and fluoride anions. Carbon dioxide evolution in a significant amount occurred only in the presence of molecular oxygen and the photocatalyst. The light-induced degradation of trifluoroacetic acid, pentafluoropropanoic acid, nonafluorobutanoic acid, pentadecafluorooctanoic acid, nonafluorobutanesulfonic acid, and heptadecafluorooctanesulfonic acid in the presence of titanium dioxide was also studied. The perfluorocarboxylic acids under investigation are degraded to generate CO(2) and fluoride anions while both perfluorinated sulfonic acids are persistent under the experimental conditions employed in this study. For all compounds photonic efficiencies of the mineralization reaction were estimated to be smaller than 1x10(-5). To increase the photocatalytic activity mixed systems containing homogeneous phosphotungstic acid and heterogeneous titanium dioxide catalysts were also investigated. In the mixtures of these two photocatalysts, the formation rate of CO(2) increased with illumination time.     

Hydrometallurgical recovery of zinc from ashes of automobile tire wastes

Study has been performed on the investigation of metal leaching behavior for fly and bottom ashes from automobile tire wastes using acid and alkaline solutions from both viewpoints of environmental protection and resource utilization. The two ashes were found to contain substantial amounts of zinc and iron along with small quantities of cobalt, manganese, magnesium, copper, titanium and aluminum. The fly ash contained a much larger amount of zinc than the bottom ash, and seems to be a promising secondary source for the metal. Effects of such experimental parameters as temperature, time and solid-liquid ratio on the leaching behavior were investigated. Using three mineral acids and citric acid, selective leaching of zinc was successfully attained; the concentration of zinc in the leach liquors from the fly ash reached as high as 20 g l(-1) while the iron leaching was much suppressed. Selective separation of zinc was also attained in the leaching with alkaline solutions, though the percent leaching was lower than that in the acid leaching. Moreover, solvent extraction and precipitation were applied to the metal-loaded leach liquors as downstream processing to evaluate the feasibility of zinc recovery.     

Evaluation of the effect of small organic acids on phytoextraction of Cu and Pb from soil with tobacco Nicotiana tabacum

Phytoremediation, the use of plants to extract contaminants from soils and groundwater, is a promising approach for cleaning up soils contaminated with heavy metals. However its use is limited by the time required for plant growth, the nutrient supply and, moreover, by the limited metal uptake capacity. Synthetic chelators have shown positive effects in enhancing heavy metal extraction, but they have also revealed several negative side-effects. The objective of this study was to investigate the use of three natural low molecular weight organic acids (NLMWOA) (citric, oxalic, and tartaric acid) as an alternative to synthetic chelators. Slurry-, column-, toxicity- and phytoextraction experiments were performed. For the phytoextraction experiment the three NLMWOA were applied to a copper- and a lead-contaminated soil respectively. A significant increase in copper uptake was visible only in the citric acid treatment (67 mg kg-1) in comparison to the EDTA treatment (42 mg kg-1). The NLMWOA application showed no enhanced effect concerning the lead phytoextraction. A possible explanation for this lack of significance could be the rate of the degradation of NLMWOA. This rate might well be too high for these heavy metals with low mobility and bioavailability such as lead. The amounts of NLMWOA applied to the soil were very high (62.5 mmol kg-1 of soil) and the effect was too little. In this respect EDTA, which was applied in very small amounts (0.125 mmol kg-1) was more efficient. Thus making NLMWOA unsuitable to enhance phytoextraction of heavy metals from soil.     

酒石酸强化重金属复合污染模拟土壤电动修复过程及机理分析

为提高电动修复重金属复合污染土壤的效率,通过配制重金属复合污染模拟土壤,构建电动修复实验装置,利用2因素完全随机实验设计研究了酒石酸浓度和时间对重金属去除效果的影响;采用BCR法对土壤金属赋存形态进行了分析表征。结果表明：与对照相比,以酒石酸为电解液显著提高了重金属的去除率;重金属去除率受酒石酸浓度和修复时间影响显著;以0.05 mol·L⁻¹酒石酸为电解液修复120 h后,重金属去除效果最好,重金属总去除率为86.15%,Cu²⁺、Mn²⁺、Cd²⁺、Pb²⁺、Zn²⁺的去除率分别为75.67%、98.11%、85.1%、70.75%和90.9%。BCR分析表明,酒石酸有助于提高土壤中弱酸提取态重金属含量,提高了重金属的迁移性能,从而有利于电动修复过程。