Environmental availability and ecological risk assessment of heavy metals in zinc leaching residue

Four different methods,namely mineralogical analysis,three-stage BCR sequential extraction procedure,dynamic leaching test and Hakanson Potential Ecological Risk Index Method were used to access the environmental activity and potential ecological risks of heavy metals in zinc leaching residue.The results demonstrate that the environmental activity of heavy metals declines in the following order：CdZnCuAsPb.Potential ecological risk indices for single heavy metal are CdZnCuAsPb.Cd has serious potential ecological risk to the ecological environment and contributes most to the potential toxicity response indices for various heavy metals in the residue.

Heavy metal availability and impact on activity of soil microorganisms along a Cu/Zn contamination gradient

All the regulations that define a maximum concentration of metals in the receiving soil are based on total soil metal concentration. However, the potential toxicity of a heavy metal in the soil depends on its speciation and availability. We studied the effects of heavy metal speciation and availability on soil microorganism activities along a Cu/Zn contamination gradient. Microbial biomass and enzyme activity of soil contaminated with both Cu and Zn were investigated. The results showed that microbial biomass was negatively affected by the elevated metal levels. The microbial biomass-C （Cmic）/organic C （Corg） ratio was closely correlated to heavy metal stress. There were negative correlations between soil microbial biomass, phosphatase activity and NH4NO3 extractable heavy metals. The soil microorganism activity could be predicted using empirical models with the availability of Cu and Zn. We observed that 72% of the variation in phosphatase activity could be explained by the NH4NO3-extractable and total heavy metal concentration. By considering different monitoring approaches and different viewpoints, this set of methods applied in this study seemed sensitive to site differences and contributed to a better understanding of the effects of heavy metals on the size and activity of microorganisms in soils. The data presented demonstrate the relationship between heavy metals availability and heavy metal toxicity to soil microorganism along a contamination gradient.

Thermal behaviors and heavy metal vaporization of phosphatized tannery sludge in incineration process

The high concentration of heavy metal (Cu, Cr, Zn, Pb) in tannery sludge causes severe heavy metal emissions in the process of incineration. In the present investigation, the tannery sludge was treated with 85% phosphoric acid before the incineration process in the tube furnace to control the heavy metal emissions. The thermal behavior and heavy metal vaporization of pre-treated tannery sludge were investigated, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were also implemente...

Behavior features of heavy metals in the Haikou Bay waters

Dissolved Cu, Ph, Zn and Cd in the Haikou Bay waters were measured to be respectively in the range concentrations of 0.47-1.16 μg/dm^3, 0. 94-- 2. 36μg/dm^3, 1.28-4.83 μg/dm^3 and 0. 005-0.072μg/dm^3; with respectively average values of 0.78μg/dm^3, 1.36μg/dm^3, 3.14 g/dm^3 and 0. 03 μg/dm^3. Dissolved Cu and Zn concentrations are relatively high at the stations near the Longkun Road Outfall for domestic sewage, the Xiuying Outfall for industry waste water and the Haidian Island Estuary, but dissolved Pb and Cd concentrations are low in these stations. The values in Other stations are comparatively homogenous. Vertical dissolved Cu, Pb and Zn concentrations at the bottom layer are higher than at the surface layer, but dissolved Cd concentration appears to be on the opposite. The measurement results of Cu, Pb, Zn and Cd in suspended particle show that particulate matters in the Haikou Bay seawater play a role in purifying heavy metals. The study on strong complexed form and non-liable form of dissolved copper show that the ratio of strong complexed form and dissolved form is about 85%, and non-liable form is very low with a value lower than 5 nmol/dm^3. Therefore, copper in the Haikou Bay seawater cannot cause influence on marine organisms.

Leaching Behavior and Mechanism of Cement Solidified Heavy Metal Pb in Acid Medium

The relationship between Pb leaching concentration and the solution＇s pH with time was analyzed when cement in its solidified form was leached in an acid medium. The effects of the particle size of the solidified form, the cement adding method, and the hydration degree on Pb solidification were also investigated. The experimental results indicate that cement is quickly dissolved and hydrated in the acid medium, forming a C-S-H gel or silicic acid sol with good adsorption. When cement-Pb solidified form is leached in an acetate solution, the hydrated product erodes with time, so the Pb concentration increases slightly in the beginning. Then, some of the Pb ions are absorbed by the newly generated silicic acid sol, C-S-H. Others produce Pb（OH）2 precipitation for secondary solidification, leading to a gradual decrease in the Pb concentration in a leaching time of more than two hours. Moreover, the particle size of the solidified form has important effects on the Pb dissolution. When the amount of added cement is low, with a pH of less than 9.5, the solidification affects the sequence of the original cement powder, the cement hydrated powder, and the cement- Pb solidified form. When the added amount of cement increases with a pH of more than 11, the effect of adding methods on solidification decreases, and the solidified form is a little better than others.

Assessment of locomotion behavioral defects induced by acute toxicity from heavy metal exposure in nematode Caenorhabditis elegans

Locomotion behaviors are susceptible to disruption by a broad spectrum of chemicals and environmental stresses. However, no systematic testing of locomotion behavior defects induced by metal exposure has been conducted in the model organism of nematode Caenorhabditis elegans. In this study, the acute toxicity from heavy metal exposure on the locomotion behaviors was analyzed in nematodes. Endpoints of head thrash, body bend, forward turn, backward turn, and Omega/U turn were chosen to evaluate the locomotio...

Leaching behavior of V,Pb,Cd,Cr,and As from stone coal waste rock with different particle sizes

This paper investigates the leaching behavior of heavy metals(V,Pb,Cd,Cr,and As) from stone coal waste rocks with various particle sizes using dynamic leaching experiments.The results show that the dissolved concentrations of V and As initially increased and then slightly decreased as time progressed and that the dissolved concentrations of Pb,Cd,and Cr were high in the early stage before decreasing.The particle size of the stone coal waste rocks strongly influenced the heavy metal concentration in the leaching solutions.The effects of the particle size of the stone coal waste rocks on the dissolved concentrations of V,Pb,and As decreased in the order fine fraction > medium fraction > coarse fraction,and the effects of particle size on the dissolved concentrations of Cr and Cd decreased in the order medium fraction > coarse fraction > fine fraction and coarse fraction > medium fraction > fine fraction,respectively.The quantities of heavy metals dissolved from the stone coal waste rock with fine particle sizes were observed to decrease in the order V(17104.36 μg/kg) > As(609.41 μg/kg) > Pb(469.24 μg/kg) > Cr(56.35 μg/kg) > Cd(27.52 μg/kg),and the dissolution rates decreased in the order As(2.96%) > Pb(0.93%) > V(0.35%) > Cd(0.25%) > Cr(0.01%).The specific surface area,pore size of the stone coal waste rocks,and chemical forms of heavy metals also influenced the release of heavy metals from the stone coal waste rocks.Kinetic analysis showed that the dissolution of heavy metals fundamentally agreed with the rate equation controlled by the shrinking core model.The results of this study are expected to serve as a reference for the evaluation of heavy metals contamination from stone coal waste rocks.

Leaching behavior of Pb and Zn in air pollution control residues and their modeling prediction

Increasing attention has been paid to air pollution control （APC） residues in China recently due to the rising proportion of waste incineration and the hazardous characteristics of the residues, among which heavy metal leaching toxicity plays an important role. Leaching behavior and potential risk of Pb and Zn in the APC residues from a Shanghai municipal solid waste （MSW） incinerator was studied, based on the leaching tests under different conditions and theoretical calculation using a geochemical thermodynamic equilibrium model MINTEQA2. Results showed that, extractant species and liquid to solid （L/S） ratio predominantly controlled the leaching toxicity of Pb and Zn, while ionic strength, vibration method and leaching time had less effect on the metals release. Leachate/final pH determined the metal leaching behavior, which changed the speciation of heavy metals in the extraction system. The equilibrium aqueous speciation, precipitation-dissolution of Pb and Zn was investigated according to the model computation, which was well in agreement with the experimental results.

Effect of Heavy Metal Pollution on Potassium Behavior in Typic Udic Ferrisol

The indirect influence of heavy metal contamination of soil on nutrient availability, an important aspect of soil quality, may need to be taken into consideration when determining overall effects of heavy metals. A laboratory experiment was performed to study the effects of combined pollution of Cu, Ph, Zn and Cd on soil K status as indicated by chemical fractions, adsorption-desorption and quantity/intensity (Q/I) relationship of K in a Typic Udic Ferrisol (generally called red soil), by employing uniform design and single factor design. Compared to the control, content of exchangeable K was decreased, but that of soluble K increased in the samples contaminated with heavy metals. Due to heavy metal pollution, potassium adsorption was reduced by 5% to 22%, whereas the desorption percentage of adsorbed K increased by 2% to 32%. The Q/I curves shifted downward, potassium buffering capacity (PBCK) decreased, and equilibrium activity ratio values (ARoK) increased with increasing heavy metal pollution. These influences followed the sequences of Ph>Cu>Zn and combined pollution>single one. Displacement of K from canon exchange sites and decrease in soil CEC due to heavy metals should be responsible for the changes of soil K behaviours. The findings suggest that heavy metal pollution of soil might aggravate the degradation of soil K fertility by decreasing K adsorption and buffering capacity and increasing desorption.

Behavior of Cu, Pb, and Zn in Ash during the Endothermic Burning of Mixed Industrial Wastes

The behaviors of Cu, Pb, and Zn during the endothermic burning of heterogeneous wastes were investigated using a variety of operational parameters, i.e., the mixed waste ratio, burning temperature, and burning time, to obtain fundamental knowledge to generate an optimal burning operation and recycling strategy for bottom ash. Changing these parameters had no impact on the Cu content of the ash, whereas the Pb content depended on the burning temperature and the mixed ratio, and the Zn content was affected by all three parameters. It was found in this study that the optimal burning conditions were a temperature of 1100?C, a time of 15 minutes, and either the current waste conditions or waste conditions with double the waste plastic and wood content.

Comments on“Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al_2O_3 particles”

Recently, Hsieh and Horng [1] published the paper entitled as above. In section 3 results and discussion, the authors mentioned the first and the second order kinetic models without any quotations. In fact these two kinetic models have been published [2-5]. In order to distinguish a kinetics model based on the ad- sorption capacity of a solid from the one based on the concentration of a solution, Lagergren＇s first-order rate equation has been called pseudo-first-order [6-7]. The Lagergren＇s equation has been widely cited, but there are far more mistakes made in the quotation and in the reference section of papers, including the title, the author＇s name, journal title, year of publishing, volume, and page number [3]. In addition, the second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho [8].

Physicochemical and environmental properties of arsenic sulfide sludge from copper and lead-zinc smelter

Physicochemical properties of arsenic sulfide sludge(ASS) from copper smelter(ASS-I) and lead-zinc smelter(ASS-II) were examined by XRD, Raman spectroscopy, SEM-EDS, TG-DTA, XPS and chemical phase analysis method. The toxicity characteristic leaching procedure(TCLP), Chinese standard leaching tests(CSLT), three-stage sequential extraction procedure(BCR) and batch leaching experiments(BLE) were used to investigate the environmental stability. The ASSs from different smelters had obviously different physicochemical and environmental properties. The phase composition and micrograph analysis indicate that ASS-I mainly consists of super refined flocculent particles including amorphous arsenic sulfide adhered with amorphous sulfur and that ASS-II mainly consists of amorphous arsenic sulfide. The valence state of arsenic in both sludges is trivalent, but the valence composition of sulfur is quite different. The ASSs have thermal instability properties. The results of TCLP and CSLT indicate that the concentrations of As and Pd in the leaching solution exceed the standard limits. More than 5% and 90% of arsenic are in the form of acid soluble and oxidizable fractions, respectively, which explains the high arsenic leaching toxicity and environmental activity of ASS. This research provides comprehensive information for the disposal of ASS from copper and lead-zinc smelter.

共价有机骨架材料(COFs)对Cr(Ⅵ)的吸附行为分析

以三醛基间苯三酚为一种合成单体采用水热合成法制备了两种共价有机骨架材料(TpBD COFs和MICOFs)并将其作为重金属离子Cr(Ⅵ)的吸附剂考察共价有机骨架材料的吸附行为。结果表明:水热合成法成功制备了两种有机共价材料,且材料具备丰富的孔道,比表面积分别为81.461和110.500 m^(2)/g。对铬离子的吸附结果表明TpBD COFs、MICOFs材料的平衡吸附时间分别为20 min、10 min,静力学吸附行为均符合单分子层表面吸附的Langmuir等温吸附模型,动力学吸附行为均符合准一级动力学行为,两种材料的吸附时间短,吸附效果理想,具备将其用于废水中重金属离子富集净化的可行性。

Derivation of soil Pb/Cd/As thresholds for safety of vegetable planting: A case study for pakchoi in Guangdong Province,China

Regional guidelines for soil heavy metals,in conjunction with specific crops,are proposed to better assess soil environmental quality.In this study,large amounts of soils with different levels of Pb/Cd/As pollution were collected in Guangdong Province,China,to carry out a pot experiment,which was closer to the actual situation and properties of the heavy metal contaminated soils.Taking the widely planted vegetable pakchoi as the research object,we analyzed the correlations between the Pb/Cd/As concentrations in pakchoi and the total or available soil Pb/Cd/As concentrations and established their optimal regression equations.And then,the total and available soil Pb/Cd/As thresholds for pakchoi were calculated according to the allowable Pb/Cd/As limits in pakchoi and were compared with the current soil assessment standards.Furthermore,a lot of paired vegetable-soil samples in field were collected and their pollution situations were assessed by both the current limit thresholds and the calculated thresholds.Obviously,it was more consistent to assess the Cd and As pollution situation of the vegetable and soil samples with the calculated soil thresholds than the current soil assessment thresholds.It further proved that it was necessary to explore the soil heavy metal thresholds for safety of vegetable in specific regions,which would be more scientific and practical to guide safety production of local agricultural products and effective utilization of soil resources.

施用有机肥和调理剂对田间土壤重金属有效态变化影响及水稻降镉效应研究

以春优84和中浙优8号为试验材料,在浙江衢州典型镉污染农田开展大田小区试验,研究有机肥与土壤调理剂施用对土壤酸碱度(pH)、土壤重金属元素(Cd、Fe、Mn、Zn等)有效态、水稻植株(稻草、籽粒)重金属元素积累量的影响,并探究了施用有机肥与土壤调理剂降低籽粒Cd积累的机理。结果表明,单施有机肥(1.5 t/hm^(2))对土壤金属元素有效态、稻草和籽粒重金属元素含量无显著影响;在有机肥(1.5 t/hm^(2))+土壤调理剂(2.7 t/hm^(2))联合施用处理后,土壤pH增加9.48%,土壤重金属有效态含量和植株中重金属元素含量均呈下降趋势。其中,土壤有效态Cd含量降低16.41%(DTPA提取)和48.96%(CaCl_(2)提取),稻草和籽粒Cd含量分别降低40.04%和48.22%。逐步回归和通径分析表明,稻草Cd含量、土壤Cd有效态与籽粒Cd含量显著相关。由此可见,施用土壤调理剂通过提升土壤pH,从而降低土壤重金属元素有效态含量,其中有效态Cd含量下降尤为显著,以此调控水稻稻草和籽粒中的Cd积累。说明供试土壤调理剂可以在酸性土地区推广应用,具有提升酸性土壤pH、降低稻米Cd富集的效果。

两种调理剂对水稻土pH值和重金属吸收的影响

探明两种调理剂对近中性水稻土pH值、重金属有效性和水稻吸收的影响,及其与土壤性质的关系,为调理剂的科学开发及合理施用提供科学依据。选取水淬高炉渣源调理剂(T1)及其腐殖质改性调理剂(T2),分别设置2个施用量梯度(T1L、T1H和T2L、T2H),通过盆栽试验分析了两种调理剂及不同用量对土壤pH值、有效硅、镉、锌、铜含量,以及水稻籽粒和秸秆镉、锌、铜含量的影响。与对照(CK)相比,2个施用T1调理剂处理土壤pH值分别升高0.64和1.02,2个施用T2调理剂处理pH值分别升高0.27和0.56(P<0.05),土壤pH值随调理剂施用量的增加而增加。T1L和T1H处理土壤有效硅含量与CK相比分别提高5和22倍(P<0.05),且显著高于施用T2调理剂处理。与CK相比,T1H处理土壤有效镉、锌、铜含量分别降低37.21%、45.57%和95.30%(P<0.05);T2L和T2H处理土壤有效锌含量分别降低31.55%和30.67%,有效铜含量分别降低6.53%和19.32%(P<0.05)。与CK相比,T1L和T1H水稻籽粒锌含量分别降低23.44%和18.12%(P<0.05);施用T2调理剂后,籽粒和秸秆锌、铜含量无显著变化。土壤pH值、有效硅含量与土壤有效镉、锌、铜含量呈显著或极显著负相关,土壤有效硅含量与籽粒、秸秆镉含量呈显著负相关。研究表明,在近中性水稻土上施用富含硅的强碱性调理剂,既有利于提高土壤p H值和有效硅含量,又可有效降低土壤重金属有效性及其水稻吸收量。

中轻度重金属污染农田土壤的时空特征及改良

为研究农田土壤重金属与速效养分的时空特征以及氮磷增效剂对农田土壤重金属的影响,本试验以受中、轻度污染的酸性棕壤和典型潮土为研究对象,采用田间试验、盆栽试验与室内分析相结合的方法进行研究。结果表明:农田土壤中Cd、Cu、Pb、Zn 4种重金属元素含量在0~20 cm土层显著高于深层土壤;棕壤0~20 cm土层Cd含量超标204%,潮土0~20 cm土层Cd、Zn含量分别超标104%、419%;农田土壤0~20 cm土层重金属有效态含量占比高于深层土壤,棕壤中重金属有效态含量占比高于潮土。棕壤0~20 cm土层全氮、碱解氮、铵态氮、硝态氮、有效磷和速效钾含量均显著高于深层土壤,且随土壤深度增加呈逐渐减小趋势,而潮土中仅全氮、碱解氮和有效磷含量显著高于深层土壤;农田土壤速效养分随时间波动变化,其中硝态氮和铵态氮波动幅度最大,最大变异系数分别为44.1%和47.3%。受污染农田土壤的小麦植株体内Cd、Pb、Cu主要积累在叶片,Zn主要积累在籽粒;不同重金属元素从小麦茎、叶向籽粒的迁移程度差异较大,其中Cd迁移率最小,Zn迁移率最大。氮磷增效剂能显著减少棕壤中重金属有效态含量,底肥+氢醌+双氰胺+生物炭处理的有效态Cd、Cu、Pb、Zn含量较对照(仅加底肥,不加氮磷增效剂)处理分别显著降低24.7%、19.5%、23.7%、18.1%,而在潮土中施用效果不明显。研究表明,农田土壤重金属与土壤养分之间存在一定的相关性,且在土壤垂直分布上大体一致,土壤类型是氮磷增效剂对重金属有效态产生不同影响的重要因素。

羟基磷灰石与秸秆生物炭对青菜镉积累的钝化效应

农田重金属污染通过食物链危害人体健康,对土壤改良实现安全利用和保障农产品质量安全成为重要现实需求。本研究实地采集苏北Cd污染农田土壤分别进行模拟培养和温室蔬菜盆栽试验,探讨施加不同用量的羟基磷灰石(HAP,1%、2%)、水稻秸秆生物炭(BC,1%、2%)及其组合施用(0.5%HAP+0.5%BC、1%HAP+1%BC)对土壤Cd活性的钝化效率和降低青菜Cd吸收的效果并分析其作用机制。青菜盆栽试验表明,不同钝化剂处理均提高了叶片的净光合速率,生物量增加3.78%~124%,青菜Cd含量与土壤有效态Cd浓度分别降低16.1%~81.7%、15.8%~69.9%;40 d土壤培养试验后,各钝化剂对有效态Cd的降幅达28.9%~87.6%,主要机理是土壤pH显著提高了0.38~0.98个单位、Cd残渣态含量增加19.5%~37.0%、酸溶态含量减少21.1%~25.6%。可见,2种类型的钝化剂均主要通过降低土壤中Cd的化学活性和植物有效性来阻控其被蔬菜吸收积累,而在同等用量下的酸性污染土壤中,无机型材料HAP对提高蔬菜生物量和降低Cd吸收效果最佳且起效更快,其次则是HAP+BC复配的无机-有机复合型改良剂,但有机型材料BC则效果偏弱且起效慢,需要协同施用HAP提升钝化效率。

黔西南露天煤矿废弃地重金属污染特征研究

以黔西南某典型露天煤矿为研究对象,采集弃渣区、覆土区、植物修复区及矿区周边对照区的土壤样品,测定土壤pH值、重金属含量及其形态,采用静置淋溶方法分析重金属污染扩散过程。结果表明:废弃地弃渣区、覆土区和植物修复区土壤的pH值分别为2.86、3.49和4.90,均小于未开采对照区(6.48),废弃地土壤严重酸化;弃渣区土壤重金属Cu和Cd含量分别超过贵州省土壤背景值的4.57倍和3倍,超过土壤污染风险筛选值的1.86倍和0.73倍,弃渣区重金属Cr含量超过贵州省土壤背景值的1.14倍,超过土壤污染风险筛选值的0.37倍。弃渣区重金属Cu和Cd达中度及以上污染,重金属Cr和Pb为中度污染,植物修复区Pb、Zn、Cr污染程度与对照区无显著差异;内梅罗污染指数、土壤污染负荷指数、土壤综合潜在生态危害指数表明植物修复区、覆土区污染等级为轻度污染,弃渣区为重度污染;弃渣区、覆土区土壤Cu、Cr和Cd弱酸可提取态占比明显高于植物修复区和对照区;弃渣区土壤重金属淋溶释放速率及释放量均高于其他区域。土壤pH值与重金属Cr、Cu和Pb形态特征存在显著相关性,pH值降低显著提升了重金属弱酸可提取态占比,土壤酸化明显促进了重金属元素的迁移释放及生物有效性的提升,淋溶加剧了土壤酸化及重金属污染的扩散。