3种含铁材料对重金属和砷复合污染底泥稳定化处理

选用3种含铁材料FeCl3、Fe(OH)3和FePO4,开展重金属和砷(As)复合污染底泥的稳定化处理实验,并用毒性浸出测试(TCLP)的结果和底泥交换态重金属(Pb、Cd、Cu、Zn)及As的含量来评价其稳定化效果。结果表明,(1)FeCl3和FePO4降低了底泥pH值,Fe(OH)3轻微地提高了底泥pH值。(2)FeCl3活化了底泥中Pb、Cd、Cu、Zn,使其浸出量和交换态含量增加,对As浸出量的影响不大,但使底泥中As交换态含量明显降低,且在最大添加量(8.00 g/kg)时As交换态含量未检测出;Fe(OH)3降低了Cd交换态和浸出量,稍增加了As交换态和浸出量,但对Pb、Cu、Zn交换态和浸出量影响不明显;FePO4明显降低了Pb的浸出量和交换态含量,略微降低了交换态Cd、Zn含量,对交换态Cu影响不大,但明显增加了As的浸出量和交换态含量。综上,FeCl3对As具有较好的稳定化效果,但明显活化了底泥中的4种重金属;Fe(OH)3亦对底泥中Cd有一定稳定化效果;FePO4对Pb的稳定化效果较好,但明显活化了底泥中的As。显然,3种含铁材料都不能实现底泥中重金属和As的同时稳定化。     

Heavy metal availability,bioaccessibility, and leachability in contaminated soil: effects of pig manure and earthworms

A pot experiment and a leaching experiment were conducted to investigate the effects of earthworms and pig manure on heavy metals (Cd, Pb, and Zn) immobility, in vitro bioaccessibility and leachability under simulated acid rain (SAR). Results showed manure significantly increased soil organic carbon (SOC), dissolved organic carbon (DOC), available phosphorus (AP), total N, total P and pH, and decreased CaCl₂-extractable metals and total heavy metals in water and SAR leachate. The addition of earthworms significantly increased AP (from 0.38 to 1.7 mg kg^?1), and a downward trend in CaCl₂-extractable and total leaching loss of heavy metals were observed. The combined earthworm and manure treatment decreased CaCl₂-extractable Zn, Cd, and Pb. For Na₄P₂O₇-extractable metals, Cd and Pb were decreased with increasing manure application rate. Application of earthworm alone did not contribute to the remediation of heavy metal polluted soils. Considering the effects on heavy metal immobilization and cost, the application of 6% manure was an alternative approach for treating contaminated soils. These findings provide valuable information for risk management during immobilization of heavy metals in contaminated soils.

     

Removal of Cu, Zn, and Cd from aqueous solutions by the dairy manure-derived biochar

Purpose

Biochar derived from waste biomass is now gaining much attention for its function as a biosorbent for environmental remediation. The objective of this study was to determine the effectiveness of biochar as a sorbent in removing Cd, Cu, and Zn from aqueous solutions.

Methods

Biochar was produced from dairy manure (DM) at two temperatures: 200°C and 350°C, referred to as DM200 and DM350, respectively. The obtained biochars were then equilibrated with 0–5 mM Cu, Zn or Cd in 0.01 M NaNO₃ solution for 10 h. The changes in solution metal concentrations after sorption were evaluated for sorption capacity using isotherm modeling and chemical speciation Visual MINTEQ modeling, while the solid was collected for species characterization using infrared spectroscopy and X-ray elemental dot mapping techniques.

Results

The isotherms of Cu, Zn, and Cd sorption by DM200 were better fitted to Langmuir model, whereas Freundlich model well described the sorption of the three metals by DM350. The DM350 were more effective in sorbing all three metals than DM200 with both biochars had the highest affinity for Cu, followed by Zn and Cd. The maximum sorption capacities of Cu, Zn, and Cd by DM200 were 48.4, 31.6, and 31.9 mg g^?1, respectively, and those of Cu, Zn, and Cd by DM350 were 54.4, 32.8, and 51.4 mg g^?1, respectively. Sorption of the metals by the biochar was mainly attributed to their precipitation with PO ₄ ^3? or CO ₃ ^2? originating in biochar, with less to the surface complexation through –OH groups or delocalized π electrons. At the initial metal concentration of 5 mM, 80–100 % of Cu, Zn, and Cd retention by DM200 resulted from the precipitation, with less than 20 % from surface adsorption through phenonic –OH complexation. Among the precipitation, 20–30 % of the precipitation occurred as metal phosphate and 70–80 % as metal carbonate. For DM350, 75–100 % of Cu, Zn, and Cd retention were due to the precipitation, with less than 25 % to surface adsorption through complexation of heavy metal by phenonic –OH site or delocalized π electrons. Among the precipitation, only less than 10 % of the precipitation was present as metal phosphate and more than 90 % as metal carbonate.

Conclusions

Results indicated that dairy manure waste can be converted into value-added biochar as a sorbent for sorption of heavy metals, and the mineral components originated in the biochar play an important role in the biochar's high sorption capacity.     

The Capture of Heavy Metals from Incineration Using a Spray Dryer Integrated with a Fabric Filter Using Various Additives

ABSTRACT

This study investigated the effects of feedstock additives [polyvinyl chloride (PVC) and NaCl] and spray dryer additives (SiO₂, CaCl₂, NaHCO₃) on heavy metal and fly ash removal efficiencies, and on particle size distribution of heavy metals. A spray dryer with an integrated fabric filter was used as an air pollution control device (APCD). Removal efficiencies for fly ash and heavy metals were greater than 95 and 90%, respectively. When additives of PVC or NaCl were used, the concentration of heavy metals distributed in fly ash apparently varied when the particle diameter was <1 μm. Although the effects of the additives SiO₂, CaCl₂, and NaHCO₃ on the elemental size distribution of Cr were insignificant, these additives did slightly increase concentrations of Cd, Zn, and Pb partitioning in coarser particles (>1μm).     

复合纳米材料对土壤重金属离子吸持固化的模拟研究

土壤中过量重金属离子可通过食物链和地表水系统危害人群健康。通过土柱淋溶模拟实验,研究了SiO2-Al2O3-Fe2O3等复合纳米材料对土壤溶液中Cu2+、Cd2+、Pb2+、Zn2+和Ni2+的吸持与固化特征。分别向重金属含量4倍于土壤二级标准(GB15618-1995)的土壤中添加0%、4%、6%和10%的复合纳米材料,分析不同深度土壤渗滤液以及土柱上栽培植物不同部位中重金属的含量。结果表明,碱性壤质土壤中重金属向下的迁移量很少;在含4%复合纳米材料土柱中,其吸持固化土壤溶液中63%的Cu、79%的Cd、68%的Pb、89%的Zn和76%的Ni;在含6%复合纳米材料土柱中,其吸持固化土壤溶液中82%的Cu、92%的Cd、76%的Pb、91%的Zn和88%的Ni;再增加土柱中复合纳米材料的含量,其吸持固化效果并不再显著增加。     

Adsorption,desorption, potential and selective distribution op heavy metals in selected soils of japan

Abstract

Adsorption, desorption, potential and selective distribution of Cu, Zn, Cd, Pb and Ni were investigated in three typical soils of Japan under flooded condition.

The results indicate that the sorption of all heavy metals was linear upto the maximum concentration (500 μg/g soil) employed in the present studies in all the soils. The magnitude of sorption in general was in the order of Pb > Cu > Zn > Cd > Ni. The adsorption coefficients showed wide variations among different soils as well as metal ions. The hysteresis of sorption and desorption by KNO₃ was well pronounced for both the metal ions and the soils. The desorption rate was greater than the fixation rate indicating the predominance of the chemosorption over physical processes. The major portion of sorbed metals were retained in the unextractable form, which over all accounted for more than 50% of the sorbed metals.     

The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings

A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (C_pw) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8-5.7 and 1.4-2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the C_pw of Cd and Zn, increasing the C_pw of As, and increasing the iron plaque blocking capacity for Cd and Pb.     

Competitive sorption of heavy metal by soils. Isotherms and fractional factorial experiments

Competing ions strongly affect heavy metal sorption onto the solid surfaces of soil. This study evaluated competitive sorption of Cd, Cu, Ni, Pb and Zn on three soils: Calcixerollic Xerochrept, Paralithic Xerorthent and Lithic Haplumbrept. Monometal and competitive sorption isotherms were obtained at 25 degrees C. The individual effect of ions on retention of the others was ascertained by a fractional factorial analysis design. Most of the sorption isotherms belonged to type L subtype 2 in the classification of Giles. In competitive sorption the initial linear part was shorter and the knee sharper when compared with monometal sorption isotherms. Parameters related to sorptive capacity, such as Point B, Langmuir monolayer and Freundlich distribution coefficient, were higher in monometal than in competitive sorption, and in basic soils than in acidic soil. Calcium desorbed at different points of the sorption isotherms indicated that cationic exchange with Ca was the main retention mechanism in calcareous soils. For Pb, the ratio Ca desorbed/Pb sorbed was close to one; for Cu, Ni and Zn the ratio ranged from 1.20 to 1.37, probably due to partial dissolution of calcium carbonates by hydrolytic processes during retention. On the other hand, Cd had a ratio around 0.6 reflecting another additional retention mechanism, probably surface complexation. Fractional factorial design confirmed that the presence of the cations investigated reduced the amount of the five metals retained, but the presence of Cu and Pb in the system depressed Ni, Cd and Zn sorption more than the inverse. Cation mobility was enhanced when equilibrium concentration increased and the effect was higher in Ca-saturated soils.     

Impact of lime-stabilized biosolid application on Cu,Ni, Pb and Zn mobility in an acidic soil

A soil column leaching study was conducted on an acidic soil in order to assess the impact of lime-stabilized biosolid on the mobility of metallic pollutants (Cu, Ni, Pb and Zn). Column leaching experiments were conducted by injecting successively CaCl₂, oxalic acid and ethylenediaminetetraacetic acid (EDTA) solutions through soil and biosolid-amended soil columns. The comparison of leaching curves showed that the transport of metals is mainly related to the dissolved organic carbon, pH and the nature of extractants. Metal mobility in the soil and biosolid-amended soils is higher with EDTA than with CaCl₂ and oxalic acid extractions, indicating that metals are strongly bound to solid-phase components. The single application of lime-stabilized biosolid at a rate ranging from 15 to 30 t/ha tends to decrease the mobility of metals, while repeated applications (2?×?15 t/ha) increase metal leaching from soil. This result highlights the importance of monitoring the movement and concentrations of metals, especially in acid and sandy soils with shallow and smaller water bodies.     

Elevated CO2 concentration increase the mobility of Cd and Zn in the rhizosphere of hyperaccumulator Sedum alfredii

The effects of elevated CO₂ on metal species and mobility in the rhizosphere of hyperaccumulator are not well understood. We report an experiment designed to compare the effects of elevated CO₂ on Cd/Zn speciation and mobility in the rhizosphere of hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii grown under ambient (350 μl l^?1) or elevated (800 μl l^?1) CO₂ conditions. No difference in solution pH of NHE was observed between ambient and elevated CO₂ treatments. For HE, however, elevated CO₂ reduced soil solution pH by 0.22 unit, as compared to ambient CO₂ conditions. Elevated CO₂ increased dissolved organic carbon (DOC) and organic acid levels in soil solution of both ecotypes, but the increase in HE solution was much greater than in NHE solution. After the growth of HE, the concentrations of Cd and Zn in soil solution decreased significantly regardless of CO₂ level. The visual MINTEQ speciation model predicted that Cd/Zn–DOM complexes were the dominant species in soil solutions, followed by free Cd²⁺ and Zn²⁺ species for both ecotypes. However, Cd/Zn–DOM complexes fraction in soil solution of HE was increased by the elevated CO₂ treatment (by 8.01 % for Cd and 8.47 % for Zn, respectively). Resin equilibration experiment results indicated that DOM derived from the rhizosphere of HE under elevated CO₂ (HE-DOM-E) (90 % for Cd and 73 % for Zn, respectively) showed greater ability to form complexes with Cd and Zn than those under ambient CO₂ (HE-DOM-A) (82 % for Cd and 61 % for Zn, respectively) in the undiluted sample. HE-DOM-E showed greater ability to extract Cd and Zn from soil than HE-DOM-A. It was concluded that elevated CO₂ could increase the mobility of Cd and Zn due to the enhanced formation of DOM–metal complexes in the rhizosphere of HE S. alfredii.     

Eighty-year sedimentary record of heavy metal inputs in the intertidal sediments from the Nanliu River estuary, Beibu Gulf of South China Sea

²¹⁰Pb analysis in the sediment core C11 was used to reconstruct the historical fluxes of Hg, Cu, Pb, Zn, Cd, Cr and As in the Nanliu River estuary during the last ∼81 year. The ²¹⁰Pb_xs-derived sedimentation rates, molar C/N ratios, enrichment factors and excess fluxes indicated that the natural inputs prevailed till the early 1990s. When the erosion related to land-use modifications enhanced, it promoted higher accumulation rates of the sedimentary material. In the recent sediments they were found a moderate enrichment of Cd and Hg (maximum 3.5- and 2.8-fold corresponding to the local background levels, respectively) and a slight enrichment of Cr, Zn, As and Pb (maximum 1.3-, 1.3-, 1.3- and 1.2-fold, respectively). The excess metal fluxes also showed a consistently increasing tread since the early 1990s, which could be associated with the intensive use of phosphate fertilizers and the combustion of fossil fuels derived from human activities.     

Vaporization of heavy metals during thermal treatment of model solid waste in a fluidized bed incinerator

This paper investigated the volatilization behavior of heavy metals during thermal treatment of model solid waste in a fluidized bed reactor. Four metal chlorides (Cd, Pb, Cu and Zn) were chosen as metal sources. The influence of redox conditions, water and mineral matrice on heavy metal volatilization was investigated. In general, Cd shows significant vaporization especially when HCl was injected, while Cu and Pb vaporize moderately and Zn vaporization is negligible. Increasing oxygen concentration can lower heavy metal vaporization. Heavy metal interactions with the mineral matter can result in the formation of stable metallic species thus playing a negative effect on their behavior. However, HCl can promote the heavy metal release by preventing the formation of stable metallic species. The chemical sorption (either physical or chemical) inside the pores, coupled with the internal diffusion of gaseous metal species, may also control the vaporization process. With SO₂ injected, Cd and Pb show a higher volatility as a result of SO₂ reducing characteristics. From the analysis, the subsequent order of heavy metal volatility can be found: Cd > Cu ? Pb ? Zn.     

A comparative study of heavy metal accumulation and antioxidant responses in Vaccinium myrtillus L. leaves in polluted and non-polluted areas

The purpose of this study was to explore a possible relationship between the availability of metals in soil (Cd, Fe, Mn, Pb and Zn) and their concentrations in leaves of Vaccinium myrtillus L. as a species which has been reported to be a successful colonist of acid-and-heavy metal-contaminated soil. Analysis also concerned the antioxidant response of plants from three heavily polluted (immediate vicinity of: zinc smelter, iron smelter and power plant) and three relatively clean sites (nature reserve, ecological site and unprotected natural forest community) in southern Poland. The contents of glutathione, non-protein thiols, protein, proline and activity of guaiacol peroxidase in leaves of bilberry were measured. Generally, the concentrations of metals in the HNO₃ and CaCl₂ extracants of the soil from the polluted sites were higher. Moreover, the antioxidant responses were also elevated in bilberries in the polluted sites. Significant positive relationships between Cd, Pb and Zn concentrations in soil and in the plants were found. In the leaves of V. myrtillus from the polluted sites, higher concentrations of Cd, Pb and Zn were noted (In Miasteczko ?l?skie respectively 6.26, 157.09 and 207.17 mg?kg^?1?d.w.). We found a positive correlation between the increase in the NPTs and protein contents as well as the Cd, Pb and Zn concentrations in V. myrtillus. Cd, Pb and Zn also decreased guaiacol peroxidase activity. However, the activity of this enzyme increased under Fe. A decreasing trend in glutathione contents was observed with increasing iron and manganese concentrations in bilberry leaves. Parameters such as protein, non-protein –SH groups and changes in GPX activity seem to be universal, sensitive and correlated well with heavy metal stress.     

Heavy metal contamination in surface sediments of Yangtze River intertidal zone: An assessment from different indexes

Surface sediments (0-5 cm) from 59 stations within the Yangtze River intertidal zone (YRIZ) were sampled for metal contamination analysis in April and August 2005. The concentrations ranged (in mg kg⁻¹ dry weight): Al, 40,803-97,213; Fe, 20,538-49,627; Cd, 0.12-0.75; Cr, 36.9-173; Cu, 6.87-49.7; Mn, 413-1,112; Ni, 17.6-48.0; Pb, 18.3-44.1; and Zn, 47.6-154; respectively. Among the 59 sampling stations, enrichment factors (EF) indicate enrichment of Cd (52 stations), Cr (54 stations), Cu (5 stations), Ni (26 stations), Pb (5 stations) and Zn (5 stations). Geoaccumulation indexes (I_geo) also suggest individual metal contamination in localized areas. This study indicates that Cd, Cr and Ni enrichment in the YRIZ sediment is widespread whereas Cu, Mn, Pb and Zn enrichment is localized or nonexistent. Factor and cluster analyses indicate that Cd is associated with total organic carbon whereas Cu, Cr, Ni, Pb and Zn have a close association with Mn.     

Heavy metal accumulation by poplar in calcareous soil with various degrees of multi-metal contamination: implications for phytoextraction and phytostabilization

The object of this study was to assess the capacity of Populus alba L. var. pyramidalis Bunge for phytoremediation of heavy metals on calcareous soils contaminated with multiple metals. In a pot culture experiment, a multi-metal-contaminated calcareous soil was mixed at different ratios with an uncontaminated, but otherwise similar soil, to establish a gradient of soil metal contamination levels. In a field experiment, poplars with different stand ages (3, 5, and 7 years) were sampled randomly in a wastewater-irrigated field. The concentrations of cadmium (Cd), Cu, lead (Pb), and zinc (Zn) in the poplar tissues and soil were determined. The accumulation of Cd and Zn was greatest in the leaves of P. pyramidalis, while Cu and Pb mainly accumulated in the roots. In the pot experiment, the highest tissue concentrations of Cd (40.76 mg kg^?1), Cu (8.21 mg kg^?1), Pb (41.62 mg kg^?1), and Zn (696 mg kg^?1) were all noted in the multi-metal-contaminated soil. Although extremely high levels of Cd and Zn accumulated in the leaves, phytoextraction using P. pyramidalis may take at least 24 and 16 years for Cd and Zn, respectively. The foliar concentrations of Cu and Pb were always within the normal ranges and were never higher than 8 and 5 mg kg^?1, respectively. The field experiment also revealed that the concentrations of all four metals in the bark were significantly higher than that in the wood. In addition, the tissue metal concentrations, together with the NH₄NO₃-extractable concentrations of metals in the root zone, decreased as the stand age increased. P. pyramidalis is suitable for phytostabilization of calcareous soils contaminated with multiple metals, but collection of the litter fall would be necessary due to the relatively high foliar concentrations of Cd and Zn.     

Isotherms and sequential extraction procedures for evaluating sorption and distribution of heavy metals in soils

Heavy metals are potentially toxic to human life and the environment. Their contaminating effect in soils depends on chemical associations. Hence, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. We utilized a sequential extraction procedure and sorption isotherms (monometal and competitive) to evaluate the mobility and distribution of Cd, Cu, Ni, Pb, and Zn in four soils differing in their physicochemical properties: Calcixerollic Xerochrepts (Cx1 and Cx2), Paralithic Xerorthent (Px) and Lithic Haplumbrept (Lh). Most of the metals retained under point B conditions of sorption isotherms were extracted from the more mobile fractions: exchangeable and carbonates, in contrast with the profiles of the original soils where metals were preferently associated with the residual fraction. In soils having carbonate concentration under 6% (Cx1 and Lh), the exchangeable fraction was predominant, whereas in calcareous soils (Cx2 and Px) metals extracted from carbonates predominated. Partitioning profiles were in accordance with the affinity sequences deduced from the initial slope of isotherms and showed that the soils had a greater number of surface sites and higher affinity for Pb and Cu than for Cd, Ni, or Zn. In general, the simultaneous presence of the cations under study increased the percentages of metals released in the exchangeable fraction. The tendency towards less specific forms was more noticeable in Cx2 and Px soils and for Ni, Zn, and Cd. The affinity of inorganic surfaces was larger for Zn than for Cd or Ni, but the affinity of organic surfaces was larger for Cd or Ni than for Zn.     

Comparison of EDTA-enhanced phytoextraction and phytostabilisation strategies with Lolium perenne on a heavy metal contaminated soil

Phytoremediation is a promising and cost-effective strategy to manage heavy metal polluted sites. In this experiment, we compared simultaneously phytoextraction and phytostabilisation techniques on a Cd and Zn contaminated soil, through monitoring of plant accumulation and leaching. Lolium perenne plants were cultivated for 2 months under controlled environmental conditions in a 27.6 dm³-pot experiment allowing the collect of leachates. The heavy metal phytoextraction was promoted by adding Na-EDTA (0.5 g kg⁻¹ of soil) in watering solution. Phytostabilisation was assessed by mixing soil with steel shots (1%) before L. perenne sowing. Presence of plants exacerbated heavy metal leaching, by improving soil hydraulic conductivity. Use of EDTA for phytoextraction led to higher concentration of heavy metal in shoots. However, this higher heavy metal extraction was insufficient to satisfactory reduce the heavy metal content in soil, and led to important heavy metal leaching induced by EDTA. On the other hand, addition of steel shots efficiently decreased both Cd and Zn mobility, according to 0.01 M CaCl₂ extraction, and leaching. However, improvement of growth conditions by steel shots led to higher heavy metal mass in shoot tissues. Therefore, soil heavy metal mobility and plant metal uptake are not systematically positively correlated.     

Effect of metals on a siderophore producing bacterial isolate and its implications on microbial assisted bioremediation of metal contaminated soils

A bacterial isolate producing siderophore under iron limiting conditions, was isolated from mangroves of Goa. Based on morphological, biochemical, chemotaxonomical and 16S rDNA studies, the isolate was identified as Bacillus amyloliquefaciens NAR38.1. Preliminary characterization of the siderophore indicated it to be catecholate type with dihydroxy benzoate as the core component. Optimum siderophore production was observed at pH 7 in mineral salts medium (MSM) without any added iron with glucose as the carbon source. Addition of NaCl in the growth medium showed considerable decrease in siderophore production above 2% NaCl. Fe⁺² and Fe⁺³ below 2 μM and 40 μM concentrations respectively, induced siderophore production, above which the production was repressed. Binding studies of the siderophore with Fe⁺² and Fe⁺³ indicated its high affinity towards Fe⁺³. The siderophore concentration in the extracellular medium was enhanced when MSM was amended with essential metals Zn, Co, Mo and Mn, however, decreased with Cu, while the concentration was reduced with abiotic metals As, Pb, Al and Cd. Significant increase in extracellular siderophore production was observed with Pb and Al at concentrations of 50 μM and above. The effect of metals on siderophore production was completely mitigated in presence of Fe. The results implicate effect of metals on the efficiency of siderophore production by bacteria for potential application in bioremediation of metal contaminated iron deficient soils especially in the microbial assisted phytoremediation processes.     

Biochar- and phosphate-induced immobilization of heavy metals in contaminated soil and water: implication on simultaneous remediation of contaminated soil and groundwater

Long-term wastewater irrigation or solid waste disposal has resulted in the heavy metal contamination in both soil and groundwater. It is often separately implemented for remediation of contaminated soil or groundwater at a specific site. The main objective of this study was to demonstrate the hypothesis of simultaneous remediation of both heavy metal contaminated soil and groundwater by integrating the chemical immobilization and pump-and-treat methods. To accomplish the objective, three experiments were conducted, i.e., an incubation experiment was first conducted to determine how dairy-manure-derived biochar and phosphate rock tailing induced immobilization of Cd in the Cd-contaminated soils; second, a batch sorption experiment was carried out to determine whether the pre-amended contaminated soil still had the ability to retain Pb, Zn and Cd from aqueous solution. BCR sequential extraction as well as XRD and SEM analysis were conducted to explore the possible retention mechanism; and last, a laboratory-scale model test was undertaken by leaching the Pb, Zn, and Cd contaminated groundwater through the pre-amended contaminated soils to demonstrate how the heavy metals in both contaminated soil and groundwater were simultaneously retained and immobilized. The incubation experiment showed that the phosphate biochar were effective in immobilizing soil Cd with Cd concentration in TCLP (toxicity characteristics leaching procedure) extract reduced by 19.6 % and 13.7 %, respectively. The batch sorption experiment revealed that the pre-amended soil still had ability to retain Pb, Zn, and Cd from aqueous solution. The phosphate-induced metal retention was mainly due to the metal–phosphate precipitation, while both sorption and precipitation were responsible for the metal stabilization in the biochar amendment. The laboratory-scale test demonstrated that the soil amended with phosphate removed groundwater Pb, Zn, and Cd by 96.4 %, 44.6 %, and 49.2 %, respectively, and the soil amended with biochar removed groundwater Pb, Zn, and Cd by 97.4 %, 53.4 %, and 54.5 %, respectively. Meanwhile, the metals from both groundwater and soil itself were immobilized with the amendments, with the leachability of the three metals in the CaCl₂ and TCLP extracts being reduced by up to 98.1 % and 62.7 %, respectively. Our results indicate that the integrated chemical immobilization and pump-and-treat method developed in this study provides a novel way for simultaneous remediation of both metal-contaminated soil and groundwater.     

Effects of phosphorus amendments and plant growth on the mobility of Pb, Cu, and Zn in a multi-metal-contaminated soil

Purpose

Phosphorus amendments have been widely and successfully used in immobilization of one single metal (e.g., Pb) in contaminated soils. However, application of P amendments in the immobilization of multiple metals and particularly investigations about the effects of planting on the stability of the initially P-induced immobilized metals in the contaminated soils are far limited.

Methods

This study was conducted to determine the effects of phosphate rock tailing (PR), triple superphosphate fertilizer (TSP), and their combination (P+T) on mobility of Pb, Cu, and Zn in a multimetal-contaminated soil. Chinese cabbage (Brassica rapa subsp. chinensis) (metal-sensitive) and Chinese kale (Brassica alboglabra Bailey) (metal-resistant) were introduced to examine the effects of planting on leaching of Pb, Cu, and Zn in the P-amended soils.

Results

All three P treatments greatly reduced CaCl₂-extractable Pb and Zn by 55.2?C73.1% and 14.3?C33.6%, respectively. The PR treatment decreased CaCl₂-extractable Cu by 27.8%, while the TSP and P+T treatments increased it by 47.2% and 44.4%, respectively. All three P treatments were effective in reducing simulated rainwater leachable Pb, with dissolved and total leachable Pb decrease by 15.6?C81.9% and 16.3?C64.5%, respectively. The PR treatment reduced the total leachable Zn by 16.8%, while TSP and P+T treatments increased Zn leaching by 92.7% and 78.9%, respectively. However, total Cu leaching were elevated by 17.8?C178% in all P treatments. Planting promoted the leaching of Pb and Cu by 98.7?C127% and 23.5?C170%, respectively, especially in the colloid fraction, whereas the leachable Zn was reduced by 95.3?C96.5% due to planting. The P treatments reduced the uptake of Pb, Cu, and Zn in the aboveground parts of Chinese cabbage by up to 65.1%, 34.3%, and 9.59%, respectively. Though P treatments were effective in reducing Zn concentrations in the aboveground parts of the metal-resistant Chinese kale by 22.4?C28.9%, they had little effect on Pb and Cu uptake.

Conclusions

The results indicated that all P treatments were effective in immobilizing Pb. The effect on the immobilization of Cu and Zn varied with the different P treatments and evaluation methods. Metal-sensitive plants are more responsive to the P treatments than metal-resistant plants. Planting affects leaching of metals in the P-amended soils, specially leaching of colloid fraction. The conventional assessment on leaching risks of heavy metals by determining dissolved metals (filtered through 0.45-??m pore size membrane) in leachates could be underestimated since colloid fraction may also contribute to the leaching.