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1.
Soil components from different environments (forest (OF), semiarid (SZ), and sand (AS)) were separated from fulvic and humic substances, characterized by DRX, EDS(SEM), and zero-charge points were determined. The sorption of U(VI) by these materials was determined considering contact time, concentration of U(VI), pH, ionic strength, and presence of sodium chloride and humic acids. The time to reach the kinetic sorption equilibrium was ca. 1 min for the components of the SZ and AS soils, whereas those from OF required longer times. The zero-charge points of the materials indicate that in the experimental conditions, the surfaces of the materials are positively charged, as are uranyl ions. The sorption kinetic data were well fitted to the pseudo-second-order model, which indicates chemical sorption. The maximum sorption capacities for U(VI) obtained from data fitted to the Langmuir model of OF and SZ were 49 and 19.8 mg g?1 respectively. Sorption isotherm data for AS were best fitted to the Freundlich model (qe?=?5.4 mg g?1). The maximum values of distribution coefficients (Kd) were 23?±?7 L kg?1, 545?±?64 L kg?1, and 1178?±?229 L kg?1 for AS, SZ, and OF, respectively; these values may depend on pH, contact time, initial concentration of U(VI), and the composition of the materials. Sodium chloride in the aqueous solutions affects U(VI) sorption by the materials SZ and AS. The effect of humic acids depends on pH, only in acid media soluble humate complexes may be formed.  相似文献   

2.

Purpose

Many amendments have been applied to immobilize heavy metals in soil. However, little information is available on the changes of immobilization efficiencies of heavy metals in contaminated soils over time. This work investigated the immobilization efficiencies of copper (Cu) and cadmium (Cd) in contaminated soils in situ remediated with one-time application of three amendments for 1 year and 4 years.

Materials and methods

Apatite, lime, and charcoal were mixed with the topsoil of each plot with the amounts of 22.3, 4.45, and 66.8 t/ha, respectively. Soil chemical properties and fractions of Cu and Cd were examined after in situ remediation for 1 year and 4 years. Soil sorption and retention capacities and desorption proportions for Cu and Cd were investigated by batch experiments.

Results and discussion

The addition of amendments significantly increased soil pH, but decreased exchange acid and aluminum (Al). The amendments significantly decreased the CaCl2 extractable Cu and Cd and transformed them from active to inactive fractions. After the application of amendments for 1 year, the maximum sorption capacities ranged from 35.6 to 38.8 mmol/kg for Cu and from 14.4 to 17.0 mmol/kg for Cd, which were markedly higher than those of the application of amendments for 4 years (Cu, 29.6–34.7 mmol/kg; Cd, 10.9–16.4 mmol/kg). Desorption proportions (D) of Cu and Cd using three extractants followed the order of \( {D}_{{\mathrm{NaNO}}_3}<{D}_{{\mathrm{CaCI}}_2}<{D}_{{\mathrm{MgCI}}_2} \) . Moreover, the retention capacities (R) of Cu and Cd both increased and followed the order of R apatite?>?R lime?>?R charcoal, resulting in higher Cu and Cd in the amended soils than the untreated soil.

Conclusions

Apatite, lime, and charcoal increased the soil sorption and retention capacities of Cu and Cd and resulted in higher immobilization efficiencies in the amended soils than the untreated soil. However, the immobilization efficiencies of Cu and Cd decreased with the decrease of sorption capacities after 4 years. It was concluded that apatite had the best effect on the long-term stability of immobilized Cu and Cd and can be applied to immobilize heavy metals in contaminated soils.  相似文献   

3.
Stormwater biofilters, which are recommended for application in both Water-Sensitive Urban Design and Low Impact Development, can remove up to 80% or 90% of total metals found in stormwater. However, their winter operation is a common concern. That was addressed in this study by investigating the metal removal effectiveness of replicate laboratory biofilter mesocosms at 2°C, 8°C and 20°C. As recommended for cold climate bioretention, coarse filter media were implemented and in the top 100 mm layer topsoil was added to increase the sorption capacity. Cd, Cu, Pb and Zn concentrations measured in the biofilter effluent were far below those in the influent and this significantly improved the treated stormwater quality. Contrary to a common notion that coarse media in the main filter body impair dissolved metal sorption, satisfactory removals of dissolved metals were found in this study with most metal burdens retained in the top layer of the filter in which the sorption capacity was enhanced by topsoil. Some metal uptake by the plants was also detected. Temperature did not affect Cd, Pb and Zn removals in general, but Cu removals increased with decreasing temperatures. This was explained by increased biological activities in the filters at warmer temperatures, which may have led to an increased release of Cu with dissolved organic matter originating from root turnover and decomposition of organic litter and debris. Furthermore, plant uptake and biofilm adsorption may also be influenced by temperature. However, even in the worst case (i.e. at 20°C), Cu was removed effectively from the stormwater. Further research needs were identified including the effects of road salts on stormwater biofiltration during the winter period.  相似文献   

4.
Cr(III) ions sorption onto sawdust of spruce (Picea smithiana) has been studied thoroughly using radiotracer technique. Maximum sorption (94%) of Cr(III) ions (8.98×10?5 M) onto sorbent surface is achieved from deionized water in 20 min agitation time using 200 mg of sawdust. The sorption data followed the Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms. Freundlich constants l/n = 0.86 ± 0.07 and C e = 85.0 ± 25.8 mmole g?1 have been estimated. Sorption capacity, X m = 0.82± 0.3 mmole g?1, β = ?0.00356± 0.00017 kJ2 mole?2 and energy, E = 11.9± 0.3 kJ mole?1 have been evaluated using D-R isotherm. The Langmuir constants Q = 5.8± 0.2 μmole g?1 and b = (7.4± 0.5)×104 dm3 mole?1 have been calculated. The variation of sorption with temperature yields thermodynamic parameters Δ H = ?11.6± 0.3 kJ mole?1, Δ S = ?16.2± 0.9 J mole?1 K?1 and Δ G = ?6.8± 0.3 kJ mole?1 at 298 K. The negative value of enthalpy and free energy reflect the exothermic and spontaneous nature of sorption respectively. Among the anions studied oxalate, citrate, carbonate and borate have reduced the sorption. The cations Y(III), Ce(II) and Ca(II) suppressed sorption. The sawdust column can be used to separate Cr(III) ion from Cs(I), I(I),Tc (VII) and Se (IV).  相似文献   

5.
A neutrophilic, autotrophic bacterium that couples iron oxidation to nitrate reduction (iron-oxidizing bacteria [IOB]) under anoxic conditions was isolated from a working bioremediation site in Trail, British Columbia. The site was designed and developed primarily to treat high concentrations of Zn and As that originate from capped industrial landfill sites. The system consisted of two upflow biochemical reactor cells (BCR) followed by three vegetated wetland polishing cells with sub-surface flow and a holding pond. During a 5-year period (2003–2007), the system treated more than 19,100 m3 of contaminated water, removing and sequestering more than 10,700 kg of As, Zn and sulfate at average input water concentrations of: As, 58.6 mg?l?1 (±39.9 mg?l?1); Zn, 51.9 mg?l?1 (±35.4 mg?l?1) and SO4 2?, 781.5 mg?l?1 (±287.8 mg?l?1). The bacterium was isolated in order to better understand the mechanisms underlying the consistent As removal that took place in the system. Analysis using Basic Local Alignment Search Tool (BLAST) database showed that the closest homologies are to Candidatus accumulibacterphosphatis (95 % homology), Dechloromonas aromatica (94 %), and Sideroxydans lithotrophicus ES-1 (92 %) Within the BCR cells, the IOB oxidized Fe2+ generated by iron-reducing bacteria (IRB); the source of the iron was most likely biosolids and coatings of iron oxide on locally available sand used in the matrix. We have provisionally designated the novel bacterium as TR1.  相似文献   

6.
Artemisia vulgaris (mugwort) is a tall (1.0?C2.0 m) high biomass perennial herb which accumulates considerable amounts of metals on contaminated sites. An outdoor pot experiment was conducted on a sandy, slightly alkaline soil of moderate fertility to study the uptake of cadmium and the distribution of Cd in plant tissues of A. vulgaris. Cadmium was applied as CdCl2 (a total of 1 l solution of 0, 10, 50 and 100 mg Cd l?1) to 12-l pots with a height of 25 cm. HNO3- and water-extractable concentrations of Cd were correlated with the applied Cd at 2-cm soil depth, but were not correlated at 20-cm soil depth, suggesting that Cd was either not mobile in the soil or completely taken up by mugwort roots. The Cd concentrations in different organs of A. vulgaris and litter increased with increasing soil contamination. Leaf/soil concentration ratios (BCFs) up to 65.93?±?32.26 were observed. Translocation of Cd to the aboveground organs was very high. The leaf/root Cd concentration ratio (translocation factor) ranged from 2.07?±?0.56 to 2.37 ± 1.31; however, there was no correlation of translocation factors to Cd enrichment, indicating similar translocation upon different soil contamination levels. In summary, A. vulgaris is tolerant to the metal concentrations accumulated, has a high metal accumulating biomass and accumulates Cd up to about 70% in the aboveground parts. Both a high phytoextraction potential and a high value for phytostabilisation would recommend mugwort for phytoremediation.  相似文献   

7.
Heavy metal-polluted water has become a problem for sustainable environment, agriculture, and human health. Phyto-accumulation is an eco-friendly technique for decontamination of metal-polluted water and soil. The efficiency of phyto-accumulation and rhizo-filtration can be enhanced by the application of certain nutrients to accumulator plants. In this study, we focused on the role of iron (Fe) in rhizo-filtration and phyto-accumulation of cadmium (Cd) from polluted water/media, using Ricinus communis plant. Medium was contaminated with 10 ppm Cd while Fe (2.50, 5.00, and 7.50 ppm) was applied both as foliar spray and medium addition separately. Accumulation of Cd and concentrations of soluble proline, phenolic compounds, and chlorophylls were measured in plant tissues. Addition of Fe into media significantly increased biomass in the plants but decreased Cd absorption by roots and its accumulation in other tissues of the plants. Foliar application of Fe, especially 7.5 ppm, significantly increased biomass as well as accumulation of Cd in tissues of the plants. Contents of soluble proline (41.88?±?3.56 ppm) and phenolics (171.00?±?4.98 ppm) in leaves were highly increased by foliar spray of 7.5 ppm Fe on the plants. On the other hand, highest concentrations of free proline (67.00?±?2.00 ppm) and total phenolics (82.67?±?2.52 ppm) in plant roots were observed in 7.5 ppm Fe added to media and as foliar spray, respectively. Strong correlations were observed between phenolics content in roots and leaves with Cd accumulation after foliar application of 7.5 ppm Fe.  相似文献   

8.
This study assessed the accumulation of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the sediment and biomass of P. australis (Cav.) Trin. ex Steud. in a combined constructed wetland (CW) designed for the treatment of domestic wastewater of 750 population equivalents. The CW consists of two vertical subsurface flow (VSSF) reed beds followed by two horizontal subsurface flow (HSSF) reed beds. The sediment in the VSSF reed bed was contaminated with Cu (201 ?±? 27 mg kg?1 DM) and Zn (662 ?±? 94 mg kg?1 DM) after 4 years of operation. Concentrations of Cd, Cu, Pb and Zn in the sediment generally decreased along the treatment path of the CW. On the contrary, higher Al, Cr, Fe, Mn and Ni concentrations were observed in the sediment of the inlet area of the HSSF reed bed. Redox conditions were presumably responsible for this observed trend. Metal concentrations in the reed biomass did not show excessive values. Accumulation in the aboveground reed biomass accounted for only 0.5 and 1.4% of, respectively, the Cu and Zn mass load in the influent. The sediment was the main pool for metal accumulation in the CW.  相似文献   

9.
Interactions between Zn and Cd on the accumulation of these metals in coontail, Ceratophyllum demersum were studied at different metal concentrations. Plants were grown in nutrient solution containing Cd (0.05–0.25 mg l?1) and Zn (0.5–5 mgl?1). High concentrations of Zn caused a significant decrease in Cd accumulation. In general, adding Cd solution decreased Zn accumulation in C. demersum except at the lowest concentration of Zn in which the Zn accumulation was similar to that without Cd. C. demersum could accumulate high concentrations of both Cd and Zn. The influence of humic acid (HA) on Cd and Zn accumulation was also studied. HA had a significant effect on Zn accumulation in plants. 2 mg l?1 of HA reduced Zn accumulation at 1 mg l?1 level (from 2,167 to 803 mg kg?1). Cd uptake by plant tissue, toxicity symptoms and accumulation at 0.25 and 0.5 mg l?1, were reduced (from 515 to 154 mg kg?1 and from 816 to 305 mg kg?1, respectively) by addition of 2 mg l?1 of HA. Cd uptake reached a maximum on day 9 of treatment, while that of Zn was observed on day 15. Long-term accumulation study revealed that HA reduced toxicity and accumulation of heavy metals.  相似文献   

10.
The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g?1 Hg, 6.5?C250.3 mg g?1 Cu, 0.059?C0.245 mg g?1 Pb, 0.004?C0.066 mg g?1 Cd, and 31.8?363.1 mg g?1 Zn in roots and 0.033?C0.888 mg g?1 Hg, 2.2?C70.7 mg g?1 Cu, 0.005?C0.086 mg g?1 Pb, 0.001?C0.03 mg g?1 Cd, and 12.6?C140.4 mg g?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.  相似文献   

11.
The sorption behavior of fluoride ions by hydroxyapatite in a column system from both fluoride aqueous solutions and drinking water from Ojocaliente, Zacatecas, Mexico, was evaluated. The time between two consecutive elutions allowed the rearrangement of the active sites and diffusion of fluoride ions in the hydroxyapatite, resulting in an increase of its sorption capacity. This behavior was not observed with drinking water, probably due to its high bicarbonate ion concentration. The maximum value of C e/C 0 reached for both drinking water and fluoride solutions was 0.73?±?0.05. The data were fitted to the model of Thomas. Both values of K Th and q 0 increased with the number of elutions, and their maximum values were 1.72?×?10?3?L?min?1?mg?1 and 9.91 mg?g?1, respectively.  相似文献   

12.
Paper mulberry (Broussonetia papyrifera) leaf powder was used to remove heavy metal ions from aqueous solutions. The specific uptakes of Cu (II), Pb (II), and Cd (II) by the leaf powder were 43.40?±?0.2, 43.9?±?0.5, and 30.65?±?0.9 mg g?1, respectively, when 500 mg L?1 of the metal solutions were used. The data fitted well to the Langmuir isotherm. The process followed the pseudo-second-order kinetic equation and intraparticle diffusion played an important role in the adsorption process. On the basis of the calculated thermodynamic parameters such as standard enthalpy (??H°), entropy (??S°) and free energy change (??G°), it was inferred that the sorption process was endothermic and spontaneous in nature. The surface properties of the leaf powder (revealed by scanning electron microscopic observations) were suitable for the metal adsorption process. Energy dispersive X-ray fluorescence analysis confirmed the sequestration of the metal ions by the leaf powder. Fourier transform infrared spectroscopy implicated that different functional groups on the leaf powder were involved in the metal adsorption process. The results obtained from this study implicated that the B. papyrifera leaf powder was a good choice as a metal adsorbent. This abundantly available natural and eco-friendly biosorbent could be effectively used to develop a technology in the future.  相似文献   

13.

Purpose

The effect of soil heavy metals on crops and human health is an important research topic in some fields (Agriculture, Ecology et al.). In this paper, the objective is to understand the pollution status and spatial variability of soil heavy metals in this study area. These results can help decision-makers apportion possible soil heavy metal sources and formulate pollution control policies, effective soil remediation, and management strategies.

Materials and methods

A total of 212 topsoil samples (0–20 cm) were collected and analyzed for eight heavy metals (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) from agricultural areas of Yingbao County in Lixia River Region of Eastern China, by using four indices (pollution index (PI), Nemerow pollution index (PIN), index of geo-accumulation (I geo), E i /risk index (RI)) and cluster analysis to assess pollution level and ecological risk level of soil heavy metals and combining with geostatistics to analyze the concentration change of heavy metals in soils. GS+ software was used to analyze the spatial variation of soil heavy metals, and the semi-variogram model is the main tool to calculate the spatial variability and provide the input parameters for the spatial interpolation of kriging. Arcgis software was used to draw the spatial distribution of soil heavy metals.

Results and discussion

The result indicated that the eight heavy metals in soils of this area had moderate variations, with CVs ranging from 23.51 to 64.37 %. Single pollution index and Nemerow pollution index showed that about 2.7 and 1.36 % of soil sampling sites were moderately polluted by Cd and Zn, respectively. The pollution level of soil heavy metals decreased in the order of Cd?>?Zn?>?Pb?>?As?>?Cu?>?Cr?>?Ni?>?Hg. The I geo values of heavy metals in this area decreased in the order of Zn?>?Cd?>?As?>?Pb?>?Cu?>?Cr?>?Hg?>?Ni. According to the E i index, except Cd that was in the moderate ecological risk status, other heavy metals in soils were in the light ecological risk status, and the level of potential ecological risk (RI) of soil sampling sites of the whole area was light.

Conclusions

The results of four indices and the analysis of spatial variation indicated that the contents of Cd and Zn were contributed mainly by anthropogenic activities and located in the south-east of this study area. However, the contents of Hg, As, Cu, Pb, Cr, and Ni in soils were primarily influenced by soil parent materials.
  相似文献   

14.
Flooded post-harvest rice paddies were examined as systems for reducing diazinon (organophosphate insecticide) concentrations in stormwater runoff. Two paddies were cultivated in Oryza sativa L. and amended with a 3-h simulated stormwater diazinon runoff event. Initial diazinon adsorption peaked at 347 and 571 μg kg?1 (3% mass load reduction) for mean above-ground plant tissue concentrations in each pond, respectively. Subsequent senescence of above-ground tissue showed significant decreases in tissue mass (r 2?=?0.985) and adsorbed diazinon mass (90?±?4% and 82?±?1%) within 1 month of amendment. There were no corollary increases in water column diazinon concentrations. Furthermore, control O. sativa tissue placed within the treatment ponds had below-detectable levels of diazinon throughout the decomposition phase, suggesting a lack of within pond transference of dissipated diazinon. This study shows the relative effectiveness of diazinon adsorption by post-harvest rice plants and a potential mitigation strategy of senescence and pesticide degradation for contaminated tailwater.  相似文献   

15.
Pot culture experiments were conducted to study the remediation potentials of a newly found accumulator Kalimeris integrifolia Turcz. ex DC. under different cadmium (Cd) concentrations with same fertilizer level, as well as the same Cd dose under different fertilizer doses. At medium (100 g/kg) chicken manure level, Cd concentrations in roots, stems, leaves, inflorescences, and shoots of K. integrifolia grown in the soils contaminated with 2.5, 5, 10, and 25 mg/kg Cd significantly decreased (p?<?0.05) in average by 23.8%, 29.9%, 24.0%, 30.1%, and 38.6%, respectively, when compared to those of the pots without addition of chicken manure. In contrast, the medium urea amendment level (1 g/kg) showed no effect on the bioaccumulated Cd concentrations of K. integrifolia regardless of the spiked Cd doses. However, Cd extraction capacities (micrograms per pot) of K. integrifolia shoots were significantly increased (p?<?0.05) due to the gain in biomass (more than one- to twofolds) by the soil fertilizing effect of urea and chicken manure. Particularly, Cd extraction capacities (micrograms per pot) of K. integrifolia shoots amended by urea were higher than that of chicken manure. Under the condition of 25 mg/kg Cd addition, shoot biomasses of K. integrifolia were significantly increased (p?<?0.05) with the amendment of chicken manure (50, 100, and 200 g/kg) and urea (0.5, 1, and 2 g/kg). As a result, the Cd extraction capacities (micrograms per pot) were increased in treatments even though soil extractable Cd concentrations were significantly decreased (p?<?0.05) by amendment with chicken manure and maintained by urea addition. For practical application concerns, chicken manure is better used as phytostabilization amendment owing to its reducing role to extractable heavy metal in soil, and urea is better for phytoextraction.  相似文献   

16.
Spatial and seasonal mobilization trends of metals in surface water were evaluated in the US–Mexico San Pedro River (SPR). Water samples were collected at five sampling stations for the analysis of dissolved oxygen, pH, electric conductivity, sulfates, and metals (Cd, Cu, Fe, Mn, Pb, and Zn). Quality of the water was characterized through Ecological Criteria of Water Quality (ECWQ) established in Mexico and Water Quality Criteria (Environmental Protection Agency (EPA)). High total metal concentrations were detected as follows: Fe?>?Cu?>?Mn?>?Zn?>?Pb?>?Cd. Metal concentrations were slightly higher in dry season than in rainy season: Cd (below detection limit (BDL)–0.21 mg L?1), Cu (BDL–13 mg L?1), Fe (0.16–345 mg L?1), Mn (0.12–52 mg L?1), Pb (BDL–0.48 mg L?1), and Zn (0.03–17.8 mg L?1). Low pH and dissolved oxygen values as well as high sulfate content were detected in both seasons. High values of metals (Cd, Cu, Fe, Mn, Pb, Zn) were detected at station E1 representing pollution source, as well as at stations E2 (Cd, Cu, Fe, Mn), E3 (Fe, Mn, Pb), and E4 and E5 (Fe, Mn). Detected concentrations exceeded maximum permissible established in ECWQ and Water Quality Criteria (EPA). Efflorescence salts on sediments in the dry season could increase levels of metals in water column. This study provides valuable information on the potential mobility of metals in surface water of SPR located in an arid environment where transport processes are strongly linked to climate. The information derived from this study should help the regional and national authorities to address present environmental regulations.  相似文献   

17.
To determine nitrogen (N) fate and environmental impact of applying anaerobic digestion slurry (ADS) to rice paddy (Oryza sativa L.), a field experiment was established using three treatments based on contrasting N application rate. The ADS (with ammonium-N accounting for >80 % of total N) treatment at a conventional application rate of 270 kg N?ha?1 was compared to a negative control (no N fertilizer) and a positive control of urea applied at 270 kg N?ha?1. The N budget showed the following distribution of applied N from ADS and urea: 41.3?±?5.1 % for ADS and 36.6?±?4.4 % for urea recovered by the rice plant (including straw, grain, and root), 16.4?±?3.7 % for ADS and 7.4?±?1.8 % for urea lost via ammonia volatilization, 0.26?±?0.15 % for ADS and 0.15?±?0.12 % for urea lost by direct N2O emission, 1.9?±?0.5 % for ADS and 2.3?±?0.8 % for urea leached downward, 0.70?±?0.15 % for ADS and 0.67?±?0.12 % for urea discharged with floodwater drainage, and 39.4?±?8.4 % for ADS and 53.0?±?9.1 % for urea retained by soil or lost by N2 emission. Compared to urea application, ADS application impacts the environment mainly through gaseous N losses rather than water N losses. ADS application had a positive impact on rice grain yield and reduced chemical fertilizer use. Considering the wide distribution of paddy fields and the ever-increasing quantities of ADS, ADS may serve as a valuable N source for rice cultivation, although mitigating ammonia and N2O losses should be further investigated.  相似文献   

18.

Purpose

The main objective of this study was to evaluate the potential of a counter-current leaching process (CCLP) on 14 cycles with leachate treatment at the pilot scale for Pb, Cu, Sb, and Zn removal from the soil of a Canadian small-arms shooting range.

Materials and methods

The metal concentrations in the contaminated soil were 904?±?112 mg Cu kg–1, 8,550?±?940 mg Pb kg–1, 370?±?26 mg Sb kg–1, and 169?±?14 mg Zn kg–1. The CCLP includes three acid leaching steps (0.125 M H2SO4?+?4 M NaCl, pulp density (PD)?=?10 %, t?=?1 h, T?=?20 °C, total volume?=?20 L). The leachate treatment was performed using metal precipitation with a 5-M NaOH solution. The treated effluent was reused for the next metal leaching steps.

Results and discussion

The average metal removal yields were 80.9?±?2.3 % of Cu, 94.5?±?0.7 % of Pb, 51.1?±?4.8 % of Sb, and 43.9?±?3.9 % of Zn. Compared to a conventional leaching process, the CCLP allows a significant economy of water (24,500 L water per ton of soil), sulfuric acid (133 L H2SO4 t–1), NaCl (6,310 kg NaCl t–1), and NaOH (225 kg NaOH t–1). This corresponds to 82 %, 65 %, 90 %, and 75 % of reduction, respectively. The Toxicity Characteristic Leaching Procedure test, which was applied on the remediated soil, demonstrated a large decrease of the lead availability (0.8 mg Pb L–1) in comparison to the untreated soil (142 mg Pb L–1). The estimated total cost of this soil remediation process is 267 US$ t–1.

Conclusions

The CCLP process allows high removal yields for Pb and Cu and a significant reduction in water and chemical consumption. Further work should examine the extraction of Sb from small-arms shooting range.  相似文献   

19.
The main objective of this study was to evaluate the contribution of sorption to the removal of two commonly used antibiotics (amoxicillin and ciprofloxacin) from wastewater. These antibiotics are excreted in large quantities with more than 75% of them being unmetabolized and are therefore likely to end up in domestic wastewater in significant quantities. The specific objectives were to determine the sorption behavior in synthetic wastewater (SWW), the effect of pH and contribution of microbial surfaces, to the sorption of these antibiotics. The SWW, adjusted to various pH levels, was used and sorption kinetics conducted at 100 and 250 ??g L?1 concentrations. Adsorption isotherms were determined at different pH levels. The SWW (pH 6.6) was inoculated with Rhodococcus sp. B30 strain to determine the contribution of microbial surfaces to sorption. Generally, both antibiotics revealed a decrease in sorption with pH increase, suggesting that lowering the solution pH of the wastewater may reduce their amounts in wastewater solution. Comparatively, ciprofloxacin exhibited higher sorption than amoxicillin. The sorption distribution coefficient (K d) values for ciprofloxacin ranged from 0.4356 to 0.8902 L?g?1, with pH?=?5.5 exhibiting the highest K d, while that for amoxicillin ranged from 0.1582 to 0.3858 L?g?1 with the highest K d at pH?=?3.5. There was a significant difference (p?<?0.05) in K d values between various pH levels for both antibiotics except between the pH of 5.5 and 6.6. Both antibiotics were not degraded within 48 h by Rhodococcus sp. B30 strain. These results indicate that degradation may not be the major process of removal of compounds from wastewater treatment plants and hence the importance of sorption as an intervention technique.  相似文献   

20.
Hydroponic and pot experiments were conducted to assess the uptake of heavy metals (Cd and Zn) by a common crop plant, African basil, Ocimum gratissimum. In addition, the effects of soil amendments, hydroxyapatite (HA) and cow manure on plant growth and metal accumulations were compared. In the hydroponic study, plants were exposed to various concentrations of Cd (2.5 and 5 mg L?1) and Zn (10 and 20 mg L?1) for 15 days. O. gratissimum was shown to be a Cd accumulator more than a Zn accumulator. Cadmium concentration in its shoots exceeded 100 mg kg?1. In the pot experiments, soils from a heavily Cd-contaminated site (Cd 67.9 mg kg?1 and Zn 2,886.8 mg kg?1) were treated with cow manure and HA at the rates of 10% and 20% (w/w), and 0.75 and 1.5% (w/w), respectively. Plants were grown in the greenhouse for 3 months. The addition of cow manure resulted in the highest biomass production and the lowest accumulations of Cd in plant parts, while HA was more efficient than cow manure in reducing Zn uptake. Leaves of African basil showed a decreased Cd concentration from 1.5 to 0.3 mg kg?1 (cow manure) and decreased Zn concentration from 69.3 to 34 mg kg?1 (HA). This clearly demonstrates the efficiency of HA and cow manure in reducing metal content in leaves of plants grown on high metal-contaminated soil to acceptable or close to acceptable values (0.2 mg kg?1 for Cd, 99.4 mg kg?1 for Zn).  相似文献   

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