Metal Concentrations In Leachates Research Articles

Bio-treatment of municipal solid waste incineration fly ash: A sustainable path for recyclability

This study investigates the impact of bio-treatment on Municipal Solid Waste Incineration Fly Ash (MSWIFA), comparing bio-treated MSWIFA (BFA) to raw MSWIFA (RFA). BFA exhibited a larger particle size and the presence of microbial-induced calcium carbonate precipitation (MICP) gels. Both RFA and BFA maintained highly alkaline pH levels, with mineral analysis showing reduced chlorine content in BFA and the presence of Monocarboaluminate (Mc), suggesting potential concrete strength improvements. Bio-treatment effectively reduced polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) levels, meeting standards. Biomineralization stabilized heavy metals in MSWIFA, reducing leaching concentrations and meeting national standards. Blending BFA with magnesium phosphate cement (MPC) improved compressive strength, especially in early stages, further enhanced by calcium acetate. SEM images confirmed MICP gels on paste surfaces, contributing to increased strength. Analytical techniques (X-ray diffraction, Fourier transform infrared, and thermal gravimetric analysis) supported superior performance in hydration and strength. SEM-EDS analysis showed effective solidification/stabilization of heavy metals, reduced chlorine content, and enhanced biomineralization. Leaching tests confirmed reduced heavy metal concentrations in leachate. In summary, bio-treatment enhances the properties and environmental impact of MSWIFA, offering sustainable waste management opportunities.

Investigating Landfill Leachate and Groundwater Quality Prediction Using a Robust Integrated Artificial Intelligence Model: Grey Wolf Metaheuristic Optimization Algorithm and Extreme Learning Machine

The likelihood of surface water and groundwater contamination is higher in regions close to landfills due to the possibility of leachate percolation, which is a potential source of pollution. Therefore, proposing a reliable framework for monitoring leachate and groundwater parameters is an essential task for the managers and authorities of water quality control. For this purpose, an efficient hybrid artificial intelligence model based on grey wolf metaheuristic optimization algorithm and extreme learning machine (ELM-GWO) is used for predicting landfill leachate quality (COD and BOD5) and groundwater quality (turbidity and EC) at the Saravan landfill, Rasht, Iran. In this study, leachate and groundwater samples were collected from the Saravan landfill and monitoring wells. Moreover, the concentration of different physico-chemical parameters and heavy metal concentration in leachate (Cd, Cr, Cu, Fe, Ni, Pb, Mn, Zn, turbidity, Ca, Na, NO3, Cl, K, COD, and BOD5) and in groundwater (Cd, Cr, Cu, Fe, Ni, Pb, Mn, Zn, turbidity, EC, TDS, pH, Cl, Na, NO3, and K). The results obtained from ELM-GWO were compared with four different artificial intelligence models: multivariate adaptive regression splines (MARS), extreme learning machine (ELM), multilayer perceptron artificial neural network (MLPANN), and multilayer perceptron artificial neural network integrated with grey wolf metaheuristic optimization algorithm (MLPANN-GWO). The results of this study confirm that ELM-GWO considerably enhanced the predictive performance of the MLPANN-GWO, ELM, MLPANN, and MARS models in terms of the root-mean-square error, respectively, by 43.07%, 73.88%, 74.5%, and 88.55% for COD; 23.91%, 59.31%, 62.85%, and 77.71% for BOD5; 14.08%, 47.86%, 53.43%, and 57.04% for turbidity; and 38.57%, 59.64%, 67.94%, and 74.76% for EC. Therefore, ELM-GWO can be applied as a robust approach for investigating leachate and groundwater quality parameters in different landfill sites.

Assessment of ecotoxicity of spent fluid catalytic cracking (FCC) refinery catalysts on Raphidocelis subcapitata and predictive models for toxicity

The 17 spent fluid catalytic cracking refinery catalysts (SFCCCs) from different petroleum refineries were collected and the leachates of SFCCCs were prepared. The ecotoxicity of SFCCC leachates to Raphidocelis subcapitata was assayed. The results showed that the toxicity of the 17 SFCCCs differ greatly. Ji SFCCC was the most toxic to R. subcapitata with a 96 h EC50 value of 1.38%, while Ha SFCCC was the least toxic, with the EC50 value was >100%. The relationships between the toxicity of SFCCCs and the metal concentrations in leachates were analyzed. The concentration of Ni (p = 0.001), La (p = 0.001), Mn (p = 0.014), Ce (p = 0.017), Co (p = 0.018), and Ca (p = 0.031) in leachates showed significant correlation with EC50 values. The predictive model for the ecotoxicity of SFCCCs were established with the concentrations of Ni and La in leachates as:ln(EC50) = 0.817 + exp(1.356 – 1.736 × CNi - 0.262 × CLa) (R2 = 0.926).The main toxic ingredients of SFCCC to microalgae were identified for the first time in this work. The results and predictive model of this study are significance for toxicity determination and management of SFCCCs.

Heavy metals removal from dumpsite leachate by algae and cyanobacteria

A living consortium of green algae (Ankistrodesmus) and cyanobacteria (Nostoc and Anabaena) was tested for the removal of heavy metal ions (Fe (II), Cu (II), Pb (II), Cr (VI) and Zn (II)) from dumpsite leachate under natural climatic conditions. Metal removal experiment was performed at 5 and 10 mg L−1 initial metal concentration in leachate and 0.8 and 1.6 g L−1 of biomass doses. Metal removal was in the order of Pb > Cu > Zn > Fe > Cr. Among all the metals algae and cyanobacteria removed the highest amount of Pb (7.03 ± 0.6 mgg−1) at 10 mgL−1 initial metal concentration and algal dose of 0.8 gL−1 and, the lowest amount of Cr metal (0.98 ± 0.6 mgg−1) was taken up at 5 mgL−1 initial metal concentration and 1.8 gL−1 of biomass dose. Metal removal by unit biomass mass (mgg−1) increases with an increase in initial metal concentration in leachate and decrease in biomass concentration however, the removal rates (percent removal per unit time) of metal ions has positive relationship with the initial biomass concentration. With an increase in initial metal concentration, the chances of collision between metal ions and available cations at the cell surface of biomass increases, resulting in increased metal uptake until the equilibrium is achieved after which the metal uptake remains constant. At small initial doses relatively a large number of adsorption sites at cell walls of algae and cyanobacteria are exposed, shifting the sorption equilibrium toward the biomass side resulting in rapid saturation of binding sites and increased bio sorption capacity of algae and cyanobacteria. This study reveals that living consortium of algae and cyanobacteria can be used as potential organisms for heavy metal removal from dumpsite leachate under natural climatic conditions.

Mobility of metal(loid)s in Pb/Zn tailings under different revegetation strategies

Metal tailings are potential sources of strong environmental pollution. In situ remediation involves the installation of a plant cover to stabilize materials and pollutants. Whether metal(loid)s are effectively immobilized in remediated tailing ponds submitted to heavy rainfall remains uncertain. In this study, tailing materials were collected from bare tailings (control), grass-planted (G) and grass-shrub planted (GS) areas on a former Pb/Zn mine site. Batch column experiments were performed with three rainfall intensities of 0.36, 0.48, and 0.50 mL min−1 for 18 d in the lab. The pH, Eh, Cd, Pb, Zn and As concentration in leachate were recorded. Selected leached tailing materials were finally characterized. Results showed that leachates from control were strongly acidic (pH 3.11–4.65), and that Cd, Pb, Zn and As were quickly released at high rate (e.g., 945 mg L−1 Zn). During the experiment up to 4% Cd present in the material was released and almost 1% Zn. With material collected from the G area, leachates were even more acidic (2.16–2.84) with a rainfall intensity of 0.50 mL min−1 and exhibited a high redox potential (588–639 mV). However, concentrations of metals in leachates were much lower than that in the control, except for Zn (e.g., 433 mg L−1), and they tended to decrease with time. Cumulative leaching rate was still relatively high (e.g., 0.68% Cd; 0.75% Zn) during the first eight days (stage I). However, with the GS treatment, leachate pH gradually raised from acid to alkaline values (3.9–8.2) during stage I, then remained high until the end of the experiment (stage II). Also, amounts of elements released during the 18 d were low in general. The releasing ratios of Cd (R2 > 0.95), Pb (R2 > 0.95), As (R2 > 0.87), and Zn (R2 > 0.90) fitted well with a two-constant model. In conclusion, under subtropical climate with heavy rainfall, phytostabilization is effective but immobilization of metals is higher with a combination of grass and shrub than with only grass to reduce leaching of As and Zn.

Towards Understanding the Mechanism of Heavy Metals Immobilization in Biochar Derived from Co-pyrolysis of Sawdust and Sewage Sludge.

Biochar was prepared by mixing sewage sludge with sawdust via a co-pyrolysis with different mixture ratios and temperatures. The results showed that the sawdust addition resulted in a lower yield of biochar with higher C content. The total concentrations of Pb and Cd in biochar were reduced. Besides, pyrolysis can transform the potentially toxic Pb and Cd to stable fractions. However the sawdust addition had slight influence on the chemical forms of Pb and Cd in the biochar. The biochar with 50% sawdust at 600°C exhibited a remarkable reduction of the leachable metal concentrations. The possible transformation mechanisms of Pb and Cd were inferred as the formation of aluminum and silicon-containing minerals. These results provide insights into the influence of sawdust addition on the characteristics of biochar and the possible Pb and Cd immobilization mechanisms during co-pyrolysis process.

Heavy Metal Concentrations in Leachates and Crops Grown Around Waste Dumpsites in Sekondi-Takoradi in the Western Region of Ghana

Heavy Metal Concentrations in Leachates and Crops Grown Around Waste Dumpsites in Sekondi-Takoradi in the Western Region of Ghana

Assessment of heavy metal release from dredged materials for different disposal scenarios: Study of Anzali international wetland, Iran

In aquatic systems, heavy metals are accumulated in sediments that can release from loosely bound fractions during dredging and disposal operations. Five sediment samples were collected from the entry of the Pasikhan River to Anzali wetland, where dredging is carried out. The heavy metal distribution in sediments was determined using a sequential extraction procedure that showed Pb and Cd contribution mostly to non-residual phase (>80%). Heavy metal release from dredged materials was assessed for different disposal scenarios using pathway specific leaching tests. The highest release was attributed to Pb and Cd in open-water disposal (232 and 12.6μg/L, respectively), confined disposal facilities (CDF) (180 and 12.2μg/L, respectively), and landfilling (679 and 5.6μg/L, respectively). The metal bioavailability and bioaccessibility were assessed using single extraction methods for agricultural use and other disposal scenarios. The metal bioavailability was in the order of Cd ∼ Pb>Cu>Mn>Zn>Fe>Ni>Cr. In case of open-water disposal, metal concentrations in water column were higher than water quality standards but lower than background amounts at the disposal site. In confined disposal, the concentrations in effluent and leachate of CDF occasionally exceeded the allowable limits. Finally, in case of landfilling, metal concentrations in leachate exceeded that of other methods, but remained below the USEPA recommended limits. According to implemented risk assessment indices, the risk level for heavy metal bioavailability and bioaccessibility was medium and very high, respectively, and Cr had carcinogenic and non-carcinogenic risk for human health.

Influence of sodium chloride on leaching behavior of fly ash stabilized with carbide lime

Fly ash (FA) stabilized with carbide lime (CL) and sodium chloride (NaCl) can possess excellent mechanical properties within a short curing period. However, potential leachability of undesirable chemical constituents from FA, CL and their combinations under different proportions, densities, curing temperatures, sodium chloride and curing periods has not been investigated. In this study, acid digestion and water leaching batch tests were conducted to determine the total and water leachable chemical constituents in FA and CL. Batch tests results showed that FA could have water leachable concentrations of arsenic (As), chromium (Cr) and selenium (Se) above the drinking water limits, but CL did not contain any leachable metal concentrations. Furthermore, several series of column leaching tests were conducted with blends of FA, CL and NaCl under different conditions, using deionized water as permeant to assess the leachability of chemical constituents. The results from the column tests showed that the hydraulic conductivity (k) varies depending on the blend composition, density and curing conditions. The addition of NaCl in the mixtures affects the retention capacity of some metals (e.g., Se, Cr, and Al) in the cementitious matrix, resulting in higher concentrations of these metals in the leachate. The variation in time and temperature of curing, amount of carbide lime, and density influenced the concentration of chromium in the column leach extract. The stabilization/solidification technique allowed the reduction of the release of heavy metals.

Fuels, vegetation, and prescribed fire dynamics influence ash production and characteristics in a diverse landscape under active pine barrens restoration

BackgroundAn important consequence of wildland fire is the production of ash, defined as a continuum of mineral to charred organic residues formed by the burning of wildland fuels. Ash may impact soil health depending on its elemental composition and other factors, which are influenced by fuel quantity and quality, and by combustion completeness. To investigate how ash properties relate to variation in fuels and fire, we collected and analyzed ash samples following prescribed fires in a pine barrens landscape spanning grassland, shrubland, conifer woodland, and deciduous forest. At some plots, mechanical brush cutting was applied, and woody fuels were added or removed to experimentally manipulate fuel loads.ResultsAsh load averaged 2 Mg ha−1, or approximately 12.5% of fuel consumption, and was positively related to maximum temperatures estimated by temperature-sensitive paint tags. Ash load also increased in cut brush and fuel addition treatments. Fuel consumption in grasslands, estimated from maximum paint tag temperatures by calibration, was increased by woody fuel addition. Total nutrient stocks in ash was greatest at conifer sites (i.e., nitrogen, N; phosphorus, P; potassium, K; magnesium, Mg; and iron, Fe) and lowest at grassland sites (P; K; calcium, Ca; Mg; and manganese, Mn). Concentrations of leachable nutrients in ash were high for cations Ca (>20 g kg−1), K (>4 g kg−1), and Mg (>5 g kg−1), which resulted in high ash pH (mean ± standard error = 8.4 ± 0.1). Leachable cations were positively related to total ash cation concentrations, but leachable metal concentrations (Fe; Mn; copper, Cu) were low despite their high content in ash.ConclusionsWe observed differences in ash production and composition that corresponded to variation in vegetation cover, fuel loads, and paint tag temperatures. High concentrations of leachable cations in ash suggested that repeated prescribed fire may act to decrease cation availability in soils if cations are leached through sandy soils over time. In the case of pine barrens, prescribed fires, which decrease carbon (C) stocks while producing high concentrations of leachable nutrients in ash, may contribute to decreased soil nutrient stocks, and more limited tree growth, thus helping to maintain and restore critically endangered barrens ecosystems.

Heavy metal leaching and plant uptake in mudflat soils amended with sewage sludge.

The leaching and uptake of Cd, Cu, Pb, and Zn by maize (Zea mays L.) in mudflat saline-alkali soils amended by sewage sludge was examined using a greenhouse leaching column experiment. Application of sewage sludge caused decreased pH, increased DOC, and increased Cd, Cu, Pb, and Zn concentrations in leachates. The similar temporal dynamics of DOC and the metal concentrations in leachates suggested complexation of the metals with DOC. There was downward movement of metals as evidenced by the metal enrichment in the bottom layer (20-40-cm depth) of leaching columns (p < 0.05). The enrichment of metals was contributed by the acid-soluble/exchangeable fraction (EX), reducible fraction (RG), oxidizable fraction (OXI), and residual fraction (RES), indicating redistribution of leached metals from the top 20-cm layer. The sewage sludge application also enhanced plant uptake of metals. However, even under the greatest sludge application rate (150gkg-1), very small proportions, averagely 0.65% and 0.35%, of the applied metals were leached and taken up by maize, respectively, over the experimental period. Long-term field-scale research is warranted for further investigation of the effects of sewage sludge amendment on heavy metal fractionation and distribution in mudflat soil-plant-water system.

Prediction of heavy metals concentration in the leachate: a case study of Ukrainian waste

A lifetime of landfill with the waste composition and conditions specific to big and small towns of Ukraine is reproduced with landfill simulation reactors in 12-week period. The heavy metals concentrations (lead, nickel, chromium, cadmium) and physico-chemical parameters affecting (pH, reduction potential, conductivity, DOC, COD) are measured in the leachate formed during the reactors exploitation. The results show a quite high content of the heavy metals. Higher concentrations are found where more organic fraction is present in the waste. There are conditions inside the reactors, especially acidity, which are crucial at the early stages. Further, a significant impact can be caused by unequal distribution of heavy metals in the waste body. Also due to accelerated water regime in the reactors, the heavy metals concentrations in a landfill leachate are predicted up to 50–55 years. Forecast shows multiple (2–18 times) exceeding the allowable concentrations of all heavy metals.

Remediation of an acidic mine spoil: Miscanthus biochar and lime amendment affects metal availability, plant growth, and soil enzyme activity

Biochar may be a tool for mine spoil remediation; however, its mechanisms for achieving this goal remain unclear. In this study, Miscanthus (Miscanthus giganteus) biochar was evaluated for its ability to reclaim acidic mine spoils (pH < 3) through reducing metal availability, improving soil microbial enzymatic activity, and initial growth of grass seedlings. Biochar was applied at 0, 1, 2.5 and 5% (w/w) along with lime/no lime and fertilizer additions. Blue Wildrye (Elymus glaucus cv. ‘Elkton’) was planted and later the shoots and roots were collected and metal concentrations determined. Afterwards, each pot was leached with deionized water, and the leachate analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC) and soluble metal concentrations. After drying, the spoil was extracted with 0.01 M CaCl2 and Mehlich 3 (M3) to determine extractable Al, Cu, and Zn concentrations. Additionally, microbial activity was measured using a fluorescent β-glucosidase and N-acetyl-β-d-glucosaminidase assay. Spoil treated with lime and biochar had significantly greater pH and EC values. Significantly greater β-glucosidase activity occurred only in the 5% biochar plus lime treatment, while N-acetyl-β-d-glucosaminidase activities were not altered. Metal concentrations in rye shoot and roots were mixed. Lime additions significantly reduced extractable metal concentrations. Increasing biochar rates alone significantly reduced leachate DOC concentrations, and subsequently reduced leachable metal concentrations. Surprisingly, miscanthus biochar, by itself, was limited at mitigation, but when combined with lime, the combination was capable of further reducing extractable metal concentrations and improving β-glucosidase enzyme activity.

Co-treatment of flotation waste, neutralization sludge, and arsenic-containing gypsum sludge from copper smelting: solidification/stabilization of arsenic and heavy metals with minimal cement clinker.

Flotation waste of copper slag (FWCS), neutralization sludge (NS), and arsenic-containing gypsum sludge (GS), both of which are difficult to dispose of, are major solid wastes produced by the copper smelting. This study focused on the co-treatment of FWCS, NS, and GS for solidification/stabilization of arsenic and heavy metals with minimal cement clinker. Firstly, the preparation parameters of binder composed of FWCS, NS, and cement clinker were optimized to be FWCS dosage of 40%, NS dosage of 10%, cement clinker dosage of 50%, mill time of 1.5h, and water-to-binder ratio of 0.25. On these conditions, the unconfined compressive strength (UCS) of the binder reached 43.24MPa after hydration of 28days. Then, the binder was used to solidify/stabilize the As-containing GS. When the mass ratio of binder-to-GS was 5:5, the UCS of matrix can reach 11.06MPa after hydration of 28days, meeting the required UCS level of MU10 brick in China. Moreover, arsenic and other heavy metals in FWCS, NS, and GS were effectively solidified or stabilized. The heavy metal concentrations in leachate were much lower than those in the limits of China standard leaching test (CSLT). Therefore, the matrices were potential to be used as bricks in some constructions. XRD analysis shows that the main hydration products of the matrix were portlandite and calcium silicate hydrate. These hydration products may play a significant role in the stabilization/solidification of arsenic and heavy metals.

Sustainable clean pervious concrete pavement production incorporating palm oil fuel ash as cement replacement

The significant increase in global urban population and rapid growth of impervious urban surfaces result in erosion of stream channels, flooding, and damage to stormwater infrastructures. The aim of this research was to study pervious concrete pavement as a sustainable solution to control the stormwater at source, reducing heat island effect and enhancing safety of driving. The sustainability of pervious concrete can be increased and the carbon dioxide emissions reduced by replacing a huge amount of ordinary Portland cement with waste materials such as palm oil fuel ash. Palm oil fuel ash is a waste material obtained from the combustion of oil palm shells and fibers in palm oil industry to produce electricity, which caused environmental problems in countries such as Indonesia and Malaysia. This study presented experimental investigations to assess the substitution of control pervious concrete with palm oil fuel ash up to 40% (by mass) to produce sustainable and eco-friendly pervious concrete pavement. Density and void content of specimens were determined at fresh and hardened-state. Falling head permeability test was carried out to investigate the stormwater filtration capacity. Compressive and tensile strengths were conducted on pervious concrete specimens. Skid and abrasion resistances were also employed to evaluate the effects of palm oil fuel ash on safety of driving and surface durability of the pervious concrete pavement. The results showed that void content and water permeability of pervious concrete increased slightly with increasing palm oil fuel ash, while compressive and tensile strengths decreased. They satisfy the typical range for pervious concrete according to American Concrete Institute. A minor effect of palm oil fuel ash on the skid resistance was observed, increasing its substitution levels caused the abrasion resistance of pervious concrete mixtures to decrease. The heavy metal concentrations in leachates of the pervious concrete containing 40% palm oil fuel ash were significantly lower than recommended in the standard. The pervious concrete containing 20% palm oil fuel ash presented the most optimum mixture both technically and environmentally.

Recycling red mud from the production of aluminium as a red cement-based mortar.

Current management for red mud is insufficient and a new method is needed. A series of experiments have been carried out to develop a new approach for effective management of red mud. Mortars without or with 3%, 6% and 9% red mud were prepared and their fresh and hardened properties were measured to access the possibility of recycling the red mud in the production of red cement-based mortar. The mechanisms corresponding to their mechanical performance variations were explored by X-ray powder diffraction and scanning electron microscopy. The results show that the fresh mortars with red mud present an increase of viscosity as compared with the control. However, little difference is found when the content of red mud is altered. It also can be seen that red mud increases flow time and reduces the slump flow of the mortar. Meanwhile, it is found that mortar with red mud is provided with higher air content. Red mud is eligible to adjust the decorative mortar colour. Compressive strength of mortar is improved when less than 6% red mud is added. However, overall it has a slightly negative effect on tensile bond strength. It decreases the Ca(OH)2 content and densifies the microstructure of hardened paste. The heavy metal concentrations in leachates of mortars with red mud are much lower than the values required in the standard, and it will not do harm to people's health and the environment. These results are important to recycle and effectively manage red mud via the production of red cement-based mortar.

Municipal landfill leachate characteristics and feasibility of retrofitting existing treatment systems with deammonification – A full scale survey

Leachate characteristics, applied technologies and energy demand for leachate treatment were investigated through survey in different states of Germany. Based on statistical analysis of leachate quality data from 2010 to 2015, almost half of the contaminants in raw leachate satisfy direct discharge limits. Decrease in leachate pollution index of current landfills is mainly related to reduction in concentrations of certain heavy metals (Pb, Zn, Cd, Hg) and organics (biological oxygen demand (BOD5), chemical oxygen demand (COD), and adsorbable organic halogen (AOX)). However, contaminants of concern remain COD, ammonium-nitrogen (NH4N) and BOD5 with average concentrations in leachate of about 1850, 640, and 120 mg/L respectively. Concentrations of COD and NH4N vary seasonally, mainly due to temperature changes; concentrations during the first quarter of the year are mostly below the annual average value. Electrical conductivity (EC) of leachate may be used as a time and cost saving alternative to monitor sudden changes in concentration of these two parameters, due to high correlations of around 0.8 with both COD and NH4N values which are possibly due to low heavy metal concentrations in leachate. The decreased concentrations of heavy metals and BOD5 favor the retrofitting of an existing biological reactor (nitrification/denitrification) with the deammonification process and post denitrification, as this lowers average annual operational cost (in terms of energy and external carbon source) and CO2 emission by €25,850 and 15,855 kg CO2,eq respectively.

The Leachability of Heavy Metals from Alkali-Activated Fly Ash and Blast Furnace Slag Matrices

The ability of alkali-activated materials (AAMs) to fix and immobilize heavy metals was investigated. Two raw materials were used to prepare alkali-activated matrices – high-temperature fly ash and blast furnace slag (BFS). NaOH served as an alkaline activator. Two heavy metals (Mn, Ni) were added in different amounts to find out the influence of dosage of heavy metal on the mechanical properties of the matrices and the leachability. Leachability was measured as concentration of heavy metals in leachates (ČSN EN 12457-4) by inductively coupled plasma/optical emission spectrometry (ICP/OES). Structure of prepared matrices was characterized by scanning electron microscopy (SEM). Increasing of addition of heavy metals led to decrease of mechanical properties of matrices. The leaching tests showed, that both matrices can immobilize Mn and Ni in dosages of 0.1 – 2,5%. Higher dosages caused deterioration of the matrices and increased the leachability. After alkali activation both heavy metals were transformed into the form of insoluble salts.

Immobilization of Cu(II) and Zn(II) in simulated polluted soil using sulfurizing agent

Potential immobilization of Cu(II) and Zn(II) in soil by using sodium sulfide (Na2S) and sodium diethyl dithiocarbamate (DDTCNa) were investigated in terms of immobilizing agent dosage and leaching pH by column leaching tests. The formation of metal sulfide products and the immobilization mechanism were systematically studied by XRD measurements and chemical equilibrium analysis. Leaching test results indicated that great reduction rate of heavy metals in polluted soil was obtained when sulfuring agent was used as immobilizing agent. Especially, DDTCNa showed better immobilization effect on heavy metals than Na2S. With the increase of immobilizing agent dosage, heavy metal concentrations in leachate decreased. When immobilizing agent dosage was higher than 45gkg−1, the reduction rate of Cu(II) and Zn(II) enhanced slightly. Immobilization of Cu(II) and Zn(II) was strongly dependent on leaching pH. The optimal immobilization effects on Cu(II) and Zn(II) were obtained in alkaline and neutral pH range for Na2S and DDTCNa, respectively. XRD measurements and chemical equilibrium analysis indicated that Na2S and DDTCNa could immobilize heavy metals by the formation of metal sulfide precipitates.

Multivariate analysis of heavy metal leaching from urban soils following simulated acid rain

Heavy metal pollution in urban soils and its effect on urban ecological environment and human health are of increasing concern. In this study, a leaching experiment was conducted to assess the effect of simulated acid rain (SAR) on the migration of Cd, Pb, Cu, and Zn and their transformation and speciation in nine natural urban soils from Guangzhou, China, combined with two-dimensional hierarchical cluster analysis (2-D HCA) heat map and principal component analysis (PCA). The maximum concentrations of Zn and Cu in leachates were lower than Grade III of Chinese Environmental Quality Standards for Ground and Surface water, although being seriously contaminated with Zn (up to 19,570mg/kg) and Cu (322.4), thereby suggesting that Zn and Cu leached from urban soils receiving SAR pose little risk of water pollution. However, the maximum concentrations of Pb and Cd in leachates exceeded Grade III and V of the standards, respectively. The proportions of metals in the non-residual fractions were generally decreased after the leaching test for S(oil)5 (with high concentrations of metals in leachate), representing the decreased contamination risk in the soil–water system. A similar trend was observed for S(oil)6 (with low concentrations of metals in leachate) in terms of Zn and Cu, whereas the proportions of Cd and Pb in the non-residual fractions of S6 increased after leaching. Significantly positive relationships were observed between the concentration of heavy metal in leachate and all fractions of heavy metal, as well as the total concentration of soil heavy metals. In terms of Zn, Cd, and Pb, there were negative relationships between the concentration of heavy metal in leachate and clay and silt, respectively, while the inverse relationships were observed for Cu. The release of heavy metals from soil was strongly associated with their fractions and such soil properties as pH, soil texture, and organic matter.