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The potential leaching of pollutants present in harbor sediments has to be evaluated in order to choose the best practices for managing them. Little is known about the speciation and mobility of heavy metals in these specific solid materials. The objective of this paper is to determine and model the leachability of copper, lead, and zinc present in harbor sediments in order to obtain essential new data. The mobility of inorganic contaminants in a polluted harbor sediment collected in France was investigated as a function of physicochemical conditions. The investigation relied mainly on the use of leaching tests performed in combination with mineralogical analysis and thermodynamic modeling using PHREEQC. The modeling phase was dedicated to both confirm the hypothesis formulated to explain the experimental results and improve the determination of the main physico-chemical parameters governing mobility. The experimental results and modeling showed that the release of copper, lead, and zinc is very low with deionized water which is due to the stability of the associated solid phases (organic matter, carbonate minerals, and/or iron sulfides) at natural slightly basic conditions. However, increased mobilization is observed under pH values below 6.0 and above 10.0. This methodology helped to consistently obtain the geochemical parameters governing the mobility of the contaminants studied. [ABSTRACT FROM AUTHOR]

Coal combustion ashes, gasification ashes, and pyrolysis chars were used to simulated the residues of " three zones" from underground coal gasification, which are oxidization zone, reduction zone and dry distillation zone. The distribution characteristics of mercury, arsenic, fluorine, chromium, lead five trace elements in the leaching solution was analyzed, and compared with that in raw coal, in order to investigate their potential threat to groundwater. The results indicate that total contents of the five trace elements in the leaching solution of raw coal and the residues of "three zones" follow the order of dry distillation zone>oxidization zone>reduction zone>raw coal,within the scope of of national standard GB 20426-2006. The contents of Pb follow the order of dry distillation zone > raw coal > oxidization zone>reduction zone, they are very low and the average value of Pb is only 0. 003 0 mg/L. The contents of As follow the order of oxidization zone >>reduction zone>dry distillation zone>raw coal, and the residues in oxidization zone have the highest As leaching content of 0.1450 mg/L, almost 63 times of that in raw coal. The contents of F- follow an order of dry distillation zone>oxidization zone>reduction zone >>raw coal, and 476 times higher than that of the other four heavy metals. The leaching of Hg and Cr are not detected. [ABSTRACT FROM AUTHOR]

Abstract: Since contaminated river-bed sediments in the Cam River-mouth (Vietnam) are regularly dredged and disposed on land, an understanding of the influence of time, pH and oxidation on the leaching behavior of heavy metals (Cd, Cu, Mn, Pb and Zn) and arsenic is necessary for the management of these dredged materials. A 96h pHstat-leaching test to examine the leaching behavior of elements at pre-set pH values (2, 4, 6, 8 (natural), 9 and 11) and a BCR 3-step extraction to clarify the element fractionation, were performed on a freshly-collected wet suboxic sediment and a dry oxidized sediment. All heavy metals and arsenic display a V-shaped pH-dependent leaching pattern with important releases at pHs 2 and 11. At the investigated pH values, the release of As, Mn, Pb and Zn from the oxidized sediment is slower and lower if compared with the suboxic sediment while the opposite trend is found for Cd and Cu at pHs 2–8. The transfer from the acid-soluble (exchangeable and carbonate-bound) fraction to the reducible (Fe and Mn hydr/oxide-bound) fraction is consistent with the lower leachability of As, Mn and Zn at pHs 2–8 and Pb at pHs 4–8 after oxidation, while the transfer from the oxidizable (organic matter and sulfide-bound) fraction to the reducible fraction relates to the higher leachability of Cd and Cu at pHs 2–8. The lower leachability of all elements at alkaline pHs 9–11 is due to lower leached concentration of organic matter from the oxidized sediment. Sulfides only play a minor role in controlling the leachability of heavy metals and arsenic. [Copyright &y& Elsevier]

Abstract: The feasibility and mechanism of incorporating simulated lead-laden sludge into low-cost ceramic products was investigated by observing the reaction of lead with two kaolinite-based precursors under sintering conditions. To investigate the phase transformation process of lead, lead oxide (PbO) mixed with a kaolinite or mullite precursor were fired at 500–950°C for 3h. Detailed X-ray diffraction analysis of sintered products revealed that both precursors had crystallochemically incorporated lead into the lead feldspar (PbAl2Si2O8) crystalline structure. By mixing lead oxide with kaolinite, lead feldspar begins to crystallize at 700°C; maximum incorporation of lead into this structure occurred at 950°C. However, two intermediate phases, Pb4Al4Si3O16 and a polymorph of lead feldspar, were detected at temperatures between 700 and 900°C. By sintering lead oxide with the mullite precursor, lead feldspar was detected at temperatures above 750°C, and an intermediate phase of Pb4Al4Si3O16 was observed in the temperature range of 750–900°C. This study compared the lead leachabilities of PbO and lead feldspar using a prolonged leaching test (at pH 2.9 for 23d) modified from the toxicity characteristic leaching procedure. The results indicate the superiority of lead feldspar in stabilizing lead and suggest a promising and reliable strategy to stabilize lead in ceramic products. [Copyright &y& Elsevier]

Abstract: Fly ash from a municipal solid waste incinerator (MSWI) is commonly classified as hazardous waste. High-energy electron beam irradiation systems have gained popularity recently as a clean and promising technology to remove environmental pollutants. Irradiation effects on leaching behavior and form of heavy metals in MSWI fly ash have not been investigated in any significant detail. An electron beam accelerator was used in this research. Electron beam irradiation on fly ash significantly increased the leaching potential of heavy metals from fly ash. The amount of absorbed dose and the metal species affected leaching behavior. When electron beam irradiation intensity increased gradually up to 210kGy, concentration of Pb and Zn in the leachate increased linearly as absorbed dose increased, while that of Cu underwent no significant change. Concentration of Pb and Zn in the leachate increased up to 15.5% (10.7mg/kg), and 35.6% (9.6mg/kg) respectively. However, only 4.8% (0.3mg/kg) increase was observed in the case of Cu. The results imply that irradiation has significant effect on the leaching behavior of heavy metals in fly ash, and the effect is quite different among the metal species tested in this study. A commonly used sequential extraction analysis which can classify a metal species into five forms was conducted to examine any change in metal form in the irradiated fly ash. Notable change in metal form in fly ash was observed when fly ash was irradiated. Change in Pb form was much greater than that of Cu form. Change in metal form was related to leaching potential of the metals. Concentration of heavy metal in leachate was positively related to the exchangeable form which is the most mobile. It may be feasible to treat fly ash by electron beam irradiation for selective recovery of valuable metals or for pretreatment prior to conventional processes. [Copyright &y& Elsevier]

Growing environmental concern is promoting the necessity of additional ceramic tests. The use of unknown materials with potential contamination conditions requires further studies to demonstrate that the piece encapsulates the pollutant and that during its firing it does not produce the emission of harmful volatile elements. The objective of this work was to perform both tests in a ceramic paste made with slip-casting wastes and electro-plating residues. The leaching methods for determining the encapsulation of potential harmful elements were performed following the TCLP, EP-Tox norm. Having precise chemical analysis of both crude and fired brick, the problem of emissions losses during the firing can be solved by the gain/loss techniques used in geological studies. In particular, the Isocon method that permits a quick visualization of the lost elements is useful. Once the volatile elements were determined, their amount was calculated considering a constant element and the chemical concentrations normalized by the loss of ignition, or using the crude/fired brick ratio densities. The leaching tests indicate that the ceramic brick does not produce harmful leachates according to Argentinean specifications. The leachates of B and Ca are high. Ca does not seem to be a problem while the B content is beyond the permitted limits. During the firing, volatilized elements are Ag, Br, Cl, F, Hg, S, Se, and HO. The loss of Ag, Br, and Se are negligible. For F and Cl the potential emission rate is very low (100 mg/kg) while in the case of S, the 2,600 mg/kg rate is high. However, extrapolated emission rates at the chimney assuming an air-to-brick ratio of 2.5 N m/kg, are approximately 1,040 mg/N m for S and 40 mg/N m for F and Cl, falling inside environmentally acceptable values. The geochemical procedures proved to be useful tools to assess the element mobilization during firing of ceramic wares and in the analyzed case, the results indicate that the paste is environmentally acceptable. [ABSTRACT FROM AUTHOR]

Abstract: This work deals with the regeneration of a KOH solution to use in a chemical absorption process for biogas upgrading. The proposed method consists in the caustic recovery of the spent absorption solution by carbonation of selected industrial residues and allows to store the separated CO2 in a solid phase (calcite). This paper presents the main results of the lab scale experiments carried out to evaluate the effects of selected operating parameters on the carbonation reaction so to identify the conditions that allow to maximize the CO2 uptake of the solid residues and the percentage of KOH that can be regenerated for the absorption process. Furthermore, the effects of the tested treatments on the leaching behavior of the residues are also examined. The results presented in this paper were obtained within the UPGAS-LOWCO2 project (LIFE08 ENV/IT/000429) funded by the European Commission. [Copyright &y& Elsevier]

Abstract: This study investigated the mechanisms of stabilizing lead-laden sludge by blending it into the production process of aluminum-rich ceramics, and quantitatively evaluated the prolonged leachability of the product phases. Sintering experiments were performed using powder mixtures of lead oxide and γ-alumina with different Pb/Al molar ratios within the temperature range of 600–1000 °C. By mixing lead oxide with γ-alumina at a Pb/Al molar ratio of 0.5, the formation of PbAl2O4 is initiated at 700 °C, but an effective formation was observed when the temperature was above 750 °C for a 3-h sintering time. The formation and decomposition of the intermediate phase, Pb9Al8O21, was detected in this system within the temperature range of 800–900 °C. When the lead oxide and γ-alumina mixture was sintered with a Pb/Al molar ratio of 1:12, the PbAl12O19 phase was found at 950 °C and effectively formed at 1000 °C. In this system, an intermediate phase Pb3(CO3)2(OH)2 was observed at the temperature range of 700–950 °C. Over longer leaching periods, both PbAl2O4 and PbAl12O19 were superior to lead oxide in immobilizing lead. Comparing the leaching results of PbAl2O4 and PbAl12O19 demonstrated the higher intrinsic resistance of PbAl12O19 against acid attack. To reduce metal mobility, this study demonstrated a preferred mechanism of stabilizing lead in the aluminate structures by adding metal-bearing waste sludge to the ceramic processing of aluminum-rich products. [Copyright &y& Elsevier]

The leaching behavior of nitrogen was studied in single rice paddy production ecosystems in Tsukuba, Japan after 75 years of consistent fertilization regimes (no fertilizer, ammonium sulfate, a combination of composted rice straw with soybean cake, and fresh clover). During the 75-year period, management was unchanged with respect to rice planting density, irrigation, and net N fertilization for each field to which an N-source was added. Percolation water was collected, from May 2001 to April 2002, using porous suction cups installed in the fields at depths of 15, 40, and 60 cm. All water samples were taken to the laboratory for the measurement of both NH-N and NO-N concentrations using a continuous-flow nitrogen analyzer. The result indicated that there were significant differences in N leaching losses between treatments during the rice growing season. Total N leaching was significantly lower with the application of composted rice straw plus soybean cake (0.58 kg N ha) than with ammonium sulfate (2.41 kg N ha), which resulted in N leaching at a similar level to that with the fresh clover treatment (no significant difference). The majority of this N leaching was not due to NO-N loss, but to that of NH-N. The mean N leaching for all fertilizer treatments during the entire rice growing season was 1.58 kg N ha. Composted rice straw plus soybean cake produced leaching losses which were 65-75% lower than those with the application of fresh clover and ammonium sulfate. N accumulation resulting from nitrification in the fallow season could be a key source of nitrate-N leaching when fields become re-flooded before rice transplanting in the following year; particular attention should be paid to this phenomenon. [ABSTRACT FROM AUTHOR]

This study aims to develop a methodology for analysis of characteristics of heavy metals in MSWI fly ash. It performed analysis of composition of heavy metals, leaching toxicity, leaching behavior as a function of pH, specification distribution and corresponding mineral components of residue derived from each step of the sequential extraction. It is found that content of heavy metals follows the sequence of Zn > Pb > Cu > Cr > As > Ni > Cd approximately Hg in both plants, and that total heavy metals account for less than 1% by mass of fly ash, Major hazardous heavy metals in fly ash are As, Cd, Hg, Pb and Zn, whose leaching ratios exceed the limit value described in hazardous waste identification standard. Measured leaching results of Cu, Pb and Zn are essentially consistent with the simulated results at pH between 0 and 13. Content of calcium-silicates, alumina-silicates and glass phases in residue derived from sequential extraction procedure increases steadily from the first step to the fifth step of the sequential extraction procedure. Cu, As, Cr, Hg, Cd, and Ni, relatively stable under strong basic conditions, can be leached out under strong acidic conditions, while Zn and Pb tend to be leached out under both strong acidic and basic conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • In this study, we have analyzed the adsorption–desorption behavior of Glyamifop in different types of soils and study their relationship with soil physicochemical properties (organic matter content, mechanical composition, pH value). • To evaluate the adsorption capacity of soil to Glyamifop under different environmental factors (temperature and initial solution pH) and foreign additives (different surfactants, humic acids). • To explore the migration characteristics of Glyamifop in soil. • Verify the Glyamifop residue analysis methods in different types of soil. Rice weeds strongly inhibit the production of rice because they compete with rice. Glyamifop is a novel herbicide for controlling rice weeds and being tested in paddy fields. Based on our previous studies, Glyamifop offers excellent control for rice weeds and has no negative effects on rice plant growth as well as rice yields. However, the adsorption–desorption and migration behaviors of Glyamifop in paddy soils are still not well resolved. In this study, we investigated the adsorption–desorption and migration characteristics of Glyamifop in paddy soils collected from four provinces in China, using batch equilibrium, soil column leaching, and thin-layer chromatography tests combined with liquid chromatography–tandem mass spectrometry (LC-MS) analysis. The results showed that all the soils had a relatively high adsorption capacity for Glyamifop, and both Freundlich adsorption and desorption constants were positively correlated with soil cation exchange capacity, organic carbon content, and organic matter content (P < 0.05). Moreover, despite the initial solution pH, temperature, humic acids, and surfactants also had strong effects on the adsorption of Glyamifop in soil, while the leachability and mobility of Glyamifop were very low in most soils. Therefore, due to the relatively low leachability and mobility of Glyamifop as well as its high adsorption capacity in soil, Glyamifop can serve as an excellent herbicide for rice weeds and cause little pollution to the environment. [ABSTRACT FROM AUTHOR]

Cuttings are the main solid residues which are generated from drilling operations. Due to the presence of heavy and radioactive elements, the environment risk posed by cuttings has attracted increasing attention. In this work, a short-term static immersion experiment was carried out to investigate the leaching of polycyclic aromatic hydrocarbons (PAHs) from oil-based residues of shale gas drilling cuttings. Furthermore, the effects of some relevant environmental factors controlling the leaching behavior were evaluated, including the different particle sizes, pH, extraction time, solid-to-liquid (S/L) ratio and dissolved organic matter (DOM) concentration. The results showed that (1) the concentrations of leached PAHs gradually increased with prolonged leaching time, but the cumulative amount of PAHs released during leaching was less than 3% of the total. (2) The Elovich, parabolic diffusion and power function models were found to fit the experimental data better than the first-order kinetic equation, indicating that the leaching of PAHs was controlled by the coupling of diffusion and chemical reactions at the source surface. (3) Different environmental factors had different impacts on the leaching of PAHs: the shaking time and presence of DOM increased leachability, the particle size and S/L ratio decreased leachability, and the pH did not affect the leachability of PAHs. Therefore, PAHs leaching was a complex process, and it is of scientific and environmental interest to conduct the leaching tests under the simulated environmental conditions. [Display omitted] ● PAHs leaching included fast and slow processes. ● Different environmental factors had different impacts on the leaching of PAHs ● The Elovich model could better describe PAHs leaching in oil-based cuttings. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, sorption, persistence, and leaching behavior of three microcystin variants in Chinese agriculture soils were examined. Based on this study, the values of capacity factor and slope for three MCs variants in three soils ranged from 0.69 to 6.00, and 1.01 to 1.54, respectively. The adsorption of MCs in the soils decreased in the following order: RR>Dha7 LR>LR. Furthermore, for each MC variant in the three soils, the adsorption rate in the soils decreased in the following order: soil A>soil C>soil B. The calculated half-time ranged between 7.9 and 17.8days for MC-RR, 6.0–17.1days for MC-LR, and 7.1–10.2days for MC-Dha7 LR. Results from leaching experiments demonstrated that recoveries of toxins in leachates ranged from 0–16.7% for RR, 73.2–88.9% for LR, and 8.9–73.1% for Dha7 LR. The GUS value ranged from 1.48 to 2.06 for RR, 1.82–2.88 for LR, and 1.76–2.09 for Dha7 LR. Results demonstrated the use of cyanobacterial collections as plant fertilizer is likely to be unsafe in soils. [Copyright &y& Elsevier]

Two acidic ferrisols, i.e., red soil (RS) and yellow red soil (YRS), from the vicinity regions of non-ferrous ores in Hunan province of China, were leached with simulated acid rain through artificial column experiments. The results show that the total leaching mass of metals are m(Zn)> m(Cu) > m(Cd) from the original soils and m(Cd)> m(Zn) >> m(Cu) from the contaminated soils with external metals after leaching for 60 d continuously, leaching quantities of Cd and Zn from the contaminated red soil (CRS) are more than that from the contaminated yellow red soil (CYRS), but for Cu, i is almost the same. The preferential fractions for leaching are mainly in exchangeable forms, and content of exchangeable forms decreases significantly in the contaminated soil profiles. The unstable fractions of Cd, Cu and Zn in the RS and YRS increase significantly with the decrease of pH value of simulated acid rain. Changes of fractions of external Cd, Cu, and Zn in the residual CRS and CYRS profiles are significantly affected by the acidity of acid rain, too. After leaching for 60 d continuously, Cd exists mostly in exchangeable form, Cu exists mainly in exchangeable, manganese oxide-occluded and organically bounding forms, and Zn exists in residual in CRS and CYRS profiles. Most of exchangeable Cd and Zn exist only small in surface layer (0–20 cm) and are transferred to the sub-layers, contrarily, Cu accumulates mostly in the topsoil (0–20 cm) with low translocation. [ABSTRACT FROM AUTHOR]

Abstract: The understanding of the leaching behavior of organic carbon from incinerator bottom ash is an important aspect for the control of organic carbon emissions from landfills in order to minimize their potential risk to the environment. The leaching behavior of organic carbon from incinerator bottom ash samples, obtained from two different solid waste sources, as well as the effects of calcium (Ca) on organic carbon (DOC) leaching associated with pH were therefore investigated in this paper. The effect of pH on the leaching of DOC and other major elements from bottom ash was ascertained through pH-stat leaching experiments. Column leaching experiments were carried out to evaluate the dependence of the leached amount of DOC on Ca leaching. It was found that the bottom ash produced by incineration of municipal solid waste (MSW) was composed of two DOC fractions: DOC leached independent (fraction I) of Ca leaching, observed at alkaline–neutral pH, and DOC leached dependent (fraction II) on Ca leaching, observed at acid pH. However, the bottom ash produced by incineration of industrial solid waste (ISW) was composed of only DOC fraction I. The addition of calcium oxide during incineration and the differences in the paper to plastic ratio in the physical composition of the solid wastes incinerated would explain the distinct organic carbon leaching behaviors of bottom ash samples. [Copyright &y& Elsevier]

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

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

Abstract: Surface characterization of coal fly ash (CFA) was carried out by use of X-ray photoelectron spectroscopy (XPS), especially focusing on the occurrence of As. A peak in the XPS spectrum of CFA was assigned to oxide forms of As(3d). The molar ratios of Al, As, Ca, Fe, and S normalized to Si were obtained from XPS analysis (MR-X). Also, the molar ratios of those elements were calculated from bulk analysis (total element concentration in CFA) (MR-B). The MR-X/MR-B ratio of As was much higher than those of other elements, suggesting that As is highly enriched on the surface of CFA. When eight CFA samples were analyzed, there was an approximate relationship between the MR-X values and MR-B values for As. The leaching of elements from CFA was examined by XPS analysis and by bulk analysis. The leaching tests using EDTA and HNO3 resulted in a great decrease in the As(3d) peak area; the %leaching of As obtained by XPS analysis was almost equal to that by bulk analysis. [Copyright &y& Elsevier]

Incineration technology has been widely employed, as an effective method to decrease the volume of waste disposal. In this review, relationships between municipal solid waste (MSW) inputs and residues after combustion―specifically, the incineration bottom ashes (IBA) of MSW, were discussed, with an emphasis on the geoenvironmental impacts of IBA associated with the complex crystal and amorphous phase reactions and changes during combustion and from their downstream treatments, whereas, their influences on IBA leaching behaviors are considered as another focus. This review summarizes the IBA leaching behaviors based on literature, showing the leaching variabilities induced by natural weathering and artificial intervention conditions, such as accelerated carbonation, washing treatment, stabilization/solidification, and thermal treatments, all of which can be attributed to changes of mineral phases and microstructure. It helps to understand IBA characteristics and transitions in application-environment nexus, and better reuse it for multiple applications. [Display omitted] • Akermanite, Calcite, Gehlenite, Quartz has relatively high proportions (>5%) in IBA. • Phase changes occurs under various treatments to impact the IBA leaching behaviours. • Metal inclusion, adsorption & complexation are main mechanisms of IBA stabilization. • Salt removal may significantly reduce the heavy metal leaching from the IBA. [ABSTRACT FROM AUTHOR]

The arsenic long-term leaching behavior of the cemented paste backfill obtained from the construction and demolition waste (CPB-CDW) is captured, which can be utilized in the potential engineering application. Laboratory studies were conducted on samples obtained from a mining site and the test results were imported into a numerical simulation model. It was found that the Elovich equation can describe well the As leaching behavior. Initially, the As concentrations decreased in the roadway in the mine and then increased along the roadway and attained a maximum concentration (8.149 × 10−3 mg/L) at the lower segment. When the groundwater was in the static mode, the As concentration increased dramatically followed by a gradual increase. Eventually, the concentration decreased gradually. For the dynamic condition, the As tended to move in a cluster form and the associated leaching and mass transfer process of As in the CPB-CDW were similar to those observed when the groundwater was in a static condition. However, the difference in the distribution of the amount of As in the leachate fluctuated continuously and the overall trend was to approach a steady state. As such, the time frame of such a mass transfer in the mobilized water is reduced significantly. [Display omitted] • The Elovich equation can better display the leaching rule of arsenic. • The maximum predicted value of arsenic leaching concentration is below threshold. • As leaching value first decreased and then increased in the slurry flow direction. • The state of water flow field affects the As leaching concentration distribution. • CDW for backfilling mining shows long-term pro-environmental behavior. [ABSTRACT FROM AUTHOR]

During the leaching process of ionic rare earth ore (ICREO), ion-exchangeable phase calcium (IEP-Ca) and ion-exchangeable phase aluminum (IEP-Al) are leached along with rare earth, which causes many problems in the enrichment process, such as increasing the precipitant agent consumption and rare earth loss, etc. The agitation leaching kinetics and the column leaching mass transfer process of IEP-Ca and IEP-Al were studied to understand the leaching behavior of impurity in ICREO, which provides guides for the adjustment of the leaching process and to limit the co-leaching of impurities. IEP-Ca and IEP-Al were leached by ion exchange, with the leaching agent cations and the leaching kinetics described by an internal diffusion-controlled shrinking core model with an apparent activation energy of 8.97 kJ/mol and 10.48 kJ/mol, respectively. In addition, a significant reduction in the leaching efficiency of aluminum was caused by the hydrolysis reaction reinforced by the increase in MgSO4 concentration and temperature. The leaching kinetic data of IEP-Ca and IEP-Al was verified by the column leaching mass transfer process. There was a synchronous increase in the peak concentration of the outflow curve and leaching efficiency of calcium with the concentration of MgSO4 since IEP-Ca was easily leached. Therefore, as the leaching efficiency of calcium was already very high in the 0.20 mol/L MgSO4 leaching process, the leaching rate of calcium was limited by the leaching temperature and injection rate of MgSO4. For aluminum, the hydrolysis of Al3+ was promoted by increasing the MgSO4 concentration and the leaching temperature, thereby effectively reducing the content of aluminum in the leachate. [ABSTRACT FROM AUTHOR]

• The fragmentation of PC MPs was accompanied with the decline of molecular weight. • Dropped intermediates were trapped in the particles or released to the leachate. • The amount of BPA (369.57 ± 5.47 μg/g) occupied 2.7 % of the TOC leached out. • The integral estrogenic activity of leachates from aged MPs should be highlighted. Bisphenol A polycarbonate (BPA-PC) is a kind of widely used engineering plastics. However, excessive usage causes the production of plastic wastes, following property changes of polymers and high risks of released chemicals during outdoor weathering. In this study, we systematically investigated the photoaging behavior of PC microplastics (MPs) in aquatic environment and evaluated the potential risk of released intermediates. Light irradiation along with mechanical abrasion facilitated the fragmentation of PC MPs and stimulated photooxidative modification during 640 h of ultraviolet (UV) exposure. Continuous degradation of the polymer was accompanied with dramatic decline of molecular weight. Also, BPA was released from irradiated PC MPs with a trend of an initial rapid increase followed by a decrease versus the irradiation time, and the maximum concentration of dropped BPA was detected up to 652.80 ± 72.89 μg/g (43.39% and 56.61% respectively in particles and leachates). However, the releasing amount of BPA in the leachate merely occupied 2.7% of the total organic carbon (TOC) leached out, suggesting that a great number of unknown organic products were produced other than BPA. Liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis showed that these organic compounds forming MPs-derived dissolved organic matter (MPs DOM) were partly composed of 4,4'-dihydroxybenzophenone (DHB), p-hydroxybenzoic acid (p-HBA) and methyparaben (MeP), which would also contribute to the estrogenic activity. The degradation pathway of PC MPs was elaborated with the photolysis process of PC dimer and BPA, and the remarkable photoaging of PC MPs was mainly dominated by the generated reactive oxygen species (ROS). The findings of this study indicated that understanding the photoaging process of PC MPs was vital to evaluate their integral cumulative estrogenic activity in aquatic environment, and further highlighted the notable possible risks of plastic leachates to exposed biota. [Display omitted] [ABSTRACT FROM AUTHOR]

• The activity of aluminum dross was modified through calcination. • The hydration heat of blended binders containing aluminum dross was investigated. • The hydration evolution of blended binders containing aluminum dross was accessed. • The leaching behavior of blended binders containing aluminum dross was examined. To reduce the environmental hazards caused by aluminum dross (AD), this paper aims to investigate the potential application of AD in CaO-activated superfine slag. The hydration heat, hydration evolution, and leaching behavior of blended binders with different calcined AD (CAD) dosages were evaluated experimentally. Additionally, the mechanical strength and pore size distribution of hardened backfill with different blended binders were measured. The results showed that the activity of AD was promoted by calcination, which increased the number of disordered network structures. The exothermic peak of blended binders was retarded by the increased dosage of CAD, and the peak value decreased from 2.86 mW/g to 2.52 mW/g with a reduction of 0.34 mW/g. At 3 d hydration, all blended binders containing CAD had lower chemically bound water (CBW) than control sample, while at 28 d hydration, the blended binder with 5% CAD had a relative higher CBW (24.89%) than control sample (24.7%). Increased addition of CAD decreased the formation of hydration products but contributed to the incorporation of Al into C–S–H, which enhanced the Al/Ca and Si/Ca atomic ratio. In addition, increasing the addition of CAD, the mechanical strength of hardened backfill dropped because of less formation of hydration products and larger porosity. These experimental findings will be beneficial to the practical utilization of AD in backfill technology. [ABSTRACT FROM AUTHOR]

• Artificial fine aggregate produced by contaminated soil was applied in mortar. • The leaching behavior was fully characterized by both of TCLP and TANK tests. • Detailed comparisons of Cu and Cr on solidification. • Prediction of the long-term leaching tendency by curve fitting. The feasibility of recycling contaminated soil by preparing artificial fine aggregate (AFA) and applying in artificial fine aggregate mortars (AFAM) was investigated systematically. Properties and heavy metal immobilization status of AFA, compressive strength and heavy metal leaching behavior of AFAM were tested. Results showed that Cu reduced the melting and crystallization temperatures of AFA, whereas Cr improved that. Heavy metal addition had a negative impact on the compressive strength of AFAM, but the toxicity characteristic leaching procedure (TCLP) test indicated that the AFAM system was is suitable for solidification of heavy metals. Moreover, it was observed that Cu leaching almost disappeared in the initial periods, while it tended to dissolve in the terminal periods. The leaching mechanism of AFAM with Cr at the initial periods conformed to Fick's law of diffusion, and it tended to deplete in the terminal periods. These results are practically instructive the recycling of heavy metal contaminated solid waste in the field of construction materials. [ABSTRACT FROM AUTHOR]

The aim of this research work was the evaluation of the feasibility to utilize industrial by-products, such as electric arc furnace steel slags, for sustainable concrete production. The paper evaluated the environmental and mechanical properties of steel slags and concrete, respectively. Specifically, the release of contaminants from steel slags was investigated by leaching test and the properties of fresh and hardened concrete were evaluated for a concrete mixture designed with a partial substitution (30%) of natural coarse aggregates with electric arc furnace steel slags. The results show that the concentrations of pollutants were lower than the legal limits imposed by the Ministerial Decree 186/2006 and the addition of steel slag can enhance the mechanical performance of concrete. The compressive strength of cubic specimens was also measured after different cycles of alternate wetting–drying. The steel slag incorporation results in a stiffness comparable to that of a traditional concrete. Overall, the mechanical and leaching characterization has shown that the reuse of electric arc furnace steel slags for sustainable concrete production is feasible and reliable. [ABSTRACT FROM AUTHOR]

Mercury (Hg) that leaches from municipal sewage sludge (MSS) landfill under natural rain is of increasing concern. The column leaching experiments were conducted to investigate the leaching characteristics of total mercury (THg) and methylmercury (MeHg) as well as pH, total organic carbon (TOC), and total suspended solids (TSS) in the raw sludge (RS) and lime-conditioned sludge (LCS) under simulated rain with different acidities (pH 6.5 and 2.9). Results showed the release of MeHg in the leachates presented different patterns from THg. And the final amounts of MeHg in the MSS columns were 1.49 (RS at pH = 6.5), 1.88 (RS at 2.9), 1.97 (LCS at pH = 6.5), and 2.06 times (LCS at pH = 2.9) higher than the initial amounts, suggesting methylation of inorganic Hg (IHg) occurred in the leaching process. The leaching efficiencies of THg and MeHg in RS was lower than that in LCS, indicating lime was more favorable for the release of THg and MeHg. And lower values of pH of the simulated rain promoted the release of THg and MeHg from RS while the opposite was true for LCS. This study provides a better understanding of the release and biogeochemical transformations of Hg in MSS. • Leaching characteristic of MeHg was different from THg in the landfill. • The effects of simulated rain on the release of MeHg and THg differed in raw sludge and lime-conditioned sludge. • Lime treatment was more favorable for the release of MeHg. • Methylation of inorganic mercury in a column leaching experiment was observed. [ABSTRACT FROM AUTHOR]

• CS can achieve a 28-day reactivity index of above 90% by reducing the water content. • At a 50% replacement level, CS causes radiological hazards. • Reuse of CS as a partial cement replacement poses leaching risks of heavy metals. • Fe in CS seems to play an important role in stabilizing the heavy metals. Copper slag (CS) is a potential supplementary cementitious material (SCM). However, unified reactivity indices of different types of CS do not yet exist. In addition, little is known about the safety of reusing CS as a SCM. Here, we collected 10 CS samples, including 5 air-cooled and 5 water-cooled samples, to establish reactivity indices and assess the safety (i.e., the soundness, radioactivity and leaching of heavy metals). Geochemical modeling was subsequently used to reveal the leaching mechanisms. The results show that the 28-day reactivity indices range from 66.6–68.2% for the air-cooled samples and 67.3–74.3% for the water-cooled samples; by reducing the water content, they can be increased to approximately 90% and above 95%, respectively. Neither the air-cooled nor the water-cooled CS causes soundness problems, but at a 50% replacement level, they both cause radiological hazards. Moreover, reuse of CS as a partial cement replacement poses leaching risks of Cu, Pb, Zn, Ni and As. The geochemical simulation indicates the important role of the Fe element in stabilizing the heavy metals, since Cu, Pb, As, Cr and Mn heavy metals are all controlled by Fe-related phases (specific adsorption and co-precipitation). In addition, some heavy metals can also be controlled by oxides, silicates and chromate precipitates. Our results extend the knowledge of using CS as a SCM and call attention to its potential hazards. [ABSTRACT FROM AUTHOR]

Abstract: Cs-titanosilicate, which is a pollucite-related phase, was synthesized and the Cs-leaching behavior of Cs-titanosilicate was evaluated in a NaCl aqueous solution and ion-exchanged water. CsNO3, TiO2 and SiO2 powders were mixed in ethanol by ball-milling and then the mixed powder was heated at temperatures of 600 to 900°C under atmospheric and reduced pressures of air. Under reduced pressure, the Cs-titanosilicate phase was crystallized at 700°C, which was lower than that under atmospheric pressure because CsNO3 decomposition was promoted under reduced pressure. The Cs-leaching ratio of the Cs-titanosilicate in a NaCl aqueous solution is higher than that in ion-exchanged water. On the other hand, the Cs-leaching ratio of the Cs-titanosilicate synthesized under the reduced pressure was lower than that under atmospheric pressure. It was considered that the lower negative zeta potential of the Cs-titanosilicate synthesized under the reduced pressure diminished the amount of Na+ ion adsorbed on the particles surface of the Cs-titanosilicate, which resulted in the suppression of Cs-leaching. [ABSTRACT FROM AUTHOR]

The reliable immobilization of nuclear waste, particularly high-level waste (HLW), is a key issue for sustainable utilization of nuclear energy. Annealing process is adopted in nuclear waste vitrification to improve mechanical properties of products; however, its efficacy on chemical stability of treated HLW glass remain uncertain. This study aims to reevaluate the effects of moderate annealing on chemical durability of sodium borosilicate glass matrix incorporated with simulated HLW. Two types of leaching tests, i.e. acid leaching and the modified Product Consistency Test (PCT), were performed to examine the leaching behavior of HLW glassy products controlled by corrosion mechanisms of ion exchange and hydrolysis, respectively. The acid leaching results showed that annealed glass samples released lanthanum (La) species at a faster rate than that of quenched samples, but the effects of annealing on the release behavior of alkaline and alkaline-earth elements were limited. In contrast, the PCT results showed minor difference between quenched and annealed samples, which suggests that the small structure modification caused by moderate annealing was not comparable with the dominant hydrolysis reaction occurred in the PCT process. According to the free-volume theory, as well as evidences derived from Raman characterization and thermodynamic measurements, La was inferred to exist in the free-volume region in the HLW glass, and the annihilation of free volume during annealing could mobilize La from its stable surrounding environment, and thus reducing the chemical stability of nuclear waste glass. Image 1 • The durability of high-level waste glass was assessed by two types of leach tests. • Annealed glass sample showed increased release rate of lanthanum in acid leach test. • Lanthanum existing in free volume of nuclear waste glass is mobilized by annealing. • Annealing caused micro structure change showing minor effect on glass hydrolysis. [ABSTRACT FROM AUTHOR]

• Hydration of BOF in pavement was recognized after years of service. • Negative impact of BOF aggregate on water is controllable. • The concentrations of elements in BOF highly correlate with those in soil. The evolution of physic-chemical characteristics of Basic Oxygen Furnace Slag (BOF) aggregates in asphalt pavement and their environmental impactions on soil after long-term service were studied. Specific hydration products were found in the BOF aggregates from pavement, indicating their hydration after loss of asphalt. The leachates from asphalt mixture and BOF were both falling below limits. The accumulation of toxic metals released from BOF highly correlated with those in soil beneath construction site. It was then concluded that the current high-risk condition of soil results in long-term accumulation of toxic elements released from exposed BOF. [ABSTRACT FROM AUTHOR]

The objective of the paper is to assess the feasibility of using solid waste incineration (MSWI) bottom ash (BA) as cement-stabilized macadam (CSM) aggregate. CSM was prepared by replacing natural limestone aggregate with MSWI BA in different proportions (0%, 5%, 10%, 20%, and 30%). The physical properties, chemical properties, and micro-morphology of MSWI BA were studied to explore the mechanism of MSWI BA aggregate in CSM. The mechanical properties (unconfined compressive strength, cleavage strength, compressive resilience modulus), drying shrinkage, freezing resistance, and leaching behavior of CSM were tested. The results showed that MSWI BA had low density, low strength, high water absorption, high porosity, hydraulicity, and cementitious activity. Substitution of MSWI BA for natural limestone reduced the unconfined compressive strength, the cleavage strength, and the compression modulus of resilience of CSM, but these parameters still met the requirements of the specification. The CSM containing MSWI BA had higher cumulative water loss rate and smaller average dry shrinkage coefficient than traditional CSM. Adding 0–20% MSWI BA reduced the cumulative dry shrinkage strain of CSM. The residual strength ratio of CSM increased slightly at first and then decreased rapidly, and the CSM containing 0–30% MSWI BA met the freezing resistance requirements of semi-rigid base materials. The leaching concentration of heavy metals of CSM curing 7 days with 30% MSWI BA was still far below the limit of Chinese standard GB 5085.3. [ABSTRACT FROM AUTHOR]

• A lithium-rich bauxitic clay was characterized. • Calcination – acid leaching process was proposed for selective extraction of lithium. • Effect of influential parameters on extraction of lithium was investigated. • Leaching mechanism of lithium was discussed. The explosive demand for lithium calls for new lithium resources. A lithium-rich bauxitic clay was selected, and its material composition, phase transformation, lithium leaching efficiency using sulfuric acid were investigated after calcination treatment. In this study, XRF, ICP-AES, ICP-MS, XRD and SEM were employed to characterize bauxitic clay and its calcining products and leaching residues. The results show that bauxitic clay mainly consists of diaspore, illite, montmorillonite and anatase with a major chemical composition of Al 2 O 3 (48.01%), SiO 2 (33.06%), K 2 O (3.88%), TiO 2 (2.25%), Fe 2 O 3 (1.07%), MgO (0.46%), and lithium 3170 μg/g. The optimum calcination temperatures were 500 and 600 °C, with 72.34% and 73.61% lithium extracted, respectively, using 15% sulfuric acid leaching for 1 h. The optimal leaching conditions for lithium extraction were a leaching reaction time of 60 min and a 20% (wt/v) sulfuric acid concentration. Lithium leaching in this study was considered to occur via ion exchange instead of mineral dissolution. The findings of this study would be useful and interesting for lithium recovery from bauxitic clay. [ABSTRACT FROM AUTHOR]

• Surface properties of the reinforced coating are affected by the granular particle. • The addition of granular particle inhibits the leaching efficiency of PSO. • Adding granular particle changes the leaching behavior of PSO. • The PVCM value depends on the bulk modulus. • Leaching efficiency of PSO is inversely proportional to the bulk modulus. For polydimethylsiloxane (PDMS)-phenylmethylsilicone oil (PSO) blend coatings, the leaching of PSO could improve the antifouling performance of the blend coatings. In this study, granular particles reinforced PDMS-PSO blend coatings were investigated, including the surface properties, the mechanical properties, especially the leaching behavior of PSO and the antifouling performance. The results showed that increasing surface roughness of the blend coatings increased the water contact angle of the blend coatings. Yet for fumed silica and nano-silica reinforced blend coaiting, the hydroxyl groups from particles decreased the water contact angle of the blend coatings. The enhancement of the mechanical properties increased the difficulty of leaching PSO, which caused the decrease of biofilm detachment performance. Further, with the increase of the pigment volume concentration (PVC) value, the bulk modulus of the reinforced coating increased which increased the difficulty of leaching PSO in the interior of the reinforced coating by the form of oil storage sac. Under the same content of PSO, the bulk modulus value of the reinforced coatings with different granular particles was the same, when the PVC value was up to PVC M , which was defined as the minimum PVC value without leaching PSO. It also indicated that the effect of granular particles on the leaching behavior of PSO depended mainly on the change in the bulk modulus of the reinforced coatings. [ABSTRACT FROM AUTHOR]