Metal release from contaminated estuarine sediment under pH changes in the marine environment

The contaminant release from estuarine sediment due to pH changes was investigated using a modified CEN/TS 14429 pH-dependence leaching test. The test is performed in the range of pH values of 0-14 using deionised water and seawater as leaching solutions. The experimental conditions mimic different circumstances of the marine environment due to the global acidification, carbon dioxide (CO2) leakages from carbon capture and sequestration technologies, and accidental chemical spills in seawater. Leaching test results using seawater as leaching solution show a better neutralisation capacity giving slightly lower metal leaching concentrations than when using deionised water. The contaminated sediment shows a low base-neutralisation capacity (BNCpH 12 = -0.44 eq/kg for deionised water and BNCpH 12 = -1.38 eq/kg for seawater) but a high acid-neutralisation capacity when using deionised water (ANCpH 4 = 3.58 eq/ kg) and seawater (ANCpH 4 = 3.97 eq/kg). Experimental results are modelled with the Visual MINTEQ geochemical software to predict metal release from sediment using both leaching liquids. Surface adsorption to iron- and aluminium- (hydr)oxides was applied for all studied elements. The consideration of the metal-organic matter binding through the NICA-Donnan model and Stockholm Humic Model for lead and copper, respectively, improves the former metal release prediction. Modelled curves can be useful for the environmental impact assessment of seawater acidification due to its match with the experimental values.This work was supported by the Spanish Ministry of Economy and Competitiveness, Project No. CTM 2011-28437-C02-01, ERDF included. M. C. Martı´n-Torre was funded by the Spanish Ministry of Economy and Competitiveness by means of FPI. Fellowship No. BES-2012-053816

Chemical engineering analysis of SOx and HCl from municipal solid waste in grate-fired waste-to-energy (WtE) combustors

SO2 and HCl emission data from a large-scale Waste-to-Energy (WtE) plant are analysed as a function of combustion process parameters. Basic principles of flow, mass transfer and reactor engineering are applied to the waste layers on the grates in order to explain the obtained results. Strong similarity with fixed bed reactor systems is observed. The findings from this study contribute to the understanding of mechanisms of S and Cl release from waste in WtE processes, and support developments in areas of emissions reduction and corrosion abatement in WtE plants. To the authors’ knowledge, such extensive analysis has never been performed before on the industrial scale of WtE.status: accepte

Stabilization of antimony in MSWI bottom ash

Sb leaching from MSWI bottom ash (BA) often exceeds the Dutch standard for unrestricted reuse of secondary materials. However, only very little is known about the leaching mechanisms of Sb compared to other oxyanion forming metals e.g. Cr, As. Recent studies suggest that the mobility of Sb in inorganic matrices such as MSWI BA is mainly controlled by (a) the availability of calcium to form calciumantimonate structures called romeites(b) adsorption of Sb(OH)3 and Sb(OH)6- to Fe-(hydr)oxides(c) incorporation of Sb(OH)6- in ettringite structures and (d) formation and precipitation of tripuhyite (FeSbO4). To lower the Sb leaching from MSWI BA and to determine the main Sb stabilization mechanism(s), 2.5% CaO, 5% CaCl2, 5% CaCO3, 2.5% Fe2(SO4)3 and 1% FeCl3 were added to the sand fraction (0,6-2 mm) of mixed MSWI BA obtained from Afvalzorg/Ballast Nedam. Samples of each combination were submitted to a one step leaching test (L/S=10, 24h, DIN 38414-S4). All additives decreased the Sb leaching and their influence is not only related to the change in pH of the matrix. The highest decrease in Sb leaching was obtained by adding 2.5% CaO, but because of the increase in pH from 11.4 to 12.5, the leaching of Pb increased from 0.11 to 22.7 mg/kg (Dutch limit value = 2.3 mg/kg). However, when only 0.5% CaO was added, the decrease in Sb leaching was comparable to the decrease obtained with the other additives, whereas also the Pb leaching remained below the limit value. When 2.5% CaO or 5% CaCl2 were added in combination with 2.5% Fe2(SO4)3 or 1% FeCl3 their effects were additional, indicating that Ca and Fe containing additives involve different Sb binding mechanisms i.e. most likely formation of less soluble Ca rich romeites and adsorption to Fe-(hydr)oxides or formation of tripuhyite. So, addition of Ca and/or Fe containing compounds e.g. by means of a complementary material containing these compounds in the right concentrations to MSWI BA can decrease the Sb leaching below the Dutch limit of 0.32 mg/kg, without increasing the leaching of other elements above the limit values.status: publishe

Recycling of spent adsorbents for oxyanions and heavy metal ions in the production of ceramics

Spent adsorbents for oxyanion forming elements and heavy metals are classified as hazardous materials and they are typically treated by stabilization/solidification before landfilling. The use of lime or cement for stabilization/solidification entails a high environmental impact and landfilling costs are high. This paper shows that mixing spent adsorbents in the raw material for the production of ceramic materials is a valuable alternative to stabilize oxyanion forming elements and heavy metals. The produced ceramics can be used as construction material, avoiding the high economic and environmental impact of stabilization/solidification followed by landfilling. To study the stabilization of oxyanion forming elements and heavy metals during the production process, two series of experiments were performed. In the first series of experiments, the main pollutant, Mo was adsorbed onto iron-based adsorbents, which were then mixed with industrial sludge (3w/w%) and heated at 1100°C for 30min. Mo was chosen, as this element is easily adsorbed onto iron-based adsorbents and it is the element that is the most difficult to stabilize (i.e. the highest temperatures need to be reached before the concentrations in the leachate are reduced). Leaching concentration from the 97/3 sludge/adsorbent mixture before heating ranged between 85 and 154mg/kg; after the heating process they were reduced to 0.42-1.48mg/kg. Mo was actually stabilized, as the total Mo concentration after addition was not affected by the heat treatment. In the second series of experiments, the sludge was spiked with other heavy metals and oxyanion forming elements (Cr, Ni, Cu, Zn, As, Cd and Pb) in concentrations 5 times higher than the initial concentrations; after heat treatment the leachate concentrations were below the regulatory limit values. The incorporation of spent adsorbents in ceramic materials is a valuable and sustainable alternative to the existing treatment methods, saving raw materials in the ceramics production process and avoiding the use of stabilizing agents. Besides, spent adsorbents added to the raw material for ceramic products, may improve their aesthetic and structural properties.publisher: Elsevier articletitle: Recycling of spent adsorbents for oxyanions and heavy metal ions in the production of ceramics journaltitle: Waste Management articlelink: http://dx.doi.org/10.1016/j.wasman.2015.07.006 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Selenium removal from mining and process wastewater: A systematic review of available technologies

Selenium is an important element that is required for humans, animals, plants and other life forms. Selenium is naturally present in the Earth's crust and its worldwide distribution has led to complex interactions between selenium and the natural environment (water, soil, sediments and air). The discharge of selenium contaminated water into the environment from industrial processes is a topic of regulatory (WHO – 40 μg/L, EU – 10 μg/L), environmental and health concern. The removal of selenium from water is complex, determined by its speciation and often expensive due to the characteristics of the wastewater and the stringent discharge limits for selenium and its oxyanions. In this review, selenium chemistry and its toxic effects on human health and the environment have been examined. An overview of the different physico-chemical and biological technologies used for the removal of selenium from contaminated water were discussed wherein adsorption capacities in the range of 0.22–120 mg/g and 0.135–127 mg/g, respectively, were reported in the literature. The challenges and future research directions in this progressive research field have also been stated

Selenium removal from mining and process wastewater: a systematic review of available technologies

© 2018 IWA Publishing. Selenium is an important element that is required for humans, animals, plants and other life forms. Selenium is naturally present in the Earth's crust and its worldwide distribution has led to complex interactions between selenium and the natural environment (water, soil, sediments and air). The discharge of selenium contaminated water into the environment from industrial processes is a topic of regulatory (WHO - 40 μg/L, EU - 10 μg/L), environmental and health concern. The removal of selenium from water is complex, determined by its speciation and often expensive due to the characteristics of the wastewater and the stringent discharge limits for selenium and its oxyanions. In this review, selenium chemistry and its toxic effects on human health and the environment have been examined. An overview of the different physico-chemical and biological technologies used for the removal of selenium from contaminated water were discussed wherein adsorption capacities in the range of 0.22-120 mg/g and 0.135-127 mg/g, respectively, were reported in the literature. The challenges and future research directions in this progressive research field have also been stated.status: publishe

Immobilization of antimony in waste-to-energy bottom ash by addition of calcium and iron containing additives

The leaching of Sb from waste-to-energy (WtE) bottom ash (BA) often exceeds the Dutch limit value of 0.32mgkg(-1) for recycling of BA in open construction applications. From the immobilization mechanisms described in the literature, it could be concluded that both Ca and Fe play an important role in the immobilization of Sb in WtE BA. Therefore, Ca and Fe containing compounds were added to the samples of the sand fraction of WtE BA, which in contrast to the granulate fraction is not recyclable to date, and the effect on the Sb leaching was studied by means of batch leaching tests. Results showed that addition of 0.5 and 2.5% CaO, 5% CaCl2, 2.5% Fe2(SO4)3 and 1% FeCl3 decreased the Sb leaching from 0.62±0.02mgkgDM(-1) to 0.20±0.02, 0.083±0.044, 0.25±0.01, 0.27±0.002 and 0.29±0.02mgkgDM(-1), respectively. Due to the increase in pH from 11.41 to 12.53 when 2.5% CaO was added, Pb and Zn leaching increased and exceeded the respective leaching limits. Addition of 5% CaCO3 had almost no effect on the Sb leaching, as evidenced by the resulting 0.53mgkgDM(-1) leaching concentration. This paper shows a complementary enhancement of the effect of Ca and Fe, by comparing the aforementioned Sb leaching results with those of WtE BA with combined addition of 2.5% CaO or 5% CaCl2 with 2.5% Fe2(SO4)3 or 1% FeCl3. These lab scale results suggest that formation of romeites with a high Ca content and formation of iron antimonate (tripuhyite) with a very low solubility are the main immobilization mechanisms of Sb in WtE BA. Besides the pure compounds and their mixtures, also addition of 10% of two Ca and Fe containing residues of the steel industry, hereafter referred to as R1 and R2, was effective in decreasing the Sb leaching from WtE BA below the Dutch limit value for reuse in open construction applications. To evaluate the long term effect of the additives, pilot plots of WtE BA with 10% of R1 and 5% and 10% of R2 were built and samples were submitted to leaching tests at regular intervals over time. The Sb leaching from untreated WtE BA was just below or above the Dutch limit value. The Sb leaching from the pilot plots of BA with additives first remained stable around 0.13mgkg(-1) but had a tendency to slightly increase after 6months, indicating the need for further research on the effect of weathering, and more specifically of carbonation, on Sb leaching from WtE BA.publisher: Elsevier articletitle: Immobilization of antimony in waste-to-energy bottom ash by addition of calcium and iron containing additives journaltitle: Waste Management articlelink: http://dx.doi.org/10.1016/j.wasman.2016.05.007 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Effect of dedicated additives and pretreatment on lead and chloride leaching from waste-to-energy fly ash and air pollution control residues

Most of the fly ash (FA) and air pollution control residue (APC residue) of modern waste-to-energy (WtE) plants do not meet the Waste Acceptance Criteria (WAC) for hazardous waste landfills set by the EU Council decision 2003/33/EC, primarily because the leaching of lead (Pb) and/or chlorides (Cl-) is too high. In this work, the effect of selected additives on Pb leaching from APC residue was investigated. Addition of 10% by mass of FeCl3 had the highest effect on the Pb leaching from APC residue, which decreased immediately from 1694 mg.kgDM-1 to 9.7 mg.kgDM-1 and remained almost constant upon further curing. Addition of 10% by mass of Na2CO3 or Fe2(SO4)3 immediately decreased the Pb leaching by about 50% but further curing of the S/S material was needed to reach the WAC. The effect of all these additives surpassed that of the effect of the pH change they caused. A second series of leaching experiments showed that addition of cement to mixed FA and APC residue reduced the Cl- leaching by about 35%, which was not sufficient to reach the WAC. Additional experiments showed that washing of residues prior to landfilling can reduce the Cl- leaching of the washed residues by about 90% to values below the WAC. Addition of Na2CO3 , Fe2(SO4)3, FeSO4 or H3PO4 to APC residue prevented co-elution of Pb during the washing step and assured that the Pb leaching of the washed residues was well below the WAC. An economic evaluation taking into account additive and landfilling cost showed that addition of 0.2 Mg Na2CO3, 0.25 Mg FeSO4 or 0.1 Mg H3PO4 per Mg of APC residue were cheaper options than adding 0.4 Mg cement.status: accepte

Comparison of solidification/stabilization of fly ash and air pollution control residues from municipal solid waste incinerators with and without cement addition

© 2014, Springer Japan. Solidification/stabilization (S/S) of fly ash and air pollution control residues from MSWI was studied, with and without the use of cement. It appeared that metal and oxyanion leaching from these stabilised residues was comparable after 75 days of curing. Leaching of chloride and sulfate did not decrease by the addition of cement during S/S treatment. In an LCA perspective the environmental impact of the S/S treated mixtures with cement in the toxicity related impact categories was higher than the impact of the S/S treated mixtures without cement. Moreover, the production of cement for application in S/S also causes an impact in the impact categories climate change and terrestrial acidification. For environmental considerations in an LCA perspective S/S without cement should be preferred.status: publishe