T. Van Gerven

Influence of carbonation and carbonation methods on leaching of metals from mortars

Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, some samples were carbonated in a CO2 chamber, others were carbonated using supercritical CO2 (SCC). Porosity and carbonation depth of treated and untreated samples were compared. Leaching was tested using the diffusion (NEN 7345) and extraction test (based on DIN 38414-S4). The results show that carbonation decreases the porosity of the samples. The decrease is more important with increasing w/c ratio. Carbonation runs deeper into the monolith with increasing w/c ratio. In the supercritical method, not all samples were carbonated to the same extent. The diffusion test shows that carbonation decreases leaching of Na, K, Ca, Ba, Cu, and Pb and increases leaching of Mg. Ni leaching depends on the pH induced by carbonation. Influence of pH and formation of metal carbonates is evaluated with the extraction test and enhances understanding of metal leaching in the diffusion test.

Effect of carbonation on the leaching of organic carbon and of copper from MSWI bottom ash

In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is recycled as secondary raw material. In view of recycling a higher percentage of bottom ash, a particular bottom ash fraction (Ø 0.1-2mm) was studied. As the leaching of this bottom ash fraction exceeds some of the Flemish limit values for heavy metals (with Cu being the most critical), treatment is required. Natural weathering and accelerated carbonation resulted in a significant decrease of the Cu leaching. Natural weathering during 3 months caused a decrease of Cu leaching to <50% of its original value, whereas accelerated carbonation resulted in an even larger decrease (to ca. 13% of its initial value) after 2 weeks, with the main decrease taking place within the first 48 h. Total organic carbon decreased to ca. 70% and 55% of the initial concentration in the solid phase, and to 40% and 25% in the leachate after natural weathering and after accelerated carbonation, respectively. In the solid material the decrease of the Hy fraction was the largest, the FA concentration remained essentially constant. The decrease of FA in the leachate can be attributed partly to an enhanced adsorption of FA to Fe/Al (hydr)oxides, due to the combined effect of a pH decrease and the neoformation of Al (hydr)oxides (both due to carbonation). A detailed study of adsorption of FA to Fe/Al (hydr)oxides showed that significant adsorption of FA occurs, that it increases with decreasing pH and started above pH 12 for Fe (hydr)oxides and around 10 for Al (hydr)oxides. Depending whether FA or Hy are considered the controlling factor in enhanced Cu leaching, the decreasing FA or Hy in the leachate explains the decrease in the Cu leaching during carbonation.

Strategic selection of an optimal sorbent mixture for in-situ remediation of heavy metal contaminated sediments: Framework and case study

Aquatic sediments contaminated with heavy metals originating from mining and metallurgical activities pose significant risk to the environment and human health. These sediments not only act as a sink for heavy metals, but can also constitute a secondary source of heavy metal contamination. A variety of sorbent materials has demonstrated the potential to immobilize heavy metals. However, the complexity of multi-element contamination makes choosing the appropriate sorbent mixture and application dosage highly challenging. In this paper, a strategic framework is designed to systematically address the development of an in-situ sediment remediation solution through Assessment, Feasibility and Performance studies. The decision making tools and the experimental procedures needed to identify optimum sorbent mixtures are detailed. Particular emphasis is given to the utilization and combination of commercially available and waste-derived sorbents to enhance the sustainability of the solution. A specific case study for a contaminated sediment site in Northern Belgium with high levels of As, Cd, Pb and Zn originating from historical non-ferrous smelting is presented. The proposed framework is utilized to achieve the required remediation targets and to meet the imposed regulations on material application in natural environments.

Investigation of washing, heating and carbonation as treatment techniques for the improvement of environmental characteristics of MSWI bottom ash, in view of recycling

MSWI-bottom ash often may not be recycled as construction material in Flanders, because leaching of Cu exceeds the limit value of 0.5 mg/kg. Leaching of other components such as Mo and Sb is critical as well, but limit values for these elements are to date only informal. Three treatment techniques were investigated to lower Cu leaching: thermal treatment destroying organic matter still present in the incinerator residue and ligands that may form complexes with Cu and enhance leaching, washing with solutions of organic complexants to extract Cu and accelerated carbonation. Carbonation decreases pH and causes metal hydroxides to react to carbonates. Heating the bottom ash to 400°C decreases Cu leaching to 0.1 mg/kg. Washing was performed with six solutions, of which washing with citric acid and ammoniumcitrate decreases Cu leaching to below the limit value. Carbonation decreased Cu leaching from 3.3 mg/kg to 1.0 mg/kg, but further improvement should be possible. Although heating and washing gave better results in the laboratory, accelerated carbonation seems to be the most promising technique.

Influence of dissolved gases on sonochemistry and sonoluminescence in a flow reactor

In the present work, the influence of gas addition is investigated on both sonoluminescence (SL) and radical formation at 47 and 248 kHz. The frequencies chosen in this study generate two distinct bubble types, allowing to generalize the conclusions for other ultrasonic reactors. In this case, 47 kHz provides transient bubbles, while stable ones dominate at 248 kHz. For both bubble types, the hydroxyl radical and SL yield under gas addition followed the sequence: Ar>Air>N2>>CO2. A comprehensive interpretation is given for these results, based on a combination of thermal gas properties, chemical reactions occurring within the cavitation bubble, and the amount of bubbles. Furthermore, in the cases where argon, air and nitrogen were bubbled, a reasonable correlation existed between the OH-radical yield and the SL signal, being most pronounced under stable cavitation at 248 kHz. Presuming that SL and OH originate from different bubble populations, the results indicate that both populations respond similarly to a change in acoustic power and dissolved gas. Consequently, in the presence of non-volatile pollutants that do not quench SL, sonoluminescence can be used as an online tool to qualitatively monitor radical formation.

Characterization of stable and transient cavitation bubbles in a milliflow reactor using a multibubble sonoluminescence quenching technique

The bubble type, generated by an ultrasonic field, was studied in a batch and flow reactor using a multibubble sonoluminescence (MBSL) quenching technique with propanol and acetone. The influence of frequency and transducer configuration was evaluated using the same piezoelectric element in both setups. Results show that the bubble type not only depends on the frequency, but also on the input power or transducer configuration. Additionally, the effect of flow on sonoluminescence yield and bubble type was studied in the continuous setup at various frequencies. As the flow becomes turbulent, the sonoluminescence signal reaches a plateau for three out of four frequencies, and a transition from transient to stable cavitation occurs for frequencies below 200 kHz.

Selective composite cation-exchange membrane based on S-PVDF

A novel cation-exchange membrane composed of a blend of polyvinylidene fluoride (PVDF) and sulfonated PVDF (S-PVDF) was synthesized. The membranes were prepared with different fractions of S-PVDF to optimize their performance in desalination. The ion-exchange capacity (IEC), transport number, apparent selectivity, ion conductivity, crystallinity, water uptake, contact angle, and performance in electrodialysis (ED) were evaluated. With increasing S-PVDF fractions, the transport number and permselectivity decreased, while the IEC and membrane conductivity increased. Finally, the salt extraction in ED obtained for a 70% S-PVDF membrane was 67.6%, which had a better performance than that of a commercial membrane. Also the membranes showed a good selectivity for bivalent cation removal. Membrane structure was evaluated by XRD and showed a decrease in ordering by increase in S-PVDF.

Characterisation of copper slag in view of metal recovery

Abstract In this study, the copper bearing particle of a fayalitic copper slag was assessed using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and X-ray computed tomography (CT). The copper content of the slag was ∼0·87 wt-%. Copper in this slag was present as sulphidic droplets. The content and particle size distribution of the major sulphide phases (bornite, chalcopyrite and chalcocite/digenite) were quantified using QEMSCAN. The copper bearing particles had a wide particle size distribution from a few micrometres up to millimetre level. Large copper bearing particles (>100 μm) were composed mainly of bornite and chalcocite/digenite and tended to accumulate in the lower part of the slag layer. As characterised with CT, ∼70% of the copper value was present in these large copper bearing particles.

Treatment and Reuse of Incineration Bottom Ash

Abstract Considerable technical advances in the cleaning of flue gases from waste incineration have increasingly made solid residues from the process the main emission route for inorganic contaminants. Appropriate strategies to manage waste incineration residues are therefore required and have driven scientific research toward finding environmentally sound solutions. Among the various types of solid residues from waste incineration, bottom ash (BA) is generated in the largest amounts and is recognized as the most suited for use. Several techniques have been developed for processing incinerator BA in view of reuse in various applications. Generally, valuable components of BA include ferrous and nonferrous metals as well as the mineral fraction. This chapter provides, on the basis of documented scientific literature studies and information about technical applications, an overview of the physical, chemical, mineralogical, and leaching properties of incinerator BA, along with relevant techniques proposed for BA processing. The chapter was compiled by members of the pHOENIX working group on Management of Municipal Solid Waste Incineration Residues, which was established in 2002 in Vienna with a focus on promoting sustainable solutions with respect to the treatment, use, and disposal of incineration residues. In 2002, the working group was included as a task group under the International Waste Working Group.

Characterization of Copper Slag

Copper slag can be treated as a secondary resource since it usually contains a substantial amount of copper and other valuable metals. Characterization of the slags to determine the expected metal recovery is essential for the design of separation flow sheets. In this study, the chemical and mineralogical composition of a copper slag from El Teniente, Chile were characterized. The copper content of the fayalite based slag is around 0.87 wt% which is higher than for certain copper ores. Copper exists as sulfides in the form of droplets in the slag. The content and particle size distribution of the major sulfide phases (bornite, chalcopyrite and chalcocite) were quantified using analytical scanning electron microscopy (QEMSCAN). The copper bearing particles have a wide particle size distribution from a few microns up to mm level. Large copper bearing particles (> 100 µm) are composed mainly of bornite and chalcocite and tend to accumulate in the lower part of the slag layer. As characterized with X-ray computed tomography (CT), around 70 volume% of copper value exist in these large copper bearing particles.