ERE4.2

Municipal solid waste incineration fly ash (MSWI-FA) is one of the solid by-products of MSWI treatment, accounting for about 1–3% of the total incinerated waste. FA forms in the plant purification system and bears important amount of heavy metals and salt (chloride and sulphate), therefore it is considered as hazardous waste (Bernasconi et al, 2022). For this reason, FA is required to undergo stabilization/inertization treatment (one of the most common is water washing), before being landfilled or used as secondary/supplementary raw materials. In this latter case, many studies have evaluated the incorporation of FA into alkali silicate-based geopolymer. This material is obtained by the reaction between an aluminosilicate source (metakaolin, MTK) and alkali hydroxide (NaOH, KOH), to obtain polymer-like condensation product (Wang et al, 2019). This material is characterized by higher durability and greenness with respect to the conventional Portland cement (OPC), thus gaining interest recently as a promising partial substitute to OPC. On the other hand, much less attention has been focused on acid-based geopolymer, in which the alkali hydroxide is substituted by phosphoric acid, thus producing an Al-O-P/Si-O-P polymeric matrix (Wang et al, 2019). This material has displayed better performance than the traditional alkali-silicate geopolymer, in terms of corrosion resistance (Wagh et al, 2011), thermal stability (Celerier et al, 2019) and mechanical strength. However, there are also some drawbacks, mainly related to the expensive cost of the starting materials, since MTK is obtained by high-temperature (750°C) calcination of kaolinite. The introduction of FA would be economically beneficial both by reducing the amount of MTK needed and providing a destination for a waste residue which otherwise would require important management costs.

In this work, (previously washed) FA partial replacement of MTK has been tested in the phosphate-based geopolymer formulation, up to 50 wt%. Different synthesis conditions have been evaluated, in terms of Al/P molar ratio, liquid-to-solid ratio and curing temperature. The resulting reaction products have been investigated by a combined analytical approach, involving spectroscopies (ATR-FTIR and Solid-state NMR) and powder X-ray diffraction techniques, while their morphology was inquired by SEM-EDS analysis. Moreover, compressive strength tests have been employed to evaluate the mechanical properties, which demonstrated the good performances of FA blended phosphate-based geopolymers, with compressive strength values over 30 MPa.

Reference

• D. Bernasconi, C. Caviglia, E. Destefanis, A. Agostino, R. Boero, N. Marinoni, C. Bonadiman, A. Pavese. Influence of speciation distribution and particle size on heavy metal leaching from MSWI fly ash, Waste Management, 138 (2022), 318-327.
• Y. Wang, Y. Alrefaei, J. Dai. Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review, Frontiers in Materials, 6 (2019), 106.
• A.S. Wagh. Phosphate geopolymers, Ceramic Engineering and Science Proceeding, 32, 10 (2011), 91-103.
• H. Celerier, J. Jouin, A. Gharzouni, V. Mathivet, I. Sobrados, N. Tessier-Doyen, S. Rossignol. Relation between working properties and structural properties from ²⁷Al, ²⁹Si and ³¹P NMR and XRD of acid-based geopolymers from 25 to 1000 °C, Materials Chemistry and Physics, 228 (2019), 293-302.

How to cite: Bernasconi, D., Viani, A., Mácová, P., Zárybnická, L., Caviglia, C., Destefanis, E., Bordignon, S., Gobetto, R., and Pavese, A.: MSWI fly ash incorporation into acid-based geopolymer: reactivity and performance impact, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2411, https://doi.org/10.5194/egusphere-egu22-2411, 2022.

The growth of the world population pressures for an increasing demand for the extraction of the Earth's non-renewable mineral resources, which are essential for modern living. The heavy mining operations associated with this extraction have several negative environmental and societal impacts, including the emission of greenhouse gases and the production of large volumes of solid waste. Green mining aims to adapt the mining operations to reduce the negative impacts, while maintaining the interests of stakeholders.

Basalt is a mafic volcanic rock that is widely available in the Earth's surface and often occurs in a variety of ore deposit systems. Traditionally, basalt is used in various ornamentation and construction purposes. However, recently, novel agricultural, environmental and even industrial applications of basalt emerged. When basalt is crushed to a reasonable size (preferably ≤250 µm) and applied to soils in an adequate application rate (5 to 20 t ha^-1), it acts as a natural fertilizer. Basalt is predominantly composed of Ca-rich plagioclase, pyroxene and olivine. These rock-forming minerals have a fast weathering rate compared to other silicate minerals. When they come in contact with water and CO₂, from the atmosphere, they dissolve releasing a broad spectrum of macronutrients, micronutrients and beneficial elements (e.g., Si, Fe, Ca, Mg, Mn, Na, K, P, S, Ti, V, Cu, Zn, Co & REEs), which are important for plant growth. During this natural enhanced weathering process, an adequate amount of CO₂ is sequestered from the atmosphere.

Here, a novel green mining technique is proposed for ore deposits, hosted in or associated with basalt. This technique proposes the separation of the barren or very weakly mineralized basaltic bodies from the remaining solid waste. These bodies should be further crushed and distributed over local farmlands and forests. Crushed basalt will act as a slow release, natural fertilizer, which will rejuvenate weathered soils, boost soil fertility, neutralize soil acidity and enhance plant growth. This will increase the green cover and yield and will reduce the farming costs, which will have positive socio-economic impacts on the local community. More importantly, this green mining technique will reduce the amount of solid mining waste and will sequester a considerable amount of CO₂ from the atmosphere, during the enhanced weathering process, which could compensate for the CO₂ emitted from the mining operations. Although the process appears straightforward and of high benefit for the environment, the mining sector and the local society, a special monitoring program should be initiated to assess the heavy metal content of the distributed basalt dust to avoid contaminating soils, especially in the case of high application rates (>5 t ha^-1).

This ongoing research aims to develop sustainable green mining programs to recycle and reuse the solid mine waste for CO₂ sequestration and for the development of natural, slow release, low cost, eco-friendly fertilizers.

How to cite: El Desouky, H.: Role of Basalt in Green Mining, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3176, https://doi.org/10.5194/egusphere-egu22-3176, 2022.

This work is focused on the possible reutilization of municipal solid waste incinerator (MSWI) fly ash as a metakaolin replacement in the acid-based geopolymer. This type of geopolymer, obtained by the reaction between an aluminosilicate source (metakaolin) and phosphoric acid to form an Al-O-P/Si-O-P matrix (Wang et al, 2019), have displayed better performance than the traditional alkali-silicate geopolymer, in terms of corrosion resistance (Wagh et al, 2011), thermal stability and mechanical strength (Celerier et al, 2019). The replacement of up to 30 % wt has proved to not significantly alter the remarkable performance of the material, obtaining compressive strength values higher than 30 MPa. However, since fly ash contains dangerous substances as chlorides, sulfates, and heavy metals, which must be stabilized, it is important to evaluate the leching stability of the final materials.

Therefore, test cube blocks of 1x1x1 cm size, containing 10, 20 and 30 % wt of previously washed fly ash replacement with respect to metakaolin are prepared, with Al/P molar ratio of 1, liquid-to-solid ratio raging from 0.95-1 and 3 days at 60°C as curing temperature. 

Leaching tests, according to the European standards EN-12457 (2002), using deionized water at a ratio liquid to solid of 10, are applied to geopolymers blocks to evaluate the concentration of salts and heavy metals that usually exceeds the law threshold in the raw fly ash. Leachates are analyzed by ionic chromatography and ICP-MS: the results show that the concentrations of chlorides are under the legislation limits provided for not dangerous waste, as well as sulfates and fluorides; relatively to heavy metals Zn, Pb, Cd exceed the concentrations limits. Further tests and analyses are carried out to evaluate the impact of synthesis parameters on the leaching stability of these materials.

Reference

• Wang, Y. Alrefaei, J. Dai. Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review, Frontiers in Materials, 6 (2019), 106.

A.S. Wagh. Phosphate geopolymers, Ceramic Engineering and Science Proceeding, 32, 10 (2011), 91-103.

• Celerier, J. Jouin, A. Gharzouni, V. Mathivet, I. Sobrados, N. Tessier-Doyen, S. Rossignol. Relation between working properties and structural properties from ²⁷Al, ²⁹Si and ³¹P NMR and XRD of acid-based geopolymers from 25 to 1000 °C, Materials Chemistry and Physics, 228 (2019), 293-302.

How to cite: Caviglia, C., Destefanis, E., Bernasconi, D., Pastero, L., Pavese, A., Viani, A., Mácová, P., and Zárybnická, L.: Environmental suitability of MSWI fly ash geopolymers: evaluation by leaching tests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4272, https://doi.org/10.5194/egusphere-egu22-4272, 2022.

Both nitrogen (N) and phosphorous (P) are essential for life and their supply sustain the global population growth, thus, the question about “how correctly manage nutrient-rich wastewaters?” is a primary issue for many countries. The storage and the subsequent thoughtless use of these materials, as breeding farm and biogas plants wastewaters, has enormous impacts on the environment, causing eutrophication of water bodies and greenhouse gas emissions. The development of low-cost, low environmental impact and high yield treatment technologies is thus necessary to incentivize the circularity of resources, promoting their reuse and encouraging recycling in agri-food systems.

The recovery of N and P by struvite precipitation (MgNH₄PO₄·6H₂O) is a promising strategy, but these technologies are in general too expensive, energy-demanding, or they alter the treated wastewaters, making them not suitable for agricultural purposes unless additional treatments are carried out.

This work investigates an innovative wastewater treatment processes that foresee the use of a natural chabazite-rich zeolitite (rock containing more than 50 % of zeolite minerals) in combination with struvite chemical precipitation. The adsorption batch (phase 1) is intended to improve the NH₄⁺/Mg²⁺ and NH₄⁺/PO₄^3- molar ratios, to enhance struvite yield (phase 2) with fewer amounts of reagents required, thus to improve both the efficiency and the cost-effectiveness of struvite production. For the 1^st phase, both natural zeolitite (N_ZT) and the K⁺-enriched (K_ZT) zeolitite were tested. K_ZT was intended to counteract any possible interference for struvite precipitation, which could instead happen with N_ZT due to the input of Ca²⁺ ions in solution.

In the 2^nd phase (struvite precipitation), 2 different Mg:NH₄:PO₄ molar ratios were tested, in particular a condition of NH₄⁺ excess (MR1) and a condition with Mg²⁺ in excess (MR2).

Treatments in which N_ZT (NZT-S) and K_ZT (KZT-S) were added prior to struvite precipitation were compared to a conventional struvite precipitation method without the use of zeolitites (CNTR).

NZT-S_MR1 was found to be the most feasible strategy because of the highest NH₄⁺-N removal efficiency, highest struvite precipitation efficiency (less waste of reagents), and less unwanted alterations of the treated wastewater. The precipitate obtained was 89.9 mass % composed of struvite with 3.5 % N, poor in hazardous heavy metals.

The NH₄⁺-N removal efficiency was in order: NZT-S > KZT-S > CNTR, with the highest reduction of 84.8 % recorded by NZT-S_MR1 and the lowest recorded by the CNTR (67.2 and 75.0 % for MR1 and MR2 respectively).

The addition of a “zeolite phase” in struvite precipitation process thus represents i) a valuable method for improving the efficiency of struvite production ii) a method for saving chemical reagents in struvite production and iii) an efficient way to recover and recycling N in agriculture.

How to cite: Galamini, G., Ferretti, G., Medoro, V., Eftekhari, N., Faccini, B., and Coltorti, M.: The use of a natural chabazite-rich zeolitic tuff improved struvite precipitation and nutrient recovery from anaerobically digested wastewater, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4563, https://doi.org/10.5194/egusphere-egu22-4563, 2022.

Asbestos minerals, namely chrysotile and fibrous amphiboles, have long been used as components in construction materials, as for instance the cement-asbestos (CA) slates used in roofing, exploiting their capability to increase mechanical strength. As well known, asbestos minerals have been recognised toxic and banned almost worldwide. Current remediation approaches include confinement, encapsulation and removal (followed by disposal in controlled landfills). A more attractive solution, strongly recommended by the EC, is detoxification and reuse, in a perspective of circular economy.

In the present contribution we explored the possibility to reuse thermally treated and deactivated CA powder (a mixture of glass and Ca-Mg silicates typical of cement – details in Vergani et al. 2021) as filler in: i) flour-elastomers (FKM type, characterized by high resistance to oil and temperature) and bi-component epoxy resins (bisphenol-A, epichlorohydrine based resins) used in flooring. For each application, different formulations (different proportions of conventional raw materials and deactivated CA powder) have been prepared and tested according to conventional quality test protocols and SEM micro-textural observations.

As regard the reuse in epoxy resin, the inert CA powder was used either as unique inorganic filler (up to 30 wt%) or admixed to conventional ones (barite), in varying proportions (up to 10 wt%). Mechanical tests and SEM observations have shown encouraging results for all formulations, suggesting feasible reuse in this field.

The application of the inert CA powder as filler in fluor-elastomers in substitution of wollastonite (~22 wt%) or barite (~7 and ~14 wt%), has given some controversial results. Although rheological properties such as cure kinetics, viscosity and scorch temperature are comparable to the standard reference samples, some important physical-mechanical properties worsen because of compatibilization and dispersion problems. As demonstrate by SEM observations, the CA powder tends to agglomerate, and similarly to the coarser particles saved from ball-milling – the grain size distribution of the CA powder is tri-modal with peaks at ~35-40, ~4-5 and ~0.7-0.8 µm – separate from the elastomer, adding porosity with detrimental effects on breaking load, elongation at fracture and related M50 and M100 modules.

At the moment, in a perspective to keep the fine fraction low and to reduce the coarse particles, alternative milling procedures, including microwave and ultrasonic treatments and sieving, are evaluated.

Reference: Vergani et al. (2021) J. Mater. Cycles Waste. https://doi.org/10.1007/s10163-021-01320-6

How to cite: Fabrizio, V. and the Progetto Dear: Reuse of deactivated cement-asbestos waste as inorganic filler in elastomers and epoxy resins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4981, https://doi.org/10.5194/egusphere-egu22-4981, 2022.

Gallium (Ga) and germanium (Ge) are technologically essential critical elements. This study focuses on old metallurgical slags generated by processing non-ferrous metallic ores in Tsumeb, northern Namibia, containing interestingly high concentrations of these elements (up to 156 ppm Ga and 441 ppm Ge). Mineralogical investigation indicated that the slags were composed of olivine-, melilite- and spinel-group phases, metal(loid)-rich glass, and sulfide/metallic inclusions. The FEG-EPMA and LA-ICP-MS data confirmed that major carriers of Ga were Zn-Fe-Al spinels (up to 1370 ppm), and Ge was primarily bound in a glassy phase (up to 470 ppm), especially in the case of granulated slags. The abiotic extraction tests, simulating a hydrometallurgical recovery via agitation leaching, were carried out in sulfuric, nitric, and hydrochloric acids (pH = 0.2-0.3, 25 °C and 70 °C, pulp density of 1%) to determine the release of Ga and Ge from slags. Their leaching attained a steady state after 6 hours for granulated slags and 2 hours for finely ground slags. The extractability of both Ga and Ge was slightly higher for the high-temperature trials. The overall recovery was the best for the sulfuric acid extractions and attained 100% and 96% for Ga and Ge, respectively. Our investigation indicates that understanding the specific binding of critical elements is crucial for their potential recovery from slags. This study was supported by the Czech Science Foundation project (GAČR 19-18513S).

How to cite: Ettler, V., Mihaljevic, M., Jedlicka, R., Kribek, B., Mapani, B., Kamona, F., Bowell, R. J., and Hrstka, T.: Gallium and germanium in metallurgical slags: mineralogy and potential recovery, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6971, https://doi.org/10.5194/egusphere-egu22-6971, 2022.

Asbestos-containing material (ACM) still represents an emergency in Europe because of the related health problems. Based on dedicated legislation, ACM must be managed through several different operations such as: i) confinement, ii) encapsulation and iii) removal (with disposal in controlled landfills). A more attractive alternative to these non-ideal solutions, safer and sustainable, is the transformation of the ACM through thermal, thermo-chemical or thermo-mechanical methods into a non-hazardous secondary raw material. In this contribution, we explore the re-use of ACM thermally treated at 1100 °C in the production of sanitary ware ceramics.

Sanitary-ware vitreous bodies (VB) are generally obtained from mixtures of three fundamental raw materials: i) clay, mostly kaolinite, which provides plasticity to the ceramic mixture; ii) quartz, which acts as filler, forming the skeletal network of the ceramic body; iii) feldspar, a fluxing agent, which promotes the greification of the body and the dissolution of component like quartz upon firing (buller T 1200-1240 °C; Carty & Senapati, 1998).

The product of the thermally treated ACM, i.e. a mixture of non-hazardous Ca-Mg-rich silicates (akermanite, bredigite, merwinite and larnite) and glass, was added to a ceramic mixture as a partial substitute (5 wt%) of feldspar (mixture VBX), and characterized according to a standard protocol before and after firing in the industrial tunnel kiln (buller T 1230°C). The results pointed out a very good greification level of the VBX slip, as corroborated by very low water absorption. These results motivated us to better evaluate the greification behavior of the VBX slip at 6 different buller T by means of gradient kiln. From the mixture VBX, we prepared six samples which were heated at 1140, 1160, 1180, 1200, 1220, and 1240 °C, and characterized the mechanical, mineralogical and microstructural properties. For comparison, the same T steps and analyses were applied to six standard ceramic mixtures (i.e., vitreous China, VC).

XRPD indicates that VBX and VC have very similar mineralogical composition, with glass, quartz, feldspar and mullite as major constituents and minor Fe and Ti oxides. SEM observations suggest that VBX and VC have also similar microstructure, dominated by a glassy matrix embedding numerous 10-60 µm-sized particles of quartz, feldspar and mullite. Overall, thermally treated ACM seems a good candidate to substitute feldspar up to 5 wt% in the production of sanitary ware ceramics. This conclusion is further supported by the fact that VBX and VC display a very similar greification level at T>1200°C.

Carty, W. M., & Senapati, U. (1998). Porcelain—raw materials, processing, phase evolution, and mechanical behavior. Journal of the American Ceramic Society, 81(1), 3-20.

How to cite: Pellegrino, L., Bernasconi, A., Galimberti, L., Vergani, F., Marian, N. M., Viti, C., and Capitani, G.: Recycling of thermically treated asbestos-containing material in the production of sanitary-ware vitreous bodies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7014, https://doi.org/10.5194/egusphere-egu22-7014, 2022.

The presence of active volcanoes often influences human life both in terms of health impact and socio-economic consequences. Explosive eruptions can release into the atmosphere huge quantities of ashes which then fall to the ground, causing many inconveniences to communities living and working in close proximity to the volcano. A further problem is represented by the high costs that the involved administrations (Civil Protection or Municipalities) of the interested areas must face whenever this material, considered as waste, needs to be collected and disposed of in landfill.

To overcome this problem, it would be suitable to find ‘‘end of waste” alternatives for volcanic ash as raw material in the productive sectors, e.g., in building materials (tiles, bricks, mortars, concretes, etc.). A paradigm shift leading to consider ashes no longer as a waste but a resource.

This contribution deals with an experimental study aimed at assessing the possible re-use of volcanic ash as temper in the manufacture of ceramic tiles. Volcanic ashes recently erupted by Mount Etna volcano in Sicily (Southern Italy), one of the most active basaltic volcanoes in the world, have been here chosen as case study for such a purpose. Ceramic test-tiles were manufactured by mixing volcanic ash with a calcareous clayey raw material, by using specific proportions of clay/temper. In order to assess the quality of the products, the tiles underwent several physical–mechanical tests including: a) water absorption; b) bending resistance; c) impact resistance; d) resistance to deep abrasion; e) thermal shock resistance; f) frost resistance; and g) accelerated aging test by salt crystallization (Belfiore et al. 2020). The obtained results have been then compared with those of a reference product manufactured by using another volcanic material known as azolo (i.e., finely ground basalt) for a long time on the market. Our data demonstrate how basaltic ash recovering through this methodological approach is highly promising in the sector of building materials.

Reference

Belfiore C.M., Amato C., Pezzino A., Viccaro M., 2020. An end of waste alternative for volcanic ash: A resource in the manufacture of ceramic tiles. Construction and Building Materials, 263, 120118, doi: 10.1016/j.conbuildmat.2020.120118

How to cite: Belfiore, C. M. and Viccaro, M.: Recycling Etna volcanic ash for the production of ceramic materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9769, https://doi.org/10.5194/egusphere-egu22-9769, 2022.