Durgaprasad Ramteke (PhD)

Alkali activation of inorganic waste

The growing population and urbanization in the world leading to new challenge of generated waste and its management. Every single person is concern about the waste management, as in the broader perspective it can affect the health of living animals and ecosystem. In the past, the most solid waste dump in the open land and this landfills are now piles of solid waste with no proper managements. So measure need to be taken for proper waste management for better future. Glass is the common solid waste found in the daily life as liquor bottles, wine bottles, soft drinks bottles, glass jars and as empty cosmetic bottles. According to the data published on the United States Environmental Protection Agency [1], the glass waste generated in 2015, only 26 % of glass waste recycled, 12 % used for combustion with recovery energy and around 60 % of total generated glass were ended up in the landfills. The glass ended up in the landfills has the different color cullets, metal particle, plastic particle and organic contamination.  The cost of separating these for in specific group is much more. It is possible to overcome these problem by consider the idea of “open loop cycling” or “down cycling”, i.e. reuse in the other form than original e.g. glass foam [2].

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The glass foam possesses unique sets of properties like low density, light weight, low thermal conductivity, resistant to steam, fire and bacteria or insects, and easy handling [3]. These properties allow one to use these foam as building materials as insulation material or as bricks. These foams doesn’t require traditional melting process but the formation of foams depends on the viscous flow sintering and gas evolution [2,3]. The rate of oxidation reaction or decomposition depends on the amount of additive added with the glass.  The idea of “open loop cycling” or “down cycling” for making the glass foam is the good solution for waste glass management. Traditionally the SiC or carbon black are use as additive as foaming agents but novel alkali activation method provides the new approach for foam glass. The alkali activated materials are commonly termed as the “geopolymers”. The idea of alkali activation comprises of reaction of silica and alumina in the concentrated alkali solution like NaOH or KOH. The alkali activation were further extended to the glasses as raw materials [3-8]. With proper balance between silica, alumina calcium and sodium, it possible to form the sodium alumino-silicate hydrate (N–A–S–H) and calcium alumino-silicate hydrate (C–A–S–H) as binders for building industry [3]. The molecular balance is the key to achieve the mechanical strength and chemical durability.

There are number of reports available on the alkali activation glasses. Rincón et al [3] studied the alkali activated soda lime glass foam with different sintering temperatures. The total porosity among these one of foams 89 % and mechanical strength comparable with commercial ones. Santaquiteria et al [9] shows that alumino- silicate glasses are the alternative to fly ash and still mill slag. They also conclude that up take in calcium content can change the mechanical strength of foam drastically. The idea glass foam formation through alkali activation were extended to   vitrified bottom ash (VBA) by Rincón et al [10]. Carrasco et al [11] discuss the effect of humidity during the curing on mechanical properties of foam obtained by from soda lime glass. The alkali activation approach for treatment of waste glass is widely accepted and work were in progress to increase the strength and chemical durability of the glass foams by maintaining the ratio of constitutes.

References

1. Glass: Material-Specific Data, https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/glass-material-specific-data

2. Rincón A, Giacomello G, Pasetto M, Bernardo E, Novel ‘inorganic gel casting’ process for the manufacturing of glass foams, J Eur Ceram Soc. 2017; 37(5); 2227-2234.

3. Scarinci G, Brusatin G, Bernardo E, Glass foam. In: Scheffler M, Colombo P, Editor. Cellular Ceramics: Structure, Manufacturing, Properties and Applications, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2005; p. 158-176.

4. Puertas F, Torres-Carrasco M, Use of glass waste as an activator in the preparation of alkali-activated slag. Mechanical strength and paste characterization, Cement Concrete Res. 2014; 57; 95-104.

5. Torres-Carrasco M, Puertas F, Waste glass in the geopolymer preparation. Mechanical and microstructural characterization, J Clean Prod. 2015; 90; 397-408.

6. Toniolo N, Rincón A, Roether J, Ercole P, Bernardo E, Boccaccini A, Extensive reuse of soda-lime waste glass in fly ash-based geopolymers, Constr Build Mater. 2018;188; 1077-1084

7. Rincón A, Toniolo N, Boccaccini A, Bernardo E, Glass-Ceramic Foams from ‘Weak Alkali Activation’ and Gel-Casting of Waste Glass/Fly Ash Mixtures, Materials. 2019; 12(4); 588

8. Rincón A, Desideri D, Bernardo E, Functional glass-ceramic foams from ‘inorganic gel casting’ and sintering of glass/slag mixtures, J Clean Prod. 2018; 187; 250-256.

9. Santaquiteria C, Fernández-Jiménez A, Palomo A, Alternative prime materials for developing new cements: Alkaline activation of alkali aluminosilicate glasses, Ceram. Int. 2016; 42(8); 9333-9340.

10. Rincón A, Salvo M, Bernardo E, Up-cycling of vitrified bottom ash from MSWI into glass-ceramic foams by means of ‘inorganic gel casting’ and sinter-crystallization, Constr Build Mater. 2018; 192; 133-140

11. Torres-Carrasco M, Puertas F, Waste glass as a precursor in alkaline activation: Chemical process and hydration products, Constr Build Mater. 2017; 193; 342-354.