Porous alkali activated materials with slow alkali release dynamic. Role of composition

Abstract

Alkali activated materials (AAM) based on calcined metakaolin or illite clay together with waste by-products, such as waste glass or aluminium scrap recycling waste, were tested as value-added materials for pH stabilization in biogas technology where decrease of pH should be avoided. Porous materials with ability to slowly leach alkalis in the water media thus providing continuous control of the pH level were obtained. XRD, FTIR, SEM and titration methods were used to characterize AAM and their leaching properties. It is clear that composition of the material has an important effect on the diffusion of alkali from structure. Namely, higher Si/Al and Na/Al molar ratios may increase pore solution transfer to the leachate. The leaching rate of alkalis from the structure of AAM is high for the first few days, decreasing over time. It was possible to calculate the buffer capacity from the mixture design of AAM. RESUMEN: Materiales activados alcalinamente porosos con liberación lenta de álcalis. Efecto de la composición.En este estudio se han ensayado materiales activados alcalinamente (AAM) basados en metacaolín o arcilla de ilita junto con subproductos tales como residuos de vidrio o aluminio reciclado, como materiales con valor añadido para la estabilización del pH en tecnologías de biogás donde se debe evitar la disminución del pH . Se obtuvieron materiales porosos con capacidad para lixiviar lentamente los álcalis en medios acuosos, proporcionando así un control continuo del nivel de pH. Se utilizaron técnicas de DRX, FTIR, SEM y métodos de tritación para caracterizar los AAMs y sus propiedades de lixiviación. La composición del material tiene un efecto importante en la difusión del álcali de la estructura. Es decir, mayores relaciones molares de Si / Al y Na / Al pueden aumentar la transferencia de la solución del poro al lixiviado. La tasa de lixiviación de los álcalis desde la estructura de los AAMs es alta durante los primeros días, disminuyendo con el tiempo. Se ha calculado la capacidad del efecto tampón a partir del diseño de mezcla de AAM.Palabras clave: Cemento activado alcalinamente; Tratamiento de residuos; Difusión; Microestructura, pH ORCID ID: G. Bumanis

Innovative application for bauxite residue: Red mud-based inorganic polymer spheres as pH regulators

“…After the 28 th day, the pH decay was 2.4 and 2.6, respectively, for compositions 50RM_0.30 and 50RM_0.40. The pH fluctuation over time of the RM-based spheres is narrower than that reported for metakaolin-waste inorganic polymers (~ 4-5 [25] and ~ 3-4 [19]), and metakaolin-based geopolymer spheres (3.7 [16]), which demonstrates the potential of the RM-based spheres as pH regulators. Other studies have reported lower pH decay over time: 1.6-1.9…”

Low-Calcium, Porous, Alkali-Activated Materials as Novel pH Stabilizers for Water Media

“…The leaching of alkalis is affected by three main factors: Chemical composition of raw materials (type of precursor and activator, alkali activator solution/solid ratio), physical properties (porosity, pore structure), and production method of AAM (curing conditions, thermal treatment, etc.) [2,5,[11][12][13]. The previous results from different studies have shown that calcined illite clay [3], biomass-fly ash [5], natural zeolite [14], glass waste and slag blend [15], and metakaolin [2,16] can be used as raw materials for production of AAM.…”