In this study, a blast furnace slag (BFS) and fly ash (FA) based adsorbent geopolymer to be used for removing Pb2+ from aqueous solutions were synthesized using the hydrothermal method at 60 °C for 24 h, and then cured at 25 °C for another six days. The alkali activator applied in this work was a combination of sodium hydroxide and sodium silicate solutions at a mass ratio of 2. The geopolymer slurry was adjusted to a Si/Al molar ratio of 3. A BFS-based geopolymer (GS) having a specific area of 23.56 m2/g and pore size and volume of 7.8 nm and 73 cm3/kg, respectively, surpassed the raw material surface by approximately 13-fold. An FA-based geopolymer (GA) having a specific area of 35.97 m2/g and a size and porous volume of 9 nm and 124 nm, respectively, surpassed the raw material surface by approximately 23-fold. In addition, GS and GA showed a cation exchange capacity (CEC) of 241.30 and 286.96 Meq/100 g, respectively. X-ray diffraction (XRD) determined sample crystallinity and it was proven by scanning electron microscopy (SEM), showing that both geopolymers were constituted of unreacted particles surrounded by amorphous and semi-amorphous products. Through Fourier transform infrared spectroscopy (FTIR), a band that was assigned to the asymmetric stretching vibration of Si-O-M (M = Na+ and/or Ca2+) non-bridging oxygen type was observed, which suggested that Na and Ca could serve as exchangeable ions in the ionic exchange process. Adsorption test data indicated that good adsorption was obtained when a neutral pH was used at room temperature, and the adsorption isotherm showed that GA had more adsorption sites than GS, which meant greater maximum adsorption capacity.
The aim of this study was to determine the Cd2+ removal capacity of a biosorbent system formed by Saccharomyces cerevisiae in calcium alginate beads. The adsorption of Cd2+ by a S. cerevisiae–alginate system was tested either by batch or fixed-bed column experiments. The S. cerevisiae–alginate system was characterized using dynamic light scattering (DLS, zeta potential), size, hardness, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy. Beads of the S. cerevisiae–alginate system showed a spherical–elliptical morphology, diameter of 1.62 ± 0.02 mm, 96% moisture, negative surface charge (−29.3 ± 2.57 mV), and texture stability during storage at 4 °C for 20 days. In batch conditions, the system adsorbed 4.3 µg of Cd2+/g of yeast–alginate beads, using a Cd2+ initial concentration of 5 mg/L. Adsorption capacity increased to 15.4 µg/g in a fixed-bed column system, removing 83% of total Cd2+. In conclusion, the yeast–alginate system is an efficient option for the removal of cadmium at low concentrations in drinking water.
Los alimentos funcionales producen un efecto benéfico en la salud de quien los consume. Algunos de ellos se desarrollan adicionando probióticos o compuestos bioactivos, que son sensibles a condiciones adversas presentes durante la vida de anaquel del alimento o al pasar por el tracto gastrointestinal. En ambos casos, una alternativa para protegerlos, es encapsularlos en matrices grado alimenticio. Se co-encapsularon Lactobacillus plantarum y ácidos grasos omega-3 (Ω3) en una matriz de alginato-pectina. Los Ω3 se obtuvieron por extracción en frío de aceite de linaza; su análisis cuantitativo por cromatografía de gases mostro un contenido del 58 %. La relación de matriz polimérica que produjo mejores cápsulas fue 2:1, usando concentraciones de 1.5 % y 2.0 %, de alginato y pectina, respectivamente. La mejor relación matriz-probiótico-linaza fue de 5.0:1.0:1.0 (suspensión celular conteniendo aproximadamente 2.8 x 108 UFC/mL). Se obtuvieron cápsulas esféricas con carga superficial, negativa (- 4.6± 0.41 mV) y diámetros entre 150 y 200 μm. La eficiencia de encapsulamiento de L. plantarum fue del 85 %, observándose una disminución de 0.7±0.14 Log UFC/g, después de liofilizar las microcápsulas para mejorar su estabilidad durante el almacenamiento. Después de 30 días a -20 °C, no se observaron diferencias (p > 0.05) en la sobrevivencia del probiótico, ni cambios en la concentración de peróxidos del aceite co-encapsulados, indicando que el encapsulamiento protegió tanto a L. plantarum como a los Ω3. Estos micro-encapsulados podrían utilizarse en la formulación de productos funcionales debido a su bajo costo de producción y fácil estabilización.
The main aim of this paper is to evaluate the influence of the recycled expanded polystyrene as lightweight aggregate on the mechanical properties of lightweight cement mortar when subjected to high temperatures.Various tests have been carried out on different mixtures of mortar. The water/cement mix proportion has always been the same and only the nature of the aggregates has changed, with a partial replacement of the conventional aggregate by recycled ground EPS (EPS-G) with values ranging from 10% to 30%, achieving significant results in relation to exposure to high temperatures. In this research, the samples have been subjected to different temperatures of exposure, in order to analyze the influence of the lightweight recycled arid dosage in the mechanical properties of mortars.The results of this study show the ability of mechanical response at high temperatures with light mortars EPS-G. This study shows how this new mix can be used in different building types, optimizing construction materials and reducing mortars density while transforming a residual product into an active product.
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