Biomass Fly Ash Self-Hardened Adsorbent Monoliths for Methylene Blue Removal from Aqueous Solutions

Abstract

The use of methylene blue (MB) by several industries generates contaminated industrial wastewaters that must be purified before discharge into the environment. Its removal can be achieved by adsorption, and low-cost and easily available materials should be used as adsorbents. Biomass fly ash (BFA) generated from biomass combustion, for heat and power generation, is increasing worldwide since the process is considered CO2 neutral. However, most of the ash is still landfilled. This study aims to evaluate the valorisation of BFA as a low-cost porous bulk adsorbent for MB removal from wastewaters. The monoliths were obtained after 14 days of curing just after adding water and a porogenic agent (aluminium powder) to the BFA, using the self-hardening ability of this waste. The BFA was characterised for chemical (XRF) and mineralogical (XRD) composition, particle size distribution (laser diffraction-COULTER) and morphology (SEM). The monolith sample cured for 14 days was characterised for density, porosity (total and open), microstructure, compressive strength, and MB removal ability (batch tests). The results showed that the addition of aluminium powder (0.09 wt.%) promoted an increase in interconnected porosity and the MB removal efficiency reached 80% for the most porous samples. The equilibrium data for the adsorption process were well characterised by a type 2 Langmuir isotherm equation with a monolayer adsorption capacity (qmax) that ranged from 0.22 to 0.66 mg/g.

Valorization of Kraft Pulp and Paper Mill Slaker Grits and Biomass Fly Ash as Fillers in a Commercial Screed Mortar Formulation

“…The XRD pattern of the BFA samples shows that α-quartz (α-SiO 2 ), calcite (CaCO 3 ), microcline (KAlSi 3 O 8 ), and muscovite (KAl 2 (AlSi 3 O 10 )(OH) 2 ) are the main crystalline detected phases. These findings are in line with the results obtained in XRF and with the crystalline phases reported in the literature (quartz and calcite) [ 4 , 13 , 14 , 15 ]. When qualitatively comparing the BFA1 and BFA2 diffractograms with those of the sieved fractions (BFA1_S and BFA2_S), it is possible to observe that the peaks referring to α-quartz decrease in intensity.…”

“…Their surface is generally rough and not strongly vitreous. These morphology features fit the descriptions made by other authors [ 4 , 15 , 16 , 17 ].…”

“…The antagonistic behaviors verified in the mechanical properties by the increase in the percentage of the sieved ashes revealed that BFA2_S, not only for the physical effects but also for its chemical composition, increased the mechanical resistance of the samples, overcoming the diminution in OPC content and the slight increase in w/b. This suggests hydraulic or pozzolanic activity of this ash, as often referred to in the literature ([ 3 , 4 , 5 , 6 , 7 , 9 , 15 ]). Sigvardsen et al [ 21 ] studied the phase and strength development of 10 wt.% substitution of cement by wood ash in cement pastes.…”

“…It was assumed that the chemical composition and the LOI of BFA1_GS and BFA2_GS were maintained as equal to their parent samples, BFA1 and BFA2, respectively, because no amount of those powders was wasted during the applied pre-treatments. Other studies also pointed to SiO 2 and CaO as the major oxides present in fly ash generated from biomass combustion in bubbling fluidized bed boilers [ 4 , 13 , 14 , 15 , 16 ]. The observed compositional differences between the two sorts of BFA can be a consequence of variations in the biomass used as fuel [ 16 ].…”

Review of recycling alternatives for paper pulp wastes

“…The prepared monoliths were positively tested for MB adsorption. It was shown that the dye adsorption kinetics can be described by the pseudo-first-order equation and the adsorption process was characterised by the Type 2 Langmuir isotherm model with a maximum sorption capacity of ~0.66 mg/g, determined for the samples with the higher total porosity, ~72% (Capela et al, 2022).…”