# Biomass Fly Ash Self-Hardened Adsorbent Monoliths for Methylene Blue Removal from Aqueous Solutions
## 2 Materials and Methods
### Raw Materials and Self-Hardened Monoliths Characterization  
The chemical composition of BFA and PLC was determined by X-ray fluorescence (XRF) (Philips X'Pert PRO MPD spectrometer, Almelo, The Netherlands) on a compressed powder pellet (10 g of sample was homogenised with five drops of polyvinyl alcohol and pressed to a standardised shape). The loss on ignition (LOI) at 1000 \({}^{\circ}\)C (15 min dwell time) was also determined. The specific surface area was measured by physical nitrogen adsorption isotherms using the Brunauer, Emmett, and Teller (BET) method (Micromeritis, Gemini 2370 V5.00, Norcross, GA, USA). The particle size distribution was obtained by the laser diffraction technique (Beckman Coulter LS 230 FM, Brea, CA, USA) employing the Fraunhofer model and the wet (water) procedure. The true density was determined by the helium pycnometer technique (Anton Paar GmbH, Ultrapyc 3000, Graz, Austria).  
The mineralogical composition of BFA and self-hardened samples was evaluated by X-ray powder diffraction (XRD) at room temperature. The XRD was conducted on a \(\theta\)/\(\theta\) diffractometer ([PERSON], PANalytical, X'Pert Pro3, Almelo, The Netherlands), equipped with a fast RTMS detector (Malvern PANalytical, PIXcel 1D, Almelo, The Netherlands), with Cu K\(\alpha\) radiation (45 kV and 40 mA, 10-80\({}^{\circ}\) 20 range, with a virtual step scan of 0.026\({}^{\circ}\) 20 range, and virtual time per step of 100 s). For this analysis, the samples were grounded in an agate mortar until the whole sample passed through a 63 \(\upmu\)m sieve.  
The morphology of BFA, PLC and AP powders, and the microstructure of the prepared monoliths cured for 14 days were accessed by scanning electron microscopy (SEM) (Hitachi, SU-70, Tokyo, Japan). Before SEM examination, the samples were coated with a carbon thin film (Emitech, K950, Fall River, MA, USA) to provide a conducting layer. The microstructure of the monoliths cured for 14 days was also observed in an optical microscope (Leica EZ4 HD, Wetzlar, Germany).  
For each composition, three cubical samples (14 days curing) were used for uniaxial compressive strength determination. The tests were performed, at room temperature, in a Universal Testing Machine (Shimadzu, model AG-25 TA refresh, Kyoto, Japan; provided with a 250 kN load cell running at a displacement rate of 0.5 mm/min). The density of the monoliths was obtained by measuring their mass and dimensional volume.  
Monoliths total porosity (\(x_{t}\)) was measured by the Archimedes method, taking the weight of the samples in the dry (\(wt_{1}\)) and wet (\(wt_{2}\)) conditions and immersed in water (\(wt_{3}\)), following the Equation (2):  
\[x_{t}=1-\frac{\rho_{w}}{\rho_{th}}\times\frac{wt_{1}}{wt_{2}-wt_{3}} \tag{2}\]  
where \(\rho_{w}\) is the density of liquid water at atmospheric conditions of pressure and temperature, and \(\rho_{th}\) is the true density of the hardened samples determined by the helium pycnometer technique. The reported values are the average of three measurements. Open porosity (\(x_{0}\)) was also calculated by the Equation (3):  
\[x_{0}=\frac{wt_{2}-wt_{1}}{wt_{2}-wt_{3}} \tag{3}\]