## 2 Materials and Methods
### Washing Process and Analysis Method  
The physical morphology (in the macro picture and under a light microscope) and initial chemical composition of MF010-Min measured using the X-ray fluorescence (XRF) are provided in Figure 2 and Table 1, respectively. As shown, MF010-Min is generally constructed from relatively fine materials and possesses a primary particle distribution of 0.2-0.5 mm (sieve analysis). Since this fraction has already been classified thoroughly, its composition mainly consists of silicon (Si) and calcium (Ca), with only low levels of aluminum (Al) and iron (Fe). Coupled with the XRF result, the X-ray diffraction (XRD) result of MF010-Min is provided in Figure 3. Regardless of indivisible peaks representing highly heterogeneous materials, various silicate phases are indicated to dominate the composition of MF010-Min. The detected primary substances include quartz (SiO\({}_{2}\)), wollastonite (CaSiO\({}_{3}\)), akermanite (Ca\({}_{2}\)MgSi\({}_{2}\)O\({}_{7}\)), diopside (CaMgSi\({}_{2}\)O\({}_{6}\)), anorthite (CaAl\({}_{2}\)Si\({}_{2}\)O\({}_{8}\)), and various olivine groups (M\({}_{2}\)SiO\({}_{4}\)--M: Ca; Fe; Mn; Ni; Mg; etc.). Furthermore, despite being relatively low in  
Figure 1: Mass balance (in wt.%) from raw IBA into various fractions upon processing in IBA treatment plants [2; 21] and extended separation techniques proposed in [19; 20]. concentration compared with silicon, some calcium-bearing phases, including anhydrite (CaSO\({}_{4}\)) and calcite (CaCO\({}_{3}\)), are also captured, along with typical iron oxide phases (hematite and magnetite). Interestingly, as supported by the metallography image shown in Figure 2b, a certain amount of residual metallic particles (represented by bright particles upon observation under a light microscope) should be expected, which could be iron or aluminum, as explicitly detected by the XRD observation in Figure 3.  
The washing experiments sequence of MF010-Min is represented in Figure 4, which were conducted in a 300 mL beaker glass at a room temperature of around 25 \({}^{\circ}\)C to examine the applicability of citric acid in removing heavy metals, focusing on iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn). Moreover, variations were applied across several parameters, including the concentration of citric acid, the effect of washing duration, the \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Elements** & **wt.\%** & **Elements** & **wt.\%** & **Elements** & **ppm** \\ \hline Silicon (Si) & 30.1 & Chlorine (Cl) & 0.35 & Zirconium (Zr) & 263 \\ Calcium (Ca) & 10.2 & Zinc (Zn) & 0.33 & Tin (Sn) & 112 \\ Aluminum (Al) & 2.7 & Phosphorus (P) & 0.29 & Nickel (Ni) & 93 \\ Sodium (Na) & 2.6 & Copper (Cu) & 0.20 & Antimony (Sb) & 87 \\ Iron (Fe) & 1.5 & Barium (Ba) & 0.20 & Cobalt (Co) & 40 \\ Magnesium (Mg) & 1.0 & Lead (Pb) & 0.09 & Rubidium (Rb) & 34 \\ Potassium (K) & 0.88 & Manganese (Mn) & 0.07 & Vanadium (V) & 27 \\ Titanium (Ti) & 0.60 & Chromium (Cr) & 0.03 & Molybdenum (Mo) & 19 \\ Sulfur (S) & 0.50 & Strontium (Sr) & 0.03 & Niobium (Nb) & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Initial chemical composition of MF010-Min. Figure 3: XRD result of MF010-Min before the washing process. Figure 2: (**a**) Macro representation and (**b**) metallography (stitching) image of MF010-Min. influence of agitation and heat, the type of solvent used, and the liquid-to-solid (L/S) ratio (mL/gram). In the case of concentration, a certain amount of citric acid crystal was dissolved in water, where tap water was compared with distilled water. Specifically, six solution concentrations (M: mol\(\cdot\)L\({}^{-1}\)) were used: 0 M, 0.5 M, 1.25 M, 2.5 M, 4 M, and 6 M, which were selected to approach its solubility limit. The effects of continuous agitation at 500 rpm and heating at 40 \({}^{\circ}\)C were also investigated. Conclusively, three different L/S ratios were also involved: four, eight, and ten.