## 4 Applicability and Effect of Citric Acid-Based Treatment  
### Exploration of the General Tendencies and Behavior of Silicon  
The applicability of citric acid solution as an alternative treatment agent for adjusting the chemical composition of MF010-Min has been elucidated through comparative concentration analysis. Generally, the results of the present study indicate that major phases (those  
Figure 10: Washing results of MF010-Min in mixed variation of different washing durations, citric acid concentrations, and L/S ratios. Figure 9: Washing results of MF010-Min after 6 h with different L/S ratios. present at relatively notable concentrations) containing the studied elements (Si, Ca, Al, Fe, Cu, Zn, and Mn) should be affected by the washing process using the citric acid solution to a certain degree and behavior. However, three essential results should be initially considered before eventually identifying which major phases are most likely affected (dissolved) by the citric acid solutions. First, those major phases should plausibly not be dissolvable in water within the duration of the investigated washing process. The argument is empirically supported by the results provided in Figures 7 and 8 that a constant or minor fluctuation in the concentration of the studied elements is detected after a water-only washing process (0 M citric acid), which contextually amplifies the report provided by [PERSON] and [PERSON] [22]. The second essential outcome is the behavior of silicon as the major component with the highest concentration in MF010-Min, as listed in Table 1. Based on the chemical composition analysis after the washing process, the silicon content was measured as relatively constant or increasing instead, which was most likely related to the compositional constraint effect due to a significant decrease in the other explored elements. In the case of the water-only washing process, this behavior of silicon can be correlated with the solubility of the silicate phase in water, which is negligible, according to [PERSON] et al. [23]. This characteristic was also previously well documented by [PERSON] and [PERSON] [24] and supported by [PERSON] and [PERSON] [25], especially for quartz as the most stable form of silica. According to their reports, the solubility of quartz in water can be increased if organic acids are involved, including citric acid [26,27]. Nonetheless, according to [PERSON] et al. [26], the increased solubility of quartz in citric acid correlates with a higher pH value but is susceptible to the existence of other cations. This perspective of other cations is more relevant in the case of MF010-Min, which is considered in the present study to be a heterogeneous material despite the dominance of silicate phases. The phenomenon was further elucidated by [PERSON] et al. [28], who studied the nature of the cation solubilization of silicate minerals. According to their observations, organic acids decompose silicate minerals through an acid attack (directly dissolved) and chelation (forming a soluble complex) process. In this case, the order of solubilization is determined by the mineral composition and structure, where the presence of other cations could be chelated first ahead of silicon [29] or even retard quartz chelation, as reported by [PERSON] and [PERSON] [30]. Conclusively, the behavior of silicon in the present study should be correlated with the decreasing dissolution rate because of the low pH, which is aggravated by the existence of other cations that react more favorably in the citric acid solution. As MF010-Min interacts with the citric acid solution, an initial sequence of acid attack and chelation occurs at the interface between the particle and the solvent. Subsequently, cations at the interface react and dissolve into the solution. As a result, on the boundary of the low reaction rate for silicon and the number of other mobilized cations, the dissolution of silicon was relatively overtaken during the explored washing duration.