# Utilization of Natural Adsorbents in the Purification of Used Sunflower and Palm Cooking Oils
## 4 Discussion
Zeolites are crystalline aluminosilicates in which the three components, aluminum, silicon, and oxygen, are organized into a consistent framework, featuring uniform-sized pores and cavities [62]. Natural zeolite contains certain cations such as Ca\({}^{2+}\), Na\({}^{+}\), K\({}^{+}\), Mg\({}^{2+}\), a statement supported by the results of chemical analysis. These positive ions can be readily exchanged for negative ions in a solution [63]. The use of zeolites in the removal of polar compounds from WCO involves their addition for the purpose of adsorbing polar compounds such as water, FFA, and other water-soluble impurities. After that, the impurity-laden zeolites can be separated from the treated oil, usually by filtration or other separation techniques [64; 65; 66]. The effectiveness of the process depends on the type of zeolite used, the specific operating conditions, and the exact composition of the WCO. The Si/Al ratio, or ratio of tetravalent (Si, Ge, etc.) to trivalent (Al, B, etc.) atoms, significantly influences the polarity of the material. For instance, zeolites with a higher Al content, also referred to as low-silica zeolites, exhibit greater affinity for polar compounds, such as water, compared to high- or pure-silica zeolites [67]. The higher the dose of zeolite added, the lower the value of the PV in the oil, thus increasing the quality of the purified oil [68]. Consequently, our results also indicate that the AV, PV, and TPC values decrease with increase in the dose of zeolite added to the sunflower--WCO. Our results show that both zeolite and eggshell can reduce the acidity of residual oil. Natural zeolite from Rupe-Brasov, Romania, was used for the first time as an absorbent to reduce the AV and PV of WCO. The results are comparable to those in the literature [23; 35]. The hydrolysis process of cooking oil is expedited by the presence of water within the oil [69]. RI is a valuable parameter to assess the degree of oil unsaturation. As the number of conjugated double bonds in the oil increase, the RI correspondingly increases [70]. [PERSON] and [PERSON] [71] demonstrated that gradual increases in AV are noticeable for sunflower oils with increasing frying time. Similarly, in our result, the AV increases in the case of fresh sunflower oil from 0.73 mgKOH/g to 6.4 mgKOH/g in the case of the food mix, 9.4 mgKOH/g in the case of the oil in which potatoes were fried, and 11.41 mgKOH/g for the oil in which the chicken meat was thermally treated. In addition, the same trend is observed in the case of palm oil, where an increase from 1.39 mgKOH/g to 4.66 mgKOH/g is recorded for the oil in which bakery products were fried and 6.62 mgKOH/g in the case of frying the food mix. Furthermore, earlier studies [72] have shown a rise in AV if the number of frying cycles increases. SV represents the average molecular weight or chain length of the fatty acids contained in an oil, primarily in the form of triglycerides [73]. SV was 193.01 mg KOH/g oil in sunflower fresh oil and 188.38 mg KOH/g in palm fresh oil and between 198.94 and 213.03 mg KOH/g oil in sunflower--WCO and between 210.69 and 213.03 mg KOH/g oil for palm--WCO, similar to values obtained by [PERSON] et al. [74]. The higher value of SV, however, suggests that the mean molecular weight of fatty acid is higher or that the number of ester bonds is more. This might imply that the fat molecules do interact with each other. A higher SV indicates a greater mean molecular weight of fatty acids or a higher number of ester bonds. This observation suggests a potential interaction among the fat molecules [75]. The degradation of vegetable oils is evidenced by the decrease in IV. IV is used to quantify unsaturation or the average number of double bonds in fats and oils [76]. IV is a measure of the degree of unsaturation of fatty acids present in fat and oil [77]. The greater the IV of an oil, the higher its level of unsaturation.