# Potassium Recovery from Potassium Solution and Seawater Using Different Adsorbents
## 4 Conclusions  
The K sorption characteristics with three adsorbents, natural zeolite, ammonium acetate-treated zeolite, and manganese nodule, were studied and compared to see the potential use of manganese nodule as an alternative K adsorbent. The amounts of K adsorption with all three absorbents increased with increasing initial K concentration. However, these three absorbents showed different sorption characteristics depending on pH conditions. The manganese nodules show a comparable and, sometimes, better K recovery than the zeolite-based absorbents under certain conditions; however, zeolite  
Figure 7: Changes in the potassium (K) sorption capacity with repeated sorption tests: (**a**) natural zeolite; (**b**) ammonium acetate\(-\)treated zeolite. The adsorbents were regenerated after each sorption test with 0.5 N HCL.  
based absorbents were generally still more suitable for K recovery considering competition between mixtures of ions in waters and seawaters. In particular, the natural zeolite can potentially be reused up to three times without losing its K sorption capacity. The K sorption capacity of the ammonium acetate-treated zeolite was higher than that of the natural zeolite, but the loss of K sorption capacity with the repeated uses was greater with the ammonium acetate-treated zeolite. Overall, the results show that the manganese nodule can potentially be used to recover K under certain conditions, but the zeolite-based absorbents are generally better for K recovery from K-containing waters. This suggests that more studies on the K recovery using zeolite, including surface modified zeolite, are necessary to enhance the K recovery from seawater. Furthermore, studies on other alternative adsorbents are required.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11188660/s1](https://www.mdpi.com/article/10.3390/app11188660/s1)]([https://www.mdpi.com/article/10.3390/app11188660/s1](https://www.mdpi.com/article/10.3390/app11188660/s1)), Figure S1. SEM images of three adsorbents used in this study. (a) Natural zeolite, (b) ammonium acetate-treated zeolite, and (c) manganese nodule.  
S.S.: methodology, formal analysis, visualization, writing--original draft, writing--review and editing; E.H.J.: conceptualization, data curation; methodology; formal analysis; writing--original draft; writing--review and editing; visualization; supervision; project administration; funding acquisition; H.P.: conceptualization; methodology; writing--review and editing, funding acquisition; S.L.: conceptualization; methodology; writing--review and editing; J.H.K.: data curation; formal analysis; writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This study was funded by the National Research Foundation of Korea (NRF-2018R1C1B6002702; NRF-2020R11A1A010/0853; NRF-2021R1A2C4001746).  
Not applicable.  
The data presented in this study are available upon request from the corresponding author.  
This study was funded by the National Research Foundation of Korea (NRF-2018R1C1B6002702; NRF-2020R11A1A010/070853; NRF-2021R1A2C4001746). The authors also thank [PERSON] for helping with the preparation of the experiments.  
The authors declare no conflict of interest.