Abstract
The potassium (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. In general, the Langmuir isotherm could fit the K sorption in the KCl solutions at different pH conditions better than the Freundlich isotherm. Based on the Langmuir parameters, the maximum K sorption was greater for the zeolite-based adsorbents (i.e., 40–42 mg g−1) than the manganese nodule (i.e., 2.0 mg g−1) at acidic conditions, while the manganese nodule (i.e., 9.7 mg g−1) showed better K sorption at neutral conditions. With the seawater samples, the zeolite-based adsorbents showed higher K recovery (4–14%) than the manganese nodule (0–8.8%). The K sorption on the zeolite-based adsorbents followed the pseudo-second-order kinetics and the K sorption rates were higher for the treated zeolite than the natural zeolite. The repeated sorption tests showed that the natural zeolite could potentially be reused up to three times without any significant loss of K sorption capacity, while the ammonium acetate-treated zeolite lost its K sorption capacity after the single sorption test. Overall, the results show that the manganese nodule may potentially be the alternative to zeolite for K recovery under certain conditions, yet the zeolite-based adsorbents are generally better than the manganese nodule. Thus, more studies to enhance the K recovery using zeolite, including surface modified zeolite, are recommended.
Highlights
The adsorption process has been widely applied to recover valuable elements, such as lithium (Li), potassium (K), uranium (U), and strontium (Sr) from seawater, wastewaters, or concentrated brines produced in the desalination process [1,2,3]
The Kd value indicating the affinity of the binding sites of the manganese nodule was higher than that of the ammonium acetate-treated zeolite (Table 1). These results suggest that the manganese nodule has the higher affinity for K sorption than the ammonium acetate-treated zeolite, but there may be less binding sites available for K sorption on the manganese nodule than the ammonium acetate-treated zeolite
The Kfor sorption characteristics with threezeolite adsorbents, natural zeolite, ammonium was greater the ammonium acetate-treated than the natural zeolite (Figure 7);acetate-treated zeolite, and manganese nodule, were studied and compared to theofpohowever, the natural zeolite tends to maintain its K sorption capacity up to threesee times tential use of manganese nodule as an alternative
Summary
The adsorption process has been widely applied to recover valuable elements, such as lithium (Li), potassium (K), uranium (U), and strontium (Sr) from seawater, wastewaters, or concentrated brines produced in the desalination process [1,2,3]. Due to the vast amount of seawater, the presence of elements at very low concentrations in seawater can provide useful amount of elements [2]. Previous studies tried to recover K from seawater, both synthetic seawater and real seawater, at a laboratory scale [4,5]. Different methods, such as precipitation and extraction [6,7], membrane separation [5], and adsorption on sorbents [1,4] have been used to recover K. K-selective adsorbents have been synthesized to enhance the K recovery from seawater [4,8]
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