Berlin green-based battery deionization-highly selective potassium recovery in seawater

As the global demand for potassium continues to increase, the potassium in natural resources is gradually insufficient. The potassium resources in the ocean are extremely rich. In this paper, a new battery deionization method (BDI) was developed to selectively recover potassium from seawater using a Fe[Fe(CN)6] (BG) battery electrode. The BG-based electrode exhibited totally different insertion behavior to the most abundant cations in seawater, with the capacity order of K+>Na+>Li+>Ca2+>Mg2+. Using the battery cell assembled with BG and activated carbon electrode, the recovery capacity of K+ arrived at 177 μmoL/g under the discharge stage of battery from 0.8 to 0 V, and no significant variation was found even in the presence of 37 times higher concentration of Na+ than that of K+. In synthetic seawater, the BG battery electrode still kept the recovery of 69.6% for K+ with the separation factor α(K+/Na+) of 141.7. Moreover, energy consumption is calculated to be 15.4 kJ/mol, 10 times lower than that of the capacitive deionization method. Meanwhile, the BG battery electrode is very stable with the adsorption amount retaining 86% over 150 cycles. The three-cell stack test in synthetic seawater proves that the current BDI device is easy to be amplified for recovering potassium from seawater. [Display omitted] •K+ recovery by Berlin green battery deionization is demonstrated.•High separation factor α(K+/Na+) of 141.7 is achieved in synthetic seawater.•The recovery of K+ in synthetic seawater arrives at near 70%.•The energy consumption of the battery system is quite low.•The recovery can be improved by increasing battery stack.