“…Therefore, such purification is recommended in order to reduce the cost of potassium ferrate. It should be noted that these recommendations refer only to the synthesis of ferrates from iron(III) nitrate and do not affect other cheaper iron compounds, in particular, chlorides, sulfates or hydroxides: (5) whose use in the economics may be more practical [12]. In addition, the use of 11 M potassium hydroxide solutions for recycling, proposed in [8], does not meet the requirements for modern technologies, in which it is recommended to use solutions with a higher KOH concentration [2, 5, 10].…”