Removal of Cu(II), Co(II) and Cd(II) from water solutions by layered-double hydroxides with different [Mg(II)]/[Fe(III)] molar ratios

This work presents a study of sorption of heavy metals (HMs)—Cu(II), Co(II) and Cd(II)—from water media by carbonated and calcined forms of layered-double hydroxides (LDH) with various Mg(II)/Fe(III) molar ratios, which are obtained by precipitation. It is ascertained that the maximum sorption (99.9%) of the HM ions stated is observed with the use of calcined forms of LDH at $$\mathrm{pH}\,{>}\,2.8$$ (pH after sorption $$\ge 8.3$$ ). Such an increase in the pH of the aqueous suspension causes sorption of the HM ions by the mechanism of their precipitation in the form of hydroxides or hydroxocarbonates (for Cu(II)). Sufficiently high degrees of sorption of HMs, even at low pH of the aqueous medium, are apparently caused not only by the precipitation of their hydroxide forms, but also due to the complex formation with ferrinol groups of brucite sorbent layers. An increase in the Mg/Fe ratio from 2 to 4 and a corresponding decrease in the positive charge of the layers, which determines the size of the interlayer space in the LDH, have virtually no effect on the degree of extraction of HMs. The presented results suggest that the use of the studied-LDH in practice might be promising.