Aqueous nickel sequestration and release during structural Fe(II) hydroxide remediation: the roles of coprecipitation, reduction and substitution

摘要

Aqueous Ni2+ removal by structural Fe(II) hydroxides (SFH) under well-controlled experimental conditions was investigated in this study, and a possible mechanism for Ni2+ release from solid products was revealed. Experiments with SFH and Ni2+ showed the excellent reactivity of SFH towards aqueous Ni2+ when the molar ratio of [Fe(II)]/[OH-] was below 1 : 2. The reaction started with adsorption and precipitation of Ni2+, followed by reduction of Ni(II) and substitution of Fe(II) with the formation of Ni(II)/ Fe(III) layered double hydroxides. However, at long reaction time, Ni(II) release from Ni(OH)(2) and NixFe(1-x)(OH)(2) precipitates was observed due to the delivery of dissolved Fe2+ and Fe3+, which were determined to substitute Ni(II) by forming Fe(OH)(2), Fe(OH)(3) and Fe-III Fe-(1+2x/3)(II) ((1-x))(OH)(5). The presence of O-2 and NO3 reduced the removal efficiency of Ni2+ and promoted its release by consuming Fe(II) and promoting Fe3+ delivery. However, CO32- and PO43- might enhance the removal of Ni2+ and inhibit its release. For wastewater containing a high Ni2+ concentration, using SFH is also beneficial to Ni2+ recycling, as removed Ni(II) could be released and enriched, followed by future utilization.