Abstract

Ni-Fe pyroaurite-type hydroxychlorides were prepared by aerial oxidation of Ni(II)-Fe(II) hydroxides precipitated in aqueous solution with various P = Fe/Ni ratios. When P< or =1/3, Ni(II)-Fe(II)-Fe(III) hydroxychlorides characterized by a specific Fe(III)/[Fe(II)+Ni(II)] ratio of 1/3, corresponding to the idealized formula of Ni II (sub 3-x) Fe IIx Fe III (OH) 8 Cl.nH 2 O) (with 0< or =x< or =3), were obtained at the end of the first stage of oxidation. In a second reaction stage, these hydroxychlorides oxidize with deprotonation of hydroxyl ions into O (super 2-) ions, i.e. the remaining Fe II (OH) 2 groups are transformed into Fe III OOH groups. Along with the Ni(II)-Fe(III) hydroxychloride which contains a part of the Fe III OOH groups a second phase is obtained. It is an amorphous Fe(III) or Ni(II)-Fe(III) oxyhydroxide when 1/3<P< or =3/2, and a ferric oxyhydroxide identified as gamma -FeOOH (lepidocrocite) when P>3/2. On the other side of the domain, when P<1/3, the Fe(III)/[Fe(II)+Ni(II)] ratio cannot reach the specific value of 1/3; this gives rise to a pyroaurite-type Ni(II)-Fe(III) hydroxychloride with a lower chloride content, that is with an average composition of Ni II (sub 3+gamma ) Fe III (sub 1-gamma ) (OH) 8 Cl (sub 1-gamma ) .nH 2 O where gamma = {[4/(1+P)]-3}, down to minimum Fe(III) and Cl contents corresponding to gamma = 1/3 (P = 1/5). The in situ mechanisms of oxidation of Ni(II)-Fe(II) hydroxides into Ni(II)-Fe(II)-Fe(III) hydroxychlorides are discussed.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.