Affinage electrolytique des ferronickels

Electrorefining of ferronickels is possible in a cell without diaphragm with the electrolyte CaCl₂ 5 M at 98°C.Behavior of the following impurities have been studied: Ag(I), Au(III), Bi(III), Cd(II), Co((II), Cu(I), Fe(II), Hg(II), Ni(II), Pb(II), Pd(II), Sb(III) and Sn(II).The electrochemical system Ni(II)/Ni(O)is much more reversible in this electrolyte and the only other electrochemical system which appears at the same potential is Cu(I)/Cu(O).Ferronickels of 23.2;72.2 and 94.4% in nickel have been refined in this medium without purification of the electrolyte. Nickel of a purity between 98.7 and 99.7% is obtained.In order to increase the nickel purity and for continuous operation of the method a purification of the electrolyte is necessary. Two methods are proposed: anion exchange resin and liquid—liquid extraction with tri-n-butyl phosphate (TBP).Partition coefficients and ion-exchanger capacities are given for following impurities: Fe(III), Fe(II), Co(II), Cu(II), Mn(II), Zn(II), Cr(III) and Pb(II).Percent extracted by TBP for following impurities are given: Fe(III), Fe(II), Co(II), Cu(II), Zn(II), Mn(II), Cr(III), Pb(II), Al(III), Bi(III), Sb(III) and Sn(IV).A continuous purification of the electrolyte by ion-exchange has been done in the refining of a ferronickel 94.4% in nickel. Nickel obtained is 99.74%.CaCl₂ 5 M appears to be a good electrolyte for electro-refining of nickel.