Nickel electrowinning using a Pt catalysed hydrogen-diffusion anode. Part II: Batch tank with a sulphate bath

A batch tank of 1.6 L capacity has been designed for Ni electrowinning usin g a Pt catalysed H-2-diffusion anode and a stainless steel/Ni cathode, both of 100 cm(2) area. The anode has high stability for sulphate baths of pH 3 .5 with 35 gL(-1) H3BO3 and Ni2+ concentrations from 10 g L-1 up to saturat ion. Linear correlations between the cell voltage and current intensity are found, as expected for ohmic control of the process. Good electrowinning c onditions at room temperature are obtained for Ni2+ contents from 50 gL(-1) , using an interelectrode gap of 2 cm and regulating the solution pH by NaO H addition for periods of 30 min. Current efficiencies greater than or equa l to 93% are always found. The energy costs increase linearly with increasi ng current density from 10 to 50 mA cm(-2), with values much lower than tho se obtained using a conventional lead anode. This indicates that the Pt cat alysed H-2-diffusion anode is preferable for Ni electrowinning. The crystal s are composed of high-purity Ni and have a face-centred cubic structure. S urface analysis by SEM shows that the grain size gradually increases with i ncreasing current density, with no significant influence of the Ni2+ concen tration.