Mechanism of nodular growth in copper electrorefining with the inclusion of impurity particles under natural convection

Abstract

Nodular growth behavior with the inclusion of impurity particles in copper electrorefining was investigated herein by quantitative analyses of impurity elements inside nodules, observations of crystal structures, and numerical simulations of natural convection based on the tertiary current distribution. Impurity contents were higher in the upper half of the nodule than in either the lower half or electrolytic copper with non-nodulous growth. Impurity particles, such as suspended slime, were considered to be preferentially taken into the upper part of nodules due to frequent collisions with the upper part as they circulated along the convection vortex that emerged above the nodule. The inclusion of impurity particles changed the electrodeposition morphology and growth direction, and eventually produced granular irregularities and buds of new nodules on the upper surface of the initial nodule.