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

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. [Display omitted] • Nodules contained high levels of impurities, especially in their upper half. • Each nodule evokes upward flow associated with a vortex in the solution. • Due to the vortex, slime particles are taken into the upper part of the nodule. • Inclusion of the particles promotes 3D growth and subsequent irregular deposition. [ABSTRACT FROM AUTHOR]