The nodulation of electrolytic copper is a critical issue in copper electrorefining due to the loss of current efficiency and impurity entrainment. A more detailed understanding of the behavior of nodulation and its growth is important for advances in industrial processes. Based on the basic behavior of nodule growth by a simplified model electrolyte, the effects of impurity elements of Ni(II) and Sb(III) ions on nodule growth were evaluated in electrolysis experiments using a nodule-mimicking protrusion preliminarily attached to the cathode and simulations of current distribution. These impurities promoted the transition of the internal microstructure type of electrodeposited copper from an unoriented dispersion to a field-oriented texture and basis reproduction (BR), resulting in a rougher surface of coarse grains. Once microscopic unevenness had formed on the protrusion, an increase in the effective surface area resulted in further current concentration at the protrusion, thereby promoting its growth. Microscopic unevenness also grew progressively in a self-promoting manner due to the local current concentration at its convexity, eventually forming irregular macroscopic deposits. A decrease in electrolyte conductivity further accelerated nodule growth by the local current concentration. Preventing the transition of the growth mode to BR is important for suppressing the rapid growth of nodules.Graphical Abstract: