Gold Fractal Growth during Its Recycling from Waste Printed Circuit Boards by Slurry Electrolysis

Waste printed circuit boards, especially from mobile phones, possess an extremely higher resource value. The key to current electronic waste disposal is to efficiently recycle valuableand precious metals under the condition of ensuring its environ-mental friendliness. Slurry electrolysis has been identified to be aneffective method to recover valuable and precious metals fromwaste printed circuit boards. Meanwhile, copper fractal growthcauses higher energy consumption during this process and has beenextensively investigated. However, the mechanism of precious metalfractal growth, especially gold, is still unclear. In this work, thefactors that impact two-dimensional gold dendritic patterns arediscussed in detail. These results indicate that increasing the appliedvoltage and chloroauric acid and hydrochloric acid concentrationscould increase the probability of particle movement, which would enter the inner growing point due to the reduction of the tipshielding effect, further resulting in an increase in the fractal dimension. Additives, trisodium citrate and poly(vinylpyrrolidone)(PVP), can inhibit fractal growth to a certain extent by varying surface chemical properties. The minimum fractal dimension is 1.742under the conditions of 0.12 mol/L chloroauric acid, 0.25 mol/L hydrochloric acid, 80 mg/L PVP, and 25 V. The diffusion-limitedaggregation simulation result is consistent with the gold fractal growth experiment under the condition that the electrocrystallizationtime is significantly less than that of diffusion. The Materials Studio simulation result indicates that additives, PVP in particular,which provide particles with unique hydrogen bonding and steric hindrance, can promote the growth of gold atoms on crystal planes,especially the (111) crystal planes. Based on the results of fractal growth, the addition of 160 mg/L trisodium citrate and PVP to aslurry electrolysis recovery system of WPCB-MPs significantly increases the gold recovery rate and the current efficiency from 31.5,0.2% to 77.9, 1.7% and 66.0, 2.2%, respectively. These results are conducive to further enriching the theory and enhancing the recovery of precious metals from e-waste by slurry electrolysis

Automated summary

This study discusses in detail the factors that impact two-dimensional gold dendritic patterns, finding that increasing the applied voltage and the concentrations of chloroauric acid and hydrochloric acid can increase the probability of particle movement, leading to an increase in the fractal dimension. Additives PVP and trisodium citrate can inhibit fractal growth and improve the recovery rate and current efficiency of gold.