Study of Metal Leaching from Printed Circuit Boards by Improved Electrochemical Hydrochlorination Technique Using Alternating Current

Abstract

This paper presents the results of the leaching of metals from computer PCBs by electrochemical hydrochlorination using alternating current (AC) with an industrial frequency (50 Hz). Leaching was carried out with a disintegrator-crushed computer motherboard with a particle size (d) of <90 μm. In the course of the research, the leaching efficiency of metals including Fe, Sn, Mn, Al, Cu, Zn, Pb, Ni, Ti, Sb, Cr, Co and V was evaluated depending on process parameters, such as AC density, experiment duration, hydrochloric acid concentration in the electrolyte solution, solid/liquid ratio, electrolyte temperature, and the loading option of raw material (loading option 1 involving loading into the electrolyte solution, and loading option 2 involving loading into the filter containers attached to electrodes). The research results showed that AC superimposition significantly intensifies the leaching of metals. It was established that the complete leaching of metals including Al, Mn, Sn, Ti and Zn, under experimental conditions (loading option 2, CHCl = 6 mol·L−1, i = 0.80 A·cm−2, S/L = 8.6 g·L−1), is reached after 1.5 h, and that of Cu and Ni is reached after 2 h from the beginning of the experiment. At the same time, the degree of leaching of other metals after 2 h is Co-78.8%, Cr-84.4%, Sb-91.7%, Fe-98.9%, V-98.1% and Pb-5.1%. The paper also reports the results on the leaching of all abovementioned metals, as well as Ag and Pd, with disintegrator-crushed mixed computer PCBs with d < 90 μm and loading option 1.

Economic Aspects of Mechanical Pre-Treatment’s Role in Precious Metals Recovery from Electronic Waste

“…According to our previous research [49,50] using a pre-treatment of mechanical disintegration of the PCB, and using for the valuable metals extraction fractions with its highest concentrations-> 90, 90-180 and 180-350 µm particles size. The fractions, fractions content to whole PCB (Raw PCBs) and metal content in wt.% are given by fractions and fraction part from initial PCB amount in the Table 1.…”

“…For the self-cost estimation of the innovative approach, PCB complex pre-treatment, which includes selective disintegration [49] and electrochemical metal leaching-electrohydro-chlorination (alternating current action in hydrochloric acid electrolytes) [50,51], was used, as it was previously approved and described in detail in previous studies [49][50][51]. PCBs were subjected to disintegration once as raw materials.…”

“…was used, as it was previously approved and described in detail in previous studies [49][50][51]. PCBs were subjected to disintegration once as raw materials.…”

“…Subsequently, particles larger than 2.8 mm were subjected to repeated milling and designated as X1(>2.8) + X2 (see Figure 7). was used, as it was previously approved and described in detail in previous studies [49][50][51]. PCBs were subjected to disintegration once as raw materials.…”

“…To establish metal content, the chemical treatment (leaching) of three representative samples (0.500 g each) was carried out. The electrochemical hydrochlorination was carried out according to developed technology, where active chlorine is generated in situ during the alternate current electrolysis [49,50]. ICP-OES was used for the quantitative determination of metal content in electrolyte solutions obtained as a result of electrochemical leaching.…”