Selective recovery of nickel from obsolete mobile phone PCBs

Abstract

In the present investigation, the selective recovery of nickel from a leach solution of delaminated metal clads from obsolete mobile phone PCBs using the industrial reagent ACORGA M5640 has been studied. As a first step, copper is selectively separated from the mixed metal leach liquor by solvent extraction at pH 2, to leave a nickel-rich raffinate solution. A second stage solvent extraction process conducted at pH 8 then permits recovery of the nickel. Small quantities of zinc and cadmium are also co-extracted. In this study, the conditions for most suitable nickel extraction and stripping have been explored. Results indicate that quantitative extraction of nickel (99.7%) can be achieved using a 1:5 organic (10 vol% extractant in kerosene) to aqueous (pH 8) phase ratio in 60 min. The nickel in the organic phase is readily stripped from the extractant, with more than 95% recovered, along with low levels of zinc (1.7 mg/L) and cadmium (0.6 mg/L), following a 0.5 M hydrochloric acid or 1 M nitric acid strip step. Cyclic usage of the extractant organic layer revealed that its effectiveness to extraction has remained equivalent to the first cycle. Finally, the separation of trace elements such as lead, tin and cadmium from the raffinate of stage 2 solvent extraction is also studied by cementation with zinc powder. The study reveals that the removal of these elements and the generation of pure zinc solution can be obtained by adding 300% excess zinc powder (74 μm) at 50 °C with 500 rpm stirring speed in 60 min. The separation of copper in stage 1, nickel from copper-free aqueous solution in stage 2 and other minor elements from the raffinate of stage 2 solvent extraction ensures the proposed process is sustainable and avoids complexity in the sequential metal recovery processes.