CEMENTATION OF SILVER FROM SYNTHETIC LEACH SOLUTIONS OF WASTE OF
PRINTED CIRCUIT BOARDS (WPCB)
E. Y. Yazici
Hydromet B&PM Research Group, Dept. of Mining Eng., Karadeniz Technical University
Trabzon, Turkey ( eyazici@ktu.edu.tr
, +90462 377 3683)
A. D. Bas
Dept. of Mining, Metallurgical and Materials Engineering, Laval University,
Quebec City, Canada ( ahmet-deniz.bas.1@ulaval.ca
)
* H. Deveci ( Corresponding author )
Hydromet B&PM Research Group, Dept. of Mining Eng., Karadeniz Technical University
Trabzon, Turkey ( hdeveci@ktu.edu.tr
, +90462 3773681)
ABSTRACT
The leach solutions of waste of printed circuit boards (WPCB) may contain a wide range of base and precious metals with different concentrations due to heterogeneity of these wastes in composition.
Therefore, selection of a suitable metal recovery method is of practical importance for downstream processing of pregnant leach solutions of WPCB. Sulphuric acid leaching of WPCB in the presence of a suitable oxidant is capable of dissolving base metals as well as precious metals such as silver. In this study, cementation of silver from sulphuric acid leach solutions of WPCB using metallic copper, aluminum and zinc was studied. The WPCB sample was assayed to have a silver content of 694 g/t. A synthetic leach solution containing 20 mg/L Ag in sulphuric acid solution (0.51 M H
2
SO
4
) was prepared based on the silver concentration in pregnant leach solutions of oxidative sulphuric acid leaching tests. Total sulphate concentration ([SO
4
2]
T
) was kept constant using sodium sulphate at 1 M. Metallic powders of copper (-850
+600 µm), aluminum (-425 +45 µm) and zinc (-45 µm) were used in the cementation tests. The effects of metal type (Cu, Al or Zn), dosage of metal powders (above the stoichiometric ratio by up to 2000-fold) and temperature (20-80°C) on the rate and extent of silver extraction from the solution was investigated. The effect of presence of copper on the cementation performance was also tested. Under suitable conditions high silver recoveries (>90%) was achieved using metallic copper and zinc while aluminum yielded the lowest silver recovery (i.e. 40% Ag). The kinetics of cementation by zinc was comparatively higher than that of other metals. Increasing the temperature was observed to significantly enhance both the rate and extent of silver cementation. SEM-EDS studies were performed to characterise the metallic powders after cementation.
KEYWORDS
Waste electrical and electronic equipment (WEEE), Waste of printed circuit boards (WPCB), Cementation,
Silver, Precipitation, Metal recovery