TITLE:
Recovery of Gold and Silver and Removal of Copper, Zinc and Lead Ions in Pregnant and Barren Cyanide Solutions
AUTHORS:
Gabriela Figueroa, Jesus L. Valenzuela, Jose R. Parga, Victor Vazquez, Alejandro Valenzuela
KEYWORDS:
Electrochemical Process, Precipitation Process, Gold and Silver Cyanides
JOURNAL NAME:
Materials Sciences and Applications,
Vol.6 No.2,
February
12,
2015
ABSTRACT: Over the past decade the concern about toxic metals in freshwater has increased. Environmental
laws such as the Clean Water Act have forced industries that produce metal containing wastewater
to treat their wastewater prior to discharge. The purpose of this study was to investigate the use of
a novel method for the minimization of heavy metals in the wastewater from the mining industry.
A very promising electrochemical treatment technique that does not require chemical additions is
electrocoagulation (EC) and sulphide precipitation. The present study has been done for the recovery
of gold and silver contained in pregnant solution from the cyanidation process using the
electrocoagulation technology with iron electrodes; that is a developed alternative technology for
the Merril-Crowe process. The average gold and silver content in pregnant solution was 4.27 and
283 ppm respectively and the recoveries were 92% for gold and 95% for silver, with optimum
operating parameters of pH 10, residence time of 20 minutes and addition of sodium chloride of 4
gr/L. The results of precipitation process show that the elimination of lead, zinc, cooper and iron
ions from the barren solution was successful, with optimum operating parameters of pH 3 and
residence time of 15 minutes, and the recoveries were 99% of these ions. Finally the characterization
of the solid products of gold and silver formed during the EC process with Scanning Electronic
Microscope was performed. Results suggest that magnetite particles and amorphous iron oxyhydroxides
(lepidocrocite) were present.