Scale-Up and Operating Factors for Electrolytic Silver Recovery from Effluents of Artisanal Used-Gold-Jewelry Smelting Plants in the Philippines

Abstract

Background. The Marilao, Meycauayan and Obando river system (MMORS), in the Philippines is home to many precious metals refineries, where local artisanal gold smelting industries use silver to draw gold out of used jewelry. Copper recovers the silver. The copper-rich wastewater contributes to local pollution. Alternative methods for silver recovery include electrolytic recovery: removal of silver ions from solution, and conversion of the ions into metallic silver. Objectives. Explore operation and scale-up for the electrolytic recovery of silver for small-to-medium-scale used gold smelting plants. Methods. Effects of current and time were investigated in a laboratory scale, magnetically-stirred electrolysis reactor, using a sintered platinum anode and a stainless steel cathode. Silver recovery (the removal of silver ions from solution) was evaluated at different levels of constant operating current, and data was used to determine charge dose as the scale up and operating factor. Charge dose was then used to obtain the operating conditions on a pilot scale (100 L) system. A preliminary pilot test assessed silver recovery performance. Results. Higher silver removal rates were noted at higher operating currents. Electrodeposition at 9 amperes showed 98.7% silver recovery after 30 mins. The charge dose for silver electrodeposition was 1.23 coulombs/mg silver ions removed, while the average electrolysis energy requirement was about 0.59 kilowatt hours/kg of silver removed. Conclusions. Preliminary comparisons on a 100-liter scale, showed the electrolytic process had a higher silver removal (~ 90%) compared to copper displacement (~ 65%). Results are useful for the process design of a complete field test system.