Abstract
The Merrill-Crowe or Cementation process is used for concentration and purification of gold and silver from cyanide solutions. Among other available options for recovery of precious metals from cyanide solutions, Electrocoagulation (EC) is a very promising electrochemical technique for the recovery of this precious metals. In this work first, an introduction to the fundamentals of the Merrill Crowe and EC process are given, then Kinetic aspects conditions and results of the both process, for the removal of gold and silver from cyanide solutions are presented, and finally the characterization of the solid products formed during the EC process with X-ray Diffraction and SEM are shown. Results suggests that The cementation of both gold and silver by suspended zinc particles conforms to well-behaved fist order kinetics and for the EC process the results show that is an excellent option to remove Au and Ag from cyanide solution by using iron electrodes. Finally, 99.5% of gold and silver were removed in the experimental EC reactor, and it was achieved in 5 minutes or less.
Highlights
Cyanide leaching processes have been used by the mining industry for over 150 years in the extraction of noble metals, the popularity of cyanidation is based mostly on the simplicity of the process
Results suggests that The cementation of both gold and silver by suspended zinc particles conforms to well-behaved fist order kinetics and for the EC process the results show that is an excellent option to remove Au and Ag from cyanide solution by using iron electrodes
The equilibrium concentration profiles, the results were found to conform to the first-order rate process for over 99% removal as shown in Figure 3 (Au/Zn(CN)– system) and (Ag/Zn(CN)– system). From these data it is evident that the cementation of both gold and silver by zinc conforms to well-behaved fist order kinetics
Summary
Cyanide leaching processes have been used by the mining industry for over 150 years in the extraction of noble metals, the popularity of cyanidation is based mostly on the simplicity of the process. The efficiency of the reaction is significantly improved by removing dissolved oxygen from the system prior to zinc addition, using a vacuum deaeration technique. This reaction of cementation is sensitive to suspend solids in the leach solution and requires solution clarification before cementation. Process selection depends on the specific conditions for particular operation and the facilities already available Another new process is the Electrocoagulation (EC) technology and has recently been reviewed as an alternative for gold and silver recovery from alkaline cyanide solutions [3]. Literature reviewing showed that the potential of EC as an alternative to traditional treatment recovery of precious metals (silver and gold cyanide) has not yet been exploited
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