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Other Leaching Processes
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2017
Cyanidation has become the dominant process for recovery of gold and silver from their ores. It has also been successfully applied to the processing of sulfidic resources of copper. Currently, the ten largest free world gold-producing mines (all in South Africa) use the cyanidation process. The annual rate of gold production from the mines is estimated at about 368.6 ton per year. Cyanidation is now synonymously attached with gold metallurgy. The popularity of the process is based mostly on its simplicity. At ambient conditions, a dilute solution of sodium or potassium cyanide (about 1 g/1) is capable of complexing finely disseminated gold paticles (down to the size of a few microns) even at very low concentrations (a few parts per million), and dissolve it as aurcyanide complex. Equally efficiently, ore is able to precipitate gold out of the dilute aqueous solution using a zinc dust cementation process, commonly known as the Merrill-Crowe process.
Hydrometallurgical Waste Production and Utilization
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
Once the gold has been dissolved in the cyanide, it is then extracted from the pregnant leach solution. The common processes for recovery of gold from the leach solution include carbon adsorption, ion exchange, Merrill Crowe and EW. Traditionally, the Merrill Crowe process was used to precipitate gold from a cyanide solution by using zinc dust. Nowadays, the use of AC has proven to be very popular and successful. Activated carbon has a remarkable affinity for gold and, under the right conditions, can become loaded with gold up to a level of more than 30% of its mass (typically 1000–4000 g/ton) (Marsden and House, 2006). The major advantage of carbon-in-pulp recovery over Merrill–Crowe recovery is the elimination of the solid–liquid separation unit step. After the loading step, the loaded carbon is removed from the slurry, and the adsorbed gold is stripped out at high temperature and pressure using sodium hydroxide and cyanide solutions to form a high-value electrolyte solution. Gold bullion is then recovered from the electrolyte by EW. In recent years, some operations have started replacing carbon with resin as the phase that gold is adsorbed on. The process used in resin absorption is similar to carbon adsorption, but synthetic spherical resin particles replace the grains of AC (Fleming and Cromberge, 1984; Kotze et al., 1993; Green et al., 2002; Pilśniak-Rabiega and Trochimczuk, 2014).
Converting Minerals to Metals
Published in Karlheinz Spitz, John Trudinger, Mining and the Environment, 2019
Karlheinz Spitz, John Trudinger
In general, there are two basic types of cyanidation operations: tank leaching and heap leaching. Tank leaching involves one of three distinct types of operations, Carbon-in-Pulp (CIP), Carbon-in- Leach (CIL), and the Merrill Crowe Process. In CIP operations, the ore pulp is leached in an initial set of tanks with carbon adsorption occurring in a second set of tanks. In CIL operations, leaching and carbon recovery of the gold values occur simultaneously in the same set of tanks. The Merrill Crowe process uses zinc to remove the gold from solution and is generally used for ores that have high silver to gold ratios.
Opportunities for an en-route to polymer inclusion membrane approach from conventional hydrometallurgical recycling of WPCBs: a mini-review
Published in Canadian Metallurgical Quarterly, 2022
Rohit Jha, Gautam Mishra, Munmun Agrawal, Mudila Dhanunjaya Rao, Arunabh Meshram, Kamalesh K. Singh
Since the 1890s, Merrill-Crowe Process is the commercially accepted procedure for the recovery of Au and Ag from cyanide leach solution employing Zn as the cementing agent. In the process, pregnant leach solution is passed through the shavings of Zn to precipitate out the target metal, taking the advantage of the high affinity of Zn for cyanide ions as well as the low reduction potential of Zn [54]. The major reactions that take place during the cementation of Au are shown in Eq. 2. However, impurities such as lead, arsenic, nickel, antimony and sulphur present in the leach liquor are detrimental to the cementation of gold. Besides that, too low concentration of cyanide in the solution might lead to the formation of a passive layer of Zn(OH)2 over the surface of Zn, which hinders the further reaction [11].