A Review on Alternative Reagents to Cyanide and an Economic Evaluation of a Thiosulfate Leaching Plant for Gold Extraction
Author : Vibas, Cleo Clarice A.
Major Adviser : Alcantara, Jerico Z.
Committee Members : Gatdula, Kristel M.; Bataller, Butch G.
Year : 2021
Month : January
Type : Thesis
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Various factors affecting cyanidation has been studied to understand how the dangers of cyanide use can be minimize and to understand its complexity and compare it with other methods. These factors are particle size, solids density, sodium cyanide concentration, dissolved oxygen concentration, temperature, pH and retention time. Cyanide consumption can be reduced by oxidative pretreatment and/or addition of lead nitrate. Cyanide-free alternative lixiviants such as iodine, bromine, chlorine, thiocyanate, thiourea, thiosulfate, aqua regia, α-cyclodextrin, and glycine has been studied to identify which could successfully replace cyanide. Thiosulfate leaching was proven as the most plausible alternative due to its high yield, simplicity, reagent regeneration, proven large- scale applications and it is cheaper. A 1000-ton thiosulfate leaching plant has lower capital investment (644,525,906.9 PHP) than a cyanidation plant (1,669,824,518 PHP) with the same capacity. Although cyanidation has higher annual profit with 2,649,969,803.00 PHP as compared to the 2,362,772,113.00 PHP annual profit of a thiosulfate leaching plant, the thiosulfate leaching plant is still more cost-efficient than a cyanidation plant based on their return of investment and payback period. Its return of investment is 3.66591 which is more than twice that of cyanidation with 1.58698. And it has a payback period of 0.22258 which is less than half of a cyanidation plant with 0.48851.
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