Regarding the efficiency of the Caro’s Acid process in free cyanide destruction, it is necessary to establish a comparison parameter based on treatment cost relative to ore throughput. In 2002, the average cost of cyanide destruction with Caro’s Acid was $1.22/t of ore treated, while in 2006 it was $0.93/t. Cyanide destruction efficiency was 93.7%, and after optimization, the cost decreased to 0,30$/t, with efficiency reaching 99.9% Figure 3 - Caro’s Acid cost ($/t) Vs Cyanide destruction efficiency (%). One important parameter to highlight is the comparison between the cost of cyanidation in ore treatment for gold and silver recovery and the cost of cyanide destruction with Caro’s Acid. Figure 4 shows that during 2002 and 2003, cyanide destruction costs with Caro’s Acid were 1.22 and 0.87 $/t of ore treated, while cyanidation process costs were 0.79 $/t. Thus, in this period, destruction costs were higher than ore treatment costs. In subsequent years, the trend reversed as a result of process optimization. Figure 4 - NaCN cost ($/t) Vs Caro’s Acid ($/t). Cyanide destruction costs relative to total cyanide in the tailings dam solution recirculated to the plant show that in 2002, the average cost of Caro’s Acid was 1.22$/t of ore treated, with average total cyanide in the recirculated solution at 18ppm. By 2006, the average cost was $0.93/t, 92.5 92.9 93.3 95.0 94.6 97.5 99.3 99.9 99.9 1.22 0.87 0.70 0.84 1.02 0.91 0.61 0.42 0.30 0 0.2 0.4 0.6 0.8 1 1.2 1.4 88 90 92 94 96 98 100 102 2002 2003 2004 2005 2006 2007 2008 2009 2010 Caro’s Acid ($/t) Destruction efficiency of NaCN % Destruction efficiency of NaCN % Caro’s Acid ($/t) 0.79 0.79 0.87 1.02 1.87 2.06 1.55 1.43 1.31 1.22 0.87 0.70 0.84 1.02 0.91 0.61 0.42 0.30 0 0.5 1 1.5 2 2.5 2002 2003 2004 2005 2006 2007 2008 2009 2010 ( $ /t ) NaCN ($ / t ) Caro’s Acid ( $ / t )
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