585 4. OPTIMIZATION OF FREE CYANIDE DESTRUCTION IN TAILINGS WITH CARO’S ACID AT ANTAPITE PROCESSING PLANT CIP cyanidation tailings at the Antapite processing plant, containing 40 - 42% solids and an average of 250 ppm of free cyanide, are treated with Caro’s Acid directly in the discharge line to destroy free cyanide before disposal in the tailings dam. Since the beginning of operations at Antapite, effluent discharge has been maintained at “zero,” due to the scarcity of water resources in the area. Therefore, it is necessary to recirculate clarified solution from the tailings dam, free of cyanide, to sustain continuous operations at the processing plant in a sustainable manner. The characteristics of the recirculated solution (“industrial water”), after treatment with Caro’s Acid and reused in the processing plant between 2002 and 2006, are shown in Table 1. Table 1 - Characteristics of Caro’s Acid Treatment (2002–2006) Total Cyanide (ppm) Caro’s Acid Molar Ratio (H2SO4 /H2O2) Consumption (Kg Ácido de Caro / Kg CN-) Cost of Caro’s Acid ($/t) Caro’s Acid Destruction Efficiency (%) 15.2 1.35 10.5 0.93 93.7 As observed in Table 1, the characteristics of industrial water offered opportunities for improvement in the following areas: SAFETY AND HEALTH: The use of industrial water in the processing plant presented high levels of total cyanide, posing risks of dissociation of weakly and strongly complexed cyanides into free cyanide and hydrogen cyanide, affecting the safety and health of personnel in direct contact with the industrial water during operations. ENVIRONMENT: These levels of total cyanide in industrial water represented risks to local flora and fauna, migratory birds, and other species in the tailings dam water surface and in the two 600m3 storage tanks supplying the plant, due to potential overflows or contingencies. COMMUNITY RELATIONS: It is important to maintain trust, transparency, and harmony with surrounding communities. Although the tailings dam operates with zero effluent discharge to the environment, it is necessary to provide information to the population regarding responsible water management and compliance with national legislation. In the unlikely event of seepage, contamination of downstream groundwater bodies would be minimal, since the solution complies with permissible cyanide limits.
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