582 OPTIMIZATION OF THE CARO’S ACID PROCESS FOR CYANIDE DESTRUCTION IN CIP CYANIDATION TAILINGS AS A CONTRIBUTION TO THE QUALITY OF INDUSTRIAL REUSE WATER AT THE ANTAPITE PROCESSING PLANT J. Marquina Metallurgist Consultant ABSTRACT This Technical Report presents the results obtained during the optimization of cyanide destruction in tailings pulp from the CIP cyanidation process at the Antapite processing plant, which operates at 600 metric tons per day (TPD). As part of the project engineering, Compañía de Minas Buenaventura S.A.A. built a zero-discharge tailings dam, functioning as a natural sedimentation basin for metallurgical tailings previously treated. This facility enables the recovery of solution as industrial water, free of cyanide, to be reused in the processing plant. From the evaluation of various cyanide destruction processes carried out by the company, the most effective method for reducing an average of 250 ppm of cyanide in tailings was the Caro’s Acid Process (H2SO5 ).Its advantages include high destructive efficiency, fast reaction kinetics, strongly exothermic chemical reaction with rapid mixing, no need for catalytic agents, and specific applicability to tailings pulp. Optimization tests of the Caro’s Acid Process were conducted between 2006 and 2010, focusing on the molar ratio H2SO4 /H2O2, ranging from 1.5 to 3.0, with the objective of achieving cyanide concentrations in reuse water that comply with all parameters established by current mining, environmental, and social legislation. At the end of the optimization, a significant reduction in total cyanide levels was achieved in reuse water for the processing plant, from 15.2 ppm to 0.14 ppm, with a molar ratio H2SO4/H2O2 between 1.3 and 1.4. The efficiency of cyanide destruction increased from 93.7% to 99.9%, consumption of Caro’s Acid per kilogram of cyanide decreased from 10.5 to 2.2, and treatment costs were reduced from $0.93/t to $0.30/t. This represents a viable alternative for gold and silver beneficiation plants using CIP – CIL processes, with zero-discharge tailings facilities and scarce or limited water resources, in a sustainable manner. KEYWORDS Caro’s Acid, Free Cyanide, Total Cyanide, Molar Ratio, Maximum Permissible Limits, Tailings Pulp. 1. BACKGROUND Cyanidation–adsorption tailings, consisting of pulp with 40% solids and an average of 250 ppm of free cyanide, undergo natural sedimentation in which solids and liquids separate, forming a clarified solution surface. In addition, the tailings dam serves as a containment reservoir for rainwater, storing sufficient volume to ensure operational continuity, while maintaining zero discharge. At the start of operations at Antapite in 2001, free cyanide in tailings pulp from the processing plant was treated using hydrogen peroxide with copper sulfate catalyst. Cyanide destruction performance reduced concentrations from 250 ppm to 120 ppm, with operating costs of $1.51/t. of ore treated for hydrogen peroxide and 0.23$/t. for copper sulfate. The total cost was therefore 1.74$/t., demonstrating the process to be inefficient and costly. Under these conditions of high cyanide content, reuse of the solution in the processing plant was impossible due to its high toxicity.
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