From mesophilic to moderate thermophilic populations in an industrial heap bioleaching process Pamela Soto 1 , Mauricio Acosta 1 , Pierina Tapia 1 , Yasna Contador 1 , Antonio Velásquez 3 , Cristian Espoz 3 , Carlos Pinilla 3 , Pedro Galleguillos 2,1 and Cecilia Demergasso 1,2 (*) 1. Centro de Investigación Científica y Tecnológica para la Minería (CICITEM), Antofagasta, Chile. 2. Centro de Biotecnología “Profesor Alberto Ruiz”, Universidad Católica del Norte, Antofagasta, Chile. 3. Superintendencia de Metalurgia - Sulfuros, BHP-Billiton, Minera Escondida Ltda. Email: pasoto@ucn.cl, macostag@ucn.cl, pitapia@ucn.cl, ycontador@ucn.cl, antonio.aa.velasquez@bhpbilliton.com, Cristian.PV.Espoz@bhpbilliton.com, Carlos.CA.Pinilla@bhpbilliton.com, cdemerga@ucn.cl Keywords: bioleaching; mesophilic and moderate thermophilic communities; copper sulfide ore; data analysis Abstract. A comprehensive monitoring program by culturing and molecular techniques, physicochemical analysis plus the record of the operational conditions have been performed at an industrial bioleaching process for run-of-mine (ROM) material at Escondida mine since 2006. The data collected have been systematized in a data base to allow further analysis for advancing the understanding of commercial bioheap applications. The microbial succession during a heap bioleaching cycle has been formerly described by means of the analysis of the data obtained from the first lift of the industrial process. Data visualization techniques were used to analyze the information and to find patterns in the data. When only the first and second floor of the heap was operative, the mesophile population, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, was predominant in the microbial community. After the start of the third lift operation, a relevant change in the abundance of the moderate thermophile population was evident. Leptospirillum ferriphilum (optimum temperature 35-39°C) and Sulfobacillus thermosulfidooxidans (optimum temperature 45-50°C) became the most abundant microorganism. In addition, the specific iron oxidation activity showed by the moderate thermophilic dominated community is higher than the mesophilic dominated one. A patched distribution of Sulfolobus allowed us to infer the temporal occurrence of small niches with temperature over 50°C inside the heap. The temperature turned out to be a key factor driving the dynamic of the microbial community mainly after the start of the third lift. That shift had a relevant impact on the metallurgical performance of the industrial process. Introduction The microbial succession during a heap bioleaching cycle of low grade copper sulfides has been described [1-3] by means of the analysis of the data obtained from the first lift of the industrial process at Escondida mine. The second and the third lifts of the heap were set up during 2008 and 2010, respectively. It is known that the temperature inside the heap is affected by the heap height as well as by the irrigation and aeration rates and feed solution conditions, and by the concentration of the sulfidic minerals because of exothermic oxidation reactions among other factors [4]. However, commercial heap leach operations is mainly used to leach low grade ores, resulting in low mineral concentration per unit volume heap and hence low heat generation rates. In addition, in those Run of Mine (ROM) processes a poor distribution of solution and air, and the occlusion of mineral in Advanced Materials Research Vol. 825 (2013) pp 376-379 Online available since 2013/Oct/07 at www.scientific.net © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.825.376 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 146.83.124.230, Universidad Católica del Norte, Antofagasta, Chile-20/12/13,14:48:14)