Chemical Engineering Journal 187 (2012) 217–221 Contents lists available at ScienceDirect Chemical Engineering Journal j ourna l ho mepage: www.elsevier.com/locate/cej On the optimization of sphalerite bioleaching; the inspection of intermittent irrigation, type of agglomeration, feed formulation and their interactions on the bioleaching of low-grade zinc sulfide ores Taghiyeh Saririchi, Reza Roosta Azad ∗ , Daryush Arabian, Asghar Molaie, Fahimeh Nemati Department of Petroleum and Chemical Engineering, Sharif University of Technology, Iran a r t i c l e i n f o Article history: Received 6 June 2010 Received in revised form 5 October 2010 Accepted 7 October 2010 Keywords: Acidithiobacillus ferrooxidans Bioleaching Low-grade ores Sulfide Taguchi method Zinc a b s t r a c t In this study, we have investigated the bioleaching potential of a native strain of Acidithiobacillus ferroox- idans isolated from zinc and lead sulfide mines under varied ambient conditions of growth and substrate consumption. The effects of intermittent irrigation, type of agglomeration, feed formulation in terms of acid, enriched salt solution, initial number of microorganism, and their interactions on the bioleaching of low-grade zinc sulfide ores (containing 5.78% zinc) on growth and biooxidation efficiency of the bacteria have been evaluated. Bioleaching capacities of the isolate were optimized by the utilization the Taguchi method (e-qualitic-4) for design of experiments. As a result, eight column bioreactors with 5.7 kg ore (100% <12 mm) capacity were fabricated. Through the analysis, continuous inoculation of the ores with the solution of A. ferrooxidans type and spraying a bacterial-rich solution into the agglomerator were found to be the most significant factors, whereas intermittent irrigation and interactions of parameters have less effect within the ranges investigated. The extraction of zinc was obtained under the optimal conditions more than 70% in 80 days, which is noticeable to compare with conventional bioleaching. © 2012 Published by Elsevier B.V. 1. Introduction The remaining minerals resources of the world are gradually becoming more challenging to exploit by the conventional process- ing technologies [1]. Also, as high grade surface mineral deposits are worked out, the traditional pyrometallurgy-based metal recovery processes become less economically viable and mining companies have been required to find new processes to work the remaining lower grade deposits. The economic extraction of metals from low- grade ores requires low-cost processing methods such as dump and heap leaching [2]. Apparently, microbe-based processes have economic advantages in the extraction of metals from many low- grade sulfide deposits [3]. The reactions involved in the biological oxidation of zinc sulfide are [4,5]: ZnS(s) + 2Fe 3+ → Zn 2+ + 2Fe 2+ + S 0 (s) (1) 4Fe 2+ + O 2 + 4H + bacteria -→ 4Fe 3+ + H 2 O (2) S 0 (s) + 1.5O 2 + H 2 O bacteria -→ H 2 SO 4 (3) ∗ Corresponding author. Tel.: +98 21 66005210; fax: +98 21 66005310. E-mail address: roosta@sharif.edu (R.R. Azad). There are a number of operating parameters controlling bioleaching process, which are required to be maintained within a certain range in operation condition whereby the activity of bac- teria with the resultant of maximum extraction of metals can be optimized. In this study we have evaluated the effect of intermittent irrigation, type of agglomeration, feed formulation in terms of acid, microorganism and enriched salt solution, and their interactions, on the growth and activity of indigenous bacterium that has been isolated from Koshk Zn/Pb sulfide mine, central of Iran. Taguchi method has been utilized for design of optimization experiments under eight equal size column bioreactors. 2. Materials and methods 2.1. Ore Ore sample supplied by Kooshk Bafgh mine (Yazd province, Iran) was used in this study. XRF (X-ray Fluorescence) and XRD (X-ray diffraction) tests were employed for the mineralogical identifica- tion of the ore. The mineral ore used in this study mainly consisted of Pyrite (FeS 2 ), Quartz (SiO 2 ), Gypsum (CaSO 4 ), Calcite (CaCO 3 ), Dolomite ((Ca,Mg)(CO 3 ) 2 ), and Mica-Illite (KAlSi 2 O 5 (OH) 4 ). The XRF analysis of sample is shown in Table 1. 1385-8947/$ – see front matter © 2012 Published by Elsevier B.V. doi:10.1016/j.cej.2010.10.013