BIOLEACHING FOR THE RECOVERY OF METALS PEMISAHAN UNSUR LOGAM DENGAN BIOLEACHING

MAKALAH ILMIAH BIOLEACHING FOR THE RECOVERY OF METALS PEMISAHAN UNSUR LOGAM DENGAN BIOLEACHING Rita Susilawati Center for Geological Resources Jl Soekarno Hatta no 444 Bandung 40254 Email: ABSTRACT A simple laboratory experiment has been conducted in order to demonstrate the ability of bacteria to leach the metal elements from insoluble ores or solid substrates. The experiment was conducted in a leaching column that was set up using 5 cc syringe that contained 1 cc of glass wool and 3.5cc of mine tailings. The basal salt was used as an inoculation media while mine tailing was used as a leaching subject and a source of bacterial leaching. Bacterial leaching was isolated using the most probable number (MPN) technique. Overall, the results of the experiment showed the capability of bioleaching process to recover metals from the mine tailings. Keywords: bacteria, bioleaching, metals SARI Kemampuan bakteri untuk memisahkan unsur-unsur logam (bioleaching) dari tailing diperlihatkan melalui eksperimen sederhana yang dilakukan di laboratorium. Eksperimen dilakukan dengan menggunakan kolom yang dibuat dari syringe berukuran 5cc yang telah diisi oleh 1cc benang kaca dan 3.5cc tailing. Tailing digunakan sebagai objek pemisahan dan juga sumber dari bakteri peluruh logam, sementara garam basal digunakan sebagai media untuk merangsang pertumbuhan bakteri tersebut. Isolasi bakteri pemisah logam yang terkandung dalam tailing dilakukan dengan menggunakan teknik MPN (Most Probable Number). Secara umum, eksperimen yang dilakukan berhasil menunjukkan kemampuan bakteri dalam memisahkan logam-logam yang terkandung dalam tailing. Kata kunci: bakteri, bioleaching, logam Buletin Sumber Daya Geologi Volume 10 Nomor 3 - 2015 211 MAKALAH ILMIAH INTRODUCTION In general, bioleaching is a process described as being the use of microorganisms to transform elements (metal) from insoluble ores or solid substrates so that the elements can be extracted from a material when water is filtered through it. In this process, the mobilization of metal ion occurred either directly by the metabolism of leaching bacteria or indirectly by ferric iron (Fe3+) that is regenerated from ferrous iron (Fe2+) by bacterial oxidation (Escobar et al., 2010). Bioleaching is mainly applied in the recovery of low grade sulfide ores and concentrates, that cannot be processed economically by conventional methods (Suzuki, 2001). Bioleaching is also used as a natural bioremediation control to heavy metal pollution in sulfuric mine waste (Southam & Beveridge, 1992). A variety of acidophilic and chemoautolithotrophic bacteria such as Thiobacillus thiooxidans (sulfur) and Thiobacillus ferrooxidans (both iron and sulfur) as well as Leptospirillum ferrooxidans facilitate metal solubilization from solid wastes or other solids (Escobar et al., 2010 ; Suzuki, 2001 ; Mielke et al., 2003). The bacteria can catalyze the oxidation of elemental sulfur or reduced sulfur compounds to sulfuric acid and obtain energy from the oxidation of elemental sulfur or reduced sulfur compound, and cause bioacidification and solubilization of heavy metals (Southam & Beveridge, 1992). Examples of metals extracted by bioleaching are Copper from Chalcopyrite, Zinc from Sphalerite, Uranium from Uraninite and Gold from gold bearing Arsenopyrite. Using simple laboratory experiment, the paper aims to demonstrate the capability of bioleaching process to recover metal ions from mine tailings. The paper also discusses several key factors that may need to be considered for optimizing the recovery of metals through bioleaching. METHODS Material In this experiment, mine tailings was used as a leaching subject and a source of bacterial leaching. Mine tailings sample was provided by Geomicrobiology Lab at the School of Earth Sciences, University of Queensland, Australia and no information provided about the source location of the tailing. The basal salt was used as an inoculation media, which containing (per L of deionized water): 0.4 gr (NH4)2SO4, 0.1 gr K2HPO4, 0.4 gr MgSO4.7H2O, 0.33 gr CaCl2.2H2O and 18 mg FeSO4.7H2O, pH 2.3. Bioleaching experiment was carried out in a simple leaching column that was set up using 5 cc syringes. The syringe contained 1 cc of glass wool and 3.5 cc of tailings (Figure 1). Figure 1. Leaching column for bioleaching experiment (left) and tubes prepared for enumeration of iron oxidizing bacteria (right) 212 Buletin Sumber Daya Geologi Volume 10 Nomor 3 - 2015 : 211 - 221 MAKALAH ILMIAH Enumeration of Bacteria using Most Probable Number (MPN) Method In the laboratory, bacterial leaching which are the dominant iron and sulfur oxidizing bacterium from the tailings were isolated using the MPN technique (Cochran, 1950). One gram of mine tailings subjected to tenfold serial dilution (10-1 to 10-5) and diluted into 5 steriles 16x100 mm test tubes (with push caps) containing 9 ml of basal salt media. Inoculation was done with transferring 0.5 mL of each fold dilution into 50 sterile 13x100 mm test tubes (with push caps), containing 4.5 mL of basal media. The tubes are then divided into 2 groups. The first 25 tubes prepared for enumeration of iron oxidizing bacteria (e.g: Acidithiobacillus ferrooxidans) where additional 0.5 mL sterile FeSO4 7H2O (33.3 gr/100mL, pH 2.3) was added into each tubes as a source of energy. The second group also consist of 25 tubes and prepared for enumeration of sulfur oxidizing bacteria (e.g: Acidithiobacillus thiooxidans ) where a thin film of So was added into each tubes after the bacteria have been inoculated. All culture tubes were then incubated for 2 weeks under stationary conditions at room temperature. At the end of inoculation, tubes were scored for positive growth and iron and sulfur oxidizing bacteria population density was calculated. Bioleaching Experiment Four mL of basal salts (pH = 2.3) was added to the bioleaching column (Figure 1) at the start of the experiment (T=0) while 2 mL was added in each subsequent week to promote the growth of iron and sulfur oxidizing bacteria. The column was incubated for 4 weeks in room temperature. The leachate was collected each week for inductively coupled plasma atomic emission spectroscopy (ICP AES) elemental analysis. The pH of pool leachate was also recorded each week. Carbonate Analysis The amount of carbonates in the tailings was determined using a simple gravimetric procedure as described by Bauer et al. (1972). The method estimates soil capacity to neutralize acid, or to produce CO2 on treatment with acid (HCl), and then calculate the weight of carbonate present on the assumption that it is all present as CaCO3 (Calcite). RESULTS Bacterial Enumeration Positive growth was only observed in sulfur oxidizing bacterial tubes (Table 1), while all iron oxidizing bacterial tubes reveal negative results. Using MPN method, it is calculated that the number of sulfur oxidizing bacteria present in the tailings was 90 MPN/gr of tailings. Table 1. Result of bacterial e (...truncated)