INNOVATIVE BIOHYDROMETALLURGICAL PROCESSES FOR DECONTAMINATION OF ACID MINE DRAINAGE

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1 Proceedings of the 13 th International Conference on Environmental Science and Technology Athens, Greece, 5-7 September 2013 INNOVATIVE BIOHYDROMETALLURGICAL PROCESSES FOR DECONTAMINATION OF ACID MINE DRAINAGE UBALDINI S. 1, LUPTAKOVA A. 2, MACINGOVA E. 2, FORNARI P. 1 and PIZZICHEMI P. 1 1 Istituto di Geologia Ambientale e Geoingegneria, CNR, Area della Ricerca di Roma RM 1 - Montelibretti Via Salaria Km 29, Monterotondo Stazione (ROMA) - Italy (stefano.ubaldini@igag.cnr.it) 2 Department of Mineral biotechnology, Institute of Geotechnics of Slovak Academy of Sciences, Watsonova 45, Kosice, SK , Slovak Republic EXTENDED ABSTRACT The main aim of this experimental work is to investigate remediation biohydrometallurgical processes for toxic metals removal (Zn, Cu, Mn, Al and Fe) from Acid Mine Drainage (AMD), recovering purified useful metals. Water drainages have an appreciable metal content over the permitted standard. The metals of primary concern are Cu, Cr, Fe, Al, Mn, Hg, Ni, Pb, As and Zn. The processes studied are innovative, intended to reaching a specific purpose, economically and environmentally. These could be integrated with physical treatments, with the dual aim of reducing pollution of inland waters at the same time producing useful metals (copper, nickel, zinc, etc.). The benefit for the environment will result in the reduction of toxic effects on living organisms. Biohydrometallurgical applications - constituted by bioprecipitation/electrowinning - have demonstrated the technical feasibility of the process, aimed to the removal of toxic metals from AMD samples; in fact, at the end of the process, the metals concentration decreased under the recommended legislation limit, achieving metals at high degree of purity (about 95%). Keywords: Biohydrometallurgy, Heavy metals, Electrowinning, Bioprecipitation, Acid Mine Drainage. 1. INTRODUCTION The mining industry (active and abandoned sites), metal processing, electronics, plating, tanning and treatment of complex industrial wastewater, produce significant quantities of residues and waste products, that contain a wide variety of heavy metals, chromium, mercury, cadmium, lead, copper, nickel etc. In many cases, these wastes are not treated in a appropriate manner and compatible with environmental regulations, which provide far more and more restrictive discharge and disposal of liquid and solid in suitable landfill (Vegliò et al., 2003). The main cause of river water pollution in Western and Central European regions and in South America regions is undoubtedly represented by metal sulphide (copper, zinc, iron, SO 4 etc.) ore deposits and tailings abandoned near to closed and/or open mines (Ubaldini et al., 2010). In this scenario, is clearly of considerable interest to develop physical, chemical and biotechnological operations (usually integrated), that tend to reduce emissions of pollutants into the environment from industrial waste, technologically and economically, viable to restore areas already contaminated (Vegliò et al., 2003; Luptakova et al., 2010).

2 Biohydrometallurgical processes can be integrated by different operative step such as Electrowinning, Leaching-Bioleaching, Bioadsorption, Bioaccumulation, Chemical- Bioprecipitation (Ubaldini et al., 2006; Beolchini et al., 2009; Luptakova et al., 2012a). As far as electrowinning process, the following reactions occur to the electrodes during Zn, Cu, Ni, Cd, Mn and Fe deposition (Vegliò et al., 2003; Ubaldini et al., 2006). Cathodic reactions: Zn e- = Zn E = V Ni e- = Ni E = V Cd e- = Cd E = V Cu e- = Cu E = V Mn e- = Mn E = V Fe e- = Fe E = V Anodic reaction: 2H 2O = O 2 + 4H+ +4e - Mn H 2O = MnO 2 + 4H+ +2e - E = 1.23 V E = 1,23 V During bioleaching, the organisms involved obtain energy from the oxidation of ferrous iron and reduced sulphur compounds. They are therefore able to oxidize gold-bearing sulphide minerals such as pyrite, phyrrotite, stibnite, chalcopyrite and arsenopyrite. The mechanism of the attack may be direct and indirect. Various kinds of microorganisms can be involved: Thiobacillus ferrooxidans, Thiobacillus thiooxidans, Sulpholobus, Leptospirillum, Sulphobacillus.(Luptakova et al., 2008). Bioadsorption phenomena are not associated with the activity of metabolism. Occurs on non-living biomass. Phenomena may be due to physical adsorption, by formation of complex phenomena of precipitation and ion exchange. These processes can be applied by olive pomace, Rizophus oligosporus, Sphaerotilus natans ect. (Beolchini et al., 2009). Bioaccumulation mechanisms are dependent on cellular metabolism. These are often associated with an active defense system of microorganisms. Ultimately, the organisms react to the presence of a given toxic metal center. Microorganisms as Arthrobacter sp., Acidithiobacillus sp and Leptospirillum sp. can be involved (Beolchini et al., 2009). Bioprecipitation process can be applied by cultures of sulphate-reducing bacteria (SRB) genera Desulfovibrio, Desulfotomaculum, Desulfomonas, Desulfuromonas. This method involves three stages: the biological hydrogen sulphide production, the heavy metals precipitation by the bacterial produced hydrogen sulphide and the heavy metal sulphides separation (Luptakova et al., 2012b; Luptakova et al., 2012c). 2. MATERIALS AND METHODS The AMD under study coming from zinc mine located in Montevecchio Mine (Sardinia - Italy), lead and zinc mine located in Tùnel Kingsmill outlet of the Rio Yaulì, district of Yauli (Perù) and Cu Fe ore deposits located in Smolník (Slovakia) (Tables 1-3). The experimental tests have been conducted at laboratory scale. A preliminary technoeconomic feasibility analysis has been elaborated.

3 Table 1. Composition in mg/l of AMD sample from Zinc-Mine, Monte Santu Miali Sardinia, Italy. Ni 4.40 Cd 3.85 Cu 0.55 Zn 1520 As Sb Pb Mn Fe Hg 0.02 Cr Sn S 1507 ph Table 2. Composition in mg/l of AMD sample from lead and zinc mine located in district of Yauli (Perù). Al Ni Cd 0,156 Cu Zn Cr As Sb Pb Mn Fe Hg Ca Mg 49.5 Na 3.8 K 1.1 ph 3.5

4 Table 3. Composition in mg/l of AMD sample from copper and iron mine located in Smolnik (Slovak Republic). Fe Cu 4.31 Zn Al Mn Mg Ca Na SO ph 3.5 Experimental research intends to investigate an environmentally friendly and low-cost technique for the mitigation of pollution of mine waters by the application of new technologies such as electrowinning and bioprecipitation. Electrowinning tests (Ubaldini et al., 2006) have been carried out after chemical ironaluminum precipitation, that permitted a complete Fe removal. HNO 3 has been added to the synthetic solution, with the aim to oxidise Fe 2+ to Fe 3+. In a subsequent step, sodium hydroxide (NaOH) was added to reach ph 4.0. Successively, the deposit has been separated by filtration. Electrowinning tests have been performed in a cylindrical glass laboratory cell of 200 cm 3 volume, at constant cathodic potential, for an electrolysis time of 2 h. The cell was connected to a potentiostat-galvanostat (AMEL, Mod. 568). With the scope to study the electrodeposition kinetic, liquid samples of 5 cm 3 have been whitdrawn and submitted to chemical analysis by ICP-MS, while the purity of the solid deposit was determined by X-Ray Diffraction technique (Marabini et al., 1993). Metallic content of the deposit was analysed by ICP-MS, after dissolution by HCl. Table 4. Main experimental conditions for metals recovery by electrowinning tests. Factors Value Cathode Vs. SCE (V) Cell voltage (V) Current intensity (ma) Current density (ma/cm 2 ) ph 4.0 Bath temperature ( C) 40 Electrolysis time (h) 6 Stirring conditions (revolution per min.) 200

5 Table 5. Main experimental conditions of the electrowinning tests for MnO 2 recovery. Factors Value Cathode Vs. SCE (V) Cell voltage (V) Current intensity (ma) Current density (ma/cm 2 ) ph 0.97 Bath temperature ( C) 95 Electrolysis time (h) 6 Stirring conditions (revolution per min.) 200 The culture of sulphate-reducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests (Luptakova et al., 2012a). The treatment of AMD by SRB is based on the ability of SRB to reduce sulphates to hydrogen sulphide, which binds readily with metals to form sparingly soluble precipitates. The cultures of SRB used for the experiments, were isolated a mixed colture from potable mineral water (Gajdovka spring, Kosice-north, Slovakia). The bioprecipitation of heavy metals form AMD sample was performed by two interconnected bioreactors with a capacity 1000 ml (the first bioreactor) and 250 ml (the second bioreactor). This method contains three stages: biological hydrogen sulphide production, metals precipitation by the biologically produced hydrogen sulphide and heavy metal sulphides separation. The selective precipitation of Cu and Zn was realized by the bacterial produced H 2S in the second bioreactor at ph 3.5 and 4.2, respectively. 3. RESULTS During preliminary electrowinning tests, Fe deposits to the cathode with low adherence, while the deposition was low after 1 h. On the basis of these results, preliminary precipitation step has been carried out before electrowinning. During this phase, also Al deposition has been achieved. The liquor prepared was treated by using an electrowinning lab-scale operation, to verify the technical feasibility of the metals deposition. Manganese deposited to the anode as MnO 2 and to the cathode as Mn +. After 6 hours, 90-95% of the metals have been removed by a quantitative cathodic deposition. In particular, % Zn and % of Mn - as MnO 2 - have been achieved. An high grade purity of the metallic deposit has been achieved (Zn over to 95 %), such as it was demonstrated from the results of analysis conducted by XRD. The kinetic of the selective bio-precipitation of heavy metals has been investigated (Figure 1). Achieved results demonstrate the 98-99% elimination (in particular of Cu and Zn) by bacterially produced H 2S. Cu was precipitated under form of CuS. The suspension of precipitates (CuS) was filtered and the ph value of the filtrate was adjusted at 4.2 using 10N NaOH. The filtrate was returned into the second reactor and submitted again to the effect of biologically produced H 2S (the subsequent precipitation). The decreasing of zinc concentration from 10.0 mg/l to less than 0.05 mg/l was registered too. Zinc precipitation was not selective; in fact, the co-precipitation of iron was detected.

6 Figure 1. The schematic diagram of the bioprecipitation process. 1 - the biological hydrogen sulphide production; 2 - the precipitation of metals by the bacterially produced hydrogen sulphide; 3 - the catching of the untreated hydrogen sulphide. Tables 6-8 show the main results achieved by the application of the biohydrometallurgical process in the treatment of the Peruvian sample (Table 6), Italian sample (Table 7), Slovak sample (Table 8). Main results of Zn and MnO 2 electrodeposition have been reported in Table 9. On the basis of the results achieved it is possible list the main advantages of the study carried out on scale of laboratory: - the processes described are innovative; - the processes proposed are intended to reaching a specific purpose, economically and environmentally; - these processes could be integrated with physical treatments and procedures followed by biohydrometallurgical applications, with the dual aim of reducing pollution of inland waters at the same time producing useful metals (copper, nickel, zinc, etc.); - the benefit for the environment will result in the reduction of toxic effects on living organisms. Table 6. Metal concentrations of the Italian AMD sample after electrowinning process Metal Concentration Legal limit for (mg/l) wastewater (mg/l)* Zn Ni < Cd < Cu < Mn Fe *(Italian D.Lgsl.152/1999)

7 Table 7. Composition of AMD sample from Perù AMD, legal limit of water for irrigation and drinking water, metal concentrations after precipitation-electrowinning process. Initial Peruvian After After content legal limit precipitation electrowinning for wastewater Element mg/l Quality III mg/l mg/l (mg/l)* Al Ni Cd Cu Zn Cr As Sb Pb Mn Fe Hg (*) Ca Mg Na K ph (*) μg/l Table 8.The metal removal efficiency from real AMD Slovak samples (Electrowinning- Bioprecipitation). Metal Fe Cu Al Zn Mn Input concentration (mg/l) Output concentration (mg/l) < 0.05 < 0.02 < 0.04 < 0.01 < 0.03 Metal removing (%) Table 9. Main results of Zn and MnO 2 electrodeposition. Time [min] R [%] * [%] E* [kwh/kg] Zn MnO ,

8 5. CONCLUSIONS Integrated process constituted by chemical precipitation/electrowinning, demonstrates the technical feasibility to remove toxic metals such as Zn, Cu, Mn, Al and Fe from AMD. In particular, as far as Zn electrowinning, it was possible to achieve high Zn removal: about 97 % Zn at the end of the process, and after chemical precipitation by NaOH. The successive running of the hydrogen sulphide bacterial production and the metals precipitation by the bacterial produced hydrogen sulphide, i.e. the application of two interconnected reactors, allowed the faster metals elimination, as well as the possibility of selective copper precipitation in the form of sulphides. ACKNOWLEDGEMENTS This activity was supported by Joint Project of the CNR/SAV (2013/2015), Project CNR RSTL n , Joint Project n.2 of the CNR/CONCYTEC (2009/2011), SRDA and the Scientific Grant Agency No. 2/0166/11. REFERENCES 1. Beolchini F., Dell Anno A., De Propris L., Ubaldini S., Cerrone F. and Danovaro R. (2009), Auto- and heterotrophic acidophilic bacteria enhance the bioremediation efficiency of sediments contaminated by heavy metals, Chemosphere, 74, 10, Luptakova A., Ubaldini S., Macingova E., Fornari P. and Giuliano V (2012a), Application of Physical-chemical and Biological-chemical Methods for Heavy Metals Removal from Acid Mine Drainage, Process Biochemistry, 47, Luptakova A., Ubaldini S., Fornari P. and Mačingova E. (2012b), Physical-chemical and biological-chemical methods for treatment of acid mine drainage, Chemical Engineering Transactions, 28, Luptakova A., Ubaldini S., Macingova E. and Kotulicova I. (2012c), Study of precipitating methods for elimination of heavy metals from acid mine drainage, Nova Biotechnologica et Chimica, 11, 2, Luptakova A., Ubaldini S., Macingova E., Fornari P. and Giuliano V. (2010), Application of Physical-chemical and Biological-chemical Methods for Heavy Metals Removal from Acid Mine Drainage, Journal of Biotechnology, 150, supplement 1, Luptakova A., Macingova E., Ubaldini S. and Jencarova J. (2008), Bioleaching of antimony minerals by bacteria Acidithiobacillus and Desulfovibrio Desulfuricans, Chemickè Listy, 102, Issue 15, Marabini AM., Contini G., Cozza C. (1993), Surface Spectroscopic Techniques applied to the Study of Mineral Processing, International Journal of Mineral Processing, 38, Ubaldini S., Luptakova A., Macingova E., Massidda R. and Fornari P. (2010), Application of biohydrometallurgical processes for heavy metals removal from acid mine drainage, Nova Biotechnologica, 10, 1, Ubaldini S., Massidda R., Veglio F., Beolchini F. (2006), Gold stripping by hydro-alcoholic solutions from activated carbon: Experimental results and data analysis by a semi-empirical model, Hydrometallurgy, 81, Veglio' F., Quaresima R., Fornari P. and Ubaldini S. (2003), Recovery of Valuable Metals from Electronic and Galvanic Industrial Wastes by Leaching and Electrowinning, Waste Management, 23,

Microorganisms In Biohydrometallurgy

Lecture 4 Microorganisms In Biohydrometallurgy Keywords: Mining Microorganisms, Acidithiobacillus, Thermophiles Some chemolithotrophic bacteria useful in biohydrometallurgy are listed below: Acidithiobacillus