Biooxidation and precipitation for iron and sulfate removal from heap bioleaching effluent streams
Introduction
In bioleaching processes biological oxidation of iron and sulfur is exploited to solubilize and recover metals from low-grade sulfide ores. Solutions from these processes typically have very low pH values and high sulfate and ferric iron concentrations. Other metals may also be present but the chemical composition of these effluents varies with the source. Dissolved iron and sulfate accumulate in heap bioleaching circuits because of solution recirculation. The accumulation is problematic and excess iron and sulfate need to be removed because they may otherwise interfere with process kinetics due to precipitate formation (Nemati et al., 1998, Watling, 2006) and with the subsequent metal recovery (Dutrizac and Riveros, 2006, Cunha et al., 2008). The final effluents from these processes have to be treated effectively to neutralize the streams and to remove iron and sulfate as stable end products as the effluents cause severe problems if dispersed in the environment (for reviews, see Johnson, 2003, Johnson, 2006). Iron is commonly removed through hydroxide precipitation by adding lime or limestone to increase the pH approximately to 3. This conventional treatment process creates major sludge handling and disposal problems due to the generation of voluminous sludge (Cunha et al., 2008, Dutrizac and Riveros, 2006, White et al., 2006). Jarosite precipitation is also a common chemical iron removal method especially in zinc industry. Jarosite precipitation produces iron precipitates with relatively good settling, filtering and washing characteristics, but various other metal ions may co-precipitate, and elevated temperatures are preferred for the process (Tamargo et al., 1996, Ismael and Carvalho, 2003). Biological and combined biological and chemical iron and sulfate removal systems have been examined, especially for the treatment of acid mine drainage (AMD) as reviewed, for example, by Johnson and Hallberg, 2005, Gaikwas and Gupta, 2008, Kaksonen et al., 2008. These AMD treatment systems often help to decrease the chemical costs and improve the handling characteristics of the sludge produced. Examples of active treatment processes employing iron-oxidizing microorganisms include aerated lagoons and stirred tanks (Umita, 1996), packed-bed bioreactors (Diz and Novak, 1999) and rotating biological contactors (Olem and Unz, 1980, Nakamura et al., 1986). High-rate iron oxidation has been achieved with bioreactors using immobilized iron-oxidizing microorganisms, e.g. packed-bed bioreactors (Diz and Novak, 1999) and rotating biological contactors (Olem and Unz, 1980, Nakamura et al., 1986). In the laboratory scale, a treatment process has been developed consisting of a packed-bed bioreactor for iron oxidation and a fluidized-bed reactor for chemical precipitation of iron onto the surface of seed particles (Diz, 1998, Diz and Novak, 1998). These applications have been developed for treating AMD and, in contrast, a very limited amount of information has been published on the treatment of bioleaching solutions. In our previous study (Nurmi et al., 2009) a bioprocess was developed based on a fluidized-bed reactor (FBR) for Fe2+ oxidation by a Leptospirillum ferriphilum dominated biofilm coupled with a gravity settler for precipitative removal of ferric iron. Only few patents have addressed biological iron oxidation for iron removal; e.g., Das and Das (2004) described a process that included simultaneous oxidation and precipitation of iron in hydrometallurgical leach liquors in the presence of Acidithiobacillus ferrooxidans, and Maree and Johnson (1999) designed a bioprocess scheme for the treatment of acidic “raw” (undefined) water containing high concentrations of dissolved ferrous ions.
The solubility of Fe3+ is a function of the pH in leach solutions. Generally, Fe3+ has an extremely low solubility at pH above 2.5. In sulfate-rich environments Fe3+ precipitates mainly as jarosites (Fe(III)-hydroxysulfates, MFe3(OH)6(SO4)2 where M can be Na+, K+, NH4+ or H3O+ or a divalent metal ion at ambient temperatures and pressures) at pH values < 4 and as oxyhydroxides and oxides at higher pH values. Goethite, an Fe(III)-oxyhydroxide (α-FeOOH), or schwertmannite, an Fe(III)-hydroxysulfate (ideally Fe16O16(OH)12(SO4)2·nH2O) can also form at similar pH ranges. Jarosite formation is enhanced at high concentrations of monovalent cations, Fe3+ and SO42− (Nemati et al., 1998, Gramp et al., 2008). The lower threshold pH for jarosite formation is close to pH 1.5, but this depends on the temperature and ionic composition of the solution.
The purpose of this study was to develop a high-rate, high-efficiency process for iron oxidation and precipitation together with sulfate. A combined iron and sulfate removal bioprocess was conceived by employing ferrous sulfate oxidation by iron-oxidizing bacteria followed by precipitation through partial neutralization. The process was developed for the treatment of heap bioleaching effluents. Solid phase samples were characterized in an effort to relate precipitate properties to pH adjustments with two different neutralizing chemicals.
Section snippets
Reactor setup
A fluidized-bed reactor (Fig. 1) based system was used for the experiments at 37 ± 2 °C. The reactor setup was as described in Nurmi et al. (2009) except that the settling tank had a 40 L capacity and retention time of 1 h interfaced with a pH adjustment unit (capacity of 4.5 L, retention time of 0.12 h). The surface loading rate of the settling tank (flow of solution through the settling tank divided by the surface area of the settling tank) was 0.29 m/h throughout the experiments. Prior to these
Oxidation and precipitation of iron
In our previous study (Nurmi et al., 2009a) the highest relative iron precipitation obtained was 30–40%. Ferric iron was precipitated as jarosite during the regeneration of heap leaching solution in the combined FBR and gravity settler system at pH 2. In the present study, the process was further developed for iron and sulfate removal from bioleaching effluent using KOH and CaCO3 to neutralize the pH in the range of 2.5–3.5. The performance of the FBR at different pH values is described in
Conclusions
Based on the development of the integrated bioprocess for controlled ferrous iron oxidation and precipitative ferric iron and sulfate removal, the following conclusions can be drawn:
- 1.
Sulfate and oxidized iron precipitated in the pH range of 2.5–3.5 as jarosite. When the pH was increased with KOH or CaCO3, the formation of goethite or gypsum, respectively, was also observed and the relative proportion of amorphous fraction increased.
- 2.
With 6.0 ± 1.5 g Fe2+/L in the feed the highest Fe2+ oxidation and
Acknowledgements
This research was partially funded by the Talvivaara Mining Company Plc. KS acknowledges funding from the Japan Society for the Promotion of Sciences (JSPS 20656147) and OHT from the Finnish Funding Agency for Technology and Innovation (Finland Distinguished Professor Program, 402/06).
References (33)
- et al.
Possibilities to use oxidic by-products for precipitation of Fe/As from leaching solution for subsequent base metal recovery
Miner. Eng.
(2008) - et al.
Kinetic study of biological ferrous sulphate oxidation by iron-oxidising bacteria in continuous stirred tank and packed bed bioreactors
Process Biochem.
(2003) - et al.
Monovalent cation concentrations determine the types of Fe(III) hydroxysulfate precipitates formed in bioleach solutions
Hydrometallurgy
(2008) - et al.
Iron recovery from sulphate leach liquors in zinc hydrometallurgy
Miner. Eng.
(2003) Biohydrometallurgy and the environment: intimate and important interplay
Hydrometallurgy
(2006)- et al.
Acid mine drainage remediation options: a review
Sci. Total Environ.
(2005) - et al.
High-rate iron oxidation at below pH 1 and at elevated iron and copper concentrations by a Leptospirillum ferriphilum dominated biofilm
Process Biochem.
(2005) - et al.
Field determination of Fe2+ oxidation rates in acid mine drainage using a continuously-stirred tank reactor
Appl. Geochem.
(1998) - et al.
Effect of operation conditions on biological Fe2+ oxidation with rotating biological contactors
Water Res.
(1986) - et al.
Biological oxidation of ferrous sulphate by Thiobacillus ferrooxidans: a review on the kinetic aspects
Biochem. Eng. J.
(1998)
Process for biological oxidation and control of dissolved iron in bioleach liquors
Process Biochem.
Biological mine drainage treatment
Resour. Conserv. Recycl.
The bioleaching of sulphide minerals with emphasis on copper sulphides — a review
Hydrometallurgy
American Public Health Association. Standard Methods for the Examination of Water and Wastewater
The selective oxide system: a new active treatment for acid mine drainage which avoids the formation of sludge
Mine Water Environ.
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- 1
Present address: Department of Environmental Engineering, Faculty of Civil Engineering, Davutpasa Campus, Yildiz Technical University, TR-34342 Istanbul, Turkey.
- 2
Present address: CSIRO Land and Water, Underwood Ave, Floreat, WA 6014, Australia.