Title of Invention

"A PROCESS FOR BIOLOGICAL ABATEMENT OF IRON FROM HYDROMETALLURGICAL LEACH LIQUOR"

Abstract

The process of the present invention relates to the preferential iron precipitation from leach liquor by adjustment of pH, in the presence of microorganism. In this process for biological abatement of iron from hydrometallurgical leach liquor, the essential steps of the process are simultaneous iron oxidation and iron precipitation in the presence of Thiobacillus ferrooxidans at a higher pH in the range of 2.5 to 2.9. The oxidation of ferrous sulfate to ferric sulfate followed by simultaneous precipitation of the later to crystalline jarosite compounds in the presence of Thiobacillus ferrooxidans is effected at a higher pH in the range of 2.5 to 2.9. The process is carried out at an ambient temperature and iron precipitated as crystalline jarosite compounds. The precipitate is separated by known methods from the leach liquor. Thus iron free leach liquor is obtained which can be treated by known methods for the recovery of other useful metal ions.

Full Text

This invention relates to a process for biological abatement of iron from hydrometallurgical leach liquor. This invention particularly relates to a biological method to abate iron from acidic hydrometallurgical leach liquor. This invention more particularly relates to a process wherein preferential iron precipitation from leach liquor is done by the adjustment of pH, in the presence of microorganism. Hydrometallurgical leach liquor is released from the mine sites as well as from the sites of metallurgical industries. The leach liquor contains iron along with other metal ions. Iron is present in various concentrations which varies with the different leach liquors. The pH of the leach liquors also vary. The iron needs to be removed from the leach liquor prior to its treatment for the removal of other metal ions. Iron is the second most abundant metal in the lithosphere and is usually extracted commercially from oxide ores. Oxide ores of iron are hematite, magnetite and goethite. In sulfide ores, iron is present in pyrite and pyrrhotite. Reference may be made to Habashi Fathi (ed.) 1997 In: Handbook of extractive metallurgy. Vol 1, Wiley-VCH. The sulfide of iron is associated with other base metal sulfide ores such as chalcopyrite, bornite, arsenopyrite, stannite, pentlandite and the presence of iron in these ores are regarded as gangue minerals. Therefore the gangue minerals are to be removed from the ore during beneficiation, before further use of the ore for commercial recovery of metal values. The success of iron removal from ore during beneficiation depends on the extent of association of the former with the main mineral. When iron is an integral part of the ore mineral such as chalcopyrite, bornite, and pentlandite then in that case, iron cannot be separated from the ore mineral. Thus iron is an integral part of most of the base metal deposits. Reference may be made to T. Das, G. Roy Chaudhury and S Ayyappan. 1998 a,b Use of Thiobacillus ferroxidans for iron oxidation and precipitation. Biometals, 11(2): 125-129. There are several processes by which iron can be removed from the solution such as adsorption, ion exchange and precipitation but the efficiency and economics of the processes are not very appealing. Therefore various alternatives have been tried to remove iron from the solution. Reference may be made to United States Patent no.: 6,139,753, titled: Method for treating acidic waste water, wherein the invention relates to a method of treatment of acid waste waters or acid drainage waters containing metals comprising ferrous and ferric ions, the method comprising increasing the pH of the acid waste to at least 7.5 by addition of an alkaline reagent under conditions such that ferrous ions are stable with respect to oxidation to ferric ions, to form a precipitate and collecting the precipitate. Reference may be made to Patent no.: CA227089: A process for the treatment of waste waters containing chemically reducible dissolved organic and inorganic pollutants and suspended matter in particulate or colloidal fonn. The process comprises contacting the water with metallic iron or ferrous ions (Fe2+), or mixtures thereof, in the presence of promoter metals, such as Cu, Pd, Pt, Au, Ag, and Ni, or oxides, sulfides and other insoluble compounds of these metals, which catalyze the redox reactions carried out by the iron or ferrous reagents. The production of ferric ions (Fe3+) as a final iron oxidation product allows for the simultaneous coagulation and precipitation of suspended colloidal and particulate solids out of the aqueous phase. In addition to the main reductive reaction scheme, the system performs a multitude of secondary reactions involving the ferrous and ferric ions produced in-situ which allows for the simultaneous removal of specific target pollutants, such as phosphate and hydrogen sulfide. The net effect of a treatment in accordance to this invention is the decrease in a wide range of carbonaceous, nitrogenous and other targeted pollutants present in a waste water stream in a dissolved, colloidal or particulate form and the chemical conversion, commonly referred to as "softening", of non-readily biodegradable pollutants through a generally complex set of reactions and physical processes. As a result, the implementation of the process prior to or in parallel to conventional biological treatment makes the latter more feasible, more efficient, more economical in terms of both capital investment and operating cost and, also, the finally discharged water more compatible with environmental demands. The biological process of iron control is more promising as it provides several alluring advantages such as operational simplicity, low capital and operating cost and shorter construction time that no other alternative process can provide. Reference may be made to Koichi Koiwasaki, Yoshimasa Hanbow, Kazue Tazaki, Tadahiro Mori. Experimental study on formation of jarosite and ammoniojarosite with Thiobacillus ferrooxidans. Jpn. J. 1993, 47(6), 493-505; M Nemati., S.T.L Harrison., and G.S Hansford,. Webb C. 1998 Biological oxidation of ferrous sulfate by Thiobacillus ferrooxidans: a review on the kinetic aspects. Biochem Eng. J. 1: 171-190. Reference may be made to US patent No. 5, 698, 107, titled: Treatment for acid mine drainage, wherein is disclosed an apparatus and method for removing contaminating metal ions and sulfate ions from acidic aqueous solution such as waste mine water which features passing the solution between pairs of electrodes. Each pair of electrode is impressed with a voltage selected according to specific ion species and then adding chemical agents to raise the pH and form precipitates of the metal and sulfate ions. The precipitate is then separated from the water with settling and filtering steps. Application of a magnetic field is applied during at least the first mixing step. The major drawback of the above referred patents is the use of chemicals for the treatment of the solution. Though some attempts have been made to precipitate iron from leach liquor by using acidophilic Thiobacillus ferrooxidans. but very few literature is available, where the acidophilic microorganisms are used extensively for iron oxidation and control because these microorganisms are usually used in bio leaching operations where care is taken to avoid precipitation of iron during leaching process as it forms product layer thus reducing the leaching kinetics. The bacterial oxidation of ferrous to ferric is an acid consuming reaction, hence the pH of the solution tends to increase. Due to increase of pH the ferric is being precipitated as hydroxide which slowly gets converted to goethite. In presence of alkali metal ions or ammonium salt, ferric precipitates as various kinds of jarosite. Reference may be made to R.B. Bhappu 1986 Behavior of iron in dump and heap leaching. In: Iron control in hydrometallurgy. pp. 183-201. Dutrizac, J.E. and Monhemious, A.J (ed). Ells Norwood Publishers, Joh'n Wiley and Sons. Therefore, if conditions are maintained properly, the bacterial method would prove to be very promising for separating iron from leach liquor. The main objective of the present invention is to provide a process for biological abatement of iron from hydrometallurgical leach liquor. Another objective of the present invention is to provide a biological method, such as using microorganisms to abate iron from acidic hydrometallurgical leach liquor. Yet another objective of the present invention is to provide a thermodynamic analysis of the iron oxidation and precipitation and to provide a commercially viable process for the effective abatement of iron from hydrometallurgical leach liquor. Still another objective of the present invention is to provide a process wherein iron can be precipitated at an ambient temperature.Still yet another objective of the present invention is to provide a process wherein the precipitated iron is in a crystalline form, therefore enable easy separation of the precipitate from the solution. A further objective of the present invention is to provide a process wherein the precipitate in the crystalline form can be disposed off without causing any environmental pollution. A still further objective of the present invention is to provide a process wherein during precipitation reaction there is no loss of other metal ions by co-precipitation or other phenomenon. The process of the present invention relates to the preferential iron precipitation from leach liquor by adjustment of pH, in the presence of microorganism. In this process for biological abatement of iron from hydrometallurgical leach liquor, the essential steps of the process are simultaneous iron oxidation and iron precipitation in the presence of Thiobacillus ferrooxidans at a higher pH in the range of 2.5 to 2.9. The oxidation of ferrous sulfate to ferric sulfate followed by simultaneous precipitation of the later to crystalline jarosite compounds in the presence of Thiobacillus ferrooxidans is effected at a higher pH in the range of 2.5 to 2.9. The process is carried out at an ambient temperature and iron precipitated as crystalline jarosite compounds. The precipitate is separated by known methods from the leach liquor. Thus iron free leach liquor is obtained which can be treated by known methods for the recovery of other useful metal ions. Accordingly the present invention provides a process for biological abatement of iron from hydrometallurgical leach liquor, which comprises; characterized in treating hydrometallurgical leach liquor with Thiobacillus ferrooxidans of bacterial concentration in the range of 104 cells / ml to 105 cells / ml, at ambient temperature, under constant agitation and aeration, at a pH in the range of 2.5 to 2.9, to obtain the ferrous present in the hydrometallurgical leach liquor as precipitate in the form of crystalline jarosite compounds, separating the precipitate from the leach liquor by known methods to obtain iron free leach liquor. In an embodiment of the present invention the bacteria Thiobacillus ferrooxidans are subjected to repeated sub-culturing under conditions such as initial pH from 1.25 to 2.5, biomass concentration (Log of initial bacterial concentration) from 3.18 to 13.63, initial Fe(ll) (ferrous concentration) from 3.2 to 9.4 ig/l and initial Fe(lll) concentration (ferric concentration) from 0.6, 0.9, 1.07, 1.6 g/l. In another embodiment of the present invention, the reaction temperature is preferably in the range of 30°C to 35°C. In still another embodiment of the present invention, the reaction time is for a period of up to 30 hours. In still yet another embodiment of the present invention, agitation is of the order of 120 rpm. In a further embodiment of the present invention, the pH of the solution in the bioreactor is maintained by adjusting the pH of the feed using sulfuric acid. In a yet further embodiment of the present invention, the known methods for separating the precipitate from the leach liquor are such as decantation, filtration. In a still further embodiment of the present invention, enhanced precipitation is effected using nucleating materials such as hematite, Fe(OH)3, jarosite. In the process of the present invention for biological abatement of iron from hydrometallurgical leach liquor, the non-obvious inventive step involves simultaneous iron oxidation and iron precipitation in the presence of Thiobacillus ferrooxidans at a higher pH in the range of 2.5 to 2.9. This results in the novelty of abatement of iron from hydrometallurgical leach liquor, thus making it iron free and allowing recovery of useful metal ions by known methods. For the growth of Thiobacillus ferrooxidans, four parameters that affect the growth kinetics of the bacteria were varied, such as pH (Initial pH were 1.25, 1.5, 1.75, 2.0 and2.5), biomass concentration (Log of initial bacterial concentration were 3.18, 4.4, 5.82, 7.87, 9.56, 11.53, 13.63), initial Fe(ll) (ferrous concentration in g/l were, 3.2, 4.9, 6.6 and 9.4) and initial Fe(lll) concentration (ferric concentration in g/l were, 0.6, 0.9, 1.07, 1.6). The bio-oxidation rate showed a positive trend for all the variables except Fe (III) concentration. The bacteria Thiobacillus ferrooxidans are subjected to repeated sub-culturing in 9K medium maintained at pH 2.5, initial ferrous concentration of 10 g/l, initial bacterial concentration of 10® cells/ml, temperature of the growth medium maintained at 35°C, supplying oxygen and carbon dioxide to the medium by frequent aeration. After adaptation of the bacteria to the growth medium, bio-oxidation and simultaneous precipitation of iron from hydrometallurgical leach liquor was carried out using Thiobacillus fenrooxidans at pH of the leach liquor raised to 2.75, initial ferrous concentration of 8 g/l (may vary upto 15 g/l), initial bacterial concentration of 109 cells/ml and temperature 35°C, the reaction time varied from 0 hours (when the bacteria was inoculated into the leach liquor and the process of bio oxidation of iron begins) to 30 hours (when above 90% of iron present in the leach liquor is precipitated) and ferrous was precipitated as crystalline jarosite compounds which were successfully separated from the leach liquor. In the present invention, Eh-pH diagrams were developed in order to study the thermodynamics of iron precipitation. In the present invention to enhance the precipitation, the initial pH was raised. The iron precipitation and oxidation rate were studied by varying the initial pH from 2.5, 2.6, 2.75 and 2.9. In the present invention, bio oxidation and precipitation kinetics of iron were evaluated in the presence of various metal ions. Eh-pH diagram were developed for the thermodynamic analysis of iron oxidation and precipitation, it was observed from the same that iron can be precipitated in our experimental conditions. Therefore, various nucleating agents such as hematite, jarosite and hydroxides were used in order to enhance the precipitation. But by addition of nucleating agent, there was hardly any improvement regarding iron precipitation. Therefore the other alternative to enhance the iron precipitation, was to raise the initial pH. The iron precipitation and oxidation rate were studied by varying the initial pH from 2.5, 2.6, 2.75 and 2.9. The percentage of iron removal increased with increase of pH up to 2.75 and thereafter it attained a stationary phase. The process was tested using two different leach liquor, such as, laterite nickel ore and zinc tailings. Both the leach liquor contains iron around 7 g/l. The lateritic nickel leach liquor contains Ni and Mn, and minor amounts of Zn, Cu and Co along with Fe. The leach liquor from Zn tailing leaching contains mainly Zn and Fe. Initially, the microorganisms were adapted to the growth medium by repeated retransfer. After adaptation, the iron oxidation and precipitation studies were carried out in a bioreactor. The iron oxidation rate was observed to be 500 and 450 mg/l for Zn leaching and lateritic nickel ore leach liquor. In both the cases, the iron removal efficiency was more than 90%. The reaction time was varied from 0 to 30 hours and all the reactions were carried out at an ambient temperature. The process of bio oxidation and bio precipitation in presence of Thiobacillus ferrooxidans, were simultaneous. The loss of valuable metal ions during iron precipitation was negligible and by XRD analysis of the precipitate it was confirmed that iron was being precipitated as jarosite. Residue samples for different time intervals were analysed by XRD. It was observed that in all cases the XRD pattern showed the peaks of jarosite and the crystalinity improved with time as the peak intensity increased. The novelty of the process of the present invention lies in obtaining iron free hydrometallurgical leach liquor through a biological phenomenon resulting in crystalline precipitate of jarosite. The crystalline precipitates can be easily separated from the hydrometallurgical leach liquor without posing any difficulty for solid liquid partition. The precipitate can also be disposed safely without causing any environmental stress. The novelty of abatement of iron from hydrometallurgical leach liquor, thus making it iron free and allowing recovery of useful metal ions by known methods, is achieved by the non-obvious inventive step involving simultaneous iron oxidation and iron precipitation in the presence of Thiobacillus ferrooxidans at a higher pH in the range of 2.5 to 2.9. The process of the present invention is illustrated by the following examples, which should not be construed to limit the scope of this invention. In the following examples illustration of the process of the present invention, specifically iron oxidation and precipitation studies were carried out in a specially fabricated bioreactor using Thiobacillus ferrooxidans. The bacteria were cultured in 9K media (Silvermann M.P. and Lundgren D.G. 1959 Studies on the chemoautotrophic iron bacterium Ferobacillus ferrooxidans. I. An improved medium and a harvesting procedure for securing high cell yields, J. Bacteriol. 77: 642-647). The bioreactor was designed to vary the airflow rate, agitation speed and temperature. It had facilities to measure pH, temperature, air flow rate and dissolved oxygen. The capacity of the bioreactor was 2 liter. The bioreactor was maintained at constant temperature by circulating water through the bioreactor jackets from constant temperature baths controlled by a temperature controller. The pH of the solution in the bioreactor was maintained by adjusting the pH of the feed to the bioreactor using sulfuric acid. Mixing and gas dispersion was achieved by a six-blade turbine impeller rotating at a specific speed, located 2 cm from the base of the bioreactor, via a flexible coupling linked to a motor and a speed controller. The inlet gas was supplied by an oil free air compressor. The flow rate to the bioreactors was controlled at the required rate using mass flow controller. The dissolved oxygen of the solution, was measured by an oxygen probe. Wall growth was minimized by shutting down the reactor after each experiment and scrubbing the walls of the reactor and all available surfaces with a bottle brush and was washed with diluted hydrochloric acid solution followed by distilled water. Example 1 The initial pH was 2.5 and throughout the experiment the pH was maintained at a constant value. At pH 2.5, initial Fe(ll) concentration of 3g/l and initial bacterial concentration of 105 cells/ml, about 50% of iron was precipitated in 15 hours. The growth of the microorganism was constantly monitored by analysis of the samples at regular intervals. Example 2 The initial pH was 2.6 and throughout the experiment the pH was maintained at a constant value. At pH 2.6, initial Fe(ll) concentration of 3g/l and initial bacterial concentration of 105 cells/ml, about 60% of iron was precipitated in 18 hours. The growth of the microorganism was constantly monitored by analysis of the samples at regular intervals. From experiments as given in the above examples it was observed that iron removal efficiency was partially improved with increase of pH. Example 3 Iron oxidation and precipitation studies were carried out, by raising the initial pH from 2.6 to 2.75. At pH 2.75, initial ferrous concentration of 3 g/l, initial bacterial concentration of 105 cells/ml more than 90% iron precipitation could be achieved in less than 20 hours. Example 4 Studies were carried out at pH 2.9, initial ferrous concentration of 3 g/l, initial bacterial concentration of 105 cells/ml. More than 90% of iron was precipitated within 27 hours after the initiation of the bio oxidation and precipitation reaction. The iron removal efficiency at pH 2.75 and 2.9 was observed to be the same but at pH 2.9 the growth kinetics of the bacteria was slow which is obvious from the elongation of the reaction time period. In the above examples the experiments detailed were conducted in batch scale. So far in the bioreactor, all the experiments were conducted in batch scale as the reactor has no provision to run in continuous mode. In order to find out whether our existing process will work in continuous mode or not further experiments were carried out as given in the following examples. Example 5 A fixed amount of solution was drawn at fixed interval and replaced with equal volume after steady state. To start with 25 ml of solution was drawn at an interval of 15 minutes. It was observed that total iron concentration even after 25 hours remained unchanged, therefore it was concluded that at a flow rate of 25 ml/15min, the bacteria could be able to maintain the oxidation and precipitation efficiency. So gradually the flow rate was increased and equilibrium was not disturbed up to flow rate of 35 ml/15 min and beyond that the equilibrium was disturbed. In this run the initial bacterial concentration was around 105 cells per ml and the overall ferrous precipitation was more than 95% during the continuous mode of iron oxidation and precipitation. In the following example experiment was carried out to check and evaluate whether the activities of the microorganisms are affected by the presence of other metal ions. Example 6 Evaluation of the bio-oxidation and precipitation kinetics in presence of metal ions such as Mn, Co, Zn, Cu and Ni was done as follows: The bacteria were adapted to different metal ions individually and collectively by regular sub-culturing. It was observed that after adaptation, the activities of the microorganisms were unaffected in terms of bio-oxidation and precipitation. During precipitation of iron, the loss of other metal ions due to adsorption/coagulation was less than 1%. Example 7 Zn leach liquor was used to test the overall process. The leach liquor was obtained after processing of Zn-tailings. The pH of both the leach liquor was 1.5 therefore the pH was raised to 2.75 to carry out the biooxidation and precipitation studies in the bioreactor. During pH adjustment the loss of metal ions were negligible. The iron oxidation and precipitation studies were carried out as described above. The loss of valuable metal ions during iron precipitation was less than 1 % and by XRD analysis of the precipitate it was confirmed that iron was being precipitated as jarosite. Residue samples for different time intervals were analysed by XRD. It was observed that in all cases the XRD pattern showed the peaks of jarosite and the crystallinity improved with time as the peak intensity increased . The main advantages of the process of the present invention are: 1. Eco-friendly process which does not destroy the environmental equilibrium. 2. Iron can be precipitated at ambient temperature. 3. More than 90% of iron was precipitated at ambient temperature. 4. The precipitated iron is in a crystalline form. Therefore it is easy to separate the precipitate from the solution. 5. Since the precipitate is in the crystalline form, it can be disposed off without causing any environmental pollution. 6. During precipitation reaction there is no loss of other metal ions by co-precipitation or other phenomenon. 7. The process does not require operational sophistication and is economically viable in the industrially developing countries. We Claim: 1. A process for biological abatement of iron from hydrometallurgical leach liquor, which comprises; characterized in treating hydrometallurgical leach liquor with Thiobacillus ferrooxidans of bacterial concentration in the range of 104 cells / ml to 105 cells / ml, at ambient temperature, under constant agitation and aeration, at a pH in the range of 2.5 to 2.9, to obtain the ferrous present in the hydrometallurgical leach liquor as precipitate in the form of crystalline jarosite compounds, separating the precipitate from the leach liquor by known methods to obtain iron free leach liquor. 2. A process as claimed in claim 1, wherein the bacteria Thiobacillus ferrooxidans are subjected to repeated sub-culturing under conditions such as initial pH from 1.25 to 2.5, biomass concentration (Log of initial bacterial concentration) from 3.18 to 13.63, initial Fe(ll) (ferrous concentration) from 3.2 to 9.4 ig/l and initial Fe(lll) concentration (ferric concentration) from 0.6, 0.9, 1.07, 1.6 g/l. 3. A process as claimed in claim 1-2, wherein the reaction temperature is preferably in the range of 30°C to 35°C. 4. A process as claimed in claim 1-3, wherein the reaction time is for a period of up to 30 hours. 5. A process as claimed in claim 1-4, wherein agitation is of the order of 120 rpm. 6. A process as claimed in claim 1-5, wherein the pH of the solution in the bioreactor is maintained by adjusting the pH of the feed using sulfuric acid. 7. A process as claimed in claim 1-6, wherein the known methods for separating the precipitate from the leach liquor are decantation, filtration. 8. A process as claimed in claim 1-7, wherein enhanced precipitation is effected using nucleating materials such as hematite, Fe(OH)3, jarosite. 9. A process for biological abatement of iron from hydrometallurgical leach liquor, substantially as herein described with reference to the examples.

Documents:

1427-DEL-2004-Abstract-(02-11-2010).pdf

1427-del-2004-abstract.pdf

1427-DEL-2004-Claims-(02-11-2010).pdf

1427-del-2004-claims.pdf

1427-del-2004-correpsondence-others.pdf

1427-DEL-2004-Correspondence-Others-(02-11-2010).pdf

1427-DEL-2004-Description (Complete)-(02-11-2010).pdf

1427-del-2004-description (complete).pdf

1427-del-2004-form-1.pdf

1427-del-2004-form-18.pdf

1427-del-2004-form-2.pdf

1427-DEL-2004-Form-3-(02-11-2010).pdf

1427-del-2004-form-3.pdf

1427-del-2004-form-5.pdf