Patent Application
20170058377
The current invention is related to the iron production industry. Particularly, with a biotechnological procedure to remove magnetic sulfur impurities that are present on iron concentrate samples, using autotrophic sulfur-oxidizing microorganisms under potassium limiting conditions. Among the sulfur-oxidizing microorganisms, Acidithiobacillus thiooxidans is used, and predominantly the deposited strain DSM 17318, denominated Licanantay. Concerning the potassium (K+) limiting conditions, the present invention requires no addition of potassium as nutritional supplement for microbial activity. With respect to magnetic sulfur impurities present on iron concentrates, the use of strain Licanantay without potassium addition, allows impurities oxidation, which after a magnetic concentration stage of the treated iron concentrate, removes such impurities with an efficiency above 80% in 21 days, with a maximum iron loss of 3%.
Based on the described examples it is possible to conclude that the use of strain Licanantay under potassium limiting condition is technically feasible to achieve an efficient removal of magnetic sulfur impurities from iron concentrate.
The production of iron concentrate by means of magnetic concentration and inverse flotation may involve a high content of sulfur, mainly due to Pyrrothite (Fe(1-x)S) contamination of secondary concentrate. Depending on the ore characteristics (extraction ore, tailings among others), iron concentrates with a variable content of magnetic sulfur impurities are produced. The presence of such impurities is penalized on iron concentrate sale contracts, where a maximum content tolerated is 0.1% S.
Based on the previous, there is a need for procedures to decrease the content of magnetic sulfur impurities on iron concentrates.
U.S. Pat. No. 4,269,699, describes the use of microorganisms as biosurfactants that selectively adsorb to the ore surface, rendering part of it hydrophilic, which is later mechanically separated from the hydrophobic fraction. However, this method does not mention the oxidation of magnetic sulfur impurities, and therefore it addresses the technical problem in a different way than the present invention.
Patent application US 2005/0084949 describes an air biofilter that reduces the content of sulfur compounds, particularly hydrogen sulfide (H2S). This biofilter uses particles with a hydrophilic nucleus and a hydrophobic coating. The hydrophobic coating includes a metallic agent, and may include microorganisms and nutrients, including phosphorous, nitrogen and potassium. The action of the metallic agent as well as the microorganisms is to that assist in the efficient breakdown of H2S, absorbing the sulfur residue in the biofilter. The metallic agent increases the bio-filtration efficiency. However, this document refers to the decrease of sulfur compounds in an air current, and does not described its use to the removal of magnetic sulfur impurities from iron concentrate.
To solve the stated technical problem, the present invention describes a procedure to remove the magnetic sulfur content from iron concentrate samples, that involves the inoculation of non-sterile cultures of Acidithiobacillus thiooxidans, on iron concentrates with a particle size below 0.15 mm, in such a way to generate, together with the addition of water with pH between 1.0 and 9.0 and without addition of potassium, the ore agglomeration for a further heap leaching treatment under controlled operating conditions.
Among the strains used as inocula, the present invention describes the use of the deposited strain DSM 17318, named Licanantay, which allows a removal with an efficiency above 80%, reaching 0.16% of final sulfur content in 21 days, and more particularly a final sulfur content below 0.1%.
Present invention allows to decrease the percentage of iron loss with respect to the loss due to alternative procedures, which in this case have a maximum of 3%.
According to the magnetic sulfur impurities removal kinetics observed from samples of iron concentrate during the application of strain Licanantay, transformation reactions take place based on the oxidation catalyzed by the sulfur-oxidizing microorganisms, together with precipitation phenomena that occur under the operation conditions. First, the inoculated sulfur-oxidizing microorganisms under potassium limiting condition catalyze the pyrrothite (here represented as FeS) magnetic sulfur impurities oxidation:
Practically keeping unaltered the non-magnetic sulfur compounds such as pyrite (FeS2), and selectively reducing the presence of magnetic sulfur impurities on the iron concentrate. Simultaneously, sulfate and/or jarosite precipitation reactions occur:
FeSO4+0.5H2SO4+0.25O2→0.5Fe2(SO4)3+0.5H2O
3Fe2(SO4)3+14H2O→2H3OFe3(SO4)2(OH)5+5H2SO4
3Fe2(SO4)3+Na2SO4+12H2O→2NaFe3(SO4)2(OH6)+6H2SO4
These reactions are pH dependent and generate precipitates over the iron concentrate surface that need to be mechanically removed via magnetic concentration process, represented by the Davis tube test (Dtt).
Present invention discloses a procedure to achieve an efficient removal of magnetic sulfur impurities content from iron concentrate to reach a final sulfur of 0.1%.
The disclosed procedure of the present invention to remove magnetic sulfur impurities includes:
to bioleach iron concentrate ores agglomerated in heaps, under temperature conditions between 5 and 35° C., inoculating the iron concentrates with cultures of Acidthiobacillus thiooxidans, with an inoculation concentration of between 104 to 106 cel/g and addition of water supplemented with nitrogen and phosphorous sources (0.01 to 0.5 g (NH4)2HPO4/L), without potassium addition, with a pH adjusted between 1.0 to 9.0, and a feeding between 5 and 15 L/h/m2.
Two iron concentrate ore samples were used. First sample named “Sample 1” with 28.39% Fe and 1.096% S. Second sample named “Sample 2” with 40.70% Fe and 0.950% S. Besides, a mineralogical analysis was performed to both samples including a liberation analysis. The basic chemical characterization of iron concentrate ore samples is shown in Table 1.
A microbiological characterization of the iron concentrate ore samples was done by quantitative PCR (qPCR) based on patented methodologies (U.S. Pat. No. 8,492,093 and U.S. Pat. No. 8,207,324), and is shown in Table 2, indicating the sole presence of heterotrophic species of the genus Sulfobacillus in low concentrations. Chemolitoautotrophic sulfur-oxidizing species were not detected.
Sulfobacillus
A.
A.
Leptospirillum
Acidiphilium
Ferroplasma
ferrooxidans
thiooxidans
The mineralogical composition of both iron concentrate ore samples was done using the statistical method of dot counting using an integration plate. The summary of the mineralogical characterization for each sample is given in Table 3.
The mineralogical characterization confirms the presence of pyrrothite as the main magnetic sulfur impurity present on iron concentrate ore samples.
As part of the iron concentrate ore sample mineralogical analysis, a liberation analysis for main minerals was performed, based on a statistical method of free, mineral/gangue associated and mineral/gangue included dot counting, using an integration plate. Results are shown in Table 4.
Such analysis showed that pyrrothite is mainly free (60 and 85%), and on a lesser extent associated to pyrite and magnetite (20 and 15%), depending on the sample, with no observed pyrrothite fraction included in gangue. This analysis indicates that the magnetic sulfur fraction present in these iron concentrate ore samples is bio-available towards the sulfur-oxidizing activity of strain Licanantay.
Later and once the iron concentrate ore samples were characterized, each sample was inoculated with strain Licanantay DSM 17318, in order to incorporate the sulfur oxidizing autotrophic activity that promotes an optimal oxidation of the magnetic sulfur impurities.
The determination of the magnetic sulfur impurities removal kinetics from both iron concentrate ore samples through the application of strain Licanantay was done in column assays, packing 500 g of iron concentrate ore previously agglomerated with water and inoculum at a dose of 106 cel/g, and mixed by rolling over a plastic liner. At the beginning of the leaching cycle, every column was fed at a rate of 5 L/h/m2 with water adjusted to pH 3.0 and addition of 0.5 g (NH4)2HPO4/L. Assays were done from 7 up to 60 days with forty columns in total, divided in two groups of twenty columns each. The first group of twenty columns (Group I) included potassium addition (0.006 g KH2PO4/L) as part of the feeding solution, while the second group (Group II) was modified without any potassium addition on the feed. The two iron concentrate ore samples were included on both groups. Tables 5 and 6 specify the operating conditions for both groups of columns.
To determine the magnetic sulfur impurities removal kinetics through the application of strain Licanantay DSM17318 on both iron concentrate ore samples, with and without potassium addition, columns were drained and discharged at the end of the operation times indicated on Tables 5 and 6. Dry samples of treated ore were analyzed for % Fe and % S before and after the Davis test tube (Dtt) for magnetic concentration.
The determination of the magnetic sulfur impurities removal kinetics for columns of Group II under potassium limiting conditions is shown in
Complementing the previous and as shown on
