EP3374531A1 - Method and apparatus for the dephosphorization of iron ore - Google Patents

Method and apparatus for the dephosphorization of iron ore

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Publication number
EP3374531A1
EP3374531A1 EP16820328.9A EP16820328A EP3374531A1 EP 3374531 A1 EP3374531 A1 EP 3374531A1 EP 16820328 A EP16820328 A EP 16820328A EP 3374531 A1 EP3374531 A1 EP 3374531A1
Authority
EP
European Patent Office
Prior art keywords
unit
iron ore
roasting
grinding
leaching
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP16820328.9A
Other languages
German (de)
French (fr)
Other versions
EP3374531B1 (en
Inventor
Luca TOMMASI
Florina Liliana ARSENE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Danieli and C Officine Meccaniche SpA
Original Assignee
Danieli and C Officine Meccaniche SpA
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Application filed by Danieli and C Officine Meccaniche SpA filed Critical Danieli and C Officine Meccaniche SpA
Priority claimed from PCT/IB2016/056794 external-priority patent/WO2017081646A1/en
Publication of EP3374531A1 publication Critical patent/EP3374531A1/en
Application granted granted Critical
Publication of EP3374531B1 publication Critical patent/EP3374531B1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/02—Roasting processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/11—Removing sulfur, phosphorus or arsenic other than by roasting

Definitions

  • Embodiments described here concern a method and an apparatus for the dephosphorization of iron ore.
  • the iron ore is extracted from mines, typically open or subterranean.
  • mines typically open or subterranean.
  • contaminating compounds such as phosphorus, sulfur and arsenic.
  • compounds based on phosphorus, sulfur, arsenic, zinc, copper, lead and mercury which are the main contaminating compounds that are frequently found in ferrous mines.
  • the content of phosphorus-based compounds can also be more than 1% in weight, which greatly limits the use thereof.
  • the iron ore in particular consists to a large extent of small particles, with a diameter generally less than 0.1 mm, of an oolite form, that is, ovoid morphological structures that have generated through enucleation, very compact and very difficult to treat with the conventional technique of grinding and magnetic separation, and also by leaching.
  • the minerals containing phosphorus typically apatite minerals, Ca 5 (PO 4 )(F, CI, OH), can be dispersed very finely in the ferrous matrix, which greatly limits the impact that grinding and also leaching can have.
  • a purpose of the present invention is to perfect a method for the dephosphorization of iron ore that makes available a final concentrate of iron ore with a content of phosphorus that is at least acceptable for the metallurgy industry.
  • the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
  • Embodiments described here concern a method for the dephosphorization of iron ore with a phosphorous content greater than 0.5% of magnetite, hematite or mixed type.
  • the method comprises: a preconditioning of the iron ore by means of a solid or pre-conditioning compound or in solution, with a content less than 5% in weight of the total ferrous mixture, said pre-conditioning compound being able to induce, by subsequent heating, a stress inside the material; an oxidizing roasting of the iron ore; a subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction higher than 85%.
  • the pre-conditioning is preferably performed upstream of the oxidizing roasting.
  • the apparatus comprises a pre- conditioning unit of the iron ore operating through a pre-conditioning compound that generates gas when it is heated, an oxidizing roasting unit of the iron ore fed and a leaching unit from which a concentrate of iron ore is obtained with a reduced phosphorous content.
  • FIG. 1 is a schematic block diagram of a method in accordance with embodiments described here;
  • FIG. 2 is a schematic block diagram of a method in accordance with other embodiments described here;
  • FIG. 3 is a schematic block diagram of a method in accordance with other embodiments described here;
  • - fig. 4 is a schematic block diagram of a method in accordance with even more embodiments described here;
  • FIG. 5 is a schematic block diagram of a method in accordance with even more embodiments described here;
  • FIG. 6 is a schematic block diagram of an apparatus in accordance with embodiments described here;
  • FIG. 7 is a schematic block diagram of an apparatus in accordance with other embodiments described here;
  • FIG. 8 is a schematic block diagram of an apparatus in accordance with other embodiments described here;
  • FIG. 9 is a schematic block diagram of an apparatus in accordance with even more embodiments described here;
  • FIG. 10 is a schematic block diagram of an apparatus in accordance with even more embodiments described here.
  • the present description also includes the intervals that derive from uniting or overlapping two or more intervals described, unless otherwise indicated.
  • the present description also includes the intervals that can derive from the combination of two or more values taken at different points, unless otherwise indicated.
  • Embodiments described here concern a method for the dephosphorization of iron ore.
  • Embodiments described here also concern the iron ore obtainable using the method for the dephosphorization of iron ore described here.
  • the dephosphorized iron ore obtainable according to the method described here can be used to produce steel.
  • embodiments described here concern an iron ore with an oolite ore structure.
  • a possible example of iron ore can provide a total content of iron of about 50-65% w/w and a mean content of phosphorus of about 0.8% w/w.
  • a big part of the phosphorus content is in the mineralogical form of apatite, or multiple inclusions of fine ferrous oxides carrying apatite.
  • Other minerals containing phosphorus in minimum parts or traces are also present, such as calcium-apatite.
  • Fig. 1 is used to describe embodiments of the method according to the present description, which include a pre-conditioning of the iron ore, with a phosphorus content greater than 0.5%, using a granulate or solution containing a preconditioning compound which, through subsequent heating, induces a stress inside the material, particularly the apatite, for example by developing a gas or a chemical attack on the phosphorus.
  • the pre-conditioning compound can be solid or in solution and with a content of less than 5% in weight of the total ferrous mix.
  • the pre-conditioning can be performed upstream of the oxidizing roasting.
  • the method then provides the oxidizing roasting of the iron ore and subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction of more than 85%.
  • the pre-conditioning of the iron ore using a granulate or solution containing a preconditioning compound which, through heating, generates a gas can provide to use a solution of calcium chloride (CaCl 2 ), or calcium carbonate (CaCO 3 ) or manganese chloride (MnCl 2 ), or iron chloride (FeCl 3 ).
  • the preconditioning of the iron ore due to a mechanism that not only generates stress on the level of the mineral matrix, also attacks the apatite, making it more soluble in the solution of the acid or base leaching agent and therefore improves the removal of the phosphorus in the subsequent leaching step, after the oxidizing roasting of the pre-conditioned ore.
  • a possible secondary grinding and a possible magnetic separation (fig. 5) it is provided to immerse it in the solution or it is mixed with the granulate containing the pre-conditioning compound.
  • the pre-conditioning time can be as much as 3 hours, for example, but not restrictively, from 1 to 3 hours, in particular from 1.5 to 2.5 hours, for example 2 hours.
  • the material can be filtered and subjected to heating through drying, for example in a kiln or analogous drying device, or loaded directly into the roasting kiln.
  • a high concentration solution is used during immersion, for example up to about 30%, in particular from about 15% to about 30%, more particularly from about 20% to about 25%.
  • the preconditioning compound is CaCl 2 and that the solution has a high concentration, about 20-22%.
  • the operating conditions of the pre- conditioning of the iron ore can be:
  • the method can provide a mixing and homogenization of the granulate with the material, for example in a vertical or horizontal mixer.
  • the pre-conditioning time can be reduced to 1 hour, for example but not restrictively, it can go from 5 min to 1 hour, in particular from 10 min to 45 min, for example 30 min.
  • the material can be loaded directly into the roasting kiln.
  • a granulate of CaCl 2 is used with a mass percentage added to the iron ore, for example up to about 5%.
  • the operating conditions of the preconditioning of the iron ore can be:
  • the cracking effect of the oolite structures is increased, creating further new channels for the leaching agent to penetrate.
  • the pre-conditioning also contributes to creating new mineral phases which involve the phosphorus, such as for example phospho-chlorates, calcium phosphates (substitution by means of solid diffusion during the oxidizing roasting), allowing a better overall leaching of these mineral phases created ex novo.
  • the oxidizing roasting of the iron ore can be performed in an oxidizing atmosphere, in particular using air as high-temperature comburent, in particular for example at a temperature between about 800°C and 1050°C, in particular between 850° and 1000°C.
  • oxidizing roasting can not only modify the mineral phases present, it also has a cracking effect on the particles with oolite structure, creating micro-channels that promote the penetration of the leaching agent during leaching.
  • the operating conditions of the oxidizing roasting can be:
  • leaching can be performed with an acid leaching agent, or a base leaching agent.
  • acid leaching agent can be sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ) or hydrochloric acid (HC1).
  • An example of a base leaching agent can be sodium hydroxide (NaOH).
  • Applicant has found that the leaching agent, acid or base, reduces the content of apatite in the final concentrate thanks to the phenomenon of phosphorus leaching. The leaching phenomenon is facilitated and made operative by the cracking of the oolite structures obtained during oxidizing roasting, which exposes the phosphorus to the attack of the leaching agent. This effect is further increased, if combined with the pre-conditioning of the iron ore before oxidizing roasting, for the presumed chlorination of the apatite itself, as explained in more detail hereafter.
  • Leaching can be performed by immersing the material in a solution of leaching agent, which is kept stirred to guarantee an adequate mass transfer and to promote contact between the ore and the leaching agent, limiting the phenomenon of surface passivation. At the end of leaching, a filtration is provided, followed by washing and rinsing in water, to remove the leached phosphorus, preventing it from remaining in the final concentrate. Leaching can be performed, for example at a temperature between about 20°C and 60°C, and taking into account the influence of the temperature on the kinetics of the process and, at the same time, the variation in the solubility of the compounds present in solution as a function of the temperature: low temperatures allow to obtain better results.
  • leaching of a large part of the phosphorus can occur generally in about 15-30 minutes, or in order to reduce the content of other acid components such as silica and alumina, this period of time can be increased to 6 hours.
  • the leaching agent selected is H 2 SO 4 .
  • the concentration of H 2 SO 4 can reach 15%, in particular from 1% to 15%, more particularly from 3% to 5%.
  • the mass percentage of immersed solid of the iron ore subjected to leaching goes from about 10% to 65%.
  • the operating conditions of leaching with H 2 SO 4 can be:
  • the leaching agent selected is HC1.
  • the concentration of HC1 can go for example up to 10%, in particular from 1% to 10%, more particularly from 1% to 4%.
  • the mass percentage of immersed solid of the ore subjected to leaching goes from about 10% to 65%.
  • the operating conditions of leaching with HC1 can be:
  • - concentration of HC1 about 1%, 2%, 3%, 5% or 10%;
  • Two-phase leaching consists in treating the iron ore by the acid or base leaching agent with a very high concentration in solution and with a higher percentage of solid at the beginning, so as to maximize the solubilized reaction speed of the phosphorus-based compounds.
  • the treatment is followed by a dilution of the concentration of the leaching agent and solid, so as to prevent a regression of the reaction equilibrium, optimizing the ratio between the quantity of leaching agent with respect to the removal of phosphorus and minimizing the leaching times.
  • FIG. 2 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description which include a floatation of the iron ore.
  • the floatation can be performed, in particular, between the oxidizing roasting of the iron ore and subsequent leaching, to obtain a final concentrate with a reduced phosphorus content.
  • the embodiments described using fig. 2 are combinable with the embodiments described using fig. 1, so that the method can include not only floatation but also pre-conditioning upstream of the oxidizing roasting.
  • floatation can be an inverse floatation, configured to separate at least the apatite or part of it from the remaining iron ore after oxidizing roasting and before leaching. In this way, floatation can allow to reduce the quantity of leaching agent needed later, to obtain the same reduction of phosphorus in the final concentrate.
  • Fig. 3 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description that include, as a preliminary operation, a primary crushing/grinding of the iron ore.
  • the primary crushing/grinding as described with reference to fig. 3, can be performed upstream of the pre-conditioning, for example in the embodiments described using figs. 1 and 2. If the embodiments described using fig. 3 are combined with the embodiments described using fig. 2, in possible embodiments the method can therefore include primary crushing/grinding of the iron ore, pre-conditioning, oxidizing roasting and leaching.
  • the primary crushing/grinding can be performed for example either dry or wet, so as to reduce the ore to a sufficiently small nominal size, for example less than 1 mm, so as to be able to be processed in the concentration plant.
  • the iron ore can initially be crushed to 90-100% less than 3.35 mm.
  • the ore can be ground with a ball mill in an open or closed circuit with dimensional classifiers such as for example hydrocyclones or dynamic air classifiers to obtain the desired dimensional distribution, for example 80% under 45 micrometers of nominal diameter (P 80 of 45 micrometers).
  • a high pressure grinding roll (HPGR) apparatus for the primary crushing/grinding a high pressure grinding roll (HPGR) apparatus can be used, which can be advantageous in terms of electricity consumption and to facilitate subsequent grinding, considering that the liberation size of the apatite material can be very fine.
  • HPGR high pressure grinding roll
  • Fig. 4 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description which include, as preliminary operation, a dry or wet treatment of the iron ore.
  • the dry treatment can include primary crushing/grinding, magnetic separation obtained precisely dry, pre-conditioning of the iron ore using a granulate containing a pre-conditioning compound, to be performed before the oxidizing roasting, followed by a subsequent secondary grinding before leaching.
  • the embodiments described are particularly advantageous economically if performed dry, given no intermediate filtration is necessary and given the reduced risk of depositing of the wet ore.
  • a magnetic separation can follow, performed dry with low intensity, for example with an intensity of the magnetic field between 1000 - 2000 Gauss.
  • the decision to adopt, for example, a LIMS technique can be made according to the results of the LIMS test performed dry. Following the dry magnetic separation the non-magnetic material is separated with losses that depend on the nature of the iron oxides, in particular between 10- 20%, for example 13%.
  • Fig. 5 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description that can include a reducing roasting. In possible implementations, a possible subsequent magnetic separation can also be provided.
  • the possible reducing roasting and/or possible subsequent magnetic separation can, in particular, be performed before the oxidizing roasting and, if pre- conditioning is provided as described with reference to figs. 1, 2 and 3, also before the pre-conditioning.
  • the possible reducing roasting and/or possible subsequent magnetic separation can be performed after the primary crushing/grinding of the iron ore.
  • the reducing roasting can be performed to convert the non-magnetic minerals, such as hematite or goethite, to synthetic magnetite, operating in a reducing atmosphere.
  • non-magnetic minerals such as hematite or goethite
  • maghemite can also be converted into magnetite.
  • An example of reducing atmosphere can be a mixture of CO, CO 2 , N 2 and possibly H 2 and/or H 2 O. Possible quantities of the reducing mixture are for example about 10% CO, 30% CO 2 , 60% N 2 .
  • other compounds with a base of hydrogen, nitrogen, oxygen and carbon can be contained in the gas, depending on the process used to obtain it.
  • Reducing roasting is performed similarly to oxidizing roasting, only the atmosphere is reducing and the temperatures are lower.
  • Reducing roasting can, in particular, be performed at a controlled high temperature under 900°C, in particular between 600°C and 800°C, to prevent the formation of wustite and metal iron.
  • a rotary kiln can be used for example for the reducing roasting. The time spent in the rotary kiln can go from 1 to 2 hours.
  • the magnetically roasted material is discharged and cooled, preferably in water, so that it can be ground.
  • the operating conditions of the reducing roasting can be:
  • composition of the reducing gas 5-20% CO, 10-50% CO 2 , 0-40% H 2 , 0-20% FL , 40-70% N 2 .
  • a time spent in the kiln of about 1.5 hours can ensure that all the material reacts and is suitably magnetized in these operating conditions.
  • a secondary grinding, or regrinding, of the iron ore can be provided.
  • a secondary wet or dry grinding, or regrinding, of the iron ore can be provided.
  • the secondary grinding or regrinding can be performed to obtain, for example, a dimensional distribution of P 80 of 45 micrometers.
  • the specific choice of the secondary grinding parameters has for example been defined and tested experimentally by Applicant using a wet or dry grinding mill on a laboratory scale with a load of graduated grinding balls and by carrying out the Davis tube test to select the grinding size P 80 .
  • the magnetic separation which can be performed for example after the primary crushing/grinding, and/or after the reducing roasting and/or after the secondary grinding when provided, can be a low-intensity magnetic separation (LIMS) performed wet or dry, for example with an intensity of the magnetic field between about 1000 and 2000 Gauss.
  • LIMS low-intensity magnetic separation
  • a mass recovery can be obtained of more than 90%, thanks to the magnetic separation performed wet, with a removal between 30 and 35% of phosphorus in the magnetic concentrate.
  • the starting ore contains 0.8% phosphorus, this can be reduced to 0.53% phosphorus.
  • a mass recovery can be obtained of more than 85%, thanks to the magnetic separation performed dry, without any prior reducing roasting, with a removal between 35 and 40% of phosphorus in the magnetic concentrate.
  • the ore introduced contains 0.8% phosphorus, this can be taken to a concentration of 0.61%.
  • a pre-concentration of the iron ore can be provided using magnetic separation.
  • a non- magnetic material is separated, which is subjected to reducing roasting, from a magnetic material which is subjected to secondary roasting if provided, and then to the possible magnetic separation, or, if secondary grinding is not provided, sent directly to the possible magnetic separation subsequent to the reducing roasting.
  • the pre-concentration of the iron ore by magnetic separation can be a low- intensity magnetic separation (LIMS), for example with an intensity of the magnetic field of about 1000-2000 Gauss, or a medium intensity magnetic separation (MIMS).
  • LIMS low- intensity magnetic separation
  • MIMS medium intensity magnetic separation
  • this separation can be performed by a belt-type magnetic separator drum, also called a dry cobber.
  • more than 90% of the material can be concentrated with pre- concentration, obtaining:
  • floatation can also be provided as in the cases described using figs. 3 and 4, between oxidizing roasting and leaching, or, in other variants, floatation may not be performed.
  • the magnetic separation after primary crushing/grinding, and/or after reducing roasting, and/or possibly after secondary grinding can be provided, or not.
  • Embodiments described here also concern an apparatus 10 for the dephosphorization of iron ore.
  • Fig. 6 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a pre-conditioning unit 14 of the iron ore using a solution containing a pre-conditioning compound which, through heating and attacking the phosphorus based compounds, generates a gas, before the oxidizing roasting unit 12 and the leaching unit 13.
  • Fig 7 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes the pre-conditioning unit 14, the oxidizing roasting unit 12, a floatation unit 15 and the leaching unit 13.
  • Fig. 8 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a primary crushing/grinding unit 16 of the iron ore, the possible pre-conditioning unit 14, the oxidizing roasting unit 12 and the leaching unit 13.
  • the primary crushing/grinding unit 16 of the iron ore is before at least the oxidizing roasting unit 12 and, if provided, also before the pre-conditioning unit 14.
  • Fig. 9 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a primary crushing/grinding unit 16 of the iron ore, the magnetic separation unit 18, the pre-conditioning unit 14, the oxidizing roasting unit 12, the secondary grinding/regrinding unit 19 and the leaching unit 13.
  • the primary crushing/grinding unit 16 of the iron ore is positioned before the oxidizing roasting unit 12 and also before the pre- conditioning unit 14.
  • Fig. 10 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes the possible primary crushing/grinding unit 16, a subsequent reducing roasting unit 17, a possible subsequent magnetic separation unit 18, the possible pre-conditioning unit 14, the oxidizing roasting unit 12, the floatation unit 15 and the leaching unit 13.
  • the embodiments of the apparatus 10 described with reference to fig. 5 can also include a secondary grinding unit 19, between the reducing roasting unit 17 and the possible magnetic separation unit 18, and a pre-concentration unit using magnetic separation 20 of the iron ore, between the primary crushing/grinding unit 16 and the reducing roasting unit 17.
  • Embodiments described here allow to considerably reduce the phosphorus content in the final concentrate, for example a reduction of up to about 0.12- 0.13% w/w in the case of the embodiments described here without preconditioning, or even up to about 0.02-0.03% w/w in the case of the embodiments with pre-conditioning, with for example a total content of iron of about 60-64%.
  • the reducing roasting was performed under the following conditions:
  • composition of the reducing gas 10% CO, 30% CO 2 , 60% N 2 .
  • the secondary grinding was performed with a feed size P 80 of about 1 mm, a percentage of solid of 50%.
  • the magnetic separation was performed under the following conditions:
  • the pre-conditioning where provided wet (1 st and 4 th test) was performed with a solution of CaCl 2 with a concentration of 20-22%, percentage of solid 30%, rotor speed 350 rpm, immersion time 2 hours, immersion temperature 25°C. Furthermore, where provided dry (5 test), the pre-conditioning was performed with a granulate of CaCl 2 in a mass percentage of about 4%, with a mixing and homogenization time of 1 hour, environmental temperature (i.e. 25°C).
  • Oxidizing roasting was performed under the following conditions:
  • the total iron content is assessed using XRF, that is, expressed as Fe 2 O 3 % measured with XRF (X-ray fluorescence) x 0.6994.
  • the total phosphorus content is assessed using XRF, expressed as P 2 O 5 % measured with XRF (X-ray fluorescence) x 0.4364.

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Abstract

Method for the dephosphorization of iron ore with a phosphorous content greater than 0.5% of magnetite, hematite or mixed nature, comprising: - pre-conditioning of the iron ore by means of a solid or pre-conditioning compound or in solution, with a content less than 5% in weight of the total ferrous mixture; - an oxidizing roasting of the iron ore; - a subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction higher than 85%.

Description

"METHOD AND APPARATUS FOR THE DEPHOSPHORIZATION OF IRON ORE"
FIELD OF THE INVENTION
Embodiments described here concern a method and an apparatus for the dephosphorization of iron ore.
BACKGROUND OF THE INVENTION
It is known that steel can be produced starting from iron ore, possibly combined with scrap iron.
It is also known that the iron ore is extracted from mines, typically open or subterranean. Here, apart from compounds based on silica, alumina, calcium and magnesium, there may be deposits of magnetite, hematite or mixed, lacking or almost lacking in contaminating compounds such as phosphorus, sulfur and arsenic. However, as these deposits are progressively exhausted, it is necessary to find the iron ore from other mine deposits where it may be mixed with compounds other than iron-based compounds, contaminating compounds that are not useful and in particular can negatively influence the quality of the final steel. Examples of such compounds are compounds based on phosphorus, sulfur, arsenic, zinc, copper, lead and mercury, which are the main contaminating compounds that are frequently found in ferrous mines.
In this context, it is therefore known to intervene on the iron ores to reduce the content of compounds other than iron-based compounds, before the metallurgical operations or directly from the molten metal, but this latter approach can be more complex and costly. The reduction rate, more or less high, is typically selected depending on the higher or lower quality required for the final steel.
A common, traditional and economical approach, widely used in the metallurgy industry, provides to subject the iron ores to grinding and separation, magnetic or gravitometric or by floatation.
For non-ferrous minerals such as copper, silver or gold, a commonly used technique for removing such pollutants is leaching, using acids or bases. At least in laboratory tests, leaching applied to iron ores appears to be able to supply encouraging results in terms of reducing the phosphorus content. However, on an industrial level, there is the disadvantage of the high costs connected to the consumption of the acid or base agent, and also the fact that often this technique does not give the hoped-for results in the case of iron ores with a particular morphology that prevents direct exposure of the contaminated ore particles to the acid or base attack, for example a morphology with an oolitic matrix. Indeed, due to the oolitic nature of these materials, the liberation size of the apatite mineral containing phosphorus is very fine: in practice, this limits the effectiveness of the crushing and grinding.
Considering their vastness and geographic presence, interest in sedimentary oolitic iron deposits is becoming very great in the field. Unfortunately, in such deposits the content of phosphorus-based compounds can also be more than 1% in weight, which greatly limits the use thereof. In such deposits, as they are of sedimentary origin, the iron ore in particular consists to a large extent of small particles, with a diameter generally less than 0.1 mm, of an oolite form, that is, ovoid morphological structures that have generated through enucleation, very compact and very difficult to treat with the conventional technique of grinding and magnetic separation, and also by leaching. In such structures with an oolite matrix, in fact, the minerals containing phosphorus, typically apatite minerals, Ca5(PO4)(F, CI, OH), can be dispersed very finely in the ferrous matrix, which greatly limits the impact that grinding and also leaching can have.
Other limitations and disadvantages of conventional solutions and technologies will be clear to a person of skill after reading the remaining part of the present description with reference to the drawings and the description of the embodiments that follow, although it is clear that the description of the state of the art connected to the present description must not be considered an admission that what is described here is already known from the state of the prior art.
There is therefore a need to perfect a method and an apparatus for the dephosphorization of iron ore that can overcome at least one of the shortcomings of the state of the art.
In particular, a purpose of the present invention is to perfect a method for the dephosphorization of iron ore that makes available a final concentrate of iron ore with a content of phosphorus that is at least acceptable for the metallurgy industry.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
SUMMARY OF THE INVENTION
The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
Embodiments described here concern a method for the dephosphorization of iron ore with a phosphorous content greater than 0.5% of magnetite, hematite or mixed type.
According to one embodiment of the invention, the method comprises: a preconditioning of the iron ore by means of a solid or pre-conditioning compound or in solution, with a content less than 5% in weight of the total ferrous mixture, said pre-conditioning compound being able to induce, by subsequent heating, a stress inside the material; an oxidizing roasting of the iron ore; a subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction higher than 85%.
The pre-conditioning is preferably performed upstream of the oxidizing roasting.
Other embodiments described here also concern a dephosphorized iron ore, that is, with a reduced phosphorous content, obtainable by means of a method according to the present description.
Other embodiments described here concern an apparatus for the dephosphorization of iron ore.
According to one embodiment of the invention, the apparatus comprises a pre- conditioning unit of the iron ore operating through a pre-conditioning compound that generates gas when it is heated, an oxidizing roasting unit of the iron ore fed and a leaching unit from which a concentrate of iron ore is obtained with a reduced phosphorous content.
These and other aspects, characteristics and advantages of the present disclosure will be better understood with reference to the following description, drawings and attached claims. The drawings, which are integrated and form part of the present description, show some forms of embodiment of the present invention, and together with the description, are intended to describe the principles of the disclosure.
The various aspects and characteristics described in the present description can be applied individually where possible. These individual aspects, for example aspects and characteristics described in the attached dependent claims, can be the object of divisional applications.
It is understood that any aspect or characteristic that is discovered, during the patenting process, to be already known, shall not be claimed and shall be the object of a disclaimer.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:
- fig. 1 is a schematic block diagram of a method in accordance with embodiments described here;
- fig. 2 is a schematic block diagram of a method in accordance with other embodiments described here;
- fig. 3 is a schematic block diagram of a method in accordance with other embodiments described here;
- fig. 4 is a schematic block diagram of a method in accordance with even more embodiments described here;
- fig. 5 is a schematic block diagram of a method in accordance with even more embodiments described here;
- fig. 6 is a schematic block diagram of an apparatus in accordance with embodiments described here;
- fig. 7 is a schematic block diagram of an apparatus in accordance with other embodiments described here;
- fig. 8 is a schematic block diagram of an apparatus in accordance with other embodiments described here;
- fig. 9 is a schematic block diagram of an apparatus in accordance with even more embodiments described here;
- fig. 10 is a schematic block diagram of an apparatus in accordance with even more embodiments described here.
To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
We shall now refer in detail to the various embodiments of the present invention, of which one or more examples are shown in the attached drawing. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one embodiment can be adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.
Before describing these embodiments, we must also clarify that the present description is not limited in its application to details of the construction and disposition of the components as described in the following description using the attached drawings. The present description can provide other embodiments and can be obtained or executed in various other ways. We must also clarify that the phraseology and terminology used here is for the purposes of description only, and cannot be considered as limitative. The use of terms such as "including", "comprising", "having" and their variations is intended to include the elements listed after them and their equivalents, and also additional elements.
Unless otherwise defined, all the technical and scientific terms used here and hereafter have the same meaning as commonly understood by a person with ordinary experience in the field of the art to which the present invention belongs. Even if methods and materials similar or equivalent to those described here can be used in practice and in the trials of the present invention, the methods and materials are described hereafter as an example. In the event of conflict, the present application shall prevail, including its definitions. The materials, methods and examples have a purely illustrative purpose and shall not be understood restrictively.
All the temperatures, unless otherwise indicated, are expressed in degrees Celsius.
All the percentages and ratios indicated are referred to the weight (w/w), unless otherwise indicated.
All the percentage ranges reported here are supplied with the provision that the sum with respect to the total is 100%, unless otherwise indicated.
All the intervals reported here shall be understood to include the extremes, including those that report an interval "between" two values, unless otherwise indicated.
The present description also includes the intervals that derive from uniting or overlapping two or more intervals described, unless otherwise indicated.
The present description also includes the intervals that can derive from the combination of two or more values taken at different points, unless otherwise indicated.
Embodiments described here concern a method for the dephosphorization of iron ore.
Embodiments described here also concern the iron ore obtainable using the method for the dephosphorization of iron ore described here.
According to some embodiments, the dephosphorized iron ore obtainable according to the method described here can be used to produce steel.
In particular, embodiments described here concern an iron ore with an oolite ore structure. A possible example of iron ore can provide a total content of iron of about 50-65% w/w and a mean content of phosphorus of about 0.8% w/w. Generally speaking, a big part of the phosphorus content is in the mineralogical form of apatite, or multiple inclusions of fine ferrous oxides carrying apatite. Other minerals containing phosphorus in minimum parts or traces are also present, such as calcium-apatite.
Fig. 1 is used to describe embodiments of the method according to the present description, which include a pre-conditioning of the iron ore, with a phosphorus content greater than 0.5%, using a granulate or solution containing a preconditioning compound which, through subsequent heating, induces a stress inside the material, particularly the apatite, for example by developing a gas or a chemical attack on the phosphorus. The pre-conditioning compound can be solid or in solution and with a content of less than 5% in weight of the total ferrous mix. In particular, the pre-conditioning can be performed upstream of the oxidizing roasting. After pre-conditioning, the method then provides the oxidizing roasting of the iron ore and subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction of more than 85%.
In some embodiments, combinable with all the embodiments described here, the pre-conditioning of the iron ore using a granulate or solution containing a preconditioning compound which, through heating, generates a gas can provide to use a solution of calcium chloride (CaCl2), or calcium carbonate (CaCO3) or manganese chloride (MnCl2), or iron chloride (FeCl3). Advantageously, the preconditioning of the iron ore, due to a mechanism that not only generates stress on the level of the mineral matrix, also attacks the apatite, making it more soluble in the solution of the acid or base leaching agent and therefore improves the removal of the phosphorus in the subsequent leaching step, after the oxidizing roasting of the pre-conditioned ore.
According to possible implementations, to pre-condition the iron ore, which can have been subjected for example to primary crushing/grinding (fig. 4) and possibly to a reducing roasting, a possible secondary grinding and a possible magnetic separation (fig. 5), it is provided to immerse it in the solution or it is mixed with the granulate containing the pre-conditioning compound.
Operationally, for example, for the solution containing the pre-conditioning compound, it is possible to provide immersion in conditions of constant stirring, for example using a rotor stirrer. The pre-conditioning time can be as much as 3 hours, for example, but not restrictively, from 1 to 3 hours, in particular from 1.5 to 2.5 hours, for example 2 hours. At the end of immersion, the material can be filtered and subjected to heating through drying, for example in a kiln or analogous drying device, or loaded directly into the roasting kiln.
Advantageously, in possible implementations, to guarantee the greatest impregnation possible of the pre-conditioning compound on the surface of the ore particles, a high concentration solution is used during immersion, for example up to about 30%, in particular from about 15% to about 30%, more particularly from about 20% to about 25%. A possible example can provide that the preconditioning compound is CaCl2 and that the solution has a high concentration, about 20-22%.
For example, in possible implementations, the operating conditions of the pre- conditioning of the iron ore can be:
- concentration of the solution of CaCl2 from about 20% to 25%;
- percentage of solid about 20-50%;
- immersion time up to about 3 hours.
Operationally, for example, for the granulates containing the pre-conditioning compound, the method can provide a mixing and homogenization of the granulate with the material, for example in a vertical or horizontal mixer. The pre-conditioning time can be reduced to 1 hour, for example but not restrictively, it can go from 5 min to 1 hour, in particular from 10 min to 45 min, for example 30 min. At the end of mixing, the material can be loaded directly into the roasting kiln.
Advantageously, in possible implementations, to guarantee the greatest possible adherence of the pre-conditioning granulate on the surface of the ore particles, a granulate of CaCl2 is used with a mass percentage added to the iron ore, for example up to about 5%.
In other possible implementations, the operating conditions of the preconditioning of the iron ore can be:
- mass percentage of CaCl2 less than 5%;
- mixing time up to about 1 hour.
In the embodiments that provide pre-conditioning, with the development of gas caused by the heating taking place during the oxidizing roasting, the cracking effect of the oolite structures is increased, creating further new channels for the leaching agent to penetrate. Furthermore, the pre-conditioning also contributes to creating new mineral phases which involve the phosphorus, such as for example phospho-chlorates, calcium phosphates (substitution by means of solid diffusion during the oxidizing roasting), allowing a better overall leaching of these mineral phases created ex novo.
In some embodiments, combinable with all the embodiments described here, the oxidizing roasting of the iron ore can be performed in an oxidizing atmosphere, in particular using air as high-temperature comburent, in particular for example at a temperature between about 800°C and 1050°C, in particular between 850° and 1000°C.
Applicant has found that oxidizing roasting can not only modify the mineral phases present, it also has a cracking effect on the particles with oolite structure, creating micro-channels that promote the penetration of the leaching agent during leaching.
For example, in possible implementations, the operating conditions of the oxidizing roasting can be:
- temperature about 850-1000°C;
- duration about 1-2 hours;
- air used as oxidizing mixture.
In some embodiments, combinable with all the embodiments described here, leaching can be performed with an acid leaching agent, or a base leaching agent. Examples of acid leaching agent can be sulfuric acid (H2SO4), nitric acid (HNO3) or hydrochloric acid (HC1). An example of a base leaching agent can be sodium hydroxide (NaOH). Applicant has found that the leaching agent, acid or base, reduces the content of apatite in the final concentrate thanks to the phenomenon of phosphorus leaching. The leaching phenomenon is facilitated and made operative by the cracking of the oolite structures obtained during oxidizing roasting, which exposes the phosphorus to the attack of the leaching agent. This effect is further increased, if combined with the pre-conditioning of the iron ore before oxidizing roasting, for the presumed chlorination of the apatite itself, as explained in more detail hereafter.
Leaching can be performed by immersing the material in a solution of leaching agent, which is kept stirred to guarantee an adequate mass transfer and to promote contact between the ore and the leaching agent, limiting the phenomenon of surface passivation. At the end of leaching, a filtration is provided, followed by washing and rinsing in water, to remove the leached phosphorus, preventing it from remaining in the final concentrate. Leaching can be performed, for example at a temperature between about 20°C and 60°C, and taking into account the influence of the temperature on the kinetics of the process and, at the same time, the variation in the solubility of the compounds present in solution as a function of the temperature: low temperatures allow to obtain better results.
Advantageously, in some implementations, leaching of a large part of the phosphorus can occur generally in about 15-30 minutes, or in order to reduce the content of other acid components such as silica and alumina, this period of time can be increased to 6 hours.
In some implementations, the leaching agent selected is H2SO4. In some implementations, the concentration of H2SO4 can reach 15%, in particular from 1% to 15%, more particularly from 3% to 5%.
In some implementations, the mass percentage of immersed solid of the iron ore subjected to leaching goes from about 10% to 65%.
For example, in possible implementations, the operating conditions of leaching with H2SO4 can be:
- concentration of H2SO4: about 1%, 3%, 5% or 10%;
- temperature between 20-60°C;
- percentage of solid about 10-65%;
- leaching time from 0.1 hour to 6 hours.
In some implementations, the leaching agent selected is HC1. The concentration of HC1 can go for example up to 10%, in particular from 1% to 10%, more particularly from 1% to 4%.
In other implementations, the mass percentage of immersed solid of the ore subjected to leaching goes from about 10% to 65%.
The operating conditions of leaching with HC1 can be:
- concentration of HC1: about 1%, 2%, 3%, 5% or 10%;
- temperature between 20-60°C;
- percentage of solid about 10-65%;
- leaching time from 0.1 hour to 1 hour.
Advantageously, in some implementations, it has been found that removing the phosphorus during the leaching step can be improved for example by two- phase leaching. Two-phase leaching consists in treating the iron ore by the acid or base leaching agent with a very high concentration in solution and with a higher percentage of solid at the beginning, so as to maximize the solubilized reaction speed of the phosphorus-based compounds. The treatment is followed by a dilution of the concentration of the leaching agent and solid, so as to prevent a regression of the reaction equilibrium, optimizing the ratio between the quantity of leaching agent with respect to the removal of phosphorus and minimizing the leaching times. Fig. 2 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description which include a floatation of the iron ore. The floatation can be performed, in particular, between the oxidizing roasting of the iron ore and subsequent leaching, to obtain a final concentrate with a reduced phosphorus content. The embodiments described using fig. 2 are combinable with the embodiments described using fig. 1, so that the method can include not only floatation but also pre-conditioning upstream of the oxidizing roasting.
In some embodiments, combinable with all the embodiments described here, floatation can be an inverse floatation, configured to separate at least the apatite or part of it from the remaining iron ore after oxidizing roasting and before leaching. In this way, floatation can allow to reduce the quantity of leaching agent needed later, to obtain the same reduction of phosphorus in the final concentrate.
In possible implementations, with floatation it is possible to have a mass recovery of from 60% to 70% and a percentage reduction of phosphorus from 50% to 60%. For example, starting from a phosphorus content of 0.8% w/w, possibly subjected to magnetic separation which takes the phosphorus content to about 0.53% w/w, it can be reduced to a phosphorus content of about 0.35-0.42% w/w. This reduction, as we said, can be advantageous because it allows to use a smaller quantity of leaching agent with the same reduction of phosphorus in the final concentrate.
Fig. 3 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description that include, as a preliminary operation, a primary crushing/grinding of the iron ore. The primary crushing/grinding, as described with reference to fig. 3, can be performed upstream of the pre-conditioning, for example in the embodiments described using figs. 1 and 2. If the embodiments described using fig. 3 are combined with the embodiments described using fig. 2, in possible embodiments the method can therefore include primary crushing/grinding of the iron ore, pre-conditioning, oxidizing roasting and leaching.
In some embodiments, combinable with all the embodiments described here, the primary crushing/grinding can be performed for example either dry or wet, so as to reduce the ore to a sufficiently small nominal size, for example less than 1 mm, so as to be able to be processed in the concentration plant. In particular, according to a possible implementation, the iron ore can initially be crushed to 90-100% less than 3.35 mm. Subsequently, the ore can be ground with a ball mill in an open or closed circuit with dimensional classifiers such as for example hydrocyclones or dynamic air classifiers to obtain the desired dimensional distribution, for example 80% under 45 micrometers of nominal diameter (P80 of 45 micrometers). According to other possible implementations, for the primary crushing/grinding a high pressure grinding roll (HPGR) apparatus can be used, which can be advantageous in terms of electricity consumption and to facilitate subsequent grinding, considering that the liberation size of the apatite material can be very fine.
Fig. 4 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description which include, as preliminary operation, a dry or wet treatment of the iron ore. However, in particular, the dry treatment can include primary crushing/grinding, magnetic separation obtained precisely dry, pre-conditioning of the iron ore using a granulate containing a pre-conditioning compound, to be performed before the oxidizing roasting, followed by a subsequent secondary grinding before leaching. The embodiments described are particularly advantageous economically if performed dry, given no intermediate filtration is necessary and given the reduced risk of depositing of the wet ore.
In some embodiments, combinable with all the embodiments described here, after the primary crushing/grinding of the iron ore, with a dimensional distribution of 80% under 0.3 mm, a magnetic separation can follow, performed dry with low intensity, for example with an intensity of the magnetic field between 1000 - 2000 Gauss. The decision to adopt, for example, a LIMS technique can be made according to the results of the LIMS test performed dry. Following the dry magnetic separation the non-magnetic material is separated with losses that depend on the nature of the iron oxides, in particular between 10- 20%, for example 13%.
Fig. 5 is used to describe embodiments, combinable with all the embodiments described here, of the method according to the present description that can include a reducing roasting. In possible implementations, a possible subsequent magnetic separation can also be provided.
The possible reducing roasting and/or possible subsequent magnetic separation can, in particular, be performed before the oxidizing roasting and, if pre- conditioning is provided as described with reference to figs. 1, 2 and 3, also before the pre-conditioning.
Furthermore, if primary crushing/grinding is provided as described with reference to figs. 3 and 4, the possible reducing roasting and/or possible subsequent magnetic separation can be performed after the primary crushing/grinding of the iron ore.
In some embodiments, combinable with all the embodiments described here, the reducing roasting can be performed to convert the non-magnetic minerals, such as hematite or goethite, to synthetic magnetite, operating in a reducing atmosphere. Apart from these non-magnetic materials, maghemite can also be converted into magnetite. An example of reducing atmosphere can be a mixture of CO, CO2, N2 and possibly H2 and/or H2O. Possible quantities of the reducing mixture are for example about 10% CO, 30% CO2, 60% N2. However, also other compounds with a base of hydrogen, nitrogen, oxygen and carbon can be contained in the gas, depending on the process used to obtain it. Reducing roasting is performed similarly to oxidizing roasting, only the atmosphere is reducing and the temperatures are lower. Reducing roasting can, in particular, be performed at a controlled high temperature under 900°C, in particular between 600°C and 800°C, to prevent the formation of wustite and metal iron. By using reducing roasting, a considerable increase can be obtained in the magnetic content of the material, while contaminants such as phosphorus or arsenic do not suffer significant changes. A rotary kiln can be used for example for the reducing roasting. The time spent in the rotary kiln can go from 1 to 2 hours.
The magnetically roasted material is discharged and cooled, preferably in water, so that it can be ground.
For example, in possible implementations, the operating conditions of the reducing roasting can be:
- temperature about 600-800°C;
- time spent in kiln up to about 2 hours; - composition of the reducing gas: 5-20% CO, 10-50% CO2, 0-40% H2, 0-20% FL , 40-70% N2.
Advantageously, a time spent in the kiln of about 1.5 hours can ensure that all the material reacts and is suitably magnetized in these operating conditions.
In possible implementations of the embodiments described using fig. 5, between the reducing roasting and subsequent possible magnetic separation a secondary grinding, or regrinding, of the iron ore can be provided.
In possible implementations of the embodiments described using fig. 5, between the oxidizing roasting and subsequent leaching a secondary wet or dry grinding, or regrinding, of the iron ore can be provided.
In some embodiments, combinable with all the embodiments described here, the secondary grinding or regrinding can be performed to obtain, for example, a dimensional distribution of P80 of 45 micrometers. The specific choice of the secondary grinding parameters has for example been defined and tested experimentally by Applicant using a wet or dry grinding mill on a laboratory scale with a load of graduated grinding balls and by carrying out the Davis tube test to select the grinding size P80.
In some embodiments, combinable with all the embodiments described here, the magnetic separation, which can be performed for example after the primary crushing/grinding, and/or after the reducing roasting and/or after the secondary grinding when provided, can be a low-intensity magnetic separation (LIMS) performed wet or dry, for example with an intensity of the magnetic field between about 1000 and 2000 Gauss. The decision to use a LIMS technique for example can be made according to the results of the Davis tube test.
Advantageously, a mass recovery can be obtained of more than 90%, thanks to the magnetic separation performed wet, with a removal between 30 and 35% of phosphorus in the magnetic concentrate. For example, if the starting ore contains 0.8% phosphorus, this can be reduced to 0.53% phosphorus.
Advantageously, a mass recovery can be obtained of more than 85%, thanks to the magnetic separation performed dry, without any prior reducing roasting, with a removal between 35 and 40% of phosphorus in the magnetic concentrate. For example, if the ore introduced contains 0.8% phosphorus, this can be taken to a concentration of 0.61%. Furthermore, in other possible implementations of the embodiments described using fig. 5, after the primary crushing/grinding and before the reducing roasting, a pre-concentration of the iron ore can be provided using magnetic separation. Following the pre-concentration of the iron ore using magnetic separation, a non- magnetic material is separated, which is subjected to reducing roasting, from a magnetic material which is subjected to secondary roasting if provided, and then to the possible magnetic separation, or, if secondary grinding is not provided, sent directly to the possible magnetic separation subsequent to the reducing roasting.
In some embodiments, combinable with all the embodiments described here, the pre-concentration of the iron ore by magnetic separation can be a low- intensity magnetic separation (LIMS), for example with an intensity of the magnetic field of about 1000-2000 Gauss, or a medium intensity magnetic separation (MIMS). For example, this separation can be performed by a belt-type magnetic separator drum, also called a dry cobber.
Advantageously, more than 90% of the material can be concentrated with pre- concentration, obtaining:
- a removal of more than 15% of phosphorus in the magnetic concentrate. For example, if the starting ore contains 0.8% phosphorus, this can be reduced to 0.66% phosphorus;
- a recovery of iron greater than 95% in the magnetic concentrate.
In the embodiments described using fig. 5, floatation can also be provided as in the cases described using figs. 3 and 4, between oxidizing roasting and leaching, or, in other variants, floatation may not be performed.
In particular, possible implementations described with reference to fig. 5 can provide the following steps in succession:
- primary crushing/grinding of the iron ore;
- pre-concentration of the iron ore using magnetic separation;
- reducing roasting;
- secondary grinding;
- magnetic separation;
- pre-conditioning of the iron ore;
- oxidizing roasting; - floatation;
- leaching.
As described above, in possible implementations the magnetic separation after primary crushing/grinding, and/or after reducing roasting, and/or possibly after secondary grinding, can be provided, or not.
With reference to fig. 5, the arrows shown by dashes represent possible bypasses of the process.
Embodiments described here also concern an apparatus 10 for the dephosphorization of iron ore.
Fig. 6 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a pre-conditioning unit 14 of the iron ore using a solution containing a pre-conditioning compound which, through heating and attacking the phosphorus based compounds, generates a gas, before the oxidizing roasting unit 12 and the leaching unit 13.
Fig 7 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes the pre-conditioning unit 14, the oxidizing roasting unit 12, a floatation unit 15 and the leaching unit 13.
Fig. 8 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a primary crushing/grinding unit 16 of the iron ore, the possible pre-conditioning unit 14, the oxidizing roasting unit 12 and the leaching unit 13. The primary crushing/grinding unit 16 of the iron ore is before at least the oxidizing roasting unit 12 and, if provided, also before the pre-conditioning unit 14.
Fig. 9 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes a primary crushing/grinding unit 16 of the iron ore, the magnetic separation unit 18, the pre-conditioning unit 14, the oxidizing roasting unit 12, the secondary grinding/regrinding unit 19 and the leaching unit 13. The primary crushing/grinding unit 16 of the iron ore is positioned before the oxidizing roasting unit 12 and also before the pre- conditioning unit 14.
Fig. 10 is used to describe embodiments, combinable with all the embodiments described here, in which the apparatus 10 includes the possible primary crushing/grinding unit 16, a subsequent reducing roasting unit 17, a possible subsequent magnetic separation unit 18, the possible pre-conditioning unit 14, the oxidizing roasting unit 12, the floatation unit 15 and the leaching unit 13.
In possible implementations, the embodiments of the apparatus 10 described with reference to fig. 5 can also include a secondary grinding unit 19, between the reducing roasting unit 17 and the possible magnetic separation unit 18, and a pre-concentration unit using magnetic separation 20 of the iron ore, between the primary crushing/grinding unit 16 and the reducing roasting unit 17.
With reference to fig. 10, in the same way as provided with regard to fig. 5, the arrows shown by dashes represent possible by -passes of the apparatus.
Embodiments described here allow to considerably reduce the phosphorus content in the final concentrate, for example a reduction of up to about 0.12- 0.13% w/w in the case of the embodiments described here without preconditioning, or even up to about 0.02-0.03% w/w in the case of the embodiments with pre-conditioning, with for example a total content of iron of about 60-64%.
EXPERIMENTAL DATA
We will now report the results of five experimental tests performed (Tables 1 to 5), with different operating sequences, pre-supposing that for all these tests primary crushing/grinding was performed, for example adopting the operating conditions described above.
The reducing roasting was performed under the following conditions:
- temperature 650°C;
- time in kiln 1.5 hours;
- composition of the reducing gas: 10% CO, 30% CO2, 60% N2.
The secondary grinding was performed with a feed size P80 of about 1 mm, a percentage of solid of 50%.
The magnetic separation was performed under the following conditions:
- percentage of solid 10%; or performed dry;
- intensity of the magnetic field 1000 Gauss, or 1200 Gauss in the case of dry separation.
The pre-conditioning, where provided wet (1st and 4th test) was performed with a solution of CaCl2 with a concentration of 20-22%, percentage of solid 30%, rotor speed 350 rpm, immersion time 2 hours, immersion temperature 25°C. Furthermore, where provided dry (5 test), the pre-conditioning was performed with a granulate of CaCl2 in a mass percentage of about 4%, with a mixing and homogenization time of 1 hour, environmental temperature (i.e. 25°C).
Oxidizing roasting was performed under the following conditions:
- temperature about 900°C;
- time in kiln 1.5 hours;
- air as comburent oxidizing mixture.
Leaching was performed under the following conditions:
- concentration of H2SO4: 1%, 3%, 5% or 10%; or
- concentration of HC1: 2.2%, 3.3%;
- temperature 30°C, 60°C;
- percentage of solid 10%, 30%, 50%;
- leaching time 0.25 hour (15 minutes), 1 hour, 6 hours.
The values shown hereafter in the Tables refer to those of the final concentrate after 15 mins leaching.
In the Tables, the total iron content is assessed using XRF, that is, expressed as Fe2O3% measured with XRF (X-ray fluorescence) x 0.6994.
Moreover, in the Tables, the total phosphorus content is assessed using XRF, expressed as P2O5% measured with XRF (X-ray fluorescence) x 0.4364.
Considering the contamination from nickel and chromium due to the erosion of the rotary kiln during oxidizing roasting, the following values of the total iron must be corrected and increased by 1 to 2%.
1st test: reducing roasting, secondary grinding, magnetic separation, pre- conditioning, oxidizing roasting, leaching with H2SO4.
Table 1st test
Total iron content (%) Total phosphorus content (%)
62.1 0.03
2" test: reducing roasting, secondary grinding, magnetic separation, preconditioning, oxidizing roasting, leaching with H2SO4 (concentration of acid halved with respect to the 1st test).
Table 2nd test
Total iron content (%) Total phosphorus content (%) 62A (λ03
3rd test: reducing roasting, secondary grinding, magnetic separation, preconditioning, oxidizing roasting, leaching with HC1.
Table 3rd test
Total iron content (%) Total phosphorus content (%)
62,5 (λ08
4th test: reducing roasting, secondary grinding, magnetic separation, preconditioning, oxidizing roasting, two-phase leaching with HC1.
Table 4th test
Total iron content (%) Total phosphorus content (%)
6L6 O04
5th test: primary crushing/grinding, dry magnetic separation, dry preconditioning, oxidizing roasting, secondary grinding, two-phase leaching with HC1.
Table 5th test
Total iron content (%) Total phosphorus content (%)
6O0 m
It is clear that modifications and/or additions of parts and/or steps may be made to the apparatus 10 and method for the dephosphorization of iron ore as described heretofore, without departing from the field and scope of the present invention.
It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of apparatus 10 and method for the dephosphorization of iron ore, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.
In the following claims, the sole purpose of the references in brackets is to facilitate reading: they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.

Claims

1. Method for the dephosphorization of iron ore with a phosphorous content greater than 0.5%, with a magnetite, hematite or mixed nature, said method comprising:
a pre-conditioning of the iron ore by means of a solid or pre-conditioning compound or in solution, with a content less than 5% in weight of the total ferrous mixture;
an oxidizing roasting of the iron ore;
a subsequent leaching, to obtain a final concentrate with a reduced phosphorus content, with a reduction higher than 85%.
2. Method as in claim 1, characterized in that said pre-conditioning is performed upstream of the oxidizing roasting.
3. Method as in claim 1 or 2, characterized in that it comprises a two-phase leaching with a concentration of the acid less than 3%.
4. Method as in any of the claims from 1 to 3, characterized in that it comprises a reducing roasting before at least the oxidizing roasting.
5. Method as in any claim from 1 to 4, characterized in that it comprises a preliminary primary crushing/grinding of the iron ore, performed either wet or dry, before at least the oxidizing roasting.
6. Method as in claim 4, characterized in that it comprises a magnetic separation, before at least the oxidizing roasting and after the reducing roasting, or after the primary crushing/grinding.
7. Method as in claims 4 and 5 or 5 and 6, characterized in that said primary crushing/grinding is before the reducing roasting or before at least the magnetic separation.
8. Method as in claim 5, 6 or 7, characterized in that said method comprising a secondary grinding after the possible reducing roasting or after the oxidizing roasting.
9. Method as in claim 8, characterized in that said secondary grinding is provided between the reducing roasting and the magnetic separation.
10. Method as in claim 8, characterized in that said secondary grinding is provided between the oxidizing roasting and the leaching.
1 1. Method as in claim 8 or 9, characterized in that it comprises, after the primary crushing/grinding and before the reducing roasting, a pre-concentration of the iron ore by means of magnetic separation.
12. Dephosphorized iron ore obtainable using a method as in any claim from 1 to 1 1.
13. Use of an iron ore according to claim 11, for the production of steel with a low phosphorous content.
14. Apparatus for the dephosphorization of iron ore, said apparatus comprising: a pre-conditioning unit (14), an oxidizing roasting unit (12) of iron ore fed (F), and a leaching unit (13) from which a concentrate (C) of iron ore with a reduced phosphorus content is obtained.
15. Apparatus as in claim 14, characterized in that it comprises, before the oxidizing roasting unit (12), said pre-conditioning unit (14) of the iron ore in which a pre-conditioning granular compound or in solution is used which, through heating, generates a gas.
16. Apparatus as in claim 14 or 15, characterized in that it comprises a primary crushing/grinding unit (16) of the iron ore, positioned before at least the preconditioning unit (14).
17. Apparatus as in claim 14, 15 or 16, characterized in that it comprises, before at least the pre-conditioning unit (14), a reducing roasting unit (17).
18. Apparatus as in claim 17, characterized in that it comprises a magnetic separation unit (18) after the reducing roasting unit (17).
19. Apparatus as in claims 16 and 17, characterized in that the primary crushing/grinding unit (16) is positioned before the reducing roasting unit (17).
20. Apparatus as in claims 16 and 17, wherein the primary crushing/grinding unit (16) is positioned before the magnetic separation unit (18).
21. Apparatus as in claim 18, characterized in that it comprises a secondary grinding unit (19), positioned between the reducing roasting unit (17) and the magnetic separation unit (18).
22. Apparatus as in claim 8 or 10, characterized in that it comprises a secondary grinding unit (19), positioned between the oxidizing roasting unit (12) and the leaching unit (13).
23. Apparatus as in claim 18, characterized in that it comprises a pre- concentration unit by means of magnetic separation (20) of the iron ore, between the primary crushing/grinding unit (16) and the reducing roasting unit (17).
EP16820328.9A 2015-11-13 2016-11-11 Method and apparatus for dephosphorization of iron ore Active EP3374531B1 (en)

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ITUB20157263 2015-11-13
PCT/IB2016/056794 WO2017081646A1 (en) 2015-11-13 2016-11-11 Method and apparatus for the dephosphorization of iron ore

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114134318A (en) * 2021-12-01 2022-03-04 中钢设备有限公司 A kind of processing method of high phosphorus iron ore
WO2022267190A1 (en) * 2021-06-23 2022-12-29 中钢设备有限公司 Method for treating high-phosphorus oolitic iron ores

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022267190A1 (en) * 2021-06-23 2022-12-29 中钢设备有限公司 Method for treating high-phosphorus oolitic iron ores
CN114134318A (en) * 2021-12-01 2022-03-04 中钢设备有限公司 A kind of processing method of high phosphorus iron ore
CN114134318B (en) * 2021-12-01 2024-01-23 中钢设备有限公司 Method for treating high-phosphorus iron ore

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