Apparatus and method for processing solid material

Abstract

The present disclosure relates to an apparatus for thermal treatment of a solid material to reduce the content of heavy metal elements and / or other impurities. The apparatus comprises a reactor to heat the solid material, the reactor being configured to have both an oxidizing atmosphere and a reducing atmosphere, and the apparatus comprises a hot gas generator arranged to provide hot gas to the reactor. The present disclosure also relates to a method for thermal treatment of a solid material and a method for producing a fertilizer precursor.

Description

Technical Field

[0001] The present disclosure relates to a plant and method for thermal treatment of solid materials to reduce the content of heavy metal elements.

[0002] The present disclosure also relates to a method for producing a fertilizer precursor, wherein the method uses an apparatus and / or method for thermal treatment of solid materials. Background Art

[0003] Beneficiation of low-grade phosphate ore is a common process step used to achieve a PO content of 30% or higher. For siliceous and clay ores, conventional beneficiation techniques, including crushing, grinding, magnetic separation, flotation, scrubbing, and washing, are often used to remove gangue. However, physical separation methods are less effective for ores containing cadmium oxide, carbonates, and organic carbon.

[0004] Several technologies have been investigated to remove toxic heavy metal elements, such as cadmium, from phosphate rock. However, they all have drawbacks and are difficult to apply on an industrial scale.

[0005] For example, calcination under an oxidizing atmosphere is not feasible for temperature-sensitive phosphate ores because the process temperature required for cadmium oxide (CdO) vaporization is above the critical sintering temperature. This can cause problems in subsequent processing steps of the ore, such as leaching. Furthermore, calcination under a reducing atmosphere, such as in a fluidized bed reactor, is not feasible for temperature-sensitive phosphate ores because the process temperature exceeds the critical temperature for the formation of agglomerates. Summary of the Invention

[0006] Purpose

[0007] The present disclosure aims to provide a novel apparatus and method for treating solid materials to reduce the content of heavy metal elements and other impurities, in particular for treating low-grade phosphate rock to remove impurities such as cadmium, carbonate and / or organic carbon.

[0008] summary

[0009] According to the present disclosure, an apparatus for heat treating solid materials to reduce the content of heavy metal elements and / or other impurities is provided, the apparatus comprising: optionally, at least one drying system; optionally, at least one preheating system; a reactor for heating the solid materials to a reaction temperature; optionally, a heat recovery system; and optionally, a cooling system. The apparatus comprises only one reactor, and the reactor is arranged to have both an oxidizing atmosphere and a reducing atmosphere, and the apparatus comprises a hot gas source arranged to provide hot gas to the reactor.

[0010] According to the present disclosure, a method for heat treating a solid material to remove heavy metal elements and / or other impurities is also provided, the method comprising the following steps: optionally drying the solid material; optionally preheating the solid material; heating the solid material in a reactor to a reaction temperature to reduce the content of heavy metal elements and / or other impurities; optionally cooling the heated solid material, and obtaining a treated solid material. The heating is performed in only one reactor, the reactor has both a reducing atmosphere and an oxidizing atmosphere, and the heating of the reactor is at least partially achieved by providing hot gas via a hot gas source.

[0011] In addition, a method for producing a fertilizer precursor is provided, which uses the device for heat treatment of solid materials to reduce the content of heavy metal elements and / or other impurities according to the present disclosure, and / or the method for heat treatment of solid materials to remove heavy metal elements and / or other impurities according to the present disclosure.

[0012] By means of the apparatus and / or method disclosed herein, thermal treatment of solid materials, such as low-grade phosphate rock, allows for the removal or reduction of impurities to a level that avoids inefficiencies in downstream processes, such as acidification. Furthermore, such thermal treatment can comply with quality and health regulations associated with the final product, such as a fertilizer precursor that can be used to prepare fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of this specification, illustrate embodiments of the present disclosure, and together with the description help to explain the principles of the present disclosure. In the drawings:

[0014] Figure 1 is a block diagram illustrating one embodiment of the apparatus.

[0015] Figure 2 is a flow chart illustrating another embodiment of the apparatus.

[0016] Figure 3 is a flow chart illustrating another embodiment of the apparatus. DETAILED DESCRIPTION

[0017] In this disclosure, unless otherwise stated, the following terms and expressions have the definitions set out below.

[0018] The term "solid material" refers to the feed material (feed material) to be treated in the device or to be treated according to the method. It can be an ore, such as natural rock and / or sediment, containing valuable materials, such as phosphates. The solid material may have undergone some treatment before being used as feed material in the disclosed device / method. Typically, the ore is phosphate ore. The phosphate ore may have a phosphate content of less than 30% by weight based on the total weight of the ore. Ores with a phosphate content of less than (less than or equal to) 30% by weight are low-grade phosphate ore. The solid material is typically a granular solid material. Preferably, the solid material is a granular solid material ("fine material") having a particle size of less than 6 mm.

[0019] The term "hot gas source" refers to a system for generating hot gas. The hot gas source is typically a hot gas generator that generates hot gas, such as CO gas and H2 gas, that can provide heat and a reducing atmosphere and / or an oxygen-free atmosphere to the reactor. The hot gas source can be any source capable of providing such a gas.

[0020] Specific instructions

[0021] Apparatus and methods according to the present disclosure are provided for thermal treatment of solid materials to remove impurities, such as heavy metal species carbonates and / or organic carbon.

[0022] An energy-efficient solution is provided for the thermal treatment of solid materials, particularly granular solid materials, at elevated temperatures to reduce the content of toxic heavy metal elements, particularly cadmium and other impurities present in the feed.

[0023] One object is to provide a novel method and apparatus for removing heavy metal components such as cadmium directly from temperature-sensitive phosphate rocks. In this respect, the temperature sensitivity, together with the formation of a molten phase and the corresponding sintering, leads to agglomerates and particle agglomerates above a certain temperature.

[0024] To this end, a device for heat treatment of solid materials to reduce the content of heavy metal elements and / or other impurities is disclosed, the device comprising:

[0025] Reactor 5 is used to heat the solid material to the reaction temperature,

[0026] Optionally, at least one drying system 1, 2,

[0027] Optionally, at least one preheating system 3, 4,

[0028] Optionally, heat recovery systems 6, 7, and

[0029] Optionally, a cooling system 8 .

[0030] The apparatus comprises only one reactor 5 , and the reactor is configured to have both an oxidizing atmosphere and a reducing atmosphere. In addition, the apparatus comprises a hot gas source 9 , which is arranged to provide hot gas to the reactor 5 .

[0031] Also disclosed is a method for heat treatment of solid materials to remove heavy metal elements and / or other impurities, wherein the method comprises the following steps:

[0032] The solid material is heated to the reaction temperature in the reactor to reduce the content of heavy metal elements and / or other impurities,

[0033] Optionally, the solid material is dried,

[0034] Optionally, preheating the solid material,

[0035] Optionally, cooling the heated solid material, and

[0036] A processed solid material is obtained.

[0037] In the present method, heating is performed in only one reactor, and the reactor has both reducing and oxidizing atmospheres. The heating of the reactor is at least partially achieved by providing hot gas from a hot gas source.

[0038] The device and / or method can remove impurities, such as heavy metals and / or carbonate components, from solid materials in an energy-efficient manner. This avoids local high temperatures, since the device does not operate solely by direct combustion.

[0039] According to one embodiment, the apparatus and / or method can provide a calcined product (i.e., a treated solid material) containing phosphate (PO) having a cadmium (Cd) content of 60 mg / kg or less per PO equivalent. At least 50% by weight, or even up to 70% or 80% by weight, of Cd can be removed from the feed (i.e., the solid material).

[0040] According to a preferred embodiment, the reactor is a rotary kiln. Rotary kilns offer several advantages. One important advantage is that they provide a free-board in the furnace roof where gases can flow in opposite directions, creating two distinct atmospheres due to their elongated shape. Typically, the rotary kiln includes an overflow chute 5' through which overflow 5d can be removed.

[0041] A rotary kiln is preferred, but other reactor alternatives could be a rotary hearth furnace, a shaft furnace (blast furnace), or a fluidized bed reactor.

[0042] The effect of having both an oxidizing and a reducing atmosphere in the same reactor is that impurities to be removed, such as CdO, can be reduced to metallic Cd, but immediate reoxidation of the Cd is avoided. Instead, reoxidation occurs in the free space near the gas outlet (such as the feed end at the top of the rotary kiln), allowing the CdO to leave the rotary kiln, for example by adhering to solid particles (such as dust leaving the reactor). In this way, impurities are effectively removed.

[0043] According to a preferred embodiment, the hot gas source 9 is configured to provide hot reducing gas for heating and for providing a reducing atmosphere.

[0044] According to a preferred embodiment, the hot gas source 9 is a hot gas generator. An advantage of such a hot gas generator is that, in addition to providing heat in the form of hot gas, it can also provide a reducing atmosphere. This improves energy efficiency (energy saving) and enables control of process conditions, such as a suitable reaction temperature and a low oxygen partial pressure.

[0045] All of the above optional parts contribute to energy efficiency by providing means for heat recovery etc. Typically, low grade ores are used as feedstock in the plant and in this case energy saving is very important in order to achieve a cost effective, industrially viable plant.

[0046] According to one embodiment, the apparatus comprises a preheating system 3, 4. The preheating system preferably comprises at least one preheater 3. The preheater comprises a venturi and cyclone for separating gas and solids.

[0047] According to one embodiment, the apparatus comprises a drying system 1, 2. The drying system preferably comprises at least one dryer 1. According to one embodiment, the apparatus comprises at least one predryer 1. One purpose of the predryer is to remove surface moisture from solid material used as feed.

[0048] According to a preferred embodiment, the apparatus includes a predryer 1 and a preheater 3 located downstream of the predryer 1. After passing through the preheater, the solid material is fed to a reactor 5. The combination of the preheater and the predryer offers advantages because the use of the predryer can prevent impurities (such as Cd particles) from adhering to the preheater (which would make the processability of the solid material difficult). This can be a problem, especially if the solid material contains moisture. Furthermore, the combination of the predryer and the preheater further improves energy efficiency.

[0049] Therefore, according to one embodiment of the method, the solid material is dried in the predryer 1 and subsequently heated in the preheater 3. After heating in the preheater, the solid material is fed to the reactor 5.

[0050] According to one embodiment, the apparatus comprises a heat recovery system 6 , 7 .

[0051] According to one embodiment, the device comprises a cooling system 8 .

[0052] According to one embodiment, the solid material is an ore. Typically, the ore is phosphate rock. The phosphate rock may have a phosphate content of less than 30% by weight based on the total weight of the ore. Phosphate rock with a phosphate content of less than 30% by weight is considered low-grade phosphate rock.

[0053] According to one embodiment, the reactor 5 is a rotary kiln, and the hot gas source is configured to heat the solid material and provide the reducing gas through a counter-current gas flow.

[0054] According to one embodiment of the method, the solid material is heated in countercurrent flow.

[0055] This counter-current flow ensures that the heat and optional reducing atmosphere are provided to the correct location in the furnace. This increases the efficiency of the reactions taking place in the furnace.

[0056] According to one embodiment, the hot gas source 9 is arranged to provide hot gas to the reactor at and / or near the discharge end 5-2 of the reactor. Preferably, the hot gas contains reducing components, such as hot gas containing CO gas and H2 gas.

[0057] According to one embodiment of the present method, the heating of the reactor is at least partially achieved by providing hot gas comprising CO and H 2 via a hot gas source at and / or near the discharge end 5 - 2 of the reactor 5 .

[0058] The CO and H2 gases provide the reducing atmosphere described above. These gases are introduced at and / or near the exhaust end of the furnace to provide this reducing atmosphere at the optimal location in the furnace.

[0059] According to one embodiment, the reducing atmosphere is arranged at and / or near the discharge end 5-2 of the reactor 5, and the oxidizing atmosphere is arranged at and / or near the feed end 5-1 of the reactor 5. This arrangement provides the atmosphere for the reaction at the above-mentioned optimal position, thereby enabling the desired reaction to proceed.

[0060] According to one embodiment, the reactor 5 is a rotary kiln comprising at least two shell air fans 5b. The shell fans provide air / oxygen into the kiln. This air allows CO and H2 gases, which can be supplied by a hot gas source 9, to exchange for an oxidizing atmosphere in the kiln's free space. This oxidizes Cd back to CdO, which is typically attached to solid particles such as ash or dust and exits the kiln with the exhaust gas. These solid particles can be removed from the gas by a cyclone separator.

[0061] According to a preferred embodiment, the reactor 5 is a rotary kiln comprising at least one shell fan 5b for every 10 meters of the kiln. The frequency of the shell fan can provide sufficient air to enable the desired reaction to proceed.

[0062] According to one embodiment, the heavy metal element includes cadmium (Cd).

[0063] According to one embodiment, the reactor is configured to heat the solid material to a reaction temperature of 500-1000°C, preferably 750-900°C.

[0064] According to one embodiment of the present method, the solid material in the reactor is heated to a reaction temperature of 700-1000°C, preferably 750-900°C.

[0065] At least in the case of removing cadmium in the form of cadmium oxide from a solid material, the above reaction temperature is preferred because it is high enough to evaporate metallic Cd, but not so high as to produce undesirable side effects.

[0066] The temperature of the hot gas providing heat may be relatively high, such as 1200°C.

[0067] According to one embodiment, the apparatus comprises at least one preheater 3, to which the exhaust gases leaving a reactor 5 (such as a rotary kiln) are arranged to be directed. Directing the exhaust gases to the preheater enables energy recovery. Moreover, the gases can be purified and recycled to the hot gas source. In this way, the preheater can be used as a heat recovery system, making the apparatus and method more efficient. This integrated process is an efficient way to recover heat, thereby keeping operating costs as low as possible (through heat recovery). It can also heat other materials, such as water, to generate steam to provide preheating.

[0068] According to one embodiment, the removal of heavy metal elements from the heating step is achieved by attaching the elements to solid particles suspended in the exhaust gas stream from the reactor in such a way that these particles will not contaminate the feed (ie solid material).

[0069] According to one embodiment, the solid material used in the disclosed method is a granular solid material. Preferably, the granular solid material is a fine material, having a particle size of 6 mm or less.

[0070] Furthermore, the present invention discloses a method for producing a fertilizer precursor, wherein the method uses an apparatus according to any embodiment described herein and / or a method according to any embodiment described herein.

[0071] The accompanying drawings illustrate some specific embodiments of the apparatus according to the present disclosure.

[0072] Figure 1 1 is a block diagram illustrating an apparatus according to one embodiment. The apparatus includes a drying system (a dryer 1 for drying solid materials and a dryer cyclone 2), a preheating system (a preheater 3 and a preheater cyclone 4), a reactor 5 (a rotary kiln), a heat recovery system (a heat recovery device 6 and a cyclone 7), a cooling system (a cooler 8, a cooling water inlet line 8a, and a reflux water outlet line 8b), and a hot air source 9. Figure 1 Also shown are an inlet line 1a for supplying solid material and an outlet line 12 for discharging the processed solid material (calcined product). Dust-laden gas is removed from the dryer cyclone 2 via line 2b and supplied to a dust removal system 10. The dried solid material is supplied from the drying system to the preheater 3 via line 2a. There, dust and exhaust gas are separated and discharged via lines 10a and 10b, respectively. Gas from the preheater cyclone 4 (line 4b) is supplied to a gas cleaning system 11, where dust 11a and exhaust gas 11b are separated. The preheated solid material is supplied to the reactor 5 via line 4a. A shell fan 5b supplies air and / or oxygen to the reactor 5. Fuel (line 9b) (e.g., petroleum coke) and air (line 9c) are supplied to a hot gas source 9 (typically a hot gas generator), and the hot gas is supplied to the reactor via line 9a near the discharge end of the reactor 5. Furnace exhaust gas is circulated from reactor 5 back to preheater 3 via line 5c. Solid material (reactor discharge) treated in reactor 5 is directed to heat recovery unit 6 via line 5a. Cooling air is supplied to heat recovery unit 6 via line 6a. Preheated air is directed from cyclone separator 7 to dryer 1 via line 7b. Solid material (hot calcined product) is further directed to cooler 8 via line 7a. Cooling water is directed to cooler 8 via line 8a, while reflux water is directed out via line 8b. The treated solid material (calcined product) is discharged from the cooler via line 12.

[0073] Figure 2An apparatus according to one embodiment of the present disclosure is shown. The apparatus comprises a preheating system (preheater 3 and preheater cyclone 4), a reactor 5 (rotary kiln calciner), and a hot gas source 9 (hot gas generator). Figure 2 Also shown is an inlet line 1a for feeding solid material into the preheating system. The preheated solid material is fed to the reactor 5 via line 4a. A shell fan 5b provides air and / or oxygen to the reactor 5. The reactor has a discharge end 5-2 and a feed end 5-1. Fuel, line 9b (e.g., petroleum coke), and air, line 9c, are directed to a hot gas source 9, which is directed to the reactor via line 9a near the discharge end 5-1 of the reactor 5. The reactor system includes an overflow chute 5', and overflow is directed out via line 5d. Furnace exhaust gases are circulated from the reactor 5 back to the preheater 3 via line 5c.

[0074] Figure 3 The apparatus according to another embodiment of the present disclosure is shown, which comprises a separator 3', a reactor 5 (rotary calciner), a hot gas source 9 (hot gas generator), a post-combustion chamber 13 and a heat recovery device 14 located after the post-combustion chamber. Figure 3 Also shown is inlet line 1a for feeding solid material into reactor 5. Coarse dust is directed from separator 3' via line 3'a to line 1a, and a dust discharge (line 3'b) is directed out. A casing fan 5b provides air and / or oxygen to reactor 5. Fuel (line 9b) and air (line 9c) are directed to hot gas source 9, and hot gas is supplied to the reactor via line 9a near the discharge end of reactor 5. Air is supplied to the post-combustion chamber via line 13a.

[0075] The present disclosure provides an apparatus and method for removing cadmium from temperature sensitive low grade phosphate rock in a direct, energy efficient manner. Tests conducted in conjunction with the present invention have shown that high removal rates can be achieved (Example 1).

[0076] A very specific embodiment of the apparatus and method of the present disclosure is described below in which the solid material is low-grade phosphate rock containing cadmium oxide and other impurities to be removed by the apparatus and method according to the present disclosure.

[0077] Whenever the feed ore contains cadmium oxide as a metallic trace element, relatively high temperatures (greater than 1000°C) are required to vaporize the cadmium oxide due to its low vapor pressure. For certain (temperature-sensitive) phosphate ores, the temperature limit before agglomerates and lumps begin to form is around 800°C-900°C. These side effects can have unacceptable consequences in industrial processes, such as equipment failures and blockages that can lead to downtime.

[0078] In order to remove cadmium and avoid prohibitive high temperatures (which have the undesirable consequence of sticky material properties), cadmium oxide is reduced to its metallic form to be released from the solid. Cadmium as a metallic element has a significantly higher vapor pressure than its oxidized state and can already evaporate at temperatures above 500°C.

[0079] The heterogeneous conversion of cadmium oxide to metallic cadmium requires relatively mild reducing conditions relative to temperatures above 500° C. and ambient gas atmospheres. A gaseous reducing agent, CO (carbon monoxide), can be used.

[0080] In order to prevent the transient reoxidation and corresponding resublimation of the cadmium-containing fumes penetrating in the boundary layer of the solid bed in the reactor, a sufficiently low (close to zero) oxygen partial pressure must be maintained in the free space of the furnace, at or near the discharge end of the reactor. This is achieved by a hot gas source (such as a hot gas generator) located upstream of the reactor, which is operated under substoichiometric conditions or very close to substoichiometric conditions so that the hot gas is depleted of the oxygen present.

[0081] Post-combustion of the fuel components present in the hot gases occurs in the middle / front part of the reactor (at and / or near the feed end), where the metallic cadmium in the free space is also reoxidized. Once reoxidized, the cadmium oxide immediately resublimes on any solid surfaces it may be present on (e.g., dust particles or furnace walls). Finally, the cadmium oxide is removed from the furnace in a solid state attached to dust particles suspended in the hot exhaust gas stream from the reactor (at its feed end).

[0082] Additional systems can be used to recover heat from the hot exhaust gases from the rotary kiln and the hot calcined products to significantly reduce fuel consumption.

[0083] In the following sections, the steps of the method and the components of the apparatus are described in more detail in this very specific embodiment.

[0084] Wet solid material (e.g., filter cake) is fed to a venturi pre-dryer. This pre-drying step removes surface moisture from the ore particles and prevents cadmium- and impurity-containing dust from wet-agglomerating into the fresh material in the subsequent pre-heater, which operates using hot furnace exhaust gases. A secondary task of the pre-dryer is to screen the feed ore for ultrafine material, which is collected downstream via a dust removal system. This dust is not rich in Cd.

[0085] Recondensation of the pre-dryer exhaust gases is avoided by mixing hot fresh air with a bypass of the exhaust gases before entering the cyclone separator and dust removal unit.

[0086] The predried material is conveyed to a venturi preheater where the solid feed is further dried and heated in direct heat exchange with the hot reactor exhaust gases.

[0087] The preheated material can then be fed into the reactor via a special feed pipe to prevent dust formation. If additional reducing agent is required, very small amounts of carbonaceous material can also be fed into the furnace.

[0088] The reverse (countercurrent) operation of the furnace and the shell fan allows specific atmospheric conditions (atmospheric condition, atmosphere conditions) to be adjusted along the length of the furnace. The use of a hot gas source (hot gas generator) will allow hot reducing gas to be delivered to the furnace at a controlled temperature, avoiding any local overheating of the calcination that usually occurs in a standard furnace with a central burner. The hot calcined product (hot calcine, hot roasted sand) leaving the furnace can be screened to remove any block particles before being supplied to a two-stage venturi cooling system for air preheating. The preheated air from the venturi cooling system is then used to dry the solid material. Before the processed solid material (calcined product) can be discharged to the conveyor belt, it must be cooled to the final target temperature in the product cooler.

[0089] According to another embodiment, the drying of the solid material is carried out in a separate unit and the dried solid material is fed into a venturi preheater or directly into the reactor.The hot calcined product discharged from the rotary kiln can be cooled directly in a product cooler.

[0090] In the case of phosphate rock, a significant advantage achieved is that the thermal treatment and corresponding decomposition (calcination) of the carbonates and bound water contained in the phosphate rock facilitates the downstream leaching process and minimizes the need for acid (e.g., sulfuric acid) in the production of phosphoric acid. Phosphoric acid is a basic material for the production of phosphate fertilizers, which is one possible application for the phosphate processed by the present method and apparatus.

[0091] Several important advantages can be achieved by the apparatus and method described herein.

[0092] The embodiments described above may be used in any combination thereof. Several embodiments may be combined to form further embodiments. The apparatus or method involved in the present disclosure may include at least one of the aforementioned embodiments.

[0093] Example

[0094] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings.

[0095] The following description discloses some embodiments in detail so that those skilled in the art can use the method and device based on the present disclosure. All steps of the embodiments are not discussed in detail because many steps are obvious to those skilled in the art based on this description.

[0096] For simplicity, in the following exemplary embodiments, reference numerals will remain unchanged where components are repeated.

[0097] Figure 1 An apparatus according to one embodiment is illustrated by way of a block diagram.

[0098] Example 1 – Pilot Scale Rotary Kiln Testing: Calcination of Low-Grade Phosphate Ore

[0099] The goal of the process is to upgrade the grade of phosphate rock by removing moisture, evaporates, organic carbon and cadmium.

[0100] Low grade ore containing 28.5% P2O5 and 12% moisture is fed to the drying systems 1,2 where moisture is removed by direct contact of the ore with hot air which is preheated in the heat recovery systems 6,7.

[0101] The dried ore and air are separated by cyclone separator 2 and the dusty air 2b is conveyed to a dust removal system 10 for removing dust before being released into the atmosphere (10a dust, 10b exhaust gas). This dust can be disposed of or mixed with the final product.

[0102] The dried ore from the cyclone 2 is transferred to a preheater 3 where it is preheated to a temperature > 250°C by means of hot exhaust gases 5c from a rotary calciner 5 .

[0103] The gas and preheated solids are separated in the preheater cyclone 4. The dusty gas is conveyed to a gas cleaning system 11 to remove cadmium containing dust and any other contaminants before being released to the atmosphere (11a dust, 11b waste gas).

[0104] The preheated ore is transferred from the preheater cyclone 4 to the rotary kiln 5 (line 4a) where it is heated in a countercurrent to the hot gases flowing through the free space of the kiln.

[0105] Following the direction of gas flow, the atmosphere in the furnace changes from a reducing atmosphere (near the discharge end of the furnace) to an oxidizing atmosphere (near the feed end of the furnace) by adding air along the furnace (shell fan 5b). The reducing gas continues to burn through the air providing heat.

[0106] In the furnace, the organic carbon contained in the ore is burned and the evaporative products are removed. Cadmium oxide (CdO) contained in the ore is removed in a reducing atmosphere, turning it into metallic cadmium, which is then converted into a gaseous phase. Once the furnace atmosphere becomes oxidizing (as the gas flows toward the feed end), the cadmium metal (vapor) is oxidized into cadmium oxide (solid), which is ultimately carried as dust in the furnace exhaust.

[0107] The hot calcined products from the furnace are discharged to a heat recovery system 6 where they are cooled by direct contact with air. The air and solids are separated via a cyclone separator 7.

[0108] The solids from the cyclone 7 are transferred to a cooler where they are cooled indirectly by means of water. The preheated air from the cyclone 7 is used to dry the feed in the dryer 1 .

[0109] By using this process and equipment, it is possible to achieve a calcination degree exceeding 90% and a cadmium removal exceeding 80%. For example, the P2O5 content increased to 31.7%, while the Cd content decreased from 30 mg / kg to 6 mg / kg.

[0110] It is obvious to a person skilled in the art that, as technology advances, the basic idea of ​​the invention can be implemented in many ways. Therefore, the invention and its embodiments are not limited to the examples described above, but may vary within the scope of the claims.

Claims

1. An apparatus for heat treatment of solid materials to reduce the content of heavy metal elements and / or other impurities, the apparatus comprising: Optionally, at least one drying system (1, 2), Optionally, at least one preheating system (3, 4), Reactor (5), used to heat the solid material to the reaction temperature, Optionally, a heat recovery system (6, 7), and Optionally, a cooling system (8), Characterized in that the apparatus comprises only one reactor (5), and the reactor (5) is arranged to have both an oxidizing atmosphere and a reducing atmosphere, and the apparatus comprises a hot gas source (9) arranged to provide hot gas to the reactor; and Wherein, the reactor (5) is a rotary kiln, wherein the hot gas source is arranged to heat the solid material and provide reducing gas through countercurrent gas flow.

2. The device according to claim 1, wherein The hot gas source (9) is arranged to provide hot reducing and / or oxygen-free gas for heating and providing a reducing atmosphere.

3. The device according to claim 1 or 2, wherein: The hot air source (9) is a hot air generator.

4. The device according to claim 1 or 2, wherein: The solid material is ore.

5. The device according to claim 4, wherein The ore is phosphate rock.

6. The device according to claim 5, wherein The phosphate rock has a phosphate content of less than 30% by weight.

7. The device according to claim 1 or 2, wherein: The hot gas source (9) is arranged to provide hot gas into the reactor (5) at and / or near the discharge end (5-2) of the reactor.

8. The device according to claim 7, wherein The hot gas source (9) is arranged to provide hot gas comprising CO and H2 into the reactor (5) at and / or near the discharge end (5-2) of the reactor.

9. The device according to claim 1 or 2, wherein: The reducing atmosphere is arranged at and / or near the discharge end (5-2) of the reactor (5), while the oxidizing atmosphere is arranged at and / or near the feed end (5-1) of the reactor (5).

10. The device according to claim 1 or 2, wherein The reactor (5) is a rotary kiln comprising at least two shell fans (5b).

11. The device according to claim 1 or 2, wherein: The reactor (5) is a rotary kiln, and the rotary kiln includes at least one shell fan (5b) per 10 meters of the kiln.

12. The device according to claim 1 or 2, wherein: The reactor (5) is arranged to heat the solid material to a temperature of 500-1000°C.

13. The device according to claim 12, wherein The reactor (5) is arranged to heat the solid material to a temperature of 750-900°C.

14. The device according to claim 1 or 2, wherein: The heavy metal element includes cadmium (Cd).

15. The device according to claim 1 or 2, wherein: The apparatus comprises at least one preheater (3), and the exhaust gas (5c) leaving the rotary kiln is configured to be directed to the at least one preheater (3).

16. The device according to claim 1 or 2, wherein: The apparatus comprises a predryer (1) and a preheater (3) located downstream of the predryer (1).

17. A method for heat treatment of solid materials to remove heavy metal elements and / or other impurities, wherein: The method comprises the following steps: Optionally, the solid material is dried, Optionally, preheating the solid material, The solid material in the reactor is heated to the reaction temperature to reduce the content of heavy metal elements and / or other impurities. Optionally, cooling the heated solid material, and Obtaining processed solid material, Characterized in that the heating is carried out in only one reactor, and the reactor has both a reducing atmosphere and an oxidizing atmosphere, and the heating of the reactor is achieved at least in part by providing hot gas via a hot gas source, wherein the reactor (5) is a rotary kiln, wherein the solid material is heated in a countercurrent flow.

18. The method according to claim 17, wherein The solid material is ore.

19. The method according to claim 18, wherein The ore is phosphate rock.

20. The method according to claim 19, wherein The phosphate rock has a phosphate content of less than 30% by weight.

21. The method according to any one of claims 17 to 20, wherein: The hot air source is a hot air generator.

22. The method according to any one of claims 17 to 20, wherein: Heating of the reactor is at least partially achieved by providing hot gas comprising CO and H2 via a hot gas source at and / or near the discharge end of the reactor.

23. The method according to any one of claims 17 to 20, wherein: Removal of the heavy metal elements from the heating step is accomplished by attaching the elements to solid particles suspended in the exhaust gas stream.

24. The method according to any one of claims 17 to 20, wherein: The reactor is a rotary kiln comprising at least two shell fans.

25. The method according to any one of claims 17 to 20, wherein: The reactor is a rotary kiln comprising at least one shell fan per 10 meters of the kiln.

26. The method according to any one of claims 17 to 20, wherein: The solid material in the rotary kiln is heated to a temperature of 700-1000°C.

27. The method according to claim 26, wherein The solid material in the rotary kiln is heated to a temperature of 750-900°C.

28. The method according to any one of claims 17 to 20, wherein: The heavy metal element includes cadmium (Cd).

29. The method according to any one of claims 17 to 20, wherein: The solid material is a granular solid material.

30. The method according to claim 29, wherein The granular solid material has a particle size of 6 mm or less.

31. The method according to any one of claims 17 to 20, wherein: Before the solid material is fed to the reactor, the solid material is dried in a pre-dryer and then heated in a pre-heater.

32. A method for producing a fertilizer precursor, characterized in that The method uses an apparatus according to any one of claims 1-16 and / or a method according to any one of claims 17-31.

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