Selective magnesium removal from phosphate rock

Abstract

Selective Mg (in the form of MgO) removal from phosphate rock. Selective removal can generally include the following process steps: Mg (such as in the form of dolomite) solubilization with an acid, such as sulfuric acid, acid pulp neutralization such as by the addition of lime, vacuum filtration, and magnesium precipitation from the liquid phase or filtrate in an alkaline solution. This alkaline solution can be formed by the addition of lime. Solid magnesium precipitate, in the form of magnesium hydroxide (Mg(OH)2) is then filtered and disposed or reprocessed as a by-product or co-product of the process, while the filtrate, which is substantially water, can be recycled back in to the process. The leached phosphate rock is washed with a complexing additive, such as sodium hexametaphosphate (SHMP) to immobilize iron (Fe) and / or aluminum (Al) that could not be solubilized and removed after neutralization.

Description

[0001]Attorney Docket No.40014-1997WO01 UTILITY PATENT APPLICATION SELECTIVE MAGNESIUM REMOVAL FROM PHOSPHATE ROCK CROSS-REFERENCE TO RELATED APPLICATION The present disclosure claims the benefit of U.S. Provisional Application No.63 / 667,913, filed July 5, 2024, which is hereby fully incorporated by reference in its entirety. TECHNICAL FIELD The present disclosure relates generally to processing of phosphate rock, and more particularly, to the removal of magnesium from the phosphate rock for additional processing of the phosphate rock. BACKGROUND Phosphate rock, such as igneous phosphate rock, can be processed to produce products including phosphoric acid and phosphate fertilizers. Phosphate fertilizers can be produced using the processed rock, for example, by granulation processes, such as those described in U.S. Pat. No. 6,544,313, incorporated herein by reference in its entirety. Phosphate rock, depending on where it is sourced, can contain high magnesium content, typically in the form magnesium oxide (MgO). However, high levels of MgO content can create issues in the production of phosphoric acid and fertilizer granulation. Issues generated by the high MgO content in the production of phosphoric can include increased consumption of sulfuric acid (H2SO4) to attack the rock, additional energy consumption needed for maintenance of phosphorous (expressed as wt.% equivalent P2O5) concentrations, unintended formation of gypsum crystals Attorney Docket No.40014-1997WO01 which increases viscosity of the production streams thereby reducing filtration rates, and increased fouling on multiple unit operations or circuits, resulting in plant downtime. Issues generated by the high MgO content in fertilizer granulation including higher recycling rates, reduction of nitrogen (N) which in turn requires use of expensive additives such as ammonium nitrate to increase N, an impact on (increase in) viscosity of pre-neutralized sludge resulting in pumping difficulties, adverse effects on particle size distribution in the granulators, and impaired hardness and other physical characteristics of the material. Process difficulties due to the increase in the MgO content in phosphate rock, such as Cajati phosphate rock from the Jacupiranga apatite deposit, São Paulo, Brazil, and its economic impacts on the manufacture of phosphoric acid and dicalcium phosphate have been known for years. For example, from international data, approximately US$10.00 is lost for every 1.0% increase in MgO in phosphate rock, per ton of P2O5. A major challenge with current sources of phosphate rock is the production or availability of rock with a MgO content of less than 1.6%. For example, in 2019, North and Mesquita Sampaio mining areas had peaks of 2.8% of MgO and the Life of Mine (LOM) indicates an increase in MgO of the rock produced by the magnesian ore in the near future, indicating an increase in the MgO of all rock will occur in the near future, reaching an annual average of 2.2%. There are economic advantages of removing MgO from concentrated phosphate rock due mainly to the cost reduction and to the operational stability its removal provides. For example, the removal of MgO results in a cost reduction due to an extended LOM including an increase in the geological reserve, an increase in the recovery of apatite, and the possibility to explore dolomitic rocks, which is phosphate rock containing dolomite, an anhydrous carbonate mineral composed of calcium magnesium carbonate, CaMg(CO3)2. For the phosphoric acid plant, there is an increase Attorney Docket No.40014-1997WO01 in the productivity of the heat exchangers, reduction in viscosity, an increase in the filtration rate, a reduction in the consumption of antifoam, an improvement in the defluorinization process, and an improvement in the quality of the dicalcium phosphate used in the production of phosphate fertilizers. There remains a need for a cost effective and efficient way to remove MgO from phosphate rock. SUMMARY OF THE DISCLOSURE According to embodiments, selective Mg (in the form of MgO) removal from phosphate rock can generally comprise the following process steps: Mg (such as in the form of dolomite )solubilization with an acid, such as sulfuric acid, acid pulp neutralization such as by the addition of lime, vacuum filtration, and magnesium precipitation from the liquid phase or filtrate in an alkaline solution. This alkaline solution can be formed by the addition of lime. Solid magnesium precipitate, in the form of magnesium hydroxide (Mg(OH)2) is then filtered and disposed or reprocessed as a by-product or co-product of the process, while the filtrate, which is substantially water, can be recycled back in to the process. The leached phosphate rock is washed with a complexing additive, such as sodium hexametaphosphate (SHMP) to immobilize iron (Fe) and / or aluminum (Al) that could not be solubilized and removed after neutralization. Unlike other commercially available leaching processes, in embodiments, the addition of the neutralization step helps to reduce or avoid phosphorus losses (expressed as wt% P2O5) in the leaching process of phosphate rocks by insolubilizing a small amount of phosphorus that might have been solubilized due to a slight attack of apatite in the solubilization or leaching step. Attorney Docket No.40014-1997WO01 BRIEF DESCRIPTION OF THE DRAWINGS The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which: FIG.1 is a process flow diagram for selective magnesium removal from phosphate rock, according to an embodiment of the disclosure. FIG.2 is a graph of leached phosphate rock conditions during a pilot run. FIG.3 is a graph of magnesium decontamination and decarbonation conditions during the pilot run. FIG.4 a graph of leached phosphate rock conditions during another pilot run. FIG.5 is a pilot run flowchart. While various examples are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the claimed inventions to the particular examples described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter of the present disclosure. DETAILED DESCRIPTION Referring to FIG.1, a process 100 for the selective Mg removal from phosphate rock can generally comprise the following process steps: dolomite (calcium magnesium carbonate) solubilization with an acid, such as sulfuric acid, thereby forming an acidic pulp, acidic pulp neutralization such as by the addition of lime (calcium oxide or calcium hydroxide), vacuum Attorney Docket No.40014-1997WO01 filtration to separate the pulp into a liquid phase (filtrate) and a solid phase, and magnesium precipitation from the liquid phase or filtrate in an alkaline solution. The phosphate rock can be in the form of igneous rock, such as the Cajati phosphate rock, or can be sedimentary phosphate rocks, such as those found in Florida, United States. Beginning with rock including a dolomite (CaMg(CO3)2) solubilization step 102 or leaching, a slurry of phosphate rock 101 is combined with an acid 103. The solvent may be a weak organic acid (acetic, formic, citric acid, etc.) that is recycled in the process after the precipitation of magnesium in the form of magnesium hydroxide with adequate purity. A strong acid, such as H2SO4, HCl or H2SiF6, can also be used in highly diluted solutions, such as calcium oxide or calcium hydroxide. When a strong acid, such as sulfuric acid, is used, the following reaction is expected to occur: CanMg(CO3)1+n + (1+n) H2SO4 → nCaSO4.2H2O + MgSO4 + (1-n)H2O + (1+n) CO2 of the igneous concentrated phosphate rock. Dolomitic rocks include material with more than 10% MgO or, in mineralogical terms, more than 45% dolomite before concentration. For example, typical mineral characterization after beneficiation for Cajati phosphate rock with high MgO can present: Mineralogical characterization % Formula Apapite 63 – 58Ca5(PO4)3(F,Cl,OH)Calcite 30 – 24CaCO3Dolomite 4 – 10 CaMg(CO3)2 Phlogopite <3KMg3AlSi3O10(F,OH)2Table 1: Mineral Characterization Attorney Docket No.40014-1997WO01 MgO is present in two mineralogical phases associated with carbonate (70%) and silicates (30%). Considering the Table2 below, the feasibility of the concentrate leaching process can be assessed. This table shows a typical example of a sample of Cajati with low concentration of apatite (58%) and high concentration of MgO (4.5%). However, the MgO content of carbonate is 2.80% and the MgO silica content is 1.70%. This is an ideal sample for the leaching process. Composition ConcentrationCaOapta% 39,30 MgOcarbon% 2,80Apatite % 58,00 CaOcalc% 13,44 CaCO3 % 30,25 Calcite % 24,00 CaO dol % 3,50 MgCO3 % 5,88 Dolomite % 10,00 CaOtotal% 56,24 CO3 (CaCO3)% 18,15 MgOtotal% 4,50 MgOdol % 2,80 CO3(MgCO3)% 2,00 MgOsil % 1,70 MgOtotal% 4,50 CO3total% 20,15 MgOcarb% 2,80 CaOcarbon% 16,94 H2O % 2,00 P2O5total% 30,00 MgOcarbon% 2,80 Solids % 98,00 Table 2: Cajati’s concentrated rock with low apatite composition Table 2 demonstrates that the leachable CaO content is distributed in carbonatite CaO (CaOcalc)) and dolomite CaO (CaOdol), which corresponds to about 17% of CaO. Therefore, the main reactions expected in this step 102 are: MgCO3+ H2SO4→ MgSO4(sol)+ H2O + CO2 (gas)CaCO3+ H2SO4→ CaSO4(insol) + H2O + CO2(gas) Consequently, soluble magnesium can be extracted from the concentrate (about 80%) and calcium remains in the form of inert calcium sulphate. The leaching conditions must be kept mild enough to avoid attacking the apatite. The optimum conditions vary according to the mineralogical characteristics of the phosphate rock concentrate. The main parameters that control this reaction are particle size, pH and residency time. In one example, the temperature can be kept at 60 °C, the pH in a range of from about Attorney Docket No.40014-1997WO01 2.0 – 4.0, and more particularly, from about 3.0 – 3.5, with a residency time of about 2 – 3 hours. However, these parameters can be adjusted up or down, depending on the composition of the rock. Now turning to neutralization step 104, after the leaching step 102, the resulting pulp is neutralized with a suspension of limewater 105 to insolubilize a small amount of phosphorus that might have been solubilized due to a slight attack of apatite during step 102. In this case, the phosphorus precipitates as calcium phosphate and remains in the apatite concentrate preventing or reducing losses of this element in the process, according to the following reaction: H3PO4 + Ca (OH)2 → CaPO4.H2O(insoluble) +2H2O This step 104 of the process 100 is important to reduce or avoid phosphorus losses in the leaching process of igneous rocks. Then, neutralized solution from step 104 is directed to a vacuum belt filter in a filtration step 106, in which leached phosphate rock 109 is separated from a liquid phase (filtrate) 111 containing high MgO and washed with a 10% solution of Sodium Hexametaphosphate (SHMP). The leached phosphate rock 109 can then be subjected to an optional second filtration step 108, to further separate solid phosphate rock 107 used for the production of phosphoric acid and / or phosphate fertilizers. The liquid phase 111 from the filtration step 106, and optionally a liquid phase 113 from the second filtration step 108, is then subjected to an alkalinization step 110, in which phases 111, 113 are treated with a suspension of limewater 115 (approximately 5%-10% w / v of lime). This operation 110 is carried out at higher pH (approximately 10 or more) to precipitate the magnesium as Mg(OH)2. The resulting solution 117 is filtered in a filtration step 112, such as by press filtration, in which solid Mg(OH)2119 can be recovered. A liquid phase 121 from filtration step 112 can be recycled back into one or more steps of the process 100 or Attorney Docket No.40014-1997WO01 disposed. Examples A pilot run for this process was conducted using a sample of phosphate rock from the Cajati industrial unit. The sample contained about 32% of P2O5, 53% of CaO, and 2.30% of MgO. The purification of the concentrate, through the decarbonation reaction with a dilute solution of sulfuric acid (0.5 mM), was carried out in a reactor with a residence time of 120 minutes. The mineralogy of the sample tests is presented in Table 3 below: Mineralogical characterization % Formula ApapiteCa5Calcite CaCO3 Dolomite 4CaMg(CO3)2 Phlogopite 3KMg3AlSi3O10(F,OH)2Table 3: Concentrated rock mineralogy for pilot run 1 After the leaching step, the decarbonated concentrate was washed with a solution of 10% w / v of a complexing agent (sodium hexametaphosphate (SHMP)) to immobilize iron (Fe) and aluminum (Al) compounds that could not be solubilized and removed after neutralization. FIGs.2 and 3 show the efficiency of the process with the decontamination of up to 60% of the MgO contained in the rock, with a P2O5recuperation of more than 96%. Thus, by applying this process it is possible to obtain a concentrate with MgO content under the usual conditions of other concentrates without interfering with the manufacture of phosphoric acid. A second pilot run, with a new batch of Cajati phosphate rock was performed with a more mineralogical complex sample. This second sample contained about 30% of P2O5, 42% of CaO and 1.7% of MgO, and with a mineralogy characterization set forth in Table 4: Attorney Docket No.40014-1997WO01 Mineralogical characterization % Formula Apapite 80.5Ca5(PO4)3(F,Cl,OH)2 O For this second sample and referring to FIG. 4, the efficiency of the process with thedecontamination of up to 70% of the MgO containedin the rock, with a P2O5 recuperation of morethan 95%. A complete process flowchart for the first and second pilot runs in depicted in FIG.5. Based on information learned from these runs, it is expected that a water consumption in the process will be approximately 3.5 tH2O / t of concentrate (t = metric tonne, or 1000kg). About 1.86 t / t of concentrate will be recycled, so the consumption is estimated to be 1.64 t (clean water) / t of concentrate. Consumption of the additive (e.g. SHMP) used in the process will be 0.08t / t. concentrate. Removal of MgO from the concentrate from 60% to 70% depending on the concentrate. Embodiments of the present disclosure are directed to: Processes for selective removal of magnesium from phosphate rock, comprising: providing phosphate rock comprising magnesium and phosphorus; attacking the phosphate rock with acid to solubilize at least some of the magnesium in the phosphate rock, thereby forming an acidic pulp composed of a first solid phase containing phosphorus and a lower level of magnesium, and a first liquid phase containing magnesium; neutralizing the acidic pulp by adding a first neutralizing agent comprising a base; filtering the first liquid phase containing magnesium from the first solid Attorney Docket No.40014-1997WO01 phase to form a filtrate; neutralizing the filtrate to precipitate magnesium therefrom by adding a second neutralizing agent comprising a base to form a liquid phase composed primarily of water and a solid phase containing magnesium; filtering the liquid phase from the solid phase containing magnesium to form a second filtrate; and recycling the second filtrate into the process. The process of the preceding sentence, wherein the first neutralizing agent is calcium oxide or calcium hydroxide. The process of any of the preceding sentences of this paragraph, wherein the second neutralizing agent is calcium oxide or calcium hydroxide. The process of any of the preceding sentences of this paragraph, wherein both the first and second neutralizing agents are calcium oxide or calcium hydroxide. The process any of the preceding sentences of this paragraph, wherein the acid comprises sulfuric acid. The process of any of the preceding sentences of this paragraph, wherein the sulfuric acid is diluted to 50% or less. The process of any of the preceding sentences of this paragraph, wherein attacking the phosphate rock with acid is carried out at a pH in the range of from about 2.0 to about 4.0. The process of any of the preceding sentences of this paragraph, wherein neutralizing the acidic pulp raises the pH to about 7.0. The process of any of the preceding sentences of this paragraph, wherein neutralizing the filtrate to precipitate magnesium raises the pH up to about 10.0. The process of any of the preceding sentences of this paragraph, wherein the magnesium precipitated from the filtrate is in the form of Mg(OH)2. The process of any of the preceding sentences of this paragraph, wherein the phosphate rock is igneous rock. The process of any of the preceding sentences of this paragraph, wherein the phosphate rock is sedimentary rock. The process of any of the preceding sentences of this paragraph, wherein filtering the first liquid phase comprises vacuum filtration. The process of any of the preceding sentences of this paragraph, wherein attacking the phosphate rock with acid to solubilize at least some of the magnesium in the phosphate rock is done at conditions to minimize loss of phosphorous Attorney Docket No.40014-1997WO01 concentration. The process of any of the preceding sentences of this paragraph, wherein the first solid phase is washed with a complexing additive, to immobilize iron (Fe) and / or aluminum (Al) that could not be solubilized and removed after neutralization. The process of any of the preceding sentences of this paragraph, wherein the complexing additive comprises sodium hexametaphosphate (SHMP). Various examples of systems, devices, and methods have been described herein. These examples are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of this disclosure. Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted. Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with Attorney Docket No.40014-1997WO01 the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein. For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.

Claims

Attorney Docket No.40014-1997WO01 CLAIMS What is claimed is:

1. A process for selective removal of magnesium from phosphate rock, comprising: providing phosphate rock comprising magnesium and phosphorus; attacking the phosphate rock wWith acid to solubilize at least some of the magnesium in the phosphate rock, thereby forming an acidic pulp composed of a first solid phase containing phosphorus and a lower level of magnesium, and a first liquid phase containing magnesium; neutralizing the acidic pulp by adding a first neutralizing agent comprising a base; filtering the first liquid phase containing magnesium from the first solid phase to form a filtrate; neutralizing the filtrate to precipitate magnesium therefrom by adding a second neutralizing agent comprising a base to form a liquid phase composed primarily of water and a solid phase containing magnesium; filtering the liquid phase from the solid phase containing magnesium to form a second filtrate; and recycling the second filtrate into the process.

2. The process of claim 1, wherein the first neutralizing agent is calcium oxide or calcium hydroxide 3. The process of claim 1, wherein the second neutralizing agent is calcium oxide or calcium hydroxide.Attorney Docket No.40014-1997WO01 4. The process of claim 1, wherein both the first and second neutralizing agents are calcium oxide or calcium hydroxide.

5. The process of claim 1, the acid comprises sulfuric acid.

6. The process of claim 5, wherein the sulfuric acid is diluted to 50% or less.

7. The process of claim 1, wherein attacking the phosphate rock with acid is carried out at a pH in the range of from about 2.0 to about 4.

0.

8. The process of claim 7, wherein neutralizing the acidic pulp raises the pH to about 7.

0.

9. The process of claim 8, wherein neutralizing the filtrate to precipitate magnesium raises the pH up to about 10.

0.

10. The process of claim 1, wherein the magnesium precipitated from the filtrate is in the form of Mg(OH)2.

11. The process of claim 1, wherein the phosphate rock is igneous rock.

12. The process of claim 1, wherein the phosphate rock is sedimentary rock.Attorney Docket No.40014-1997WO01 13. The process of claim 1, wherein filtering the first liquid phase comprises vacuum filtration.

14. The process of claim 1, wherein attacking the phosphate rock with acid to solubilize at least some of the magnesium in the phosphate rock is done at conditions to minimize loss of phosphorous concentration.

15. The process of claim 1, wherein the first solid phase is washed with a complexing additive, to immobilize iron (Fe) and / or aluminum (Al) that could not be solubilized and removed after neutralization.

16. The process of claim 15, wherein the complexing additive comprises sodium hexametaphosphate (SHMP).

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