US-12617691-B2 - Recovery of commercial substances from apatite mineral

US12617691B2US 12617691 B2US12617691 B2US 12617691B2US-12617691-B2

Abstract

A method for recovery of commercial substances from apatite mineral comprises dissolving of apatite mineral in an acid comprising hydrochloride. The dissolution gives a first liquid solution comprising phosphate, calcium and chloride ions. The first liquid solution is treated into a second liquid solution comprising calcium and chloride ions. This treatment in turn comprises extracting of a major part of the phosphate ions with an organic solvent. A bleed solution is removed from the second solution. Solid gypsum comprising at least 70% in a di-hydrate crystal form is precipitated from the second solution. This precipitation of solid gypsum comprises adding the second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals. Thereby, the precipitation of solid gypsum gives a third liquid solution comprising hydrochloride. An arrangement for recovery of commercial substances from apatite mineral is also presented.

Inventors

Yariv Cohen
Angela VAN DER WERF
Viktoria WESTLUND
Cristian TUNSU
Hugo ROYEN

Assignees

EASYMINING SWEDEN AB

Dates

Publication Date: 20260505
Application Date: 20211123
Priority Date: 20201125

Claims (20)

1 . A method for recovery of commercial gypsum from apatite mineral, comprising the steps of: dissolving apatite mineral of magmatic origin in an acid comprising hydrochloride, giving a first liquid solution comprising phosphate ions, calcium ions and chloride ions, said step of dissolving apatite mineral is performed at a liquid-to-solid ratio between 1 and 5; treating said first liquid solution, resulting in a second liquid solution comprising calcium ions and chloride ions; said step of treating in turn comprising the step of extracting a major part of said phosphate ions with an organic solvent; and precipitating solid gypsum comprising at least 70% in a di-hydrate crystal form from said second solution; said step of precipitating solid gypsum in turn comprising the step of adding said second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals, whereby said precipitating of solid gypsum gives a third liquid solution comprising hydrochloride; said sulfuric acid has a concentration of at least 13 M.
2 . The method according to claim 1 , wherein said step of adding said second solution and said sulfuric acid is controlled to be performed with respective rates giving a stoichiometric excess of calcium to sulfuric acid in said continuously stirred reactor between 0-50%.
3 . The method according to claim 1 , wherein said step of precipitating solid gypsum is controlled to be performed at a temperature below 150° C.
4 . The method according to claim 1 , wherein said step of precipitating solid gypsum comprises the step of forming a slurry of gypsum and hydrochloric acid which upon filtration forms a filter cake with a dry matter content of above 50%, and of filtering the slurry to produce said solid gypsum.
5 . The method according to claim 4 , wherein said step of precipitating solid gypsum comprises a further step of washing said filtered solid gypsum with a chloride deficient wash solution in which the amount of wash water is at least sufficient to replace the cake water of said filtered solid gypsum.
6 . The method according to claim 1 , comprising further steps of: removing a bleed solution from said second solution; and recycling at least a part of said third liquid solution as at least a part of said acid comprising hydrochloride in a subsequent said step of dissolving apatite mineral.
7 . The method according to claim 1 , wherein said step of extracting a major part of said phosphate ions is performed until said second liquid solution has a residual phosphorus content of less than 10 g P per liter.
8 . The method according to claim 1 , wherein said step of extracting a major part of said phosphate ions is performed with an organic solvent at an organic-to-aqueous ratio of between 1:1 and 3:1 in at least 4 contact stages.
9 . The method according to claim 1 , wherein said step of dissolving apatite mineral is performed at a liquid-to-solid ratio between 2.8 and 3.6.
10 . The method according to claim 1 , wherein said apatite mineral further comprises silica, and wherein said step of treating said first liquid solution resulting in said second liquid solution further comprises a step of adding sodium chloride to said first liquid, resulting in precipitation of sodium fluorosilicate, and a step of removing said precipitated sodium fluorosilicate from said first liquid.
11 . The method according to claim 1 , wherein said apatite mineral further comprises rare earth elements, and wherein said step of treating said first liquid solution into said second liquid solution further comprises a step of partially neutralizing a raffinate resulting from said extracting of a major part of said phosphate to a pH>1.5 causing precipitation of phosphates of rare earth elements, and a step of filtering said precipitated phosphates of rare earth elements from said raffinate.
12 . The method according to claim 1 , wherein said apatite mineral further comprises iron, whereby the said method further comprises removing said iron by at least one of the steps: extracting iron as ferric iron from said first liquid solution by solvent extraction prior to said step of extracting phosphate ions; and reducing any ferric iron to ferrous iron prior to said step of extracting phosphate ions and removing iron hydroxide or iron phosphate precipitated from said bleed solution.
13 . The method according to claim 1 , wherein said apatite mineral further comprises arsenic, whereby the said method further comprises removing said arsenic by precipitation with sulfide and by at least one of the steps: removing arsenic sulfide precipitated from said first liquid solution; and removing arsenic sulfide precipitated from a strip solution comprising extracted phosphate ions.
14 . The method according to claim 1 , wherein said apatite mineral further comprises fluorine, whereby the said method further comprises removing said fluorine by at least one of the steps: adding sodium chloride or potassium chloride to said first liquid solution to precipitate fluorosilicates and separating precipitated fluorosilicates with nondissolved residues; stripping fluorosilicic acid as silicon tetra fluorine from a strip solution comprising extracted phosphate ions during evaporation of water from said strip solution comprising extracted phosphate ions; and adding lime to bleed solution causing precipitation of fluorosilicides and removing of said precipitated fluorosilicides.
15 . The method according to claim 6 , comprising the further steps of adding lime into said bleed solution, resulting in precipitation of calcium phosphate, removing said precipitated calcium phosphate from said bleed solution, and recirculating said removed precipitated calcium phosphate to be dissolved together with said apatite mineral in a subsequent said step of dissolving apatite mineral in an acid.
16 . The method according to claim 3 , wherein said step of precipitating solid gypsum is controlled to be performed at a temperature below 60° C.
17 . The method according to claim 4 , wherein said step of precipitating solid gypsum comprises the step of forming a slurry of gypsum and hydrochloric acid which upon filtration forms a filter cake with a dry matter content of above 70% and of filtering the slurry to produce said solid gypsum.
18 . The method according to claim 8 , wherein said step of extracting a major part of said phosphate ions is performed with an organic solvent at an organic-to-aqueous ratio of between 7:5 and 8:5.
19 . A method for recovery of commercial gypsum from apatite mineral, comprising the steps of: dissolving apatite mineral of magmatic origin in an acid comprising hydrochloride, giving a first liquid solution comprising phosphate ions, calcium ions and chloride ions; treating said first liquid solution, resulting in a second liquid solution comprising calcium ions and chloride ions; said step of treating in turn comprising the step of extracting a major part of said phosphate ions with an organic solvent; removing a bleed solution from said second solution; adding lime into said bleed solution, resulting in precipitation of calcium phosphate, removing said precipitated calcium phosphate from said bleed solution, and recirculating said removed precipitated calcium phosphate to be dissolved together with said apatite mineral in a subsequent said step of dissolving apatite mineral in an acid; and precipitating solid gypsum comprising at least 70% in a di-hydrate crystal form from said second solution; said step of precipitating solid gypsum in turn comprising the step of adding said second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals, whereby said precipitating of solid gypsum gives a third liquid solution comprising hydrochloride; said sulfuric acid has a concentration of at least 13 M.
20 . A method for recovery of commercial gypsum from apatite mineral, comprising the steps of: dissolving apatite mineral of magmatic origin in an acid comprising hydrochloride, giving a first liquid solution comprising phosphate ions, calcium ions and chloride ions; treating said first liquid solution, resulting in a second liquid solution comprising calcium ions and chloride ions; said step of treating in turn comprising the step of extracting a major part of said phosphate ions with an organic solvent at an organic-to-aqueous ratio of between 1:1 and 3:1, in at least 4 contact stages; removing a bleed solution from said second solution; and precipitating solid gypsum comprising at least 70% in a di-hydrate crystal form from said second solution; said step of precipitating solid gypsum in turn comprising the step of adding said second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals, whereby said precipitating of solid gypsum gives a third liquid solution comprising hydrochloride; said sulfuric acid has a concentration of at least 13 M.

Description

This patent application is a U.S. national stage filing under 35 U.S.C. § 371 of PCT International Application No. PCT/SE2021/051165 filed Nov. 23, 2021 (published as WO2022/115021 on Jun. 2, 2022), which claimed priority to and the benefit of Swedish Patent Application 2051374-3 filed Nov. 25, 2020. The entire contents of these applications are incorporated herein by reference. TECHNICAL FIELD The present technology relates in general to methods and arrangements for handling apatite minerals, and in particular to methods and arrangements for separating at least phosphorus from apatite minerals. BACKGROUND Large quantities of phosphorus end up in the beneficiation tailings from iron ore processing in Sweden. Phosphorus is an undesired component in the final pellets and therefore it is typically separated during the beneficiation process. The separated phosphorus is typically in the form of apatite mineral of magmatic origin. The phosphorus concentration in the beneficiation waste is typically a few percent by weight, which is of equal magnitude to e.g. the phosphorus concentration in the sole phosphate mine in Europe, in Finland. Like the phosphate mine in Finland, the ore must be upgraded by e.g. flotation to form a high-grade apatite concentrate, having about 15% phosphorus by weight, suitable for further processing. Apatite concentrate has been commercially produced in Sweden from mine tailings in Malmberget and Grängesberg by different companies, but the operations ended in the 1980's mainly because of economic reasons. In recent years there has been a renewed interest in exploring phosphorus reserves since phosphorus is listed as a critical raw material for the EU. Beside existing mine tailings, there are several apatite ores mainly in the north of Sweden that can be exploited in the future. In addition to phosphorus, the Swedish apatite minerals have a significant content (ca 0.5-0.9%) of rare earth elements, which is interesting to recover for use in high tech applications. However, in order to upgrade apatite concentrate to phosphorus products such as e.g. phosphoric acid or ammonium phosphates, in particular with the additional requirement to recover the rare earth elements, several obstacles have to be handled. These obstacles cannot be overcome by state-of-the-art technologies. Some of the Swedish apatite is of chlorapatite form in which the chloride content exceeds the allowable limits for conventional processes (<0.1% Cl) for preventing corrosion in the phosphoric acid evaporators. The arsenic content is generally far too high to fulfill the specification for e.g. modern fertilizers. Land or sea disposal of hazardous phosphogypsum, which is a major by-product, is not considered a viable option, at least not in Sweden. Recovery of rare earth elements from apatite is not possible with conventional technologies. The conventional way to digest apatite in the phosphate industry is by using concentrated sulfuric acid, i.e. 96-98% by weight. Most of the world production of phosphate fertilizers, about 90%, is based on the use of sulfuric acid. The reason is that sulfuric acid is a cheap commodity, easy to transport in a concentrated form, and enables easy separation of calcium from phosphoric acid in the form of gypsum. Several gypsum processes exist such as the dihydrate and hemihydrate processes and combination processes such as hemi-dihydrate. However, the use of sulfuric acid for apatite digestion has several disadvantages. There is a limited possibility to concentrate phosphoric acid during the digestion step due to difficulties to filter gypsum from the viscous phosphoric acid at high concentrations. This limits the possible concentration of phosphoric acid from the filter to a maximum of up to about 5 M, or 40% by weight. The relatively low acid concentration means that the residual water must be removed, typically by evaporation. The process also has a strict water-balance as all the gypsum wash water must be evaporated. One of the major disadvantages of using sulfuric acid for apatite dissolution is that the residual gypsum is of low quality and not suitable for valorization in the gypsum industry. Generally, such phosphogypsum must be disposed since it is normally is considered to be too costly to clean. Technologies for cleaning phosphogypsum are based on recrystallization processes that are both chemical and energy intensive and therefore not widely used in the industry. Another disadvantage is that about 80% of the rare earth elements are incorporated into the gypsum lattice, which does not enable the recovery of rare earth elements. About one and a half ton of gypsum is generated for each ton of apatite. The disposal of phosphogypsum (considered a hazardous waste) in Sweden is not a viable option due to the difficulties in getting permits for such operation and the large costs associated with maintenance of phosphogypsum disposal ponds or sites. Another state-of-the-art process, called t