Composite leaching agent for preferentially leaching rare earth from phosphorite and application of composite leaching agent

Abstract

The invention belongs to the technical field of comprehensive utilization of phosphorite, and particularly relates to a composite leaching agent for preferentially leaching rare earth from phosphorite and application of the composite leaching agent. The invention provides a composite leaching agent, the composite leaching agent comprises inorganic acid, organic acid and an additive, the composite leaching agent can preferentially leach 50% or above of associated rare earth in phosphorite, the grade of the phosphorite after rare earth extraction can be ensured to be 28% or above, and the grade requirement of phosphate fertilizer production is met. The associated rare earth in the phosphorite is effectively extracted by adopting the composite leaching agent, the process of extracting the rare earth from byproducts in the phosphorite utilization process at present is simplified, and the resource utilization of the rare earth is realized.

Description

Technical Field

[0001] This application belongs to the technical field of comprehensive utilization of phosphate rock, and more specifically, relates to a composite leaching agent for preferentially leaching rare earths from phosphate rock and its application. Background Art

[0002] Rare earths are a collective term for 17 elements including scandium, yttrium, and lanthanide elements dispersed in the earth's crust. Generally, they exist in the form of oxides or oxyacid salt minerals in symbiosis, and belong to non-renewable resources. Due to their unique physical and chemical properties, rare earths are widely used in fields such as petrochemical industry, metallurgy ceramics, electronic military industry, and new energy. With the rapid development of clean energy, new energy vehicles, and aerospace technology, the demand for rare earths is increasing day by day. The low reserves, non-renewability, wide application, irreplaceability, extremely uneven distribution of rare earths, and the complex technology and high environmental requirements in the extraction, separation, and processing processes make rare earth resources have extremely high value globally and become one of the focuses in the resource competition and scientific and technological development layout of various countries.

[0003] In addition to being present in various rare earth ores in nature, a considerable part of rare earth elements in the natural world coexist with apatite and phosphorite ores. The global phosphate rock reserves are about 74 billion tons, the average content of associated rare earths in phosphate rock is about 0.5 ‰, and the total amount of associated rare earths is about 37 million tons, with a quite considerable total reserve. It is a new secondary rare earth resource to alleviate the supply-demand relationship of rare earths. The exploration and processing of secondary rare earth resources have become an effective way to reconcile the supply-demand relationship of rare earths and enhance competitiveness.

[0004] Since the ionic radius of rare earths (0.848 - 0.106 nm) is very close to that of Ca 2+ (0.106 nm), more than 90% of rare earths are hosted in phosphate rock in the form of isomorphic substitution. Therefore, the rare earth grade in phosphate rock increases with the increase of phosphorus grade. After beneficiation, the phosphorus grade of phosphate rock used in industrial phosphate fertilizer production is not less than 28%, and at this time, the grade of associated rare earths in it is also relatively high.

[0005] Phosphate rock is mainly used in phosphochemical fields such as phosphoric acid and phosphate fertilizers. Currently, more than 80% of phosphate rock is treated by the wet-process phosphoric acid process, and 70% - 95% of the associated rare earths are finally concentrated in the by-product phosphogypsum. Due to the physical and chemical properties and complex composition of phosphogypsum, the global comprehensive utilization rate of phosphogypsum is only about 40% except for a few developed countries such as Japan, Germany, and Belgium with relatively high comprehensive utilization rates. Currently, its treatment method is mainly stacking. Phosphogypsum has complex composition, many impurities, and low rare earth grade. The rare earth extraction and separation process is complex, and the extraction cost is much higher than the economic value it can generate, resulting in the associated rare earths in phosphate rock being finally stored and wasted in by-products such as phosphogypsum. At the same time, the stacking of by-products has also caused environmental problems.

[0006] There are also some existing technologies that attempt to increase the leaching rate of rare earths, but phosphorus is often leached out simultaneously with the rare earths. For example, patent document CN105154689A uses dilute sulfuric acid to firstly leach rare earths and phosphorus in phosphate ore as much as possible, to obtain crude phosphoric acid and phosphogypsum containing rare earth ions, and then further leach the rare earths in the phosphogypsum, and combine the leaching solutions of the two steps to extract the rare earths. The rare earth extraction process in this method is complicated, which also affects the production of phosphoric acid.

[0007] How to effectively utilize the rare earths associated with phosphate rock, to give priority to extracting rare earths and simplify the complex process of extracting rare earths from wet phosphoric acid by-products, while ensuring that the grade of phosphate rock after rare earth extraction meets the requirements of process application, is a technical problem that needs to be solved urgently. Summary of the invention

[0008] In view of the defects of the prior art, the purpose of this application is to propose a composite leaching agent and its application for selectively and preferentially leaching rare earths and a small amount of phosphorus from phosphate ore. The composite leaching agent can preferentially leach more than 50% of rare earths in one step, while the phosphorus grade in the leached residue can be maintained at 28% or above, which can be directly used for the production of phosphate fertilizer. The purpose is to solve the technical problems that the prior art wet phosphoric acid process for treating phosphate ore leads to waste of rare earth resources and the accumulation of phosphogypsum cannot effectively utilize phosphorus resources.

[0009] To achieve the above objectives, in a first aspect, the present application provides a composite leaching agent for preferentially leaching rare earths from phosphate ore, wherein the composite leaching agent contains an inorganic acid, an organic acid and an additive, and the solvent is water; wherein: The concentration of the inorganic acid is 0.1-1 mol / L; The organic acid is one or more of formic acid, acetic acid and citric acid; The additive is one or more of polyethylene glycol, fluorite, sodium dodecylbenzene sulfonate, potassium sodium tartrate, dodecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide.

[0010] Preferably, the inorganic acid is sulfuric acid or nitric acid, and the concentration of the inorganic acid is 0.1-0.5 mol / L.

[0011] More preferably, the concentration of the organic acid is 0.2-1.5 mol / L.

[0012] Preferably, the content of P2O5 in the phosphate ore is higher than or equal to 32wt%, and the content of rare earth ReO in the phosphate ore is higher than or equal to 0.5wt%.

[0013] Preferably, the mass percentage of the additive in the composite leaching agent is 0.1-2%.

[0014] According to another aspect of the present invention, there is provided a method for preferentially leaching rare earths from phosphate rock using the above-mentioned composite leaching agent. The phosphate rock is mixed with the composite leaching agent and then stirred for leaching, followed by solid-liquid separation to obtain a leaching solution and treated phosphate rock, wherein: This composite leaching agent can inhibit the leaching of phosphorus while promoting the leaching of rare earths in phosphate rock, so that the content of P2O5 in the treated phosphate rock is 28% or more, and the leaching rate of rare earths in the phosphate rock is 50% or more.

[0015] Preferably, the solid-liquid ratio of the phosphate rock to the composite leaching agent is 1:3 - 1:8.

[0016] Preferably, the stirring time is 0.1 - 6 hours.

[0017] Preferably, the leaching temperature is 50 - 80 °C.

[0018] Generally speaking, compared with the prior art, the above technical solution conceived by the present application has the following beneficial effects: (1) In order to effectively extract the rare earths existing in phosphate rock, the present invention provides a composite leaching agent, which contains inorganic acids, organic acids and additives with appropriate concentrations, and the solvent is water. This composite leaching agent can preferentially leach the associated rare earths in phosphate rock, and the rare earth leaching rate can reach 50% or more. Moreover, it can ensure that the grade of phosphate rock after rare earth extraction is above 28%, meeting the requirements of phosphate fertilizer production.

[0019] (2) The additives used in the composite leaching agent adopted by the present invention cooperate synergistically with inorganic acids and organic acids, can inhibit the dissolution and loss of phosphorus, promote the leaching of rare earths, enable phosphate rock to preferentially leach rare earths in an acidic system, and at the same time control the phosphorus leaching rate, ensuring that the phosphorus grade of the treated phosphate rock is not lower than 28%, and the rare earth leaching rate is higher than 50%, up to 62.79% at most, realizing the effective extraction of associated rare earths in phosphate rock.

[0020] (3) The method for preferentially extracting rare earths from phosphate rock by the present invention is simple and efficient, and is suitable for industrial-scale production. Specific Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the following further details the present application in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] Due to the associated relationship between phosphorus and rare earths in phosphate rock, the rare earth grade in phosphate rock usually increases with the increase in phosphorus grade. It is very difficult to achieve the selective separation and leaching of the two. Industrially, the phosphorus grade of phosphate rock used in phosphate fertilizer production after beneficiation is generally not less than 28%, and the associated rare earth grade is relatively high at this time. In the wet-process phosphoric acid process, concentrated sulfuric acid is used to leach phosphate rock, and almost all rare earths are dissolved, and then rare earth sulfate precipitates are formed in an environment with a large amount of sulfate ions. The formation of calcium sulfate will also wrap part of the rare earths. Therefore, most rare earths are finally fixed in phosphogypsum. About 95% of the rare earths enter phosphogypsum in the hemihydrate-wet-process phosphoric acid process, and about 70-80% of the rare earths enter phosphogypsum in the dihydrate-wet-process phosphoric acid process.

[0023] The prior art uses the wet-process phosphoric acid process to treat phosphate rock. Most of the associated rare earths in phosphate rock enter phosphogypsum during the leaching process, resulting in the difficulty in utilizing the rare earths therein and causing resource waste; in some literatures, inorganic acids are used to directly leach rare earth-containing phosphate rock, and rare earths and phosphorus are often leached simultaneously to obtain crude phosphoric acid containing rare earths. Subsequently, it is necessary to further separate rare earths from the crude phosphoric acid. Not only is the rare earth extraction method complex, but it also reduces the phosphorus grade in phosphate rock and cannot be used for phosphate fertilizer production anymore.

[0024] To solve the above problems, the present invention proposes a brand-new idea for extracting associated rare earths from phosphate rock: before processing and utilizing phosphate rock, the associated rare earth resources in phosphate rock are preferentially extracted. At the same time, the phosphate rock in the leaching residue after extraction can still meet the requirements for phosphate fertilizer production (phosphorus grade not less than 28%), and then subsequent phosphate fertilizer production is carried out. The inventors of this application unexpectedly found in experiments that when the concentration of the inorganic acid is adjusted to a suitable concentration range and a composite leaching agent is formed by compounding an organic acid and a specific type of additive, the composite leaching agent can leach more than 50% of the rare earths in one step, and the phosphorus grade in the leaching residue can be maintained above 28%, which can meet the requirements for phosphate fertilizer production.

[0025] The present invention provides a composite leaching agent for preferentially leaching rare earths from phosphate rock. The composite leaching agent contains an inorganic acid, an organic acid and an additive, and the solvent is water; the concentration of the inorganic acid in the composite leaching agent is 0.1-1 mol / L; the organic acid is one or more of formic acid, acetic acid and citric acid; the additive is one or more of polyethylene glycol, fluorite, sodium dodecylbenzenesulfonate, potassium sodium tartrate, dodecyltrimethylammonium bromide, cetyltrimethylammonium bromide.

[0026] The method for selectively preferentially leaching rare earths from phosphate rock by the composite leaching agent of the present invention is specifically as follows: the phosphate rock is mixed with the composite leaching agent and then stirred for leaching, and solid-liquid separation is carried out to obtain a leaching solution and treated phosphate rock. The composite leaching agent can promote the leaching of rare earths in phosphate rock and at the same time inhibit the leaching of phosphorus, so that the content of P2O5 in the treated phosphate rock is 28% or more, and the leaching rate of rare earths in the phosphate rock is more than 50%.

[0027] In a preferred embodiment, the inorganic acid used in the composite leaching agent is sulfuric acid or nitric acid, the concentration of the inorganic acid is 0.1 - 0.5 mol / L, more preferably 0.4 - 0.6 mol / L. The concentration of the organic acid is 0.2 - 1.5 mol / L. The mass percentage of the additive in the composite leaching agent is 0.1 - 2%.

[0028] In a preferred embodiment, the additive includes polyethylene glycol, fluorite and cetyltrimethylammonium bromide, and their mass ratio is 1:(6 - 10):(0.5 - 1.5).

[0029] In some embodiments, the volume ratio of the inorganic acid aqueous solution to the organic acid aqueous solution in the composite leaching agent is 0.8 - 1.2:1; the grade of the phosphate rock before leaching is higher than or equal to 32%. The liquid-solid ratio of the composite leaching agent to the phosphate rock is 3:1 - 8:1, and the stirring time is 0.1 - 6 hours. The leaching temperature is 50 - 80 °C.

[0030] The present invention is applicable to all phosphate rocks containing associated rare earths. However, the economy of the present invention is affected by the grade of associated rare earths in the phosphate rock. Generally, the grade of associated rare earths in the phosphate rock applicable to the present invention should be at least 0.5 wt%. After leaching with the composite leaching agent, under the preferred leaching acid concentration, leaching time, leaching temperature, leaching liquid and liquid-solid ratio of the phosphate rock, as well as the additive conditions, the associated rare earths in the phosphate rock are preferentially extracted, while ensuring that the phosphorus grade of the phosphate rock is not lower than 28%, meeting the requirements for phosphorus grade in phosphate fertilizer production.

[0031] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. For the process parameters without specific conditions indicated in the following embodiments, they are usually in accordance with conventional conditions.

[0032] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0033] For the process parameters without specific conditions indicated in the following embodiments, they are usually in accordance with conventional conditions.

[0034] The embodiments of the present application use a rare earth-containing phosphate concentrate from a certain place in Shaanxi, and analyze its chemical composition. The mass fractions of its components are shown in Table 1 below: Table 1 Chemical composition and content of associated rare earth phosphate concentrate (wt%)

[0035] Comparative Example 1 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that had passed through a 200-mesh sample sieve was taken, and 3.0 mol / L sulfuric acid was added according to a liquid-solid ratio of 5:1, followed by stirring and reacting for 2 hours. The leaching solution and leaching residue were obtained by filtration. The phosphorus grade in the leaching residue was 1.72%, and the amount of rare earths entering the leaching solution accounted for 86.06% of the total rare earths in the phosphate rock.

[0036] Comparative Example 2 Other conditions were the same as in Comparative Example 1, except that the concentration of sulfuric acid was 1.5 mol / L.

[0037] The phosphorus grade in the obtained leaching residue was 11.61%, and the amount of rare earths entering the leaching solution accounted for 68.98% of the total rare earths in the phosphate rock.

[0038] Comparative Example 3 Other conditions were the same as in Comparative Example 1, except that the concentration of sulfuric acid was 1 mol / L.

[0039] The phosphorus grade in the obtained leaching residue was 13.99%, and the amount of rare earths entering the leaching solution accounted for 52.06% of the total rare earths in the phosphate rock.

[0040] Comparative Example 4 Other conditions were the same as in Comparative Example 1, except that the concentration of sulfuric acid was 0.5 mol / L.

[0041] The phosphorus grade in the obtained leaching residue was 20.3%, and the amount of rare earths entering the leaching solution accounted for 20.38% of the total rare earths in the phosphate rock.

[0042] Comparative Example 5 Other conditions were the same as in Comparative Example 1, except that the concentration of sulfuric acid was 0.25 mol / L.

[0043] The phosphorus grade in the obtained leaching residue was 28.97%, and the amount of rare earths entering the leaching solution accounted for 8.28% of the total rare earths in the phosphate rock.

[0044] Comparative Example 6 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that had passed through a 200-mesh sample sieve was taken, and 1 mol / L formic acid was added according to a liquid-solid ratio of 5:1, followed by stirring and reacting for 2 hours. The leaching solution and leaching residue were obtained by filtration. The phosphorus grade in the leaching residue was 30.71%, and the amount of rare earths entering the leaching solution accounted for 4.22% of the total rare earths in the phosphate rock.

[0045] Comparative Example 7 Other conditions were the same as in Comparative Example 6, except that formic acid was replaced with acetic acid.

[0046] The phosphorus grade in the obtained leaching residue is 30.07%, and the amount of rare earth entering the leaching solution accounts for 5.18% of the total rare earth in the phosphate rock.

[0047] Comparative Example 8 Other conditions are the same as those in Comparative Example 6, except that formic acid is replaced by citric acid.

[0048] The phosphorus grade in the obtained leaching residue is 30.94%, and the amount of rare earth entering the leaching solution accounts for 3.06% of the total rare earth in the phosphate rock.

[0049] Comparative Example 9 At 70 °C, 100 g of phosphate concentrate containing associated rare earth that has passed through a 200-mesh sample sieve is taken, and a 0.5 mol / L sulfuric acid aqueous solution and a 1 mol / L formic acid aqueous solution are added according to a liquid-solid ratio of 5:1. The volume ratio of the sulfuric acid aqueous solution to the formic acid aqueous solution is 1:1, and the mixture is stirred and reacted for 2 hours, and then filtered to obtain a leaching solution and a leaching residue. The phosphorus grade in the leaching residue is 25.48%, and the amount of rare earth entering the leaching solution accounts for 23.42% of the total rare earth in the phosphate rock.

[0050] Comparative Example 10 Other conditions are the same as those in Comparative Example 9, except that formic acid is replaced by acetic acid.

[0051] The phosphorus grade in the obtained leaching residue is 25.11%, and the amount of rare earth entering the leaching solution accounts for 26.04% of the total rare earth in the phosphate rock.

[0052] Comparative Example 11 Other conditions are the same as those in Comparative Example 9, except that formic acid is replaced by citric acid.

[0053] The phosphorus grade in the obtained leaching residue is 25.83%, and the amount of rare earth entering the leaching solution accounts for 22.85% of the total rare earth in the phosphate rock.

[0054] Comparative Example 12 At 70 °C, 100 g of phosphate concentrate containing associated rare earth that has passed through a 200-mesh sample sieve is taken, and 0.5 mol / L sulfuric acid is added according to a liquid-solid ratio of 5:1. At the same time, 0.5 g of polyethylene glycol 4000 is added as an additive, and the mixture is stirred and reacted for 2 hours, and then filtered to obtain a leaching solution and a leaching residue. The phosphorus grade in the leaching residue is 16.88%, and the amount of rare earth entering the leaching solution accounts for 25.03% of the total rare earth in the phosphate rock.

[0055] Comparative Example 13 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that has passed through a 200-mesh split sample sieve is taken, 0.5 mol / L sulfuric acid is added according to a liquid-solid ratio of 5:1, and at the same time, 0.5 g of polyethylene glycol 4000 and 2.5 g of fluorite are added as additives. Stir and react for 2 hours, then filter to obtain the leaching solution and the leaching residue. The phosphorus grade in the leaching residue is 23.29%, and the amount of rare earths entering the leaching solution accounts for 28.35% of the total rare earths in the phosphate rock.

[0056] Comparative Example 14 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that has passed through a 200-mesh split sample sieve is taken, 0.5 mol / L sulfuric acid is added according to a liquid-solid ratio of 5:1, and at the same time, 0.5 g of polyethylene glycol 4000 and 0.5 g of cetyltrimethylammonium bromide are added as additives. Stir and react for 2 hours, then filter to obtain the leaching solution and the leaching residue. The phosphorus grade in the leaching residue is 13.94%, and the amount of rare earths entering the leaching solution accounts for 29.56% of the total rare earths in the phosphate rock.

[0057] Comparative Example 15 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that has passed through a 200-mesh split sample sieve is taken, 0.5 mol / L sulfuric acid is added according to a liquid-solid ratio of 5:1, and at the same time, 2.5 g of fluorite and 0.5 g of cetyltrimethylammonium bromide are added as additives. Stir and react for 2 hours, then filter to obtain the leaching solution and the leaching residue. The phosphorus grade in the leaching residue is 22.15%, and the amount of rare earths entering the leaching solution accounts for 30.75% of the total rare earths in the phosphate rock.

[0058] Comparative Example 16 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that has passed through a 200-mesh split sample sieve is taken, 0.5 mol / L sulfuric acid is added according to a liquid-solid ratio of 5:1, and at the same time, 0.5 g of polyethylene glycol 4000, 4 g of fluorite and 0.5 g of cetyltrimethylammonium bromide are added as additives. Stir and react for 2 hours, then filter to obtain the leaching solution and the leaching residue. The phosphorus grade in the leaching residue is 26.24%, and the amount of rare earths entering the leaching solution accounts for 36.27% of the total rare earths in the phosphate rock.

[0059] Example 1 At 70 °C, 100 g of phosphate rock concentrate containing associated rare earths that has passed through a 200-mesh split sample sieve is taken, a 0.5 mol / L sulfuric acid aqueous solution and a 1 mol / L formic acid aqueous solution are added according to a liquid-solid ratio of 5:1, and the volume ratio of the sulfuric acid aqueous solution to the formic acid aqueous solution is 1:1. At the same time, 0.5 g of polyethylene glycol 4000, 4 g of fluorite and 0.5 g of cetyltrimethylammonium bromide are added as additives. Stir and react for 2 hours, then filter to obtain the leaching solution and the leaching residue. The phosphorus grade in the leaching residue is 28.98%, and the amount of rare earths entering the leaching solution accounts for 58.96% of the total rare earths in the phosphate rock.

[0060] Example 2 Others are the same as in Example 1, except that formic acid is replaced by acetic acid.

[0061] The phosphorus grade in the obtained leaching residue is 28.40%, and the amount of rare earths entering the leaching solution accounts for 62.79% of the total rare earths in the phosphate rock.

[0062] Example 3 Others are the same as in Example 1, except that formic acid is replaced by citric acid.

[0063] The phosphorus grade in the obtained leaching residue is 29.33%, and the amount of rare earths entering the leaching solution accounts for 53.10% of the total rare earths in the phosphate rock.

[0064] Example 4 Others are the same as in Example 1, except that the liquid-solid ratio is adjusted to 3:1, the leaching temperature is adjusted to 50 °C, and the stirring reaction is carried out for 6 hours.

[0065] The phosphorus grade in the obtained leaching residue is 28.6%, and the amount of rare earths entering the leaching solution accounts for 58.1% of the total rare earths in the phosphate rock.

[0066] Example 5 Others are the same as in Example 1, except that the liquid-solid ratio is adjusted to 8:1, the leaching temperature is adjusted to 80 °C, and the stirring reaction is carried out for 1 hour.

[0067] The phosphorus grade in the obtained leaching residue is 28.9%, and the amount of rare earths entering the leaching solution accounts for 59.1% of the total rare earths in the phosphate rock.

[0068] For Comparative Examples 1 to 16 and Examples 1 to 3, the detection and calculation data of the phosphorus grade in the leaching residue and the proportion of the amount of rare earths entering the leaching solution in the total rare earths in the phosphate rock are shown in Table 2: Table 2

[0069] It can be seen from Table 2 that in Comparative Examples 1 to 5, when using dilute sulfuric acid alone as the leaching agent, the higher the concentration of dilute sulfuric acid, the higher the leaching rates of rare earths and phosphorus. For example, when the concentration of dilute sulfuric acid is 3 M, the leaching rate of rare earths is as high as over 86%, and almost all phosphorus is leached into the leaching solution, and the separation of rare earths and phosphorus cannot be achieved. As the concentration of dilute sulfuric acid gradually decreases, the leaching rates of both decrease simultaneously, and the selective leaching of the two cannot be achieved, let alone the preferential leaching of rare earths.

[0070] In Comparative Examples 6 to 8, when using organic acids alone as the leaching agent, it can be seen that the leaching rates of organic acids for rare earths and phosphorus are very low. The leaching rate of rare earths is only about 3-5%, and almost no phosphorus is leached, and the preferential leaching of rare earths cannot be achieved either.

[0071] For Comparative Examples 9 to 11, a dilute sulfuric acid with a lower concentration was mixed with an organic acid in a volume ratio of 1:1 as a composite leaching agent to leach phosphate rock. It can be seen that the rare earth leaching rate was improved to a certain extent compared with that of the single dilute sulfuric acid leaching agent, and the phosphorus grade in the leaching residue increased. However, the rare earth leaching rate was still relatively low, and the phosphorus grade could not meet the requirements for phosphate fertilizer production.

[0072] For Comparative Examples 12 to 16, 0.5 mol / L dilute sulfuric acid was used as the leaching agent, and a small amount of additive was added during the leaching process. It can be seen that when different additives were introduced, compared with the case without adding additives, the rare earth leaching rate was improved to a certain extent, and phosphorus was also leached, resulting in a lower phosphorus grade in the leaching residue.

[0073] In Examples 1 to 3, a composite leaching agent was prepared by mixing dilute sulfuric acid and an aqueous solution of organic acid in a volume ratio of 1:1, and additives were introduced during the leaching process. It can be seen that the rare earth leaching rate was significantly improved, and the phosphorus grade in the leaching residue was relatively high. Especially when three additives were compounded simultaneously and acetic acid was used as the organic acid, the rare earth leaching rate was increased to 62.79%, and the phosphorus grade after leaching was still 28.4%, meeting the phosphorus grade requirements for phosphate fertilizer production. The possible reasons are as follows: (1) The mixture of dilute sulfuric acid and an aqueous solution of organic acid in a volume ratio of 1:1 further reduced the concentration of dilute sulfuric acid to 0.25 mol / L. The lower concentration of inorganic acid was beneficial to inhibiting the leaching of phosphorus and keeping phosphorus in the leaching residue; (2) Although the decrease in the concentration of dilute sulfuric acid also led to a decrease in the rare earth leaching rate, due to the synergistic effect of the organic acid and the additives, for example, additives such as polyethylene glycol and cetyltrimethylammonium bromide improved the permeability and fluidity of the sample, reduced the surface tension, and increased the contact probability between H + and rare earth. Under the complexing action of the carboxyl group of the organic acid, rare earth ions were stabilized in the leaching solution in the form of complexes, ultimately increasing the rare earth leaching rate; (3) The fluoride ions dissolved from the additive calcium fluoride promoted the destruction of the phosphate rock lattice, releasing more rare earth ions into the leaching solution and further increasing the rare earth leaching rate; (4) Under the leaching conditions of the examples, the ksp of calcium phosphate was lower than that of calcium sulfate. Adding fluorite in the examples promoted the precipitation of calcium phosphate, which was beneficial to the fixation of phosphorus in the leaching residue. Therefore, the inorganic acid, organic acid, and additives in the composite leaching agent of the examples of the present invention, by controlling appropriate concentrations and selecting appropriate types, cooperate with each other synergistically, promote the leaching of rare earth and effectively increase the phosphorus grade in the leaching residue, which is an effective method for preferentially leaching rare earth from phosphate rock.

[0074] Phosphate rock often contains associated rare earths. At present, phosphate rock is mainly used in the fields of phosphate fertilizers, phosphorus chemical industry, etc. The associated rare earths are enriched in the by-product phosphogypsum after the wet-process phosphoric acid process. The complex composition and physical and chemical properties of phosphogypsum hinder the recovery of rare earths therein, and the associated rare earth resources in phosphate rock are wasted. The present invention proposes a composite leaching agent and method for preferentially extracting the associated rare earths in phosphate rock without affecting the utilization of phosphate rock, effectively utilizing the associated rare earth resources. At present, during the utilization process of phosphate rock, more than 70% of the associated rare earths are enriched in the by-product phosphogypsum. Extracting rare earths from phosphogypsum is costly and difficult, and finally they are stacked in the mine, and the rare earth resources are not effectively utilized. The present invention controls the experimental conditions to preferentially extract the associated rare earths in phosphate rock, reduces the cost of rare earth extraction, and realizes the effective recovery of the associated rare earth resources.

[0075] As mentioned above, the above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of changes or substitutions, which should all be covered by the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims described above.

Claims

1. A composite leaching agent for preferentially leaching rare earths from phosphate rock, characterized in that, The composite leaching agent contains inorganic acid, organic acid and additives, and the solvent is water; wherein: The concentration of the inorganic acid is 0.1-1 mol / L; The organic acid is one or more of formic acid, acetic acid and citric acid; The additives are one or more of polyethylene glycol, fluorite, sodium dodecylbenzenesulfonate, potassium sodium tartrate, dodecyltrimethylammonium bromide, cetyltrimethylammonium bromide.

2. The composite leaching agent according to claim 1, wherein The inorganic acid is sulfuric acid or nitric acid, and the concentration of the inorganic acid is 0.1-0.5 mol / L.

3. The composite leaching agent according to claim 1, wherein, The concentration of the organic acid is 0.2-1.5 mol / L.

4. The composite leaching agent according to claim 1, wherein The content of P2O5 in the phosphate rock is higher than or equal to 32 wt%, and the content of rare earth ReO in the phosphate rock is higher than or equal to 0.5 wt%.

5. The composite leaching agent according to claim 1, characterized in that, The mass percentage of the additives in the composite leaching agent is 0.1-2%.

6. A method for preferentially leaching rare earths from phosphate rock using the composite leaching agent according to any one of claims 1 to 5, characterized in that, Mix the phosphate rock with the composite leaching agent and stir for leaching, then perform solid-liquid separation to obtain the leaching solution and the treated phosphate rock, wherein: The composite leaching agent can inhibit the leaching of phosphorus while promoting the leaching of rare earth in the phosphate rock, so that the content of P2O5 in the treated phosphate rock is 28% or more, and the leaching rate of rare earth in the phosphate rock is 50% or more.

7. The method according to claim 6, characterized in that, The solid-liquid ratio of the phosphate rock to the composite leaching agent is 1:3-1:

8.

8. The method according to claim 6, wherein The stirring time is 0.1-6 hours.

9. The method according to claim 1, characterized in that The leaching temperature is 50-80 °C.

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