Reagents and methods for removing heavy metals from phosphoric acid solutions

Abstract

Provided herein are methods for removing heavy metal ions from a phosphoric acid mixture by adding an effective amount of an agent containing a plurality of sulfur groups to the phosphoric acid mixture to form a heavy metal complex, and separating the heavy metal complex from the solution.

Description

Technical Field

[0001] The present invention relates generally to the purification of industrial process streams. More specifically, the present invention relates to the removal of heavy metal ions from phosphoric acid process streams. Background Art

[0002] About 90% of the world's phosphoric acid is produced according to the wet process, which is conventionally prepared by acidulating phosphate rock (which contains calcium phosphate) with sulfuric acid to produce crude wet process phosphoric acid (WPA) and insoluble calcium sulfate (gypsum).

[0003] The manufacture of phosphoric acid is well known and is the subject of numerous textbooks. A comprehensive introduction to the manufacture of phosphates and phosphoric acid is given by Becker in Phosphates and Phosphoric Acids, Marcel Dekker, Inc. 1989; and Slack in Phosphoric Acid, Part 1 and Part 2, Marcel Dekker, Inc. 1968. In this process, phosphate rock is washed in a scrubber and ground in a ball mill and then fed to a series of reactors for digestion with sulfuric acid together with recycled phosphoric acid from the process. After digestion, the reaction slurry is filtered to separate phosphoric acid from undissolved rock, newly formed gypsum and gangue. The filtered crude WPA is then sent to clarifiers and evaporators for further purification and concentration. The purified phosphoric acid is sent as commercial grade acid (MGA) or continues to make 69% P2O5 superphosphoric acid (SPA), where it can be converted into many end products ranging from chemical reagents, rust inhibitors, food additives, dental and orthopedic etchants, electrolytes, fluxes, dispersants, industrial etchants, fertilizer raw materials and components of household cleaning products. For example, crude phosphoric acid is concentrated to 54% (P2O5) before being sent for monoammonium phosphate (MAP), diammonium phosphate (DAP) or ammonium thiophosphate (APS) production.

[0004] During the production of phosphoric acid, certain metal impurities in the form of heavy metal ions (such as cadmium, copper, arsenic, lead and mercury) are present as minerals in phosphate rocks and are dissolved into phosphoric acid. These metal impurities are considered unacceptable above a certain level (depending on the application of phosphoric acid) due to their toxicity. Therefore, the metal impurities must be completely removed or their levels must be significantly reduced.

[0005] For example, cadmium (Cd) is toxic and may cause multiple problems for human health. Studies have shown that for the general population who do not smoke, the main exposure to Cd is through the intake of contaminated food. Phosphate fertilizers have been identified as an important source of Cd introduced into the soil, and Cd can be easily absorbed by agricultural plants and accumulated in the food chain ("Cadmium in phosphate fertilizers; ecological and economical aspects", CHEMIK [Chemist] 2014, 68, 10, 837-842).

[0006] Cd in phosphate fertilizer comes from phosphoric acid, which is the main raw material for producing phosphate fertilizer. In fact, most of phosphoric acid production is used to produce fertilizer. Cd in phosphoric acid further originates from the ore carrying phosphate. Therefore, Cd can be removed from phosphate ore or from phosphoric acid stream, wherein the latter is the focus of research in the past decades. Several classes of technologies for removing Cd from acid streams have been developed, and these technologies include co-crystallization with anhydrite, precipitation with sulfide ions and organic sulfur compounds, removal by solvent extraction, removal by ion exchange, removal by adsorbent and separation by membrane technology (" Progress in the development of decadmiation of phosphorus fertilizers [development progress of cadmium removal technology for phosphorus fertilizers] " Fertilizer Industry Federation of Australia, Inc. (Australian Fertilizer Industry Federation Co., Ltd.), Conference " Fertilizers in Focus " [Conference " Focus on Fertilizer "], 2001, 101-106).

[0007] U.S. Pat. No. 4,378,340 (1983) discloses a method for removing heavy metals, especially cadmium, from wet-process phosphoric acid by partially neutralizing the acid with an alkali followed by precipitation with a sulfide compound. U.S. Pat. No. 5,431,895 (1995) also discloses the removal of lead and cadmium from phosphoric acid using an alkali solution and an aqueous sulfide solution simultaneously under adequate mixing.

[0008] U.S. Pat. No. 4,986,970 (1991) discloses the use of metal salts of dithiocarbonic acid-O-esters to precipitate heavy metals, especially cadmium, from partially neutralized (pH 1.4-2) and pre-cooled (5°C-40°C) phosphoric acid. The complex can then be separated from the acid using methods such as flotation or filtration.

[0009] U.S. Patent No. 4,452,768 (1984), U.S. Patent No. 4,479,924 (1984), U.S. Patent No. 4,713,229 (1987) and European Patent No. EP 0333489 B1 (1989) disclose methods for separating heavy metals, especially cadmium, mercury and lead, from phosphoric acid using diorganophosphorodithioates and adsorbents, diorganophosphorodithioates and adsorbents, diorganophosphorodithioates and adsorbents and reducing agents, and thioorganophosphine reagents and reducing agents, respectively. U.S. Patent Publication No. 2004 / 0179984 also discloses a method for removing heavy metals from wet-process phosphoric acid by adding a mixed reagent of a diorganophosphinodithioate (or its alkali metal or ammonium salt), a first phosphorodithioate having an alkyl or alkaryl or aralkyl moiety (or its alkali metal salt or ammonium salt), and optionally a second diarylphosphorodithioate (or its alkali metal or ammonium salt).

[0010] Several scientific publications (“Cadmium(II)extraction from phosphoric media by bis(2,4,4-trimethylpentyl)thiophosphinic acid(Cyanex 302),” Fluid Phase Equilibria 145 (1998) 301-310), and “Extraction of cadmium from phosphoric acid by trioctylphosphine oxide / kerosene solvent using factorial design,” Periodica Polytechnic Chemical Engineering 55 / 2 (2011) 45–48) discusses the removal of cadmium from phosphoric acid based on solvent extraction using reagents such as bis(2,4,4-trimethylpentyl)phosphinic acid / kerosene and trioctylphosphine oxide / kerosene, respectively. Summary of the invention

[0011] Although the various reagents and methods discussed above may have some advantages and applicability in phosphoric acid production, high investment costs, high processing costs and low efficacy have limited their widespread acceptance on a plant scale (see "Cadmium in phosphate fertilizers; ecological and economical aspects", CHEMIK [Chemist] 2014, 68, 10, 837-842). Heavy metal contamination of food, especially cadmium from the use of phosphoric acid in fertilizer production, remains a public health concern. The economic impact of the heavy metal problem is enormous, and the industry needs more efficient and economical technologies than currently exist. In addition, there has recently been a regulatory push to further limit Cd levels in phosphate fertilizers (see European Commission Fact Sheet. “Circular economy: New Regulation to boost the use of organic and waste-based fertilisers.” EUMEMO-16-826, March 17, 2016, europa.eu / rapid / press-release_MEMO-16-826_en.htm).

[0012] Therefore, the compositions and methods that can be used for removing heavy metals from the phosphoric acid in the production process need further improvement at present. Because many factors (for example, ore type, temperature, stirring, reactor design, acid chemistry, foreign ions, organic matter and the viscosity of phosphoric acid medium) may all affect the performance of reagent, therefore development can be used for removing the high-efficiency reagent of heavy metal from phosphoric acid is a huge challenge. The successful reagent for removing the heavy metal in the industrial process stream (such as wet-process phosphoric acid) will be a useful progress in this area and can be accepted rapidly in industry.

[0013] In view of the above problems and challenges in the art, the inventors have described their unexpected discovery in different embodiments herein: certain heavy metal chelators containing multiple sulfur groups are effective in reagents that can be used to remove heavy metal ions from aqueous solutions containing phosphoric acid. In different embodiments, the heavy metal chelator can include 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof. Therefore, the method for removing heavy metal ions according to different embodiments of the present invention as described herein is suitable for use with different stages of wet phosphoric acid production.

[0014] Thus, in one aspect, provided herein is a method for removing heavy metal ions from a solution containing phosphoric acid by adding an effective amount of a reagent comprising a heavy metal chelator containing multiple sulfur groups to the solution to form a heavy metal precipitate and / or complex and separating the heavy metal precipitate and / or complex from the solution.

[0015] In the same or additional embodiments, the method can further include adding an effective amount of an organothiophosphorus compound to the solution containing phosphoric acid.

[0016] The present invention does not list all necessary features, and therefore, a sub-combination of these features or elements may also constitute an invention. Therefore, these and other objects, features and advantages of the present invention will become clear from the following detailed description of different embodiments of the present invention carried out in conjunction with the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a graph showing the results of Examples 1A and 1J-1 to 1J-5, which shows the percentage of As removed from plant weak phosphoric acid at dosages of heavy metal chelating agent 2,3-dimercapto-1-propanol ("DTG") at levels of 0 to 4 kg / TP2O5 at about 75°C;

[0018] Figure 2 is a graph showing the results of Examples 1C-1, 1K-1, 1K-3, 1K-4 and 1K-5, which shows the percentage of Cd removed from plant weak phosphoric acid at about 75°C with dosages of heavy metal chelator DTG at levels of 0 to 4 kg / T P2O5 and then sodium diisobutyldithiophosphinate ("Na-DTPi") at a level of 0.5 kg / T P2O5;

[0019] Figure 3 is a graph showing the results of Examples 2A and 2B-1 to 2B-4, which shows the percentage of heavy metals removed from a digested slurry of phosphoric acid at dosages of a heavy metal chelator 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt ("DMTD-2K") at levels of 0 to 9 kg / TP2O5 at about 80°C;

[0020] Figure 4 is a graph showing the results of Examples 3A and 3B-1 to 3B-4, which shows the percentage of heavy metals removed from concentrated plant phosphoric acid at dosages of heavy metal chelator DMTD-2K at levels of 0 to 4 kg / TP2O5 at about 70°C;

[0021] Figure 5is a graph showing the results of Examples 3E-1, 3C-2, and 3F-1, which illustrates the percentage of Cd removed from concentrated plant phosphoric acid with different dosages of heavy metal chelators DTG and Na-DTPi at about 70°C; and

[0022] Figure 6 is a graph showing the results of Examples 4A and 4B-1 to 4B-4, which shows the percentage of heavy metals removed from concentrated plant phosphoric acid at about 70°C at dosages of heavy metal chelating agents ranging from 0 to 10 kg / TP2O5 levels, the heavy metal chelating agent comprising polyamine / alkyl glycidyl ether / (glycidyloxypropyl)trimethoxysilane / (mercaptopropyl)trimethoxysilane ("P1"). DETAILED DESCRIPTION

[0023] The present invention relates generally to purification of solutions in industrial process streams. More specifically, the inventors describe herein for the first time a method for removing and / or recovering heavy metal ions from a solution containing phosphoric acid by adding to the solution an effective amount of a reagent comprising a heavy metal chelator having a plurality of sulfur groups.

[0024] The compositions and methods described herein provide improved and / or unexpected advantages when compared to prior art methods and compositions.

[0025] As used throughout the disclosure of the present invention, the following terms are provided to help the reader. Unless otherwise defined, all technical terms, notes and other scientific or industrial terms or technical terms used herein are intended to have the meaning commonly understood by those skilled in the art of chemistry and / or phosphoric acid production. In some cases, for the sake of clarity and / or for convenient reference, the terms with commonly understood meanings are defined herein, and unless otherwise indicated, such definitions are included herein and are not necessarily interpreted as representing considerable differences compared to the definition of terms commonly understood in the art. Unless the context clearly indicates otherwise, as used herein and in the appended claims, the singular includes plural indicators. Throughout this specification, the terms retain their definitions.

[0026] As used herein with respect to the present invention, the term "heavy metal" or "metal" shall refer to a metal having a mass greater than 5 g / cm 3 and those elements having a density of 0 and an oxidation state higher than 0 (i.e., heavy metal ions). Such heavy metal ions include, for example, one or more of copper (Cu), cadmium (Cd), nickel (Ni), mercury (Hg), zinc (Zn), arsenic (As), manganese (Mn), and lead (Pb). In any or all embodiments, cadmium ions and arsenic ions can be removed from the solution containing phosphoric acid.

[0027] As used herein, the term "heavy metal chelator" generally refers to any such compound that interacts, reacts or combines with heavy metal ions to form a "heavy metal complex". Heavy metal chelators as described herein contain multiple sulfur groups. More preferred heavy metal chelators according to the present invention are described herein. The heavy metal complexes can be solid, waxy or oily in the phosphoric acid solution. They can precipitate, float or suspend in the phosphoric acid solution.

[0028] Those skilled in the art will understand that reference to "phosphoric acid solution" or "solution containing phosphoric acid" in the context of the present invention includes any acidic aqueous solution or mixture containing crude phosphoric acid, digestion slurry, filtered acid and / or concentrated acid.

[0029] By "effective amount" is meant the dosage of any agent disclosed herein on an active basis required to provide the desired performance in the phosphoric acid system or circuit being treated (e.g., formation of heavy metal complexes) when compared to an untreated control system or a system using the agent product of the prior art.

[0030] The term "hydrocarbyl" is a general term for aliphatic, alicyclic and aromatic groups with a full carbon skeleton and composed of carbon and hydrogen atoms. In some cases, as defined herein, one or more carbon atoms constituting the carbon skeleton may be replaced or interrupted by a specific atom or group of atoms such as by one or more heteroatoms in N, O and / or S. The example of a hydrocarbyl includes an alkyl, a cycloalkyl, a cycloalkenyl, a carbocyclic aryl, an alkenyl, an alkynyl, an alkylcycloalkyl, a cycloalkylalkyl, a cycloalkenylalkyl and a carbocyclic aralkyl, an aralkenyl and an aralkynyl. The description or discussion of such hydrocarbyl includes their replacement or unsubstituted form. This concept is sometimes described as "alternatively substituted". When substituted, it may be replaced by one or more substituents as defined elsewhere herein. Unless otherwise indicated by the context, the examples and preferences represented below are also applicable to each of the hydrocarbyl substituents or hydrocarbyl-containing substituents indicated in the various definitions of the substituents of the compounds with the formula described herein.

[0031] Preferred non-aromatic hydrocarbon groups are saturated groups, such as alkyl and cycloalkyl groups. Typically, and by way of example, these hydrocarbon groups may have up to fifty carbon atoms, unless the context requires otherwise. Hydrocarbyl groups having 1 to 30 carbon atoms are preferred. Within the subset of hydrocarbon groups having 1 to 30 carbon atoms, specific examples are C 1-20 Hydrocarbon, such as C 1-12 Hydrocarbyl (e.g., C 1-6 Hydrocarbon or C 1-4 A hydrocarbon group), a specific example is from C1 to C 30 Any individual value or combination of values ​​selected in the hydrocarbon group.

[0032] As used herein, the term "alkyl" is intended to include straight chain, branched chain or cyclic hydrocarbon structures and combinations thereof. Preferred alkyl groups are C 30 or below C 30 The lower alkyl group refers to an alkyl group having 1 to 8 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl and tert-butyl, pentyl, hexyl, octyl, etc. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups having 3 to 30 carbon atoms, preferably 3 to 8 carbon atoms, and polycyclic hydrocarbons having 7 to 10 carbon atoms.

[0033] As used herein, the term "aryl" refers to a cyclic (monocyclic or polycyclic) aromatic hydrocarbon containing no heteroatoms in the ring portion. In any or all embodiments, the aryl group contains 6 to 14 carbons in the ring portion of the group. Thus, aryl includes, but is not limited to, phenyl, azulenyl, heptadenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylene, pyrenyl, naphthyl, The aryl groups are substituted with 2-, 3-, 4-, 5-, or 6-substituted phenyl or 2-8 substituted naphthyl, which may be substituted with carbon or non-carbon groups, as known to those skilled in the art. 12 The aryl group is preferred.

[0034] As used herein, the term "aralkyl" is a broad term and is used in its ordinary sense, including but not limited to, an alkyl group in which at least one alkyl hydrogen atom is replaced by an aryl moiety, such as benzyl, -CH2 (1- or 2-naphthyl), -(CH2)2 phenyl, -(CH2)3 phenyl, -CH(phenyl)2, etc. Particularly preferred are C 7-20 Aralkyl. In any or all embodiments, one or both of the alkyl and aryl groups may be optionally substituted with one or more substituents as described elsewhere herein.

[0035] Substituted hydrocarbon groups such as alkyl, aryl, aralkyl, cycloalkyl, alkoxy, and the like refer to specific substituents in which up to three H atoms in each residue are replaced by alkyl, halogen, haloalkyl, hydroxy, alkoxy, carboxyl, alkoxycarbonyl (also known as alkoxycarbonyl), carboxamido (also known as alkylaminocarbonyl), cyano, carbonyl, nitro, amino, alkylamino, dialkylamino, sulfhydryl, alkylthio, sulfoxide, sulfone, acylamino, amidino, phenyl, benzyl, halobenzyl, heteroaryl, phenoxy, benzyloxy, heteroaryloxy, benzoyl, halobenzoyl, or lower alkylhydroxy. In some cases, as defined herein, one or more carbon atoms constituting the carbon backbone may be replaced or interrupted by specific atoms or groups of atoms such as by one or more heteroatoms in N, O, and / or S.

[0036] As used herein, and unless otherwise stated, the term "about" or "approximately" means an acceptable error for a specific value as determined by one of ordinary skill in the art, which may depend in part on how to measure or determine the value. In certain embodiments, the term "about" or "approximately" means within 1, 2, 3, or 4 standard deviations. In any or all embodiments, the term "about" or "approximately" means within 50%, 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or 0.05% of a given value or range.

[0037] As used herein, the term "plurality" includes an amount of two or more of the thing modified or described by the term. For example, a heavy metal chelator with multiple sulfur groups refers to a compound that acts as a chelator for heavy metals and has two or more sulfur groups. As used herein, the term "sulfur groups" may refer to a thiol, a thiolate, or a sulfur atom present in the ring system of a compound as a heteroatom.

[0038] As used herein, the terms "comprised of" or "comprising / comprises" include embodiments "consisting essentially of" or "consisting of" the listed elements, and the terms "including" or "having" in the context of describing the invention shall be equivalent to "comprising."

[0039] Those skilled in the art will appreciate that, although preferred embodiments are discussed in more detail below, multiple embodiments of the reagent systems and methods described herein are also considered within the scope of the invention. Therefore, it should be noted that, unless otherwise stated, any feature described with respect to one aspect or an embodiment of the invention is interchangeable and / or combinable with another aspect or embodiment of the invention.

[0040] In addition, for the purpose of describing the present invention, when an element, component, or feature is said to be included in and / or selected from a list of multiple elements, components, or features, those skilled in the art will understand that in the relevant embodiments of the present invention described herein, the element, component, or feature may also be any one of these individual listed elements, components, or features, or may also be selected from a group consisting of any two or more of these explicitly listed elements, components, or features. In addition, any element, component, or feature listed in such a list may also be omitted from such a list.

[0041] Those skilled in the art will further understand that any recitation of numerical ranges by endpoints herein includes all numbers (including fractions) contained in the recited ranges, as well as the endpoints and equivalents of the ranges, whether or not explicitly recited. The term "et seq." is sometimes used to indicate numbers contained in a recited range without explicitly reciting all numbers, and should be considered a complete disclosure of all numbers in the range. Disclosure of a narrower range or more specific group in addition to a broader range or larger group is not a disclaimer of the broader range or larger group.

[0042] In various embodiments, it was unexpectedly found that certain heavy metal chelators containing multiple sulfur groups are effective in reagents that can be used to remove heavy metal ions from aqueous solutions containing phosphoric acid. In some embodiments, 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof can be used in reagents that can be used to remove heavy metal ions from aqueous solutions containing phosphoric acid.

[0043] In some embodiments, heavy metal chelators having multiple sulfur groups can be used with surfactants. In some embodiments, surfactants can be added together with 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof. The surfactant compound can be selected from the group consisting of sulfosuccinates, aryl sulfonates, alkylaryl sulfonates, diphenyl sulfonates, olefin sulfonates, sulfonates of ethoxylated alcohols, petroleum sulfonates, sulfosuccinamates, alkoxylated surfactants, ester / amide surfactants, EO / PO block copolymers, and mixtures thereof. In a preferred embodiment, the surfactant can be a sulfosuccinate. In the same or alternative embodiments, the sulfosuccinate can be dioctyl sodium sulfosuccinate. Suitable dioctyl sodium sulfosuccinate compounds include, but are not limited to, those available from Solvay SA. OT-70 and 70B. Suitable alkoxylated surfactants may include, but are not limited to, polyethylene glycol sorbitan monooleate (e.g., available from Croda 80) and polyethylene glycol sorbitan hexaoleate (available from Croda Corporation G1086).

[0044] In any or all embodiments of the present invention, 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof can be added to the crude acid or digestion slurry before gypsum filtration, or added to the filtered acid or concentrated acid to complex the heavy metals. Thereafter, the heavy metal complexes can be separated from the acid or slurry. In any or all embodiments, the separation method includes, but is not limited to, filtration, centrifugation, sedimentation, creaming, flocculation, adsorption, and / or flotation.

[0045] In any or all embodiments of the present invention, 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof can all be added to a solution containing phosphoric acid in one stage or added in several stages. In the same or other embodiments, 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof can be added as a blend, or added separately in any order (such as together simultaneously or sequentially). The processing time in different embodiments can be a few seconds (that is, 5 to 10 seconds) to 24 hours. In those cases where the reagent complexes heavy metals very quickly, the preferred processing time is about 5 seconds to 3 hours. Most typically, the processing time is 10 seconds to 60 seconds or 120 seconds.

[0046] The dosage of the reagent for complexing heavy metals and the removal efficiency for different heavy metals will depend on the amount of heavy metal impurities present in the ore and / or the solution containing phosphoric acid. Generally, the greater the number of heavy metals present and the higher their concentration, the greater the total dosage of the reagent. Those skilled in the art will be able to easily determine and establish the optimum dosage of required 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof using only routine experiments. Typically, based on the type of heavy metal ions to be removed, the dosage can be in the range of 0.01 to 50 kg (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, and thereafter to 0.10, 0.15, 0.20, 0.25, 0.30, and thereafter to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and thereafter to 10, 15, 20, 25, 30, 35, 40, 45, 50 kg) of reagent per ton of P2O5 in phosphoric acid solution. Most typically, the dosage can be 0.1 kg to 10 kg (e.g., 0.10, 0.15, 0.20, 0.25, 0.30, and thereafter to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, and 10 kg) of reagent / ton of P2O5. One of ordinary skill in the art will appreciate that any of the listed dosages (except the lowest dosage point) can also be recited as "less than" a specific dosage, such as less than 50 kg; or any of the listed dosages (except the highest dosage point) can also be recited as "greater than" a specific dosage, such as greater than 0.10 kg.

[0047] In embodiments where a surfactant is added, the ratio of heavy metal chelating agents containing multiple sulfur groups to surfactant is, in some embodiments, 1 to 2 to 100 to 1. In some embodiments where a surfactant is added, the ratio of heavy metal chelating agents containing multiple sulfur groups to surfactant is 2:1 to 50:1.

[0048] In any or all embodiments, the solution containing phosphoric acid has a P2O5 concentration of 1 wt.% to 70 wt.%. In some embodiments, the solution containing phosphoric acid has a P2O5 concentration of 20 wt.% to 70 wt.%. Specific concentrations of P2O5 contemplated for use in the present invention include 24 wt.%, 25 wt.%, 26 wt.%, 28 wt.%, 30 wt.%, 42 wt.%, 48 wt.%, 52 wt.%, 56 wt.%, 60 wt.%, and 69 wt.%.

[0049] The compositions and methods as described herein of the present invention can be used over a wide temperature range. In any or all embodiments, for example, the methods according to the present invention can be carried out at a temperature of 0° C. to 120° C. Preferably, the temperature is in the range of 10° C. to 80° C.

[0050] In any or all embodiments according to the present invention, the method may further include adding an effective amount of a reducing agent and / or an adsorbent to a solution containing phosphoric acid. Such agents are known to be used in the art. In some cases, one or both of these agents can enhance the activity of a reagent containing a heavy metal chelating agent containing multiple sulfide groups in a reagent that can be used to remove heavy metal ions from an aqueous solution containing phosphoric acid as described herein. In certain embodiments, one or both of these agents can enhance the activity of a reagent including 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures. In the same or alternative embodiments, a reducing agent and / or an adsorbent can be added to a solution containing phosphoric acid in one stage or in several stages. In the same or other embodiments, a reducing agent and / or an adsorbent can be added as a blend with a reagent containing a heavy metal chelating agent containing multiple sulfide groups in a reagent that can be used to remove heavy metal ions from an aqueous solution containing phosphoric acid as described herein. In some embodiments, the reducing agent and / or adsorbent may be added as a blend with the reagents comprising 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof, or added separately from 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof in any order (e.g., together simultaneously or sequentially). Although the nature and amount of the reducing agent and / or adsorbent used depends on the specific composition and purity specifications of the phosphoric acid in the solution, those skilled in the art will be able to determine the optimal dosage range using only routine experimentation.

[0051] Reducing agents available in any or all methods according to the present invention include, but are not limited to, iron powder, zinc, red phosphorus, iron (II) sulfate, sodium hypophosphite, hydrazine, hydroxymethane sulfonate, and mixtures thereof. In a preferred embodiment, the reducing agent comprises sodium hypophosphite. In any or all embodiments, based on the type and amount of the oxidant in the phosphoric acid solution, the reducing agent is used in an amount of 0.01 kg to 50 kg reagent / ton of P2O5, which can be easily determined by those skilled in the art using only conventional methods. In a preferred embodiment, the amount of the reducing agent is 0.1 kg to 5 kg reagent / ton of P2O5 in the phosphoric acid solution.

[0052] Adsorbents available in any or all embodiments according to the present invention include all those substances capable of adsorbing a sufficiently large amount of heavy metal ions and chelate products of 2,5-dimercapto-1,3,4-thiadiazole, 2,3-dimercapto-1-propanol, sulfur-containing polymers, derivatives thereof, and mixtures thereof on their surfaces. Such compounds include, but are not limited to, activated carbon / carbon, carbon black, ground lignite, adsorbents containing silicates (e.g., synthetic silicic acid, zeolite, calcium silicate, bentonite, perlite, diatomaceous earth, and fluorosilicates), calcium sulfate (including gypsum, hemihydrate, and anhydride), and mixtures thereof. In any or all embodiments, the adsorbent is present in an amount of 0.05wt.% to 50wt.%, and preferably 0.1wt.% to 5wt.%, based on the amount of phosphoric acid in the solution.

[0053] Although different embodiments may be described in singular form herein, those skilled in the art will recognize that any embodiment described herein can be combined as a whole. The present invention includes at least the following embodiments:

[0054] In certain embodiments, disclosed herein is a method for removing heavy metal ions from a phosphoric acid mixture, the method comprising adding an effective amount of a reagent comprising a heavy metal chelator containing multiple sulfur groups to the phosphoric acid mixture. In certain embodiments, the phosphoric acid mixture is a solution. In certain embodiments, the phosphoric acid mixture is a slurry. In certain embodiments, the heavy metal ion can be selected from the group consisting of: cadmium, copper, arsenic, mercury, lead and a mixture of any of the foregoing. In certain embodiments, the heavy metal ion is cadmium. In certain embodiments, the heavy metal ion is arsenic.

[0055] In some embodiments, the heavy metal chelator having multiple sulfur groups is selected from compounds according to Formula I(A) or I(B):

[0056]

[0057] and their salts,

[0058] wherein each M and M' in formula I(A) or I(B) is independently selected from H, Na, K, Li, NH4, NR'4, wherein each R' is independently selected from C1-C4 alkyl; and R in formula I(B) is selected from C1-C 18 Alkyl, C6-C 12 Aryl, or C7-C 18 In some embodiments, the compound according to formula I(A) or I(B) is selected from the group consisting of 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt, 5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt, and mixtures thereof.

[0059] In some embodiments, the heavy metal chelator having multiple sulfur groups is selected from the group consisting of: 2,3-dimercapto-1-propanol, 1,2-ethanedithiol, 1,3-propanedithiol, benzene-1,2-dithiol, 1,3-dimercapto-2-propanol, 1,2,3-trimercaptopropane, and mixtures thereof. In some embodiments, the heavy metal chelator is 2,3-dimercapto-1-propanol.

[0060] In some embodiments, the heavy metal chelator having multiple sulfur groups is a polymer according to the following

[0061]

[0062] Wherein each M is independently selected from H, Na, K, Li, NH4 and NR'4, each R' is independently selected from C1-C4 alkyl, and n is the number of repeating units of the polymer backbone, and is an integer from 2 to 1000. In some embodiments, n is from 2 to 100. In some embodiments, the polymer backbone comprises a backbone selected from the group consisting of polyamines, polysaccharides, polyvinyl pyrrolidone, polyglutamic acid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin, and mixtures of any of the foregoing, and copolymers of any of the foregoing.

[0063] In certain embodiments, disclosed herein is a method for removing heavy metal ions from a phosphoric acid mixture, the method comprising adding an effective amount of a reagent comprising a heavy metal chelating agent containing multiple sulfur groups as substituents to the phosphoric acid mixture, wherein the reagent further comprises an effective amount of an organic thiophosphorus compound. In certain embodiments, the organic thiophosphorus compound is selected from the group consisting of: organic dithiophosphinic acid, organic dithiophosphonic acid, organic dithiophosphoric acid, organic monothiophosphinic acid, organic monothiophosphoric acid, its corresponding salt in the form of sodium, ammonium or potassium, and mixtures thereof. In certain embodiments, the organic thiophosphorus compound comprises an organic dithiophosphinic acid or its corresponding salt, or an organic dithiophosphoric acid or its corresponding salt. In certain embodiments, the organic dithiophosphinic acid is a dialkyl dithiophosphinic acid, and the organic dithiophosphoric acid is a dialkyl dithiophosphoric acid.

[0064] In some embodiments of the methods for removing heavy metal ions from a phosphoric acid mixture disclosed herein in any and all embodiments, the phosphoric acid mixture further comprises an adsorbent. In some embodiments, the adsorbent is solid calcium sulfate particles.

[0065] In some embodiments of the methods disclosed herein for removing heavy metal ions from a phosphoric acid mixture, the method is performed at a temperature of 0° C. to 120° C. In some embodiments, the method is performed at a temperature of about 10° C. to about 80° C.

[0066] In some embodiments of the method for removing heavy metal ions from a phosphoric acid mixture disclosed herein, the phosphoric acid mixture has a concentration of 3 wt % to 70 wt % P2O5 based on the total weight of the mixture. In some embodiments, the phosphoric acid mixture has a concentration of 20 wt % to 60 wt % P2O5.

[0067] In some embodiments of the methods disclosed herein for removing heavy metal ions from a phosphoric acid mixture, a reagent comprising a heavy metal chelator containing multiple sulfur groups is added to the phosphoric acid mixture at a dosage of 0.1 kg / ton and 10 kg / ton P2O5.

[0068] In some embodiments of the method for removing heavy metal ions from a phosphoric acid mixture disclosed herein, the method further comprises the step of separating the phosphoric acid mixture. In some embodiments, the separation step further comprises flocculation. In some embodiments of the method for removing heavy metal ions from a phosphoric acid mixture disclosed herein, the separation step further comprises filtration.

[0069] In some embodiments of the methods disclosed herein for removing heavy metal ions from a phosphoric acid mixture, the separating step further comprises skimming.

[0070] In certain embodiments, disclosed herein is a reagent for removing heavy metal ions from a phosphoric acid mixture, the reagent comprising (a) a heavy metal chelating agent containing multiple sulfur groups and (b) an organic thiophosphorus compound, the organic thiophosphorus compound comprising an organic dithiophosphinic acid or its corresponding salt, or an organic dithiophosphoric acid or its corresponding salt.

[0071] In some embodiments of the reagent for removing heavy metal ions from a phosphoric acid mixture, the heavy metal chelator having multiple sulfur groups is selected from the group consisting of: (i) 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt, and 5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt; (ii) 2,3-dimercapto-1-propanol, 1,2-ethanedithiol, 1,3-propanedithiol, benzene-1,2-dithiol, 1,3-dimercapto-2-propanol, and 1,2,3-trimercaptopropane.

[0072] In some embodiments of the reagent for removing heavy metal ions from a phosphoric acid mixture, the heavy metal chelator having multiple sulfur groups is a polymer as defined by:

[0073]

[0074] Wherein each M is independently selected from H, Na, K, Li, NH4 and NR'4, each R' is independently selected from C1-C4 alkyl, and n is the number of repeating units of the polymer backbone and is an integer from 2 to 1000. In some embodiments, n is from 2 to 100. In some embodiments, the polymer comprises a backbone selected from the group consisting of polyamines, polysaccharides, polyvinyl pyrrolidone, polyglutamic acid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin, and mixtures of any of the foregoing, and copolymers of any of the foregoing.

[0075] In some embodiments, the agent comprises a mixture of any of the foregoing heavy metal chelators containing multiple sulfur groups as substituents.

[0076] In some embodiments of the agent for removing heavy metal ions from a phosphoric acid mixture, the heavy metal chelator is 2,3-dimercapto-1-propanol.

[0077] In certain embodiments, disclosed herein is a reagent for removing heavy metal ions from a phosphoric acid mixture, the reagent comprising

[0078] (a) a heavy metal chelating agent containing multiple sulfur groups, the heavy metal chelating agent comprising a member selected from the group consisting of:

[0079] (i) 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt, and 5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt;

[0080] (ii) 2,3-dimercapto-1-propanol, 1,2-ethanedithiol, 1,3-propanedithiol, benzene-1,2-dithiol, 1,3-dimercapto-2-propanol, and 1,2,3-trimercaptopropane;

[0081] (iii) The polymer as defined by the heavy metal chelator having multiple sulfur groups is a polymer as defined by

[0082]

[0083] wherein each M is independently selected from H, Na, K, Li, NH4 and NR'4, each R' is independently selected from C1-C4 alkyl, and n is the number of repeating units of the polymer backbone and is an integer from 2 to 1000, and wherein in some embodiments, n is from 2 to 100, and in some embodiments, the polymer comprises a backbone selected from the group consisting of: polyamines, polysaccharides, polyvinyl pyrrolidone, polyglutamic acid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin, and mixtures of any of the foregoing, and copolymers of any of the foregoing; and

[0084] (iv) mixtures of any of the foregoing, and

[0085] (b) an organic thiophosphorus compound, which includes an organic dithiophosphinic acid or a corresponding salt thereof, or an organic dithiophosphoric acid or a corresponding salt thereof.

[0086] In some embodiments, the heavy metal chelator is 2,3-dimercapto-1-propanol.

[0087] The following examples are provided to help those skilled in the art further understand certain embodiments of the present invention. These examples are intended for illustrative purposes and should not be construed as limiting the scope of the present invention.

[0088] The heavy metal removal performance of certain heavy metal chelators containing multiple sulfur groups (including 2,5-dimercapto-1,3,4-thiadiazole or its derivatives, 2,3-dimercapto-1-propanol or its derivatives, or sulfur-containing polymers or their derivatives, and mixtures thereof) for removing heavy metal ions from aqueous solutions containing phosphoric acid was evaluated using phosphoric acid and phosphoric acid slurry.

[0089] Phosphoric acid with different P2O5 levels was obtained from the factory. Phosphoric acid slurry was produced using a laboratory scale digestion process. To separate the heavy metal precipitate from the acid, a syringe filter or vacuum filtration was used. Afterwards, the filtrate acid was analyzed using ICP (Inductively Coupled Plasma) to determine the levels of various heavy metal elements. The general procedure used for the tests and experimental examples is outlined below.

[0090] DMTD-2K (2,5-dimercapto-1,3,4-thiadiazole dipotassium salt), DMTD (2,5-dimercapto-1,3,4-thiadiazole), bismuthiolate II (5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt), 2-aminothiophenol, and trimercapto-s-triazine trisodium salt were purchased from Sigma Aldrich. DTG (2,3-dimercapto-1-propanol) was purchased from Sigma Aldrich. Na-DTPi (sodium diisobutyldithiophosphinate) and Na-DTP (sodium diisobutyldithiophosphate) were obtained from Solvay.

[0091] 2-Aminothiophenol is metered directly into the acid without dilution. DTG is metered into the phosphoric acid / slurry as is. Solutions of the other reagents are first prepared and then metered into the phosphoric acid / slurry. For example, a 10 wt% solution of DMTD-2K in water is prepared and then metered into the acid. A 10 wt% solution of bismuthiolate II in water is prepared and then metered into the acid. A 10 wt% solution of DMTD in alkaline sodium hydroxide solution is prepared and then metered into the acid. A 10 wt% solution of trithio-s-triazine trisodium salt in water is prepared and then metered into the acid. A 5 wt% solution of sodium diisobutyl dithiophosphinate in water is prepared and then metered into the acid. A 5 wt% solution of sodium diisobutyl dithiophosphate in water is prepared and then metered into the acid. For Examples 1F-3, 1P-3, and 3D-4, a solution of 6% DMTD-2K and 2% Na-DTPi is prepared and then metered into the acid. The dosages shown in the table are calculated based on the amount of dry reagent relative to the amount of P2O5 in the acid / slurry.

[0092] Example 1 - For use at elevated temperatures (75 ℃ and 50 ℃ ) to remove heavy gold from weak phosphoric acid (about 30% P2O5) in factories Method of genus

[0093] 35g of plant phosphoric acid (about 30% P2O5, collected from the clarifier after filtration) from plant #1 and #2 was transferred to a glass jar with a magnetic stirring bar. The acid was heated to 80°C in a water bath. An effective amount of the reagent of interest (as listed in Table 1) was metered into the acid under stirring at 600rpm. For Examples 1L-3 and 1R-3, two reagents were metered simultaneously with two separate pipettes. After stirring for 1 minute and settling for another minute, the acid was transferred to a syringe and filtered with a 0.2μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis. The results are shown in Table 1.

[0094] When two reagents of interest are metered sequentially (as in Examples 1D-1, 1D-2, 1F-1, 1F-2, 1H, 1K-1 to 1K-5, 1L-1, 1L-2, 1P-1, 1P-2, 1R-1, and 1R-2), the first reagent is metered into the acid and stirred for 1 minute at 600 rpm, and then the second reagent is metered into the acid and stirred for 1 minute at 600 rpm. Afterwards, the acid is allowed to settle for another minute, and then transferred to a syringe and filtered with a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate is collected and then subjected to ICP elemental analysis.

[0095] Table 1.

[0096]

[0097]

[0098] Results from Table 1 show the performance of various reagents for removing heavy metals from different factory phosphoric acid at different temperatures. For example, DMTD-2K compound can remove up to 75.0% and 93.7% of arsenic and cadmium (Example 1N) respectively when 3kg / t P2O5 is metered into factory phosphoric acid #2 (30% P2O5) at 50°C. Similarly, DMTD and bismuth mercaptan II can also remove significant amounts of arsenic and cadmium from factory phosphoric acid. In the case of using DTG compound, a reduction of greater than 90% of arsenic is observed at a dosage of 2kg / t P2O5 (Example 1J-4). When factory phosphoric acid is treated with DMTD-2K and Na-DTPi in different metering orders, a reduction of greater than 90% of arsenic and cadmium is also observed (Example 1P-1, 1P-2, 1P-3). When factory phosphoric acid is treated with DTG and Na-DTPi, similar results are observed (Example 1R-1, 1R-2, 1R-3).

[0099] Example 2 - For use at about 80 ℃ The following method is used to remove heavy metals from digested phosphoric acid slurry (about 30% P2O5). The calcium sulfate solid particles in the

[0100] Phosphoric acid slurry was produced via laboratory scale digestion of phosphate ore using a 500 ml jacketed reactor connected to a hot bath (for maintaining the temperature at approximately 80°C). The reactor was also connected to a cooling condenser to avoid evaporation of water during digestion. Phosphoric acid and sulfuric acid were added continuously to the reactor by two peristaltic pumps (MasterFlex L / S). Phosphate rock / ore powder was added manually approximately continuously at the corresponding rates. The feed rate of sulfuric acid (52.4%) was 3.67 g / min; the feed rate of phosphoric acid (37.1%) was 7.67 g / min; and the phosphate ore powder was 2 g / min. The feed time was approximately 30 minutes. After feeding the acid and ore, digestion was continued for another 2 to 3 hours to completely digest the phosphate ore. When the reagents of interest and other additives (such as defoamer reagents) were used, an effective amount of the reagents was first mixed with the above phosphoric acid and then continuously pumped into the reactor. During the entire process, the digestion slurry was stirred with an overhead stirrer (Glas-Col Precision Speed ​​Controlled Stirrer) and a propeller impeller set at 300 rpm.

[0101] 50 g of the digested phosphoric acid slurry (about 30% solid level, about 30% P2O5) was transferred to a glass jar with a magnetic stirring bar. The slurry contained a large amount (about 30 wt%) of solid particles, most of which were calcium sulfate produced during the digestion of the phosphate ore. An effective amount (as listed in Table 2) of the reagent of interest for removing heavy metal ions was metered into the slurry under stirring at 600 rpm. After stirring for 1 minute, the slurry was transferred to a vacuum filtration funnel (on a filtration device with a 45 μm polypropylene mesh filter (Millipore PP4504700)) and vacuum filtration was started in about 15 seconds. The filtrate was collected and then subjected to ICP elemental analysis. The results are shown in Table 2 and plotted in Figure 3 middle.

[0102] When two kinds of reagents of interest were added sequentially (as in Examples 2D-1 and 2D-2), the first reagent was metered into the slurry and stirred for 1 minute at 600 rpm, and then the second reagent was metered into the acid and stirred for 1 minute at 600 rpm. Afterwards, the slurry was transferred to a vacuum filtration funnel (on a filtration device with a 45 μm polypropylene mesh filter (Millipore PP4504700)), and vacuum filtration was started in about 15 seconds. The filtrate was collected and then subjected to ICP elemental analysis.

[0103] Table 2.

[0104]

[0105] The results from Table 2 show that DMTD-2K, by itself or together with Na-DTPi, effectively removes arsenic and cadmium from industrial phosphoric acid (30% P2O5). The performance improves with increasing DMTD-2K dosage.

[0106] Example 3 - For use at elevated temperatures (70 ℃ ) or room temperature (20 ℃ ) from concentrated phosphoric acid (about 50% P2O5) Methods for removing heavy metals

[0107] 50 g of factory phosphoric acid (about 50% P2O5, concentrated from factory acid with about 30% P2O5) was transferred to a glass jar with a magnetic stirring bar. An effective amount of the reagent of interest for removing heavy metal ions (as listed in Table 3) was metered into the acid under stirring at 600 rpm. For Example 3F-4, two reagents were metered simultaneously with two separate pipettes. After stirring for 2 minutes and settling for another 2 minutes, the acid was transferred to a syringe and filtered with a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis. The results are shown in Table 3 and plotted in Figure 4 middle.

[0108] When two reagents of interest were metered sequentially (as in Examples 3D-1, 3D-2, 3D-3, 3F-1, 3F-2, 3F-3, 3J, and 3L), the first reagent was metered into the acid and stirred for 1 minute at 600 rpm, and then the second reagent was metered into the acid and stirred for 1 minute at 600 rpm. Afterwards, the acid was allowed to settle for another 2 minutes, and then transferred to a syringe and filtered with a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis.

[0109] Table 3.

[0110]

[0111]

[0112] The results shown in Table 3 indicate a significant reduction (over 80%) of arsenic and cadmium from concentrated factory phosphoric acid (50% P2O5) when treated with DMTD-2K (Examples 3B-3 and 3B-4). Similar As removal performance was observed when concentrated factory phosphoric acid was treated with DTG (Example 3E-3). In both cases, performance improved when the dosage of these compounds was increased. Excellent performance was also observed when DMTD-2K or DTG was co-dosed with Na-DTPi in different orders.

[0113] Example 4 - For use at elevated temperatures (70 ℃ ) using a thiol-containing polymer from concentrated phosphoric acid (about 46%) Method for removing arsenic from P2O5

[0114] Synthesis of thiol-containing polymer P1. Polyethyleneimine (Epomin SP-018, 5 g, 0.0028 mol) and C8-C10 alkyl glycidyl ether (GE-7, 2.64 g, 0.0117 mol) were added to a flask and stirred at 80°C for 1 h. Deionized water (95.54 g) and 10% NaOH solution (9.33 g) were added to the flask to form a clear solution, followed by the addition of (3-glycidyloxypropyl)trimethoxysilane (GPTS, 2.76 g, 0.0117 mol). After stirring for 30 min, (3-mercaptopropyl)trimethoxysilane (MPTS, 2.29 g, 0.0117 mol) dissolved in 10% NaOH aqueous solution (9.33 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of thiol-containing polymer with a polymer concentration of 10 wt%. The weight percentage of MPTS in the polymer was 18.05%.

[0115] Synthesis of thiol-containing polymer P2. Polyethyleneimine (Epomin SP-018, 0.87 g, 0.0005 mol) and C8-C 10 Alkyl glycidyl ether (GE-7, 0.46 g, 0.0020 mol) was added to a flask and stirred at 80°C for 1 h. Deionized water (6.58 g) and 10% NaOH solution (1.62 g) were added to the flask to form a clear solution, followed by the addition of (3-glycidyloxypropyl)trimethoxysilane (GPTS, 0.48 g, 0.0020 mol). After stirring at 40°C for 30 min, a solution of (3-mercaptopropyl)trimethoxysilane (MPTS, 1.19 g, 0.0061 mol), 50% NaOH aqueous solution (0.97 g) and deionized water (7.77 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of a thiol-containing polymer with a polymer concentration of 15.00%. The weight percentage of MPTS in the polymer was 39.79%.

[0116] Synthesis of thiol-containing polymer P3. Polyethyleneimine (Epomin SP-018, 0.35 g, 0.0002 mol) and C8-C 10 Alkyl glycidyl ether (GE-7, 0.18 g, 0.0008 mol) was added to a flask and stirred at 80°C for 1 h. Deionized water (2.63 g) and 10% NaOH solution (0.65 g) were added to the flask to form a clear solution, followed by the addition of (3-glycidyloxypropyl)trimethoxysilane (GPTS, 0.19 g, 0.0008 mol). After stirring at 40°C for 30 min, a solution of (3-mercaptopropyl)trimethoxysilane (MPTS, 1.59 g, 0.0081 mol), 50% NaOH aqueous solution (1.29 g) and deionized water (8.52 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of a thiol-containing polymer with a polymer concentration of 14.98%. The weight percentage of MPTS in the polymer was 68.78%.

[0117] Synthesis of thiol-containing polymer P4. Polyethyleneimine (Epomin SP-018, 0.68 g, 0.0004 mol) and C8-C 10Alkyl glycidyl ether (GE-7, 0.36 g, 0.0016 mol) was added to a flask and stirred at 80°C for 1 h. Deionized water (7.69 g) and 10% NaOH solution (0.51 g) were added to the flask to form a clear solution, followed by the addition of (3-glycidyloxypropyl)trimethoxysilane (GPTS, 0.75 g, 0.0032 mol). After stirring at 40°C for 30 min, a solution of (3-mercaptopropyl)trimethoxysilane (MPTS, 0.63 g, 0.0032 mol), 50% NaOH aqueous solution (0.51 g) and deionized water (5.04 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of a thiol-containing polymer with a polymer concentration of 15.00%. The weight percentage of MPTS in the polymer was 25.83%.

[0118] Synthesis of thiol-containing polymer P5. Polyethyleneimine (Epomin SP-018, 0.86 g, 0.0005 mol) was dissolved in deionized water (7.69 g) and 10% NaOH solution (0.64 g) in a flask at 40°C. (3-Glycidyloxypropyl)trimethoxysilane (GPTS, 0.94 g, 0.0040 mol) was slowly added to the flask. After stirring at 40°C for 30 min, a solution of (3-mercaptopropyl)trimethoxysilane (MPTS, 0.78 g, 0.0004 mol), 50% NaOH aqueous solution (0.64 g) and deionized water (5.81 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of a thiol-containing polymer with a polymer concentration of 15.00% wt%. The weight percentage of MPTS in the polymer was 30.35%.

[0119] Synthesis of thiol-containing polymer P6. Tetraethylenepentamine (0.58 g, 0.0031 mol) and C8-C 10 Alkyl glycidyl ether (GE-7, 0.69 g, 0.0031 mol) was added to a flask and stirred at 80°C for 1 h. Deionized water (7.51 g) and 50% NaOH solution (0.49 g) were added to the flask to form a clear solution, followed by the addition of (3-glycidyloxypropyl)trimethoxysilane (GPTS, 0.72 g, 0.0031 mol). After stirring at 40°C for 30 min, a solution of (3-mercaptopropyl)trimethoxysilane (MPTS, 0.60 g, 0.0031 mol), 50% NaOH aqueous solution (0.25 g) and deionized water (6.50 g) was slowly added to the flask. The mixture was stirred at 40°C for 2 h to produce a solution of a thiol-containing polymer with a polymer concentration of 15.00%. The weight percentage of MPTS in the polymer was 23.14%.

[0120] Table 4: Characteristics of thiol-containing polymers.

[0121]

[0122] To perform the heavy metal removal test, 25 g of factory phosphoric acid (about 46% P2O5) was transferred to a glass vial with a magnetic stirring bar. An effective amount of the reagent of interest for removing heavy metal ions (listed in Table 4, and pure MPTS) was metered into the acid under stirring at 600 rpm. After stirring for 30 minutes, the acid was transferred to a syringe and filtered with a 0.45 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis. The results are shown in Table 5.

[0123] Table 5.

[0124]

[0125]

[0126] The results in Table 5 show that the thiol-containing polymers and pure MPTS can effectively remove the arsenic content in the factory phosphoric acid (about 46% P2O5). The performance improves with the increase of polymer dosage. More than 90% arsenic reduction is achieved at polymer dosages less than 10 kg / T P2O5. Compared with pure MPTS, the thiol-containing polymers (except P3 and P6) show higher arsenic reduction at the same MPTS dosage.

[0127] Example 5 - For use at elevated temperatures (75 ℃ Method for removing heavy metals from weak phosphoric acid (about 30% P2O5) in factories Law

[0128] 35 g of plant phosphoric acid (about 30% P2O5, collected from the clarifier after filtration) from plant #3 was transferred to a glass jar with a magnetic stirring bar. The acid was heated to 80°C in a water bath. An effective amount of the reagent of interest (as listed in Table 6) was metered into the acid under stirring at 600 rpm. After stirring for 1 minute and settling for another minute, the acid was transferred to a syringe and filtered with a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis. The results are shown in Table 6.

[0129] Table 6.

[0130]

[0131]

[0132] The results from Table 6 indicate that DTG, 1,3-dimercapto-2-propanol, 1,2,3-trimercaptopropane, 1,2-ethanedithiol, 1,3-propanedithiol, and benzene-1,2-dithiol successfully removed arsenic from plant phosphoric acid (30% P2O5). Among them, DTG, 1,3-dimercapto-2-propanol, 1,2,3-trimercaptopropane, and 1,2-ethanedithiol successfully removed significant amounts of arsenic from plant phosphoric acid (30% P2O5).

[0133] Various patents and / or scientific literature references have been mentioned throughout this application. The disclosures of these publications are hereby incorporated by reference in their entirety, as if written herein. In view of the above description and examples, one of ordinary skill in the art will be able to implement the invention as claimed without undue experimentation.

[0134] Although the above description has shown, described and pointed out the basic novel features of certain embodiments of the present invention, it should be understood that various omissions, substitutions and changes in the form of details of the present invention as described may be made by those skilled in the art without departing from the scope of the present teachings. Therefore, the scope of the present invention should not be limited to the foregoing description or discussion, but should be defined by the appended claims.

Claims

1. A method for removing heavy metal ions from a phosphoric acid mixture, the method comprising: An effective amount of a reagent comprising a heavy metal chelator having multiple sulfur groups is added to the phosphoric acid mixture.

2. The method according to claim 1, wherein: The phosphoric acid mixture is a solution.

3. The method according to claim 1, wherein: The phosphoric acid mixture is a slurry.

4. The method according to any one of claims 1 to 3, wherein: The heavy metal ion is selected from the group consisting of cadmium, copper, arsenic, mercury, lead and mixtures of any of the foregoing.

5. The method according to claim 4, wherein: The heavy metal ion is cadmium.

6. The method according to claim 4, wherein: The heavy metal ion is arsenic.

7. The method according to any one of claims 1 to 6, wherein: The heavy metal chelating agent having multiple sulfur groups is selected from compounds according to formula I(A) or I(B): and their salts, in Each M and M' in Formula I(A) or I(B) is independently selected from H, Na, K, Li, NH4, NR'4, wherein each R' is independently selected from C1-C4 alkyl; and R in formula I (B) is selected from C1-C 18 Alkyl, C6-C 12 Aryl, or C7-C 18 Aralkyl.

8. The method according to claim 7, wherein: The compound according to formula I(A) or I(B) is selected from the group consisting of 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt, 5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt, and mixtures thereof.

9. The method according to any one of claims 1 to 6, wherein: The heavy metal chelating agent having multiple sulfur groups is selected from the group consisting of 2,3-dimercapto-1-propanol, 1,2-ethanedithiol, 1,3-propanedithiol, benzene-1,2-dithiol, 1,3-dimercapto-2-propanol, 1,2,3-trimercaptopropane, and mixtures thereof.

10. The method according to claim 9, wherein: The heavy metal chelating agent is 2,3-dimercapto-1-propanol.

11. The method according to any one of claims 1 to 6, wherein: The heavy metal chelating agent having multiple sulfur groups is a polymer according to the following: wherein each M is independently selected from H, Na, K, Li, NH4 and NR'4, each R' is independently selected from C1-C4 alkyl, and n is the number of repeating units of the polymer backbone and is an integer from 2 to 1000.

12. The method according to claim 11, wherein: n is 2 to 100.

13. The method according to claim 11, wherein: The polymer comprises a backbone selected from the group consisting of polyamines, polysaccharides, polyvinyl pyrrolidone, polyglutamic acid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin, and mixtures of any of the foregoing, and copolymers of any of the foregoing.

14. The method according to any one of claims 1 to 11, wherein: The reagent further comprises an effective amount of an organic thiophosphorus compound.

15. The method according to claim 14, wherein: The organothiophosphorus compound is selected from the group consisting of organodithiophosphinic acid, organodithiophosphonic acid, organodithiophosphoric acid, organomonothiophosphinic acid, organomonothiophosphoric acid, their corresponding salts in sodium, ammonium or potassium form, and mixtures thereof.

16. The method according to claim 15, wherein: The organic thiophosphorus compound includes an organic dithiophosphinic acid or a corresponding salt thereof, or an organic dithiophosphoric acid or a corresponding salt thereof.

17. The method according to claim 16, wherein: The organic dithiophosphinic acid is a dialkyl dithiophosphinic acid, and the organic dithiophosphoric acid is a dialkyl dithiophosphoric acid.

18. The method according to any one of claims 1 to 17, wherein: The phosphoric acid mixture further comprises an adsorbent.

19. The method according to claim 18, wherein: The adsorbent is solid calcium sulfate particles.

20. The method according to any one of claims 1 to 19, wherein: The process is carried out at a temperature of 0°C to 120°C.

21. The method according to claim 20, wherein: The process is carried out at a temperature of about 10°C to about 80°C.

22. The method according to any one of claims 1 to 21, wherein: The phosphoric acid mixture has a concentration of P2O5 of 3 wt% to 70 wt% based on the total weight of the mixture.

23. The method according to claim 22, wherein: The phosphoric acid mixture has a concentration of 20 wt % to 60 wt % of P2O5.

24. The method according to any one of claims 1 to 23, wherein: The reagents were added to the phosphoric acid mixture at dosages of 0.1 kg / ton and 10 kg / ton P2O5.

25. The method according to any one of claims 1 to 24, wherein: The method further comprises the step of separating the phosphoric acid mixture.

26. The method according to claim 25, wherein: The separating step further comprises flocculation.

27. A method according to claim 25 or claim 26, wherein: The separating step further comprises filtering.

28. The method according to any one of claims 25 to 27, wherein: The separating step further comprises skimming.

29. A reagent for removing heavy metal ions from a phosphoric acid mixture, the reagent comprising (a) a heavy metal chelating agent containing multiple sulfur groups; and (b) an organic thiophosphorus compound, wherein the organic thiophosphorus compound comprises an organic dithiophosphinic acid or a corresponding salt thereof, or an organic dithiophosphoric acid or a corresponding salt thereof.

30. The reagent according to claim 29, wherein The heavy metal chelating agent having multiple sulfur groups includes a member selected from the group consisting of: (i) 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt, and 5-mercapto-3-phenyl-1,3,4-thiadiazole-2(3H)-thione potassium salt; (ii) 2,3-dimercapto-1-propanol, 1,2-ethanedithiol, 1,3-propanedithiol, benzene-1,2-dithiol, 1,3-dimercapto-2-propanol, and 1,2,3-trimercaptopropane; (iii) a polymer as defined in claim 11; and (iv) mixtures of any of the foregoing.

31. The reagent according to claim 29 or claim 30, wherein The heavy metal chelating agent having multiple sulfur groups is 2,3-dimercapto-1-propanol.

32. The reagent according to claim 29 or claim 30, wherein The heavy metal chelating agent having multiple sulfur groups is 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt.

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