Compositions and methods for removing heavy metals from phosphoric acid containing streams

Abstract

Provided herein are compositions and methods for removing / recovering heavy metal ions in a phosphoric acid-containing stream by mixing a dialkyldithiophosphate compound having at least one alkyl chain length of C8 to C18, a dialkyldithiophosphate compound having at least one alkyl chain length of C8 to C18, and a dialkyldithiophosphate compound having at least one alkyl chain length of C18 to C18, reagents of at least one dialkyldithiophosphinate compound and at least one surfactant are added to a phosphoric acid solution or slurry to form heavy metal ion complexes, and the heavy metal ion complexes are separated from the solution or slurry.

Description

Technical Field

[0001] The technical concepts disclosed herein generally relate to the purification of industrial process streams. More particularly, the concepts disclosed herein relate to the removal of heavy metal ions from phosphoric acid-containing streams, especially cadmium, arsenic, and copper. Background Art

[0002] Approximately 90% of the world's phosphoric acid is produced according to the wet process, which is conventionally prepared by acidifying 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 [Phosphates and Phosphoric Acid], Marcel Dekker, Inc. 1989, and by Slack in Phosphoric Acid,Part 1 and Part 2 [Phosphoric Acid, Parts 1 and 2], Marcel Dekker, Inc. 1968. In this method, the phosphate rock is washed in a washing device and ground in a ball mill and then fed into 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 the phosphoric acid from undissolved rock, newly formed gypsum, and gangue. The filtered crude WPA is then sent to a clarifier and an evaporator for further purification and concentration. Crude WPA can also be produced by digestion with nitric acid or hydrochloric acid.

[0004] The purified phosphoric acid is sent out as merchant grade acid (MGA) or further processed to produce 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, soldering fluxes, dispersants, industrial etchants, fertilizer raw materials, and components of household cleaning products. For example, the crude phosphoric acid is concentrated to 54% (P2O5) before being sent out for the production of monoammonium phosphate (MAP), diammonium phosphate (DAP), or ammonium polyphosphate (APP).

[0005] During the production of phosphoric acid, certain metal impurities in the form of heavy metal ions (such as cadmium (Cd), arsenic (As), lead (Pb), copper (Cu), and mercury (Hg)) are present in the phosphate rock as minerals and dissolve into the phosphoric acid. Depending on the application of the phosphoric acid, metal impurities above a certain level are considered unacceptable due to their toxicity. Therefore, the metal impurities must be completely removed or their levels in the phosphoric acid must be significantly reduced.

[0006] For example, cadmium (Cd) is toxic and can cause various health problems to humans. Studies have shown that for the general non-smoking population, the main exposure to Cd is through the ingestion of contaminated food. Phosphate fertilizers have been identified as an important source of introducing Cd 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 2014, 68, 10, 837 - 842).

[0007] Cd in phosphate fertilizers comes from phosphoric acid, which is the main raw material used in the production of phosphate fertilizers. In fact, most phosphoric acid production is used for fertilizer production. Cd in phosphoric acid further originates from phosphate-bearing ores. Therefore, Cd can be removed either from phosphate ores or from phosphoric acid streams, with the latter being the focus of research in the past few decades. Several classes of technologies for removing Cd from acid streams have been developed, including co-crystallization with anhydrite, precipitation with sulfide ions and organosulfur compounds, removal by solvent extraction, removal by ion exchange, removal by adsorbents, and separation by membrane technology ("Progress in the development of decadmiation of phosphorus fertilizers", Fertilizer Industry Federation of Australia, Inc., Conference "Fertilizers in Focus", 2001, 101 - 106).

[0008] U.S. Patent No. 4,378,340 (1983) describes a method for removing heavy metals, especially cadmium, from wet-process phosphoric acid by partially neutralizing the acid with an alkali and then precipitating with a sulfide compound. U.S. Patent No. 5,431,895 (1995) also discloses the simultaneous use of an alkali solution and an aqueous sulfide solution for removing lead and cadmium from phosphoric acid under thorough mixing.

[0009] U.S. Patent No. 4,986,970 (1991) discloses the precipitation of heavy metals, especially cadmium, from partially neutralized (pH 1.4 - 2) and pre-cooled (5°C - 40°C) phosphoric acid using metal salts of dithiocarbonic acid - O - esters. Subsequently, methods such as flotation or filtration can be used to separate the complexes from the acid.

[0010] 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) respectively describe methods for separating heavy metals, especially cadmium, mercury, and lead, from phosphoric acid using dialkyldithiophosphates and adsorbents, dialkyldithiophosphorus compounds and adsorbents, dialkyldithiophosphates and adsorbents and reducing agents, and thioorganophosphorus reagents and reducing agents.

[0011] 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 bis(diorganodithiophosphinic acid) (or its alkali metal or ammonium salt), a first dithiophosphoric acid (or its alkali metal salt or ammonium salt) having an alkyl or alkaryl or aralkyl moiety, and optionally a second diaryldithiophosphoric acid (or its alkali metal or ammonium salt).

[0012] 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) discuss the removal of cadmium from phosphoric acid using reagents such as bis(2,4,4-trimethylpentyl)thiophosphinic acid / kerosene and trioctylphosphine oxide / kerosene respectively based on solvent extraction methods.

[0013] However, while the various reagents and methods discussed above may have some advantages and applicability in phosphoric acid production, high investment costs, high treatment costs, and low efficacy limit their widespread acceptance at the plant scale (see "Cadmium in phosphate fertilizers; ecological and economical aspects", CHEMIK 2014, 68, 10, 837 - 842). Heavy metal contamination of food, especially cadmium originating from the use of phosphoric acid in fertilizer production, remains a public health concern. The economic impact of the heavy metal problem is significant, and the industry requires technologies that are more effective and more economical than those currently available. Additionally, there is a recent regulation that drives further restriction of Cd levels in phosphate fertilizers (see European Commission Fact Sheet. "Circular economy: New Regulation to boost the use of organic and waste - based fertilisers." EU MEMO - 16 - 826, March 17, 2016, europ.eu / rapid / press - release_MEMO - 16 - 826_en.htm).

[0014] To address such regulatory hurdles, U.S. Patent No. 10,865,110 (2020) granted to the applicant provides a method for removing heavy metal ions (such as cadmium and arsenic) from phosphoric acid solutions containing such heavy metal ions by adding an effective amount of a reagent comprising an organic thiophosphorus compound and a surfactant to the phosphoric acid solution. Once the reagent forms a heavy metal complex, the heavy metal complex can be separated from the phosphoric acid solution by any means known to those skilled in the art. While this method is very effective, for phosphoric acid solutions containing increasing levels of cadmium, high doses of the organic thiophosphorus reagent are often required.

[0015] However, despite these efforts, important problems remain unresolved by these different solutions. In fact, the health problems of operators in the vicinity of the acid stream are outstanding, and especially because they may experience off - gassing of H2S when implementing the method for removing heavy metal ions.

[0016] Therefore, the compositions and methods currently available for removing heavy metals from phosphoric acid in a production process require further and / or continuous improvement. Since many factors (e.g., ore type, temperature, agitation, reactor design, acid chemistry, foreign ions, organic matter, and the viscosity of the phosphoric acid medium) can affect the performance of the reagent, developing an efficient reagent that can be used to remove heavy metals from phosphoric acid and reduce the safety risk to operators near the acid stream is a significant challenge. A successful reagent for removing heavy metals from industrial process streams such as wet-process phosphoric acid would be a beneficial advancement in the art and could be quickly accepted in the industry. Summary of the Invention

[0017] The foregoing and additional objects are obtained in accordance with the principles of the present invention, wherein the inventors have detailed the unexpected discovery that at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant as a novel reagent composition for removing heavy metal ions from a phosphoric acid-containing stream are effective, and compared to benchmark products widely used in the market, the novel reagent composition enables a significant reduction in the degassing of H2S when treating a phosphoric acid-containing stream with the composition. Thus, the methods for removing heavy metal ions according to different embodiments of the present invention described below are applicable to different stages of wet-process phosphoric acid production.

[0018] Accordingly, in one aspect, the present invention provides a composition for complexing heavy metals in a solution, wherein the composition comprises an effective amount of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate, and at least one surfactant.

[0019] In another aspect, the present invention provides a method for removing heavy metal ions from a phosphoric acid-containing solution by adding an effective amount of a reagent comprising at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant to the solution to form a heavy metal complex, and separating the heavy metal complex from the solution.

[0020] In the same or additional embodiments, the method may further comprise adding an effective amount of a reducing agent to the phosphoric acid-containing solution.

[0021] In the same or additional embodiments, the method may further comprise adding an effective amount of an adsorbent to the phosphoric acid-containing solution.

[0022] The present invention content does not list all the necessary features, and thus, sub - combinations of these features or elements can also constitute an invention. Therefore, these and other objects, features, and advantages of the present invention will become apparent from the following detailed description of the different aspects of the present invention in conjunction with the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a graph showing the results of Examples 2A - 1 to 2A - 9, where the percentage of cadmium removed from plant phosphoric acid #1 (54% P2O5) at a level of 3 kg / T P2O5 of different reagents at about 72 °C,

[0024] Figure 2 is a graph showing the results of Examples 3A - 1 to 3A - 7, where the percentages of cadmium, arsenic, and copper removed from plant phosphoric acid #2 (60% P2O5) at a level of 3 kg / T P2O5 of different reagents at about 72 °C,

[0025] Figure 3 is a graph showing the results of Examples 4A to 4P, where the concentration of H2S in the top space above plant phosphoric acid #3 (30% P2O5) was measured directly following the procedure described below, with the dose of different reagents at a level of 2 kg / T P2O5. DETAILED DESCRIPTION

[0026] The present disclosure generally relates to the purification of solutions in industrial process streams. More particularly, the inventors herein for the first time describe reagents and methods for removing and / or recovering heavy metal ions from phosphoric - acid - containing streams by adding an effective amount of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant to form heavy - metal complexes, and separating the complexes from the solution. When compared to prior - art compositions and methods, the compositions and methods described herein provide improved and / or unexpected advantages.

[0027] As used throughout this disclosure, the following terms are provided to assist the reader. Unless otherwise defined, all specialized terms, notations, and other scientific or industrial terms or nomenclature 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 clarity and / or for convenient reference, terms having commonly understood meanings are defined herein, and unless otherwise indicated, the inclusion of such definitions herein is not necessarily to be construed as representing a substantial difference compared to the definitions of terms commonly understood in the art. Unless the context clearly indicates otherwise, as used herein and in the appended claims, the singular forms include plural referents. Throughout this specification, the terms retain their definitions.

[0028] As used herein with respect to the present invention, the term "heavy metal" or "metal" shall mean those elements in the periodic table having a density greater than 5 g / cm 3 and an oxidation state above 0 (i.e., heavy metal ions). Such heavy metal ions include, for example, one or more of cadmium, chromium, arsenic, nickel, mercury, zinc, manganese, titanium, copper, and lead. In any or all embodiments, cadmium ions are removed from the phosphoric acid-containing stream. In the same or alternative embodiments, arsenic ions are removed from the phosphoric acid-containing stream.

[0029] The concept of "heavy metal complex" refers to a compound formed by reacting a heavy metal ion with a chelating agent. Heavy metal complexes can be solid, waxy, or oily in a phosphoric acid solution. They can precipitate, float, or be suspended in the phosphoric acid solution.

[0030] Those skilled in the art will understand that references to "phosphoric acid-containing stream" or "phosphoric acid solution" or "solution containing phosphoric acid" in the context of the present invention include any acidic solution containing crude phosphoric acid, digested slurry of phosphoric acid, filtered phosphoric acid, and / or concentrated phosphoric acid. Such phosphoric acid-containing streams are typically obtained from industrial phosphoric acid production plants.

[0031] "Effective amount" means the dose of any reagent (such as the composition described herein comprising at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant) on an active basis required to provide the desired performance in the phosphoric acid system or circuit to be treated (such as forming heavy metal complexes) when compared to an untreated control system or a system using a reagent product of the prior art.

[0032] As used herein, the term "alkyl" is intended to include straight-chain, branched-chain, or cyclic hydrocarbon structures and combinations thereof. Preferred alkyls are C 30 or below C 30 Those. Lower alkyls refer to alkyls having 1 to 6 carbon atoms. Examples of lower alkyls include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, and tert-butyl, pentyl, hexyl, etc. Cycloalkyls are a subset of alkyls and include 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] The term "aryl" as used herein is a cyclic aromatic hydrocarbon having no heteroatoms in the ring. In any one or all embodiments, the aryl contains from about 6 to about 14 carbons in the ring portion of the group. Thus, aryl includes, but is not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthryl, triphenylenyl, pyrenyl, tetracenyl, chrysenyl, biphenylethenyl, anthryl, and naphthyl. The aryl group can be unsubstituted or substituted as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as but not limited to 2-, 3-, 4-, 5-, or 6-substituted phenyl or 2-8 substituted naphthyl, which can be substituted by carbon or non-carbon groups as known to those skilled in the art. An aryl group of C6-C 12 is preferred.

[0034] As used herein, the term "alkaryl" is a broad term and is used in its ordinary sense, including but not limited to an aryl group in which at least one aryl hydrogen atom is replaced by an alkyl moiety. 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)2phenyl, -(CH2)3phenyl, -CH(phenyl)2, etc. Particularly preferred is C 7-20 aralkyl.

[0035] As used herein, the term "comprised of" or "comprising / comprises" includes embodiments of "consisting essentially of the listed elements" or "consisting of the listed elements", and the terms "including" or "having" in the context of describing the present invention shall be equivalent to "comprising".

[0036] Those skilled in the art will understand that although the preferred embodiments are discussed in more detail below, various embodiments of the reagent systems and methods described herein are also contemplated within the scope of the present invention. Therefore, it should be noted that unless otherwise specified, any feature described with respect to one aspect or one embodiment of the present invention is interchangeable and / or combinable with another aspect or embodiment of the present invention. Those skilled in the art will also understand that even any description of the present invention described with respect to a specific embodiment or drawing can be applied to and is interchangeable with other embodiments of the present invention.

[0037] 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 can also be any one of these individual listed elements, components, or features, or can also be selected from a group consisting of any two or more of these explicitly listed elements, components, or features. Additionally, any element, component, or feature listed in such a list can also be omitted from such a list.

[0038] Those skilled in the art will further understand that any recitation of a numerical range by endpoints herein, whether or not explicitly recited, includes all numbers (including fractions) contained within the recited range, as well as the endpoints and equivalents thereof. The term “et seq.” is sometimes used to indicate numbers contained within a recited range without explicitly reciting all numbers, and should be considered a complete disclosure of all numbers within that range. The disclosure of a narrower range or a more specific group in addition to a broader range or a larger group does not waive the right to claim the broader range or the larger group.

[0039] The dialkyldithiophosphate compounds having an alkyl chain length of C8 to C18 described herein for any or all embodiments include dialkyldithiophosphoric acids having an alkyl chain length of C8 to C18 and any salts (e.g., calcium salts, magnesium salts, potassium salts, sodium salts, ammonium salts having the formula NR1R2R3R4 + wherein R1, R2, R3, and R4 are the same or different and are independently selected from hydrogen, alkyl, or aryl); and mixtures thereof. In some embodiments, the alkyl chain of the dialkyldithiophosphate compound according to the present invention is C8 to C12. Preferably, the alkyl chain of the dialkyldithiophosphate compound according to the present invention is a C8 alkyl chain.

[0040] In the same or alternative embodiments, the dialkyldithiophosphate compounds are selected from the group consisting of: any salts of bis(1,3-dimethylbutyl)dithiophosphoric acid, bis(2-ethylhexyl)dithiophosphoric acid, bis(3,7-dimethyloctyl)dithiophosphoric acid, bis(2-butyl octyl)dithiophosphoric acid; and mixtures thereof. In a preferred embodiment, the dialkyldithiophosphate compounds are salts of bis(2-ethylhexyl)dithiophosphoric acid, bis(3,7-dimethyloctyl)dithiophosphoric acid, and bis(2-butyl octyl)dithiophosphoric acid; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compounds are salts of bis(2-ethylhexyl)dithiophosphoric acid, preferably ammonium salts of bis(2-ethylhexyl)dithiophosphoric acid.

[0041] In the same or alternative embodiments, the dialkyldithiophosphate compound is selected from the group consisting of: bis(1,3-dimethylbutyl)dithiophosphate, bis(2-ethylhexyl)dithiophosphate, bis(3,7-dimethyloctyl)dithiophosphate, bis(2-butyl octyl)dithiophosphate; and mixtures thereof. In a preferred embodiment, the dialkyldithiophosphate compound is bis(2-ethylhexyl)dithiophosphate, bis(3,7-dimethyloctyl)dithiophosphate and bis(2-butyl octyl)dithiophosphate; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compound is bis(2-ethylhexyl)dithiophosphate. Preferably, the dialkyldithiophosphate compound is ammonium bis(2-ethylhexyl)dithiophosphate.

[0042] The dialkyldithiophosphite compounds described herein for any or all embodiments include dialkyldithiophosphinic acids and any salts of the foregoing dialkyldithiophosphinic acids (e.g., calcium salts, magnesium salts, potassium salts, sodium salts, ammonium salts having the formula NR1R2R3R4 + wherein R1, R2, R3, and R4 are the same or different and are independently selected from hydrogen, alkyl, or aryl); and mixtures thereof.

[0043] In the same or alternative embodiments, the dialkyldithiophosphite compound is selected from the group consisting of: diisobutyldithiophosphinic acid, any salts of bis(2,4,4-trimethylpentyl)dithiophosphinic acid; and mixtures thereof. In a preferred embodiment, the dialkyldithiophosphite compound is sodium diisobutyldithiophosphite.

[0044] In any or all embodiments, the surfactant compound can be selected from the group consisting of: sulfosuccinates, arylsulfonates, alkarylsulfonates, diphenylsulfonates, olefinsulfonates, sulfonates of ethoxylated alcohols, petroleum sulfonates, sulfosuccinamates, alkoxylated surfactants, ester / amide surfactants, EO / PO block copolymers (ethylene oxide / propylene oxide), and mixtures thereof. In the same or alternative embodiments, the surfactant can be an alkarylsulfonate. In a preferred embodiment, the surfactant can be an alkyl diphenyl ether disulfonate. Suitable alkyl diphenyl ether disulfonate compounds include, but are not limited to, those available from Dow Chemical 8390.

[0045] In the same or alternative embodiments, the surfactant can be a sulfosuccinate. A suitable sulfosuccinate can be sodium dioctyl sulfosuccinate. Suitable sodium dioctyl sulfosuccinate compounds include, but are not limited to, those available from Solvay S.A. OT-70 and 70B.

[0046] In the same or alternative embodiments, the surfactant can be an alkoxylated surfactant. Suitable alkoxylated surfactants can include, but are not limited to, polyethylene glycol sorbitan monooleate (such as 80, available from Croda) and polyethylene glycol sorbitol hexaoleate (such as G1086, available from Croda).

[0047] In any or all embodiments of the present invention, at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphite compound, and at least one surfactant can be added to the crude phosphoric acid or the digestion slurry before gypsum filtration, or to the filtered phosphoric acid or the concentrated phosphoric acid to complex heavy metal ions. Thereafter, the heavy metal complexes so formed can be separated from the phosphoric acid or the slurry. The separation can be carried out via any suitable method known in the art for such separation. In any or all embodiments, the separation methods include, but are not limited to, filtration, centrifugation, sedimentation, creaming, skimming, flocculation, adsorption, and / or flotation.

[0048] In any or all embodiments of the present invention, at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphite compound, and at least one surfactant can be added to the phosphoric acid-containing solution all in one stage or in several stages. In the same or other embodiments, at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphite compound, and at least one surfactant are added as a blend, or separately in any order (such as together simultaneously or sequentially). In a preferred embodiment, at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphite compound, and at least one surfactant are added as a blend.

[0049] In any or all embodiments of the present invention, the treatment time can be from a few seconds (i.e., 5 to 10 seconds) to 240 minutes. In those cases where the reagent complexes the heavy metals very rapidly, the preferred treatment time is about 5 seconds to 5 minutes. Most typically, the treatment time is 10 seconds to 60 seconds or 120 seconds.

[0050] 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 phosphoric acid-containing stream. Generally, the greater the amount of heavy metals present and the higher their concentration, the greater the total dosage of the reagent. A person skilled in the art will be able to easily determine and establish the optimal dosage of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant using only routine experiments. Generally, based on the type of heavy metal ions to be removed, the dosage can range from 0.01 to 50 kg (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, and so on up to 0.10, 0.15, 0.20, 0.25, 0.30, and so on up to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and so on up to 10, 15, 20, 25, 30, 35, 40, 45, 50 kg) of reagent per ton of P2O5 in the phosphoric acid solution. Most typically, the dosage can be from 0.1 kg to 10 kg (e.g., 0.10, 0.15, 0.20, 0.25, 0.30, and so on up 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 per ton of P2O5. A person of ordinary skill in the art will understand that any of the recited dosages (except for the lowest dosage point) can also be stated as "less than" a specific dosage, e.g., less than 50 kg; or any of the recited dosages (except for the highest dosage point) can also be stated as "greater than" a specific dosage, e.g., greater than 0.10 kg.

[0051] The ratio of the sum of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 and at least one dialkyldithiophosphinate compound to the surfactant is from 1000:1 to 5:1. In a preferred embodiment, the ratio of the sum of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 and at least one dialkyldithiophosphinate compound to the surfactant is from 100:1 to 10:1.

[0052] In any or all embodiments, the ratio of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyldithiophosphinate compound is from 1:100 to 100:1. In a preferred embodiment, the ratio of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyldithiophosphinate compound is from 1:20 to 20:1. In a more preferred embodiment, the ratio of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyldithiophosphinate compound is from 1:5 to 5:1.

[0053] In any or all embodiments, the phosphoric acid-containing solution has a P2O5 concentration of 4 wt.% to 70 wt.%, typically 25 wt.% to 60 wt.%. Specific concentrations of P2O5 contemplated for use in the present invention include 25 wt.%, 28 wt.%, 30 wt.%, 42 wt.%, 44 wt.%, 52 wt.%, 54 wt.%, 57 wt.% and 60 wt.%.

[0054] The compositions and methods as described herein according to the present invention can be used over a wide temperature range. In any or all embodiments, for example, the method according to the present invention can be carried out at a temperature of from 0 °C to 120 °C. Preferably, the temperature is in the range of 20 °C to 80 °C.

[0055] In any or all embodiments according to the present invention, the method can further comprise adding an effective amount of a reducing agent and / or an adsorbent to the phosphoric acid-containing solution. Such agents are known in the art. In some cases, one or both of these agents can enhance the activity of a reagent comprising at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound and at least one surfactant. In the same or alternative embodiments, the reducing agent and / or the adsorbent can be added to the phosphoric acid stream all in one stage or in several stages. In the same or other embodiments, the reducing agent and / or the adsorbent can be added as a blend with a reagent comprising at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound and at least one surfactant, or separately from at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound and at least one surfactant in any order (such as together simultaneously or sequentially). Although the nature and amount of the reducing agent and / or the adsorbent used depends on the specific composition of the phosphoric acid in the solution and the purity specifications, those skilled in the art will be able to determine the optimal dosage range using only routine experimentation.

[0056] Reducing agents available in any or all of the methods according to the present invention include, but are not limited to, iron powder, zinc, red phosphorus, iron(II) sulfate, sodium hypophosphite, hydrazine, hydroxymethanesulfonate, and mixtures thereof. In a preferred embodiment, the reducing agent includes iron powder and sodium hypophosphite. In any or all embodiments, based on the type and amount of the oxidizing agent in the phosphoric acid solution, the reducing agent is used in an amount of 0.01 kg to 50 kg of reagent / ton of P2O5, which can be easily determined by those skilled in the art merely using conventional methods. In a preferred embodiment, the amount of the reducing agent is 0.1 kg to 5 kg of reagent / ton of P2O5 in the phosphoric acid solution.

[0057] Adsorbents can be used in any or all embodiments according to the present invention and include, but are not limited to, activated carbon / carbon, carbon black, ground lignite, adsorbents containing silicates (e.g., synthetic silicic acid, zeolites, 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 0.05 wt.% to 50 wt.%, and preferably 0.1 wt.% to 30 wt.%, based on the amount of phosphoric acid in the solution.

[0058] Although different embodiments may be described herein in the singular, those skilled in the art will recognize that any of the embodiments described herein may be combined in whole. In fact, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments listed herein. Instead, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0059] In one aspect, the present invention embodies a composition for forming complexes with heavy metal ions in a phosphoric acid-containing stream, wherein the composition comprises an effective amount of:

[0060] at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18;

[0061] at least one dialkyldithiophosphinate compound, and

[0062] at least one surfactant.

[0063] In the same or other embodiments, the dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 is selected from the group consisting of dialkyldithiophosphoric acid having an alkyl chain length of C8 to C18 and salts of any one of the foregoing dialkyldithiophosphoric acids having an alkyl chain length of C8 to C18, and these salts are calcium salts, magnesium salts, potassium salts, sodium salts, or have the formula NR1R2R3R4 +in the form of an ammonium salt — where R1, R2, R3, and R4 are the same as or different from each other and are independently selected from hydrogen, alkyl, or aryl — and mixtures thereof. In some embodiments, the alkyl chains of the dialkyldithiophosphate compounds according to the present invention are C8 to C12 chains. Preferably, the alkyl chains of the dialkyldithiophosphate compounds according to the present invention are C8 alkyl chains.

[0064] In the same or alternative embodiments, the dialkyldithiophosphate compounds are selected from the group consisting of: any salt of bis(1,3-dimethylbutyl) dithiophosphoric acid, bis(2-ethylhexyl) dithiophosphoric acid, bis(3,7-dimethyloctyl) dithiophosphoric acid, bis(2-butyloctyl) dithiophosphoric acid; and mixtures thereof, where the salt is as previously defined. In a preferred embodiment, the dialkyldithiophosphate compounds are salts of bis(2-ethylhexyl) dithiophosphoric acid, bis(3,7-dimethyloctyl) dithiophosphoric acid, and bis(2-butyloctyl) dithiophosphoric acid; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compounds are any salt of bis(2-ethylhexyl) dithiophosphoric acid, preferably the ammonium salt of bis(2-ethylhexyl) dithiophosphoric acid.

[0065] In the same or alternative embodiments, the dialkyldithiophosphate compounds are selected from the group consisting of: bis(1,3-dimethylbutyl) dithiophosphate, bis(2-ethylhexyl) dithiophosphate, bis(3,7-dimethyloctyl) dithiophosphate, bis(2-butyloctyl) dithiophosphate; and mixtures thereof. In a preferred embodiment, the dialkyldithiophosphate compounds are bis(2-ethylhexyl) dithiophosphate, bis(3,7-dimethyloctyl) dithiophosphate, and bis(2-butyloctyl) dithiophosphate. In a more preferred embodiment, the dialkyldithiophosphate compounds are bis(2-ethylhexyl) dithiophosphate.

[0066] In the same or other embodiments, the dialkyldithiophosphite compounds are selected from the group consisting of: dialkyldithiophosphinic acid and any salt of the aforementioned dialkyldithiophosphinic acid (e.g., calcium, magnesium, potassium, sodium), where these any salts are in the form of calcium salt, magnesium salt, potassium salt, sodium salt, or an ammonium salt having the formula NR1R2R3R4 + — where R1, R2, R3, and R4 are the same as or different from each other and are independently selected from hydrogen, alkyl, or aryl — and mixtures thereof.

[0067] In the same or alternative embodiments, the dialkyldithiophosphite compounds are selected from the group consisting of: diisobutyl dithiophosphinic acid, salts of bis(2,4,4-trimethylpentyl) dithiophosphinic acid; and mixtures thereof, where the salt is as defined above. In a preferred embodiment, the dialkyldithiophosphite compound is sodium diisobutyl dithiophosphinate.

[0068] In any of the foregoing or additional embodiments, the surfactant compound may be selected from the group consisting of: sulfosuccinates, aryl sulfonates, alkaryl sulfonates, diphenyl sulfonates, olefin sulfonates, sulfonates of ethoxylated alcohols, petroleum sulfonates, sulfosuccinamates, alkoxylated surfactants, ester / amide surfactants, EO / PO block copolymers, and mixtures thereof.

[0069] In the same or alternative embodiments, the surfactant may be an alkaryl sulfonate. In a preferred embodiment, the surfactant may be an alkyl diphenyl ether disulfonate. Suitable alkyl diphenyl ether disulfonate compounds include, but are not limited to, those available from The Dow Chemical Company 8390. In the same or alternative embodiments, the surfactant may be a sulfosuccinate. A suitable sulfosuccinate may be sodium dioctyl sulfosuccinate. Suitable sodium dioctyl sulfosuccinate compounds include, but are not limited to, those available from Solvay OT-70 and 70B. In the same or alternative embodiments, the surfactant may be an alkoxylated surfactant. Suitable alkoxylated surfactants may include, but are not limited to, polyethylene glycol sorbitan monooleate (such as that available from Croda 80) and polyethylene glycol sorbitol hexaoleate (such as that available from Croda G1086).

[0070] In any of the foregoing or additional embodiments, the ratio of the sum of at least one dialkyl dithiophosphate compound having an alkyl chain length of C8 to C18 and at least one dialkyl dithiophosphinate compound to the surfactant is from 1000:1 to 5:1. In a preferred embodiment, the ratio of the sum of at least one dialkyl dithiophosphate compound having an alkyl chain length of C8 to C18 and at least one dialkyl dithiophosphinate compound to the surfactant is from 100:1 to 10:1.

[0071] In any or all embodiments, the ratio of at least one dialkyl dithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyl dithiophosphinate compound is from 1:100 to 100:1. In a preferred embodiment, the ratio of at least one dialkyl dithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyl dithiophosphinate compound is from 1:20 to 20:1. In a more preferred embodiment, the ratio of at least one dialkyl dithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyl dithiophosphinate compound is from 1:5 to 5:1.

[0072] In another aspect, the present invention specifically embodies a method for removing heavy metal ions from a phosphoric acid-containing stream, and such method includes:

[0073] adding an effective amount of a reagent to the phosphoric acid-containing stream to form heavy metal ion complexes, the reagent comprising a composition for forming complexes with heavy metal ions as disclosed and specifically embodied herein, and

[0074] separating these heavy metal ion complexes from the phosphoric acid-containing stream.

[0075] In the same or other embodiments, the method is carried out at a temperature of 0 °C to 120 °C, preferably 20 °C to 80 °C.

[0076] In any one of the foregoing or additional embodiments, the phosphoric acid-containing stream has a P2O5 concentration of 4% to 70%; typically 25% to 60% of concentrated P2O5.

[0077] In any one of the foregoing or additional embodiments of the method, the method may further include adding an effective amount of a reducing agent to the phosphoric acid-containing stream.

[0078] In the same or other embodiments, the reducing agent is selected from the group consisting of sodium hypophosphite, hydrazine, iron(II) sulfate, iron powder, and mixtures of any of the foregoing. In a preferred embodiment, the reducing agent is iron powder and sodium hypophosphite.

[0079] In any or all embodiments of the method, the reducing agent may be added before the reagent or together with the reagent.

[0080] In any one of the foregoing or additional embodiments of the method, the method may further include adding an effective amount of an adsorbent to the phosphoric acid-containing stream.

[0081] In the same or other embodiments, the adsorbent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, and mixtures of any of the foregoing.

[0082] In any one of the foregoing or additional embodiments of the method, the method may include the step of filtering the phosphoric acid-containing stream before adding the reagent.

[0083] In any one of the foregoing or additional embodiments of the method, at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant are added to the phosphoric acid-containing stream simultaneously in the form of a blend.

[0084] In any of the foregoing or additional embodiments, the heavy metal ions complexed by the reagent and removed by separation are selected from the group consisting of: chromium, cadmium, arsenic, mercury, copper, lead, and mixtures of any of the foregoing. In a preferred embodiment, the heavy metal ions removed from the phosphoric acid-containing stream include cadmium and / or arsenic and / or copper.

[0085] Examples

[0086] The following examples are provided to assist those skilled in the art in further understanding certain embodiments of the present invention. These examples are intended for illustrative purposes and should not be construed as limiting the scope of the various embodiments of the present invention as defined by the claims.

[0087] The performance of a blend of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, at least one dialkyldithiophosphinate compound, and at least one surfactant in removing heavy metals was evaluated using phosphoric acid and phosphoric acid slurries. Phosphoric acids with different P2O5 levels were obtained from an industrial phosphoric acid processing plant. The phosphoric acid slurries were produced by mixing plant gypsum solids with plant phosphoric acid. To separate the heavy metal precipitates from the acid, syringe filters or vacuum filtration were used. Subsequently, the filtrate acid was analyzed by ICP (Inductively Coupled Plasma) to determine the levels of various heavy metal elements. The general procedures for the tests and experimental examples are outlined below.

[0088] Sodium diisobutyldithiophosphinate (“Na-DTPi”), sodium diisobutyldithiophosphate (“Na-C4DTP”), and sodium dioctylsulfosuccinate (AEROSOL OT70PG – “Surfactant B”) were obtained from Solvay. The alkyl diphenyl ether disulfonate surfactant solution ( 8390 – “Surfactant A”) was purchased from Dow Chemical Company. Polyethylene glycol sorbitan hexaoleate ( G1086 – “Surfactant C”) was purchased from Croda. Dialkyldithiophosphate compounds with different chain lengths were synthesized in the Solvay laboratory. Blends were prepared by combining dialkyldithiophosphate compounds with different chain lengths, Na-DTPi (sodium diisobutyldithiophosphinate), and the surfactant.

[0089] Dialkyldithiophosphate compounds with different chain lengths were synthesized as explained in Example 1 below.

[0090] Example 1 - Preparation of Dialkyl Dithiophosphate Compounds

[0091] Example 1 - A: Synthesis of Bis(1,3 - dimethylbutyl) Dithiophosphoric Acid ("C6DTP")

[0092] To a 250 ml three-necked round-bottom flask equipped with a heating mantle, magnetic stirring, a nitrogen stream, and a vent to an alkali scrubber, 150.20 g (1.4703 moles) of 1,3-dimethylbutanol (2 mole % excess) was added. After heating to 40 °C, 80.00 g of P2S5 (0.1802 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then raised to 80 °C and maintained for 4 hours. The reaction product was cooled and filtered to yield a pale yellow low-viscosity liquid.( 31 P NMR δ 82 ppm, 86.3%).

[0093] Example 1 - B: Synthesis of Bis(2 - ethylhexyl) Dithiophosphoric Acid ("C8DTP")

[0094] To a 250 ml three-necked round-bottom flask equipped with a heating mantle, magnetic stirring, a nitrogen stream, and a vent to an alkali scrubber, 155.57 g (1.1946 moles) of 2-ethylhexanol (2 mole % excess) was added. After heating to 40 °C, 65.00 g of P2S5 (0.1464 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then raised to 80 °C and maintained for 4 hours. The reaction product was cooled and filtered to yield a pale yellow low-viscosity liquid.( 31 P NMR δ 85 ppm, 85.4%).

[0095] Example 1 - C: Synthesis of Bis(3,7 - dimethyloctyl) Dithiophosphoric Acid ("C10DTP")

[0096] To a 250 ml three-necked round-bottom flask equipped with a heating mantle, magnetic stirring, a nitrogen stream, and a vent to an alkali scrubber, 159.99 g (1.0108 moles) of 3,7-dimethyloctanol (2 mole % excess) was added. After heating to 40 °C, 80.00 g of P2S5 (0.1239 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then raised to 80 °C and maintained for 4 hours. The reaction product was cooled and filtered to yield a pale yellow low-viscosity liquid.( 31 P NMR δ 85 ppm, 86.1%).

[0097] Example 1 - D: Synthesis of Bis(2 - butyloctyl) Dithiophosphoric Acid ("C12DTP")

[0098] To a 250 ml three-necked round-bottom flask equipped with a heating mantle, magnetic stirring, a nitrogen stream, and a vent to an alkaline scrubber, 162.21 g (0.8270 moles) of 2-butyl octanol (2 mole % excess) was added. After heating to 40 °C, 45.00 g of P2S5 (0.1014 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then raised to 80 °C and maintained for 4 hours. The reaction product was cooled and filtered to yield a pale yellow low-viscosity liquid.( 31P NMR δ 85.4 ppm, 88.9%).

[0099] Example 1 - E: Synthesis of Bis(2 - hexyldecyl) Dithiophosphoric Acid ("C16DTP")

[0100] Bis(2-hexyldecyl) dithiophosphoric acid was synthesized by reacting P2S5 with 2-hexyl-1-decanol using the same method as discussed in the above examples.

[0101] Example 1 - F: Method for Neutralizing Bis(2 - ethylhexyl) Dithiophosphoric Acid with Ammonium Hydroxide to Prepare Ammonium Bis(2 - ethylhexyl) Dithiophosphate ("C8DTP - NH4")

[0102] 100.00 g (0.2823 moles) of bis(2-ethylhexyl) dithiophosphoric acid prepared as in Example 1-C above was added to a 250 ml three-necked round-bottom flask equipped with a heating mantle, magnetic stirring, and a nitrogen stream. With vigorous stirring, 18.55 g of 28% aqueous ammonium hydroxide solution (2 mole% excess) was added to the reactor. An ice bath was applied and the addition rate was controlled to maintain the reaction temperature below 40 °C. The reaction product was a light yellow, low-viscosity liquid. ( 31 P NMR δ 111 ppm, 93.1%).

[0103] Example 2 - Method for Removing Heavy Metals from Plant Phosphoric Acid #1 (Approximately 54% P2O5) at an Elevated Temperature (72 °C ) Method

[0104] 50 g of commercial phosphoric acid #1 (approx. 54% P2O5, collected from the clarifier after filtration) was transferred to a glass jar with a magnetic stir bar. The acid was heated to 72 °C in a water bath. An effective amount (as listed in Table 1) of the reagent of interest was metered into the commercial phosphoric acid #1 with stirring at 350 rpm. After stirring for 1 minute and allowing to settle for another minute, the acid was transferred to a syringe and filtered through a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. The filtrate was collected and then subjected to ICP elemental analysis.

[0105] The ICP results for the remaining Cd in the filtered phosphoric acid and the corresponding calculated percentages of removed Cd are shown in Table 1. The lower the remaining Cd and the higher the percentage of removed Cd, the better the performance of the reagent.

[0106] Table 1.

[0107]

[0108] As indicated by the results in Table 1, when using a reagent containing a dialkyldithiophosphate compound having a C8 to C18 alkyl chain length, sodium diisobutyldithiophosphite (“Na-DTPi”), and surfactant A according to the described method, particularly in the case of a dialkyldithiophosphate compound having a C8 to C12 alkyl chain, a high percentage of cadmium is removed. This data supports the synergistic effect when these compounds are used together. Plotting the data of Examples 2A-1 to 2A-9 Figure 1 further demonstrates the excellent performance and synergistic effect achieved when the reagent contains a dialkyldithiophosphate compound having a C8 to C18 alkyl chain length, sodium diisobutyldithiophosphite (“Na-DTPi”), and surfactant A.

[0109] Example 3 - Method for Removing Heavy Metals from Plant Phosphoric Acid #2 (Approximately 60% P2O5) at an Elevated Temperature (72 °C ) Method

[0110] Transfer 50 g of plant phosphoric acid #2 (approx. 60% P2O5, collected from the clarifier after filtration) to a glass jar with a magnetic stir bar. Heat the acid in a water bath to 72 °C. Meter in an effective amount (listed in Table 2) of the reagent of interest into the phosphoric acid #2 with stirring at 350 rpm. After stirring for 1 minute and allowing to settle for another minute, transfer the acid to a syringe and filter through a 0.2 μm polyvinylidene fluoride (PVDF) syringe filter. Collect the filtrate and then perform ICP elemental analysis.

[0111] The ICP results for the remaining Cd in the phosphoric acid and the corresponding calculated percentages of removed Cd are shown in Table 2. The lower the remaining Cd and the higher the percentage of removed Cd, the better the performance of the reagent.

[0112] Table 2.

[0113]

[0114]

[0115] As indicated by the results in Table 2, when using a reagent containing a dialkyldithiophosphate compound having a C8 to C18 alkyl chain length, sodium diisobutyldithiophosphite (“Na-DTPi”), and a surfactant according to the described method, particularly in the case of a dialkyldithiophosphate compound having a C8 to C12 alkyl chain, a high percentage of cadmium and / or arsenic and / or copper is removed. This data supports the synergistic effect when the reagents according to the present invention are used together (particularly in the case of surfactant A). Plotting the data of Examples 3A-1 to 3A-7 Figure 2Further demonstrates the excellent performance and synergistic effect achieved when the reagent contains a dialkyldithiophosphate compound with an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphite ("Na-DTPi"), and a surfactant.

[0116] Example 4 - Method for Measuring the Degradation of a Heavy Metal Remover by H2S Degassing from Phosphoric Acid #3 (Approximately 30% P2O5) at Approximately 72 °C Figure 3 Figure 3

[0117] Weigh 40 g of factory phosphoric acid #3 (about 30% P2O5, collected from the clarification tank after filtration) into a glass jar with a magnetic stir bar and place it in a water bath at 75 °C on an immersion stirring plate. The glass jar is equipped with a lid that has a port for capturing the headspace gas in the glass jar. While stirring at 350 rpm, a valid amount (listed in Table 3) of the reagent of interest is metered into the phosphoric acid #3. Seal the jar and stir for 5 minutes. Subsequently, remove the glass jar from the water bath and let it cool at room temperature for 5 minutes. Then, use a GASTEC H2S sampling device to pierce the seal on the jar lid and take a 100 ml headspace gas sample. Record the amount of H2S in the headspace directly from the calibrated sampling tube.

[0118] The results are shown in Table 3 and plotted in Example 5 - Method for Measuring the Degradation of a Heavy Metal Remover by H2S Degassing from Phosphoric Acid #4 (Approximately 30% P2O5) at Approximately 72°C . The lower the H2S degassing, the smaller the safety concerns for the operator close to the acid stream.

[0119] Table 3.

[0120]

[0121] As indicated by the results in Table 3, when using a reagent containing a dialkyldithiophosphate compound with an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphite ("Na-DTPi"), and a surfactant according to the described method, especially compared to a blend containing sodium diisobutyldithiophosphate ("Na-C4DTP"), sodium diisobutyldithiophosphite ("Na-DTPi"), and a surfactant, we can observe a reduction in the amount of H2S in the headspace. Therefore, the use of the reagent according to the present invention enables a significant reduction in H2S degassing while removing a high percentage of cadmium and / or arsenic and / or copper. The Example 6 - Method for Measuring the Degradation of a Heavy Metal Remover by H2S Degassing from Phosphoric Acid #5 (Approximately 57% P2O5) at Approximately 72°C Further demonstrates the excellent performance achieved in reducing H2S degassing when the reagent contains a dialkyldithiophosphate compound with an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphite ("Na-DTPi"), and a surfactant.

[0122] Example 7 - Method for Measuring the Degradation of a Heavy Metal Remover by H2S Degassing from Plant Phosphoric Acid Slurry #1 (Approximately 30% P2O5) at Approximately 72°C ​

[0123] Weigh 40 g of plant phosphoric acid #4 (approx. 30% P2O5, collected from the clarification tank after filtration) into a glass jar with a magnetic stir bar and place it in a water bath at 75 °C on an immersion stir plate. The glass jar is equipped with a lid that has a port for capturing the headspace gas in the jar. While stirring at 350 rpm, meter an effective amount (as listed in Table 4) of the reagent of interest into the phosphoric acid #4. Seal the jar and stir for 5 minutes. Subsequently, remove the glass jar from the water bath and allow it to cool at room temperature for 5 minutes. Then, use a GASTEC H2S sampling device to pierce the seal on the jar lid and take a 100 ml headspace gas sample. Record the amount of H2S in the headspace directly from the calibrated sampling tube.

[0124] The results are shown in Table 4. The lower the H2S degassing, the lower the safety concerns for the operator near the acid stream.

[0125] Table 4.

[0126]

[0127] As indicated by the results in Table 4, when using a reagent containing a dialkyldithiophosphate compound with an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphite (“Na-DTPi”), and a surfactant together according to the described method, we can observe a significant reduction in the amount of H2S in the headspace. This data supports the synergistic effect when using the reagents according to the present invention together.

[0128] ​ ​

[0129] Weigh 40 g of plant phosphoric acid #5 (approx. 57% P2O5, collected from the clarification tank after filtration) into a glass jar with a magnetic stir bar and place it in a water bath at 75 °C on an immersion stir plate. The glass jar is equipped with a lid that has a port for capturing the headspace gas in the jar. While stirring at 350 rpm, meter an effective amount (as listed in Table 5) of the reagent of interest into the phosphoric acid #5. Seal the jar and stir for 5 minutes. Subsequently, remove the glass jar from the water bath and allow it to cool at room temperature for 5 minutes. Then, use a GASTEC H2S sampling device to pierce the seal on the jar lid and take a 100 ml headspace gas sample. Record the amount of H2S in the headspace directly from the calibrated sampling tube.

[0130] The results are shown in Table 5. The lower the H2S degassing, the lower the safety concerns for the operator near the acid stream.

[0131] Table 5.

[0132]

[0133] As indicated by the results in Table 5, when using a reagent containing a dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphinate ("Na-DTPi"), and a surfactant according to the described method, especially compared to a blend containing sodium diisobutyl dithiophosphate ("Na-C4DTP"), sodium diisobutyldithiophosphinate ("Na-DTPi"), and a surfactant, we can observe a significant reduction in the amount of H2S in the headspace. Thus, the use of the reagent according to the present invention enables a significant reduction in H2S degassing while removing a high percentage of cadmium and / or arsenic and / or copper.

[0134] ​ ​

[0135] Weigh 40 g of plant phosphoric acid slurry #1 (about 30% P2O5, collected from the clarification tank after filtration) into a glass jar with a magnetic stir bar and place it in a water bath at 75 °C on an immersion stirring plate. The glass jar is equipped with a lid that has a port for capturing the headspace gas in the glass jar. While stirring at 350 rpm, a valid amount (listed in Table 6) of the reagent of interest is metered into the phosphoric acid slurry #1. Seal the jar and stir for 5 minutes. Subsequently, remove the glass jar from the water bath and let it cool at room temperature for 5 minutes. Then, use a GASTEC H2S sampling device to pierce the seal on the lid of the jar and take a 100 ml headspace gas sample. Record the amount of H2S in the headspace directly from the calibrated sampling tube.

[0136] The results are shown in Table 6. The lower the H2S degassing, the lower the safety concerns for the operator near the acid stream.

[0137] Table 6.

[0138]

[0139] As indicated by the results in Table 6, when using a reagent containing a dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, sodium diisobutyldithiophosphinate ("Na-DTPi"), and a surfactant according to the described method, especially when the dialkyldithiophosphate compound has a C8 alkyl chain, and especially compared to a blend containing sodium diisobutyl dithiophosphate ("Na-C4DTP"), sodium diisobutyldithiophosphinate ("Na-DTPi"), and a surfactant, we can observe a significant reduction in the amount of H2S in the headspace. Thus, the use of the reagent according to the present invention enables a significant reduction in H2S degassing while removing a high percentage of cadmium and / or arsenic and / or copper.

[0140] Throughout this application, various patent and / or scientific literature references have been cited. The disclosures of these publications are hereby incorporated by reference in their entirety as if written herein. However, if a term in this application conflicts or contradicts a term in the incorporated references, the term in this application shall prevail over the conflicting term in the incorporated references. Given the foregoing description and examples, one of ordinary skill in the art will be able to practice the claimed disclosure without undue experimentation.

[0141] Although typical embodiments have been set forth for the purpose of illustrating the basic novel features of the invention, the foregoing description should not be construed as limiting the scope hereof. Accordingly, various modifications, adaptations, and alternatives can be envisioned by those skilled in the art without departing from the spirit and scope of the invention described herein, and the scope of the invention should be defined by the appended claims.

Claims

1. A composition for forming complexes with heavy metal ions in a phosphoric acid-containing stream, wherein the composition comprises an effective amount of: at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18; at least one dialkyldithiophosphinate compound, and at least one surfactant.

2. The composition according to claim 1, wherein The dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 is selected from the group consisting of: dialkyldithiophosphoric acid having an alkyl chain length of C8 to C18 and salts of any one of the foregoing dialkyldithiophosphoric acids having an alkyl chain length of C8 to C18, these salts being in the form of calcium salts, magnesium salts, potassium salts, sodium salts or ammonium salts having the formula NR1R2R3R4 + —wherein R1, R2, R3, and R4 are the same or different from each other and are independently selected from hydrogen, alkyl, or aryl—and mixtures thereof.

3. The composition according to claim 1 or 2, wherein, The dialkyldithiophosphate compound has an alkyl chain of C8 to C12.

4. The composition according to any one of claims 1 to 3, wherein, The dialkyldithiophosphate compound has a C8 alkyl chain.

5. The composition according to any one of claims 2 to 4, wherein, The dialkyldithiophosphate compound is selected from the group consisting of: salts of bis(1,3-dimethylbutyl) dithiophosphoric acid, bis(2-ethylhexyl) dithiophosphoric acid, bis(3,7-dimethyloctyl) dithiophosphoric acid, bis(2-butyl octanol) dithiophosphoric acid; and mixtures thereof.

6. The composition according to claim 5, wherein, The dialkyldithiophosphate compound is a salt of bis(2-ethylhexyl) dithiophosphoric acid.

7. The composition according to claim 6, wherein, The dialkyldithiophosphate compound is ammonium bis(2-ethylhexyl) dithiophosphate.

8. The composition according to any one of claims 1 to 7, wherein, The dialkyldithiophosphite compound is selected from the group consisting of: a salt of dialkyldithiophosphinic acid and any one of the foregoing dialkyldithiophosphinic acids, and these salts are in the form of a calcium salt, a magnesium salt, a potassium salt, a sodium salt or an ammonium salt having the formula NR1R2R3R4 + —wherein R1, R2, R3, and R4 are the same as or different from each other and are independently selected from hydrogen, alkyl, or aryl—and mixtures thereof.

9. The composition according to claim 8, wherein, The dialkyldithiophosphinate compound is selected from the group consisting of: diisobutyl dithiophosphinic acid, salts of bis(2,4,4-trimethylpentyl) dithiophosphinic acid; and mixtures thereof.

10. The composition according to claim 9, wherein, The dialkyldithiophosphinate compound is sodium diisobutyl dithiophosphinate.

11. The composition according to any one of claims 1 to 10, wherein, The surfactant is selected from the group consisting of: sulfosuccinates, arylsulfonates, alkylarylsulfonates, diphenylsulfonates, olefinsulfonates, sulfonates of ethoxylated alcohols, petroleum sulfonates, sulfosuccinamates, alkoxylated surfactants, ester / amide surfactants, EO / PO block copolymers; and mixtures thereof.

12. The composition according to claim 11, wherein, The surfactant is an alkylarylsulfonate.

13. The composition according to claim 12, wherein, The surfactant is an alkyl diphenyl ether disulfonate.

14. The composition according to claim 11, wherein, The surfactant is a sulfosuccinate.

15. The composition according to claim 14, wherein, The surfactant is sodium dioctyl sulfosuccinate.

16. The composition according to claim 11, wherein, The surfactant is an alkoxylated surfactant.

17. The composition according to claim 16, wherein, The surfactant is polyethylene glycol sorbitol hexaoleate.

18. The composition according to any one of claims 1 to 17, wherein, The ratio of the sum of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 and at least one dialkyldithiophosphinate compound to the surfactant is from 1000:1 to 5:1, preferably from 100:1 to 10:

1.

19. The composition according to any one of claims 1 to 18, wherein, The ratio of at least one dialkyldithiophosphate compound having an alkyl chain length of C8 to C18 to at least one dialkyldithiophosphinate compound is from 1:100 to 100:1, preferably from 1:20 to 20:

1.

20. A method for removing heavy metal ions from a phosphoric acid-containing stream, the method comprising: adding an effective amount of a reagent to the phosphoric acid-containing stream to form heavy metal ion complexes, the reagent comprising the composition according to any one of claims 1 to 19, and separating the heavy metal ion complexes from the phosphoric acid-containing stream.

21. The method according to claim 20, wherein The method is carried out at a temperature of 0 °C to 120 °C.

22. The method according to claim 20 or claim 21, wherein, The phosphoric acid-containing stream has a concentration of 4% to 70% P2O5, preferably 25% to 60% P2O5.

23. The method according to any one of claims 20 to 22, wherein, The method further comprises adding an effective amount of a reducing agent to the phosphoric acid-containing stream, wherein the reducing agent is selected from the group consisting of sodium hypophosphite, hydrazine, iron(II) sulfate, iron powder, and mixtures of any of the foregoing.

24. The method according to any one of claims 20 to 23, wherein, The method further comprises adding an effective amount of an adsorbent to the phosphoric acid-containing stream, wherein the adsorbent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, and mixtures of any of the foregoing.

25. The method according to any one of claims 20 to 24, wherein The method further comprises filtering the phosphoric acid-containing stream prior to adding the reagent.

26. The method according to any one of claims 20 to 25, wherein, The dialkyldithiophosphate compound having an alkyl chain length of C8 to C18, the dialkyldithiophosphinate compound, and the surfactant are added to the phosphoric acid-containing stream in the form of a blend.

27. The method according to any one of claims 20 to 26, wherein The heavy metal ions removed from the phosphoric acid-containing stream are selected from the group consisting of chromium, cadmium, arsenic, mercury, copper, lead, and mixtures of any of the foregoing.

28. The method according to claim 27, wherein These removed heavy metal ions are cadmium.

29. The method according to claim 27, wherein, These removed heavy metal ions are arsenic.

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