WO2024256668A1

WO2024256668A1 - Heavy metals removal from phosphoric acid containing streams

Info

Publication number: WO2024256668A1
Application number: PCT/EP2024/066628
Authority: WO
Inventors: Ravi Rajshekar HIREMATH; Franklyn BALLENTINE; Lei Zhang; Michael Moser; Joseph Calbick
Original assignee: Cytec Industrial Materials Derby Ltd; Cytec Industries Inc
Current assignee: Cytec Industrial Materials Derby Ltd; Cytec Industries Inc
Priority date: 2023-06-15
Filing date: 2024-06-14
Publication date: 2024-12-19
Anticipated expiration: 2025-12-15
Also published as: JOP20250309A1; MX2025014055A; EP4727891A1; IL324656A; AU2024303923A1; CN121311439A

Abstract

A process for removing heavy metal ions from a phosphoric acid containing stream, may include adding a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbon atoms to the phosphoric acid containing stream to form heavy metal ion complexes; and separating the heavy metal ion complexes from the phosphoric acid containing stream.

Description

HEAVY METALS REMOVAL FROM PHOSPHORIC ACID CONTAINING STREAMS

FIELD OF THE INVENTION

[0001] The technological concept disclosed herein generally relates to purification of industrial process streams. More particularly, the concept disclosed herein relates to removing heavy metal ions from phosphoric acid containing streams.

BACKGROUND

[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 yield a 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. An overall view of the manufacture of phosphates and phosphoric acid is treated by Becker in Phosphates and Phosphoric Acids, Marcel Dekker, Inc. 1989, and by Stack in Phosphoric Acid, Part 1 and Part 2, Marcel Dekker, Inc. 1968. In the process, phosphate rocks are cleaned in the wash plant and ground in the ball mill before being fed into a series of reactors for digestion with sulfuric acid along with recycled phosphoric acid from the process. After digestion, the reaction slurry is filtered to separate phosphoric acid from undissolved rocks, the newly formed gypsum, and the gangues. The filtered, crude WPA is then sent to clarifiers and evaporators for further purification and concentration. Crude WPA can also be generated through digestion with nitric acid or hydrochloric acid.

[0004] The purified phosphoric acid is either sent out as Merchant Grade Acid (MGA) or continued to make 69 % P2O5 Super Phosphoric Acid (SPA), where it can be converted to many end products ranging from a chemical reagent, rust inhibitor, food additive, dental and orthopaedic etchant, electrolyte, flux, dispersing agent, industrial etchant, fertilizer feedstock, and component of home cleaning products. For example, crude phosphoric acid is concentrated to 54 % (P2O5) before being sent for monoammonium phosphate (MAP), diammonium phosphate (DAP), or ammonium phosphate-sulfate (APS) production. 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 as minerals in the phosphate rock and are dissolved into the phosphoric acid. Depending on the application of the phosphoric acid, the metal impurities above a certain level are considered unacceptable because of their toxicity.

[0005] For example, cadmium (Cd) is toxic and can cause multiple issues to human being’ s health. Studies show that the major exposure of Cd to nonsmoking general population is through ingestion of contaminated food. Phosphate fertilizers have been identified as an important source that introduces Cd to the soil, which can be easily absorbed by agricultural plants and accumulated into the food chain (“Cadmium in phosphate fertilizers; ecological and economical aspects”, CHEMIK 2014, 68, 10, 837-842).

[0006] Cd in phosphate fertilizer comes from phosphoric acid, the major raw material used to produce phosphate fertilizer. In fact, the majority of phosphoric acid production is used to produce fertilizer. Cd in phosphoric acid further stems from the phosphate bearing ores. Therefore, Cd can be removed either from the phosphate ore or from the phosphoric acid stream, with the latter being the focus of research in the past decades. Several categories of technologies to remove Cd from acid stream have been developed, including cocrystallization with anhydrite, precipitation with sulfide ions and organic sulfurous 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).

[0007] U.S. Patent No. 4,378,340 (1983) describes a method of removing heavy metals, particularly cadmium, from wet process phosphoric acid through partial neutralization of acids with alkali, followed by precipitation with sulfide compounds. U.S. Patent No. 5,431,895 (1995) also discloses using alkali solution and aqueous sulfide solution simultaneously with thorough mixing to remove lead and cadmium from phosphoric acid. [0008] U.S. Patent No. 4,986,970 (1991) discloses using metal salt of dithio carbonic acid- O-esters to precipitate the heavy metals, especially cadmium, from partially neutralized (pH 1.4-2) and pre-cooled (5-40 °C) phosphoric acid. Afterwards, the precipitates can be separated from the acid using methods like 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. EP0333489 Bl (1989) describes methods of separating heavy metals, especially cadmium, mercury, and lead, from phosphoric acid using a diorganyldithiophosphoric acid ester and an adsorbent, a diorganyldithiophosphorus compound and an adsorbent, a diorganyldithiophosphoric acid ester and an adsorbent and a reductant, and a thioorganophosphine reagent and a reducing agent, respectively. U.S. Patent Publication No. 2004/0179984 also discloses methods of removing heavy metals from wet process phosphoric acid by adding a mixture reagents of diorgano dithiophosphinic acid (or alkali metal or ammonia salts thereof), a first dithiophosphoric acid (or alkali metal or ammonia salts thereof) with alkyl or alkylaryl or aralkyl moieties, and optionally a second diaryl dithiophosphoric acid (or alkali metal or ammonia salts thereof).

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

[0011] However, while the various reagents and approaches discussed above may have some merits and applicability in phosphoric acid production, the high investment cost, high treatment cost, and low efficacy are limiting their wide acceptance at the plant scale (“Cadmium in phosphate fertilizers; ecological and economical aspects”, CHEMIK 2014, 68, 10, 837-842). Heavy metal contamination of food, especially cadmium that stems from use of phosphoric acid in fertilizer production, continues to be a concern to public health. The economic impact for the issue of heavy metal is substantial, and the industry is in need of a more efficient and economical technology than the existing ones. Additionally, there has been a recent regulatory push to further limit the Cd level in phosphate fertilizers (“EU MEMO-16-826 on March 17, 2016”).

[0012] Accordingly, the metal impurities have to be either completely removed or their levels in the phosphoric acid have to be significantly reduced. Moreover, another consideration in the removal of heavy metals is the off-gassing of FES to which operators near the acid stream are exposed in the processing of these streams.

SUMMARY

[0013] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0014] In some aspects, embodiments disclosed herein relate to a process for removing heavy metal ions from a phosphoric acid containing stream, the process including: adding a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbon atoms to the phosphoric acid containing stream to form heavy metal ion complexes; and separating the heavy metal ion complexes from the phosphoric acid containing stream.

[0015] In some aspects, embodiments disclosed herein relate to a process of removing heavy metal ions from a phosphoric acid containing stream, the process including: adding an ammonium salt of dialkyldithiophosphoric acid having an alkyl chain length of 8 to 12 carbon atoms to the phosphoric acid containing stream to form heavy metal ion complexes; and separating the heavy metal ion complexes from the phosphoric acid containing stream.

[0016] In some aspects, embodiments disclosed herein relate to use of a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbon atoms for removing heavy metal ions from a phosphoric acid containing stream. [0017] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

[0018] In one aspect, embodiments disclosed herein relate to purification of solutions in industrial process streams. More particularly, embodiments disclosed herein relate to processes for removing and/or recovering heavy metal ions from phosphoric acid containing streams by adding a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length of C8 to C12. The diluted solution of dialkyldithiophosphate may be added to the crude phosphoric acid, digestion slurries prior to gypsum filtration, the filtered phosphoric acid, or the concentrated phosphoric acid to precipitate heavy metal ions. The precipitated heavy metal ions may be separated by filtration, centrifugation, sedimentation, decantation, creaming, flocculation, coagulation, adsorption, flotation, and combinations thereof.

[0019] As used herein, the term “alkyl” is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof.

[0020] A dialkyldithiophosphate compound having an alkyl chain length of C8 to Cl 2, according to one or more embodiments, includes a dialkyldithiophosphoric acid having an alkyl chain length of C8 to C12 and salts of the dialkyldithiophosphoric acid. Salts of the dialkyldithiophosphoric acid may include calcium, magnesium, potassium, sodium, ammonium salt with the formula NR.1R.2R.3R4 , where Ri, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups, and combinations thereof. In some embodiments, the alkyl chain of the dialkyldithiophosphate compound is a C8 alkyl chain. In other embodiments, the salt of the dialkyldithiophosphoric acid is an ammonium salt.

[0021] According to one or more embodiments, the dialkyldithiophosphate compound is selected from the group consisting of di(2-ethylhexyl) dithiophosphate, di(3,7- dimethyloctyl) dithiophosphate, di(2-butyloctanol) dithiophosphate, and mixtures thereof. In other embodiments, the dialkyldithiophosphate compound is di(2-ethylhexyl) dithiophosphate, di(3,7-dimethyloctyl) di thiophosphate, di(2-butyloctanol) dithiophosphate, and mixtures thereof. In further embodiments, the dialkyldithiophosphate compound is di(2-ethylhexyl) dithiophosphate.

[0022] According to one or more embodiments, the dialkyldithiophosphate compound is in a diluted solution when it is added to a phosphoric acid containing stream. For example, the diluted solution may include a percent active (of dialkyldithiophosphate compound) having a lower limit of any of greater than 0, 1, 2, 5, or 10% to an upper limit of any of 10, 12, 15, or 20%. The diluted solution may include water.

[0023] According to one or more embodiments, prior to adding a dialkyldithiophosphate compound to a phosphoric acid containing stream for forming heavy metal ion complexes, the dialkyldithiophosphate may be diluted. Diluting may include 1% to 20% by weight (wt%) of the dialkyldithiophosphate compound added to water to provide a diluted solution. For example, the diluted solution may include a percent active having a lower limit of any of greater than 0, 1, 2, 5, or 10% to an upper limit of any of 10, 12, 15, or 20%. In other embodiments, diluting includes 10% of the dialkyl dithiophosphate compound in the diluted solution. It is also envisioned that the dialkyldithiophosphate compound is diluted inline with its addition to a phosphoric acid containing stream.

[0024] According to one or more embodiments, the diluted solution of dialkyldithiophosphate compound may be added to a phosphoric acid containing stream. The phosphoric acid containing stream may include phosphoric acid solutions or solutions containing phosphoric acid. Embodiments of the current disclosure include any acidic solution containing crude phosphoric acid, digestion slurries of phosphoric acid, filtered phosphoric acid, and/or concentrated phosphoric acid. Phosphoric acid containing streams may be obtained from industrial phosphoric acid production plant streams.

[0025] As used herein with reference to the present invention, the term “heavy metal” or “metal” shall refer to those elements of the periodic table having a density of more than 5 g/cm³ and an oxidation state higher than 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 one or more embodiments, cadmium ions are removed from phosphoric acid containing streams. In other embodiments, arsenic ions are removed from phosphoric acid containing streams.

[0026] The concept of “heavy metal complex” refers to compounds formed by reacting heavy metal ions with chelating agents. Heavy metal complexes may be solid, waxy, or oily in the phosphoric acid solutions. The heavy metal ion complexes may precipitate, float, or suspend in the phosphoric acid solutions.

[0027] A process, according to one or more embodiments, for removing heavy metal ions from a phosphoric acid containing stream includes adding a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbons to the phosphoric acid containing stream to form heavy metal ion complexes. The process then includes separating the heavy metal ion complexes from the phosphoric acid containing stream. Separating the heavy metal ion complexes may include filtration, precipitation, centrifugation, sedimentation, decantation, creaming, flocculation, coagulation, adsorption, flotation, and combinations thereof.

[0028] In one or more embodiments, treatment of a phosphoric acid containing stream with the diluted solution of dialkyldithiophosphate compound, followed by a separation removing one or more heavy metals ion complexes may result in an acid stream having a heavy metal percent reduction of at least 25 percent. For example, the heavy metal reduction of one or more of the heavy metal ions referenced above may be at least 25, 50, 75, 90, 95, 98, 99, 99.5, 99.8 or 99.9 percent. Such heavy metal content reduction may result in a heavy metal content of one or more of cadmium, chromium, arsenic, nickel, mercury, zinc, manganese, titanium, copper or lead in the acid stream of less than 25 ppm, 10 ppm, 5 ppm, 1 ppm, 0.5 ppm, or 0.1 ppm, in one or more embodiments.

[0029] The dosage of the dialkyldithiophosphate compound for forming heavy metal ion complexes will depend on the amount of heavy metal impurities present in the ore and/or phosphoric acid containing streams. The greater number of heavy metals present and the higher their concentrations, the greater will be the overall dosage of the dialkyldithiophosphate compound. Those skilled in the art will be able to readily determine and establish the optimum dosage of the dialkyldithiophosphate compound having the alkyl chain length of C8 to C12. In one or more embodiments, the dosage is in the range of from 0.01 to 50 kilogram (kg) of dialkyldithiophosphate compound per ton of P2O5 of the phosphoric acid solution, based on the type of heavy metal ions to be removed. In other embodiments, the dosage is from 0.1 kg to 10 kg dialkyldithiophosphate compound per ton of P2O5. For example, the dosage may have a lower limit of any of 0.01, 0.1, 1, 1.5, 2, or 5 kg of dialkyldithiophosphate compound per ton of P2O5 and an upper limit of any of 5, 8, 10, 20, 25, 30, or 50 kg of dialkyldithiophosphate compound per ton of P2O5. It will be understood by those ordinarily skilled in the art that any of the recited dosages (except the lowest dosage point) can also be recited as “less than” a particular dosage, e.g., less than 50 kg; or that any of the recited dosages (except the highest dosage point) can also be recited as “greater than” a particular dosage, e.g., greater than 0.10 kg.

[0030] According to one or more embodiments, the phosphoric acid containing stream includes phosphoric acid of a P2O5 concentration from 4 percent by weight (wt. %) to 70 wt. %. In other embodiments, the phosphoric acid containing stream includes from 20 wt. % to 70 wt. %. Specific concentrations of P2O5 may include 20 wt%, 25 wt. %, 28 wt. %, 30 wt. %, 42 wt. %, 44 wt. %, 52 wt. %, 54wt. %, 57 wt. %, 60 wt. %, 69 wt% and combinations thereof.

[0031] In one or more embodiments, the process of adding a diluted solution of a dialkyldithiophosphate compound to a phosphoric acid containing stream for forming heavy metal ion complexes includes adding the diluted solution of dialkyldithiophosphate compound to the crude phosphoric acid. The dialkyldithiophosphate compound may alternatively be added to the digestion slurries prior to gypsum filtration, to the filtered phosphoric acid, or to the concentrated phosphoric acid to complex the heavy metal ions.

[0032] The process for forming heavy metal ion complexes in a phosphoric acid containing stream by adding a diluted solution of a dialkyldithiophoshate compound may be performed over a wide temperature range. According to one or more embodiments, the process is performed at a temperature from 0 °C to 120 °C. In other embodiments, the temperature is from 20 °C to 80 °C. [0033] According to one or more embodiments, adding a diluted solution of dialkyldithiophosphate compound to a phosphoric acid containing stream to form heavy metal ion complexes includes a treatment time. Treatment times may be from a few seconds (z.e., 5 to 10 seconds) to 240 minutes. In those instances where the dialkyldithiophosphate complexes the heavy metal ions very rapidly, the treatment times may be from about 5 seconds to 15 minutes.

[0034] According to one or more embodiments, a process for removing heavy metal ions from a phosphoric acid containing stream by adding a diluted solution of a dialkyldithiophosphate compound further includes adding a reducing agent and/or an adsorbing agent. The reducing agent and/or the adsorbing agent may enhance the activity of the diluted solution of the dialkyldithiophosphate compound. In one or more embodiments, the reducing and/or adsorbing agent is added to the phosphoric acid containing streams all in one stage. In other embodiments, the reducing and/or adsorbing agent is added in several stages. In further embodiments, the reducing and/or adsorbing agent is added together as a blend with the dialkyldithiophosphate compound. The reducing agent and/or adsorbing agent may be added separately or sequentially, in any order, with the dialkyldithiophosphate compound.

[0035] Adding a diluted solution of a dialkyldithiophosphate compound to a phosphoric acid containing stream for forming heavy metal ion complexes may include further adding a reducing agent. The reducing agent may include iron powder, zinc, red phosphorus, iron (II) sulfate, sodium hypophosphite, hydrazine, hydroxymethane sulfonate, and mixtures thereof. In one or more embodiments, the reducing agent includes iron powder and sodium hypophosphite. The reducing agent may be added in an amount from 0.01 kg to 50 kg of reducing agent per ton of P2O5. As known to those skilled in the art, the amount of reagent agent may be based on the type and quantity of the oxidants in the phosphoric acid containing stream. In some embodiments, the amount of reducing agent is from 0.1 kg to 25 kg of reducing agent per ton of P2O5 of the phosphoric acid containing stream. [0036] According to one or more embodiments, adding a diluted solution of a dialkyldithiophosphate compound to a phosphoric acid containing stream for forming heavy metal ion complexes includes further adding an adsorbing agent. Adsorbing agents may include activated charcoal/carbon, carbon black, ground lignite, adsorbents containing silicate (e.g., synthetic silicic acids, zeolites, calcium silicate, bentonite, perlite, diatomaceous earth, and fluorosilicate), calcium sulfate (including gypsum, hemihydrate, and anhydride), and mixtures thereof. In one or more embodiments, the adsorbing agent is added in an amount from 0.05 wt. % to 50 wt. %. In other embodiments, the adsorbing agent is added in an amount from 0.1 wt. % to 30 wt. %, based on the quantity of phosphoric acid in the solution.

[0037] According to one or more embodiments, a process for removing heavy metal ions from a phosphoric acid containing stream includes separating heavy metal ion complexes from the phosphoric acid containing stream. Separating the heavy metal ion complexes may include filtration, centrifugation, precipitation, sedimentation, decantation, creaming, coagulation, flocculation, adsorption, flotation, and combinations thereof.

[0038] Embodiments of the present disclosure may provide at least one of the following advantages. In one aspect, the process of removing heavy metal ions from a phosphoric acid stream using a diluted solution of dialkyldithiophosphate having an alkyl chain of C8 to C12 has a significant improvement in removal of the heavy metal ions from the acid, as compared to other processes known in the art.

[0039] In a further aspect, the process of removing heavy metal ions from a phosphoric acid containing stream using a diluted solution of dialkyldithiophosphate having an alkyl chain of C8 to C12 has a significant improvement in handling when the salt of the dialkyldithiophosphoric acid is ammonium. The ammonium salt is less viscous than dialkyldithiophosphoric acids with salts of potassium or sodium. The reduction in viscosity results in the ammonium salt of the dialkyldithiophosphoric acid compound being easier to handle and to pump into the phosphoric acid containing streams. These advantages are shown in the following examples. EXAMPLES

[0040] The performances of the diluted C8 dialkyldithiophosphate to remove heavy metals are evaluated with phosphoric acid and phosphoric acid slurries. The phosphoric acids with different P2O5 levels are obtained from plants. To separate the heavy metal precipitates from the acid, either a syringe filter or a vacuum filtration is used. Afterwards, the filtrate acids are analyzed with ICP (Inductively Coupled Plasma) to determine the level of various heavy metal elements. The general procedure for the test and experimental examples are outlined below. The dialkyldithiophosphates were synthesized as described below. The dilution was prepared by combining the salt of the dithiophosphate, and water at the indicated ratios.

[0041 ] Synthesis of di(2-ethylhexyl) dithiophosphoric acid (“C8DTP”)

[0042] To a 250 ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 155.57 g (1.1946 moles) of 2-ethylhexanol (2mole% excess). 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 increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (3 IP NMR 5 85ppm, 85.4%).

[0043 ] Synthesis of di(3,7-dimethyloctyl) dithiophosphoric acid (“C10DTP”)

[0044] To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 159.99 g (1.0108 moles) of 3,7-dimethyloctanol (2mole% excess). 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 increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (3 IP NMR 5 85ppm, 86.1%). [0045] Synthesis of di(2 -butyloctyl) dithiophosphoric acid (“C12DTP”)

[0046] To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 162.21 g (0.8270 moles) of 2-butyloctanol (2mole% excess). 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 increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (3 IP NMR 5 85.4ppm, 88.9%).

[0047] Neutralization process of di(2-ethylhexyl) dithiophosphoric acid with ammonium hydroxide for preparing ammonium di(2-ethylhexyl) dithiophosphate (“C8DTP-NH4”)

[0048] To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, and nitrogen flow was added 100.00g g (0.2823 moles) of di(2-ethylhexyl) dithiophosphoric acid, as prepared in Example 1-C above. With vigorous agitation, 18.55 g of 28% aqueous ammonium hydroxide (2mole% excess) was added to the reactor. An ice bath was raised, and the addition rate was controlled to maintain the reaction temperature below 40°C. The reaction product was a light yellow, low viscosity liquid. (31P NMR 5 l l lppm, 93.1%).

[0049] Neutralization process of di(2-ethylhexyl) dithiophosphoric acid with sodium hydroxide for preparing sodium di(2-ethylhexyl) dithiophosphate (“C8DTP-Na”)

[0050] In a 2-oz jar add dropwise under vigorous agitation 2.56g (32 mmol) 50% aqueous NaOH solution to 10.00g (28 mmol) of di(2-ethylhexyl)dithiophosphoric acid. The reaction product formed a clear liquid light yellow liquid that solidified on cooling to room temperature.

[0051] Neutralization process of di(2-ethylhexyl) dithiophosphoric acid with potassium hydroxide for preparing potassium di(2-ethylhexyl) dithiophosphate (“C8DTP-K”)

[0052] In a 2-oz jar add dropwise under vigorous agitation 3.59g (32 mmol) 50% aqueous KOH solution to 10.00g (28 mmol) of di(2-ethylhexyl)dithiophosphoric acid. The reaction product formed a clear nearly colorless liquid that solidified on cooling to room temperature.

[0053 ] Example 1 - Process for removing heavy metals from plant phosphoric acids from plant#l (~ 57% P2O5) at elevated temperature (72°C)

[0054] 50 g of plant phosphoric acid from plant#l (~ 57 % P2O5, collected from the clarification tank after filtration) is transferred into a glass jar with a magnetic stir bar. The acid is heated to 72 °C in a water bath. An effective amount (as listed in Table 1) of a reagent of interest is dosed into acid under agitation at 350 rpm. After agitation for 1 minute, the acid is transferred into a syringe and filtered with a 0.2 pm polyvinylidene difluoride (PVDF) syringe filter. The filtrate is collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 1. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 1 it can be seen that C8DTP NEU Salt (diluted to 10 wt% activity) was able to reduce significantly more cadmium from the acid #1 compared to the neat C8DTP NH4 Salt, even with the same dosage of active C8DTP.

Table 1.

[0055] Example 2 - Process for removing heavy metals from plant phosphoric acids from plant #2 (~ 28 % P2O5) at elevated temperature (72°C).

[0056] 50 g of plant phosphoric acid from plant #2 (~ 28 % P2O5, collected from the clarification tank after filtration) is transferred into a glass jar with a magnetic stir bar. The acid is heated to 72 °C in a water bath. An effective amount (as listed in Table 2) of a reagent of interest is dosed into acid under agitation at 350 rpm. After agitation for 1 minute, the acid is transferred into a syringe and filtered with a 0.2 pm polyvinylidene difluoride (PVDF) syringe filter. The filtrate is collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 2. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 2 it can be seen that C8DTP NEU Salt (diluted to 10 wt%) was able to reduce significantly more cadmium from the acid #2 compared to the neat C8DTP NEU Salt.

Table 2:

[0057] Example 3 - Process for removing heavy metals from plant phosphoric acids from plant #1 (~ 57 % P2O5) at elevated temperature (72°C)

[0058] 50 g of plant phosphoric acid from plant #1 (~ 57 % P2O5, collected from the clarification tank after filtration) is transferred into a glass jar with a magnetic stir bar. The acid is heated to 72 °C in a water bath. An effective amount (as listed in Table 3) of a reagent of interest is dosed into acid under agitation at 350 rpm. After agitation for 15 minutes, the acid is transferred into a syringe and filtered with a 0.2 pm polyvinylidene difluoride (PVDF) syringe filter. The filtrate is collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 3. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 3 it can be seen that diluted C8DTP Salts (NF , K and Na) were able to reduce significantly more cadmium from the acid#l compared to the neat C8DTP of similar salts. Additionally the diluted solutions of C10DTP acid and C12DTP acid were also able to reduce the cadmium levels significantly compared to the neat C10DTP and C12DTP acids at similar dosages.

Table 3:

[0059] Example 4 - Process for removing heavy metals from plant phosphoric acids from plant #1 (~ 57 % P2O5) at elevated temperature (72°C)

[0060] 50 g of plant phosphoric acid from plant #1 (~ 57 % P2O5, collected from the clarification tank after filtration) is transferred into a glass jar with a magnetic stir bar. The acid is heated to 72 °C in a water bath. An effective amount (as listed in Table 4) of a reagent of interest is dosed into acid under agitation at 350 rpm. After agitation for 15 minutes, the acid is transferred into a syringe and filtered with a 0.2 pm polyvinylidene difluoride (PVDF) syringe filter. The filtrate is collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 4. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 4 it can be seen that C8DTP NEU Salts with activity from 1 wt% to 20 wt% has better cadmium reduction potential from the acid#l compared to the other activity ranges of C8DTP NEU Salt.

Table 4:

[0061 ] Example 5 - Process for removing heavy metals from plant phosphoric acids from plant #1 (~ 57 % P2O5) at elevated temperature (72°C)

[0062] 50 g of plant phosphoric acid from plant #1 (~ 57 % P2O5, collected from the clarification tank after filtration) is transferred into a glass jar with a magnetic stir bar. The acid is heated to 72 °C in a water bath. An effective amount (as listed in Table 5) of a reagent of interest is dosed into acid under agitation at 350 rpm. After agitation for 15 minutes, the acid is transferred into a syringe and filtered with a 0.2 pm polyvinylidene difluoride (PVDF) syringe filter. The filtrate is collected and then submitted for ICP elemental analysis. The ICP results of the leftover Cd in phosphoric acid and the corresponding calculated percentage of Cd removed are shown in Table 5. The lower the leftover Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 5 it can be seen that diluted C8DTP NF Salts outperform the neat C8DTP NH4 Salt by several times. In one example the acid treated with 1 kg/T P2O5 of Diluted C8DTP NF Salt (10 wt% Active) showed 92.52% reduction in cadmium compared 61.95% cadmium reduction with 6 kg/T P2O5 dose of neat C8DTP NF Salt.

Table 5:

[0063 ] Example 6 - Process for measuring H2S off-gassing from the degradation of the heavy metals removal agents from phosphoric acid from plant # 1 (~ 57 % P2O5) at ~

72°C

[0064] 40 g of phosphoric acid from plant # 1 (~ 57 % P2O5) was weighed into a glass jar with a magnetic stir bar and placed in a water bath at 75 °C on a submersible stirred plate. The glass jar was fitted with a lid having a port for capturing the headspace gasses in the glass jar. An effective amount (as listed in Table 6) of a reagent of interest is dosed into the acid while stirring at 350 rpm. The jar was sealed and agitated for 5 minutes. Subsequently, the glass jar was removed from the water bath and allowed to cool for 5 minutes at room temperature. Afterwards the seal on the jar lid was pierced using a GASTEC H2S sampling device and 100 ml of the headspace gasses were sampled. The amount of H2S in the headspace was recorded directly from the calibrated sampling tubes. The results are shown in Table 6. The lower the H2S off-gassing, the less the safety concerns to operators next to the acid stream.

Table 6:

[0065] Example 7 - Use of NH4 counterion to make a neutralized C8DTP reagent that is easy to apply and handle

[0066] Neutralized salts of the C8-dithiophosphoric acid are more stable than the acid. Neutralizing the C8-dithiophosphoric acid will also reduce the unpleasant odor significantly. Sodium salts of DTP are used in several applications including heavy metal removal. However, these DTP’s are limited to C4 alkyl chains only. While the C8DTP can be neutralized and form Na, K and NH4 salts, only C8DTP NH4 salt can be used in a practical way.

[0067] For a reagent to be applied in a phosphoric acid plant for heavy metal reduction application, the primary aspect is the handling of the reagent. Pumps are generally used to apply the measured quantities of reagent into the phosphoric acid streams. Reagents with higher viscosities are considered difficult to handle and pump and vice versa. The NH4 salt of C8DTP in its undiluted form is a liquid at temperatures of 20 °C with viscosity of 165 centipoise. The K salt of the C8DTP in its undiluted form is a thick viscous liquid and the viscosity of this reagent at 20 °C is 5187 centipoise. With a melting point of 77 °C, the Na salt of C8DTP is a waxy solid at room temperature with a measured viscosity of 3.66 x 10⁶ centipoise at 20 °C. Based on the data discussed above, it is evident that neutralizing the C8DTP with NH4 results in a unique reagent that is easy to handle and pump.

Table 7:

[0068] While typical embodiments have been set forth for the purpose of illustrating the fundamental novel features of the present invention, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one 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 process for removing heavy metal ions from a phosphoric acid containing stream, the process comprising: adding a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbon atoms to the phosphoric acid containing stream to form heavy metal ion complexes; and separating the heavy metal ion complexes from the phosphoric acid containing stream.

2. The process of claim 1, further comprising diluting the dialkyldithiophosphate compound in water at 1 to 20% dialkyldithiophosphate to form the diluted solution.

3. The process of any of the above claims, 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 thereof.

4. The process of any of the above claims, wherein the heavy metal ions removed from the phosphoric acid containing stream are cadmium.

5. The process of any of the above claims, wherein the alkyl chain is C8.

6. The process of any of the above claims, wherein the dialkyldithiophosphate compound is selected from the group consisting of dialkyldithiophosphoric acid and salts of the dialkyldithiophosphoric acid in the form of calcium, magnesium, potassium, sodium, or ammonium salt.

7. The process of claim 6, wherein the salt of the dialkyldithiophosphoric acid is ammonium salt.

8. The process of any of the above claims, wherein the adding comprises adding the dialkyldithiophosphate compound at a dosage ranging from 0.1 kg to 50 kg of dialkyldithiophosphate compound per ton of P2O5 present in the phosphoric acid containing stream.

9. The process of any of the above claims, wherein the phosphoric acid containing stream has a concentration from 4 wt% to 70 wt% P2O5.

10. The process of any of the above claims, wherein the phosphoric acid containing stream has a concentration from 20 wt% to 70 wt% P2O5.

11. The process of any of the above claims, wherein the process is performed at a temperature from 0 °C to 120 °C.

12. The process of any of the above claims, wherein the process further comprises adding 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 thereof.

13. The process of any of the above claims, wherein the process further comprises adding an adsorbing agent to the phosphoric acid containing stream, wherein the adsorbing agent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, and mixtures thereof.

14. The process of any of the above claims, wherein the process further comprises filtering the phosphoric acid containing stream prior to adding the diluted solution of the dialkyldithiophosphate compound.

15. A process of removing heavy metal ions from a phosphoric acid containing stream, the process comprising: adding an ammonium salt of dialkyldithiophosphoric acid having an alkyl chain length of 8 to 12 carbon atoms to the phosphoric acid containing stream to form heavy metal ion complexes; and separating the heavy metal ion complexes from the phosphoric acid containing stream.

16. The process of claim 15, 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 thereof.

17. The process of claims 15 or 16, wherein the heavy metal ions removed from the phosphoric acid containing stream are cadmium.

18. The process of any one of claims 15 to 17, wherein the alkyl chain is C8.

19. The process of any of claims 15 to 18, wherein the adding comprises adding the dialkyldithiophosphoric acid with the ammonium salt at a dosage ranging from 0.1 kg to 30 kg of dialkyldithiophosphoric acid per ton of P2O5 present in the phosphoric acid containing stream.

20. The process of any one of claims 15 to 19, wherein the phosphoric acid containing stream has a concentration from 4 wt% to 70 wt% P2O5.

21. Use of a diluted solution of a dialkyldithiophosphate compound having an alkyl chain length ranging from 8 to 12 carbon atoms for removing heavy metal ions from a phosphoric acid containing stream.

22. Use of a diluted solution of claim 21, wherein the heavy metal ions removed from the phosphoric acid containing stream are cadmium.