Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/18—Phosphoric acid
  • C01B25/22—Preparation by reacting phosphate-containing material with an acid, e.g. wet process
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
  • B01J20/045—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium containing sulfur, e.g. sulfates, thiosulfates, gypsum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
  • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
  • B01J20/28016—Particle form
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/18—Phosphoric acid
  • C01B25/234—Purification; Stabilisation; Concentration
  • C01B25/237—Selective elimination of impurities
  • C01B25/238—Cationic impurities, e.g. arsenic compounds

Definitions

• the present invention generally relates to purification in industrial process streams. More particularly, the present invention relates to removing heavy metal ions from phosphoric acid process streams.
• metal impurities in the form of heavy metal ions such as cadmium, copper, arsenic, lead, and mercury, are present as minerals in the phosphate rock and are dissolved into the phosphoric acid.
• the metal impurities are considered unacceptable above a certain level, depending on the application of the phosphoric acid, because of their toxicity. Accordingly, the metal impurities have to be either completely removed or their levels have to be significantly reduced.
• 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.
• U.S. Patent No. 4,378,340 (1983) discloses 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.
• 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 complexes can be separated from the acid using methods like flotation or filtration.
• 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).
• heavy metal chelating agents comprising a plurality of sulfur groups are effective in reagents useful for removing heavy metal ions from aqueous solutions containing phosphoric acid.
• heavy metal chelating agents can include 2,5-Dimercapto-l,3,4-thiadiazole, 2,3-Dimercapto-l-propanol, a thiocontaining polymer, derivatives thereof, and mixtures thereof. Accordingly, the processes for removing heavy metal ions according to various embodiments of the present invention as described herein are applicable for use with the various stages of wet process phosphoric acid production.
• FIG. 2 is a graph illustrating the results of Examples 1C-1, IK-1, IK-3, IK-4 & IK-5, showing the percentage of Cd removed from the plant weak phosphoric acid at ⁇ 75 °C with dosages of heavy metal chelating agent DTG at 0 to 4 kg/T P2O5 level and a subsequent dosage of sodium diisobutyl dithiophosphinate (“Na- DTPi”) at 0.5 kg/T P2O5 level;
• FIG. 3 is a graph illustrating the results of Examples 2A & 2B-1 to 2B-4, showing the percentage of heavy metal removed from the digestion slurry of phosphoric acid at ⁇ 80 °C with dosages of heavy metal chelating agent 2,5-dimercapto-l,3,4- thiadiazole dipotassium salt (“DMTD-2K”) at 0 to 9 kg/T P2O5 level;
• FIG. 4 is a graph illustrating the results of Examples 3A & 3B-1 to 3B-4, showing the percentage of heavy metal removed from the concentrated plant phosphoric acid at ⁇ 70 °C with dosages of heavy metal chelating agent DMTD-2K at 0 to 4 kg/T P2O5 level;
• FIG. 5 is a graph illustrating the results of Examples 3E-1, 3C-2, & 3F-1, showing the percentage of Cd removed from the concentrated plant phosphoric acid at ⁇ 70 °C with various dosages of heavy metal chelating agent DTG and Na-DTPi; and FIG.
• FIG. 6 is a graph illustrating the results of Examples 4A & 4B-1 to 4B-4, showing the percentage of heavy metal removed from the concentrated plant phosphoric acid at ⁇ 70 °C with dosages of heavy metal chelating agent comprising polyamine/alkyl glycidyl ether/(glycidyloxypropy)trimethoxysilane/(mercaptopropyl)trimethoxysilane (“Pl”) at 0 to 10 kg/T P2O5 level.
• heavy metal chelating agent comprising polyamine/alkyl glycidyl ether/(glycidyloxypropy)trimethoxysilane/(mercaptopropyl)trimethoxysilane (“Pl”) at 0 to 10 kg/T P2O5 level.
• the present invention generally relates to purification of solutions in industrial process streams. More particularly, the inventors describe herein for the first time processes for removing and/or recovering heavy metal ions from solutions containing phosphoric acid by adding an effective amount of a reagent comprising a heavy metal chelating agent having a plurality of sulfur groups to the solution.
• heavy metal or “metal” shall refer to those elements of the periodic table having a density of more than 5 g/cm 3 and an oxidation state higher than 0, (i.e., heavy metal ions).
• heavy metal ions include, for example, one or more of copper (Cu), cadmium (Cd), nickel (Ni), mercury (Hg), zinc (Zn), arsenic (As), manganese (Mn) and lead (Pb).
• cadmium ions and arsenic ions can be removed from solutions containing phosphoric acid.
• phosphoric acid solutions or “solutions containing phosphoric acid,” in the context of the invention includes any aqueous acidic solution or mixture containing crude phosphoric acid, digestion slurries, filtered acid, and/or concentrated acid.
• hydrocarbyl is a generic term encompassing aliphatic, alicyclic and aromatic groups having an all-carbon backbone and consisting of carbon and hydrogen atoms.
• one or more of the carbon atoms making up the carbon backbone may be replaced or interrupted by a specified atom or group of atoms, such as by one or more heteroatom of N, O, and/or S.
• hydrocarbyl groups include alkyl, cycloalkyl, cycloalkenyl, carbocyclic aryl, alkenyl, alkynyl, alkylcycloalkyl, cycloalkylalkyl, cycloalkenylalkyl, and carbocyclic aralkyl, aralkenyl and aralkynyl groups.
• Recitation or discussion of such hydrocarbyl groups includes their substituted or unsubstituted forms. This concept is sometimes phrased as “optionally substituted.” When substituted, it can be by one or more substituents as defined herein elsewhere.
• the examples and preferences expressed below also apply to each of the hydrocarbyl substituent groups or hydrocarbyl-containing substituent groups referred to in the various definitions of substituents for compounds of the formulas described herein unless the context indicates otherwise.
• Preferred non-aromatic hydrocarbyl groups are saturated groups such as alkyl and cycloalkyl groups.
• the hydrocarbyl groups can have up to fifty carbon atoms, unless the context requires otherwise.
• Hydrocarbyl groups with from 1 to 30 carbon atoms are preferred.
• C1-20 hydrocarbyl groups such as C1-12 hydrocarbyl groups (e.g., C1-6 hydrocarbyl groups or Ci-4 hydrocarbyl groups), specific examples being any individual value or combination of values selected from Ci through C30 hydrocarbyl groups.
• alkyl is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof. Preferred alkyl groups are those of C30 or below. Lower alkyl refers to alkyl groups of from 1 to 8 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s- and t-butyl, pentyl, hexyl, octyl and the like. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups having from 3 to 30 carbon atoms, preferably from 3 to 8 carbon atoms as well as polycyclic hydrocarbons having 7 to 10 carbon atoms.
• aryl refers to cyclic (mono or multi-cyclic), aromatic hydrocarbons that do not contain heteroatoms in the ring portion.
• aryl groups contain from 6 to 14 carbons in the ring portions of the groups.
• aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl, anthracenyl, and naphthyl groups.
• Aryl groups 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 groups, which can be substituted with carbon or non-carbon groups such as those known to persons of skill in the art.
• Aryl groups of C6-C12 are preferred.
• aralkyl as used herein is a broad term and is used in its ordinary sense, including, without limitation, to refer to an alkyl having at least one alkyl hydrogen atom replaced with an aryl moiety, such as benzyl, -CH l or 2-naphthyl), - (CH2)2phenyl, -(CH2)3phenyl, -CH(phenyl)2, and the like. Particularly preferred are C7-20 aralkyl groups. In any or all embodiments, one or both alkyl and aryl may be optionally substituted with one or more ubstituents as described herein elsewhere.
• Substituted hydrocarbyl groups e.g., alkyl, aryl, aralkyl, cycloalkyl, alkoxy, etc., refer to the specific substituent wherein up to three H atoms in each residue are replaced with alkyl, halogen, haloalkyl, hydroxy, alkoxy, carboxy, carboalkoxy (also referred to as alkoxycarbonyl), carboxamido (also referred to as alkylaminocarbonyl), cyano, carbonyl, nitro, amino, alkylamino, dialkylamino, mercapto, alkylthio, sulfoxide, sulfone, acylamino, amidino, phenyl, benzyl, halobenzyl, heteroaryl, phenoxy, benzyloxy, heteroaryloxy, benzoyl, halobenzoyl, or lower alkylhydroxy.
• 2,5-Dimercapto-l,3,4-thiadiazole, 2,3- Dimercapto-1 -propanol, a thio-containing polymer, derivatives thereof, and mixtures thereof can be added to either the crude acid or digestion slurries prior to gypsum filtration, or to the filtered acid or the concentrated acid to complex the heavy metals. Afterwards, heavy metal complexes can be separated from the acid or slurry. In any or all embodiments, the methods of separation include, but are not limited to, filtration, centrifugation, sedimentation, creaming, flocculation, adsorption, and/or flotation.
• 2,5-Dimercapto-l,3,4-thiadiazole, 2,3- Dimercapto-1 -propanol, a thio-containing polymer, derivatives thereof; and mixtures thereof can be added to the solution containing phosphoric acid all in one stage or added in several stages.
• 2,5- Dimercapto-l,3,4-thiadiazole, 2,3 -Dimercapto- 1 -propanol, a thio-containing polymer, derivatives thereof; and mixtures thereof can be added as a blend, or separately in any order such as concurrently together or sequentially.
• Treatment times in various embodiments can be from a few seconds (z.e., 5 to 10 seconds) to 24 hours. In those instances where the reagent complexes the heavy metals very rapidly, the preferred treatment times are from about 5 seconds to 3 hours. Most typically, the treatment times are from 10 seconds to 60 seconds or 120 seconds.
• the dosage of the reagent for complexing heavy metals and removal efficiency for the various heavy metals will depend on the amount of heavy metal impurities present in the ore and/or solution containing phosphoric acid. Generally, the greater number of heavy metals present and the higher their concentrations, the greater will be the overall dosage of the reagent. Those skilled in the art will be able to readily determine and establish the optimum dosage of 2,5-Dimercapto- 1,3,4-thiadiazole, 2,3-Dimercapto-l-propanol, a thio-containing polymer, derivatives thereof; and mixtures thereof required using no more than routine experimentation. Generally, the dosages may be in the range of from 0.01 to 50 kg (e.g..).
• the dosages can be from 0.1 kg to 10 kg (e.g., 0.10, 0.15, 0.20, 0.25, 0.30, et seq.
• any of the recited dosages 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.
• the solution containing phosphoric acid has a P2O5 concentration from 1 wt. % to 70 wt. %. In some embodiments, the solution containing phosphoric acid has a P2O5 concentration from 20 wt. % to 70 wt. %. Specific concentrations of P2O5 contemplated for use with the invention include 24 wt. %, 25 wt. %, 26 wt.%, 28 wt. %, 30 wt. %, 42 wt. %, 48 wt. %, 52 wt. %, 56 wt. %, 60 wt. % and 69 wt. %.
• compositions and processes described herewith as the present invention can be used over a wide temperature range.
• the processes according to the invention can be performed at a temperature from 0 °C to 120 °C.
• the temperature is in the range from 10 °C to 80 °C.
• the process can further include adding an effective amount of a reducing agent and/or an adsorbent agent to the solution containing phosphoric acid. Such agents are known to be useful in the field.
• R’ is independently chosen from a C1-C4 alkyl group, and n is the number of repeating units of the polymer backbone, and is an integer from 2 to 1000. In some embodiments, n is 2 to 100.
• the polymer backbone comprises a backbone selected from the group consisting of: polyamine, polysaccharide, polyvinylpyrrolidone, polyglutamicacid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin and mixtures of any of the foregoing; and co-polymers of any of the foregoing.
• a process for removing heavy metal ions from a phosphoric acid mixture comprising adding to the phosphoric acid mixture an effective amount of a reagent comprising a heavy metal chelating agent comprising a plurality of sulfur groups as substituents wherein the reagent further comprises an effective amount of an organothiophosphorus compound.
• the organothiophosphorus compound is selected from the group consisting of: organodithiophosphinic acid, organodithiophosphonic acid, organodithiophosphoric acid, organomonothiophosphinic acid, organomonothiophosphonic acid, organomonothiophosphoric acid, their corresponding salts in the form of sodium, ammonium, or potassium, and mixtures thereof.
• the organothiophosphorus compound comprises organodithiophosphinic acid or corresponding salts thereof; or organodithiophosphoric acid or corresponding salts thereof.
• the organodithiophosphinic acid is a dialkyldithiophosphinic acid
• the organodithiophosphoric acid is a dialkyldithiophosphoric acid.
• the phosphoric acid mixture further comprises an adsorbent.
• the adsorbent is calcium sulfate solid particles.
• the process is performed at a temperature from 0 °C to 120 °C. In some embodiments, the process is performed at a temperature from about 10 °C to about 80 °C.
• the phosphoric acid mixture has a concentration of P2O5 from 3 weight % to 70 weight %, based on the total weight of the mixture. In some embodiments, the phosphoric acid mixture has a concentration of P2O5 from 20 weight % to 60 weight %. In some embodiments of the process for removing heavy metal ions from a phosphoric acid mixture disclosed herein, the reagent comprising a heavy metal chelating agent comprising a plurality of sulfur groups is added to the phosphoric acid mixture at a dosage from 0.1 kg/ton and 10 kg/ton of P2O5.
• the process further comprises a step of separating the phosphoric acid mixture.
• the separating step further comprises flocculation.
• the separating step further comprises filtration.
• the separating step further comprises skimming.
• a reagent for removing heavy metal ions from a phosphoric acid mixture comprising (a) a heavy metal chelating agent comprising a plurality of sulfur groups and (b) an organothiophosphorus compound comprising an organodithiophosphinic acid or corresponding salts thereof; or organodithiophosphoric acid or corresponding salts thereof.
• the heavy metal chelating agent having a plurality of sulfur groups is selected from the group consisting of (i) 2,5-dimercapto-l,3,4- thiadiazole; 2,5-dimercapto-l,3,4-thiadiazole dipotassium salt; and 5-mercapto-3- phenyl-l,3,4-thiodiazole-2(3H)-thione potassium salt; (ii) 2, 3 -dimercapto- 1- propanol; 1,2-dithioethane; 1,3 -dithiopropane; benzene- 1,2-dithiol; 1,3- dimercapto-2-propanol; and 1,2,3-tri-mercaptopropane.
• the heavy metal chelating agent having a plurality of sulfur groups is a polymer as defined by wherein each M is independently chosen from H, Na, K, Li, NH4 and NR’ 4, each R’ is independently chosen from a C1-C4 alkyl group, and n is the number of repeating units of the polymer backbone, and is an integer from 2 to 1000. In some embodiments, n is 2 to 100.
• the polymer comprises a backbone selected from the group consisting of: polyamine, polysaccharide, polyvinylpyrrolidone, polyglutamicacid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin and mixtures of any of the foregoing; and co-polymers of any of the foregoing.
• the reagent comprises mixtures of any of the foregoing heavy metal chelating agent comprising a plurality of sulfur groups as substituents.
• the heavy metal chelating agent is 2,3 -dimercapto- 1 -propanol.
• a reagent for removing heavy metal ions from a phosphoric acid mixture comprising
• a heavy metal chelating agent comprising a plurality of sulfur groups which comprises a member selected from the group consisting of:
• a polymer as defined by the heavy metal chelating agent having a plurality of sulfur groups is a polymer as defined by wherein each M is independently chosen from H, Na, K, Li, NH4 and NR’ 4, each R’ is independently chosen from a C1-C4 alkyl group, and n is the number of repeating units of the polymer backbone, and is an integer from 2 to 1000, and wherein in some embodiments, n is 2 to 100, and in some embodiments, the polymer comprises a backbone selected from the group consisting of: polyamine, polysaccharide, polyvinylpyrrolidone, polyglutamicacid, polyacrylamide, polydiacetone acrylamide, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, chitosan, dextrin and mixtures of any of the foregoing; and co-polymers of any of the foregoing; and
• an organothiophosphorus compound comprising an organodithiophosphinic acid or corresponding salts thereof; or organodithiophosphoric acid or corresponding salts thereof.
• the heavy metal chelating agent is 2,3 -dimercapto- 1- propanol.
• the phosphoric acids with different P2O5 levels are obtained from plants.
• the phosphoric acid slurries are generated with a bench-scale digestion process.
• 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.
• ICP Inductively Coupled Plasma
• DMTD-2K (2,5-Dimercapto-l,3,4-thiadiazole dipotassium salt), DMTD (2,5- Dimercapto-l,3,4-thiadiazole), Bismuthiol II (5-Mercapto-3-phenyl-l,3,4- thiodiazole-2(3H)-thione potassium salt), 2-Aminothiophenol, and Trimercapto- s-triazine trisodium salt are purchased from Sigma Aldrich.
• DTG (2,3- Dimercapto-1 -propanol) is purchased from Sigma Aldrich.
• Na-DTPi sodium diisobutyl dithiophosphinate
• Na-DTP sodium diisobutyl dithiophosphate
• a 5 wt% solution of sodium diisobutyl dithiophosphinate in water is prepared before dosed into acid.
• a 5 wt% solution of sodium diisobutyl dithiophosphate in water is prepared before dosed into acid.
• a solution of 6% DMTD-2K and 2% Na-DTPi is prepared before dosed into acid. The dosages shown in the tables are calculated based on the amount of dry reagents relative to the amount of P2O5 in acid/slurry.
• Example 1 Process for removing heavy metals from plant weak phosphoric acids ( ⁇ 30 % at elevated temperature (75°C and 50°C)
• results from Table 1 show the performance of various reagents for heavy metal removal from various plant phosphoric acids at variant temperatures.
• DMTD-2K compound when dosed at 3kg/t P2O5 to the plant phosphoric acid #2 (30% P2O5) at 50 °C, was able to remove arsenic and cadmium by up to 75.0% and 93.7% respectively (Example IN).
• DMTD and Bismuthiol II were also able to remove a significant amount of arsenic and cadmium from the plant phosphoric acid.
• DTG compound more than 90% reduction in arsenic was observed at dosages of 2 kg/t P2O5 (Example 1 J-4).
• Example 2 Process for removing heavy metals from digestion phosphoric acid slurries ( ⁇ 30 % P2O5) at ⁇ 80°C). Calcium sulfate solid particles in the slurry act as adsorbents
• the digestion is continued for an additional 2 to 3 hours to fully digest the phosphate ores.
• reagents of interest and other additives such as defoamer reagents
• effective amounts of reagents are first mixed with the aforementioned phosphoric acid and then continuously pumped into the reactor.
• the digestion slurry is stirred with an overhead stirrer (Glas-Col Precision Speed Controlled Stirrer) and a propeller-type impeller set at 300 rpm.
• phosphoric acid slurry ( ⁇ 30 % solid level, ⁇ 30 % P2O5) post-digestion is transferred into a glass jar with a magnetic stir bar.
• the slurries contain a large amount ( ⁇ 30 wt. %) of solid particles, with the majority being calcium sulfate generated during the digestion of phosphate ore.
• An effective amount (as listed in Table 2) of a reagent of interest for heavy metal ions removal is dosed into the slurry under agitation at 600 rpm.
• the 1st reagent is dosed into slurry under agitation of 600 rpm and agitated for 1 minute, and then the 2nd reagent is dosed into acid under agitation of 600 rpm and agitated for 1 minute.
• the slurry is transferred to a vacuum filtration funnel (on a filtration setup with a 45 pm polypropylene net filter (Millipore PP4504700)) and the vacuum filtration starts in ⁇ 15 seconds. The filtrate is collected and then submitted for ICP elemental analysis.
• Results from Table 2 show that DMTD-2K, by itself or with Na-DTPi, effectively removes arsenic and cadmium from the plant phosphoric acid (30% P2O5). The performance improves with increase in the dosage of DMTD-2K.
• Example 3 Process for removing heavy metals from concentrated phosphoric acids ( ⁇ 50 % P2O5) at elevated temperature (70°C) or room temperature (20°C)
• Results shown in Table 3 indicate significant reduction (over 80%) in the arsenic and cadmium from concentrated plant phosphoric acid (50% P2O5) when treated with DMTD-2K (Examples 3B-3 and 3B-4). Similar performance for As removal was observed when the concentrated plant phosphoric acid was treated with DTG (Example 3E-3). In both cases, the performance improved when the dosage of these compounds was increased. Great performance were also observed when DMTD-2K or DTG is co-dosed with Na-DTPi at various sequences.
• Example 4 Process for removing arsenic from concentrated phosphoric acids ( ⁇ 46 % P2O5) at elevated temperature (70°C) using thiol-containing polymers

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