Process for removing metal impurities from wet process phosphoric acid and compositions thereof

Abstract

The present invention process and compositions remove heavy metal ions, such as cadmium, copper, lead, nickel, arsenic, manganese and mercury ions from wet-process phosphoric acid by providing a simple, single-step process that uses relatively small amounts of reagent. The process involves treating either the crude acid prior to gypsum filtration or the filtered acid with an organic precipitating agent composition, precipitating metals such as copper, cadmium, nickel, mercury, zinc, and separating the precipitate by either filtration or flotation, to produce phosphoric acid with reduced levels of the metals. The compositions of the present invention include a 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).

What is claimed is:  
     
         1 . A process for removing heavy metal ions from wet-process phosphoric acid, comprising the steps of: 
 a) bringing crude wet-process phosphoric acid into contact with from about 0.1 to about 5.0 kgs per ton of phosphoric acid of a precipitating agent composition, said precipitating agent composition comprised of:    1) from about 20 to about 70 weight % of the composition of a diorgano dithiophosphinic acid or the alkali metal or ammonia salt thereof represented by structure I                          wherein R=linear or branched alkyl, aryl, alkylaryl, or aralkyl hydrocarbon group containing 3-20 carbon atoms and M=H, an alkali metal or ammonia, and    2) from 30 to about 80 weight % of the composition of a first diorgano dithiophosphoric acid or the alkali metal or ammonia salt thereof represented by structure II                          wherein R=a linear or branched alkyl, alkylaryl or aralkyl hydrocarbon group containing 520 carbon atoms and M=H, an alkali metal or ammonia;    b) allowing heavy metals present in the wet process phosphoric acid to precipitate; and    c) separating precipitated heavy metals from the phosphoric acid by filtration or flotation to produce phosphoric acid with reduced levels of said heavy metals.    
     
     
         2 . The process according to  claim 1 , wherein said composition further comprises a second diorgano dithiophosphoric acid or the alkali metal or ammonia salt thereof in an amount that is the remainder of 100% after subtracting the amount of structures I and II present in the composition, said second diorgano dithiophosphoric acid represented by the structure III  
       
         
           
           
               
               
           
         
         wherein R=a linear or branched alkylaryl or aralkyl hydrocarbon group containing 620 carbon atoms and M=H, an alkali metal or ammonia.  
       
     
     
         3 . The process according to  claim 1 , wherein R in Structure I is selected from the group consisting of cyclohexyl, isopropyl, iso-butyl, n-propyl, octyl, hexyl, phenylethyl, and 2,4,4-trimethyl pentyl.  
     
     
         4 . The process according to  claim 1 , wherein R in Structure II is selected from the group consisting of 4-methyl-2-pentyl and 3-methyl-2-pentyl.  
     
     
         5 . The process according to  claim 2 , wherein R in Structure III is selected from the group consisting of dicresyl, dinonylphenyl and diphenylethyl.  
     
     
         6 . The process according to  claim 1 , wherein the first dithiophosphoric acid is derived from a secondary alcohol.  
     
     
         7 . The process according to  claim 1 , wherein the heavy metal ions are selected from the group consisting of copper, cadmium, nickel, mercury, zinc, arsenic, manganese and combinations thereof.  
     
     
         8 . The process according to  claim 1 , further comprising the step of filtering the wet process phosphoric acid before contacting it with the precipitating agent composition.  
     
     
         9 . The process according to  claim 2 , wherein the dithiophosphoric acid is derived from a primary alcohol and contains a benzene ring.  
     
     
         10 . The process according to  claim 1 , wherein the crude wet-process phosphoric acid is brought into contact with the precipitating agent composition for a time period of from about 5 seconds to about 60 minutes.  
     
     
         11 . The process according to  claim 10 , wherein the time period is about 5 seconds to about 5 minutes.  
     
     
         12 . The process according to  claim 11 , wherein the time period is from about 10 seconds to about 60 seconds.  
     
     
         13 . The process according to  claim 1 , carried out at a temperature that is from about 10 to about 85° C.  
     
     
         14 . The process according to  claim 13 , carried out at a temperature that is from about 50 to about 80° C.  
     
     
         15 . A composition for removing heavy metal ions from wet-process phosphoric acid comprising: 
 from about 20 to about 70 weight % of a diorgano dithiophosphinic acid or the alkali metal or ammonia salt thereof represented by structure I                          wherein R=linear or branched alkyl, aryl, alkylaryl, or aralkyl hydrocarbon group containing 3-20 carbon atoms and M=H, an alkali metal or ammonia, and    from about 30 to about 80 weight % of a first diorgano dithiophosphoric acid or the alkali metal or ammonia salt thereof represented by structure II                          wherein R=a linear or branched alkyl, alkylaryl or aralkyl hydrocarbon group containing 5-20 carbon atoms and M=H, an alkali metal or ammonia.    
     
     
         16 . The composition according to  claim 15 , further comprising a second diorgano dithiophosphoric acid or the alkali metal or ammonia salt thereof in an amount that is the remainder of 100 weight % after subtracting the amount of structures I and II present in the composition, said second diorgano dithiophosphoric acid represented by the structure III  
       
         
           
           
               
               
           
         
       
       wherein R=a linear or branched alkylaryl or aralkyl hydrocarbon group containing 6-20 carbon atoms and M=H, an alkali metal or ammonia.  
     
     
         17 . The composition according to  claim 1 , wherein R in Structure I is selected from the group consisting of cyclohexyl, isopropyl, iso-butyl, n-propyl, octyl, hexyl, phenylethyl, and 2,4,4-trimethyl pentyl.  
     
     
         18 . The composition according to  claim 17 , wherein Structure I is diisobutyl dithiophosphinate.  
     
     
         19 . The composition according to  claim 15 , wherein R in Structure II is selected from the group consisting of 4-methyl-2-pentyl and 3-methyl-2-pentyl.  
     
     
         20 . The composition according to  claim 19 , wherein Structure II is di(4-methyl-2-pentyl) dithiophosphate.  
     
     
         21 . The composition according to  claim 16 , wherein R in Structure III is selected from the group consisting of dicresyl, dinonylphenyl and diphenylethyl.  
     
     
         22 . The composition according to  claim 21 , wherein Structure III is dicresyl diothiophosphate.  
     
     
         23 . The composition according to  claim 15 , wherein the diorgano dithiophosphinic acid (or alkali metals or ammonia salts thereof) is present in an amount that is from about 30 to about 40% by weight of the composition.  
     
     
         24 . The composition according to  claim 15 , wherein the first diorgano dithiophosphoric acid (or alkali metals or ammonia salts thereof) is present in an amount that is from about 50 to about 60% by weight of the composition.  
     
     
         25 . The composition according to  claim 15 , wherein the first dithiophosphoric acid is derived from a secondary alcohol.  
     
     
         26 . The composition according to  claim 15 , wherein the second dithiophosphoric acid is derived from a primary alcohol and contains a benzene ring.