Title : 
  Kinetics of P adsorption on crystalline and amorphous Fe- and Al - hydroxides 
 Abstract_text_1 : 
  Kinetics of P adsorption on crystalline and amorphous Fe- and Al - hydroxides . 
 Abstract_text_2 : 
  P adsorption was investigated using batch experiments on highly crystalline goethite and gibbsite , poorly crystalline 2 - line - ferrihydrite and amorphous Fe : Al - hydroxide mixtures in the molar ratio 1:0 , 10:1 , 1:1 , 1:10 and 0:1 . A solid - solution ratio of 1:20 was chosen for gibbsite , and a solid - solution ratio of 1:200 was chosen for ferrihydrite and the Fe : Al - hydroxide mixtures due to their high specific surface areas and P - adsorption capacity . The initial P - concentrations for the adsorption experiments were 150 µmol l-1 , 1000 µmol l-1 and 2000 µmol l-1 KH2PO4 for gibbsite and 1000 µmol l-1 , 2000 µmol l-1 and 5000 µmol l-1 KH2PO4 for ferrihydrite and the Fe : Al - hydroxides with a 0.01 mol l-1 CaCl2 - background electrolyte solution , adjusted to a pH of 6 . For P measurements , the gibbsite and ferrihydrite samples were centrifuged for 15 min at 336 × G , while the Fe : Al - hydroxide samples were centrifuged for 15 min at 21572 × G. The clear supernatant was filtered by using P - poor Whatman 512 1/1 filters . The elemental composition of the adsorbents was verified by using SEM - EDX , scanning electron microscopy ( DSM 962 , Zeiss , Oberkochen , Germany ) with energy dispersive X - ray spectroscopy ( X - Max 50 mm² with INCA , Oxford Instruments , Abingdon , Great Britain ) . The formation of pure Al(OH)3 and FeO(OH ) for the amorphous hydroxides was revealed . Determination of the adsorbent crystallization as well as amorphous structures was carried out by X - ray diffraction ( XRD ) using a PANalytical Empyrean powder diffractometer ( Almelo , Netherlands ) from GFZ Potsdam , with a theta - theta - goniometer , Cu - Kα radiation ( λ=0.15418 nm ) , automatic divergent and anti - scatter slits and a PIXcel3D detector . Diffraction data were recorded from 4.6 ° to 84.9 ° 2ϴ with a step - size of 0.0131 and a step time of 58.4 s. The generator settings were 40 kV and 40 mA. Specific surface areas of all adsorbents were determined with an Autosorb-1 ( Quantachrome , Odelzhausen , Germany ) using a multi - point BET - measurement ( Brunauer - Emmett - Teller ) and N2 as adsorptive medium . The P adsorption kinetics of goethite showed an adsorbed P amount of 100 % ( 0.2 µmol m-2 ) for an initial P concentration of 150 µmol l-1 , 100 % ( 1.2 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , and 100 % ( 2.4 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , respectively after an adsorption time of 2688 h ( 16 weeks ) . The P adsorption by gibbsite increased strongly with increasing initial P concentration and totaled 100 % ( 3.2 µmol m-2 ) for an initial P concentration of 150 µmol l-1 , 45 % ( 10.2 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , and 42 % ( 19.5 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of ferrihydrite showed an adsorbed P amount of 100 % ( 0.01 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 100 % ( 0.07 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 99 % ( 0.14 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 1 Fe:0 Al showed an adsorbed P amount of 100 % ( 17.6 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 100 % ( 35.7 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 100 % ( 88.5 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 10 Fe:1 Al showed an adsorbed P amount of 100 % ( 0.8 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 100 % ( 1.6 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 100 % ( 4.1 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 5 Fe:1 Al showed an adsorbed P amount of 100 % ( 0.9 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 100 % ( 1.8 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 100 % ( 4.6 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 1 Fe:1 Al showed an adsorbed P amount of 99 % ( 2.5 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 100 % ( 5.0 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 100 % ( 12.6 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 1 Fe:5 Al showed an adsorbed P amount of 89 % ( 203.8 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 91 % ( 427.5 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 97 % ( 1140.8 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 1 Fe:10 Al showed an adsorbed P amount of 83 % ( 202.5 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 85 % ( 428.0 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 94 % ( 1169.1 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. The P adsorption kinetics of 0 Fe:1 Al showed an adsorbed P amount of 65 % ( 106.2 µmol m-2 ) for an initial P concentration of 1000 µmol l-1 , 69 % ( 228.2 µmol m-2 ) for an initial P concentration of 2000 µmol l-1 , and 82 % ( 688.1 µmol m-2 ) for an initial P concentration of 5000 µmol l-1 , respectively after an adsorption time of 2688 h. Research domain : Plant Nutrition Research question : Which P bindings are formed on the various mineral Fe- and Al - hydroxide surfaces and how do inorganic and organic compounds contribute to the availability of both adsorbed / precipitated and naturally bound phosphorus from phosphate minerals ? 
 Keywords : 
  Soil , Phosphates , Phosphate fertilizers , fertilizers , farm inputs , Bones , Laboratory experimentation , Phosphorus , Adsorption , Goethite , Gibbsite , Ferrihydrite , Hydroxide , Boden , Phosphorus , Adsorption