Title : 
  P desorption kinetics from Fe- and Al - hydroxides 
 Abstract_text_1 : 
  P desorption kinetics from Fe- and Al - hydroxides    . 
 Abstract_text_2 : 
  The synthetic commercially hydroxides were goethite ( 99 % , Alfa Aesar , Haverhill , Massachusetts , USA ) , and gibbsite ( Merck Millipore , Merck KGaA , Darmstadt , Germany ) , which were of analytical grade . 2 - line - ferrihydrite was prepared , at which a 1 M KOH was added to 500 ml of a 0.2 M Fe(NO3)3 ∙ 9 H2O - solution , until a pH of 7.5 was reached . The developed precipitate was centrifuged and washed for 5 min at 12134 x G , subsequently frozen , freeze - dried , and stored in a desiccator . The mixed Fe - Al - hydroxides were prepared by mixing 0.1 M Fe(NO3)3 ∙ 9 H2O and 0,1 M Al(NO3)3 ∙ 9 H2O were mixed in molar ratios of 1:0 , 10:1 , 5:1 . 1:1 , 1:5 , 1:10 and 0:1 , and brought to a pH of 6 with 5 M KOH . After equilibration for 1 h , the precipitate was centrifuged for 5 min at 12134 x G , washed with ultrapure water , dried at 60 ° C , and ground into a powder . The elemental composition of the adsorbents was verified 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 final resulting mineral phase of pure Al(OH)3 and FeO(OH ) for the amorphous hydroxides was identified . Determination of the minerals crystallization as well as amorphous structures were verified by X - ray diffraction ( XRD ) , using an Empyrean powder diffractometer ( PANalytical , Almelo , Netherlands ) , 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 , a step time of 58.4 s , and generator settings of 40 kV and 40 mA. Prior to desorption , the hydroxides were coated on silica sand ( particle size 0.2 – 0.8 mm , Merck Millipore ) to ensure a similar sample treatment ( e.g. centrifugation times and revolutions ) . The silica sand used was finely granulated , washed , and calcined . 10 g of the hydroxide in a 0.01 M NaNO3 - solution were adjusted to pH 6 , resulting in a final volume of 100 ml . 100 g of pure silica sand was added to the suspension , and shaken for 24 h at room temperature . The supernatant was decanted and the material was washed three to five times with the 0.01 M NaNO3 - solution at pH 6 , and in a final step with ultrapure water to remove hydroxide traces and soluble salts . The coated silica sand was oven dried at 60 ° C for 48 h. The silica - hydroxide mixtures were preload with P. Therefore , 200 ml of a 2 mmol l-1 KH2PO4 solution and a 0.01 M CaCl2 background solution were added to the mixtures . After shaking horizontally for 24 h at 150 motions min-1 , the hydroxides were centrifuged for 5 min at 929 x G. The supernatant was filtrated and the adsorbed P concentration determined Desorption experiments were conducted with CaCl2 , CaSO4 , humic acid , and citric acid , adjusted to pH 6 . 2.5 g of the coated silica sand was treated with 50 ml of 0.01 M CaCl2 or 0.01 M CaSO4 . 5 g of the coated silica sand was used for desorption with 50 ml of 2 g l-1 humic acid and citric acid ( Alfa Aesar ) . A concentration of 2 g l-1 for both humic and citric acid was selected to provide a concentration similar to that of the CaCl2 and CaSO4 . For desorption experiments , treatment solutions were added to the samples , shaken at 150 motions min-1 , and centrifuged for 15 min at 2091 x g. After this , the supernatant was filtered for measurement of P. The time steps were 2 , 6 , 24 , 48 , 168 , 336 , 672 , and 1344 h. Research domain : Research question : 207 - 03 Plant Nutrition 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 , Phosphate fertilizers , fertilizers , farm inputs , Phosphates , Bones , Laboratory experimentation , Hydroxide , Phosphorus , Desorption , opendata , Boden