Influence Of Ferrihydrite Under The Reduction Condition On The Forms Of Calcium Phosphate

Iron phosphorus and calcium phosphorus are two important phosphorus forms of the sediments. They play important roles in maintaining the phosphorus in water- sediment interface normally circulation, regulating the production capacity of water bodies. Ferrihydrite is an amorphous ferric hydroxide. Compared to the other crystalline iron oxide, its specific surface area is larger and phosphorus holding capacity is stronger.The experiment simulates that under the sediment environment, commencing the reaction of ferrihydrite, inorganic phosphorus and calcium, after ferrihydrite is reduced in the condition of anaerobic, the transformation processes of the sediment phosphorus. The main conclusions are as follows:(1) No adding phosphorus solution to the system in the poscess of reduction. In the chemical reduction, the content of water soluble phosphorus increased, and it could convert to hydroxyapatite more directly on the surface of ferrihydrite which adsorbed supersaturated calcium and phosphorus. Poorly crystalline calcium phosphate minerals, such as Fe Fe2(PO4)2(OH)2, Ca3(PO4)2·2H2O and monetite, mainly occured on the surface of ferrihydrite which did’t adsorb saturated calcium and phosphorus. In the microbial reduction of ferrihydrite which both absorbed more Ca/P and Less Ca/P, products were mainly composed of vivianite, along with amorphous calcium phosphate, and the content of water soluble calcium rised first then decreased, the effectiveness of phosphorus reduced.(2) Adding phosphorus solution to the system in the poscess of reduction. When Ca/P=1, calcium and phosphate gradually formed apatite on the surface of ferrihydrite, when Ca/P=1.67, brushite first occurred, then gradually transformed to hydroxyapatite. But in the reaction system of pure calcium and phosphorus solution, the mixture of amorphous tricalcium phosphorus and brushite would first occurred, then gradually transform to hydroxyapatite with high crystallinity.(3) The higher the concentration of KCl, the higher the desorption quantity of calcium, and the desorption quantity of phosphorus on the surface of ferrihydrite with two kinds of Ca/P ratio had nothing to do with the concentrations of KCl. In the pocess of the desorption of calcium on the surface of ferrihydrite which adsorbed supersaturated calcium and phosphorus, by 0.1mol/L KCl desorption 40 hours, the desorption quantity was 166.3mg/g(water soluble calcium/ total calcium), the ratio of calcium and phosphate desorption quantity(the ratio of amount of substance) was about 0.55; after desorption, the main diffraction peaks still existed minerals were give priority to hydroxyapatite. In the pocess of the desorption of calcium on the surface of ferrihydrite which adsorbed unsaturated calcium and phosphorus, by 0.1mol/L KCl desorption 40 hours, the desorption quantity was 884.7mg/g(water soluble calcium/ total calcium), the ratio of calcium and phosphate desorption quantity(the ratio of amount of substance) was about 2.7; after desorption, the main diffraction peaks weakened or disappeared.(4) With calcium, Vc reduced ferrihydrite which absorbed calcium and phosphorus, there could be mainly producing minerals with lower crystallity, included calcium iron phosphorus hydroxylhydrate, but not forming vivianite, oxidation could inhibit the transformation to a stable morphology of calcium iron phosphorus compounds.