Study On The Preparation Of Ferric Phosphate Chemically Bonded Ceramics And Its Adsorption Of Cr(Ⅵ)

Next to silica and alumina,iron oxide is the most abundant mineral on the earth’s crust,which three main forms:wustite（Fe O）,hematite（Fe₂O₃）and magnetite（Fe₃O₄）.Because of the abundan ce of iron oxide,it has been attractive many researchers to explore methods of forming iron phosphate chemically bonded ceramics.In this study,iron phosphate chemically bonded ceramics were prepared through the reaction between magnetite and orthophosphoric acid.The influences of Fe/P and the addition of retarder on compressive strength,phase compositions and microstructure of the iron phosphate chemically bonded ceramics are fully investigated by using compressive strength test,X-ray diffraction（XRD）and scanning electron microscopy analysis（SEM）,respectively,further investigated the adsorption properties of Cr（Ⅵ）by using iron phosphate chemically bonded ceramics.Both Fe/P and addition of retarder greatly influenced the compressive strength and setting time of iron phosphate chemically bonded ceramics.When Fe/P was 3:1,the compressive strengths of iron phosphate chemically bonded ceramics at different ages reached their maximum values,which were 19.68MPa,26.83MPa,30.14MPa and36.45MPa at the ages of 1d,3d,7d and 28d,respectively.The addition of retarder remarkably prolonged setting time and enha nced compressive strength.When boric acid addition was 4.0%,the compressive strength of the magnetite based IPCs at 28d reached its highest value,which was 44.57 MPa.According to the XRD and SEM analysis,the reaction between magnetite and orthophosphoric acid resulted in the formation of amorphous phases,which acted as binder phases of iron phosphate chemically bonded ceramics.When the addition of boric acid was more than 6%,new crystalline phases,including rockbridgeite（Fe₅（PO₄）₃（OH）₅）and iron hydrogen phosphate hydrate（Fe（H ₂PO₄）₂·2H₂O）,were formed.Static adsorption experiments were carried out to investigated the adsorption properties of Cr（Ⅵ）by iron phosphate chemically bonded ceramics under different conditions systematically.The results indicated that the adsorption efficiency of Cr（Ⅵ）by iron phosphate chemically bonded ceramics increased with the increase of the addition amount,but the adsorption capa city decreased.Solution p H has a greatly effect on the adsorption of Cr（Ⅵ）using iron phosphate chemically bonded ceramics.When solution p H is less than 2,the adsorption efficiency of Cr（Ⅵ）was higher than90%.Though the adsorption efficiency of Cr（Ⅵ）was higher in the strong acid condition,which decreased sharply with the increase of solution p H.Kinetic and thermodynamic study s howed that the adsorption of Cr（Ⅵ）on iron phosphate chemically bonded ceramics fitted with pseudo-second-order and Langmuir models.Adsorption mechanisms study revealed that the adsorption of Cr（Ⅵ）onto iron phosphate chemically bonded ceramics was mainly electrostatic attraction.