title: Simultaneous uptake of Ni2+, NH4+ and PO4(3-) by amorphous CaO-Al2O3-SiO2 compounds.
abstract: Simultaneous uptake of Ni2+, NH4+, and PO4(3-) by amorphous CaO-Al2O3-SiO2 (C-A-S) compounds was investigated using batch and column methods. Fifteen different C-A-S samples with systematically varied chemical compositions were prepared by coprecipitation from ethanol-water solutions containing Ca(NO3)2.4H2O, Al(NO3)3.9H2O, and Si(OC2H5)4, using NH4OH as the precipitating agent. The resulting precipitates were dried and heated at various temperatures to produce the C-A-S samples, which were then characterized by XRD, FTIR, solid state MAS NMR, DTA-TG, and N2 adsorption. All the C-A-S samples prepared at 600-900 degrees C were amorphous, apart from the CaO-rich samples. Simultaneous uptake of Ni2+, NH4+, and PO4(3-) was determined by a batch method using a solution with an initial concentration of 2 mM. In these experiments, the uptake abilities of the C-A-S samples for Ni2+ and PO4(3-) were high, but were relatively low for NH4+. The uptake abilities for Ni2+ and PO4(3-) increased but that for NH4+ decreased as the silica content in the C-A-S decreased, suggesting that similar uptake mechanisms (ion substitution and/or precipitation) are operating for Ni2+ and PO4(3-), but the uptake mechanism for NH4+ is different (physical adsorption). The column experiments indicate that the order of uptake ability of C-A-S for the three ions is NH4+ << PO4(3-) < Ni2+. Although the silica content of the C-A-S does not have the expected influence on the uptake of these three ions, for NH4+ it plays an important role in the formation of the amorphous phase and also in the suppression of Ca2+ and/or Al3+ release from the C-A-S during the uptake experiments. The optimum uptake properties of the C-A-S can thus be controlled by adjusting the chemical compositions and heating conditions under which the samples are prepared.
authors.affiliation: Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan. kokada@ceram.titech.ac.jp
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Okada
authors.forename: Megumi
authors.initials: M
authors.lastname: Shimazu
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Kameshima
authors.forename: Akira
authors.initials: A
authors.lastname: Nakajima
authors.forename: Kenneth J D
authors.initials: KJ
authors.lastname: MacKenzie
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry* / Q000302:isolation & purification; D017610:Calcium Compounds / Q000737:chemistry*; D011232:Chemical Precipitation; D009682:Magnetic Resonance Spectroscopy; D009532:Nickel / Q000737:chemistry* / Q000302:isolation & purification; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry* / Q000302:isolation & purification; D012822:Silicon Dioxide / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D014877:Water Pollution, Chemical / Q000517:prevention & control; D018508:Water Purification / Q000379:methods*
chemical_list: D000538:Aluminum Silicates; D017610:Calcium Compounds; D009566:Nitrates; D010087:Oxides; D010710:Phosphates; D012997:Solvents; D012822:Silicon Dioxide; D000641:Ammonia; D009532:Nickel; C016538:lime; D009584:Nitrogen