TY - JOUR
T1 - Potentiometric and solubility studies of association quotients of aluminum malonate complexation in NaCl media to 75°C
AU - Ridley, Moira K.
AU - Palmer, Donald A.
AU - Wesolowski, David J.
AU - Kettler, Richard M.
N1 - Funding Information:
This research was sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy, contract DE-AC05-960R22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. and NSF grant EAR-9317075 to R. M. Kettler. The helpful suggestions of R. E. Mesmer were gratefully appreciated.
PY - 1998/7
Y1 - 1998/7
N2 - A potentiometric method was used to determine the formation quotients for aluminum-malonate (Al(Ma)(y)(3-2y), Ma ≡ CH2(CO2)22-) complexes from 5 to 75°C at four ionic strengths from 0.1 to 1.0 molal in aqueous NaCl media. Two mononuclear aluminum-malonate species, Al(Ma)+ and Al(Ma)2-, were identified, and the formation quotients for these species were modeled by empirical equations to describe their temperature and ionic strength dependencies. Differentiation of the two empirical equations with respect to temperature provided thermodynamic quantities for the Al-malonate complexes. The thermodynamic quantities obtained for Al(Ma)+ at 25°C and infinite dilution are: log K1 = 7.49 ± 0.18, ΔH1°= 19 ± 5 kJ · mol-1, ΔS1°= 208 ± 18 J · K-1 · mol-1 and ΔC(p1)°= 331 ± 120 J · K-1 · mol-1; whereas the values for Al(Ma)2- are: log K2 = 12.62 ± 0.40, ΔH2°= 29 ± 10 kJ · mol-1, ΔS2°= 340 ± 36 J · K-1 mol-1 and ΔC(p2)°= 575 ± 230 J · K-1 mol-1. These thermodynamic values indicate that Al(Ma)+, a chelate complex, is much more stable than the equivalent monodentate Al-diacetate complex (Al(Ac)2+) (Palmer and Bell, 1994). A solubility study, which was undertaken to verify the 50°C potentiometric data, was performed by reacting powdered gibbsite (Al(OH)3) with malonic acid solutions at 0.1 molal ionic strength in aqueous NaCl media. The results of the solubility study are in excellent agreement with the potentiometric data.
AB - A potentiometric method was used to determine the formation quotients for aluminum-malonate (Al(Ma)(y)(3-2y), Ma ≡ CH2(CO2)22-) complexes from 5 to 75°C at four ionic strengths from 0.1 to 1.0 molal in aqueous NaCl media. Two mononuclear aluminum-malonate species, Al(Ma)+ and Al(Ma)2-, were identified, and the formation quotients for these species were modeled by empirical equations to describe their temperature and ionic strength dependencies. Differentiation of the two empirical equations with respect to temperature provided thermodynamic quantities for the Al-malonate complexes. The thermodynamic quantities obtained for Al(Ma)+ at 25°C and infinite dilution are: log K1 = 7.49 ± 0.18, ΔH1°= 19 ± 5 kJ · mol-1, ΔS1°= 208 ± 18 J · K-1 · mol-1 and ΔC(p1)°= 331 ± 120 J · K-1 · mol-1; whereas the values for Al(Ma)2- are: log K2 = 12.62 ± 0.40, ΔH2°= 29 ± 10 kJ · mol-1, ΔS2°= 340 ± 36 J · K-1 mol-1 and ΔC(p2)°= 575 ± 230 J · K-1 mol-1. These thermodynamic values indicate that Al(Ma)+, a chelate complex, is much more stable than the equivalent monodentate Al-diacetate complex (Al(Ac)2+) (Palmer and Bell, 1994). A solubility study, which was undertaken to verify the 50°C potentiometric data, was performed by reacting powdered gibbsite (Al(OH)3) with malonic acid solutions at 0.1 molal ionic strength in aqueous NaCl media. The results of the solubility study are in excellent agreement with the potentiometric data.
KW - Aluminum
KW - Complexation
KW - Solubility
UR - http://www.scopus.com/inward/record.url?scp=0032448402&partnerID=8YFLogxK
U2 - 10.1016/S0016-7037(98)00143-4
DO - 10.1016/S0016-7037(98)00143-4
M3 - Article
AN - SCOPUS:0032448402
VL - 62
SP - 2279
EP - 2291
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
SN - 0016-7037
IS - 13
ER -