Dissolution and precipitation kinetics of gibbsite at 80°C and pH 3: The dependence on solution saturation state

摘要: Dissolution and precipitation rates of gibbsite were measured in dilute aqueous solutions at pH 3 80°C as a function solution saturation state using stirred-flow reactors. Saturation (QKeq = exp(ΔGRT); where Q is the activity quotient, keq, equilibrium quotient (or solubility), ΔGr deviation Gibbs free energy reaction (kcal mol−1) from value, R gas constant, T temperature Kelvin) was determined with respect to overall Al(OH)3(cr) + 3H+ ⇔ A13+ 3H2O. The solubility for this tightly constrained states experiments five slowest dissolution rates. The calculated (Keq aAl3+AH+3) 105.00±0.08, excellent agreement published values despite differences thermodynamic models definition measurement pH. variation rate (mol m−2 sec−1) over range −1.14 ≤ 0 kcal mol−1 given by Ratediss −(4.72 ± 0.28) × 10−10[1 − exp {(−8.12 1.02)g(3.01±0.05)}] g  ¦ΔGr¦RT. varies +0.467 according Rateppt −(2.07 0.63) −exp {g(1.20±0.31)}] or (1.94 1.55) 10−10g(1.10±0.11) The can be separated into three regions. Near (0 ≥ > −0.200 mol−1), increase gradually increasing undersaturation an approximately linear ΔGr. Over >ΔGr −0.500 suggestive surface phase change corresponding mechanism. A plausible mechanism involves opening dislocation cores form etch pits supported theoretical calculations SEM observations.