EXPERIMENTAL-STUDY OF ALUMINUM AND CALCIUM MALONATE COMPLEXATION AT 25-DEGREES-C, 35-DEGREES-C, AND 80-DEGREES-C

The solubility of gibbsite was measured at 35 and 80-degrees-C, and th e solubility of portlandite was measured at 25, 35, and 80-degrees-C, each as a function of pH and malonate concentration. The gibbsite solu bility data can be satisfactorily modelled using only one aqueous Al-m alonate species. The data rule out all possible Al(p) (OH)q (Mal)r 3p- q-2r) and Al(p)(OH)q (HMal)r 3p-q-r) stoichiometries except Al(Mal)2- and Al(Mal)2- is the dominant species, the data constrain the value fo r the log of the dissociation constant of Al(Mal)2- to be -11.3 +/- 1. 0 and -14.5 +/- 0.5 at 35 and 80-degrees-C, respectively. If Al(OH)2 ( HMal)2- is the dominant species, the values of its dissociation consta nt at 35-degrees-C and at 80-degrees-C are -27.3 +/- 1.0 and -27.6 +/- 0.5, respectively. The portlandite solubilities indicate that that Ca (Mal)0 is the dominant Ca-malonate complex, with values for the log of the dissociation constant of Ca(Mal)0 of -2.4 +/- 0.3, -2.4 +/- 0.3, and -2.9 +/- 0.3, at 25, 35, and 80-degrees-C, respectively. Thermodyn amic modelling, using these results, indicates that Al-malonate comple xation can potentially enhance the solubility of Al-bearing minerals b y up to five orders of magnitude.