studied were acetate and citrate, which possess one and three functional groups (carboxylates) respectively. Investigation into homogeneous nucleation is important in order to compare and contrast with previous work on heterogeneous nucleation, but also to help understand problems such as the formation of fines nucleating spontaneously in industrial processes.

### MATERIALS AND METHODS

# Homogeneous precipitation calculations

For homogeneous precipitation to occur, the solution needs to be supersaturated with respect to a mineral phase. The degree of supersaturation is given by the following equation (i).

SCa/P=log(IAP/Ksp)(i)

Where IAP is the ionic activity product and Ksp is the solubility constant for the calcium phosphate mineral (13).

To determine the supersaturation degree required for precipitation it is necessary to state the ionic products for each of the expected calcium phosphate minerals (equations ii-v).

Log IAPDCPD = log (Ca2+) + log (HPO42-)(ii)

Log Ksp = -6.68 (14)

Log IAPTCP = 3 log (Ca2+) + 2 log (PO43-)(iii)

Log Ksp = -28.9 (15)

Log IAPOCP = 4 log (Ca2+) + 3 log (PO43-) + log (H+)(iv)

Log Ksp = -46.9 (16)

Log IAPHAP = 5 log (Ca2+) + 3 log (PO43-) + log (OH-)(v)

Log Ksp = -57.4 (17)

For the calculation of the free ion concentrations of the lattice parameters and subsequently the supersaturation degree the computer program PHREEQC was used with the Minteq database (18). The activity was calculated using the Davies equation (vi).