Solubility of calcium phosphates.

Solubil ity is one of the most important properties of calcium phosphate salts. It is the solubil ity that determines the direction of many reactions that involve calcium phosphates such as dissolution, precipitation, hydrolysis, and phase transformation. Calcium phosphate solubil ity also plays a maior role in biological processes that involve formation and resorption ol' hard tissues as well as pathological calcif ications. This chapter wil l focus on concepts that would aid in gaining a better understanding of the solubil ity behavior of calcium phosphzrtes, rather than provide a survey of the l iterature, which has been g iven e lsewhere [El l io t . 1994] . Solubi l i ty is convent ional ly descr ibcd ns the nmount of a sol id that can d isst> lve in to a uni t vo lume of solution. Fclr calcium phosphates, this quantity often changes by several orders of magnitucle with changes in the pH and concentrations of acids and bases, such as HCI and NaOH. Thus, on the surface. the solubil ity may appear to be a complex function of these solution parameters. However, a clearer picture o1 the solubil ity properties for calcium phosphates can be gainecl by understanding the basic principles governing the solid-solution equil ibrium.