Studies of some heavy metal phosphate complex compounds.

The complex species present in solutions of tervalent aluminium, iron and titanium in aqueous orthophosphoric acid have been studied by ion exchange and other techniques. In one series of batch experiments the sign and size of the charge on the complex ions was established in all cases, and it was shown that the complexes were always singly or doubly charged anionic species with a ligand : metal ratio of 3:1. Ion exchange procedures were used to show the presence of anionic complexes and the absence of cationic complexes. Solvent extraction procedures were used to show the probable absence of neutral complexes. Whenever applicable, visible and ultra violet spectra were obtained as additional evidence. Further ion exchange experiments were carried out in the case of iron and titanium orthophosphates using trace quantities of metal and very carefully controlled conditions of pH and ionic strength and, from the results, values have been calculated for the stability constants of the complex ions present in the solutions. The calculations and the justification for the simplifications and assumptions involved are discussed in detail. Analytical procedures for the metals at very low concentrations and for the metals and orthophosphate in the presence of each other are described.