The objective of this work was to study the effect of pH and ionic matrix on product release and on the removal of uranyl ion by a Citrobacter. sp phosphatase enzyme-catalysed reaction. An improvement in the efficiency of uranyl removal was obtained by incorporating ammonium acetate (NH4Ac) into the solution. It was confirmed using X-ray diffraction (XRD), and other analytical techniques, that the insoluble, cell-bound product was NH4UO2PO4.