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The effect of aspartic acid, glutamic acid, hexaammonium tetrapolyphosphate, calcium phytate, and polyaspartic acid on calcium hydrogenphosphate dihydrate (CaHPO4‚2H2O, DCPD) crystal growth morphology was studied. The mechanism of additive-DCPD crystal interaction depends on the size and structure of the additive molecule and the structural fit between the organic molecule and the ionic structure of particular crystal face. Small molecules with low charge (aspartic and glutamic acid) do not have a significant effect, whereas small molecules with several functional groups (citrate and hexaammonium tetrapolyphosphate) adsorb on lateral faces primarily by electrostatic interactions. Molecules with hindered structures (phytate) and macromolecules (polyaspartic acid) specifically adsorb on the dominant (010) face, for which a certain degree of structural fit is necessary.

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The precipitation of magnesium phosphates in the system MgCl(2)-NH(4)H(2)PO(4)-NaOH-H(2)O was studied at a wide range of reactant concentrations at 37 degrees C and an initial pH(i) of 7.4. Precipitates were aged for 24 h and characterized by means of optical and scanning electron microscopy, x-ray diffractometry, FT-IR spectroscopy and thermogravimetry. Struvite was found to precipitate in nearly the whole concentration region investigated. Pure newberyite and a mixture of struvite and newberyite were obtained in a narrow range only with a pH(24 h)<6.4. The transformation of struvite into newberyite was studied by following changes in the liquid and solid phases. Thus, the changes of pH and the content of struvite in the precipitate as a function of time were recorded. The influence of the initial pH(i) and temperature on the transformation process is discussed. Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.