Struvite crystal growth inhibition by trisodium citrate and the formation of chemical complexes in growth solution

Effect of trisodium citrate on the crystallization of struvite was studied. To evaluate such an effect an experiment of struvite growth from artificial urine was performed. The investigations are related to infectious urinary stones formation. The crystallization process was induced by the addition of aqueous ammonia solution to mimic the bacterial activity. The spectrophotometric results demonstrate that trisodium citrate increases induction time with respect to struvite formation and decreases the growth efficiency of struvite. The inhibitory effect of trisodium citrate on the nucleation and growth of struvite is explained in base of chemical speciation analysis. Such an analysis demonstrates that the inhibitory effect is related with the fact that trisodium citrate binds NH4+ and Mg2+ ions in the range of pH from 7 to 9.5 characteristic for struvite precipitation. The most important is the MgCit− complex whose concentration strongly depends on an increase in pH rather than on an increase in citrate concentrations.