Struvite-K crystal growth inhibition by citric acid: Formation of complexes in solution and surface adsorption effects

• Citric acid increases induction time during precipitation of struvite-K. • Citric acid reduces the amount of precipitated struvite-K. • Precipitation of struvite-K is inhibited by formation of Mg citrate complexes. • Surface adsorption of citric acid affects size and shape of the struvite-K crystals. • Citric acid binds to (0 0 1) faces of growing struvite-K crystals.