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 (001) faces of growing struvite-K crystals.