The role of zinc ions in calcium oxalate monohydrate crystallization

•Zinc ions can compete with calcium ions for the oxalate anion.•Zinc ions can lower the supersaturation of the system.•Some organics can chelate with zinc ions, reducing the ion’s impact.•The presence of Tartaric Acid showed significant nucleation reduction.•Zeta potential suggests the presence of zinc ions would promote aggregation. Cystallization of calcium oxalate monohydrate was investigated in the presence of various organic molecules in combination with zinc ions. This work looked at the impacts at physiological pHs (6–8) and temperature (37 °C). It was found that the number of carboxylate and hydroxyl groups was critical in determining the degree of inhibition. This inhibition was found to be mainly due to the ability of the organics to chelate with calcium ions when zinc ions are not present. Zinc ions were found to chelate with oxalate ions leading to lower nucleation rates, but this is not strictly inhibition but a lowering of the supersaturation due to lowering of the activity of the oxalate. Organics have variable impact depending on whether the zinc ions or calcium ions preferentially chelate with the organic.