Titanium in natural surface waters: The content and coexisting forms

Results obtained in studying the content and coexisting forms of titanium in surface waters are given. It was established that the titanium concentration lies within 0.0–1180 μg/L in the world’s surface water and within 0.0–573 μg/L in the studied water bodies of Ukraine. The concentration of dissolved and suspended titanium in the water bodies studied also varies within the wide range, 0.0–86.0 and 0.0–534.6 μg/L, respectively. The concentration of its dissolved form in world’s surface water is 0.0–68.7 μg/L. The ratio of dissolved to suspended titanium in water bodies depends on the content of suspended matter and its nature. In river waters, the suspended titanium mostly dominates over the dissolved form. We found that in rivers with the high concentration of suspended matter (6.0–140.6 mg/L), mostly of mineral nature, a fraction of the suspended titanium reaches 62.3–88.6% on the average. A strong correlation between the mass of suspended matter and the concentration of suspended titanium in these surface waters shows that the nature of suspended matter affects the concentration of suspended titanium. The correlation coefficient is between 0.81–0.99 at a significance level of 0.01. The titanium content in the suspended matter and bottom sediments of world’s water bodies makes 0.2–19.8 and 0.1–24.6 mg/g of dry weight of the suspended matter, respectively. In the surface waters studied, its content ranges within 0.0–16.5 mg/g of dry weight of the suspended matter. Taking into account the average values, the titanium content in the suspended matter of the studied rivers, water reservoirs, lakes, and ponds is (mg/g in terms of dry mass): 1.0–7.5, 1.0–4.9, 1.3–3.9, and 1.2–1.3, respectively. The percentage of the adsorbed titanium in the suspended matter of the Kilia Danube delta, Kanev Reservoir, and the Lybid’ River is 91.6–97.3, 67.6–74.4, and 57.1–99.4%, respectively. The acidic (anionic), basic (cationic), and neutral fractions of the dissolved organic substances in the surface waters contained 15.7–89.4, 0.0–33.8, and 0.0–80.7% of dissolved titanium (Ti_diss) (i.e., 44.4, 13.2, and 42.4% of Ti_diss on the average). The presence of dissolved titanium in the anionic fraction shows that titanium forms complexes with humic substances or exists in the form of TiO₂ colloidal particles (nanoparticles) coated with humic substances. In the neutral fraction, a hydrated titanium oxide TiO(OH)₂ may exist as a form of its migration in natural surface waters.