Tananaev Institute of Chemistry — Subdivision of the Federal Research Centre “Kola Science Centre of the Russian Academy of Sciences”, Apatity, Russia

M. L. Belikov, Senior Researcher, Researcher Specialist in the field of water purification adsorption processes and photocatalysis, Candidate of Technical Sciences, e-mail: m.belikov@ksc.ru
S. A. Safaryan, Postgraduate Student, Research Engineer, e-mail: s.safarian@ksc.ru

Various salts of calcium, iron, aluminum, titanium, lanthanum and cerium have been considered as precipitating reagents for water purification from phosphate ions. It has been shown that it is advisable to use calcium carbonate to purify water containing >200 mg/l of phosphate ions. Iron(II) sulfate and titanyl sulfate can be used only for partial purification of water from phosphate ions. The degree of water purification at an initial phosphate ion content of 120 mg/l does not exceeds 75 %. With the help of iron(III), aluminum and lanthanum salts, it is possible to reduce the concentration of phosphate ions from 120 to 9–15 mg/l, that is, by 87.5–92.5 %. At the same time, in the case of the use of iron(III) and aluminum, secondary contamination with sodium used to adjust the pH is observed, exceeding the established norms of maximum permissible concentrations (MPC). The most effective sedimentation reagents for water purification from phosphate ions are lanthanum and cerium compounds, which reduce the concentration of phosphate ions in water by 87.5–97.5 %, while secondary contamination by components of the reagents used does not exceed the MPC standards. Cerium(III) chloride has the maximum efficiency, so, with a molar ratio Ce:P = 1.3 and pH = 7.55 the concentration of phosphate ions in water decreases from 120 to ≤3 mg/l, that is, by ≥ 97.5 %. It is shown that the process of purification of water from phosphate ions by lanthanum and cerium compounds is possible in a wide range of pH = 2.52–7.75, which is an advantage in comparison with other reagents. In addition, the use of lanthanum and cerium compounds as effective sedimentation reagents for water purification partially solves the issue of expanding the use of a large number of low-liquid light rare earth elements (REE) obtained during the extraction and processing of rare earth raw materials.

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