I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Science Center, RAS, Apatity, Russia:

V. I. Ivanenko, Chief Researcher, Head of Laboratory of Chemistry and Technology of Rare-earth Raw Materials, e-mail: ivanenko@chemy.kolasc.net.ru
R. I. Korneykov, Researcher of Laboratory of Chemistry and Technology of Rare-earth Raw Materials
K. A. Kesarev, Post-Graduate Student, Junior Researcher of Laboratory of Chemistry and Technology of Rare-earth Raw Materials
N. V. Zharov, Post-Graduate Student

We studied the possibility of purifying the technological solutions, containing toxic metals (copper, zinc, nickel, lead, cadmium, iron) and arsenic cations using the precipitation and sorption methods. Na2S.nH2O, forming the hardly soluble compounds with heavy metals and arsenic cations, was suggested as a reagent-precipitant. Purifying the solution up to the required maximum permissible concentrations of the toxic components is quite possible under the sulfide precipitation. However, due to the introduction of the excess amount of the precipitant, there is a danger of the secondary contamination of the solutions being purified with the sulfide ions. To prevent the secondary contamination of the solutions by the sulfide ions, we studied the method of the combined recovery for the heavy metals and arsenic cations, based on the sulfide precipitation with sorption post-treatment. The ion-exchangers based on the hydrated titanium (IV) oxohydrophosphates, demonstrating the high affinity to heavy metal cations were tested as a sorption collector of the recoverable elements. The proposed approach was probed, as well as its effectiveness was shown on the solutions, modeling the compositions of the real process effluents. The precipitation of the heavy metals and arsenic cations, with the subsequent sorption ending, leads to the effective purification of the process effluents, eliminates the risk of the secondary contamination by toxic ions of the precipitant. The residual toxicants content in the solution does not exceed the maximum permissible concentration values for the drinking and domestic water supply, and corresponds almost completely to the maximum permissible concentrations values of the fishery use reservoirs. The series of the selectivity Cd (II) > Fe (III) > Zn (II) > Cu (II) > Ni (II) > Pb (II) > As (III) was established on the basis of the distribution coefficients (Kd) values, obtained during the sorption pre-extraction of heavy metals and arsenic cations. The thermal treatment of the spent (cationized toxic metals) sorption material leads to the stable crystalline compounds formations which firmly retain the toxic sorbate in its structure and ensure its reliable immobilization.
Our investigations were carried out with the financial support of the Russian Science Foundation within the scientific project No.17-19-01522.

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