RU2578717C1 - Method of producing cerium (iv) nitrate by electrochemical oxidation of cerium (iii) nitrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing cerium nitrate(IV) electrochemical oxidation of cerium nitrate(III) in the anode chamber containing solution with initial concentration of cerium nitrate(III) 100-130 g/l and initial concentration of free nitric acid in an anolyte and catholyte 8-12 g/l, at current density on platinized niobic anode 1-3 A/dm². Method is characterised by that in order to increase stability of platinum coating electrolysis process is carried out in anode chamber-chamber electrolysis cell, separated from two cathode chambers anion and cation-exchange membranes, which in anode chamber is maintained constant concentration of free nitric acid 8-12 g/l.

EFFECT: using the presented method allows to prevent accumulation of free nitric acid in an anode, which is necessary to provide stability of platinized niobium anode.

1 cl, 2 tbl, 2 ex

Description

The invention relates to electrochemical methods for producing cerium (IV) nitrate from cerium (III) nitrate and can be used to separate rare-earth elements and to obtain a reagent for the oxidation of organic substances.

A known method of producing tetravalent cerium by electrochemical oxidation of cerium (III) nitrate in a nitric acid solution. Electrooxidation was carried out in a flow-through membrane electrolyzer of filter-fresh type, with an anion-exchange membrane MA-41. A platinum plate was used as an anode, a titanium plate was used as a cathode [Sedneva T.A., Tikhomirova I.A. Oxidation of cerium in a membrane electrolyzer. - Apatity. 2002 .-- 11 p. - Dep. at VINITI 08/12/2002, No. 1475-V2002]. The optimal current density for the oxidation of cerium (III) with a metal concentration of about 63 g / l in the electrolyte without stirring is in the range of 5.0-7.5 A / dm ² with an integrated current output of 58.7-31.4%, respectively.

The disadvantages of this method are the rather low integral current efficiency, as well as the use of an expensive platinum plate as an anode, since its electrolysis is accompanied by its slow dissolution [Chemodanov AN, Kolotyrkin Ya.M., Dembrovsky MA Investigation of the process of dissolution of platinum in acidic electrolytes at various polarizations using the radiochemical method. - M .: Electrochemistry, 1970. - V.6. - Vol. 4. - S. 460-467].

The closest analogue is a method for producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate [Pozdeev SS, Kondratyev ES, Gubin AF Electrochemical production of cerium (IV) ions for use in the process of wastewater treatment from organic impurities // Electroplating and surface treatment, 2014. - V. 22. - No. 4. - P. 37-39]. According to this process, niobium coated with a thin layer of platinum (platinum niobium anode), placed in the anode chamber of a two-chamber electrolyzer with an anion exchange membrane MA-41 IL, is used as the anode. In this case, the initial composition of the electrolyte in the cathode chamber of the electrolyzer is a solution of nitric acid with a concentration of 10 g / l. The initial electrolyte composition in the anode chamber is a solution of cerium (III) nitrate with a metal concentration of 115 g / l, containing 10 g / l of free nitric acid.

The disadvantage of this method is that during the electrolysis, the concentration of free nitric acid in the anolyte increases due to the transfer of nitrate ions from catholyte through the anion-exchange membrane. With an integrated current output of about 70-75% of the target anode reaction, the formation of cerium (IV) nitrate, the accumulation of free nitric acid in the anolyte reaches a value of 30 g / l. This increase in concentration reduces the stability of the platinum coating [Anodes. Platinized niobium [Electronic resource] // Metakem. Preclous Metals + Electrochemisrty.URL: http://www.metakem.de/en/produkte/anoden/platiniertes-niob.html (accessed 04/20/2015)].

The technical result that can be achieved by carrying out the invention is to provide the possibility of conducting long-term electrolysis by maintaining a constant concentration of nitric acid in the anode chamber and to ensure stable operation of the platinum anode.

This technical result is achieved by carrying out the process of producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate in a three-chamber electrolyzer with two cathode and one anode space, at a current density of 1 - 3 A / dm ² at the anode of platinum niobium.

Two cathode chambers are separated from the anode chamber by ion-exchange membranes, one cation-exchange (MK-40L), and the second anion-exchange (MA-41IL). The use of two cathode chambers with different membranes allows, on the one hand, to maintain the concentration of free nitric acid in the anolyte in the range of 8-12 g / l, and on the other hand, provides the formation of cerium (IV) nitrate.

In order to avoid an increase in voltage on the electrolyzer and to prevent an increase in the energy consumption for the process of producing cerium (IV) nitrate, the concentration of free nitric acid in the cathode chamber with an anion exchange membrane is periodically monitored and, if necessary, the catholyte is corrected by the addition of nitric acid, maintaining it within 8-12 g / l

The invention is illustrated by the following examples.

Example 1

The experiments on the electrochemical oxidation of cerium (III) ions were carried out in a two-chamber membrane-type electrolyzer at an anode current density of 2 A / dm ² . Platinum niobium was used as the anode, VT1-0 sheet titanium was used as the cathode, and an anion-exchange membrane of the MA-41IL brand was used to separate the cathode and anode spaces. The areas of the electrodes and the membrane were the same and amounted to 0.225 dm ² . Solutions of anolyte (cerium nitrate against a background of nitric acid) and catholyte (nitric acid) circulated in the cells of the electrolyzer at a rate of 13.8 l / h. The volumes of the solutions were the same and amounted to 0.2 liters. The initial concentration of nitric acid in the anolyte and catholyte was 10 g / l, the concentration of cerium (III) was 115 g / l.

The cerium concentration was determined by titration with a solution of Mohr's salt in the presence of an indicator - half-oxidized diphenylamine-4-sulfonic acid sodium salt (DAS). The concentration of nitric acid was determined by acid-base titration according to the method described in the literature [Piskareva S.K., Barashkov K.M., Olshanova K.M. Analytical chemistry. - M.: Higher School, 1994. - 384 p.].

For a quantitative assessment of the process, current output (W) and oxidation state (α,%) were used.

The current efficiency value was calculated by the formula:

VT = Qtheor / Qpract ∙ 100,%,

where Qpract is the amount of electricity spent on oxidation, Ah;

Qtheor is the theoretical amount of electricity required for oxidation, calculated according to the Faraday law, Ah.

Qtheor = C (Ce ⁴⁺ ) V / q,

where C (Ce ⁴⁺ ) is the current concentration of Ce ⁴⁺ ions in solution, g / l;

V is the volume of the treated solution, l;

q is the electrochemical equivalent, which in this case is equal to 5.224 g · equiv / (Ah).

Qpract = I · t,

where I is the current strength between the electrodes, A;

t is the electrolysis time, h

The value of the degree of oxidation of the substance was calculated by the formula:

α = C (Ce ⁴⁺ ) / C (Ce ref) 100,%,

where C (Ce Ref) is the total concentration of cerium in the treated solution, g / l.

At predetermined time intervals (1, 2, 3, 5, and 10 hours after the start of electrolysis), samples were taken from the anode chamber to determine the concentration of cerium (IV) in order to calculate the degree of oxidation and current efficiency (table 1), as well as to determine the concentration of free nitric acid (table 2).

From the presented data it is seen that during the electrolysis, an increase in the acid concentration occurs, by the end of the electrolysis the residual content of free nitric acid in the anolyte was 30 g / l, which worsens the operating conditions of the platinum coating.

Example 2

The experiments on the electrochemical oxidation of cerium (III) ions were carried out in a three-chamber membrane type electrolyzer with one cation exchange (MK-40L) and one anion exchange (MA-41IL) membranes at an anode current density of 2 A / dm ² . Platinum niobium with a surface of 0.225 dm ² and two titanium cathodes of the VT1-0 grade with a surface of 0.225 dm ² each was used as an anode. Solutions of anolyte (cerium nitrate against a background of nitric acid) and catholytes (nitric acid) circulated in the cells of the electrolyzer at a rate of 13.8 l / h. A 0.2 liter solution with an initial concentration of cerium (III) of 115 g / l containing 10 g / l of free nitric acid was placed in the anode chamber. A solution of nitric acid with a concentration of 10 g / L was placed in each of the cathode chambers.

At predetermined time intervals (1, 2, 3, 5, and 10 hours after the start of electrolysis), samples were taken from the anode chamber to determine the concentration of cerium (IV) in order to calculate the degree of oxidation and current efficiency (table 1), as well as to determine the concentration of free nitric acid (table 2).

Comparative results of the known and proposed method are presented in table 2. It is seen that when using a three-chamber electrolyzer, the acid concentration in the anolyte is kept constant.

The method of producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate

Table 1

The change in the current efficiency and oxidation state of cerium (III) in the prototype and the proposed method

Electrolysis time, hour Known method The proposed method α,% BT,% α,% BT,% one 11.9 89.8 11.6 90.5 2 23.8 88.4 24.2 89.5 3 36.1 88.0 36.8 88.8 5 56.3 87.4 57.4 89.4 10 88.4 78,4 88.3 79.9

The method of producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate

table 2

Comparison of the characteristics of the used method and prototype

Electrolysis time, hour The concentration of free nitric acid, g / l Known method The proposed method one 11,2 10.1 2 13.1 10,2 3 14.6 10.0 5 17.5 10.5 10 25,2 10.3

Claims (1)

A method of producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate in the anode chamber of an electrolyzer containing a solution with an initial concentration of cerium (III) nitrate of 100-130 g / l and an initial concentration of free nitric acid in anolyte and catholyte of 8-12 g / l, at a current density on the platinum niobium anode of 1-3 A / dm ² , characterized in that in order to increase the stability of the platinum coating, the electrolysis process is carried out in the anode chamber of a three-chamber electrolyzer, separated from the two cathode chambers of the anion-exchange and cation exchange membranes, due to which a constant concentration of free nitric acid of 8-12 g / l is maintained in the anode chamber.