RU2603642C1 - Method of producing cerium nitrate (iv) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method of producing cerium nitrate (IV) by electrochemical oxidation of cerium nitrate (III) in anode chamber, containing solution with initial concentration of cerium (III) ions equal to 100-130 g/l and initial concentration of free nitric acid in anolyte and catholyte equal to 8-12 g/l, at current density on platinated niobium anode of 1-3 A/dm². Method is characterized by that process of electrolytic oxidation of cerium (III) ions is carried out in anode chamber of three-chamber electrolyzer, separated from two cathode chambers with anion-exchange and cation-exchange membranes, wherein in anode chamber constant concentration of free nitric acid of 8-12 g/l is maintained, and at end of next cycle of electrolysis in solution of cathode chamber, separated from anode chamber with cation-exchange membrane, cerium nitrate (III), concentrated nitric acid and water are added and used as anolyte for next cycle of electrolysis.

EFFECT: use of presented method enables to eliminate losses of cerium ions due to their transfer from anolyte to catholyte.

1 cl, 2 ex, 2 tbl

Description

The invention relates to electrochemistry, in particular 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 a filter-press 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 disadvantage of this method is the relatively low integrated current efficiency and dissolution of the platinum anode.

The closest in technical essence 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. - T. 22. - No. 4. - S. 37-39]. According to this process, niobium is used as the anode, covered with a thin layer of platinum (platinum niobium anode), placed in the anode chamber of a two-chamber electrolyzer with an MA-41IL anion-exchange membrane. 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.

This method has the following disadvantage - during the electrolysis, nitrate anions are transferred from the cathode chamber to the anode one. Therefore, the concentration of free nitric acid in the anolyte continuously increases and reaches a value of more than 30 g / l. Such an increase in concentration reduces the stability of the platinum coating and leads to its gradual etching.

The technical task of this invention is to prevent the increase in the concentration of free nitric acid in the anolyte and to eliminate the loss of cerium (III) and (IV) ions as a result of their transfer to the catholyte through a cation exchange membrane.

The problem is solved in the present invention by a combination of the following techniques:

(1) Prevention of an increase in the concentration of nitric acid in the anolyte is achieved through the process of producing cerium (IV) nitrate by electrochemical oxidation of cerium (III) nitrate at a current density of 1-3 A / dm ² on a platinized niobium anode located in the anode chamber of a three-chamber electrolyzer with two cathode chambers, one of which is separated from the anode chamber by an anion exchange membrane, and the second by a cation exchange membrane.

(2) To eliminate the loss of cerium ions at the end of the next electrolysis cycle, a new portion of anolyte for the next electrolysis cycle is prepared by adding cerium (III) nitrate, concentrated nitric acid and water to the solution formed during the previous electrolysis cycle in a cathode chamber separated from the anode chamber cation exchange membrane.

Moreover, 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 its concentration within 8-12 g / l.

The invention is illustrated by the following examples.

Example 1

Experiments on the electrochemical oxidation of cerium (III) ions according to the known method 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 volume of anolyte is 0.2 l, the volume of each catholyte is 0.16 l. The initial concentration of nitric acid in the anolyte and catholytes was 10 g / l, the concentration of cerium (III) in the anolyte 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.

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:

BT = Qtheor / Qpract · 100,%,

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

Qtheor is the theoretical amount of electricity needed 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 is unacceptable for the operation of the platinum coating.

Example 2

Experiments on the electrochemical oxidation of cerium ions (III) was carried out in the three-chamber electrolytic cell of the membrane type with a cation (MK-40L) and one anion exchange (41IL MA) membranes in anodic current density of 2 A / ^dm2. Platinum-plated niobium anode with a surface of 0.225 dm ² and two titanium cathodes of the grade VT1-0 with a surface of 0.225 dm ² each were used as electrodes. Anolyte - a solution of cerium (III) nitrate with an initial concentration of 115 g / l and nitric acid 10 g / l circulated between the anode chamber of the electrolyzer and the auxiliary tank at a rate of 13.8 l / h. 0.16 L of solution with an initial concentration of free nitric acid of 10 g / L was placed in 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.

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) ions 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 platinized niobium anode 1-3 a / dm ^2, characterized in that the process of electrolytic oxidation of cerium ions (III) is carried out in a three-chamber electrolytic cell anode chamber separated from the cathode compartments of two anion and cation exchange membranes, etc. than in the anode chamber a constant concentration of free nitric acid of 8-12 g / l is maintained, and at the end of the next electrolysis cycle, cerium (III) nitrate, concentrated nitric acid and water are added to the solution from the cathode chamber separated from the anode chamber by a cation exchange membrane and used as anolyte for the next electrolysis cycle.