SU1164595A1 - Method of determining niobium (v) - Google Patents

Description

The invention relates to analytical, chemical chemistry, namely to. methods of titrimetric determination of niobium in natural and industrial objects (inorganic materials, concentrates, alloys), and can be used in the analytical control of the production of this element.

The known method, the titrimetric determination of niobium in perioxyoxide, · ¹⁰ obium., Including the formation of a niobium peroxide complex in 1M ser-. 1: 1 ratio, oxidation of potassium permanganate with an excess of hydrogen peroxide, not more than 5 included in the complex, destruction of 10 M sulfuric acid perniobate and titration with potassium permanganate of the hydrogen peroxide complex released during dissociation. The sample is transferred 20 to the solution by alkaline fusion and dissolution of melt in water with hydrogen peroxide £ 0.

The disadvantages of this method is the lack of selectivity of the analysis in relation to tantalum and titration error fast bleach solutions of permanganate,

£

The closest technical: 30

The essence and the achieved result of the proposed method is the method of titrimetric determination of niobium in niobium pentoxide, including alkali fusion of niobium pentoxide, 35

dissolving melt in water with hydrogen peroxide, bringing the acidity of the solution to 1M in sulfuric acid, titrating the excess peroxide with potassium permanganate, destroying perniobate 40 Yun. a solution of H ₂ 8O4, binding iz-. a byte of peroxide equivalent to niobium, the Mohr salt and the titration of the excess Mora salt with ammonium vanadate with an Ν-phenyl-anthranilic 45 acid £ 2}.

The disadvantage of this method is that niobium can be determined in the presence of no more than 20% of tantalum with respect to niobies50 In addition, potassium permanganate is used for titration of excess hydrogen peroxide, therefore the equivalent point is not clearly defined. A disadvantage is the use of different titrants for titration of free hydrogen peroxide and Mohr's salt.

The purpose of the invention is to increase the selectivity of the determination of niobium in relation to tantalum.

This goal is achieved by the fact that according to the method of determining niobium (V), which includes translating it into a complex with hydrogen peroxide by alkaline fusion and dissolving in an aqueous solution of hydrogen peroxide, titrating the excess hydrogen peroxide, decomposing the niobium complex formed with sulfuric acid in the presence of Mora salt and then quantitative registration by titration of an excess of the Mora salt, decomposition of the niobium complex compound is carried out in a 0.2-0.7 M solution of sulfuric acid, and for titration of excess peroxide hydrogen and Mohr's salt is used with a cerium sulfate ferroin indicator.

Hydrogen peroxide forms complexes with niobium and tantalum in a wide range of acidity, and the stability of tantalum complexes is higher. Perniobate is destroyed in a strongly sulfuric acid medium, which served as the basis for developing methods for determining niobium, described in the basic object and prototype. But under these conditions, the tantalum peroxide complex also decomposes, which explains the interfering influence of this element on the definition of niobium. '

To establish the optimal acidity range when converting niobium to a complex compound with hydrogen peroxide (as well as subsequent titrations of excess peroxide, hydrogen and salt. Sea), studies are conducted, the results of which are shown in Table 1.

Thus, the optimal range of sulfuric acid content is 0.2-0.7 M. When going beyond the specified limits, the analysis accuracy decreases due to precipitation of niobium hydroxide or a noticeable decrease in the clarity of the indicator color transition at the equivalence point during cerium sulfate titration of excess hydrogen peroxide .

Titration of excess hydrogen peroxide and Mora salts with cerium sulfate

in the presence of ferroin provides <>

further simplification and enhancement

titration accuracy.

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When using a cerium (IV) salt solution as a titrant instead of potassium permanganate and ammonium vanadate, the known advantages of this oxidizing agent are realized: unstable intermediate substances are not formed, there are no induced reactions, and equilibrium is rapidly established. The best indicators for cerimetric titration should be substances whose oxidation-reduction potential is close to the potential at an equivalent point, resistant to light, temperature, oxidizer excess, oxidized and reduced · whose forms should be contrasted with colors. Ferroin (phenanthroline complex of iron (II) or iron trischelate with 2.2 * dipyridyl) best meets these requirements.

The use of a single cerium (IV) and ferroin sulfate titrant as an indicator made it possible to achieve clear color transitions at the equivalence points both in the titration of excess hydrogen peroxide and in excess of the Mohr salt.

The method is as follows.

A portion of the analyte is fused with caustic potassium, melted with hot water, hydrogen peroxide is added, the solution is heated to boiling, cooled, adjusted to op-35 of a determined volume with water and filtered. An aliquot of the solution is removed, an excess of hydrogen peroxide and sulfuric acid are added to a concentration of 0.2-0.7 MH ₂ 50 ^ and preferably ⁴⁰ 0.5 MH ₂ 50 <y and after ten minutes keeping the solution in a boiling water bath and cooling it to U-5 ° C free of hydrogen peroxide is titrated with cerium sulfate indikato- ⁴⁵ rum ferroin to transition color of the solution from orange-red to blue. Perniobate is destroyed by Mohr's salt, which binds H ₂ O ₂ , which is equivalent to niobium, and the excess Mora salt is titrated to 5 ° with a solution of cerium sulphate with ferroine indicator before the solution and? orange-red to blue.

Example 1. The definition of niobium ⁵⁵ in niobium pentoxide.

A portion of 0.25 g of niobium pentoxide is fused in a muffle furnace at 700 ^e C

with 6 g KOH. The melt leached 150 ml of hot water, add 5 ml of 3021% H ₂ O ₂ , cool, transfer the solution to a 250 ml volumetric flask,

5 was adjusted to the mark with water, and filtered. For the determination, 25 ml of the solution are taken, 2 drops of 10 ^ -H ₂ O ₂ and 3 ml of H ₂ δθ добавляют are added (the acidity of the solution is 0.5 MH ₂ CS ^). The thief of the sample is heated in a boiling water bath for 10 minutes and then cooled to 10–5 ° C in ice,

To the cooled sample, 6 drops of a 0.025 M solution of ferroin are added and 15 excess hydrogen peroxide is titrated with a 0.05 M solution of cerium sulfate before the indicator turns from orange-red to blue. Then add 10 ml of a 0.05 M solution of Mohr's salt, cool the sample solution and titrate with the same cerium sulfate solution until the color of the ferroin indicator changes from orange-red to blue. The content of niobium is calculated by the formula

„_ (Ν, Ι <ν ₂ τ ₂ ) 0.05-0.06645-250-100 / p N L L 0 ς -: --- y

^y h ⁿ

where ν ^ is the volume of the taken Mora salt solution, mp;

ν ₂ - the volume of cerium sulfate solution, followed by titration of the excess Mohr salt, ml;

ν ₃ - the volume of the analyzed solution, taken for titration, MP;

T * is the Mohr salt correction factor;

T ₂ - correction factor solution of cerium sulfate;

H - linkage,

The titer of a 0.05 M solution of Mohr's salt is set to a 0.05 M solution of potassium dichromate in the presence of ferroin indicator (the indicator color transition at the equivalence point from greenish-yellow through blue to orange-red).

The titer of a solution of cerium sulfate is set to a 0.05 M solution of the Mohr salt with an indicator of ferroin (the transition of the indicator color at the equivalence point from green to blue to orange-red).

The results of the determinations are given in table. 2

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Example 2. Determination of niobium in technical hydroxide ni-. Oia perform similarly to example 1. The results of the determinations are given in table. 2

Example 3. The definition of niobium in, columbite concentrate perform similarly to example 1. The results of the definitions are given in table. 2

Example 4. The determination of niobium in double oxide systems niobium - tantalum is carried out as described in Example 1. The systems were obtained by alkaline fusion of mixtures of high-purity reagents II ₂ One- and Ta ₂ Ov in different ratios. The results of the determinations are given in table. 3

The results of the determination of niobium in niobium pentoxide, technical niobium hydroxide, columbite concentrate are given in table. 2

The results of the determination of niobium in the double oxide system niobium tantalum are given in table. 3

Comparative characteristics of the proposed base method and the prototype are given in Table. four.

'The invention has, in comparison with the prototype / HD and the basic method (see Table 4), the possibility of determining niobium in the presence of any amounts of tantalum as a result of the destruction of perniobate only 10 times Mora salt and reducing the acidity of the solution by 10 times. prototype as it is applied

one titrant instead of two. In addition, there is a clear transition of the indicator color at the equivalence point, which is impossible to achieve with

5 titration with permanganate, which is used as a titrant in the base object and as one of the titrants in the prototype.

10 T a b i c a 1

These studies of the effect of concentration of sulfuric acid on the results of the determination of niobium in niobium pentoxide by the proposed method

Content Pentoxide detected H ₂ ZO ^, M niobium,% 0, 10 Precipitated niobium hydroxide precipitate 0.15 0.20 99.68 0.40 100.07 0.56 99.68 0.70 100.34 1.00 100.34 , 1.50 101.93 1.80 103.93 2.0 104.86

T'a blitz •. ί Analyzed object Found content% Ν6 ₂ 0 ^ Number of definitions Zg Niobium pentoxide 99.73 + 0.21 20 0,004 Technical Niobium Hydroxide 74.09 + 0.25 sixteen 0,006 * Columbite concentrate 37.97 + 0.82 14 0,018

The standard sample of columbit concentrate SVT-A5 was analyzed, in which the content of 37.5% LY ₂ 0 ^ · and 23.7% Ta ₂ O ^ g was certified

7 '1164595 eight Tabl and c a 3 Taken,% Found Νϊ> ₂ 0 _? % 8g (p-8) s ₂ o _? 1 ta about ₅ ten 90 9.65 0.015 20 80 19.60 0.012 thirty 70 30.35 0,010 40 60 40.30 0,009 50 50 49.76 0,009 60 .40 59.70 0,008 70 thirty 70.25 0,007 80 20 70.20 0,006 90 1.0 89.85 0,006 Tabl and c a 4 Way R Titrants Acidity titration Object analysis capabilities Valid quantities tantalum one. Basic (permanganatometric) KMp0 ₊ KMp0 ₄ 1M n ₂ zo / YM N ₂ 30 “}. . Pure LY ₂ O ^ Not allowed Prototype CMO ₄ 1M H ₂ 30 ₄ Pure II ₂ O ₅ No more than 20% (vanadometric) ΝΗ ₄ νθ, YuM n ₂ 30 ₄ Proposed (cerimetric) CE (8O ₄ ) ₂ 0.5 M H ₂ 50 ₄ Net LI ₂ 0 ^. Tech. hydroxide, columbite concentrate, oxide Any quantities ί Se (50 ₄ ) ₂ 0.5 M H ₂ 50 ₄ Dual systems niobium - tantalum

Claims (2)

METHOD OF DETERMINATION NIOBIUM (U) involving its conversion into a complex with hydrogen peroxide by alkaline fusion and dissolution in an aqueous solution of hydrogen peroxide, titration of excess hydrogen peroxide characterized in that, in order to increase the selectivity of the analysis with respect to tantalum, the decomposition of the complex compound of niobium is carried out in 0.2-0.7 And sulfuric acid solution s, and 3 for the titration of excess hydrogen peroxide and Mohr's salt is used with a cerium sulfate ferroin indicator. 8Ts „„ 1164595 one 1164595 2