Analysis method for measuring high cobalt content by EDTA (Ethylene Diamine Tetraacetic Acid) complexation back titration method

Abstract

The invention relates to the technical field of zinc hydrometallurgy, and discloses an analysis method for measuring high cobalt content by an EDTA complexing back titration method, which is based on the following steps: oxidizing Co < 2 + > into Co < 3 + > by using potassium nitrite in an acetic acid medium to form cobalt potassium nitrite precipitate so as to realize separation of cobalt and interfering ions, dissolving the precipitate, complexing with excessive EDTA, and performing back titration by using a zinc standard solution. Xylenol orange is used as an indicator, and determination is completed at room temperature in a hexamethylenetetramine buffer system with the pH value being approximately equal to 5.8. Coexisting ion interference is effectively eliminated through tartaric acid, sodium fluoride, thiourea and other masking agents, the method has the advantages of being easy and convenient to operate, sensitive in end point, high in accuracy and low in cost, and the requirement for conventional analysis of high-cobalt materials can be met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zinc hydrometallurgy, and particularly relates to an analysis method for determining high cobalt content by EDTA complexing back titration. BACKGROUND

[0002] The purified cobalt residue generated in the zinc hydrometallurgy process needs to be recovered as high cobalt residue through processes such as sodium persulfate oxidation precipitation and pickling. The cobalt content of the high cobalt residue is usually higher than 15%, but the matrix is complex and contains multiple coexisting ions such as iron, manganese, zinc, cadmium and lead, which seriously interferes with the accurate determination of cobalt. The current cobalt determination methods include EDTA direct titration method, oxidation-reduction titration method, gravimetric method and ICP-OES method. Among them, the direct titration method needs to use PAN indicator under heating conditions, and the end point is not easy to control; the oxidation-reduction method and the gravimetric method have long process and low efficiency; the ICP-OES method is expensive and has high maintenance cost, and the sample dilution is easy to introduce errors. Therefore, it is urgent to establish a high cobalt content analysis method which is simple to operate, strong in anti-interference ability and accurate and reliable. SUMMARY

[0003] The purpose of the present application is to provide an analysis method for determining high cobalt content by EDTA complexing back titration to solve the problems raised in the background.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is: An analysis method for determining high cobalt content by EDTA complexing back titration, comprising the following contents: 1) Sample dissolution: accurately weigh the sample to be measured in a beaker, add sulfuric acid and hydrochloric acid, and heat at low temperature until the sample is completely dissolved to obtain a sample solution; 2) Sample pretreatment: after the sample solution is diluted, a part of the sample solution is taken, tartaric acid is added, and after dissolution, the sample solution is first adjusted to the appearance of precipitate with potassium hydroxide solution, and then adjusted to the complete dissolution of precipitate with acetic acid; 3) Cobalt oxidation and precipitation: in the acetic acid medium, slowly add potassium nitrite solution under low temperature heating, oxidize Co 2+ to Co 3+ , and form potassium cobalt nitrite precipitate, and age after precipitation; 4) Precipitate washing: filter the precipitate, and wash the precipitate and beaker with potassium nitrite washing solution and ethanol washing solution in sequence; 5) Precipitate dissolution: move the precipitate into the original beaker, add water and hydrochloric acid, heat at low temperature to completely dissolve the precipitate, and obtain a cobalt ion solution; 6) Complexing and back titration: add dimethyl phenol orange indicator in cobalt ion solution, adjust pH to about 5.8 with ammonia water, add masking agent and buffer solution, titrate to light yellow with EDTA standard solution after excess, place and back titrate to purple red end point with zinc standard solution, calculate cobalt content according to consumed EDTA and zinc standard solution volume.

[0005] The volume ratio of the sulfuric acid in step 1) is 1:9, and the added amount is 20ml; the volume ratio of the hydrochloric acid is 1:1, and the added amount is 3ml; and the heating mode is low-temperature heating for 2-3min.

[0006] The added amount of the tartaric acid in step 2) is 2g; the concentration of the potassium hydroxide solution is 200g / L; and the acetic acid is used to adjust pH to 3-5.

[0007] The added amount of the acetic acid in the acetic acid medium in step 3) is 8.0ml; the concentration of the potassium nitrite solution is 500g / L, and the added amount is 50ml; the reaction temperature is 40℃; the precipitation time is 30min; and the aging time is 2h.

[0008] The concentration of the potassium nitrite washing solution in step 4) is 30g / L, and the precipitate is washed for 5-6 times, and the beaker is washed for 2-3 times; the ethanol washing solution is an ethanol aqueous solution with a volume ratio of 4:1, and the precipitate is washed for 5-6 times, and the beaker is washed for 2-3 times.

[0009] The volume ratio of the hydrochloric acid in step 5) is 1:1, and the added amount is 5ml; and the heating mode is low-temperature heating.

[0010] The masking agent in step 6) includes sodium fluoride, thiourea and ascorbic acid, and the added amounts are 0.5g, 0.5g and 0.1g respectively; the buffer solution is a hexamethylenetetramine buffer solution, and the added amount is 15ml, and the pH is 5.8.

[0011] The concentration of the EDTA standard solution in step 6) is 0.0200mol / L; and the concentration of the zinc standard solution is 0.0200mol / L.

[0012] The high-cobalt-content sample is a high-cobalt residue produced by wet zinc smelting, and the cobalt content is more than 15%.

[0013] The potassium cobalt nitrite precipitate in step 3) is K3Co(NO2)6, and is used for selectively separating cobalt from interfering elements.

[0014] According to the above technical scheme, the present application has the following beneficial effects: 1) The present application adopts EDTA complexing back titration method, and uses potassium nitrite to oxidize Co 2+ to Co 3+And form potassium cobalt nitrite precipitation, effective separation of cobalt and iron, manganese, zinc and other interference ions, and then through the return titration method at room temperature to complete the determination, overcome the direct titration method need heating control end of the limitations.

[0015] 2) The present application further enhances the anti-interference ability by introducing tartaric acid, sodium fluoride, thiourea and other masking agents, the end color change is sensitive, the operation is simple and fast, the precision and accuracy are high, it is suitable for the conventional analysis of complex matrix high cobalt materials, the cost is low, and it has significant application value. DETAILED DESCRIPTION

[0016] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments.

[0017] Therefore, the following detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0018] In order to better understand the present application, the following description is made: The present application is in the dilute acetic acid medium containing tartaric acid, Co 2+ is oxidized to Co 3+ by potassium nitrite, and potassium cobalt nitrite precipitate [K3Co(NO2)6] which is insoluble in acetic acid is formed, which is separated from other interfering elements, and then the precipitate is completely dissolved and complexed with excess EDTA, and the excess EDTA is back titrated with zinc salt to quantitatively determine the cobalt content in the test sample.

[0019] Potassium nitrite can only oxidize Co 2+ to Co 3+ under acidic conditions, but it is also necessary to avoid the decomposition of NO2 - under strong acid conditions. Therefore, acetic acid medium is used to add potassium nitrite to form [K3Co(NO2)6] precipitate. The reaction needs to be completed at room temperature or under appropriate heating conditions (40-50℃), and high temperature will cause the decomposition of potassium nitrite; in order to ensure the complete oxidation of Co 2+ and the formation of precipitate, excess potassium nitrite needs to be added. When there are Fe 3+ , Al 3+ and other metal ions in the solution, they will react with NO2 - or form precipitate, thereby interfering with the reaction, in order to ensure the selective oxidation and precipitation of Co 2+ , other metal ions need to be masked by adding tartaric acid.

[0020] Specifically, the present application provides an analysis method for determining high cobalt content by EDTA complexometric back titration, comprising the following contents: 1. Main reagents: Sulfuric acid: (1 + 9) Hydrochloric acid: (1 + 1) Tartaric acid: AR Glacial acetic acid: AR Ammonia water: (1 + 1) Xylenol orange: 5% EDTA standard titration solution: 0.0200 mol / L ZnO standard titration solution: 0.0200 mol / L KNO2 solution: 500 g / L, prepared on site.

[0021] Washing solution: 30 g KNO2 is dissolved in 800 ml water, 8 ml glacial acetic acid is added, and water is added to a 1000 ml volumetric flask, and if necessary, it is used after filtration.

[0022] Potassium hydroxide solution: 100 g / L Ethanol washing solution: (4 + 1) Hexamethylenetetramine solution: 200 g / L, after the prepared solution is completely dissolved, adjust pH = 5.8 with HNO3 (1 + 1), and accurately measure and control with a pH meter.

[0023] Example 1: 1) Accurately weigh 0.5000-0.8000 g of sample (the sample weight can be appropriately increased or decreased according to the content of the sample) into a 400 ml beaker, add 20 ml of (1 + 9) sulfuric acid, heat for 2-3 min at low temperature, then add 3 ml of (1 + 1) hydrochloric acid, continue to heat until the sample is completely dissolved, and cool to room temperature.

[0024] 2) Move the cooled sample to a 250 ml volumetric flask, and shake well after dilution. Take 25.00 ml of the test solution into a 400 ml beaker, add 2 g of tartaric acid, and stir until completely dissolved. Adjust to pH 3-5 with 200 g / L KOH, and then adjust to pH 3-5 with acetic acid.

[0025] 3) Add 8.0 ml of acetic acid to the above solution, slowly add 50 ml of KNO2 (500 g / L) at low temperature (40°C) while stirring constantly. When Co 2+ is completely oxidized and precipitated as potassium cobalt nitrite complex [K3Co(NO2)6], keep the precipitate for 30 min, and then age at room temperature for 2 h.

[0026] ​4) The above precipitate is filtered with slow filter paper, and the precipitate is washed 5-6 times with 30 g / L of potassium nitrite solution, the beaker is washed 2-3 times, and the precipitate is washed 5-6 times with ethanol (4+1), and the beaker is washed 2-3 times.

[0027] 5) The precipitate is moved into the original beaker, about 50 ml of water and 5 ml of hydrochloric acid (1+1) are added, and low-temperature heating is used to completely dissolve the precipitate. After cooling to room temperature, 1-2 drops of 5% dimethyl phenol orange are added, (1+1) ammonia water is used to adjust to light purple red appearance and excess 1 ml (pH≈5.8), 0.5 g of sodium fluoride and thiourea are added, 0.1 g of ascorbic acid is added, 15 ml of hexamethyl tetramine buffer solution is added, 0.0200 mol / L EDTA standard solution is used for titration to light yellow, and then 2 ml of excess is added, and after 2 min, 0.0200 mol / L zinc oxide standard solution is used for back titration to purple red appearance, which is the end point.

[0028] Example 2 The material selected in the test is high-cobalt slag obtained by enrichment and recovery of wet zinc smelting purification slag, and the cobalt content of the sample is 20%-35% measured by back titration according to the method. Different content samples are selected for analysis and determination according to the method, and synchronous ICP spectrometry data comparison verification work is carried out. The comparison data of the volumetric determination results and the ICP emission spectrometry determination results are shown in Table 1 below: Table 1 Comparison data of volumetric determination results and ICP emission spectrometry determination results in Example 2

[0029] After comparison, the cobalt content in high-cobalt material analyzed and determined according to the method is basically consistent with the ICP spectrometry determination data, and the cobalt content in the same material can be accurately quantitatively analyzed.

[0030] Example 3 The same sample is selected, and the results of 3 parallel determinations are verified.

[0031] Under the same analysis and determination conditions, 0.02122 mol / L EDTA standard solution and 0.0200 mol / L ZnO standard solution are used for back titration of the test sample, and the 3 parallel determination data are shown in Table 2: Table 2 Comparison data of 3 parallel determination data in Example 3

[0032] Example 4 Select the same sample, under the same pretreatment and potassium nitrite precipitate cobalt conditions, the precipitate is moved into the original beaker, add water about 50ml, add hydrochloric acid (1+1) 5ml, low temperature heating makes the precipitate completely dissolved.Cooling to room temperature, add 5% of dimethyl phenol orange 1-2 drops, with (1+1) ammonia water to light purple red appears and excess 1ml (pH ≈ 5.8), add sodium fluoride and thiourea each 0.5g, ascorbic acid 0.1g, add acetic acid-sodium acetate buffer solution 25ml, with 0.0200mol / L EDTA standard solution titration to light yellow, then excess 2ml, place 2min, then with 0.0200mol / L zinc oxide standard solution back titration to purple red appears, the measured analysis results comparison data are shown in table 3: Table 3 Comparative data of determination results of different buffer solutions in example 4

[0033] Example 5: Select the same sample, the pretreated sample is moved into a 250ml volumetric flask, and the volume is adjusted, and 25.00ml of the test solution is taken into two 400ml beakers, one of which is added with 2g of tartaric acid, and the other is not added with tartaric acid, and both are adjusted to the appearance of precipitate with 200g / L KOH, and then adjusted to complete dissolution of the precipitate with acetic acid.The analysis test data of adding masking agent and not adding masking agent are shown in table 4: Table 4 Influence of masking agent on determination results in example 5

[0034] From the reaction phenomenon, it can be seen that there is Fe 3+ When Fe 3+ Hydrolysis occurs, and cobalt precipitates are wrapped, which interferes with the reaction, and masking agent should be added to eliminate interference.

[0035] Through experimental demonstration, the EDTA complex back titration method for determining the cobalt content in high cobalt slag has strong applicability to samples, the method is simple to operate, has high accuracy and good precision, can meet the analysis and detection needs of complex ingredient materials in wet zinc smelting, has low detection cost, and has certain application value.

Claims

1. An analytical method for determining high cobalt content using EDTA complexometric back titration, characterized in that, Includes the following steps: 1) Sample dissolution: Accurately weigh the sample to be tested into a beaker, add sulfuric acid and hydrochloric acid, and heat at low temperature until the sample is completely dissolved to obtain the sample solution; 2) Sample pretreatment: After the sample solution is brought to a final volume, a portion of the sample solution is taken, tartaric acid is added, and after dissolution, potassium hydroxide solution is used to adjust until a precipitate appears, and then acetic acid is used to adjust until the precipitate is completely dissolved. 3) Oxidation and precipitation of cobalt: In acetic acid medium, potassium nitrite solution is slowly added under low-temperature heating to oxidize and precipitate Co. 2+ Oxidized to Co 3+ It forms a potassium cobalt nitrite precipitate, which is then aged after being kept at a warm temperature. 4) Precipitation washing: Filter the precipitate and wash the precipitate and beaker sequentially with potassium nitrite washing solution and ethanol washing solution; 5) Precipitation dissolution: Transfer the precipitate back to the original beaker, add water and hydrochloric acid, and heat at low temperature to completely dissolve the precipitate, thus obtaining a cobalt ion solution; 6) Complexation and back titration: Add xylenol orange indicator to the cobalt ion solution, adjust the pH to about 5.8 with ammonia, add masking agent and buffer solution, titrate with EDTA standard solution until pale yellow, then add excess solution, let stand, and back titrate with zinc standard solution until purple-red endpoint, calculate the cobalt content based on the volume of EDTA and zinc standard solution consumed.

2. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 1), the volume ratio of sulfuric acid is 1:9, and the amount added is 20 ml; the volume ratio of hydrochloric acid is 1:1, and the amount added is 3 ml; the heating method is low-temperature heating for 2-3 minutes.

3. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 2), the amount of tartaric acid added is 2g; the concentration of the potassium hydroxide solution is 200g / L; and the acetic acid is used to adjust the pH to 3-5.

4. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 3), the amount of acetic acid added to the acetic acid medium is 8.0 ml; the concentration of the potassium nitrite solution is 500 g / L, and the amount added is 50 ml; the reaction temperature is 40℃; the precipitation time is 30 min; and the aging time is 2 h.

5. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 4), the concentration of potassium nitrite washing solution is 30 g / L, and the precipitate is washed 5-6 times and the beaker is washed 2-3 times; the ethanol washing solution is an aqueous solution of ethanol with a volume ratio of 4:1, and the precipitate is washed 5-6 times and the beaker is washed 2-3 times.

6. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 5), the volume ratio of hydrochloric acid is 1:1, and the amount added is 5 ml; the heating method is low-temperature heating.

7. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, The masking agent mentioned in step 6) includes sodium fluoride, thiourea and ascorbic acid, with added amounts of 0.5g, 0.5g and 0.1g, respectively; the buffer solution is a hexamethylenetetramine buffer solution, with an added amount of 15ml and a pH of 5.

8.

8. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, The concentration of the EDTA standard solution in step 6) is 0.0200 mol / L; the concentration of the zinc standard solution is 0.0200 mol / L.

9. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, The high cobalt content sample was high cobalt slag produced by hydrometallurgical zinc refining, with a cobalt content of over 15%.

10. The analytical method for determining high cobalt content by EDTA complexometric back titration according to claim 1, characterized in that, In step 3), the potassium cobalt nitrite precipitate is K3Co(NO2)6, which is used to selectively separate cobalt from interfering elements.

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