Method for continuously measuring content of zinc and cadmium in high-cadmium zinc-containing material by EDTA (ethylene diamine tetraacetic acid) volumetric method

Abstract

The invention discloses a method for continuously measuring the content of zinc and cadmium in a high-cadmium zinc-containing material through an EDTA volumetric method, and belongs to the technical field of germanium detection. The method comprises the following steps: completely separating zinc and cadmium in a sample under the strong alkaline condition of sodium hydroxide, taking hexamethylenetetramine with the pH value of 6 as a buffer solution, titrating the amount of zinc by using an EDTA standard solution, and back titrating the amount of cadmium by using a ZnO standard solution, and has good applicability and stability for rapidly completing the determination of the amount of independent zinc and cadmium in a material. The problems that interference is large, the analysis and detection process is tedious, the analysis method is not high in applicability and the application range is not wide in zinc and cadmium analysis and determination are solved. The method can completely carry out continuous independent quantitative determination of zinc content and cadmium content for the high-cadmium zinc-containing material, is high in applicability for an analysis method of the high-cadmium zinc-containing material in a purification process in lead-containing smoke dust and wet-process zinc smelting, and has the characteristics of simplicity, convenience and rapidness in operation, good precision, high accuracy and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of germanium hydrometallurgy, and specifically is a method for continuously determining the zinc and cadmium contents in high-cadmium zinc-containing materials by EDTA volumetric method. Background Art

[0002] In the process of zinc hydrometallurgy, the purified slag generally contains high content of zinc and cadmium. Most of the purified slag contains Zn The content of Cd is 10% to 20%, and it also contains Co: ≤1%, Ni ≤1%, Fe0.5% to 5%, and Pb1.0%. In order to better control the loss of metallic zinc during the purification process of hydrometallurgical zinc smelting, the analysis and determination of zinc and cadmium in the purified slag is an important detection indicator. However, since the chemical properties of cadmium are similar to those of zinc, when using the EDTA volumetric titration, Cd2+ and Zn2+ are determined at the same time. The conventional masking method cannot eliminate the interference between zinc and cadmium. Therefore, it is of great significance to effectively separate zinc and cadmium through pretreatment and realize the continuous determination of zinc and cadmium content in high-cadmium zinc-containing materials by EDTA volumetric method.

[0003] When this type of zinc-containing material is determined by the EDTA volumetric method, coexisting elements will interfere, and the sudden change of the titration endpoint is difficult to observe. If it is determined by polarography or atomic absorption, although there is no interference from common elements, the precision and reproducibility of the determination results are poor, which is difficult to meet production needs.

[0004] Usually in the analysis and testing of related smelting industries, the chemical analysis method for zinc in high-cadmium zinc-containing materials generally adopts Na 2 EDTA complexometric titration obtains the contents of zinc and cadmium, and then the content of cadmium is subtracted from the content to obtain the content of zinc. This method is stable and feasible for samples with low cadmium content in zinc-containing materials, but for materials such as zinc-containing soot, secondary leaching slag, cobalt-nickel slag, etc., the cadmium content is about 15% on average. If the cadmium element is not separated or masked, in the subsequent EDTA titration of zinc, the high content of cadmium will cause the titration end point to tail, and the indicator will not have an obvious jump, which seriously affects the determination of the zinc titration end point, making the existing zinc analysis conditions and analysis methods have certain limitations, resulting in inaccurate zinc content analysis results. At the same time, when determining the amount of cadmium alone, atomic absorption determination is usually used. When the cadmium content is as high as 10%, the analysis error caused by factors such as excessive dilution multiples is large. Summary of the invention

[0005] The purpose of the present invention is to provide a method for continuously determining the zinc and cadmium content in a high-cadmium zinc-containing material by an EDTA volumetric method, which completely separates zinc and cadmium in a sample under a strong alkaline condition of sodium hydroxide, uses hexamethylenetetramine with a pH of 6 as a buffer solution, uses an EDTA standard solution to titrate the zinc content, and uses a ZnO standard solution to back-titrate the cadmium content. The method has good applicability and stability for quickly completing the determination of the zinc content and cadmium content in the material, so as to solve the problems of large interference in the analysis and determination of zinc and cadmium, cumbersome analysis and detection process, weak applicability of the analysis method and limited application range.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The method for continuously determining the zinc and cadmium content in high-cadmium zinc-containing materials by EDTA volumetric method comprises the following specific steps:

[0008] 1) Accurately weigh a sample of a high-cadmium zinc-containing material and place it in a wide-mouth beaker, add hydrochloric acid to dissolve it at low temperature for about 5 minutes, and then add nitric acid to dissolve the sample completely; add sulfuric acid solution a, continue heating until white smoke is emitted, and continue for 2-3 minutes; after cooling, add sulfuric acid solution b, wash with water, and heat to a slight boil for 10 minutes; after cooling, filter it into a volumetric flask with slow filter paper, wash the precipitate and the beaker with 2% sulfuric acid 3-4 times each, wash the precipitate and the beaker with water 3-4 times each, cool to room temperature and then dilute to the scale, the filtrate is used to further separate zinc and cadmium, and the precipitate can be used to determine the amount of lead;

[0009] 2) Use a single-line pipette to transfer the filtrate obtained in step 1) into a beaker, add 15% NaOH solution, heat on a hot plate and boil for 10 minutes; after cooling, filter with slow filter paper into a triangular beaker, wash the precipitate with 5% NaOH washing solution for 5-6 times, and after washing, take a small amount of washing solution to check whether zinc ions are present to ensure that zinc and cadmium are completely separated. The filtrate is used for zinc content determination;

[0010] 3) Take the precipitate obtained in step 2) and wash it into the original beaker, dissolve the precipitate with sulfuric acid, wash with water, heat to a low boil for 5 minutes to completely dissolve the precipitate, and let it reach room temperature; add 1-2 drops of xylenol orange indicator to the test solution, adjust the solution to purple-red with ammonia water, and add 2 ml in excess; add sodium fluoride, dissolve it, adjust the solution to yellow with hydrochloric acid, add 2 ml in excess, and add ascorbic acid; adjust the solution to purple-red with ammonia water and hydrochloric acid, add thiourea and pH 6.0 hexamethylenetetramine buffer, heat to 40°C-50°C, titrate with EDTA standard solution to light yellow, and then back-titrate with ZnO standard solution until a stable light purple-red color appears, which is the end point, record the volume of the standard solution consumed, and calculate the cadmium content in the sample;

[0011] 4) Sodium fluoride and 1-2 drops of xylenol orange are added to the filtrate obtained in step 2), and sulfuric acid is used to adjust the solution to yellow, with a slight excess; ascorbic acid is added, and ammonia and sulfuric acid are used to adjust the solution to purple-red, thiourea and hexamethylenetetramine buffer solution are added, and EDTA standard solution is used to titrate until bright yellow is the end point, and the volume of the consumed standard solution is recorded to calculate the zinc content in the sample.

[0012] Further, in step 1), the sulfuric acid solution a added is (1+1) sulfuric acid, and the sulfuric acid solution b added is (1+9) sulfuric acid;

[0013] In step 3), the sulfuric acid added is dissolved into (1+1) sulfuric acid; the ammonia water used is (1+1) ammonia water; the hydrochloric acid used is (1+1) hydrochloric acid; the EDTA standard solution used is a 0.02 mol / L EDTA standard solution; the ZnO standard solution used is a 0.02 mol / L ZnO standard solution;

[0014] In step 4), the sulfuric acid used is (1+1) sulfuric acid; the ammonia water used is (1+1) ammonia water; and the EDTA standard solution used is a 0.02 mol / L EDTA standard solution.

[0015] Furthermore, in step 1), 0.2000 g of the sample is weighed into a 400 ml wide-mouth beaker, 10 ml of hydrochloric acid is added, 5 ml of the nitric acid sample is added, 8 ml of sulfuric acid solution a is added; 20 ml of sulfuric acid solution b is added; the solution is washed with water to a volume of 80 ml; after cooling, the solution is filtered with slow filter paper into a 250 ml volumetric flask;

[0016] In step 2), 20.00 ml of the filtrate was transferred to a 300 ml beaker, and 50 ml of 15% NaOH solution was added; after cooling, the filtrate was filtered through a slow filter paper into a 500 ml conical beaker;

[0017] In step 3), the precipitate is washed into the original beaker, dissolved with sulfuric acid, and washed with water to a volume of 100 ml; 0.1 g of sodium fluoride is added; 0.2 g of ascorbic acid is added; 0.5 g of thiourea is added; 10-15 ml of hexamethylenetetramine buffer solution of pH 6.0 is added;

[0018] In step 4), add 0.5 g of sodium fluoride; add 0.2 g of ascorbic acid; add 0.5 g of thiourea; and add 10-15 ml of hexamethylenetetramine buffer solution.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] In the present invention, the interfering ions such as iron, lead, manganese and a small amount of bismuth, aluminum, etc. present in the sample can be completely removed in advance by acid dissolution treatment and sodium hydroxide separation, and then the solubility characteristics of zinc and cadmium hydroxide precipitation under excessive strong alkaline conditions are utilized to effectively separate zinc and cadmium. In the analysis and determination process, the buffer medium characteristics of hexamethylenetetramine when the pH is 6.0 are utilized to eliminate the problem of OAc- and cadmium complexation in the conventional acetic acid-sodium acetate buffer medium that the endpoint is delayed, and a sharp titration endpoint color can be obtained. Using this method, it is completely possible to carry out continuous separate quantitative determination of zinc and cadmium content for high-cadmium zinc-containing materials, and the analytical method for high-cadmium zinc-containing materials in the purification process of lead-containing smoke and wet zinc smelting is highly applicable, and the method has the characteristics of simple operation, rapidity, good precision, and high accuracy. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail in the following examples.

[0022] The principle of the method of the present invention is: under strong alkaline conditions, the pretreated sample to be tested generates Cd(OH) 2 and Zn(OH) 2 White precipitate, Zn(OH) 2 It has the characteristics of amphoteric hydroxide and can be dissolved in excess sodium hydroxide solution to form zincate, while Cd(OH) 2 The precipitate does not dissolve under alkaline conditions. Thus, the zinc and cadmium in the test sample are effectively separated, and the zinc and cadmium content are quantitatively titrated with EDTA titration solution and zinc oxide titration solution respectively.

[0023] The reagent conditions used in this example are:

[0024] Hydrochloric acid 1.19 g / cm 3 ; Nitric acid 1.42g / cm 3； Sulfuric acid 1.84 g / cm 3； Sodium hydroxide AR; thiourea AR; sodium fluoride AR; ascorbic acid AR; ammonia AR; ammonia (1+1); sulfuric acid (1+1); hexamethylenetetramine 200g / L [adjusted to pH=6.0 with (1+1) nitric acid]; cobalt chloride 0.02%; ammonium mercury thiocyanate 0.15mol / L; EDTA standard solution 0.02mol / L; ZnO standard solution 0.02mol / L

[0025] Embodiment 1:

[0026] This embodiment provides a method for continuously determining the zinc and cadmium content in a high-cadmium zinc-containing material by an EDTA volumetric method, comprising the following specific steps:

[0027] 1) Accurately weigh 0.2000g of a high-cadmium zinc-containing material sample into a 400ml wide-mouth beaker, add 10ml of hydrochloric acid to dissolve at low temperature for about 5min, then add 5ml of nitric acid to completely dissolve the sample; add 8ml of 1+1 sulfuric acid solution, continue heating until white smoke is emitted, and continue for 2-3min; after cooling, add 20ml of 1+9 sulfuric acid solution, wash with water to a volume of about 80ml, and heat to a slight boil for 10min; after cooling, filter with slow filter paper into a 250ml volumetric flask, wash the precipitate and the beaker with 2% sulfuric acid 3-4 times each, wash the precipitate and the beaker with water 3-4 times each, cool to room temperature and then adjust the volume to the scale, the filtrate is used to further separate zinc and cadmium, and the precipitate can be used to determine the amount of lead;

[0028] 2) Use a single-line pipette to transfer 20.00 ml of the filtrate obtained in step 1) into a 300 ml beaker, add 50 ml of 15% NaOH solution, heat on a hot plate and boil for 10 min; after cooling, filter with slow filter paper into a 500 ml conical beaker, wash the precipitate with 5% NaOH washing solution 5-6 times, and after washing, take a small amount of washing solution to check whether zinc ions are present to ensure that zinc and cadmium are completely separated. The filtrate is used for zinc content determination;

[0029] 3) Wash the precipitate obtained in step 2) into the original beaker, dissolve the precipitate with 1+1 sulfuric acid, wash with water to a volume of about 100 ml, heat to a slight boil for 5 min to completely dissolve the precipitate, and let it reach room temperature; add 1-2 drops of xylenol orange indicator to the test solution, adjust the solution to purple-red with 1+1 ammonia water, and add 2 ml in excess; add about 0.1 g of sodium fluoride, adjust the solution to just turn yellow with 1+1 hydrochloric acid after dissolving, add 2 ml in excess, and add 0.2 g of ascorbic acid; adjust the solution to purple-red with 1+1 ammonia water and 1+1 hydrochloric acid, add 0.5 g of thiourea, 10-15 ml of hexamethylenetetramine buffer with pH=6.0, heat to 40°C-50°C, titrate with 0.02 mol / L EDTA standard solution to light yellow, and then back-titrate with 0.02 mol / L ZnO standard solution until a stable light purple-red color appears, which is the end point, record the volume of the standard solution consumed, and calculate the cadmium content in the sample;

[0030] 4) Add about 0.5 g of sodium fluoride and 1-2 drops of xylenol orange to the filtrate to be used, and adjust the solution with 1+1 sulfuric acid until it turns yellow, with a slight excess; add 0.2 g of ascorbic acid, and adjust the solution with 1+1 ammonia water and 1+1 sulfuric acid until the solution just turns purple-red, add 0.5 g of thiourea and 10-15 ml of hexamethylenetetramine buffer solution, and titrate with 0.02 mol / L EDTA standard solution until bright yellow is the end point, record the volume of the consumed standard solution to calculate the zinc content in the sample.

[0031] In this embodiment, Zn 2+ The identification method includes the following steps:

[0032] The filtrate to be tested after separation needs to be identified for zinc ions to verify whether the separation of zinc and cadmium is complete. Take a small amount of filtrate from the original solution, add hydrochloric acid to the solution, and add a small amount of 0.02% CoCl 2 solution, add 0.15 mol / L (NH 4 ) 2 Hg(SCN) 4 (2-3 drops) Stir evenly, and the appearance of sky blue precipitate within 2 minutes indicates the presence of zinc ions in the solution.

[0033] In (NH 4 ) 2 Hg(SCN) 4 When present, the generated Zn[Hg(SCN) 4 ] The white precipitate is easy to form a supersaturated solution, and the precipitation production is slow. 2+ When present, it can produce precipitation quickly. Therefore, if the generation time exceeds 2 minutes, it cannot be used as an effective criterion for determining whether there are residual zinc ions in the filtrate.

[0034] (NH 4 ) 2 Hg(SCN) 4 The solution can be 30g HgCl 2 and 33 g NH 4 SCN was dissolved in 100 ml of water.

[0035] Spiked recovery and precision test

[0036] The above experimental method was used to select the second leaching residue and cadmium oxide cotton samples for three analysis and determination, respectively, and the precision test was carried out. The test data are shown in Table 1:

[0037] Table 1: Precision test data table

[0038]

[0039] The precision test data RSD≦5%, meeting the analytical testing requirements.

[0040] The recovery rate of the spiked samples was determined by selecting 5.40 mg / ml zinc standard sample and 4.00 mg / ml Cd standard sample and the experimental test sample. The experimental data is shown in Table 2:

[0041] Table 2: Spike recovery test data

[0042]

[0043] The recovery rate of the spiked recovery test was 95%-110%, and the accuracy of the method met the requirements of analytical testing.

[0044] Verification of the effects of solution pH and buffer medium on the endpoint

[0045] Experiments show that when xylenol orange is used as an indicator to titrate zinc and cadmium content, the endpoint is sensitive between pH 5.5 and 6.0; the endpoint color is not sensitive when pH is less than 5.5; when pH is greater than 6, due to the influence of the complexing ability of EDTA and copper, when the copper content of the sample is high, 0.5g of thiourea can only mask 1mg of copper, and the use of masking agents cannot completely mask the interference of copper; when the zinc content of the sample is determined step by step, the complexing ability of EDTA and copper is controlled to be ≤6.0, which reduces the complexing ability of EDTA and copper, and 25mg of copper does not interfere with the titration.

[0046] When using conventional acetic acid-sodium acetate buffer solution at pH 5.5-6.0, it was found that quantitative determination could not be performed because a large amount of OAc was introduced. - ,OAc - It will complex with cadmium and delay the endpoint, making it impossible to accurately observe the titration endpoint. The use of hexamethylenetetramine buffer medium with a pH of 6.0 can effectively avoid the endpoint delay phenomenon. However, the requirements for analytical operations are relatively strict, and the pH value of the hexamethylenetetramine solution must be accurately adjusted to 6.0.

[0047] Verification of the influence of sodium hydroxide solution concentration and sodium hydroxide washing solution

[0048] Insufficient sodium hydroxide dosage will cause Cd(OH) 2 Incomplete precipitation results in low cadmium results and high zinc results; excessive sodium hydroxide will cause filtration difficulties and affect operating efficiency. At the same time, the amount of sodium hydroxide washing liquid used for washing must also be strictly controlled, otherwise it will cause filter paper to form knots during filtration and washing, affecting the filtration and washing effects. After testing, this method uses 10-15ml of sodium hydroxide with a concentration of 15%, and a 2%-5% sodium hydroxide solution as the washing liquid. When the sodium hydroxide concentration reaches 20%, it will cause the filter paper to form knots. Excessive washing liquid concentration will cause the solution to become viscous and the formed sodium zincate solution will be unfavorable for cleaning.

[0049] Verification of the influence of coexisting ions

[0050] The interfering ions such as iron, lead, manganese and a small amount of bismuth and aluminum in the sample are removed in advance by acid dissolution and sodium hydroxide separation. Under the test conditions, the allowable amount of coexisting ions (in mg) is: Cu 2+ (25), Co 2+ (1) Ni 2+ (0.2), Al 3+ Does not interfere with the assay.

[0051] Comparison and verification of experimental data and ICP test data

[0052] The comparison of the test data of this experimental method with ICP and polarography of the same batch of samples is shown in Table 3:

[0053] Table 3: Comparison of test data between this experimental method and ICP and polarography experiments

[0054]

[0055] Through data comparison and analysis, the data measured by this experimental method are consistent with the ICP measurement data; the polarography measurement data are greatly affected by data stability, and the accuracy of the data measured by this method is better than that of the polarography measurement data.

[0056] In summary, in the present invention, zinc and cadmium in the sample are completely separated under the strong alkaline condition of sodium hydroxide, hexamethylenetetramine with pH=6 is used as a buffer solution, EDTA standard solution is used to titrate the zinc amount, and ZnO standard solution is used to back-titrate the cadmium amount. The spiked recovery rate of zinc and cadmium is determined to be 95%-110%, and the analytical method meets the determination requirements.

[0057] Insufficient sodium hydroxide dosage will cause Cd(OH) 2 Incomplete precipitation will cause low cadmium results and high zinc results; excessive use of sodium hydroxide will cause filtration difficulties and affect operating efficiency. At the same time, the amount of sodium hydroxide washing solution used for washing must also be strictly controlled, otherwise it will cause filter paperboard to clog during filtration and washing, affecting the filtration and washing effects.

Claims

1. A method for continuously determining the zinc and cadmium content in high-cadmium zinc-containing materials by EDTA volumetric method, characterized in that: The specific steps include: 1) Accurately weigh a sample of a high-cadmium zinc-containing material and place it in a wide-mouth beaker, add hydrochloric acid to dissolve it at low temperature for about 5 minutes, and then add nitric acid to dissolve the sample completely; add sulfuric acid solution a, continue heating until white smoke is emitted, and continue for 2-3 minutes; after cooling, add sulfuric acid solution b, wash with water, and heat to a slight boil for 10 minutes; after cooling, filter it into a volumetric flask with slow filter paper, wash the precipitate and the beaker with 2% sulfuric acid 3-4 times each, wash the precipitate and the beaker with water 3-4 times each, cool to room temperature and then dilute to the scale, the filtrate is used to further separate zinc and cadmium, and the precipitate can be used to determine the amount of lead; 2) Use a single-line pipette to transfer the filtrate obtained in step 1) into a beaker, add 15% NaOH solution, heat on a hot plate and boil for 10 minutes; after cooling, filter with slow filter paper into a triangular beaker, wash the precipitate with 5% NaOH washing solution for 5-6 times, and after washing, take a small amount of washing solution to check whether zinc ions are present to ensure that zinc and cadmium are completely separated. The filtrate is used for zinc content determination; 3) Take the precipitate obtained in step 2) and wash it into the original beaker, dissolve the precipitate with sulfuric acid, wash with water, heat to a low boil for 5 minutes to completely dissolve the precipitate, and let it reach room temperature; add 1-2 drops of xylenol orange indicator to the test solution, adjust the solution to purple-red with ammonia water, and add 2 ml in excess; add sodium fluoride, dissolve it, adjust the solution to yellow with hydrochloric acid, add 2 ml in excess, and add ascorbic acid; adjust the solution to purple-red with ammonia water and hydrochloric acid, add thiourea and pH 6.0 hexamethylenetetramine buffer, heat to 40°C-50°C, titrate with EDTA standard solution to light yellow, and then back-titrate with ZnO standard solution until a stable light purple-red color appears, which is the end point, record the volume of the standard solution consumed, and calculate the cadmium content in the sample; 4) Sodium fluoride and 1-2 drops of xylenol orange are added to the filtrate obtained in step 2), and sulfuric acid is used to adjust the solution to yellow, with a slight excess; ascorbic acid is added, and ammonia and sulfuric acid are used to adjust the solution to purple-red, thiourea and hexamethylenetetramine buffer solution are added, and EDTA standard solution is used to titrate until bright yellow is the end point, and the volume of the consumed standard solution is recorded to calculate the zinc content in the sample.

2. The method for continuously determining the zinc-cadmium content in high-cadmium zinc-containing materials by EDTA volumetric method according to claim 1, characterized in that: In step 1), the sulfuric acid solution a added is 1+1 sulfuric acid, and the sulfuric acid solution b added is 1+9 sulfuric acid; In step 3), the sulfuric acid added is dissolved into 1+1 sulfuric acid; the ammonia water used is 1+1 ammonia water; the hydrochloric acid used is 1+1 hydrochloric acid; the EDTA standard solution used is 0.02 mol / L EDTA standard solution; The ZnO standard solution used is 0.02 mol / L ZnO standard solution; In step 4), the sulfuric acid used is 1+1 sulfuric acid; the ammonia water used is 1+1 ammonia water; and the EDTA standard solution used is 0.02 mol / L EDTA standard solution.

3. The method for continuously determining the zinc-cadmium content in high-cadmium zinc-containing materials by EDTA volumetric method according to claim 2, characterized in that: In step 1), weigh 0.2000 g of the sample into a 400 ml wide-mouth beaker, add 10 ml of hydrochloric acid, then add 5 ml of nitric acid sample, add 8 ml of sulfuric acid solution a; add 20 ml of sulfuric acid solution b; wash with water to a volume of 80 ml; after cooling, filter with slow filter paper into a 250 ml volumetric flask; In step 2), 20.00 ml of the filtrate was transferred to a 300 ml beaker, and 50 ml of 15% NaOH solution was added; after cooling, the filtrate was filtered through a slow filter paper and transferred to a 500 ml conical beaker; In step 3), the precipitate is washed into the original beaker, dissolved with sulfuric acid, and washed with water to a volume of 100 ml; 0.1 g of sodium fluoride is added; Add 0.2 g of ascorbic acid; add 0.5 g of thiourea; add 10-15 ml of pH 6.0 hexamethylenetetramine buffer; In step 4), add 0.5 g of sodium fluoride; add 0.2 g of ascorbic acid; add 0.5 g of thiourea; and add 10-15 ml of hexamethylenetetramine buffer solution.

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