Method for titrating sodium cyanide by using lead oxide as pretreatment agent to eliminate impurity interference
By using lead oxide pretreatment agent in gold concentrate leaching solution to selectively precipitate low-valence impurities, the problem of endpoint determination failure in sodium cyanide concentration determination was solved, and high-precision sodium cyanide concentration determination was achieved.
Patent Information
- Application Number
- CN202511141160.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-15
- Publication Date
- 2025-11-07
AI Technical Summary
Existing technologies cannot effectively eliminate interference from low-valence reducing impurities in gold concentrate leaching solutions, leading to the failure of sodium cyanide concentration determination endpoints and making it impossible to accurately determine sodium cyanide content.
Lead oxide was used as a pretreatment agent to react with low-valence impurities in an alkaline leachate, selectively precipitating interfering substances such as sulfides. The solution was then restored to a measurable state through a titration system. Potassium iodide was used as an indicator, and silver nitrate was titrated until the solution turned yellow and turbid, which was the endpoint.
It achieves accurate determination of sodium cyanide concentration, is simple in method, has an error of less than 2%, is applicable to complex systems with high sulfur, high copper, and high iron content, and ensures a clear titration endpoint.
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Figure CN120908375A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of titration technology in gold smelting, in particular to a method for eliminating impurity interference in titration of sodium cyanide by using lead oxide as a pretreatment reagent, which is simple in method and accurate in measured concentration of free sodium cyanide (NaCN). BACKGROUND
[0002] It is known that in the prior art, after gold concentrate is leached with sodium cyanide, the content of sodium cyanide (NaCN) in the solution is determined by silver nitrate titration method to control the concentration of sodium cyanide during leaching. However, when the leaching solution contains compounds of low-valence elements (such as hydrogen sulfide, sodium sulfide, etc.), compounds containing low-valence metal ions (such as Cu²⁺, Fe²⁺), etc., these reducing substances in the leaching solution are easy to react with silver nitrate to form silver sulfide (turbidity) or metal sulfide precipitate (yellow, brown), resulting in failure of end point determination. The traditional method cannot effectively eliminate low-valence reducing interference substances, resulting in that sodium cyanide cannot be determined by the traditional method. SUMMARY
[0003] The purpose of the present application is to solve the above-mentioned problems of the prior art, and to provide a method for eliminating impurity interference in titration of cyanide by using lead oxide as a pretreatment reagent, which is simple in method, accurate in measured concentration of sodium cyanide (NaCN), and selectively precipitates sulfides and other low-valence interference substances by the specific reaction of lead oxide in alkaline leaching solution, so as to restore the titration system to a measurable state, thereby accurately determining the content of sodium cyanide.
[0004] The technical solution adopted by the present application to solve its technical problems is: A method for eliminating impurity interference in titration of sodium cyanide by using lead oxide as a pretreatment reagent, characterized by the following steps: (1) Leaching solution preparation: after the complex gold concentrate is ground and slurried with water, lime (CaO) is added to adjust the pH to 11-12, and sodium cyanide (NaCN) is added for leaching to obtain a leaching solution; (2) Pretreatment stage: after the leaching solution obtained in step (1) is filtered, if turbidity or abnormal coloration occurs during direct titration, the filtered solution obtained after leaching is first added with lead oxide powder, and stirred until the solution changes from turbidity to clarity. The reaction endpoint is that the lead oxide powder no longer changes color after the filtered solution is mixed and stirred with the lead oxide powder, and a treated solution is obtained; (3) Filtration: the treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) The method for determining the concentration of sodium cyanide: take a certain volume V of the detection filtrate obtained in step (3) in a 400ml beaker, add 5% potassium iodide solution, and titrate with silver nitrate standard solution until yellow turbidity appears as the end point, record the amount of silver nitrate, the initial scale of the burette is V2, and the scale after titration is V1, The concentration calculation formula is as follows: ; In the above formula, C(NaCN) is the concentration of sodium cyanide, n / 10,000, 1 / 10,000=0.1g / L; C1 is the titration degree of AgNO3 to NaCN per milliliter, unit: mg / ml, according to the titration principle, each 1ml of AgNO3 corresponds to 4mg of NaCN consumed, and C1 is 4mg / ml; V2 is the initial scale of the burette, V1 is the scale after titration, and V1-V2 is the amount of silver nitrate, unit: ml; V is the volume of the detection solution obtained in the titration experiment, unit: ml; The final concentration of sodium cyanide is obtained .
[0005] The present application has the advantages of simple method, accurate determination of sodium cyanide concentration, specific reaction of lead oxide in alkaline leaching solution, selective precipitation of low-valence state interfering substances such as sulfides, and restoration of the titration system to a measurable state, thereby accurately determining the content of sodium cyanide. BRIEF DESCRIPTION OF DRAWINGS
[0006] Figure 1 is a titration comparison chart of leaching solution before and after lead oxide treatment. DETAILED DESCRIPTION
[0007] The present application will be further described below in conjunction with the drawings: As shown in the drawings, a method for eliminating impurity interference titration of cyanide by using lead oxide as a pretreatment reagent, characterized in that the method steps are as follows: (1) Leaching solution preparation: after the complex gold concentrate is ground with water, the slurry is adjusted, lime (CaO) is added to adjust the pH to 11-12, sodium cyanide (NaCN) is added for leaching, and the leaching solution is obtained; (2) Pretreatment stage: after the leaching solution obtained in step (1) is filtered, if direct titration appears turbidity or abnormal color development, the filtered solution obtained after leaching is first added with lead oxide powder, and stirred until the solution changes from turbidity to clarity, and the reaction end point is that the lead oxide powder no longer changes color after the filtered solution is mixed and stirred with the lead oxide powder, and a treated solution is obtained; The reaction mechanism is as follows: Reaction mechanism: PbO+ 2OH -+ H2O → [Pb(OH)4] 2- (alkaline dissolution), [Pb(OH)4]2+ S 2- → PbS↓ + 4OH - (sulfide precipitation); (3) Filtration: the treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) Method for measuring the concentration of sodium cyanide: a certain volume V of the detection filtrate obtained in step (3) is taken in a 400-ml beaker, 5% potassium iodide solution is added, and silver nitrate standard solution is added for titration until yellow turbidity appears as the end point, the amount of silver nitrate is recorded, the initial scale of the burette is V2, and the scale after titration is V1, The concentration calculation formula is as follows: ; In the above formula, C(NaCN) is the concentration of sodium cyanide, n / 10,000, 1 / 10,000=0.1 g / L; C1 is the titration degree of NaCN per milliliter of AgNO3, unit: mg / ml, according to the titration principle, 1 ml of AgNO3 is equivalent to 4 mg of NaCN, and C1 is 4 mg / ml; V2 is the initial scale of the burette, V1 is the scale after titration, and V1-V2 is the amount of silver nitrate, unit: ml; V is the volume of the detection solution obtained in the titration experiment, unit: ml; The final concentration of sodium cyanide is obtained .
[0008] The above titration principle is as follows: in an alkaline medium, potassium iodide is used as an indicator, silver nitrate standard solution is used for titration, an Ag(CN)2- complex is formed, excess silver ions react with potassium iodide to form yellow silver iodide precipitate, which is the end point, the end point of the treatment method is clear (the silver iodide precipitate jumps obviously), and the titration of calcium oxide is supported.
[0009] AgNO3 + 2NaCN = NaAg(CN)2 + NaNO3 AgNO3 + KI = AgI↓ + KNO3 The present application has the advantages of simple method, accurate measurement of free sodium cyanide (NaCN) concentration, selective precipitation of sulfide and other low-valence state interferents through the specific reaction of lead oxide in alkaline leaching solution, restoration of the titration system to a measurable state, and accurate determination of the sodium cyanide content.
[0010] Figure 1 The figure is a titration comparison of leaching solutions before and after lead oxide treatment (left: untreated turbid liquid; right: clear liquid after treatment).
[0011] Design and results of the spike recovery experiment To verify the accuracy of the method, a spike recovery experiment was designed as follows: Experimental procedure: 1. Take the leach liquor with a known concentration of sodium cyanide (background value Co) and divide it into three groups: Blank group: directly titrate without adding lead oxide.
[0012] Treatment group: titrate after adding lead oxide pretreatment.
[0013] Spiked group: add a known amount of sodium cyanide standard solution (AC) to the treated solution and then titrate.
[0014] 2. Calculate the recovery rate: Recovery rate = * 100%
[0015] Conclusion: The spike recovery rate is 100%, indicating that the method has high accuracy and that lead oxide pretreatment does not affect the quantitative analysis of sodium cyanide.
[0016] Example 1 Raw material: A high-sulfur pyrite-containing gold concentrate (containing S 8.2%, Cu 0.5%).
[0017] Treatment steps: (1) Leach liquor preparation: After grinding and slurry preparation of the complex gold concentrate with clean water, add lime (CaO) to adjust the pH to 11-12, and then add sodium cyanide (NaCN) for leaching to obtain the leach liquor; (2) Pretreatment stage: When the leach liquor obtained in step (1) is directly titrated, black turbidity (Ag2S colloid) appears, making it impossible to determine the endpoint. Add 1%-5% lead oxide powder to the filtered leach liquor, stir for 10 minutes until the solution changes from turbidity to clarity, and the reaction endpoint is reached when the lead oxide powder no longer changes color after mixing and stirring with the filtered leach liquor. The treated solution is obtained; (3) Filtration: The treated solution from step (2) is filtered twice using rapid filter paper to obtain the detection filtrate, which can be directly used for silver nitrate titration; (4) Method for determining the concentration of sodium cyanide: Take 5 ml of the detection filtrate obtained in step (3) in a 400 ml beaker, add 5 drops of 5% potassium iodide solution, and titrate with silver nitrate standard solution until a yellowish turbidity appears as the endpoint. Record the amount of silver nitrate used. The initial scale of the burette is V2, and the scale after titration is V1. The amount of silver nitrate used is V1-V2, and the concentration of sodium cyanide is measured . The measured data is shown in Table 1.
[0018] Take experiment No. 1 as an example, the calculation method is as follows:
[0019]
[0020] The theoretical value of the concentration of sodium cyanide in the patent is 30.0 / 10,000, and the error between the above experimental data and the theoretical value is less than 2%.
[0021] Table 2 below is the conclusion of the comparative experiment of adding lead oxide and not adding lead oxide:
[0022] From the above conclusion, it can be seen that the accuracy of the titration conclusion is high after adding lead oxide, and the error is less than 2% compared with the theoretical value.
[0023] Example 2 Raw material: a high-sulfur arsenic-containing gold concentrate (containing S 26.5%).
[0024] Processing steps: (1) Preparation of leaching solution: after the complex gold concentrate is ground and slurried with water, lime (CaO) is added to adjust the pH to 11-12, sodium cyanide (NaCN) is added for leaching, and the leaching solution is obtained; (2) Pretreatment stage: the leaching solution obtained in step (1) is filtered, and when the leaching solution is directly titrated, black turbidity (Ag2S colloid) appears, and the end point cannot be determined. The filtered solution obtained after leaching is first added with 1%-5% lead oxide powder, stirred for 10 minutes, and then the solution is changed from turbidity to clarity. The reaction endpoint is that the lead oxide powder does not change color after being mixed and stirred with the filtered solution, and a treated solution is obtained; (3) Filtration: the treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) Method for measuring the concentration of sodium cyanide: take 5 ml of the detection filtrate obtained in step (3) in a 400 ml beaker, add 5 drops of 5% potassium iodide solution, and titrate with silver nitrate standard solution until yellow turbidity appears as the end point. Record the amount of silver nitrate used. The initial scale of the burette is V2, and the scale after titration is V1. V1-V2 is the amount of silver nitrate used, and the concentration of sodium cyanide is measured , measured three times, and the data are as shown in Table 3.
[0025]
[0026] The theoretical value of the concentration of sodium cyanide in the patent is 30.0 / 10,000, and the error between the above experimental data and the theoretical value is less than 2%.
[0027] Table 4 below is the conclusion of the comparative experiment of adding lead oxide and not adding lead oxide:
[0028] From the above conclusion, it can be seen that the accuracy of the titration conclusion is high after adding lead oxide, and the error with the theoretical value is less than 2%.
[0029] Example 3 Raw material: a high-sulfur high-copper gold concentrate (containing S 26.5%, Cu 1.5%).
[0030] Treatment steps: (1) Preparation of leaching solution: after the complex gold concentrate is ground and slurried with water, lime (CaO) is added to adjust the pH to 11-12, and sodium cyanide (NaCN) is added for leaching to obtain a leaching solution; (2) Pretreatment stage: the leaching solution obtained in step (1) is filtered, and when the leaching solution is directly titrated, black turbidity (Ag2S colloid) appears, and the end point cannot be determined. The filtered solution obtained after leaching is first added with 1%-5% lead oxide powder, and after stirring for 10 minutes, the solution changes from turbidity to clarity. The reaction end point is that after the filtered solution is mixed and stirred with lead oxide powder, the lead oxide powder no longer changes color, and a treated solution is obtained; (3) Filtration: the treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) Method for determining the concentration of sodium cyanide: take 5 ml of the detection filtrate obtained in step (3) in a 400 ml beaker, add 5 drops of 5% potassium iodide solution, and titrate with silver nitrate standard solution until yellow turbidity appears as the end point. Record the amount of silver nitrate used. The initial scale of the burette is V2, and the scale after titration is V1. V1-V2 is the amount of silver nitrate used, and the concentration of sodium cyanide is measured , and the measured data is shown in Table 5.
[0031]
[0032] The theoretical value of the concentration of sodium cyanide in this patent is 30.0 / 10,000, and the error between the above experimental data and the theoretical value is less than 2%.
[0033] Table 6 below is the experimental conclusion of the comparison between adding lead oxide and not adding lead oxide:
[0034] From the above conclusion, it can be seen that the accuracy of the titration conclusion is high after adding lead oxide, and the error with the theoretical value is less than 2%.
[0035] Example 4 Raw material: a high-sulfur high-copper high-iron gold concentrate (containing S 26.5%, Cu 1.5%, Fe 21.4%).
[0036] Process steps: (1) Preparation of leaching solution: After the complex gold concentrate is ground with clean water, the slurry is adjusted to pH 11-12 by adding lime (CaO), and sodium cyanide (NaCN) is added for leaching to obtain a leaching solution; (2) Pretreatment stage: After the leaching solution obtained in step (1) is filtered, black turbidity (Ag2S colloid) appears when the leaching solution is titrated directly, and the end point cannot be determined. The filtered solution obtained after leaching is first added with 1%-5% lead oxide powder, and after stirring for 10 minutes, the solution changes from turbidity to clarity. The reaction endpoint is that after the filtered solution is mixed and stirred with lead oxide powder, the lead oxide powder no longer changes color, and a treated solution is obtained; (3) Filtration: The treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) Method for determining the concentration of sodium cyanide: Take 5 ml of the detection filtrate obtained in step (3) in a 400 ml beaker, add 5 drops of 5% potassium iodide solution, and titrate with silver nitrate standard solution until a yellow turbidity appears as the end point. Record the amount of silver nitrate used. The initial scale of the burette is V2, and the scale after titration is V1. V1-V2 is the amount of silver nitrate used, and the concentration of sodium cyanide is measured , and the measured data is as shown in Table 7.
[0037]
[0038] The theoretical value of sodium cyanide concentration in this patent is 30.0 / 10,000, and the error between the above experimental data and the theoretical value is <2%.
[0039] Table 8 below is the conclusion of the comparative experiment of adding lead oxide and not adding lead oxide:
[0040] From the above conclusion, it can be seen that after adding lead oxide, the accuracy of titration is high, and the error with the theoretical value is less than 2%.
[0041] The RSD (relative standard deviation) summary table of the above Examples 1-4 is as shown in Table 9:
[0042] Through supplementary repeated experimental data and statistical analysis, the stability and accuracy of the lead oxide pretreatment method under different impurity conditions are verified: 1. Precision: The RSD of all examples is <1.2%, indicating excellent repeatability of the method.
[0043] 2. Accuracy: The error is controlled to be <2%, meeting the industrial detection requirements.
[0044] 3. Applicability: Even in the complex system of high sulfur, high copper, high iron, lead oxide can still effectively eliminate interference and ensure the clear end point of titration.
Claims
1. A method for eliminating interference of impurities in titration of sodium cyanide using lead oxide as a pre-treatment reagent, characterized in that The method steps are as follows: (1) Preparation of leaching solution: after the complex gold concentrate is ground with clean water, the slurry is adjusted, lime (CaO) is added to adjust the pH to 11-12, and sodium cyanide is added for leaching, to obtain a leaching solution; (2) Pretreatment stage: after the leaching solution obtained in step (1) is filtered, if direct titration appears turbidity or abnormal coloration, the filtered solution obtained after leaching is first added with lead oxide powder, and stirred until the solution changes from turbidity to clarity, and the reaction endpoint is that after the filtered solution is mixed with the lead oxide powder and stirred, the lead oxide powder no longer changes color, to obtain a treated solution; (3) Filtration: the treated solution after step (2) is filtered twice with rapid filter paper to obtain a detection filtrate, which can be directly used for silver nitrate titration; (4) Method for determining the concentration of sodium cyanide: a certain volume V of the detection filtrate obtained in step (3) is taken in a 400ml beaker, 5% potassium iodide solution is added, and silver nitrate standard solution is titrated until yellow turbidity appears as the endpoint, the amount of silver nitrate is recorded, the initial scale of the burette is V2, and the scale after titration is V1, The concentration calculation formula is as follows: ； In the formula, C(NaCN) is the concentration of sodium cyanide, n / 10,000, 1 / 10,000=0.1g / L; C1 is the titration degree of AgNO3 to NaCN per milliliter, in mg / ml, according to the titration principle, each 1ml of AgNO3 corresponds to 4mg of NaCN consumed, and C1 is 4mg / ml; V2 is the initial scale of the burette, V1 is the scale after titration, V1-V2 is the amount of silver nitrate, in ml; V is the volume of the detection solution obtained in the titration experiment, in ml; The final sodium cyanide concentration .