A sample pretreatment method for elemental analysis of pyrite

Abstract

The application relates to a sample pretreatment method for pyrite element analysis. First, a pretreatment agent is prepared: carboxymethyl chitosan is activated on the surface through NHS / EDC, and then reacts with phosphoethanolamine to obtain the pretreatment agent; secondly, a pyrite sample is crushed into particles, and is fully ground into powder together with NaOH, NaNO3 and the pretreatment agent; then, the temperature is increased to 180-250 DEG C and then to 350-450 DEG C for heat preservation; the sintered solid is transferred into a beaker, hot nitric acid solution is added, ultrasonic is used to dissolve the solid, and after cooling, filtration is carried out into a volumetric flask, and dilute nitric acid is used for constant volume to obtain a sample to be tested. The treatment method avoids the use of a large amount of concentrated acid and perchloric acid, the reagent consumption is small, and the method is environment-friendly; the treated sample is determined by an ICP-MS instrument and the like, and the recovery rate can be ensured to be above 95%; compared with a standard value, the RSD value is not more than 5%, and the accuracy is good.

Description

Technical Field

[0001] This invention relates to the field of mineral chemical composition analysis technology, specifically to a sample pretreatment method for elemental analysis of pyrite. Background Technology

[0002] Pyrite is one of the most widely distributed sulfide minerals in the Earth's crust. It is a major mineral raw material for extracting sulfur and producing sulfuric acid, and it is also an important gold-bearing mineral. Accurate determination of major elements (such as Fe and S) and associated valuable or harmful trace elements such as Cu, Zn, As, Co, Se, and Cd in pyrite is crucial for the study of ore genesis, the formulation of mineral processing technology, and environmental assessment.

[0003] Currently, the most commonly used methods for elemental analysis of sulfide minerals are acid dissolution and ion chromatography. These methods involve dissolving the ore in a specific acid (such as nitric acid or hydrochloric acid) to extract sulfide ions (S). 2- Then, a chromatogram is used for separation and determination. This method can distinguish different forms of sulfur (such as free sulfur and acid-soluble sulfur). Although strong acid digestion methods (such as aqua regia, reverse aqua regia, nitric acid-hydrofluoric acid-perchloric acid systems) are commonly used, they have problems such as high reagent consumption, generation of toxic acid mist and waste liquid, and serious loss of volatile elements such as arsenic, selenium, and mercury. Moreover, the use of perchloric acid poses safety hazards. In addition, although high-temperature alkaline fusion methods (such as sodium peroxide fusion) can effectively decompose minerals, the reaction temperature is usually higher than 600℃. When processing pyrite, it will cause violent oxidation of sulfides, instantly releasing a large amount of SO2 gas, causing sample splashing, loss, and even danger. It also cannot effectively fix volatile elements.

[0004] Therefore, developing a pretreatment method that can safely decompose pyrite at lower temperatures and ensure the quantitative transfer of all target elements (especially volatile elements) to the test solution is key to achieving high-precision component analysis. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention designs a carboxymethyl chitosan-based flux that can safely decompose pyrite at lower temperatures.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A sample pretreatment method for elemental analysis of pyrite includes the following steps:

[0008] S1, Pretreatment agent

[0009] S1-1. Dissolve carboxymethyl chitosan in MES buffer, add N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), and activate at room temperature for 30 min.

[0010] S1-2. Continue to add ethanolamine phosphate to the reaction system and continue the reaction in a 50°C water bath for 8 hours. After the reaction is completed, cool to room temperature, drop the reaction solution into ethanol to precipitate, filter, wash with water and dry to obtain the product.

[0011] S2, Sample Processing

[0012] S2-1. Take a pyrite sample and crush it into particles. Take an appropriate amount and place it in an agate mortar. Then add NaOH, NaNO3 and pretreatment agent in sequence and grind it into powder and mix evenly.

[0013] S2-2. Transfer the mixture to a corundum crucible, place it in a muffle furnace, first heat it to 180~250℃ and hold it, then heat it to 350~450℃ and hold it. After the program is completed, let it cool naturally.

[0014] S2-3. Transfer the sintered solid to a beaker, add hot nitric acid solution, sonicate to dissolve the solid, cool and filter into a volumetric flask, and dilute to volume with dilute nitric acid to obtain the test sample.

[0015] Further, in step S1, the mass ratio of carboxymethyl chitosan, N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and ethanolamine phosphate is 1:0.3:0.45:0.3~0.5.

[0016] Furthermore, in step S2, the mass ratio of pyrite, NaOH, NaNO3, and pretreatment agent is 1:5:3:0.1~0.3.

[0017] Further, the conditions for step S2-2 are as follows: heat up to 180-250℃ at 5-8℃ / min and hold for 20 min; then heat up to 350-450℃ at 3-5℃ / min and hold for 50 min.

[0018] Furthermore, the hot nitric acid solution is 5% nitric acid at 50-60°C.

[0019] The beneficial effects of this invention are as follows: This invention prepares a carboxymethyl chitosan-based pretreatment agent, which, in conjunction with sodium hydroxide and sodium nitrate, melts and digests pyrite, avoiding the use of large amounts of concentrated acid and perchloric acid, requiring less reagent and being environmentally friendly; it can also melt pyrite at relatively low temperatures (below 500℃), inhibiting the generation of toxic gases such as SO2, and the treated sample can be measured by instruments such as ICP-MS to ensure a recovery rate of over 95%, with the RSD value not exceeding 5% compared to the standard value, demonstrating good accuracy. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1: Preparation of pretreatment agent

[0023] 1) Add 2.0 g of carboxymethyl chitosan (degree of substitution > 84%) to 100 mL of MES buffer (pH = 5.8) and stir until dissolved. Add 0.6 g of NHS and 0.9 g of EDC·HCl and activate at room temperature for 30 min.

[0024] 2) Add 0.8 g of ethanolamine phosphate to the reaction system and continue the reaction in a 50°C water bath for 8 hours. After the reaction is completed, cool to room temperature, add the reaction solution dropwise into ethanol to precipitate, filter, wash with water and dry to obtain the product.

[0025] Example 2: Sample Processing

[0026] 1) Take pyrite standard material GBW07267 and crush it into granules. Take 0.1g and place it in an agate mortar. Then add 0.5g NaOH, 0.3g NaNO3 and 0.015g pretreatment agent in sequence, and grind it into powder and mix it evenly.

[0027] 2) Transfer the mixture to a corundum crucible, place it in a muffle furnace, heat it to 220 °C at 8 °C / min and hold it for 20 min; then heat it to 420 °C at 5 °C / min and hold it for 50 min. After the program is completed, allow it to cool naturally.

[0028] 3) Transfer the sintered solid to a beaker, add 5% hot nitric acid solution (60 ℃), sonicate to dissolve the solid, cool and filter into a 50 mL volumetric flask, and dilute to volume with 2% nitric acid to obtain the test sample.

[0029] The sample was subjected to ICP-MS analysis. Standard curve solutions for elements such as Fe and S were prepared. The concentration of each element was calculated based on the standard curve and converted into the content in the sample. The recovery rate was calculated based on the standard value of the standard substance.

[0030] Table 1

[0031]

[0032] Note: Fe and S are the main macroelements, and the units are mass percentages. They were determined using ICP-OES.

[0033] The data in Table 1 show that the pyrite samples treated according to this invention, when analyzed by ICP-MS, show small differences between the measured values ​​and the standard values. The RSD values ​​of trace elements can also be controlled below 5%, and the recovery rates are all above 95%. The treatment method of this application can ensure the accuracy of detection while optimizing the treatment process, reducing the use of concentrated acid and perchloric acid, and is environmentally friendly. This is because this application uses an alkaline fusion system digester (NaOH, NaNO3) combined with a carboxymethyl chitosan-based pretreatment agent, forming a multi-synergistic effect of fluxing, sulfur fixation, and fixation of volatile elements. This invention uses commercially available sodium carboxymethyl chitosan as raw material, whose molecular chain contains abundant carboxymethyl groups. Through EDC / NHS activation-amidation reaction, ethanolamine phosphate is covalently grafted onto the side chain of carboxymethyl chitosan to obtain a phosphorylated carboxymethyl chitosan additive that combines the film-forming / dispersing properties of a polymer framework with the efficient coordination ability of phosphate groups. The alkali-fusion digester (NaOH, NaNO3) and carboxymethyl chitosan-based pretreatment agent were ground with pyrite and then subjected to programmed heating. In the first heating stage, these active groups reacted with the alkali-fusion system via an acid-base reaction, softening the polymer chains and causing plastic flow. This resulted in a uniform coating layer spreading on the mineral particle surface, promoting homogeneous contact between the digester and the mineral powder. In the second heating stage, the softened and flowing sodium salt of the carboxymethyl chitosan derivative exhibited good surface activity, improving the wettability of the alkali-fusion melt on the mineral particles and promoting solid-liquid mass transfer. This resulted in the complete decomposition of pyrite at a relatively low temperature of 350-450℃. Ultimately, this method achieved in-situ, efficient fixation of volatile / harmful elements, retaining nearly 100% in the solid product, with a recovery rate in the test solution close to the theoretical value.

[0034] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A sample pretreatment method for elemental analysis of pyrite, characterized in that, Includes the following steps: S1, Pretreatment agent S1-1. Dissolve carboxymethyl chitosan in MES buffer, add N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and activate at room temperature for 30 min. S1-2. Continue to add ethanolamine phosphate to the reaction system and continue the reaction in a 50°C water bath for 8 hours. After the reaction is completed, cool to room temperature, drop the reaction solution into ethanol to precipitate, filter, wash with water and dry to obtain the product. S2, Sample Processing S2-1. Take a pyrite sample and crush it into particles. Take an appropriate amount and place it in an agate mortar. Then add NaOH, NaNO3 and pretreatment agent in sequence and grind it into powder and mix evenly. S2-2. Transfer the mixture to a corundum crucible, place it in a muffle furnace, first heat it to 180~250℃ and hold it, then heat it to 350~450℃ and hold it. After the program is completed, let it cool naturally. S2-3. Transfer the sintered solid to a beaker, add hot nitric acid solution, sonicate to dissolve the solid, cool and filter into a volumetric flask, and dilute to volume with dilute nitric acid to obtain the test sample.

2. The sample pretreatment method for elemental analysis of pyrite according to claim 1, characterized in that, In step S1, the mass ratio of carboxymethyl chitosan, N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and ethanolamine phosphate is 1:0.3:0.45:0.3~0.

5.

3. The sample pretreatment method for elemental analysis of pyrite according to claim 1, characterized in that, In step S2, the mass ratio of pyrite, NaOH, NaNO3 and pretreatment agent is 1:5:3:0.1~0.

3.

4. The sample pretreatment method for elemental analysis of pyrite according to claim 1, characterized in that, The conditions for step S2-2 are as follows: heat up to 180-250℃ at 5-8℃ / min and hold for 20 min; then heat up to 350-450℃ at 3-5℃ / min and hold for 50 min.

5. The sample pretreatment method for elemental analysis of pyrite according to claim 1, characterized in that, The hot nitric acid solution is 5% nitric acid at 50-60°C.

Images