CN114993969A - Method for enriching and determining gold, platinum and palladium in copper-nickel sulfide ore by fire assay method - Google Patents

Abstract

The invention relates to the technical field of precious metal determination, and discloses a method for enriching and determining gold, platinum, and palladium in copper-nickel sulfide ore by a fire assay method. , and then wrap it with paper to form a paper ball; S2: put the paper ball into a test vessel in a high-temperature furnace at 950-1050°C, after the outer layer of paper is carbonized, close the furnace door, keep the temperature for 5-20min, and then The lead particles formed above the molten slag are concentrated into lead buttons, the temperature of the high-temperature furnace is reduced to 900-950 ° C, the lead button ash in the test vessel is blown into combined particles, and then the test vessel is taken out, cooled, and hammered out The composite particles; S3: Determination of the contents of gold, platinum and palladium after the composite particles are digested. The method is simple in operation, accurate in measurement results, and suitable for popularization.

Description

A method for enrichment and determination of gold, platinum and palladium in copper-nickel sulfide ore by fire-assay gold method

technical field

The invention relates to the technical field of precious metal determination, in particular to a method for enriching and determining gold, platinum and palladium in copper-nickel sulfide ore by a fire assay method.

Background technique

Copper-nickel sulfide ore is an important strategic metal mineral resource in my country, usually accompanied by a certain amount of precious metals such as gold, platinum and palladium. Due to the relatively high content of copper, nickel and sulfur in the copper-nickel sulfide ore and the low content of gold, platinum and palladium, it is difficult to determine the content of gold, platinum and palladium in the copper-nickel sulfide ore. Carrying out accurate analysis of gold, platinum and palladium content in copper-nickel sulfide ore will help increase the comprehensive utilization rate of copper-nickel sulfide ore, reduce the consumption of copper-nickel sulfide ore, and improve the comprehensive utilization level of copper-nickel sulfide ore.

Fire gold assay is one of the main methods for the determination of precious metals in geological mineral samples. According to the different collectors, it is divided into lead, nickel sulfonium, antimony, bismuth, tin, copper and other gold assay methods. Among them, the lead assay method is the most widely used. Long and common, other assay methods are developed on the basis of lead assay. The advantages of the lead assay method are that it has strong ability to capture precious metals, strong slag-making ability, and is suitable for almost all types of minerals, easy to blow, and fast in the process. Lead assay still plays an irreplaceable role in the field of precious metal analysis.

At present, the pretreatment of gold, platinum and palladium analysis in geological and mineral samples mainly adopts the lead assay method, such as the current analysis standard: Analysis of precious metals in geochemical samples Part 6: Determination of platinum, palladium and gold content Fire Assay Gold Enrichment-Emission Spectroscopy (GBT 17418.6-2010 General Administration of Quality Supervision and Inspection), Chemical Analysis Methods of Gold Ore Part 1: Determination of Gold Amount (GB/T 20899.1-2019 General Administration of Quality Supervision and Inspection), Gold Essence Mineral Chemical Analysis Methods (GB/T 7739.1-2019 General Administration of Quality Supervision and Inspection), Regional Geochemical Sample Analysis Methods Part 31: Determination of Platinum and Palladium Amounts by Fire Assay Gold Enrichment-Inductively Coupled Plasma Mass Spectrometry (DZ/T 0279.31 -2016 Ministry of Land and Resources), Regional Geochemical Sample Analysis Methods Part 12: Determination of Platinum, Palladium and Gold Quantity by Fire Assay Gold Enrichment-Emission Spectrometry (DZ/T 0279.12-2016 Ministry of Land and Resources), Platinum in Geochemical Samples , Determination of Palladium Inductively Coupled Plasma Mass Spectrometry (DB51/T 2114-2016 Sichuan Quality and Technical Supervision Bureau), etc. In addition, in the current analysis standards of commodity inspection, non-ferrous metals and other industries, the samples containing copper and nickel are also dominated by the lead assay method, such as the chemical analysis method of nickel concentrate Part 3: Determination of gold, platinum and palladium content inductance Coupled plasma mass spectrometry (SN/T 4501.3-2017 General Administration of Quality Supervision, Inspection and Quarantine), chemical analysis method for copper scrap Determination of platinum content (DB44/T 1816-2016 Guangdong Provincial Administration for Market Regulation), chemical analysis of copper anode slime Method part 3: Determination of platinum and palladium content Fire assay gold enrichment-inductively coupled plasma emission spectrometry (YS/T 745.3-2010), chemical analysis method of copper smelting silver slag part 2: platinum and palladium content Determination of Fire Assay Enrichment - Inductively Coupled Plasma Atomic (YS/T1314.2-2019), Chemical Analysis Methods for Black Copper Part 7: Determination of Platinum and Palladium Amounts Fire Assay Gold Enrichment - Inductively Coupled Plasma Atomic Emission Spectroscopy and flame atomic absorption spectrometry (YS/T 716.7-2016), etc.

It can be seen that the strong capture ability, convenient ash blowing process and simple operation method of the lead assay method still have strong vitality. However, the above methods have special difficulties for the enrichment determination of copper-nickel sulfide ore samples:

1. Copper, nickel and sulfur are easy to form matte in the process of lead testing, and compete with lead to capture precious metals, resulting in the loss of precious metals in smelting;

2. Part of copper and nickel will enter the lead button during smelting, which will affect the ash blowing of the lead button and cause the loss of precious metals during ash blowing;

3. After the sulfur enters the lead button, the lead button becomes brittle and hard, and a lot of black smoke is generated when the ash blowing, which makes it difficult to carry out the ash blowing.

Aiming at the common problem of enriching samples containing copper, nickel and sulfur by the lead assay method, such as the Chinese patent (method for determining the content of platinum and palladium in nickel ore by inductively coupled plasma emission spectrometry CN 108680565 B), first roasting to remove sulfur, and then adding oxidation The amount of lead is 7-10 times the amount of the sample. The excess lead oxide is used to make slag to eliminate the interference of nickel. Chinese patent (measurement method of palladium amount in matte CN 113376145 A), by controlling the add-on of lead oxide, 5-8g matte sample, the add-on of lead oxide is 150-250g, utilizing the strong oxidizing property of molten lead, can Make almost all copper, iron, arsenic and zinc form corresponding salts with acidic flux and alkaline flux into the slag to achieve the best ash blowing effect, which can effectively eliminate the interference of other impurity elements in matte on the determination of palladium. The method for roasting and removing sulfur is cumbersome and time-consuming, and the lead oxide added in a large amount seriously pollutes the environment. Various analytical standard methods, including the aforementioned nickel- and copper-containing substrates, are mainly used to remove impurities by increasing the amount of lead oxide. Literature (Experimental Research and Improvement of Fire Assay Method for Sulfur-Containing Gold Concentrates, Liang Yusheng et al., 2016, Nonferrous Metals in the World), for high-sulfur gold concentrates, the saltpeter method is used to eliminate the interference of sulfur, that is, first The reducing power of sulfur in the sample was tested, then potassium nitrate was added to remove sulfur, and the size of the lead button was adjusted by adjusting the amount of potassium nitrate. The improved method is suitable for gold concentrate samples with high sulfur content. For samples with high copper and nickel content, the batching method, especially the amount of lead oxide, will be adjusted according to the content of copper and nickel after calculation. This method needs to test the reducing power of the sample, which is very troublesome and cumbersome, and it is not easy to control the size of the lead button. Therefore, there is an urgent need for a method for enriching gold, platinum and palladium in copper-nickel sulfide ore by a lead assay method that can overcome the above difficulties, is simple to operate, and has accurate measurement.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the deficiencies of the prior art, and to provide a method for measuring gold, platinum and palladium in copper-nickel sulfide ore by fire assay gold enrichment, so as to at least achieve a simple method and an accurate measurement result.

The purpose of this invention is to realize through the following technical solutions:

A method for enriching and measuring gold, platinum, and palladium in copper-nickel sulfide ore by fire-assay gold method, comprising the following steps:

S1: Take the sample to be tested, add the mixed ingredients and mix well, drop the silver nitrate solution, and then wrap it with paper to form a dough;

S2: Put the paper ball into the gold test vessel in the high temperature furnace at 950-1050℃, after the outer layer of paper is carbonized, close the furnace door, keep the temperature for 5-20min, and then concentrate the lead particles formed above the slag into lead button, reduce the temperature of the high-temperature furnace to 900-950 ℃, blow the lead button ash in the test vessel into a composite grain, then take out the test gold container, cool it, and take out the composite grain;

S3: Determination of the contents of gold, platinum and palladium after the granules are digested.

It is worth noting that if the sample contains high sulfur, it is easy to form lead sulfide with lead. At this time, it is not necessary to release the furnace in a hurry. After the sulfur is oxidized to less smoke, a satisfactory lead button and result can also be obtained. The reduction of the molten beads, the lead molten beads are easily covered by the molten slag, resulting in the interruption of the oxidized ash blowing. Therefore, the ash blowing process should be observed at any time to ensure that the lead molten beads are always exposed to the air. If they are covered by the molten slag, a small amount of molten slag should be poured out. Then continue to blow.

Further, in step S1, the dosage of the sample to be tested is 5-10 g; and/or the concentration of the silver nitrate is 10 g/L, and the dosage is 2-5 drops.

Further, the purpose of wrapping the paper into a mass in step S1 is to prevent losses during the transfer process, and ordinary paper can be used.

Further, in step S1, the mixed ingredients, in parts by weight, include the following components: 5-10 parts of collector, 1-5 parts of acidic flux, 1-5 parts of alkaline flux and 1-3 parts of reducing agent The mass ratio of the mixed ingredients to the sample to be tested is 5-10:1.

Described collecting agent comprises any one in mitosang (PbO), yellow dan (Pb2O3), red dan (Pb3O4), lead acetate, basic lead carbonate, lead particle, lead powder, lead nitrate or lead sulfate;

The acidic flux includes any one of boric acid, anhydrous borax, silicon dioxide, glass powder, quartz sand or quartz powder;

Described alkaline flux comprises any one in sodium carbonate, potassium carbonate, calcium oxide or lime;

The reducing agent includes any one of flour, wheat flour, buckwheat flour, corn flour, starch, sucrose, animal fiber, activated carbon or charcoal powder;

Further, the mixed ingredients further include a protective agent; the protective agent includes any one of silver, tellurium or lead.

It is worth noting that if potassium carbonate is added to the ingredients, due to the low melting point of the flux, the melt quickly spreads in the porcelain plate, and it is easy to make some lead particles not concentrated and lost in advance due to oxidation. Therefore, add less potassium carbonate or do not add.

Further, in step S2, the test utensils need to be preheated to 950-1050°C in a high temperature furnace in advance. The purpose of preheating is to prevent the cold porcelain crucible containing the test material from being cooled due to thermal expansion after entering the furnace. Shrink and burst.

Further, in step S2, the test gold vessel is a butterfly vessel with a flat bottom.

Further, the butterfly-shaped vessel is a butterfly-shaped porcelain dish, a butterfly-shaped crucible, a small porcelain plate or a porcelain crucible cover; preferably a porcelain crucible cover, because the bottom of the porcelain crucible cover is the flattest.

According to the increase or decrease of the sample dosage, the size of the butterfly vessel can be appropriately increased or decreased. For example, the butterfly vessel used for the measurement of 10g samples has a height of about 2cm, and the 5g samples can be directly placed in 150-200mL porcelain Cover the crucible.

The traditional clay crucible has a deep interior, which is conducive to the capture of precious metals by the lead particles during the sinking process, the separation of the slag and the buckle, and at the same time to prevent the lead from being oxidized during the melting process. Excluded in the melting process, sulfur can act as a reducing agent, resulting in excessive reducing agent in the ingredients, part of the sulfur will enter the slag, and part of the sulfur will enter the lead button, affecting the subsequent ash blowing. Therefore, when using clay crucibles to measure high-sulfur samples, the treatment method is to bake the samples in advance, or add potassium nitrate to oxidize the excess sulfur, but this also requires the calculation of the reducing power of the samples, which increases the analysis steps, and the size of the lead buttons is not easy to control.

By adopting the above butterfly-shaped ceramic dish, the slag produced by oxidation spreads around, which is beneficial for the lead molten beads to be exposed in the molten slag, so that the lead molten beads are more fully contacted with oxygen, and the positive progress of the oxidation ash blowing can be promoted, and the remaining lead can be removed. Ash blowing to a minimum, and even complete lead removal.

Further, in step S2, the concentration method is as follows: open the furnace door and shake the lead pellets to concentration.

Further, in step S2, the concentration method may also be: continue to close the furnace door to keep warm until the lead particles are concentrated.

Further, in step S2, the particle size of the composite particles is 1-2 mm.

Further, in step S3, the method of described digestion is:

The granules were washed and dried, then transferred to a closed digestion tank, added with nitric acid, pre-digested on a 120-150 ℃ electric hot plate for 30-60 min, and then added with aqua regia, and after the violent reaction stopped, the digestion tank was closed, and Digest in an oven at 180-240°C for 60-360min, take out after cooling, transfer to a 50mL volumetric flask, dilute to volume with water, shake well, and let stand.

Further, in step S3, the determination method includes a titration method, a spectrophotometric method and an instrumental analysis method.

It is worth noting that the principle of this method is: 1. After the furnace door is closed, the reduction reaction is carried out, and the reducing agent reduces the lead oxide to metal lead to capture the precious metal; 2. When the furnace door is opened for ash blowing, after the oxygen in the air enters, Metal lead is oxidized to lead oxide at high temperature. Lead oxide has strong alkalinity and strong oxidizing property, which can further participate in the slag formation of gangue in the sample, and at the same time, the impurities (nickel, copper, etc.) entering the lead button are oxidized and discharged into the slag. , sulfur, arsenic, antimony, etc. are oxidized into gas volatilization. Therefore, lead oxide is not only a collector, but also an oxidant and a slag-forming agent, and the melting and ash blowing are integrated.

The beneficial effects of the present invention are:

1. The present invention does not use special test gold crucibles and ash dishes, and does not need to test the reducing power of samples in advance. Combined with the advantages of reductive smelting and enrichment and oxide ash blowing in the crucible testing method, the test gold reduction smelting and oxide ash blowing are integrated. After the sample and ingredients are mixed, they are reduced and smelted in a butterfly-shaped ceramic dish, and then oxidative smelting is carried out by using the air that enters after opening the furnace door, and the base metals such as copper and nickel entering the lead are oxidized by lead oxide, so that copper, nickel, etc. The base metals are dissolved in the slag, and at the same time, the sulfur is oxidized, and the low-priced oxides are volatilized into the air, and some of them are directly oxidized into sulfates into the slag. The analysis method is simple, the gold test speed is fast, and the ash blowing loss is small.

2. The present invention adopts a simple butterfly-shaped porcelain dish or a porcelain crucible cover as the gold test utensil. Because the concave surface of the butterfly-shaped porcelain dish is small, the lead molten beads are easily exposed to the air, thereby directly entering the substantial oxidized ash. Compared with the prior art, the sample needs to be subjected to tedious steps such as reducing power test to determine the batching. This method can simplify the complex test batching process into a unified batching, and it is not necessary to specially carry out impurities such as sulfur, copper, and nickel. exclude. The analysis cost is reduced, the analysis time is shortened, and the results are accurate and reliable.

3. the present invention is different from the traditional extraction dish gold test method, the extraction dish method is only for oxidative smelting, mainly used for relatively single component containing precious metal metallurgical products or crude lead purification, for complex sulfide ore samples, Due to the small sampling (less than 3g) and poor representativeness of the extraction dish method, the ore sample cannot be decomposed well by simply using oxidation smelting. The invention combines reduction smelting and oxidized ash blowing into one, and can better dissolve sulfide ore samples with complex composition.

4. The existing standard method does not have an analysis method for the content of gold, platinum and palladium in copper-nickel sulfide ore, but the present invention establishes an analysis method for gold, platinum and palladium in copper-nickel sulfide ore by fire assay gold enrichment-inductively coupled plasma mass spectrometry.

Description of drawings

Fig. 1 is the top view photograph of described porcelain crucible lid;

Fig. 2 is the side view photograph of described porcelain crucible lid;

Fig. 3 is the top view photograph of described butterfly-shaped porcelain dish;

Fig. 4 is the side view photograph of described butterfly-shaped porcelain dish;

FIG. 5 is a photo of using the porcelain crucible cover for ash blowing (for the convenience of shooting, the high-temperature furnace is taken out during shooting).

Detailed ways

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

Example 1

Take the national first-class standard material GBW07195 of copper-nickel sulfide ore for accuracy verification. The specific method is as follows (the same method is used for GBW07196, GBW07197 and GBW07198):

1) Assay ingredients

Weigh 5g of the sample, add the mixed ingredients according to the mass ratio of the sample flux (1:7), mix well, add 3 drops of 10g/L silver nitrate, and wrap the mixed ingredients into a dough with paper.

2) Melting and soot blowing

Put the paper ball into a test vessel that has been preheated in a high temperature furnace of 950℃ for 30min. After the paper ball is carbonized, close the furnace door, keep the temperature for 10 minutes, and open the furnace door. At this time, the lead oxide is reduced to small lead particles. Drift on the top of the slag, carefully shake the lead particles until they are concentrated into a lead button (or close the furnace door and continue to keep warm until the lead particles are concentrated), reduce the temperature to 900 ° C, and blow the lead button directly in the test utensil to oxidize the ash to a small size. Combine the granules (2mm), take out, cool, and hammer out the combined granules.

3) Synthetic digestion

The combined granules were washed with distilled water 3 times and dried. The combined granules were moved into a closed digestion tank, 3 mL of nitric acid was added, and pre-digested on a temperature-controlled electric hot plate at 140 °C for 40 min, then 5 mL of aqua regia was added to the closed digestion tank, and placed for half When the violent reaction stops within an hour, close the digestion tank, place it in an oven for digestion at 200 °C for 150 min, turn off the power of the oven, take it out after cooling, open the lid and transfer it to a 50 mL volumetric flask with water, dilute to the mark with water, shake well, and let it stand still. set. Dilute different times according to the content to be tested.

4) Standard solution

Single element standard stock solution (1000mg/L), purchased from National Nonferrous Metals and Electronic Materials Analysis and Testing Center, are certified reference materials. The mixed standard solution is prepared by diluting and mixing the above single-element standard stock solution step by step, which are respectively mixed standard solution A (the mass concentrations of gold, platinum, and palladium are all 10 μg/mL) and mixed solution B (the mass concentrations of gold, platinum, and palladium are all 10 μg/mL). The mass concentration is 250ng/mL). Pipette 0mL, 0.1mL, 0.4mL, 1.0mL of mixed solution B and 0.1mL, 0.25mL, 1.0mL of mixed standard solution A into seven 50mL volumetric flasks, add a small amount of water and 3.5mL of nitric acid in turn, and after mixing, Add 4.5mL hydrochloric acid, dilute to volume, and mix. The mass concentrations of gold platinum palladium standard working solutions were 0ng/mL, 0.50ng/mL, 2.0ng/mL, 5.0ng/mL, 20.0ng/mL, 50.0ng/mL, and 200.0ng/mL.

5) Instrument measurement

Use the tuner to tune the indicators of the instrument, so that the sensitivity, oxide, double charge, background value, resolution and other indicators meet the measurement requirements, edit the measurement method, select the measurement elements and internal elements, and use a three-way pipe to connect the internal elements. The standard solution, the blank solution, and the solution to be tested are measured in sequence. If the measurement result exceeds the measurement range of the standard curve, the sample solution should be diluted before measurement. The selected mass numbers of gold, platinum, palladium and internal elements are shown in Table 1.

Table 1

element gold platinum palladium mass number 197 195 106 Internal standard element 185Re 185Re 115In

6) Result calculation

The gold, platinum and palladium content is calculated as follows:

In the formula: w is the mass fraction of gold, platinum or palladium, ng/g; ρ1 is the mass concentration of gold, platinum or palladium in the liquid to be tested obtained from the calibration curve, ng/mL; ρ0 is obtained from the calibration curve Obtain the mass concentration of gold, platinum or palladium in the blank test solution, ng/mL; V is the total volume of the solution to be tested, mL; m is the weight of the weighed sample, g.

The measured value measured by the experiment is compared with the standard certified value, and the results are shown in Table 2:

Table 2

Example 2

Two copper-nickel sulfide ore samples were selected, including 1# (Cu 0.86%, nickel 1.07%, sulfur 3.85%) and 2# (Cu 0.46%, nickel 0.81%, sulfur 2.77%), and different methods were used for comparison. Verify the accuracy of the present invention, the detailed operation steps of the inventive method are with embodiment 1 (some parameters such as temperature, reaction time are slightly adjusted according to specific circumstances), and the experimental results are shown in Table 3:

table 3

Among them, SN/T 4501.3-2017 is the chemical analysis method of nickel concentrate in the entry-exit inspection and quarantine industry standard of the People's Republic of China; the saltpeter method refers to the literature "Experimental Research and Improvement of Fire Assay Method for Sulfur-Containing Gold Concentrate, Liang Yusheng et al., 2016, "World Nonferrous Metals" conduct experiments. It can be known from the experimental data that the content of gold, platinum and palladium measured by the method of the present invention is not much different from the data measured by the prior art measurement method, and has higher accuracy, but the operation is obviously simpler and easier, and can be used for actual production.

The foregoing are only preferred embodiments of the present invention, and it should be understood that the present invention is not limited to the forms disclosed herein, and should not be construed as an exclusion of other embodiments, but may be used in various other combinations, modifications, and environments, and Modifications can be made within the scope of the concepts described herein, from the above teachings or from skill or knowledge in the relevant field. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all fall within the protection scope of the appended claims of the present invention.

Claims (10)

1. a method for enriching and measuring gold, platinum and palladium in copper-nickel sulfide ore by fire assay method, is characterized in that, comprises the following steps: S1: Take the sample to be tested, add the mixed ingredients and mix well, drop the silver nitrate solution, and then wrap it with paper to form a dough; S2: Put the paper ball into the gold test vessel in the high temperature furnace at 950-1050℃, after the outer layer of paper is carbonized, close the furnace door, keep the temperature for 5-20min, and then concentrate the lead particles formed above the slag into lead button, reduce the temperature of the high-temperature furnace to 900-950 ℃, blow the lead button ash in the test vessel into a composite grain, then take out the test gold container, cool it, and take out the composite grain; S3: Determination of the contents of gold, platinum and palladium after the granules are digested. 2. method according to claim 1, is characterized in that: in step S1, the consumption of described sample to be tested is 5-10g; And/or the concentration of described silver nitrate is 10g/L, the consumption is 2-5 drop. 3. The method according to claim 1, characterized in that: in step S1, the mixed ingredients, in parts by weight, include the following components: 5-10 parts of collectors, 1-5 parts of acidic flux, 1- 5 parts of alkaline flux and 1-3 parts of reducing agent; the mass ratio of the mixed ingredients to the sample to be tested is 5-10:1. 4. method according to claim 3, is characterized in that: Described collecting agent comprises any one in mitosang, huangdan, red dan, lead acetate, basic lead carbonate, lead particle, lead powder, lead nitrate or lead sulfate; The acidic flux includes any one of boric acid, anhydrous borax, silicon dioxide, glass powder, quartz sand or quartz powder; Described alkaline flux comprises any one in sodium carbonate, potassium carbonate, calcium oxide or lime; The reducing agent includes any one of flour, wheat flour, buckwheat flour, corn flour, starch, sucrose, animal fiber, activated carbon or charcoal powder. 5 . The method according to claim 1 , wherein in step S2 , the assay vessel needs to be preheated to 950-1050° C. in a high-temperature furnace. 6 . 6. The method according to claim 1, wherein in step S2, the test gold vessel is a flat bottom butterfly vessel. 7. The method according to claim 6, wherein the butterfly-shaped vessel is a butterfly-shaped porcelain dish, a butterfly-shaped crucible, a small porcelain plate or a porcelain crucible cover. 8. The method according to claim 1, characterized in that: in step S2, the concentrated method is: opening the furnace door and shaking the lead particles to a concentration, or continuing to close the furnace door to keep warm until the lead particles are concentrated. 9 . The method according to claim 1 , wherein in step S2 , the particle size of the combined particles is 1-2 mm. 10 . 10. method according to claim 1, is characterized in that: in step S3, the method for described digestion is: The granules were washed and dried, then transferred to a closed digestion tank, added with nitric acid, pre-digested on a 120-150 ℃ electric hot plate for 30-60 min, and then added with aqua regia, and after the violent reaction stopped, the digestion tank was closed, and Digest in an oven at 180-240°C for 60-360min, take out after cooling, transfer to a 50mL volumetric flask, dilute to volume with water, shake well, and let stand; And/or, the methods for the determination include titration, spectrophotometry and instrumental analysis.

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