Task description
The content of gold in ore is generally low, about 0. XX ~ x.xxg/t, Therefore, the enrichment method is usually used first when testing. Fire gold test is mainly lead gold test, and wet enrichment includes foam plastic enrichment and activated carbon enrichment. Then, it was determined by atomic absorption spectrophotometry. Through the study of this topic, we can understand the experimental conditions of gold enrichment by foam plastics and master the operation methods of gold enrichment by foam plastics. Be able to fill in the data record form and the experimental results correctly.
Task implementation
I. Preparation of Instruments and Reagents
(1) instruments: atomic absorption spectrophotometer, gold hollow cathode lamp.
(2) Foam: Soak 100g soft polyurethane foam (about 5mm thick) in 400mL tri-n-octylamine ethanol (3%) solution, repeatedly squeeze it to soak it evenly, then dry it at 70 ~ 80℃, and cut it into about 0.2g pieces for use (no change within one week).
(3) thiourea-hydrochloric acid mixed solution: hydrochloric acid (2%) solution containing 5g/L thiourea.
(4) Gold standard solution: weigh 0. 1000g pure gold and put it in a 50mL beaker, add 10mL aqua regia, heat it on an electric heating plate until it is completely dissolved, add 5 drops of sodium chloride (200g/L) solution, evaporate it in a water bath, add 2mL hydrochloric acid to dry it (repeat for 3 times), and add/kloc-. Take this solution to prepare gold-containing standard solution [hydrochloric acid (100%) medium] to 100μg/mL and 10μg/mL.
Second, the analysis steps
Weigh 5 ~ 30g samples into a porcelain boat, bake them in a high-temperature furnace at 550 ~ 650℃ for/~ 2h, stir them for 2 ~ 3 times, cool them, move them into a 300mL conical flask, add 50mL aqua regia (1+ 1), and heat them on an electric heating plate for about/kloc-0. Acid-soluble silicate should be added with 5 ~ 10g sodium fluoride, boiled), diluted to 100mL with water, added with about 0.2g foam plastic (pre-wetted with water), plugged with a rubber stopper, vibrated on a reciprocating vibrator for 30 ~ 90 min, taken out of the foam plastic, fully rinsed with tap water, then dried with filter paper, and added with 25mL thiourea-. Heat it in a boiling water bath for 65438±05min, squeeze the foam with a glass rod for several times, take out the foam, fix the volume to 50mL, and determine it by atomic absorption spectrometry according to the working conditions of the instrument. Do reagent blank test with samples.
Drawing of working curve: Absorb 2.50mL, 5.00mL, 10.00mL, 15.00mL, 20.00mL gold standard solutions containing 10μg/mL gold into a 50mL volumetric flask, and add 25mL thiourea solution (10g/L According to the same conditions of the sample, it was determined by atomic absorption spectrometry.
Three. Calculation of analysis results
Calculate the gold content in the sample according to the following formula:
Rock mineral analysis
Where: w(Au) is the mass fraction of gold, μg/g；/g; /g； M 1 is the mass of gold in the sample solution found from the calibration curve, μ g; M0 is the mass of gold in the sample blank found from the calibration curve, μ g; M is the mass of the weighed sample, g.
Fourth, fill in the quality form.
After the task is completed, fill in quality tables 3, 4 and 7 in appendix 1.
task analysis
First, the method principle.
The sample was decomposed with aqua regia. Gold was adsorbed by polyurethane foam loaded with trioctylamine in aqua regia medium of about 10% (volume fraction), and then the adsorbed gold was heated with 5g/L thiourea -2% (volume fraction) hydrochloric acid solution, and gold was directly determined by flame atomic absorption spectrometry.
Second, the method advantage
The separation and enrichment of gold by polyurethane foam has the advantages of large extraction capacity, good selectivity and high recovery rate (above 97%). The method is simple, rapid, stable, easy to master and low in cost, and is suitable for the analysis of mass production samples.
Three. Brief introduction of separation and enrichment methods of foamed plastics
Foam plastic (PF) is a kind of soft plastic, which is a polymer crosslinked by toluene diisocyanate and polyether or polyester through amide bond.
Foam plastics have been widely used in the separation and enrichment of precious metals. The mechanism of separation and enrichment may include surface adsorption, adsorption, extraction, ion exchange, cation chelation and so on. The efficiency of metal adsorption by foam plastics depends on the types and properties of foam plastics and metal complex ions, the formation environment of complex ions in solution, diffusion rate and adsorption mode. Foam is suitable for accepting monovalent and divalent anions because of its polyether oxygen structure, and its adsorption behavior is similar to that of anion exchange resin, so its adsorption is selective. Gold, thallium, etc. When it exists in the form of ions, it is hardly adsorbed by foam plastics, and can only be adsorbed when it forms [me x4]- type anions.
Foam forming is mainly used for gold adsorption and separation. The quality, structure and performance of foam plastics produced by different manufacturers are different, and the adsorption capacity of gold is also different, usually between 50 and 60 mg/g. Foam adsorption can be divided into dynamic adsorption and static adsorption. Static adsorption is to put the foam block into the gold-containing solution to adsorb gold by oscillation. Dynamic adsorption is to make foam into a foam column, and the gold solution flows into the column for adsorption. The aqua regia concentration has no obvious effect on the adsorption in the range of (4+96) ~ (15+85), and it is slightly lower when the aqua regia concentration is lower than (2+98). When the aqua regia concentration is greater than (1+4), the foam turns black. When the volume of solution is 50 ~ 200 ml, it has no effect on adsorption, and the adsorption can be basically completed by shaking for 30min. Using 0.4 g foam to adsorb 20 ~ 100 μ g gold, the adsorption rate can reach above 98%.
The dynamic adsorption rate is slightly higher than the static adsorption rate. Foam plastics can adsorb gold in aqua regia (1+9) medium, the adsorption rate can reach over 99%, and its adsorption flow rate can vary in a wide range, preferably less than 10mL/min.
The loaded foam prepared by loading extractant or chelating agent on foam has two functions of extraction and foam adsorption, so it has great enrichment ability for gold. The adsorption performance of supported foam depends on the type and properties of extractant supported on foam. At present, the carrier foams most widely used in the analysis and determination of gold are tributyl phosphate (TBP) foam, tri-n-octylamine foam, dithizone foam, methyl isobutyl ketone foam, di-n-octyl sulfoxide foam, diphenyl thiourea foam, triphenylphosphine foam, amide foam and carbon-filled foam prepared by combining activated carbon with foam. Among them, diphenyl sulfide foam, tri-n-octyl amine foam, di-n-octyl sulfoxide foam and dithizone foam have better gold enrichment performance.
After adsorption, gold needs to be desorbed, and there are usually the following methods for desorption:
1. Ash combustion method
Wrap the gold-adsorbed foam with filter paper and put it into a 30mL porcelain crucible for ashing and burning. After cooling, 2 drops of potassium chloride solution (200g/L) and 3mL of aqua regia were added and evaporated in a water bath. Then add 10 drop of concentrated hydrochloric acid, and evaporate the nitric acid again. And then determined by spectrophotometry or atomic absorption spectrometry.
2. Thiourea desorption method
When the gold-adsorbed foam is soaked in thiourea hot solution, thiourea will reduce Au (Ⅲ) to Au (Ⅰ) and form Au (Ⅰ) thiourea complex. The reaction formula is as follows:
r-aucl 4+3SC(NH2)2+H2O→Au2SC(NH2)2+RCl+2 HCl+OC(NH2)2
Therefore, gold ions can be eluted from the foam. The conditions of gold desorption by thiourea are that the acidity should be neutral solution or hydrochloric acid solution less than 0.5 mol/L. When the concentration of hydrochloric acid is greater than 0.5 mol/L, the monomer sulfur is easy to precipitate and the result is low. It can be seen from the reaction formula that the existence of hydrochloric acid is obviously not conducive to desorption. At room temperature, the ability of thiourea to desorb gold is low, and it can not be completely desorbed in 4 h, but it can be completely desorbed in boiling water bath for 20min, and the recovery rate can reach over 95%. The holding time of 20 ~ 90 min does not affect the results. The concentration of thiourea is 10 ~ 50g/L, usually 20 ~ 30g/L. This method is simple, rapid and low cost. It is suitable for direct determination by atomic absorption spectrometry.
3. Nitric acid-potassium chlorate decomposition method
Foam plastics can be decomposed by oxidizing inorganic acids and oxidants. The experiments of decomposing foam plastics with nitric acid, sulfuric acid-potassium permanganate, nitric acid-hydrogen peroxide, nitric acid-perchloric acid and nitric acid-potassium chloride show that nitric acid-potassium chloride has the best decomposition effect. Under the action of HNO3-KClO3, the foam quickly turned into a brown-black block, softened and dissolved, and a yellow oily substance floated on the surface of the solution. When heated, a violent reaction will occur and a large amount of NO2 gas will be released. For 0.2~0.3 g foam, the dosage of nitric acid is more than 8mL and potassium chlorate is more than 0.05 g, which is enough to completely decompose the foam and finally get a yellow clear solution.
4. Desorption method of methyl isobutyl ketone
MIBK is an effective extractant for gold. Using the extraction performance of MIBK, the gold adsorbed by foamed plastics can be desorbed. Using 20mL MIBK and shaking violently for 2min, the recovery rate of gold can reach 95% ~ 100%.
4. Enriching gold in ore by lead analysis.
The classical fire assay-lead method has been applied to the enrichment of gold and silver for a long time, and the method is relatively perfect. At the beginning of the 20th century, people tried to enrich platinum group metals in samples by classical lead analysis. Because platinum group metals are rarer than gold and silver in nature, the enrichment effect is poor. Because of this, in the late 1950s, copper-nickel-gold assay, tin-gold assay, nickel-matte-gold assay and antimony-gold assay appeared one after another. As a reliable method, pyrometry has been widely used for a long time, because the sampling amount of pyrometry is large, generally 20 ~ 40g, sometimes exceeding 100g, which not only reduces the sampling error, but also makes the results more representative. At the same time, the enrichment multiple of fire assay gold is very large (more than 105 times), and the precious metals in dozens of grams of samples can be enriched into several milligrams of gold assay particles, with simple particle composition and convenient for subsequent determination. However, fire assay also has its disadvantages: it requires huge equipment; It also requires high temperature operation, which is labor-intensive, and produces a lot of lead oxide and other vapors during smelting, which pollutes the environment. Therefore, analysts have been trying to find a new method to replace it for many years. In recent years, progress has been made in this field. Some methods are comparable to pyrometry, but their adaptability to different samples is not as good as that of lead method. Therefore, the laboratory still uses lead content determination for routine analysis or checking the analysis results of other methods.
The whole process of lead-gold test can be divided into several steps, such as batching, smelting, soot blowing and gold separation. Different kinds of samples have different batching methods and dosage ratios. According to different components, lead determination methods can be divided into flour method, nail method and saltpeter method. Flour method uses wheat flour as reducing agent. Nail method uses nails as reductant, and nails can also be used as desulfurizer for samples with high sulfur content. Nitrite method uses potassium nitrate as oxidant to decompose samples containing a large amount of arsenic, tellurium, antimony and high sulfur. This method is not easy to master and is generally not used. Flour method is commonly used to reduce lead oxide to lead with flour, so that lead and precious metals can form an alloy and be separated from slag.
1. Seasoning
Before the sample is melted, a certain amount of trapping agent, reducing agent and flux should be added.
(1) Collector: Lead oxide is used as a collector in lead analysis. In the smelting process, lead oxide is reduced to metal lead by reducing agent, which can form alloy with precious metals in the sample, commonly known as "lead buckle" and be separated from slag.
The purity requirement of lead oxide is not strict, as long as it does not contain precious metals, such as Lithuania, it can be used.
(2) Reducing agent: adding reducing agent to reduce lead oxide to lead. Carbon powder, wheat flour, sugar, tartaric acid, iron nails (iron powder), sulfide, etc. are all acceptable, and wheat flour is mostly used in China.
(3) Fluxes: Commonly used fluxes include glass powder, sodium carbonate, calcium oxide, boric acid, borax, silicon dioxide, etc. According to the composition of the sample, adding different amounts of these fluxes can reduce the melting temperature, make the slag flow better, and make the lead buckle and slag easy to separate.
Blending is the key step of lead-gold inspection, and improper blending will make lead-gold inspection fail. The ingredient is to weigh the fine powder of trapping agent, reducing agent and flux according to a certain proportion, and mix it evenly with the sample. The proportion of ingredients in each laboratory is not exactly the same, but slightly different.
The sample and various reagents should be mixed evenly, so that the reduced metal lead beads are evenly distributed in the sample during smelting, and the maximum efficiency of dissolving precious metals is exerted. There are four mixing methods:
(1) Put the sample and various reagents into a gold crucible and stir them evenly with a metal spoon or scraper;
(2) Roll back and forth on the glass paper and stir evenly, and put it into a gold crucible together with the paper. Calculate the reducing power of cellophane and add less wheat flour;
(3) Weigh the sample and various reagents in a jar, cover it and shake it evenly, and then pour it into a gold crucible;
(4) Weigh the samples and various reagents, put them into a polyethylene plastic bag with the weight of 1g, the length of which is 30cm, the width of which is 30cm, tie the bag mouth tightly and shake it evenly for 5min. Then put the plastic bag into the gold crucible. When batching, the reducing ability of plastic bags should be considered to reduce the dosage of reducing agent.
2. Melted
Put the crucible containing the mixture into a gold test furnace and heat it. Therefore, lead oxide is reduced to metallic lead; After the precious metals in the sample are collected, they are condensed and dripped to the bottom of the crucible to form a lead button. This process is called smelting. In the process of smelting, the size and slagging of the molded lead buckle should be controlled to prevent the volatilization loss of precious metals.
There are three kinds of commonly used gold test furnaces: diesel furnace, coke furnace and electric furnace, among which electric furnace is more convenient.
The total volume of samples and various reagents should not exceed three-quarters of the crucible volume, and different types of crucibles can be used according to the number of components. Cover the mixture in the crucible with a layer of salt or boron glass powder to prevent the splashing and volatilization of precious metals and the corrosion of the crucible by lead oxide. After the crucible is put into the gold test furnace, the temperature should be raised slowly to prevent water, carbon dioxide and other gases from escaping quickly, resulting in sample loss. After the temperature is raised to 600 ~ 700℃, it is kept for 30 ~ 40 min, so that the added reducing agent and some reducing components in the sample react with lead oxide to generate metallic lead, and lead dissolves precious metals to form alloy gold. Then the temperature is raised to 800 ~ 900℃, and the materials in the crucible begin to melt and gradually flow. When gases such as carbon dioxide produced in the reaction escape, it will stir the melt and promote the better capture and condensation of lead. The density of lead alloy is higher than that of slag and gradually drops to the bottom of crucible. Finally, the temperature is raised to1100 ~1200℃ and kept at 10 ~ 20min to completely separate the slag from the lead alloy. Take out the crucible and pour it into a dry iron mold. When the temperature drops to 700 ~ 800℃, the molten slag is stirred with iron chopsticks, and the slagging situation is observed to improve the burden ratio. If the slag is too acidic and has poor fluidity, it will affect the settlement of lead; Too strong alkalinity will seriously corrode the crucible, which may cause perforation of the crucible and cause rework.
After the melt is cooled, it is poured out of the iron mold, the slag on the lead buckle is discarded, and the lead buckle is hammered into a cube. The amount of lead buckle obtained is preferably between 25 and 30g to avoid precious metals remaining in the slag. If the lead buckle is too large (more than 40g) or too small (less than 15g), it should be reworked. The lead buckle is too large, indicating that too much reducing agent is added during batching; The lead buckle is too small, indicating that the reducing agent is added too little. Therefore, the dosage of reducing agent should be appropriately reduced or increased when redoing. According to the reducing ability of reducing agent, how much reducing agent should be added or reduced is calculated.
Calculation method of reducing power of reducing agent: If the reducing agent used is pure carbon powder, it will react with lead oxide during smelting as follows:
2Pb 0+C→2Pb+CO2
It can be calculated from the reaction formula that 1 g carbon can reduce lead oxide to 34 g lead.
Assuming that sucrose is used as reducing agent, the reaction is as follows:
24 PBO+c 12 h22 o 1 1→24Pb+ 12co 2+ 1 1H2O
According to the reaction formula, it can be calculated that 1 g sucrose can reduce lead oxide to 14.0 g lead. Gold testers often say that the reducing power of sucrose is14.0g; ; The reducing power of carbon is 34g；; ; The reducing power of wheat flour is10 ~12g; The reducing power of crude tartaric acid is 8 ~ 12 g, etc.
The composition of the sample is complex, some have oxidation ability and some have reduction ability. Reducing agent should be added less to samples with reducing ability; More reducing agent should be added to the samples with oxidizing ability. For example, for samples containing sulfides, reducing agents should be added less, because sulfides have the following functions:
3PbO+ZnS→ZnO+SO2+3Pb
When it is difficult to determine the proportion of components in unfamiliar samples, the contents of various elements can be determined by laboratory tests, or the contents of main mineral components can be determined by phase analysis, or the composition and proportion of components can be determined by testing the oxidizing power or reducing power of samples.
If the lead buckle is found brittle and hard when hammering, it means that the lead buckle contains copper, arsenic or antimony. In this case, it is necessary to weigh less samples, use potassium nitrate as a component and re-smelt.
The main slagging components of ores and Iwao Dan minerals are: SiO2, FeO, CaO, MgO, K2O, Na2O, Al2O3, MnO, CuO, PbO, etc. Except a few of these oxides can be melted at the temperature of a single gold test furnace, most of them will not be melted, so it is necessary to add flux. If it is acidic oxide ore, alkaline flux should be added; Acidic flux should be added to alkaline oxide ore, and iron nails or iron powder can be added to sulfide samples for flux treatment.
Step 3: Blow the dust
The function of soot blowing is to separate lead and precious metals from lead buckles. Lead is oxidized into lead oxide in the process of soot blowing, and then absorbed by the ash dish; However, the precious metal was not oxidized, and remained on the gray dish in a spherical shape, and was separated from lead.
Gray plates are made of ash and cement, tamped with water and then pressed on a plate press. The ash dish with high ash content has good performance of absorbing lead oxide, but it is difficult to form the ash dish. The proportion of cement and ash should be determined through specific tests. The grey dish is shallow, porous, resistant to high temperature and corrosion, and weighs about 40 ~ 50g. Before use, put the clean grey dish into a high-temperature furnace above 1000℃ and preheat it 10 ~ 20min to drive away the moisture and gas in the grey dish. After heating, if cracks are found in the grey dish, it should be discarded. After cooling, put the lead buckle in the center of the gray dish and heat it to 675℃, and the lead buckle melts and presents a silver luster. Open the oven door slightly (note: don't open the oven door too wide to prevent cold air from blowing directly on the ash tray, which will lead to excessive oxidation and splash). At this time, lead is oxidized into lead oxide, which gradually falls off the surface of the lead buckle and is absorbed by the gray dish. Impurities such as copper and nickel are oxidized into copper oxide and nickel oxide, which also have wetting effect on the grey dish and penetrate into the grey dish.
The soot blowing temperature should not be too high, but it should be controlled at 800 ~ 850℃ to keep lead in a molten state. If the temperature is too low, lead oxide and lead buckle are not easy to separate. Lead oxide wraps the lead buckle, which can make the lead solidify immediately. This phenomenon is called "freezing". After curing, heating and soot blowing will increase the loss of precious metals. Appropriate temperature can make lead oxide volatilize to the edge of the gray dish and appear feather-like crystals; If feather-like lead oxide crystals appear on the surface of the dish, it means that the temperature is too low.
Trace impurities, such as copper, iron, zinc, cobalt and nickel. Part of it is converted into oxide and absorbed by the ash dish, and part of it is volatilized. The same is true of lead, most of which becomes lead oxide and is absorbed by the grey dish, and a small part is volatilized. Most precious metals will not be oxidized. Such as gold, silver, platinum, palladium, etc. Strong cohesion, condensed into a ball, not absorbed by the gray dish, not volatile. After almost all the lead in the lead buckle disappears, you can see that the spherical surface is covered with a layer of rainbow mirror (or glow). Then rainbow mirror disappeared and the ball turned silver-gray. Close the oven door for 2 minutes to further remove trace residual lead, and then take out the ash dish to cool. If the lead removal process is not carried out for 2min, when the ash dish is taken out, flash will be produced due to the violent oxidation of trace residual lead, resulting in the loss of precious metals.
Excessive furnace temperature will also cause the loss of precious metals. Although gold, silver, platinum, palladium, etc. Less volatile, at high temperature, they will be partially oxidized and penetrate into the mortar together with lead oxide. The higher the temperature during soot blowing, the greater the loss of gold, silver, platinum and palladium, so the temperature should be strictly controlled at 800 ~ 850℃.
4. Weigh in gold
Gold separation refers to the process of separating gold and silver from metal particles obtained by pyrometallurgy, which is suitable for gravimetric determination of gold and silver. If there are only gold and silver in the obtained gold-silver composite particles, gold and silver can be separated by using the characteristic that silver solution is soluble in hot dilute nitric acid and gold is insoluble.
Nitric acid used for gold separation cannot contain oxidants such as hydrochloric acid and chlorine.
5. Behavior of platinum group elements in lead analysis
The behavior of platinum group elements in lead assaying is very complicated, such as ruthenium and osmium, which are easily oxidized into trioxide and volatilized during smelting and soot blowing, so it is difficult to determine ruthenium and osmium by lead assaying.
In the smelting process of lead analysis, iridium does not form an alloy with lead, but is suspended in molten lead. So when the lead buckle is separated from the slag, the loss of iridium is very serious. Rhodium is insoluble in silver during soot blowing, and the oxidation loss is serious. Therefore, it is not suitable to separate and enrich iridium and rhodium by lead method.
The behavior of platinum and palladium in lead analysis is similar to that of gold. Soluble in lead during smelting and silver during soot blowing, with little loss during smelting and soot blowing. Only the samples containing nickel cause serious losses of platinum and palladium, which can be separated and enriched by matte assay and antimony assay.
6. separating gold from silver, platinum and palladium
If there are gold, silver, platinum, palladium and lead in the test, the aggregate obtained after soot blowing is gray. When the content of platinum and palladium is large, the molten beads may "solidify" before the lead is completely oxidized and absorbed by the ash dish during soot blowing, and the surface of the obtained metal compact is rough.
When the silver content in metal particles is more than 10 times that of platinum and palladium, it is necessary to separate gold with dilute nitric acid for many times. Platinum and palladium can be separated from gold when silver is completely dissolved in acid. The residual gold was washed, dried and weighed to obtain the determination result of gold.
The acidic solution after gold separation is heated and evaporated to remove acid, and hydrogen sulfide is introduced to precipitate silver. Silver sulfide can precipitate sulfides such as platinum and palladium together. Wrap the sediment with a thin lead plate, and then blow it. When the obtained metal particles are heated with concentrated sulfuric acid, silver is dissolved and platinum and palladium are insoluble, so they are separated.
The above sulfides can also be dissolved by aqua regia. Add ammonia water, and if there is any insoluble residue, filter to remove it. Evaporating the filtrate to dryness, adding water to dissolve, adding saturated ethanol solution of potassium chloride, standing for platinum to form K2 [ptcl6] precipitate, and filtering with a constant weight glass sand core funnel. Was with 80% alcohol, drying in a constant temperature box, and weigh. This method is only suitable for samples with high platinum content. Silver, platinum and palladium can also be determined in the same solution by atomic absorption spectrophotometry or emission spectrometry.
7. Common ore components in lead analysis
See Table 7-2 for common ore components in lead analysis.
Table 7-2 List of Common Ore Components in Lead Analysis
sequential
8. Several factors to improve the accuracy of gold test results
The whole process of gold assay analysis has complicated manual operation, which seems to be a rough process, but in fact, every step of operation must be meticulous. In order to improve the accuracy of the analysis results, in addition to operating carefully in accordance with the operating procedures, we must also start from the following aspects and work hard to achieve the goal.
(1) Material and production of grey disc. Animal ashes, cement or magnesium oxide should be used as mortar materials. After natural drying, use 500 # cement and cement tray with water pressure 10% ~ 15%. Due to the large gap in the cement dish, the loss of precious metals during soot blowing is large, the aggregate is easy to bond with the cement dish, and the analysis error is large, so it is generally only used for the analysis of turnover materials in the factory when the furnace ash is scarce. Animal ashes, preferably cattle and sheep bones, are burned into ashes, and then ground into ashes below 0. 175 mm, and then 10% ~ 15% water pressure is added to make the urn, which is used after natural drying for 3 months. Before blowing, put the ash dish into a muffle furnace and burn it at about 900℃ for 20 minutes to remove possible organic matter.
Because in the process of soot blowing, lead oxide and base metal oxide are absorbed by the ash dish except for a small amount of volatilization into the air. Grey vegetables will also absorb some gold and silver, which is called gold and silver loss. Therefore, it goes without saying that the pressure difference in the process of making gray plates will inevitably lead to the difference in the gap between gray plates, which will lead to the difference in blowing loss of gold and increase the analysis error. This requires that the ash from the same batch of materials should be treated with the same pressure; In the case of artificial processing, the same box of gray plates should be processed by the same person; Don't choose the dishes in different boxes when the dishes are almost finished, so as not to cause the analysis error to expand. Moreover, it is not allowed to use grey discs from different sources in mixed batches.
(2) Flame analysis ventilation requirements and compensation measures of muffle furnace. The soot blowing process is actually the oxidation process of the parent metal and lead in the sample at high temperature, so it is required that the molten material in the ash dish has a uniform contact opportunity with air to ensure the consistent oxidation speed. Ideally, the lead buckle should be melted at the same time, and the soot blowing should be carried out at the same time, and the glow point should be achieved at the same time. This requires the muffle furnace to have suitable air inlet and outlet channels. Because the commonly used muffle furnace can't be ideal, besides the improvement of design and manufacture, we should also consider the difference of air contact and temperature in different positions in the furnace. Samples from different regions should be calibrated with corresponding standards, and the principle is to make the standards as representative as possible.
Experimental guide and safety tips
Tri-n-octylamine can exchange with some metal anions in acidic solution, and foam has adsorption properties for some organic and inorganic substances. Therefore, the use of tri-n-octylamine-loaded foam enhances the adsorption performance of [aucl4]- 1 and will not be washed off after repeated washing with water. For 0.5 ~ 1000 μ g of gold, the adsorption recovery rate is 96% ~ 65438.
The acidity range of gold adsorption by this method is wide, that is, 0.5 ~ 6 mol/L hydrochloric acid or 5% ~ 30% (volume fraction) aqua regia medium can quantitatively adsorb gold; However, when the concentration of nitric acid is too high, the adsorption rate of gold decreases.
In the case of impure standard, the adsorption rate of gold decreases with the decrease of gold grade and the increase of sample number. For example, for a 30g sample with a gold content of 0.0xg/t, the oscillation adsorption time needs to be extended to 90min, and the general sample oscillation adsorption time only needs 30min.
Without tartaric acid and sodium fluoride, antimony 20mg, tungsten 10mg, iron 4000mg and soluble silica less than 200mg can be allowed. Adding 1 g tartaric acid can eliminate the interference of 300mg antimony and 100mg tungsten. Adding 5 g sodium fluoride can make 5000mg iron exist. Soluble silica needs to be added with 4.2 g of sodium fluoride to form sodium fluosilicate crystal precipitation to eliminate interference.
For the samples with high arsenic content, the roasting should start at low temperature, gradually raise the temperature to 1 ~ 2h at 480℃ to volatilize arsenic, and then continue roasting to remove sulfur, otherwise it will volatilize due to the formation of low-boiling arsenic-gold alloy, resulting in gold loss, and the determination result is low.
Except for tungsten, antimony, iron and acid-soluble silicate, other elements in the ore have no interference. The interference of tungsten and antimony can be eliminated by adding tartaric acid, and the interference of a large amount of iron and a certain amount of acid-soluble silicate can be eliminated by adding sodium fluoride to form sodium fluosilicate (Na2SiF6) crystal precipitation.
Preservation of gold standard solution: au3+ solution with concentration of 2.5 ~ 25 μ g/ml can be stably preserved in glass container for 300 days. When the concentration of gold is low, it can be adsorbed by glassware. When pH = 2, the adsorption capacity of gold is the largest, with glassware adsorbing about 30% and timely glassware adsorbing about 60%. When pH = 2 ~ 7, the adsorption of gold on filter paper is as high as 40%. Therefore, when preparing the standard solution of gold, it cannot be filtered by filter paper. In order to improve the stability of [aucl4]-, it is suggested that sodium chloride, KCl and chloride of alkaline earth metal should be added to the gold standard solution.
Expansion and improvement
Determination of Gold in Ore Samples by Inductively Coupled Plasma Mass Spectrometry
1. Method principle
After burning at 800℃, the sample was dissolved in aqua regia, excited by argon plasma and determined by inductively coupled plasma mass spectrometry.
2. Reagents and equipment
Nitric acid (ρ = 1.42g/ml), hydrochloric acid (ρ = 1. 19g/ml), thallium standard solution (1mg/mL): national standard solution GSB G62070-90.
Thallium internal standard working solution: transfer 2.5mL thallium standard solution into a 2000mL volumetric flask, add 250mL aqua regia, dilute to scale with water, and mix well. This standard solution contains thallium 0.25 μ g/ml.
Gold standard stock solution: weigh 1.000 g of pure gold (purity greater than 99.99%, wipe off the surface oxide layer before use) in a 250mL beaker, add 100mL water and 60mL aqua regia, decompose by heating, cool, transfer to a 1000mL volumetric flask, dilute with water, and then. The standard solution contains 1 mg/ml of gold.
Gold standard working solution: transfer 2.50mL of gold standard stock solution into a 100mL volumetric flask, add 1mL aqua regia, dilute with water to scale, and mix well. The standard solution contains 25 μ g/ml of gold.
Preparation of standard solution: Transfer 0.00 ml, 1.00 ml, 2.00 ml and 4.00mL of gold standard working solution to a series of 100mL volumetric flasks, add 10mL thallium internal standard working solution, and make constant volume with water. The gold contents in the solution are 0.00, 2.50, 5.00 and 65438 respectively.
Argon (> 99.99%).
Analytical balance: sensitivity 0.000 1 g.
Plasma mass spectrometer: ELAN9000.
3. Analysis steps
Weigh two samples according to the table, put them in a 75mL evaporating dish, burn them at 800℃ for 2 h, move them into a 500mL beaker, add 20mL hydrochloric acid, heat for 5min, add 50mL aqua regia, heat and concentrate them to 10 ~ 20ml, take them out, cool them, decompose them by heating, cool them, move them into a 200mL volumetric flask, dilute them with water, and mix them evenly.
Table 7-3 Fractional Doses
Transfer 1.00mL sample into a 50mL volumetric flask with 5mL thallium internal standard added in advance, use water for constant volume, mix well, and determine the standard solution and test solution in turn by ICP-MS. The isotope mass number of the tested elements is Au 197, Tl 205.