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Determination of precious metals in ores by nickel matte assay
Source: Mine Road Network 20 17-07-242784
Nickel matte gold assay (also known as nickel sulfide gold assay) is to capture matte composed of nickel sulfide, iron sulfide (and copper sulfide).
Precious metal, suitable for capturing gold and all platinum group elements. It can also be used for other high-sulfur and high-nickel samples that are difficult to smelt by gold method. Nickel sulfide has a sufficient density (5.3g/cm3) and is easy to be separated from slag and crushed. Nickel matte button has a strong ability to capture precious metals, and the weight of gold test button is above 12g, which can completely capture precious metals in 50g samples. The silicification degree of slag in nickel matte gold assay is preferably between 1.5-2.0. However, it should be noted that the acidity of the slag should not be too large, otherwise the slag is very sticky, which is not conducive to the separation of matte and slag. Generally, matte is dissolved with hydrochloric acid, and sulfur escapes into hydrogen sulfide. Copper, iron and nickel (including silver) enter the solution in the form of chlorine complexes, while gold and platinum group metals remain in the residue. When the matte button is dissolved with concentrated hydrochloric acid, the loss of osmium is relatively large, and platinum and palladium will also lose to some extent. Dissolution with dilute hydrochloric acid or closed dissolution can reduce the loss of these elements. The reproducibility of gold determination by nickel matte assay is not very good, which includes both the enrichment efficiency of gold and the loss of gold when it is dissolved in hydrochloric acid. Tellurium precipitation method can improve the recovery and reproducibility of gold. Sulfur should be added as reducing agent and vulcanizing agent in nickel matte gold assay, and the amount of sulfur should be appropriate. If it is added less, the loss of osmium and ruthenium will increase when the belt buckle is dissolved with hydrochloric acid. Too much brings difficulties to the disintegration of the gold test buckle. In order to avoid excessive sulfur, iron sulfide can be used to replace part of sulfur, so that the gold test buckle can be pulverized by itself in water.
First, the characteristics of matte nickel assay
1 Nickel sulfide analysis
(1) can capture all platinum group elements.
(2) The composition changes of different types of samples are relatively small.
(3) Samples containing sulfur and nickel do not need to be removed in advance.
(4) The ratio of flux to sample is small, so a large number of samples can be processed.
(5) Nickel sulfide button can be directly used for laser ablation.
2. Limitations of matte nickel analysis
(1) blank height. Sometimes the blank value of some elements can reach hundreds of pg/g level. Especially the blank of nickel reagent is high, so it is suggested to use high purity carbonyl nickel powder.
(2)Os volatilizes in the form of OsO4.
(3) When nickel sulfide button is dissolved with hydrochloric acid, some precious metal elements such as Ru and Pd will be lost by volatilization in the form of chloride or chlorine-containing complex.
(4) Because the collection efficiency of nickel sulfide is low or the separation of tellurium precipitate is incomplete, the recovery rate of single element will be poor (
(5) When nickel sulfide button is dissolved with hydrochloric acid, it will produce a large amount of hydrogen sulfide gas, which requires effective flue gas discharge equipment.
The reagent blank can be reduced by reducing the gold test buckle of nickel sulfide. It is usually necessary to add early nickel sulfide gold analysis.
Nickel with a ratio of 10g or more is now about a few grams (depending on the content range of platinum group elements in the sample and the properties of the sample matrix.
Second, the nickel matte composition analysis
Mixing is the key step of nickel matte analysis. First of all, we should know the type of sample to determine the melt formula. According to the composition of the substances in the sample and the expected silicification degree of the slag, the addition amount of various reagents in the ingredients can be obtained by calculating the reaction formula.
1. General composition range of general geological samples
(1) Rocks, sediments and soils, such as timely, pyroxene, olivine, calcite, sedimentary rocks, soil, river sediments and marine sediments. The formula is generally (20g sample): Na2B4O5(OH)4:20-25g, Na2CO3: 10-65.
(2) Used for ore samples, such as chromite, ultrabasic rocks, pyrite, chalcopyrite, sphalerite, nickel ore, etc. The formula is generally (20g sample): Na2B4O5(OH)4 or Li2B4O7:25g, Na2CO3: 15-20g, Ni: 3.5-6g, SiO.
Many chromites often contain more platinum group elements. Chromite is a kind of refractory mineral, and the flux formula is very important for the smelting of chromite. Sodium metaphosphate can be added to completely melt chromite, and its flux formula is: sample 10g, SiO 29g, (NAPO3) x 15g, Li2b4o730g, Ni 7.5g, S4.5g The melting temperature must reach 1200℃.
2. Adjustment points of different material formulas
(1) Silica sample: Silica accounts for more than half of the silicate sample, and there is a small amount of calcium, magnesium and aluminum, so it is necessary to add more sodium carbonate and proper amount of borax.
(2) Carbonate samples: The main components of this kind of samples are calcium carbonate and magnesium carbonate. When melting the samples, carbon dioxide decomposes and escapes into calcium oxide and magnesium oxide, so more acidic flux silicon dioxide and more borax must be added when melting the samples.
(3) Oxidized ore sample: Oxidized ore sample refers to a sample containing more hematite and magnetite, which has certain oxidizing ability and can consume part of reducing agent, and should be considered when batching.
(4) Sulfide ore sample: contains more sulfides and has strong reducing ability. More sodium carbonate should be added to reduce the sulfur content.
Copper concentrate, copper-nickel sulfide ore, stibnite, nickel ore, pyrite and other minerals often contain platinum group elements and gold and silver, so it is relatively difficult to smelt the ore, so it is necessary to increase the dosage of sodium carbonate and silicon dioxide when batching.
Third, the application examples
Determination of precious metals in ores by matte nickel assay-inductively coupled plasma mass spectrometry
The determination of osmium is not included in most gold analysis -ICP-MS analysis procedures of osmium and nickel, because osmium is oxidized to osmium tetroxide and lost by volatilization. In the past, osmium was distilled first, and then the residue was dissolved with aqua regia to determine osmium. This method is too long, which is not conducive to large-scale sample analysis. An improved method for the determination of platinum group elements by nickel matte gold assay-tellurium precipitation ICP-MS combines the sealed dissolution of precious metal sulfide filter residue with isotope dilution method, which solves the determination of all platinum group elements and gold including osmium, avoids distillation separation and/or separate determination of osmium, and simplifies the analysis process. The key point of that method are as follows:
1. Sample processing steps
(1) Put 20g sample in a glass triangular flask, add mixed flux, shake well, and then transfer to a clay crucible.
(2) add an appropriate amount of osmium diluent accurately, cover a small amount of flux, and put it in a muffle furnace heated to 1 100℃ for melting1.5h.
(3) taking out the crucible, pouring the melt into the iron mold, cooling, taking out the matte nickel button, and crushing. Transfer to a beaker, add 60mL concentrated hydrochloric acid, and heat to dissolve until the solution becomes clear and no longer bubbles.
(4) adding tellurium precipitant 1 mL (containing 0.5mg of tellurium) and 1mol/L tin tetrachloride solution 1 mL, heating for 0.5h, and standing for several hours to solidify tellurium.
(5) negative pressure filtration with 0.45μm filter membrane, and multiple precipitation with 2mol/L hydrochloric acid.
(6) Transfer the precipitate and the filter membrane to a sealed PTFE sample dissolver with a nut, add 1 mL aqua regia, seal, and dissolve at about 100℃ on an electric heating plate for 2-3h.
(7) After cooling, transfer it to a 10 mL colorimetric tube and measure it with constant volume of water.
2. Determination of Platinum Group Elements
The sample solution was directly determined by ICP-ms, and RuRhPdIrPt was standardized by conventional standard solution. Determination of Os by isotope dilution method. The internal standard is 10ng/ mL Cd and Tl standard solution. Although sealed slag method is adopted, isotopic dilution determination of osmium is still necessary. On the one hand, there is no gas leakage because of sealing dissolution; On the other hand, even if there is no leakage loss of osmium in the dissolution process, because the sensitivity of osmium with different oxidation degrees in ICP technology is very different, the standardization of standard solution will cause great errors in the analysis results.
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