GB/T 7739.8-2022 in English

1. Background of standard formulation and technological evolution

GB/T7739.8-2022 is Part 8 of "Chemical Analysis Methods for Gold Concentrates", which mainly stipulates the determination method of sulfur content and effective sulfur content. Compared with the old version, the new standard has made many optimizations in technical details:

• Deleted the "allowable difference" requirement
• Increased the amount of mixed solvent in Method 1
• Changed the ignition temperature of Method 1
• Added the "repeatability" and "reproducibility" requirements
• Changed the air intake method of Method 2
• Added the determination of effective sulfur (see Chapter 6)

2. Standard Framework Comparison Table

3. Detailed interpretation of sulfur content determination method

3.1 Method 1: Barium sulfate gravimetric method

Barium sulfate gravimetric method is a classic method for determining sulfur content. Its principle is to convert sulfur into sulfate ions through high-temperature melting, and then react with barium chloride to form barium sulfate precipitation.

• Principle: After the sample is semi-melted with a mixed flux (sodium carbonate, zinc oxide, potassium permanganate) at 780°C, the soluble matter is dissolved with water. The sulfur element is converted into sulfate ions, which react with barium chloride to form barium sulfate precipitation.
• Reagents and instruments: - Mixed flux: anhydrous sodium carbonate, zinc oxide, potassium permanganate in a mass ratio of 1:1:0.1 - Analytical balance (sensitivity 0.1mg) - Muffle furnace (maximum temperature not less than 1100℃)
• Steps: 1. Melt the sample, dissolve it with water and filter it 2. Adjust to acidic conditions, add barium chloride to form a precipitate 3. Filter, burn and weigh

This method is suitable for samples with a sulfur mass fraction of 5.00%~50.00%.

3.2 Method 2: Combustion Neutralization Titration

Combustion Neutralization TitrationSulfur is converted into sulfur dioxide through high-temperature combustion, which is then absorbed and oxidized into sulfuric acid with hydrogen peroxide, and finally titrated with a sodium hydroxide standard solution.

• Principle: The sample is burned in a high-temperature air flow at 1250℃~1300℃, and the generated sulfur dioxide is captured by hydrogen peroxide absorption liquid and oxidized to sulfuric acid.
• Reagents and instruments: - Potassium permanganate-sodium hydroxide solution - Lead sulfate standard reagent
• Steps: 1. Connect the measuring device and check the airtightness 2. Place the sample in a high-temperature electric furnace to burn 3. Titrate to the endpoint

This method is suitable for samples with a sulfur mass fraction of 5.00%~50.00%.

3.3 Method 3: Effective sulfur determination-combustion neutralization titration method

Effective sulfur determination method is mainly for sulfur in monomer sulfur and sulfide, which is converted into sulfur dioxide through high-temperature combustion and absorbed by hydrogen peroxide solution.

• Principle: The sample burns in a high-temperature air flow at 850℃, and the generated sulfur dioxide is captured by the hydrogen peroxide solution and oxidized to sulfuric acid.
• Reagents and instruments: - Color-changing silica gel - Potassium permanganate - Sodium hydroxide solution
• Steps: 1. Place the sample in a high-temperature electric furnace and burn 2. Titrate to the endpoint

This method is suitable for samples with an effective sulfur mass fraction of 3.94%~45.84%.

4. Implementation suggestions