GB/T 14635-2020 in English

Oxalate gravimetric method (Method 1)

Principle:Acid decomposition→Ammonia precipitation separation→Oxalic acid precipitation→950℃ calcination and weighing

Applicable instruments:Platinum crucible/porcelain crucible, high temperature furnace (≥1000℃)

EDTA titration method (Method 2)

Principle: Acid dissolution → Sulfosalicylic acid masking → EDTA titration at pH 5.5

Key reagents: EDTA standard solution (0.01mol/L), hexamethylenetetramine buffer system

1. Method selection:For overlapping range, the oxalate weight method with higher accuracy (relative standard deviation ≤ 0.5%) is preferred
2. Special sample treatment:Samples containing uranium need to be dissolved in nitric acid, and rare earth fluoride must be dissolved in a polytetrafluoroethylene beaker
3. Titration endpoint judgment:The EDTA method recommends the use of methyl orange and p-nitrophenol as dual indicators
4. Quality control:Each batch of tests must be verified with a standard sample (such as GSB04-3256-2015), and the recovery rate should be controlled between 98% and 102%

This standard integrates seven standard methods including the original GB/T 8762.1-1988. The main improvements include:

• Introduction of sulfide rare earth determination to meet the needs of new rare earth smelting processes
• Expansion of the determination range to adapt to the utilization of low-grade rare earth resources
• Optimization of calculation formula, and addition of a mixed rare earth average molar mass calculation module