GB/T 18882.3-2019 specifies methods for the determination of silica content in mixed rare earth oxides of ionic rare earth minerals, including Spectrophotometric method, spec-trophotometry and weighting method. Spectrophotometric method, spec-trophotometry is suitable for the measurement range of 0.10% to 2.00%, weighting method is suitable for the measurement range of 1.00% to 5.00%, and Spectrophotometric method, spec-trophotometry is used as the arbitration method when the ranges overlap. The standard describes in detail the sample processing, reagent preparation and measurement steps to ensure the accuracy of measurement results, providing a reliable technical basis for the analysis of rare earth minerals.