This standard specifies the method summary, reagents and materials, apparatus, sample, test procedure, calculation and expression of result and precision of method for the determination of arsenic in coal by molybdenum blue spectrophotometric method. The molybdenum blue spectrophotometric method is the arbitration method.
This standard is applicable to lignite, soft coal and anthracite.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 483 General rules for analytical and testing methods of coal
GB/T 2304 Chemical reagent - Zinc granular free from arsenic
3 Molybdenum blue spectrophotometric method
3.1 Method summary
Mix coal sample with Eschka reagent, ignite the mixture and dissolve the igniting matter with sulfuric acid and hydrochloric acid, then add reducing agent to restore the pentavalent arsenic to trivalent arsenic, add zinc granular to make the arsenic released in the form of arsenic hydride gas, absorb and oxidize with iodine solution to generate arsenic acid, add ammonium molybdate - hydrazine sulfate solution to generate molybdenum blue, and then determine with spectrophotometer.
3.2 Reagents and materials
Unless otherwise specified, only the reagents recognized of analytical quality and distilled water or deionized water or water with equivalent purity shall be used during the analysis.
3.2.1 Zinc free from arsenic: in accordance with GB/T 2304, sift out the zinc granule with size no less than 3mm for use.
3.2.2 Eschka reagents (hereinafter referred to as aldrin): commercially available or mix two parts by mass of light magnesium oxide and one part by mass of anhydrous sodium carbonate, grind the mixture to the size of less than 0.2mm, and then store it in a closed container.
