Iron and particle size: two key criteria
Specify what iron means
State whether the limit is elemental iron or Fe₂O₃, then % or ppm. A unit error can invalidate a comparison. Include the method and detection limit.
Describe the distribution
A maximum size alone does not describe a distribution. Use a sieve curve or fineness indicators with the test method. Fines and coarse particles may behave differently.
Test the parameters together
Evaluate size and chemistry using a controlled trial. Agree on receipt limits that match successful samples, including explicit tolerances.
Every application needs a suitable grade and testing. OPR confirms grades, processing and availability; no ultra-high-purity grade or certification is assumed.
Source : USGS — Silica