Silicates and silica in pulp (wet ash method), Test Method T 245 cm-07
This method describes a procedure for determining the silicates and silica content of pulp.
The pulp is wet-ashed using nitric and sulfuric acids. The insoluble residue is filtered, washed, ignited, and weighed as silicon dioxide.
For a faster but less accurate procedure for measuring all acid insoluble material see TAPPI T 244 “Acid-Insoluble Ash in Pulp.”
The ashing temperature used in this method has been changed from 575°C (T 245 om-88) to 525°C. This is consistent with recent changes in TAPPI T 211 “Ash in Wood and Pulp,” and is also consistent with current ASTM and ISO ash methods. The purpose behind this is to prevent the degradation of calcium carbonate that can occur at the higher temperature. Please note that the precision statement contained in section 10 was developed using an ashing step at 575°C, and has not been repeated at the lower ashing method of 525°C.