ASTM STANDARDIZATION OF THE ACID NEUTRALIZATION POTENTIAL ACIDITY TITRATION IN THE LOW RANGE (ANPAL) FOR INVESTIGATION OF 'UNCERTAIN' RESULTS

摘要

Classical acid-base accounting using modified Sobek titration methods has resulted in interpretation of results for materials with neutralization potential (NP) less than 20 tons of CaCO_3/1000 tons of material (2% CaCO_3) as 'uncertain' due to lack of sensitivity within that content range. Standardization of a 'fizzless' acid neutralization potential (ANP) method was undertaken in the American Society for Testing and Materials (ASTM) International using two ranges of sulfuric acid additions based on reaction pH and carbonate carbon estimates rather than subjective fizz testing as well as hydrogen peroxide additions to correct for mineral acidity. The method is identified as the acid neutralization potential acidity (ANPA) titration method. During interlaboratory testing a positive bias was discovered within the 'uncertain' range which was further investigated and resolved by increasing the test sample weight from one to five grams for samples needing improved accuracy in materials with ANP ＜2% CaCO_3. Test results from the interlaboratory testing of the low range method is presented and compared with the results from the original ANPA method in the paper.