Acidic Surface Functional Groups and Mineral Elements in Lakra Coal (Sindh, Pakistan)

Abstract

Surface acidity of virgin coal (Lakra Sindh, Pakistan) and variously extracted/leached coal samples leached with HNO₃, NaOH, and KMnO₄, were investigated by aqueous potentiometric titration employing KOH as a titrant. The titration curve of virgin coal showed that its surface might contain carboxylic, carbonyl, phenolic and other weak acidic functional groups such as enols and C-H bond. The titration curves of leached coal samples showed inflections at pH 4-11, being not similar the inflections of carboxylic groups. This inflection might be given by functional groups like CO₂, phenolic, enols and C-H. Mineral matter such as Fe, K, Zn, Mn and Ni were determined in the ash of coal by atomic absorption spectrophotometer and was found that Fe (3104 µg/g) in the highest and Ni (36.05 µg/g) in the lowest quantity is present in virgin coal sample.