Studies of mono- and polynuclear iron hydroxy complexes in brown coal

Iron hydroxy complexes were added to brown coal by a stepwise pH adjustment of solutions of Fe(III) mixed with coal. The amounts of NaOH used to adjust the pH and the amount of Fe(III) added to coal were consistent with the addition of both mono- and polynuclear iron complexes to coal. Analysis of the bulk sample and of the sample sieved into smaller and larger particles, and SEM-EDX examination of large and small particles, revealed an uneven distribution of iron, with higher concentrations in smaller coal particles. XPS and TOF-SIMS data show that mono- and polynuclear iron species form in the coal samples. Computer molecular modeling has illustrated the structure and bonding of the mono- and polynuclear species in brown coal and the variation in the relative distribution of these species as the amount of added iron is increased. Computer models have also been used to show similarities between low-temperature pyrolysis of brown coal containing large amounts of iron and the thermal decomposition of iron carboxylates.