Relative effectiveness of short-range ordered Mn(IV), Fe(III), Al, and Si oxides in the synthesis of humic acids from phenolic compounds

Open Access
Publisher Website
Google Scholar
Abstract
The relative effectiveness of short-range ordered Mn(IV), Fe(III), Al, and Si oxides in the catalytic synthesis of humic acids from phenolic compounds was investigated. The Mn(IV) oxide markedly accelerated the synthesis of humic acids from hydroquinone, resorcinol, and phloroglucinol. The catalytic effect of the Fe(III) oxide was remarkable on the synthesis of humic acids from catechol, pyrogallol, protocatechuic acid, and gallic acid. The catalytic effects of the Al and Si oxides on the formation of these humic acids were limited or not observed under the current conditions of examination. The synthetic humic acids showed a high degree of humification. From hydroquinone and resorcinol, which do not display a chelating ability, the yields of humic acids synthesized and the amounts of metal ions dissolved during the synthesis of humic acids were much higher in the Mn(IV) oxide system than in the Fe(III) oxide system. On the other hand, from catechol, which shows a chelating ability, the yield of humic acid was much higher in the Fe(III) oxide system than in the Mn(IV) oxide system, but the reverse was true for the amount of metal ions dissolved. On the basis of these results, the mechanisms of the interaction between the phenolic compounds and the oxides were discussed.