<![CDATA[<B>A comparative evaluation on the oxidative approaches for extraction of humic acids from low rank coal of Mukah, Sarawak</B>]]>

Abstract

Produtos derivados de ácidos húmicos têm bom mercado; entretanto, estes não são populares nessa região, devido ao alto custo imposto aos produtos importados. Por esta razão, é essencial identificar uma fonte nativa de ácidos húmicos como condicionador de solo. Carvões de baixa classe são encontrados em abundância em Mukah, com aplicação não energética largamente explorada. Estudos preliminares mostraram que o tratamento químico com ácido nítrico poderia aumentar potencialmente o rendimento essencial de ácidos húmicos de 20 a 85%. Entretanto, ácido nítrico é um item caro, o que pode aumentar o custo, portando a possibilidade de empregar outros oxidantes precisa ser avaliada. Neste estudo, os ácidos húmicos foram extraídos de carvão de baixa classe de Mukah, com oxidação usando HNO 3 , H 2 O 2 e KMnO 4 e foram comparados em termos de rendimento, características químicas e espectroscópicas. Os resultados indicaram que a oxidação com H 2 O 2 envolveu considerável perda de peso, sendo desfavorável para a produção de ácidos húmicos. A oxidação com permanganato de potássio não é recomendada, pois uma quantidade substancial de compostos inorgânicos foi introduzida aos produtos e o rendimento essencial obtido foi baixo. A oxidação com ácido nítrico continua sendo a escolha no processo de extração de ácidos húmicos, uma vez que a perda de massa envolvida foi aceitável; o rendimento de ácidos húmicos obtido foi alto com características de baixo teor de cinzas e alto teor de grupos funcionais ácidos. Humic acid-based products are well marketed; nevertheless, these products remain unpopular in this region possibly due to the higher selling price resulted from the cost imposed on the imported products. For this reason, it is essential to identify the indigenous source of humic acids as the soil conditioner. Abundant of low rank coals are found in Mukah and the non-energy application of the source are largely unexplored. Preliminary study reported that chemical treatment with nitric acid could potentially increase the essential yield of humic acids from 20% to 85%. Nitric acid is an expensive item, which could add on to the cost, hence possibility of employing other oxidative approaches need to be evaluated. In this study, the humic acids were extracted from the low rank coal of Mukah with HNO 3 , H2O 2 and KMnO 4 oxidation and were compared in terms of yield, chemical and spectroscopical characteristics. Results indicated that H 2 O 2 oxidation involved considerable weight losses upon oxidation render it unfavorable for production of humic acids. Potassium permanganate oxidation however was not recommended, as a substantial amount of inorganic compounds was introduced to the products and the essential yield generated was low. Nitric acid oxidation remains the choice of the process for extraction of humic acids as the weight losses involved was acceptable; the yield of humic acids obtained was high with characteristics of low ash content and high acidic functional groups.

Impact of HNO3 Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield

“…5, 2017 Oxidation of carbonaceous matrices employing nitric acid solution with different concentrations (5 to 25%) has been used with both fossil coal and biochar. 11,15 Fong et al…”

“…Usually, spectroscopic and chemical characterization is focused on the coal HA since the purification of this fraction is easily attainable. [10][11][12] The difficulty in analyzing the chemical composition of the organic fraction of coal matrices arises from the presence of inorganic components. To overcome the interference of the inorganic matrix in the spectroscopic, thermic, pyrolitic and chemical analyses, the treatment with diluted hydrofluoric acid (HF) solution has been used in soil samples in order to concentrate carbon and remove paramagnetic compounds.…”

“…11,15 Fong et al 11 tested three different reagents (HNO 3 , H 2 O 2 and KMnO 4 ) for the oxidation of low rank coal samples from Indonesia. The obtained HA from the different methods were compared in light of their gravimetric yields and chemical characteristics determined by spectroscopic techniques.…”

“…5, 2017 Oxidation of carbonaceous matrices employing nitric acid solution with different concentrations (5 to 25%) has been used with both fossil coal and biochar. 11,15 Fong et al11 tested three different reagents (HNO 3 , H 2 O 2 and KMnO 4 ) for the oxidation of low rank coal samples from Indonesia. The obtained HA from the different methods were compared in light of their gravimetric yields and chemical characteristics determined by spectroscopic techniques.…”

“…The oxidized coal with 10% HNO 3 solution produced a higher HA yield which showed a greater exchangeable acidity (-COOH and OH-phenolic) when compared to HA from samples treated by other methods. Besides increasing the oxygen-containing groups in the coal structure due to the oxidation of alkyl groups, 11 it is proposed that the treatment with nitric acid promotes the carboxylic and nitro substitution on the aromatic ring. …”