ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2015.18979 INTRODUCTION Humic acids are metastable polymeric intermediates of fossilization of plant materials subjected to air oxidation. These are polyphenolic polycarboxylates with carbonyl, alcoholic and other functionalities. In addition to carbon, hydrogen and oxygen these also contain small amounts of nitrogen and traces of other elements. Their molecular weights range from 2 to 300 KD. Characteristics like colour, percentage of carbon and cation exchange capacity change gradually with the increase in length of the polymer chain and degree of oxidation 1 . Humic acids are considered to be excellent soil condi- tioners. These not only improve the texture of the soil by impro- ving its cation exchange capacity but also improve pH and organic content of the soil. Their water holding capacity by gelling with water molecules decrease the water demand. These substances have been reported to significantly increase the supply of vital micronutrients and available phosphorous to plants by chelation and bridging between root hair and nutrients involving their multi-active functionalaties 2-5 . Although humic acids occur naturally as outcrop in coal mines or in mineral deposits such as lignite or leonardite, these substances can also be prepared on industrial scale by oxidation of low grade brown coals 6 . Virtually it has now become the need of the hour to search for economically viable methods of preparation of humic acids because natural surces of humic Chlorine Dioxide Mediated Oxidation of Sub-Bituminous Coal for Humic Acid Production ABID NAZIR GILL 1 , MUHAMMAD AKBAR 2 , MUHAMMAD ABDUL QADIR 2 , MUHAMMAD PERVAIZ 1 and AHMAD ADNAN 1,* 1 Department of Chemistry, Government College University, Lahore, Pakistan 2 Institute of Chemistry, University of the Punjab, Lahore, Pakistan *Corresponding author: E-mail: adnan_biochem@yahoo.com Received: 2 January 2015; Accepted: 27 May 2015; Published online: 16 July 2015; AJC-17382 Humic acids are metastable degradation products of plant origin. These are used as soil conditioner to improve the texture of soil and uptake of nutrients. In nature, these are found in mineral deposits such as lignite or leonardite. However, these can also be prepared by the oxidation of low grade coals using a variety of oxidation processes. Different samples of coal were tested for their oxidizability to humic acids using chlorine dioxide as the oxidant. A sample of coal from Dukki area of Baluchistan gave maximum yield of humic acids. The coal sample was oxidized by chlorine dioxide produced in situ by the reaction between potassium chlorate, sulphuric acid and a reductant such as methanol or hydrochloric acid. Humic acids yield of 76 % was obtained at 65 °C when 100 g coal was treated with chlorine dioxide produced by the reaction between 8 g KClO3, 30 g HCl and 50 mL 50 % H2SO4. Keywords: Humic acid, Coal, Methanol, Chlorine dioxide. Asian Journal of Chemistry; Vol. 27, No. 11 (2015), 3961-3964 acids are near to exhaust but their market demand is growing owing to their effectiveness. Various methods of dry and wet oxidation of low rank coals have been investigated with oxidants like oxygen gas, alkaline KMnO4, hydrogen peroxide, nitric acid, electrolytic oxidation etc. 7-12 . In present study attempts were made to oxidize the coal with chlorine dioxide (ClO2), produced in situ by the reaction of KClO3 with a reducing agents such as HCl, H2O2 or methanol, in the presence of excess H2SO4. ClO3 – + 2H + + e – → ClO2 + H2O E° = 1.152 V The reaction of chlorine dioxide with organic compounds takes place in two steps. In the first stage of the reaction, the ClO2 molecule accepts an electron and chlorite ion is formed (ClO2 – ). In the second stage, ClO2 – ion accepts 4 electrons to produce a chloride ion (Cl – ) 13 . ClO2 (aq) + e – → ClO2 – E° = 0.95 V ClO2 – + 2H2O + 4e – → Cl – + 4OH – E° = 0.76 V Chlorine dioxide based oxidative production of humic acids has been found a promising way for the production of humic acids suggesting the possibility of the low rank coal for commercial production of humic acids. EXPERIMENTAL Preparation of coal sample: The coal samples from different mines of the Punjab and Baluchistan were collected