Modification of Lakra (Pakistani) coal by chemicals washing and heat treatment and its application for removal of organic acids (prop ionic acid and chloroacetic acid) from aqueous solution

In the present study, Lakra coal was heat treated and washed with different chemicals (KMnO₄ (0.5M), NaOH (0.1M), HNO₃ (0.1M), HCl (0.1M), and H₂O₂ (0.1M)) and investigated as adsorbent for the removal of organic acid pollutants such as propionic and chloroacetic acids from aqueous solution. The results revealed that virgin coal despite of evacuating for generating porosity the adsorption of both acids near to nil. Pre-treatment of coal samples with a variety of chemicals increased the adsorption capabilities as compared to virgin coal. KMnO₄, HCl and HNO₃ treated samples showed maximum adsorption among all the samples. Prominent pores generation was observed in the treated samples shown by SEM images of virgin and variously treated coal samples. The aforementioned chemicals also reduced ash, volatile matter, sulphur and ash contents of the coal. At 210 minutes maximum adsorption capacities for chemicals modified coal samples were observed and above no appreciable change was found. The results showed that kinetics of sorption properties of organic acids fitted well with Lagergern pseudo second order model with high correlation coefficiency (r²) for modified coal samples. For the adsorption of both propionic acid and chloroacetic acid Langmuir model best described the adsorption process. It is concluded that only heat treatment of the coal cannot increase the adsorption capacity for effective adsorption pre-treatment with either of the chemical would be more effective.