Study On The Adsorption Of Azo Dye By Heat-Treated Lignite

With the rapid development of China's textile industry,the total amount of wastewater occupy the third in all industrial sectors in the country.The highest proportion of azo dyes are poisonous and carcinogenic,posing a huge threat to ecological stability and human health.Adsorption method is an effective method for treating dye wastewater.Lignite is rich in reserves,has well-developed pore structure and reactive group,and can be used as an potential adsorbent for adsorbing pollutants due to avoiding the problem of adsorbed sediment treatment.However,the efficiency of lignite treating on dye wastewater is not satisfactory.Therefore,heat treatment of lignite is a prerequisite for the efficient adsorption of azo dyes.In this paper,a series of different heat-treated lignite were prepared by using Mengdong lignite as raw material.Through physical and chemical analysis of lignite with heat treatment conditions of 300°C-8 min,600°C-8 min,and 900°C-8 min,it could be obtained that with the heat treatment temperature increased,the surface of lignite gradually became rough and porous.Moreover,the content of functional groups continuously decreased.Under the heat treatment conditions of 300°C-8 min,the surface functional group and pore structure of lignite slightly damaged.When the heat treatment condition was 600°C-8 min,the O=C-O content on the surface of lignite was rapidly reduced to 0.27%,and the content of C=O also decreased.The ¹³C NMR spectrum showed that the aliphatic carbon peak,carboxyl carbon and carbonyl carbon peak substantially disappeared.Lignite at 900°C-8 min heat treatment condition contained a large number of pore structure and the surface area sharply increased to117.740 m²*g^-1,and the surface functional groups were decomposed completely,containing only a small amount of C-O.Lignite treated under different heat treatment conditions used to adsorb four kinds of azo dyes.When the heat treatment condition of lignite was 900°C-8 min,the adsorption efficiency of congo red was 94.12%,the direct yellow brown D3G was93.05%,and the methyl orange and direct fast blue B2RL was 99.97%and 99.46.%.The multi-linear regression mathematical method was used to correlate the adsorption efficiency of 300°C-8 min,600°C-8 min,and 900°C-8 min different heat-treated lignite on azo dyes with experimental data of lignite specific surface area,total pore volume and oxygen content.The relevant equations obtained.The adsorption experiment results verified that the accuracy of the fitting equation was high,and the heat treatment temperature of lignite was positively correlated with the azo dyes adsorption efficiency.Azo dyes of congo red,methyl orange,direct yellow brown D3G and direct fast blue B2RL were adsorbed by heat-treated lignite to explore the effects of adsorption time,solution pH value,dosage of lignite and initial azo dyes concentration on the adsorption.It could be concluded that with the increase of adsorption time and adsorbent dosage,the adsorption efficiency of four dyes increased and then stabilized.Meanwhile,the lower the pH value of the solution,the better the adsorption efficiency.The initial concentration of the dye continuously increased,the adsorption efficiency decreased,but the amount of adsorption increased.The adsorption thermodynamics and kinetics of four azo dyes adsorbed by heat-treated lignite were studied.It was found that the adsorption of four dyes was more consistent with the Freundlich adsorption isotherm model and the Lagergren quasi-secondary adsorption rate equation.