煤浆法烟气脱硫中草酸和紫外线强化煤砷浸出过程

Oxalic acid and UV enhanced arsenic leaching from coal in flue gas desulfurization by coal slurry

以N_(2)、O_(2)、SO_(2)三种气体模拟烟气,在1 L的光反应器中,研究了主要因素对煤砷浸出、As(Ⅲ)氧化以及SO_(2)脱除的影响规律,分析了过程机理,确定了浸出过程速率控制步骤。结果表明,紫外线照射和草酸均能有效提高砷浸出率,180 min时,在遮光和pH为2.5的条件下,加入1.0 mmol/L草酸能使砷浸出率提高32.9%,在紫外线照射下,可使砷浸出率再提高21.3%,且浸出液中的As(Ⅲ)占总砷之比小于13%,还能提高SO_(2)脱除率。低pH有利于煤中砷的浸出,但对SO_(2)的脱除不利。煤砷浸出率和SO_(2)脱除率均随温度的提高而显著增大。动力学分析计算得出煤砷浸出过程的表观活化能为4.9 kJ/mol,说明砷浸出过程受已反应固体层内的扩散过程控制。自由基猝灭实验表明,硫酸根自由基和羟基自由基是紫外线照射下草酸强化煤砷浸出体系中的主要自由基。ATR-FTIR与XPS表征结果进一步证实了浸出液的测定结果。

Currently,coal is still the main energy source in our country.During coal combustion,arsenic will be discharged into the atmosphere with flue gas.Arsenic is highly toxic and harmful to the environment and human health.Therefore,it is of great practical significance to study the arsenic removal technology from coal.Using N_(2),O_(2)and SO_(2)to simulate flue gas,the effects of main factors on arsenic leaching from coal,As(Ⅲ)oxidation and SO_(2)removal were studied in a 1 L photoreactor.The process mechanism was analyzed,and the rate control step of the leaching process was determined.The results showed that both ultraviolet(UV)irradiation and oxalic acid could effectively increase the extraction ratio of arsenic.At 180 min,under pH 2.5 and dark conditions,adding 1.0 mmol/L oxalic acid could increase the arsenic extraction ratio by 32.9%.Under UV irradiation,the arsenic extraction ratio could be further increased by 21.3%,and the ratio of As(Ⅲ)in the leaching solution to the total arsenic was less than 13%,and the SO_(2)removal efficiency could also be improved.Low pH was beneficial for arsenic leaching from coal,but unfavorable for SO_(2)removal.Both arsenic extraction ratio and SO_(2)removal efficiency increased significantly with the increase of temperature.The apparent activation energy for process of arsenic leaching from coal was calculated to be 4.9 kJ/mol,indicating that the arsenic leaching process was controlled by the diffusion process in the reacted solid layer.The free radical quenching experiments showed that sulfate radical and hydroxyl radical were the main free radicals in the oxalic acid-enhanced coal arsenic leaching system under UV irradiation.ATR-FTIR and XPS characterization results further confirmed the measured results of the leaching solution.