Study On Leaching Behavior Of Arsenic In Stone Coal Under The Action Of SO 2

As the most prevalent traditional fossil fuel,the human demand for coal is great.Arsenic,one of the toxic elements in coal,can be released into air during coal combustion,damaging environment and human health.Fly ash can also pollute environment,if it is not disposed of properly.In China and other places in the world there exist the problems of arsenic pollution in varying degree.Commonly,the content of arsenic in stone coals is high,and therefore its arsenic pollution problem is more serious.To protect environment and human health,it is of practical significance to research technology of removing arsenic from coal prior to combustion.In this study,experiments of arsenic removal from stone coal collected from Anhui were carried out using a bubbling reactor.The slurry was prepared using stone coal of a certain size fraction.N₂?O₂ and 1% SO₂ were used to simulate flue gas to leach arsenic from the coal.The effects of main parameters on the arsenic leaching process were studied.Experimental results showed that,for same reaction time,the iron and arsenic conversions and the trivalent arsenic concentration all increased with increasing SO₂ concentration(500×10^-6-2000×10^-6).SO₂ removal efficiency,iron and arsenic conversions increased with increasing O₂ concentration.But,because of oxygen oxidation,the aqueous concentration of trivalent arsenic decreased with the increase of O₂ concentration?3%-20%?.As the O₂ concentration was increased to 10%,the increase of iron and arsenic conversions became smaller with further increase of O₂ concentration.Temperature experimental results showed that SO₂ removal efficiency,iron and arsenic conversions,and trivalent arsenic concentration all increased with the increase of temperature?20-65??.This is because the reaction rate and the reducibility of pyrite increase with increasing temperature.The experimental results at different solid-liquid ratios?1:10-1:40?indicated that the SO₂ removal efficiency,leached iron and arsenic concentration increased with the increase of solid-liquid ratio,whereas the iron and arsenic conversion decreased with increasing solid-liquid ratio.The experimental results at different p H values?1.5,2,3,4?showed that the conversions of iron and arsenic increased with decreasing pH.But lower pH was unfavorable to the removal of SO₂.The SO₂ removal efficiency,trivalent arsenic concentration,iron and arsenic conversions increased with decreasing coal particle size?76?m-450?m?.For same amount of coal,as the coal particle size decreases,the total surface area of coal particles increases,which is beneficial to the surface reaction.The results of iron and arsenic conversions showed that the leaching process can be described by the reaction-controlled shrinking core model.At same reaction time,the arsenic conversion was larger than that of iron.The reason is that the leached iron is mainly from pyrite,whereas the acid-leachable arsenic includes the pyrite-associated arsenic and the exchangeable arsenic,etc.