Geochemical Characteristics,iron Dissolution And Biological Activity Of Iron Bearing Minerals In Particulate Matters From Xuanwei Coal Combustion

Air pollution usually means that the content of gas,solid particles and other pollutants in the air environment exceeds the standard value,which would harm the human body and other organisms.Many respiratory diseases have been proved to be directly related to air pollution.One of the most serious malignant diseases is lung cancer.Due to air pollution,Xuanwei has become one of the areas with the highest mortality rate of lung cancer in China.Researches show that the high incidence of lung cancer in Xuanwei is closely related to the air pollution caused by local life and coal production.And a large number of iron bearing mineral particles have been found in Xuanwei coal,such as chlorite and kaolinite,thought to play important roles in the pathogenesis of high incidence rate of lung cancer in this area.Some studies further point out that the changes of soluble iron in these particles between oxidation and reduction state produce potentially toxic free radical species,which could harm human health.This paper explores the acidolysis of iron-containing minerals in Xuanwei coal under different physical and chemical environments,including the acidolysis process of chlorite with different acidolysis time,p H value,temperature,solid-liquid ratio and particle size,as well as the dissolution of chlorite,illite,kaolinite and pyrite in different acidic environment and different acidity.On the basis of these studies,the life style of local residents is further simulated.Guangming,Lijiawu,Zhanyi raw coal and corresponding bottom ashes are collected by Anderson sampler.Also,different particle size of particulate matters from coal combustion,fine particles and ultrafine particles are collected to explore the dissolution rules,oxidation potential and biological activity of soluble iron.The physicochemical properties of coals,bottom ashes and particulate matters from coal combustion are characterized by SEM-EDS,TEM,BET,XRD,ICP-OES and XRF;the redox activity and biological activity are evaluated by DTT and MTT,respectively,and finally the health effects of particulate matters from coal combustion are discussed in detail through mice experiments.The main conclusions are as follows:(1)The iron rich minerals chlorite,illite and kaolinite in Xuanwei coal,as multi-layered clays,have presented multi-stage dissolution process under different acidic conditions.That is,the initial dissolution rate is fast,then followed by a continuous and slow increase of soluble iron concentration.Under the same conditions,the order of iron dissolution rate is pyrite>illite>chlorite>kaolinite,and higher temperature,lower solid-liquid ratio,smaller particle size can greatly promote the dissolution process of mineral iron.(2)For Guangming,lijiawu and Zhanyi raw coals,bottom ashes,particulate matters from coal combustion and iron rich minerals,because of high acid strength,high concentration of H⁺is easier to destroy the structure of minerals and release structural and interlayer irons.And the dissolution of Fe(II)in acid solution is easier than that of Fe(III).When the concentration of H⁺decreases,it is generally more favorable for the dissolution of Fe(II)in these iron bearing minerals(except for HNO₃).During the dissolution process,H₂SO₄has the strongest overall dissolution ability for each iron containing particle,followed by HCl and HNO₃.(3)The oxidation potential(DTT)analysis of acid soluble irons in iron rich minerals(chlorite,illite and kaolinite),raw coals,bottom ashes and particulate matters from coal combustion shows that the dissolved iron in acid solution has obvious oxidation potential,and with the increased concentration of dissolved irons,the oxidation potential of the samples also increased,besides,the increasing trend has a significant corresponding relationship with the concentration of soluble iron,especially corresponding to the change of Fe²⁺in solution.For raw coals,bottom ashes and particulate matters from coal combustion.In the same sample,the redox activity of dissolved irons in bottom ash is the highest,followed by that in raw coal,and that in particulate matters from coal combustion is the lowest.On the whole,Zhanyi sample shows the highest redox activity,followed by lijiawu and Guangming samples,and the oxidation potential is also consistent with the order of soluble iron concentration in acid solution under the same conditions.The oxidation potential of dissolved iron decreased after chelation with resin.However,the oxidation potential of the soluble irons increases with the increase of particle size,indicating that the oxidation potential is directly related to Fe²⁺.And the oxidation potential of the chelated sample is still bottom ash?raw coal?particulate matters from coal combustion.In fact,it is also the order of iron dissolving ability of samples.(4)The biological activity(MTT)analysis of acid soluble iron in raw coals,bottom ashes and particulate matters from coal combustion shows that the bottom ash with the strongest ability to dissolve iron under acidic conditions also showed the strongest cytotoxicity;the second is grade 5,grade 4 particle and raw coal;the cytotoxicity of coarse particles is the worst.After chelation,the toxicity of the chelated sample is significantly reduced,and the proportion of reduction is equivalent to that of Fe(II)solution.The experimental results show that the total composition of different raw coal,bottom ash and particulate matters from coal combustion is different and presenting that the smaller the particle size,the greater the toxicity.Moreover,the toxicity of sample particles themselves is much greater than that of water-soluble metal ions from the same particle sample.(5)Study on lung tumor induced by aerosol inhalation of ultrafine coal particles(grade 5)in mice(?1.1?m)showed that all of them can cause lung injury in mice.Particularly,the damage degree of the total components for particulate matters from coal combustion in Guangming,lijiawu and Zhanyi is the largest.Similarly,the effects of these fractions on Ig G,Ig E and the inflammatory factors of TNF-??IFN-??IL-4?IL-13 in lung homogenate of mice are also remarkable.Except for the whole components,water-soluble components(soluble Fe(II))can also cause lung injury in mice,and these pneumonic injuries are at risk of cancer.