| Incineration technology has become an important mean to deal with solid waste in the world.Large amounts of PVC and NaCl in the waste make chlorides become one of the most important forms of heavy metals in the incineration gas.Improving the high temperature adsorption of heavy metal chloride needs to be focused on.So,the adsorption laws and mechanisms between heavy metal chlorides and non-carbon adsorbents is explored.The adsorption efficiency and leaching ability of natural kaolin,zeolite,calcium oxide and silica are investigated and the best adsorbents is selected.Meanwhile,the adsorption ability of the best adsorbent for other heavy metal chlorides(Cu,Zn and Cd)are studied.The results show that adsorption capacity of adsorbents to lead chloride(900?,O2)in turn is: natural kaolin > calcium oxide > zeolite > silica.Pore structure,specific surface area and chemical composition of adsorbents are important factors for adsorption.Water significantly increases the adsorption capacity of kaolin,but has little effects on the adsorption of the other three sorbents.The leaching ability of natural kaolin is small,but adsorption efficiency is high,so kaolin is an excellent adsorbent.At 600?~900?,for natural kaolin,the adsorption efficiency of lead is the highest,followed by cadmium,copper and zinc.For the four chlorides,the leachable part occupy a very small proportion.Based on the above study,the effects of H2 O,O2 and temperature on the adsorption law and eutectic melting mechanism between natural kaolin and lead are studied by using the two stage vertical tube furnace.Thermodynamic equilibrium calculation is carried out to guide theoretical analysis.The results shows that H2 O promotes the adsorption;O2 promotes adsorption at high temperature(> 800 ?).In any atmosphere,the form of lead in natural kaolin is mainly unleachable,and the leaching rate decreases with the increase of temperature.The main adsorption products between natural kaolin and lead chloride are lead aluminosilicate.The phase and crystal type of adsorption products are related to atmosphere and temperature.The crystallinity of the adsorbed products at 900? is stronger than that at 600?.Three kinds of forms of the surface morphology of natural kaolin after adsorption are found,there are lamellar,semi-melting and melting.The melting mechanism is closely related to H2 O and temperature.The effect of moisture on the adsorption capacity of natural kaolin can be explained as the following reasons:(1)Moisture can participate in the adsorption reaction and provide the oxygen atoms which needed for the reaction.(2)Moisture promotes the eutectic melting of kaolin surface,and proper melting is beneficial for adsorption.Finally,the effects of hydroxyl group,H2 O and temperature on the adsorption of PbCl2 on kaolin are studied.The results show that moisture and high temperature can promote the adsorption of metakaolin,and the lead mainly exists in the form of unleachability,and the leaching rate decreases with the increase of temperature.Four kinds of lead aluminosilicate are formed in the reaction of metakaolin and PbCl2,and the crystallinity of the products enhances with the increase of temperature.Metakaolin may reacts directly with PbCl2 and H2 O to form PbO·Al2O3·2SiO2,or PbCl2 turn to PbO first,and then PbO reacts with metakaolinite.The melting mechanism of metakaolin is similar to natural kaolin,but there is a special phenomenon in the melting process of the metakaolin.The effects of hydroxyl group and moisture on the adsorption are as follows: Co-operation of hydroxy and moisture > hydroxy > moisture> neither hydroxy nor moisture.The optimum conditions for PbCl2 adsorption is choosing natural kaolin,adding moisture and keeping the temperature at 700?. |
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