Treatment Of Pinus Massoniana Lamb Bark With Low Temperature Plasma And Its Adsorption Of Heavy Metals

Heavy metals are non-biodegradable and accumulated in living organisms through the food chain which can cause various diseases.At present,there is no separate process for the removal of heavy metals in water in domestic wastewater treatment plants,which has low efficiency,low efficiency and is more passive.Pinus massoniana Lamb is the main timber species in Fujian Province,a large number of bark are left unutilized every year,which not only waste natural plant resources,but also cause a burden to the environment.In this thesis,the bark of Pinus massoniana Lamb was modified by low temperature plasma with oxygen as the treatment gas.The adsorption experiment of heavy metal ions(copper and zinc)were carried out to expl-ore the better adsorption parameters of bark powder before and after modification.The result shows that:(1)the morphology of bark powder of Pinus massoniana Lamb bark with different diameters was slightly different under the macro condition.The bark powder which its particle size range from 100 to 120 mesh appeared agglomeration phenomenon in water,and 120 mesh bark powder appeared fragments that some bark cells were destroyed.The bark of Pinus massoniana Lamb was mainly composed of bone stone cells,sieve cells,cork cells,phloem parenchyma cells,phloem ray parenchyma cells and phloem fiber cells.the density of bark powder is so smaller than that of water that it is easy to float on the water.Among its chemical components,lignin content is the largest(36.70%)and tannin content is 6.08%.The content of organic solvent in bark powder is less than that in bark powder,and the higher the extraction content,the lower the physical adsorption at room temperature.(2)The optimal treatment parameters for bark powder treated by low temperature plasma are as follows:treatment power 100W,pressure 40 Pa,time 87 s.Respectively,the predicted adsorption capacity of modified bark powder for copper ion is 71.62 mg·g-1 and zinc ion is 40.30 mg·g-1.The adsorption capacity of modified bark powder for copper ion was 71.44 mg·g-1 and 40.12 mg·g-1 for zinc ion,which was close to the predicted value,that means the plasma treatment parameters were available.The optimal adsorption time for heavy metal ions was 300 min,the optimal adsorption pH for copper ion was 5 while for zinc ion was 6.Through the kinetic equation,the pseudo-second-order kinetic equation and Langmuir isotherm adsorption model could accurately describe the adsorption of bark powder.The whole process of heavy metal adsorption is mainly chemisorption and endothermic reaction.(3)By optimizing the response surface,the model of the adsorption parameters of heavy metal ions before and after bark powder modification was obtained,and the correlation coefficients of the fitting model for the adsorption of both copper ion and zinc ion were all greater than 90%.Under the conditions of the better adsorption parameters obtained by simulation,the verification experiments were carried out.The adsorption capacity of heavy metals was 45.32 mg·g-1 for copper ion and 23.31 mg·g-1 for zinc before modification while it was 105.11 mg·g-1 for copper ion and 69.30 mg·g-1 for zinc after modification,which indicated that the model could describe the adsorption effect among the bark powder particle size,initial concentration of metal ions and bark powder concentration.The surface of bark powder may be etched by oxygen low temperature plasma after modification,the macroscopic morphology of bark powder changed little,only when the magnification of outside surface was 4.5,which was observed that the surface shadow of modified bark powder increased slightly.The chemical components of bark powder were basically the same before and after moditication.After the adsorption of heavy metal ions,the content of tannin and lignin decreased obviously,which indicated that tannin and lignin could be chelated with copper and zinc to adsorb them.The adsorption effect of bark powder was enhanced after treatment by low temperature plasma.Compared with the FTIR of bark powder,it was found that hydroxyl,phenolic hydroxyl and carboxyl groups were the main active groups.Copper ion was mainly adsorbed by phenolic hydroxyl groups while zinc ion was by carboxyl groups.It can be concluded that the tannins contained in bark powder of Pinus massoniana Lamb belong to condensation type which can chelate with copper and zinc ion to form stable chelates.At the same time,these heavy metal ions were reduced from high valence state to low valence state.The specific surface area of bark powder is slightly increased agter modifition,that is,the etching effect produced by low temperature plasma exists only in some areas.The oxygen content of modified bark powder was significantly higher than it's unmodifition.After adsorption of copper ion,the oxygen and hydrogen content of the modified bark powder was decreased,while the carbon and hydrogen elements was decreased after the adsorption of zinc ion.The surface area of the modified bark powder is slightly higher than it's unmodifition.The changes in element content and specific surface area are consistent with the results of it's FTIR.In mixed heavy metal solution,copper and zinc ion were competitive with each other about the adsorption activity sites,that caused the adsorbion of both heavy metal ions by bark powder being decreased.The desorption rate of bark powder on copper ion was more serious than that on zinc.The desorption rate of bark powder to heavy metal ions was more than 87%,that is,the desorption effect was better.The resolution rate of modified bark powder was slightly better than that of unmodified bark powder.