Post Remediation Treatment Of Assenic Hyperaccumulator Plant Pteris Vittata L. And The Resourceful Utilization

The disposal techniques,extraction and incineration technologies,of arsenic hyperaccumulator Pteris vittata L.were studied in order to investigate the feasibility of these technologies on disposal of the arsenic-containing hyperaccumulator Pteris vittata L.plants that were harvested from arsenic-contaminated land,which provides insight into developing harmless disposal or resource-reuse-oriented methods for disposal of the plants used for large-scale phytoremediation application.The Pteris vittata L.plant grown in artificial wetland systems specially designed for adsorbing the arsenic in the highly contaminated soil and wastewater,which contains high arsenic concentration,was harvested and used to carry on disposal research.The harvested plants were washed by water clean then by deionized water, disinfected in oven for 10 minutes at 115℃,then at 70℃for 24h,dried to constant weight,ground into powder and kept in the desiccator for later use.The muffle experiment investigates the variation of arsenic concentration in the ash of fresh Pteris vittata L.and in the ash of oven-dried Pteris vittata L.during incineration.The arsenic concentration in the ash of fresh plants were lower than that in the 70℃-oven-dried Pteris vittata L.ash,which means oven-dry disposal process decreased the arsenic loss in the ash,however,the difference was not marketable. Also,there was little difference between arsenic concentration in the ash of the plant digested by direct microwave digestion of fresh Pteris vittata L.and that in the ash of plant digested after 24 hours oven-dry.The affect of oven-dry seemed little.And the disposed plants were applied to the later incineration experiment.In the extraction experiment,the effect of extraction condition including time, temperature and extraction liquid etc.on extraction were examined.The different extraction media including water and H₂SO₄(0.5 mol/L and 1.0 mol/L)and different temperature at 30℃,40℃,50℃set to extract arsenic from the arsenic-containing Pteris vittata L.plants for 1hour and 3 hours were stueied.The H₂SO₄ extraction had high extraction concentration which was above 8mg/L,the arsenic concentration were from 8.01mg/L～8.69mg/L.The water had very high arsenic recovery rate of 91.0% ～99.8%.The arsenic concentration in the extraction residue were getting lower and lower when extraction time and temperature increased.Acid extraction had better extraction efficiency,and extracted more arsenic compounds than water.The minitype furnace was used to burn Pteris vittata L.plant materials aiming at testing the behavior of arsenic emission during incineration.Incineration experiments were conducted under the oxygen flux of 0.12 L per minute,and at the temperature of 550℃,650℃,750℃,850℃and 950℃respectively.At the mean time,CaO,K₂HPO₄ and Fe₂(SO₄)₃ were added to control arsenic in the incineration flue gas and in the residual ash.Results showed the mass percentage of arsenic in the residual ash were 13.7%～17.5%with no additives,and 12%～20%when additives were added.It seemed that adding CaO increased the arsenic in the residual ash, while adding iron salt reduced arsenic in the residual ash.At the temperature of 550℃～950℃,arsenic losing rates in the flue gas increased when temperature goes up.At the temperature about arsenic melting point of 814℃,the arsenic vaporized easily,which resulted in the decrease of arsenic recovery rate.When incineration time were15 mins and 30 mins,the correlation coefficient of the arsenic recovery rate of residual ash and temperature were pretty well.Adding CaO had a distinct increase to the arsenic recovery rate in the residual ash,which was about 5%～20% increase of arsenic at different incineration temperature.However,the arsenic losing rates in the flue gas decreased no more than 2%.This could be explained as a result of arsenic fixation by CaO.Further more,adding K₂HPO₄ and Fe₂(SO₄)₃ decreased the arsenic recovery rate,while adding K₂HPO₄ increased arsenic emissions into incineration flue gas.This phenomenon was similar to adding lime in the coal to fix the sulfur.