Mercury Removal From Aqueous Solution Using Sulfuretted Limonite:Capacity And Mechanism

In this paper,limonite and pyrite collected from Xinqiao deposited in Tongling,Anhui province were mixed-calcined under N₂ atmosphere to prepared limonite-pyrrhotite（L-Pyr）as sulfide limonite.The structural transformation of L-Pyr after calcination was analyzed by a series of characterization methods as XRD,XRF,TG-DTA,BET and SEM.The effects of different experimental conditions on Hg（Ⅱ）removal by L-Pyr were investigated through a series of batch experiments,and the removal capacity and mechanism of L-Pyr after the experiment were characterized by XRD,TEM and XPS.Three dynamic columns were prepared to compared the continuous mercury removal effect of L-Pyr,Modified Pyrite（MPy）and natural Pyrite（Py）,and to investigated the continuous Hg（Ⅱ）removal capacity of L-Pyr.The experimental results as follows:（1）Under the reaction temperature of 550℃and reaction time of 4 hours in a nitrogen atmosphere,limonite could be completely transformed into nanometer-sized pyrrhotite with extremely increased specific surface area.The mass ratio of limonite and pyrite was1:5.（2）Batch experiment results indicated that L-Pyr was an extremely effective material in Hg（Ⅱ）removal.Under the experimental conditions of p H 6 and temperature 308 K,the adsorption process of L-Pyr to mercury in water was consisted with the Langmuir isothermal adsorption model（R²>0.998）,and the maximum adsorption capacity was up to 210.36 mg/g.The Hg（Ⅱ）removal capacity of L-Pyr increased under higher temperature（288～308 K）,higher p H（2～6）,and longer reaction time（10～1440 min）within a certain scope.The highest adsorption efficiency of L-Pyr was 0.4 g/L.The promoted the reaction.The pseudo second-order rate equation fitted the experimental data well（R²>0.998）,and the adsorption fundamental of L-Pyr was chemical adsorption.The thermodynamic data showed that the adsorption process of L-Pyr was a spontaneous endothermic reaction,which was mainly driven by adsorption entropy.Chemical precipitation was the main reaction form in the adsorption process,and Hg S was the main fixed form of mercury in the adsorbent.（3）The characterization analysis showed that the adsorption process of Hg（Ⅱ）in the solution mainly involved chemical precipitation,surface complexation and ion exchange reactions.The fixed mercury mainly existed in the form of Hg S and mercury complex.The main mechanism of Hg（Ⅱ）removal by L-Pyr and MPy were the adsorption and chemical precipitation between the adsorbent and Hg（Ⅱ）.It could be seen from analysis that L-Pyr had an extremely strong adsorption activity and a large processing capacity.（4）The column experiment showed that L-Pyr were an effective sorbent for continuous Hg（Ⅱ）removal.The effluent Hg（Ⅱ）concentration was lower than the integrated wastewater discharge standard of China（0.05 mg/L）,and the removal rate was higher than 99.8%before breakthrough.The input capacity was 185.5 L when the column breakthrough and the sorption amount of L-Pyr were 122.75 mg/g.The Hg（Ⅱ）content in the used L-Pyr sorbent was up to 40%.