Removal Of Cu(Ⅱ) And Cr(Ⅵ) Using Nanoscale Zero-valent Iron Supported On Different Material

With the development of industry and agriculture,heavy metal pollution leads to serious problems in water.Nowadays,wastewater treatments is a hot issue.It is a very popular by using Nanoscale zero-valent iron to purify heavy metal.Nanoscale zero-valent iron was widely used in treatment of heavy metal,nitrate and chlorine organic pollutants because of its advantages of larger specific surface area,strong reactivity.Meanwhile,the performance of nanoscale zero-valent iron using in removal contaminants is hard to increase because of its instability in air and spontaneous combustion and easy agglomeration in water.Aiming to solve these problems mentioned above and to improve the reactivity and lifetime of nanoscale zero-valent iron,we prepared a variety of loaded type nanoscale zero-valent iron system and applied to remove Cu（Ⅱ）,Cr（Ⅵ）in aqueous.We have explored removal mechanism and main affected factors in systems.Finally,we applied nanoscale zero-valent iron to constructed wetlands and probed into its feasibility in practical application.The main conclusions of these paper are as follows:（1）Inorganic mineral materials were with porous structure,and nanoscale zero-valent iron can be supported on the surface or interior space.After this process,the stability of the nanoscale zerovalent iron was improved.In this paper,nanoscale zero-valent iron was supported on four kinds of inorganic minerals（sepiolite-nZVI,Na-montmorillonite-nZVI,Ca-montmorillonite-nZVI and zeolite-nZVI）,which used for removing Cu（Ⅱ）and Cr（Ⅵ）.The results indicated that: 4:1 of minorganic mineral: mFe²⁺ was the optimal ratio in Cu（Ⅱ）and Cr（Ⅵ）removal.And Cu（Ⅱ）removal of four kinds of inorganic mineral-nZVI in the order was Na-montmorillonite-nZVI（98.26%）≈ sepiolite-nZVI（98.17%）> Ca-montmorillonite-nZVI（69.85%）> zeolite-nZVI（63.11%）,the removal rate of Cr（Ⅵ）in the order was Na-montmorillonite-nZVI（98.76%）> zeolite-n ZVI（95.68%）> sepiolite-nZVI（88.55%）> Ca-montmorillonite-nZVI（82.27%）.After 15 days experiments by using nanoscale zero-valent iron and fresh nanoscale zero-valent iron in air,we found that: sepiolite-nZVI and Na-montmorillonite-nZVI had good stability,and the stability of Ca-montmorillonite-nZVI and zeolite-nZVI particles was worse.The removal rate of Cu（Ⅱ）fell by 7.92% and 7.93%,respectively.The removal rate of Cr（Ⅵ）fell by 9.59% and 35.16%,respectively.Na-montmorillonite-nZVI had better performance in Cu（Ⅱ）and Cr（Ⅵ）removal.（2）We investigated the effects of pH value,initial heavy metal ions concentration and Namontmorillonite-nZVI（Mt-nZVI）dosage on the removal of Cu（Ⅱ）,Cr（Ⅵ）in systems.We found that better removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）was shown by using Mt-nZVI comparing to that by using ordinary n ZVI.Significant impact was found by using different initial pH value,initial heavy metal ions concentration and Mt-nZVI dosage on the Cu（Ⅱ）,Cr（Ⅵ）removal efficiency.The removal efficiency of Cu（Ⅱ）increased with the rising of pH,while the removal rate of Cr（Ⅵ）increased with the decreased of pH.The removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）increased with the decreased of initial concentration,while the removal rate of Cu（Ⅱ）and Cr（Ⅵ）increased with the rising of Mt-nZVI dosage.The adsorption kinetics experiments were carried out as well,the adsorption conformed to the pseudo-second-order equation with a good correlation.The adsorption process was better described by the Langmuir model.The maximum adsorption capacity of Cu（Ⅱ）was 133.51 mg/g,and the maximum adsorption capacity of Cr（Ⅵ）was 24.09 mg/g.（3）The embedding method could put Mt-nZVI particles into sodium alginate（SA）beads.Using SA beads was not only improved the quality of water and eased the burden of separation,but also alleviated fears about potential risk of nano material.With the increasing mass transfer resistance,the removal rate of Cu（Ⅱ）and Cr（Ⅵ）by SA/Mt-nZVI beads definitely decreased,and the removal time last to 24 h.The results indicated that: 2.0 wt% SA with 6.0 wt% Mt-nZVI was the optimal ratio in Cu（Ⅱ）and Cr（Ⅵ）removal in treatments.The removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）were 92.11% and 89.49%,respectively by SA/Mt-nZVI at 24 hours.Compared to the removal efficiency by using Mt-nZVI,it was not significantly decreased.In addition,the removal efficiency of Cu（Ⅱ）increased with the rising of pH,while the removal efficiency of Cr（Ⅵ）decreased with the rising of pH.Besides,the removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）decreased with the rising of initial concentration.The adsorption kinetics experiments were carried out as well,the adsorption conformed to the pseudo-second-order equation with a good correlation.And the adsorption process was better described by the Langmuir model.The maximum adsorption capacity of Cu（Ⅱ）was 63.90 mg/g,and the maximum adsorption capacity of Cr（Ⅵ）was 17.25 mg/g.The removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）was kept at 59.52%,96.82% after treatments in triplicates.Overall,SA/Mt-nZVI was efficient in Cu（Ⅱ）and Cr（Ⅵ）removal for wastewater treatment.（4）The SA/Mt-nZVI beads was put into constructed wetlands（CWs）for exploring the feasibility of its application.The results showed that,SA/Mt-nZVI beads were more suitable for CWs usage compared to that of Mt-nZVI particles.The results indicated that external SA/MtnZVI beads remarkably improved the reduction of Cu（Ⅱ）and Cr（Ⅵ）in CWs.With the increasing dosage of SA/Mt-nZVI beads in CWs,the removal efficiencies of Cu（Ⅱ）and Cr（Ⅵ）presented a rising trend and the concentration of Fe²⁺ and total iron both had a positively linear correlation with the dosage of SA/Mt-nZVI beads.The removal efficiency of Cu（Ⅱ）and Cr（Ⅵ）was 95.11% and 64.57% after treatments in twice in CWs.The removal of contaminants was higher than that in CWs without SA/Mt-nZVI beads.In a word,SA/Mt-nZVI beads used for purifying wastewater in CWs had feasibility and workable.