The Efficiency And Mechanism About The Removal Of Cr(?) And Sb(?) In E-waste Pickling Wastewater By Modified Magnetic Nanoscale Iron-based Materials

In recent year,with the development of electronic industry,the replacement of the electronic products is of a rapid speed,which leads to a significant accumulation of Waste Electrical and Electronic Equipment?WEEE?.In some traditional e-waste recycling sites?Like Qingyuan and Guiyu?,because of the traditional undeveloped pickling process for the treatment of e-waste,a large amount of pickling waste water was discharged to the environment.These pickling waste water are contaminated by various heavy metals and it thus caused serious heavy metal pollution.Chromium?Cr?and antimony?Sb?are two typical heavy metals in pickling waste water.Magnetic nanomaterials,as a new class of sorbent,have great potentials in the field of environmental protection.But magnetic nanomaterials still have some technological inadequacy.For example,high surface energy will let it easily reunite.The narrow range of working pH,the precipitation of metal hydroxides will caused limited efficacy during the treatment.To improve the adsorption efficiency of magnetic nanoscale magnetic iron-based materials,nanoscale zero-valent iron?nZVI?and magnetite nanoparticles?Fe₃O₄?are chosen for the removal of Cd and Sb in the waste water.In this work,the carboxymethyl cellulose?CMC?and humic acid?HA?were selected to modify nanoscale zero-valent iron?nZVI?and magnetite nanoparticles?Fe₃O₄?,respectivley.The investigation on the metals removal was carried out with various parameters with respect to the initial pH of the aqueous solution,the initial concentration of Cr???and Sb???,magnetic nanomaterials dosage,reaction time and temperature.The experimental results were summarized as follows:?1?pH value of the aqueous solution has significant impacts on the removal of Cr???and Sb???by magnetic nanomaterials.When the pH is 3,the removal efficiency of Cr???and Sb???reach the maximum value.The removal efficiency deceresed with pH increased.After adding CMC,the range of nZVI's working pH become wider,while the range of Fe₃O₄'s working pH become narrow after adding HA.?2?With the increase of initial concentration of Cr???and Sb???,the removal efficiency of Cr???and Sb???decreased in general.But at low initial concentrations,the removal efficiency was promoted with the increase of the initial concentration.The CMC modified nZVI can keep high removal efficiency at high initial concentrations of Cr???and Sb???.However,the removal efficiency of HA-Fe₃O₄ decreased at the identical initial concentration.?3?.The improvement of the dosage of magnetic nanomaterials can observably increase the removal efficiency of Cr???and Sb???.The increase of removal efficiency was insignificant when the dosage of magnetic nanomaterials increased to a certain degree.CMC-nZVI can enhance the removal efficiency of Sb???but have little effect on the removal of Cr???.Comparing with the system using Fe₃O₄ as sorbent,the removal efficiency of HA-Fe₃O₄decreased with the same dosage of sorbent.?4?.The removal of Cr???and Sb???by nZVI is a rapid reaction,which can get equilibrium in 30 min,while the Fe₃O₄ reaches the equilibrium within 3 h.The removal of Cr???and Sb???by nZVI and Fe₃O₄ could be expressed by pseudo second stage reaction kinetics.CMC-nZVI can increase the reaction rate of Cr???and Sb???,which can get equilibrium in 5 min.The removal rate and removal efficiency of Fe₃O₄ will significantly decrease after adding HA.?5?.The removal efficiency of Cr???and Sb???increased with the increasing of reaction temperature.When the reaction temperature is becoming high,the effect of the removal efficiency is insignificant.Under the same temperature,the removal efficiency of CMC-nZVI is higher than that of HA-Fe₃O₄.Based on the results,the mechanism of removing Cr???and Sb???by nZVI and Fe₃O₄consist of chemical reduction and flocculation,both CMC and HA have an effect on magnetic nanoscale ferrous materials.After modified by CMC,CMC-nZVI become stabler in aqueous solution and it can remove Cr???and Sb???more effectively.On the contrary,the removal efficiency of HA-Fe₃O₄ is inhibited after it modified by HA.