Study On Ferrite Technology In Heavy Metal Treatment At Ambient Temperature

Heavy metal pollution is becoming an increasingly serious problem,which seriously affects food safety and human health.Therefore,it is urgent to explore the efficient,economical and environmentally friendly technologies for heavy metals wastewater treatment.Alkali precipitation was widely used because of its low cost and simple operation.However,the precipitation after treatment has some shortages such as large volume,high moisture content,lower dewatering performance and property instability.Ferrite overcome the disadvantage of alkali precipitation and become the hot research topic of heavy metal treatment all over the world.Nevertheless,the chelated metal in wastewater has the disadvantage of high solubility and strong stability,which is the bottleneck of the wastewater treatment.The effluent can not satisfy relevant standard by using single ferrite process.The temperature of conventional ferrite process must be higher than 65℃.The cost was increased and its application was limited.Therefore,it is necessary to exploit a ferrite process to treat wastewater containing chelated metal at room temperature.In view of this,in this study,ferrite process coupled with advanced oxidation process was used to treat the wastewater containing chelated metals.The mechanism of transformation from green rust to ferrite is discussed,and a ferrite process under room temperature is constructed.Ferrite process coupled with Fenton oxidation method and Fe-carbon micro-electrolysis method to realize the efficient removal of wastewater containing chelated metal and the recycling of ferrite sludge.Finally,the research was extended to the stabilization of heavy metals in soil,and the application of ferrite process in heavy metal contaminated soil was preliminarily discussed at room temperature.It extend the application of ferrite process at room temperature.It has a good practical significance and scientific research value.Therefore,the main research results of this paper were:（1）Green rust sulfate as a sorbent was used to treat wastewater containing chelated copper.The pseudo-second order and Langmuir isotherm model were discussed.The transformation of green rust sulfate to ferrite was studied using response surface methodology（RSM）.The optimum reaction conditions of ferrite were discussed and the ferrite process at room temperature was constructed.The result shows that the pseudo-second order and Langmuir isotherm model can fit the data more accurately.It showed remarkable maximum adsorption capacity and maximum removal efficiency can reach up to 126.41 mg g^-1and 97.0%,respectively,when pH=8.0.The ferrite formation process was analyzed using RSM method.The optimum ferrite formation points of solution pH,stirring rate and contact time were 10,100 rpm and 2.38 h,respectively.The ferrite process at room temperature was constructed by using these reference datas.The formation of ferrite at room temperature was promoted through the aging of green rust,adding of seed and pH adjustment in the alkaline conditioning tank.The sedimentation velocity and volume of ferrite were 1.23 times faster and 2.20times lower than that of green rust,respectively,demonstrating the excellent settlement and densification of ferrite sludge.（2）The established ferrite process combined with Fenton oxidation（FO-RF）at room temperature was used to treat the wastewater containing chelated metal.The aims of this chapter were to:investigate the optimum reaction conditions and the efficiency of decomplexation in FO stage,obtain the optimal range of major operating parameters at ferrite process,observe the continuous operating condition using coupled process and analyse the compactness,settlement and stability of the final sludge.The optimum condition of Fenton reaction was that Fe²⁺and H₂O₂concentration were 450.0 mg L^-1and 1800.0 mg L^-1,respectively.At this time,the removal efficiency of TOC can reached up to 88.30%,implying a higher decomplexation efficiency.The optimum ranges of ferrite process at room temperature were:pH=10.0～11.2,X（the molar ratio of Ni/T-Fe）=0.05～0.075and sludge reflux ratio=0.17～0.25.The reactor is basically in a stable state after 10h in the optimum operating experiment.ORP remained around-750 mV vs.Ag/AgCl and the concentration of nickel in effluent was below 0.40 mg L^-1.Besides,the EDS and XRD tests result revealed that the structural formula of the resulting sludge can be expressed using Ni_0.064Fe_2.936O₄,implying that the nickel ions incorporated into the lattice of the ferrite.The TCLP（Toxicity Characteristic Leaching Procedure）results also showed the same conclusions.Finally,the real electroplating wastewater was used to verify the treatment efficiency of the coupling process and the stability of the final sludge,which proved the feasibility of the coupling process for the treatment of wastewater containing chelated metal.（3）In this study,a combined process of interior microelectrolysis-Fenton-recycle ferrite（IM-Fenton-RF）was developed to further discuss the course of chelated metal wastewater treatment.The optimum reaction conditions of microelectrolysis/Fenton and ferrite process were discussed.A new IM packing was prepared using ferrite sludge to finish the recycling of finally sludge.The research shows that Fe/C microelectrolytic packing can be prepared by calcining ferrite powder and coke powder at 800℃.IM-Fenton-RF system based on IM packing was used for the treatment of wastewater containing chelated metal.The optimal conditions for copper removal after decomplexation were Ferrite/C ratio=2,pH=2.5 and IM packing/water ratio（V/V）=5:6.The ferrous concentration in IM process can reach up to 856.1 mg L^-1.The efficiency of decomplexation was nearly 84.6%when IM process combined with Fenton method.RF process was analyzed using RSM method,and the optimum reaction conditions for copper removal were:reflux ratio of 0.37 and Fe²⁺concentration of 9.20 g/L at pH of 10.18 in mixing tank.The IM-Fenton-RF system basically stayed in an equilibrium state after 17 h.Under this conditions,the ORP leveled off-733 mV--794 mV vs Ag/AgCl.Meanwhile,the TCLP results were lower than the Identification Standards for Hazardous Wastes in China.The saturation magnetization through VSM analysis reached up to 59.79 emu g^-1,suggesting that the resulting sludge is a soft magnetic material.（4）Ferrite process was used for in-situ remediation of heavy metal contaminated soil.The optimal conditions for treating heavy metal contaminated soil by ferrite at room temperature was studied.The study shows that the optimum conditions were:Fe²⁺/Fe³（the molar ratio）=1/2,T-Fe/soil（m/m）=2.5,pH=9.0,water content=45%.Under this conditions,the leaching concentration of heavy metal was 1.85 mg L^-1 and the leaching rate was only 0.74%.The ferrite particles could be observed by TEM in the soil,and its particle size is nearly at 83.2 nm-162.7 nm.VSM was used to test the saturation magnetization of the stabilized soil at 27℃,and its value was 17.2 emu g^-1,which represented that the strength of magnetic was weak.Plant toxicity test showed that the length of stem,root and leaf of the lettuce after 28 days of growth in the stabilized soil were 0.95 cm,4.90 cm and 7.15 cm,respectively.The results were better than those of the control group.Therefore,the ferrite process has certain effect on soil heavy metal remediation.