Preparation And Application Research Of Magnetic Ceramic Particles And Modified Clay In Remediation Of Heavy Metal Contaminated Groundwater

In recent years,with the rapid development of in-situ remediation technology,Permeable Reactive Barrier（PRB）has become one of the most widely used in-situ remediation technologies.The effectiveness of PRB depends on the fill material that reacts with the pollutants.Therefore,it is necessary to develop new cost-effective materials to remediate heavy metal-contaminated groundwater.In this study,printing and dyeing sludge（PADS）was used as an additive and magnetic clay prepared by co-precipitation was used as the raw material to successfully prepare magnetic ceramsite.FeS and nano zero-valent iron（NZVI）modified clay materials were also prepared.Through static batch experiments on various factors,such as material preparation conditions,dosage,p H,and contact time,the removal of Cu（Ⅱ）and Cr（Ⅵ）by magnetic ceramsite and modified clay was systematically studied.The physical properties of the materials were characterized using BET,SEM,EDS,XRD,and VSM.The removal mechanisms were studied by fitting the data to kinetic and isothermal curves.Furthermore,PRB simulation experiments were conducted to further investigate the removal effect of mixed filter media A600-3-20 and FeS-B on copper ion（Cu（Ⅱ））and hexavalent chromium（Cr（Ⅵ））in simulated groundwater.The preparation of magnetic ceramsite and removal experiments of Cu（II）and Cr（VI）showed that the optimal preparation conditions for magnetic ceramsite were temperature=600℃,magnetic attapulgite:magnetic bentonite=3:1,PADS=40%,and iron content=20%.Characterization analysis showed that Fe₃O₄ particles were successfully loaded onto the surface of the ceramsite.The magnetic saturation intensity of A600-3-20 was 26.83 emu/g,which facilitated solid-liquid separation by magnetic selection.The removal rate of Cu（II）from 40 mg/L solution by A600-3-20 reached 90%-98%under the adsorption conditions with the dosage of A600-3-20=15 g/L,solution p H=6,and contact time=120 min.The adsorption kinetics and isotherm followed a pseudo-second-order kinetic model and Langmuir isotherm model,with a maximum adsorption capacity of 2.27 mg/g.The adsorption mechanism mainly involved chemical adsorption,including ion exchange and surface complexation.A600-3-20 had a good removal effect on Cu（II）,while the removal rate of 40 mg/L Cr（VI）was only 36.7%.Preparation and remediation of Cr（VI）by FeS-clay and NZVI-clay were conducted and the test results showed that the modified clay materials prepared by liquid-phase precipitation/reduction method with clay:FeS=2:1 and clay:Fe=1:1 had the best removal effect for Cr（VI）.Characterization results indicated that FeS and NZVI were successfully loaded onto the surface of attapulgite（ATP）and bentonite（NB）,respectively,which still had magnetic separation ability.The removal rate of Cr（VI）from 50 mg/L solution by modified clays reached 93%-99%under the conditions with the dosage of modified clays=4g/L,solution p H=6,and contact time=120 min.The removal of Cr（VI）conformed to the pseudo-second-order kinetic model and Freundlich isotherm model,and the possible mechanisms were chemical adsorption and reduction.PRB simulation experiments showed that the permeability coefficient of the mixed filter material A600-3-20 and FeS-B was 3.93×10^-4 cm/s.The breakthrough point of 70mg/L of Cr（VI）was around 84 h.After running for 312 h,the cumulative removal amount of Cr（VI）was 932.5 mg,with a removal rate of 59%.Under the same conditions,the removal rate of 25 mg/L of Cu（II）by PRB simulation columns was 100%.The influent flow rate had a significant effect on the removal of Cr（VI）,with a larger flow rate leading to smaller cumulative removal amounts.The removal mechanism of the mixed filter material for Cr（VI）included chemical adsorption and reduction,while the removal mechanism for Cu（II）was chemical adsorption.Although the removal effect of Cr（VI）was poor,the magnetic ceramsite particle had no risk of heavy metal leaching and a good reusability.It was an environmentally friendly and low-cost adsorbent for removing Cu（II）from water.The modified clay material FeS-B had a good removal effect on Cr（VI）,but was susceptible to oxidation.During the use of the mixed filter material A600-3-20 and FeS-B,the leaching rate of Fe was low,which met the relevant standards.