Immobilization Of Cd In River Sediment By Two Kinds Of Typical Nanomaterials

The content of heavy metals in the sediments of our river system is generally close to the threshold of ecological risk,especially the content of heavy metals of cadmium(Cd)with high toxicity is generally high.Nanomaterials have good adsorption or fixation properties for heavy metals in sediment or soil because of their specific surface area effect,small size effect,high reactive activity and so on.Therefore,two typical nanomaterials(nano hydroxyapatite(nHAP)and nano zero valent iron(nZVI)were selected to repair heavy metals Cd in sediment.At the same time,in order to improve the restorative effects of Cd and reduce the negative impact of material on the sediment environment,biological carbon(BC)and sodium alginate(SA)were used to modify nano hydroxyapatite(nHAP)and nano zero valent iron(nZVI).The researches are as follows:Scanning electron microscopy(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectrometer(EDS)were used to observe the apparent morphology,particle size and surface phase composition of the material.The results showed that nZVI exhibited chain stripe,and its particle size was about 50~80 nm,and the outer surface of nZVI had a layer of oxide shell with thickness of 3~4 nm.SA/nZVI particles dispersed uniformly and showed spherical shape with a particle size ranging from 100~120 nm,which was mainly due to the coating of SA.No iron oxide peaks were observed in XRD images,indicating that SA/nZVI was not oxidized.There were many white particles on the surface of BC/nHAP compared with the SEM image of BC.From the EDS image,it could be concluded that these white particles were hydroxyapatite.The results of XRD showed that the nano hydroxyapatite was not only dispersed on the surfac e of the biological carbon,but also partly dispersed in the pores of the biological carbon,so the peak value of the corresponding characteristic peaks was reduced.Therefore,SA modified nZVI and BC modified nHAP were successfully prepared in this experi ment.Stability research of heavy metals of Cd in sediment by biochar modified nano hydroxyapatite(BC/nHAP).After 30 days of remediation,the conversion rate of residual in BC,HAP and BC/nHAP treated sediment samples was 36.1%,40.2% and 62.0%,respectively.The conversion rate of residual of Cd in BC/nHAP treatment group was the highest,indicating that the material had the best effect on Cd immobilization.At the same time,TCLP toxicity leaching experiment indicated that the content of leachable state of Cd was the lowest in BC/nHAP group with the value of 0 mg/kg.The changes of pH and CEC were closely related to the repair mechanism of Cd.The content of available phosphorus in BC/nHAP treatment group was the lowest.It may be that biological carbon acts as an adsorbent and adsorbs phosphate released from the phosphate material,which greatly reduces the risk of secondary pollution.Stability research of heavy metals of Cd in sediment by sodium alginate modified nano zero valent iron(SA/nZVI).SA/nZVI with different concentrations had better stability for Cd compared with nZVI.The 0.1 wt% SA/nZVI had the best effect on the remediation of Cd.After 30 days of remediation,the maximum residual fraction of Cd increased by 41.79% compared with the sediment samples without any reagents.The stability mechanism of Cd by SA/nZVI was mainly adsorption and chelation.The activity of urease and catalase in sediment samples showed an increasing trend.The activity of urease and catalase increased by 4.75 and 1.7 7 times in 0.10% SA/nZVI treated sediment samples,respectively.The increase of enzyme activity may be because the addition of nanomaterials increases the residue content of Cd in the sediment,and increases its stability and reduces its bioavailability.Compared with the control group,nanoscale iron material changed the structure of the bacterial community in the sediment,and the modified nZVI significantly improved the diversity of the bacteria community in the sediment.