Remediation Of Cr(?) Contaminated Soil Using Long-duration Agent Supported By Micro-nano Networks

In recent years,the heavy metal pollution of soil is becoming more serious and has already become one of the very acute world environmental problems.The heavy metal pollution of soil causes the reduction of crops,threatening the sustainable development of agriculture.More importantly,Heavy metals accumulate through the food chain in crops could be ingested by human beings,endangering human healthy.In this work,Cr(VI)(actually the K2Cr2O7)was chosen as the representative heavy metal because Cr(VI)is one of the extremely toxic heavy metals in soil mainly attributed to the discharge of chromiumcontaining waste from ore refining,steel and alloys production,metal plating,tannery,pigmentation and so on.Cr(VI)and Cr(III)were two of the most stable states of chromium in soil,wherein Cr(VI)displayed higher toxicity,carcinogenicity,solubility and mobility,compared with Cr(III).Hence,the reduction of Cr(VI)to Cr(III)is critical for the remediation of Cr(VI)contaminated soil(CCS).Sodium thiosulfate(ST)a typical reductant with desirable reductive capacity,could be used to treat Cr(VI).However,because of the good solubility,ST tends to be lost with water,which will lead to a lower utilization efficiency.Herein,attapulgite(ATP)modified by high-energy electron beam(HEEB)irradiation was used as a matrix to support ST and reduce the loss of ST with water.The results are as follows:1.ATP displayed the most highest adsorption performance on Cr(VI)compared with other clays.HEEB irradiation could effectively enhance the adsorption performance of natural attapulgite(NA)on Cr(VI).2.ST was mixed with HA10 to obtain a HA10-ST composite which possessed both adsorption and reduction abilities on Cr(VI).The highest removal efficiency of HA10-ST was designated as the LRA by leaching experiment.The results show that the RE of the HA10 was only 42.0%,while the RE of LRA was 99.4%.3.The leaching loss ratio of ST 69.6% in sand,however the leaching loss ratio of ST from LRA was only 23.7%.This result indicated that HA10 played a key role in prolonging the duration and thus improving the utilization efficiency of ST.4.The result of scanning electron microscope(SEM)indicates that NA tends to aggregate and form compact bunches consisting of plenty of nano rods.After HEEB irradiation,the originally compact NA bunches became obviously loose and transformed to nano-networks.FTIR measurements displaying that HA10 successfully bound ST,but noobvious chemical reactions occurred in the fabrication process of LRA,and the main interaction between HA10 and ST was a physical process.The characterization results of XRD illustrating that ST did not intercalate the crystal layers of HA10.That was to say,ST was probably adsorbed in the micro/nano pores and nano channels of HA10.5.Pot experiments demonstrate that LRA could effectively increase the heights of corns in CCS,decrease the areas and dry weight ratios of yellow leaves,and this phenomenon became more obvious with the increasing LRA amount in a range.