| Cadmium pollution in soil has become one of the most serious environmental problems in the world.Cadmium in soil is easy to be enriched by plants and enter the food chain,which eventually leads to agricultural losses and affects human health.Therefore,the remediation of soil cadmium pollution is very urgent.In order to reduce the cost of soil remediation and promote the recycling of resources,using industrial wastes as immobilized materials to treat cadmium-contaminated soil has become one of the hot research topicsIn this study,phosphorus slag(PS),a byproduct from the production of yellow phosphorus,has been used as immobilized material.The adsorption characteristics of phosphorus slag on cadmium and the ability of phosphorus slag to immobilize cadmium in soil were studied by adsorption experiment and soil incubation experiment,and the effect of simulated acid rain on the release of cadmium and phosphorus in soil immobilized by phosphorus slag was investigated by soil column leaching experiment.In addition,pot experiment was conducted to investigate the effects of inorganic material(phosphorus slag,PS)and organic materials(beer lees,BL;beer lees biochar,BC)alone and/or combined application on soil nutrients,the fraction distribution of Cd in soil,soil enzyme activity and soil microbial community structure diversity,as well as the effects on the growth physiological characteristics and Cd accumulation of Chinese cabbage.The results are as follows:(1)The results of adsorption experiment showed that the removal rate of phosphorus slag(45 g/L)to Cd(Ⅱ)reached 96.7% in Cd(Ⅱ)contaminated solution(22.41 mg/L).The adsorption equilibrium times was about 60 minutes for the adsorption of Cd(Ⅱ)on PS in aqueous solution.The solution p H value,temperature and initial Cd(Ⅱ)concentration could increase the unit adsorption amount.The quasi-second-order kinetic,Langmuir model could describe the whole process of the adsorption process.Furthermore,it can be concluded that the adsorption of Cd(Ⅱ)on PS was an endothermic and spontaneous chemical adsorption process when the results combined with thermodynamic research.The added amount of PS of 2 g/L was used to treat the Cd contaminated solution(2.08 mg/L),the cadmium content can meet the requirements of the national environmental quality standard for surface water quality(GB 3838-2002)for grade ii water quality(0.005 mg/L),and the release of phosphorus meets the requirements of the standard for grade v water quality(0.4 mg/L),which will not cause secondary pollution to the environment.(2)The results of incubation experiment showed that PS has a better immobilizationeffect than other immobilized materials(fly ash,biochar,humus,cow dung,zeolite,lime).After the immobilized treatment of PS,the change of Cd fraction in soil was balanced in the third week.The exchangeable Cd decreased significantly with the increase of the amount of PS,the 2%(w/w)PS reduced the exchangeable fraction of Cd by 99.69%,which also increased the p H,electrical conductivity,cation exchange capacity,available phosphorus,and available silicon of the soil.(3)The results of simulated acid rain leaching experiment showed that the p H of soil leaching solution decreases with the decrease of simulated acid rain p H.The addition of PS could increase the p H of leached solution and reduce the cadmium content of leached solution.At the same time,the release of phosphorus in PS also increased the content of phosphorus in leached solution.But the content of phosphorus and cadmium in leached solution were both lower than the requirements of surface water environmental quality standard(GB 3838-2002)(total phosphorus content 0.4 mg/L;cadmium content 0.01mg/L),the releases of phosphorus and cadmium to the surrounding water pollution risk is small.(4)The results of pot experiment showed that the single application of PS(PS treatment)and the combined application of PS and BL(PS+BL treatment)were most effective in decreasing exchangeable Cd(decreased by 91.2% in PS treatment;64.0% in PS+BL treatment),However,the soil enzyme activity and the average well color development(AWCD)were decreased in the PS treatment.In contrast,the combined application of PS and BL could increase not only soil enzyme activity,but also AWCD and the functional diversity indices.Moreover,the combined application of PS and BL could significantly reduce the accumulation of Cd in Chinese cabbage(decreased by 81.5% in root;72.5% in aboveground).It could also increase the aboveground height and chlorophyll content of Chinese cabbage while reducing the content of MAD.Therefore,the combined application of PS and BL is more effective. |
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