Remediation Of Cd And Ni Contaminated Soil By Cattle-manure-derived Biochar And Zeolite

Soil heavy metal pollution has become a serious environmental threat due to their toxic effect on ecosystem and food security.The possible remediation option has been considered to address the mobility of heavy metals in soil and water.In this study,we evaluate the efficiency of zeolite（Zeo）,heated zeolite（ZeoΔ）,cattle manure（CM）,cattle manure derived biochar（CMB）,co-pyrolysis of cattle manure and zeolite（（CM+Zeo）Δ）,the mixture of cattle manure derived biochar（CMB+ZeoΔ）as soil amendments to immobilize soil Cd and Ni.The remediation effect of soil Cd and Ni were estimated by BCR and TCLP extraction techniques.The mechanism of remediation was explored by adsorption experiment.The study was aimed to provide theoretical basis for the application of CMB and Zeo in remediation of heavy metal pollution in soil.The main result as follow:1.All the 6 amendments are alkaline（pH 6.85-7.50）and the proportion of mesoporous materials is above 50%.Zeo and ZeoΔ have large specific surface area（19.59 m²/g and 19.57 m²/g）,CMB,（CM+Zeo）Δ and（CMB+ZeoΔ）had great CEC（117.56 cmol/kg-132.77 cmol/kg）.In addition,the CMB was rich in carboxyl,hydroxyl and alkyl benzene and other functional groups.The greater surface adsorption site concentration 23.24mmol/g of CMB was observed as compared to 9.77mmol/g of（CM+Zeo）Δ and 2.07 mmol/g of zeolite.2.In the adsorption experiment,the adsorption of Cd by Zeo,ZeoΔ,CMB,（CM+Zeo）Δ and（CMB+ZeoΔ）reached at equilibrium in 4h.The adsorption capacity of Cd²⁺ increased with the increase of p H in the range of 3-7.The adsorption of Cd²⁺ and Ni²⁺ with all 5 amendments can be better fitted by Langmuir equation as compared to Freundlich.The adsorption capacity of Cd²⁺ and Ni²⁺ by all 5 amendments is 3.26 mg/g-4.86 mg/g and 2.74 mg/g-4.38 mg/g,respectively.Among them,（CMB+ZeoΔ）offered the greatest adsorption for Cd²⁺ and CMB hand largest adsorption for Ni²⁺.3.The result of the competitive adsorption of Cd²⁺ and Ni²⁺ by all 5 amendments showed that,the removal rate of Cd²⁺ and Ni²⁺ on ZeoΔ in the mixed solution of Cd²⁺ and Ni²⁺ was much lower than that in single solution.The removal rate of Cd²⁺ and Ni²⁺ decreased by 11.63%-30.08% and 12.71-57.56%,respectively.But the removal rate of Cd²⁺ on CMB and（CMB+ZeoΔ）increased by-2.95%-47.63% and-16.02%-13.65%,respectively.On contrary the removal rate of Ni²⁺ decreased by 52.89%-64.35% and 45.86%-56.91%.Therefore,Cd²⁺ showed stronger competitive ability as compared to Ni²⁺ with all amendments.4.The CMB has high content of water soluble carbon 56.16 mg/kg and phosphorus 3.15 mg/g,which might increase Cd²⁺ and Ni²⁺ adsorption through precipitation with PO43-and CO32-.These results were confirmed by the XRD technique after batch adsorption study.5.The soil pH and CEC were significantly increased by 0.20-1.05 units and 3.14%-10.37%,respectively with the addition of the 5 soil amendments,in which the CMB treatment had the largest increase of soil pH.6.Compared with the CK（treatment without amendment）,all applied amendments significantly reduces the bio-availability of Cd and Ni in soil.The acid extractable Cd and Ni in all the treatments significantly decreased by 22.3%-62.5% and 2.3%-13.2%,respectively.Meanwhile,the TCLP extractable Cd and Ni decreased by 41.6%-49.2% and 55.1%-64.1% respectively.Particularly,the（CMB+ZeoΔ）offered the best remediation effect for Cd and Ni in soil,followed by CMB.