Study On Adsorption Performance And Competitive Mechanism Of Sludge-Based Biochar On Heavy Metals In Water

In recent years,with the development of industry,pollution incidents caused by heavy metals have occurred frequently,and the adsorption of heavy metals by biochar has made great progress.However,its adsorption capacity is limited.Modification of biochar can improve the adsorption performance of sludge biochar to heavy metals in water.In this paper,dewatered sludge was used as raw material,and the adsorption characteristics of sludge-based biochar and modified sludge-based biochar were analyzed using kinetics and adsorption isotherm models,combined with X-ray diffraction（XRD）and Fourier transform infrared spectroscopy(Various characterization methods such as FT-IR,scanning electron microscope（SEM）and X-ray photoelectron spectroscopy（XPS）discussed the adsorption mechanism,and finally discussed the competitive adsorption between heavy metals.The main results are:（1）The sludge-based biochar（BC）was prepared by the high-temperature calcination method for the study of the adsorption of heavy metals in water.The results revealed that when the p H value was equal to 4,the adsorption capacity of BC for Pb²⁺and Cu⁶⁺reached the maximum,which reached 159.87 mg/g and 72.82 mg/g and When the p H value was equal to 3,the adsorption capacity of BC for Cr⁶⁺reached the maximum,up to 67.82 mg/g.The kinetics and isotherms of phosphate adsorption onto BC could be well described with a pseudo-second-order and Langmuir models,respectively.Furthermore,the adsorption mechanism of the above process was diverse mainly controlled by electrostatic adsorption,C-O bond and Si-O-Si functional group.（2）The nano-zero-valent iron sludge biochar（n ZVI-BC）was successfully prepared by the liquid-phase reduction method,which was used for the study of the adsorption of heavy metals in water.The results revealed that when the p H value was equal to 3,the adsorption capacity of n ZVI-BC for Cr⁶⁺reached the maximum of 177.10 mg/g.When the p H value was equal to 4,the adsorption capacity of n ZVI-BC for Pb²⁺and Cu²⁺reached the maximum of 616.00 mg/g and 221.07 mg/g.The kinetics and isotherms of phosphate adsorption onto BC could be well described with a pseudo-second-order and Langmuir models,respectively.Furthermore,the adsorption mechanism of the above process was diverse mainly controlled by electrostatic adsorption,C-C bond,C-O bond and O-C=O functional groups.（3）The co-existing cations Na⁺and Mg²⁺and the co-existing anions Cl^-and SO₄^2-produced competitive adsorption with Pb²⁺,Cu²⁺and Cr⁶⁺in the unitary system,and inhibited the adsorption.The inhibitory effect was greatest when the concentration is 1%.When the concentration of HA was 1 mg/L,it competed with Pb²⁺,Cu²⁺and Cr⁶⁺in the unary system,and inhibited the adsorption.Coexisting cations Na⁺and Mg²⁺and coexisting anions Cl^-and SO₄^2-and Pb²⁺,Cu²⁺,Cu²⁺,and Cr⁶⁺in the binary system all produced competitive adsorption,and inhibited the adsorption.The inhibitory effect was greatest when the concentration was1%.When the concentration of HA was 1 mg/L,it competes with Pb²⁺,Cu²⁺,Cu²⁺,and Cr⁶⁺in the binary system,and had an inhibitory effect on the adsorption.However,with the increasing concentration of HA,the adsorption capacity of BC and n ZVI-BC on Pb²⁺and Cu²⁺increased,and the increase of HA concentration promoted the adsorption of Pb²⁺and Cu²⁺by BC and n ZVI-BC.（4）In this paper,BC and n ZVI-BC were successfully prepared using sludge as raw material for the adsorption of Pb²⁺,Cu²⁺,Cr⁶⁺.The modified sludge biochar had a good adsorption performance.This method has provided a new way for resource utilization of sludge,and improved the adsorption performance of Pb²⁺,Cu²⁺,and Cr⁶⁺.