| As the typical hard biodegradation materials,both heavy metals and antibiotics in wastewater have posed a serious threat to ecological system and public health.Thus,it is a hot subject to economically and effectively remove the heavy metals and antibiotics of environmental waters.In this paper,magnetic alkaline Ca-bentonite(MACB)was organically modified by chitosan/sodium carboxymethyl cellulose copolymer film(CC).The as-prepared material,CC-modified magnetic alkaline Ca-bentonite(MACB/CC)was used as the adsorbent for the adsorption of heavy metals Cu(Ⅱ)&Mn(Ⅱ),and antibiotic doxycycline(DC)from aqueous solutions.The adsorption parameters were studied and the adsorption isotherms and kinetic models were also investigated.The main mechanisms of Cu(Ⅱ)&Mn(Ⅱ),and DC removal by MACB/CC were explored through results of adsorption models and characterizations including FE-SEM and FT-IR.Main results are as follow:(1)The results of batch experiments of Cu(IIⅡ)&Mn(Ⅱ)adsorption on MACB/CC indicated that the adsorption rates of Cu(Ⅱ)&Mn(Ⅱ)on MACB/CC were rapid initially but slowed down thereafter.The respective adsorption of Cu(Ⅱ)&Mn(Ⅱ)on MACB/CC were 97%and 85%with 60 min contact time.Meanwhile,the adsorption was strongly dependent on the initial pH and Cu(Ⅱ)&Mn(Ⅱ)adsorption on MACB/CC increased with the initial pH increased.Cu(Ⅱ)&Mn(Ⅱ)adsorption reached 99%and 92%at pH 7.0,respectively.The results also showed the competition adsorption ability between Cu(Ⅱ)&Mn(Ⅱ)was in the order of Cu(Ⅱ)>Mn(Ⅱ).After five recycles,Cu(Ⅱ)&Mn(Ⅱ)adsorption on MACB/CC still maintained above 93%and 90%,respectively.The adsorption isotherms were well described by the Langmuir model with the respective Langmuir adsorption capacities of Cu(Ⅱ)&Mn(Ⅱ)being 94 mg·g-1 and 38 mg·g-1.The adsorption kinetics study demonstrated that the adsorption process fitted the pseudo-second order model well,indicating that the rate-determination step for MACB/CC was chemical adsorption.(2)The results of DC adsorption on MACB/CC showed that adsorption efficiency of DC was rapidly increased with the dosage of MACB/CC increased.With an increase in the initial pH from 2.0～7.0,there was an increase in the adsorption of DC.Adsorption process was found to be optimal in the pH range of 7.0～11.0,with DC adsorption maintained above 95%.The existence of low concentration of Cu(Ⅱ)and humic acid made positive effect on DC adsorption,whereas Mn(Ⅱ)was inhibited.Adsorption capacity of DC on MACB/CC was still higher than 290 mg·g-1 after 5 reuse times.Equilibrium data were well fitted by the Langmuir model and kinetic data were fitted by pseudo-second order model very well,pointing that the adsorption process was monolayer and chemical adsorption.The maximum sorption capacity was 599 mg·g-1 based on the Langmuir model.(3)The main mechanisms of Cu(Ⅱ)and Mn(Ⅱ)removal by MACB/CC were cation exchange,precipitation and complexation.At low pH,Cu(Ⅱ)&Mn(Ⅱ)could be adsorbed on MACB/CC by cation exchange reaction.With the initial pH of solutions increased,Cu(Ⅱ)&Mn(Ⅱ)could be precipitated with hydroxide ions on the surface of MACB/CC and chelated with the deprotonated organic functional groups of MACB/CC.The main mechanisms of DC adsorption on MACB/CC were dependent on the different forms of DC in various pH conditions.When DC existed as cationic or neutral form at acidic condition,cation exchange and electrostatic interactions were the main mechanisms of DC adsorption on MACB/CC.At neutral and alkaline conditions,Ca2+ was a vital role in the adsorption which acted as a bridge between MACB/CC surface and the anionic species of DC.Due to the excellent adsorption performance and reusability,MACB/CC could be deemed as a highly promising adsorbent for wastewater treatment with heavy metals and antibiotics. |
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