| The extraction process of ion-type rare earth mine will produce a large amount of lowconcentration rare earth solution,which is easy to cause the loss of rare earth resources and environmental pollution.Urban excess sludge is a potential organic resource with large yield and high organic content.In this paper,the residual municipal sludge was used as raw material,dried and ground to make dry sludge(DS),and the carbonization products of sludge were prepared by different carbonization techniques,and then used as the adsorbent of rare earth ions for low concentration rare earth wastewater.The adsorption efficiency and action characteristics of low-concentration rare earth ions by low-temperature carbonized sludge(LCS)were investigated,the optimization experiments of single factor condition and response surface method were carried out,the structural characteristics of the sludge carbonized material and the kinetics,isotherm and thermodynamics of the adsorption of low-concentration rare earth ions were investigated,and the microscopic mechanism of the adsorption of low-concentration rare earth ions was revealed,and the desorption experiment of LCS was carried out.The main contents are as follows:(1)Sludge carbonization products prepared by hydrothermal,microwave-assisted hydrothermal,high-temperature and low-temperature carbonization technologies were respectively used in the treatment of low-concentration rare earth wastewater(rare earth ion concentration 185.70 mg/L,calculated by REO).The results showed that: Low temperature carbonization technology(LCS)has the best adsorption effect on low concentration of rare earth ions,and the adsorption capacity can reach 91.7 mg/g(adsorption rate is 98.77 %).The optimum conditions for the preparation of carbonization products by low temperature carbonization technology are as follows: temperature350 ℃,time 1.5 h,initial DS weight 4 g.(2)The optimization tests of LCS as adsorbent and response surface method(rare earth ion concentration 103.45 mg/L,calculated as REO)were carried out.The results showed that the optimal adsorption conditions were as follows: stirring time 87 min,oscillation time 70 min and standing time 8 h.The predicted value of adsorption rate was 94.843 %,and the average measured value of adsorption rate was 94.075 %,which were in line with the predictive value.(3)XRF,XRD,SEM/EDS,FTIR and BET were used to characterize the LCS before and after adsorption.The results showed that the structure of the adsorbed LCS was cube shape,large volume,no obvious micro channels on the surface,containing large structure channels,rough surface and a large number of rare earth ions.The low temperature carbonization technology increased the specific surface area of dry sludge(DS)by 69 % and the adsorption rate by 32.79 %.It is speculated that there are many functional groups distributed on LCS,and hydroxyl radical plays an important role in the adsorption process of rare earth ions.(4)The kinetic and thermodynamic processes of LCS adsorption of rare earth ions were fitted respectively.The results show that the adsorption process conforms to the quasi-first-order adsorption kinetics model and Langmuir equation,indicating that the LCS rare earth ion adsorption process is mainly physical adsorption.The adsorption process of LCS on rare earth ions with low concentration is a physicochemical process mainly based on physical adsorption and supplemented by chemical complexation.(5)The cyclic regeneration experiment of LCS was carried out,and the results showed that:HCl(concentration 0.5 mol/L,dosage 50 m L)was used to desorption LCS adsorbed rare earth ions(desorption amount 1g,desorption time 1h,cycles 6 times).The desorption effect of the first two times was good,maintaining above 98.67 %,and the following four times the desorption rate could maintain above 70 %,showing good desorption effect. |
PDF Full Text Request