Adsorption Of Cobalt In Aqueous Solution By Active Magnesium Oxide

Adsorption,a high-efficiency method,is often used to treat the wastewater and developing new adsorbents with high separation efficiency and low-cost become a hotspot in recent years.Active magnesium oxide has attracted considerable attention due to the excellent characteristic of magnesium oxide,itself larger specific surface area and high activity is widely used in the field of wastewater treatment,so has strong adsorption of heavy metals from wastewater.However,their chemical property is unstable,and it is easy to be corroded and agglomerated.In the present,Direct Precipitation Method and Homogeneous Precipitation Method were used to prepare active magnesium oxide?D-MgO/H-MgO?,and their adsorption behavior of Co???on D-MgO/H-MgO were studied,which provided the theoretical basis for treating the ⁶⁰Co???radioactive wastewater.D-MgO and H-MgO were used to remove Co???from aqueous solution by static adsorption experiments,respectively.These materials were mainly characterized by scanning electron microscope?SEM?,energy spectrum?EDS?,X-ray diffraction?XRD?,fourier transform infrared spectoscopy?FT-IR?,etc.The adsorption behaviors of cobalt by varying the solid-to-liquid ratio,solution pH value,contact time,temperature,initial Co???radiactive concentration were investigated on D-MgO and H-MgO.The experimental datas were fitted by isothermal adsorption and kinetic,and the thermodynamics parameters??H,?S and?G?were calculated.The results of the study are as follows:1.SEM showed that D-MgO belonged to amorphous state with uneven grain sizes,and their particles became larger after adsorption;H-MgO belongs to microspheric state,it is made up of many nanosheets with uniform grain sizes,H-MgO nanosheets were agglomerated after the adsorption.XRD indicated that both D-MgO and H-MgO generated the magnesium hydroxide by hydrating when reacted.FT-IR indicated that the activity of H-MgO was stronger than D-MgO.2.When the temperature was 293 K,the best adsorption conditions for D-MgO and H-MgO showed that pH value of solution was 5.0,the contact time was 40 min,the solid-to-liquid ratio was 0.3 g·L^-1,the initial Co???concentration was 20 mg·L^-1 and 75mg·L^-1for D-MgO and H-MgO.The removal rate of Co???reached around 97%and 99%respectively,adsorption capacity of Co???reached around 65 mg·g^-1 and 248 mg·g^-1respectively.The adsorption processes were both well defined by the Langmiur isotherm,Thermodynamic functions?H>0 indicated that reaction belonged to endothermic reaction.For D-MgO,dynamic behavior conformed to Pseudo-second-order kinetic,E_a>40 kJ·mol^-1indicated that adsorption belonged to chemical adsorption;for H-MgO dynamic behavior conformed to Pseudo-second-order kinetic,E_a<40 kJ·mol^-1 indicated that adsorption belonged to physical and chemical adsorption.3.The ion strength had inhibited effect on the adsorption of Co???on active magnesium oxide?H-MgO?,and the effect was increased with the increase of ionic strength.Both cation and anion had a certain inhibitory effect on the adsorption.The effect of Ca²⁺,Mg²⁺and NH₄⁺was stronger than that of K⁺and Na⁺.The strong acid ion had little effect on the adsorption,but the weak acid ion had big effect.Selective adsorption experiment showed that active magnesium oxide also had strong adsorptivity to other heavy metal ions in wastewater,so the capacity of selective adsorption of Co???was weak.4.Elution experiment repeated that the best eluent was 7 mol·L^-1NH₃·H₂O,for D-MgO,the desorption rate was 67%,the removal rate and adsorption capacity of Co???was 86.28%and 57.52 mg·g^-1 when used for 4 times.For D-MgO,the desorption rate was58%,the removal rate and adsorption capacity of Co???was 44.06%and 110.16 mg·g^-1when used for 4 times.