| Fluoride is the necessary trace elements for human being.An appropriate concentration of fluoride can be beneficial effects to keep bones and teeth healthy.However,excessive intake of fluoride can cause fluorosis,and even lead to neurological diseases,leading to death.Among some treatment technologies,the adsorption method has been widely concerned due to its simple operation,reliable operation,and no secondary pollution.Most of the existing adsorbents have problems such as low adsorption capacity,slow initial adsorption speed,and high price,which limits the application of the adsorption method.In this study,a new granular activated adsorbent(ALCt)was prepared,which originated from the aluminate cement and was thermally activated at different temperatures.Batch sorption experiments were conducted to study the influence of various factors such as activation temperature,Particle size,equilibrium contact time,p H,co-existing and ionic strength on the sorption of fluoride.The surface morphology,internal structure characteristics and adsorption mechanism were analyzed by TGA,XRD,FT-IR and SEM.The desorption and regeneration properties of the prepared adsorbent materials were studied,and the application prospect of alumina cement as a new cheap and efficient fluoride adsorbent was explored.The results of the study are as follows:(1)After thermally activation,there are obviously changes of physical and chemical properties of hydrated aluminate cement.The dehydration of hydration products of aluminate cement samples gradually occurs with the increase of temperature.The surface area and the pore volume of samples fluctuate along with the increase of activation temperature,The surface of samples become more rough and porosities increase at 600℃,ALC600 and ALC700 get more larger surface area up to 24.1 m2/g and 24.8 m2/g.After calcination at 900℃,the surface of sample is cracked.The specific surface area of ALC900 is reduced to 7.2m2/g(2)The amount of fluoride adsorbed by ALCt fluctuated with the increase of activation temperature.The adsorption capacity of fluoride at 600℃(ALC600)was the highest at 17.42 mg/g(C0=100mg/L,adsorbent dose 5g/L,T=25℃,p H=7,t=72h).And the adsorption capacity at 1h reaches 5.42mg/g,which has the advantage of faster initial adsorption rate compared to other activation temperatures.Determine 1-2mm as the optimal particle size of the adsorbent due to its large adsorption capacity and low initial adsorption speed.(3)The adsorption of fluoride ion by ALC600 reaches equilibrium after 72h;ALC600 has good defluoridation performance in a large p H range(5-9);The effects of co-existing anions on the sorption of fluoride followed the decreasing order of CO32->HCO3->PO42->NO3->SO42->Cl-,and the adsorption capacity was almost not affected by the ionic strength.(4)The adsorption processes were fitted as pseudo-second-order model and Langmuir model,and maximum adsorption capacity was over 223mg/g.thermodynamic results show that the adsorption process is a spontaneous process of endothermic and entropy increase.According to the change of crystal structure,chemical bond and surface morphology of ALC600,the process of fluoride removed by ALC600 was mainly due to chemical adsorption,internal complexion and surface precipitation,the ion exchange and electrostatic interaction were also involved(5)The results of repeated regeneration showed that 0.25mol/L Al2(SO4)3 solution had the best regeneration effect on ALC600,and the regeneration time was 3h.ALC600 still has a high adsorption capacity under a limited number of regeneration conditions. |
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