| Excess fluoride in bodies of water can lead to dental, skeletal, and nonskeletal forms of endemic public health problem. According to the WHO standards, the permissible limit of fluoride ions in drinking water is1.5mg/L. Chinese drinking water standard for it has been amended to lowering fluoride content in the in drinking water to less than1.0mg/L. Among some treatment technologies, adsorption because of its simplicity and conveniency, is still one of the most extensively used methods. Unfortunately, low adsorption capacities, slow adsorption processes and narrow optimum pH ranges of the most materials, though cheap, limit their practical applications. Therefore, an adsorbent with high fluoride adsorption capacity, fast adsorption processes and wide some optimum pH ranges is desired. In order to solve the above-mentioned technique problems, in the present paper, zirconium modified attapulgite (Zr-A) and Zr/Al/Ce system (Zr-Al-Ce) adsorbents were prepared by simple methods. The optimization preparation processes were carried out and the results showed that the Zr-A and Zr-Al-Ce adsorbents showed higher adsorption capacities in comparision with other adsorbents.The Zr-A composite adsorbent was characterized by XRD, FT-IR, SEM and ED AX analyses showed that the structure of attapulgite was destroyed to some extent during the modification process and the ZrO2nanoparticles were formed in the interlayers of attapulgite or on the surface of attapulgite. The fluoride adsorption capacity of the Zr-A adsorbent was higher in comparison with attapulgite, which was due to the changes of the surface charge of the adsorbent and the generation of abundant hydroxyl ions. The solution pH is very important for fluoride adsorption, which controls the adsorption of fluoride at the absorbent-water interface. Fluoride was adsorbed on the adsorbent via the ion-exchange mechanism.The adsorption data were better represented by the Langmuir isotherm than the Freundlich isotherm. A Langmuir maximum adsorption capacity of24.55mg/g was obtained at an initial pH of3.14and temperature of30℃. The adsorption process followed the pseudo-second-order model for fluoride. The fluoride adsorption was influenced by the phosphate, sulfate and bicarbonate ions, but not by the chloride and nitrate ions. After six regeneration and reuse cycles, the Zr-A adsorbent still showed high adsorption capacity. The results of adsorption and reuse experiments indicated that the Zr-A adsorbent could be employed as a promising adsorbent for fluoride adsorption from drinking water.From a practical perspective, the Zr-A adsorbent granulation and fixed-bed adsorption experiments were carried out. The optimal preparation conditions of the granular Zr-A adsorbent were as follows, the concentration of the caking agent was10wt.%and the heating temperature was70℃. The fixed-bed adsorption results indicated that the breakthrough capacity of the granular Zr-A adsorbent increased with the decrease of the water discharge and the increase of the initial fluoride concentration. After five regeneration cycles, the Zr-A adsorbent still showed high adsorption capacity.XRD and ζ analysis indicated that the Zr-Al-Ce composite was not a simple mixture of the ZrO2, Al2O3and CeO2. FT-IR analysis indicated that the hydroxyl groups on the adsorbent surface were involved in the fluoride adsorption. XPS analysis demonstrated that the hydroxyl groups bonded to metal (M-OH) were involved in fluoride adsorption but not the hydroxyl groups attributed to oleic acid (C-OH).The fluoride adsorption data on the Zr-Al-Ce adsorbent agreed well with the Langmuir mode. A Langmuir maximum adsorption capacity of250.0mg/g was obtained at an initial pH of6.80±0.20and temperature of30℃, which indicates that the Zr-Al-Ce adsorbent has a high fluoride adsorption capacity. The thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. The adsorption process followed the pseudo-second-order model for fluoride. The effects of co-existing anions on the sorption of fluoride followed the decreasing order of PO43-> SO42-> HCO3-> NO3-> CI-. The Zr-Al-Ce adsorbent still showed high adsorption capacity after three regeneration and reuse cycles. The results of adsorption and reuse experiments indicated that the Zr-Al-Ce adsorbent could be employed as a promising adsorbent for fluoride adsorption from drinking water.The granulation experiments indicated that the optimal preparation conditions of the Zr-Al-Ce granular adsorbent were as follows, the mass ratio of the Zr-Al-Ce adsorbent to attapulgite was1:2, the concentration of the caking agent was15wt.%, and the heating temperature was80℃. The fixed-bed adsorption results indicated that the breakthrough capacity of the granular Zr-Al-Ce adsorbent increased with the increase of the initial fluoride concentration and the decrease of the water discharge. After regeneration and reuse experiments, the breakthrough capacity of the granular Zr-Al-Ce adsorbent was just decreased about8%, which indicated that the granular Zr-Al-Ce adsorbent had a good adsorption property and could be employed as a promising adsorbent for fluoride adsorption from drinking water.
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