Abstract
In present study, fine calcium hydroxyphosphate (Ca 5 (PO 4 ) 3 (OH), HAP) particles with spiny hierarchical-structured morphology were prepared through a unique phase-transformation process of solid CaSO 4 ·2H 2 O in a controlled double jet precipitation system. The obtained spiny hierarchical-structured-HAP powder was tested on its defluoridation efficiency by using the synthetic solution and real coal mine water samples respectively, and it was confirmed that the spiny nanowhiskers on the surface of the HAP played an indispensible role that made it much better than the commercial HAP particles. The adsorption kinetics and isotherm behavior were also investigated, and the maximum adsorption capacity for fluoride was evaluated as 12.2 mg/g at the neutral pH. All coexisting anions like sulfate, chloride, nitrate, phosphate and carbonate were found to cause about 10–20% decrease in the defluoridation efficiency only when their concentrations were 2–200 factors larger than that of fluoride, and it could be reused for at least 5 cycles of adsorption/elution without decreasing the adsorption efficiency drastically in a batch adsorption mode. The real coal mine water sampled from Ejin Horo Qi, Ordos city, Inner Mongolia, was used for the column adsorption test, and even after 3 cycles of adsorption/elution it still maintained high defluoridation efficiency. The present study provided a promising defluoridation method to remove the excessive fluoride from the real coal mine water efficiently by a cheap and effective way. • A facile novel process to prepare spiny hierarchical-structured HAP particles on large scale were proposed successfully. • Phase transformation of CaSO 4 ·2H 2 O to Ca 5 (PO 4 ) 3 OH is essential to the formation of spiny hierarchical-structure. • Spiny HAP particles had much better defluoridation capability than commercial HAP directly at neutral pH. • Nanowhiskers of HAP was observed by TEM on the surface of the obtained Ca 5 (PO 4 ) 3 OH. • Fluoride in the real coal mine water was efficiently removed by spiny HAP particles.
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