Enhanced Defluoridation of Water Using Zirconium—Coated Pumice in Fixed-Bed Adsorption Columns

Abstract

Millions of people across the globe suffer from health issues related to high fluoride levels in drinking water. The purpose of this study was to test modified pumice as an adsorbent for the purification of fluoride-containing waters. The adsorption of fluoride onto zirconium-coated pumice (Zr–Pu) adsorbent was examined in fixed-bed adsorption columns. The coating of zirconium on the surface of VPum was revealed by X-ray diffractometer (XRD), Inductively coupled plasma-optical emission spectroscopy (ICP-EOS), and X-ray fluorescence (XRF) techniques. The degree of surface modification with the enhanced porosity of Zr–Pu was evident from the recorded scanning electron microscope (SEM) micrographs. The Brunauer-Emmett-Teller (BET) analysis confirmed the enhancement of the specific surface area of VPum after modification. The Fourier transform infrared (FTIR) examinations of VPum and Zr–Pu before and after adsorption did not reveal any significant spectrum changes. The pH drift method showed that VPum and Zr–Pu have positive charges at pHPZC lower than 7.3 and 6.5, respectively. Zr–Pu yielded a higher adsorption capacity of 225 mg/kg (2.05 times the adsorption capacity of VPum: 110 mg/kg), at pH = 2 and volumetric flow rate (QO) of 1.25 mL/min. Breakthrough time increases with decreasing pH and flow rate. The experimental adsorption data was well-matched by the Thomas and Adams-Bohart models with correlation coefficients (R2) of ≥ 0.980 (Zr–Pu) and ≥ 0.897 (VPum), confirming that both models are suitable tools to design fixed-bed column systems using volcanic rock materials. Overall, coating pumice with zirconium improved the defluoridation capacity of pumice; hence, a Zr–Pu-packed fixed-bed can be applied for defluoridation of excess fluoride from groundwater. However, additional investigations on, for instance, the influences of competing ions are advisable to draw explicit conclusions.

Fixed-Bed Adsorption: Comparisons of Virgin and Zirconium Oxide-Coated Scoria for the Removal of Fluoride from Water

“…Fluoride levels in surface water ranged from 0.01 to 0.3 mg/L, while groundwater levels range from less than 1 to more than 35 mg/L [2,3]. Fluoride is thought to have beneficial effects in trace amounts in drinking water, but prolonged exposure to fluoride in drinking water, or combined effect with exposure to fluoride from other sources, could result in some negative effects [4][5][6][7]. It can prevent the incidence of dental caries, particularly in children under the age of 8 years, if taken in the drinking water at an optimum level (~0.5-1.5 mg/L) [8].…”

“…However, if the permissible level is exceeded, dental fluorosis or mottled enamel will appear, and if the concentration is greater than 3 mg/L, it will also cause skeletal fluorosis [9]. Groundwater is the safest and most economically viable option of all available drinking water sources for many communities around the world, as is the case for many communities in rural and urban areas of the main African rift valley [4,5,7]. In recent years, the entry of geogenic pollutants, such as fluoride, into groundwater aquifers has become a serious environmental problem worldwide.…”

“…In recent years, the entry of geogenic pollutants, such as fluoride, into groundwater aquifers has become a serious environmental problem worldwide. Over 200 million people around the world, including in East Africa, are drinking fluoride-containing groundwater beyond the permitted limit (1.5 mg/L), which has a significant impact on human well-being [5,7,10]. Fluorosis is by far the most common geochemical disease in the East African rift, impacting more than 80 million individuals [7,11,12].…”

“…Different treatment techniques such as ion exchange, membrane, precipitation, and adsorption have been employed for the uptake of fluoride [20]. Among the existing techniques, adsorption remains the most widely employed and most suitable method because of its applicability for uptake of fluoride even at small doses, economic feasibility, high efficiency, and simplicity of design [5,7,20].…”

Amino Acid Complexes of Zirconium in a Carbon Composite for the Efficient Removal of Fluoride Ions from Water

“…The zirconium coordination complexes and fluoride show a strong interaction [ 21 , 22 ], so this could be an attractive candidate for purification of groundwater, industrial waste, and drinking water. Several zirconium-based materials have been reported, for example hybrid zirconium (IV)-hexamethylenediamine and amorphous zirconium phosphate [ 23 ], zirconium (IV)-doped polypyrrole/zirconium (IV) iodate [ 24 ], β-cyclodextrin modified hydrous zirconium oxide [ 25 ], iron (III)-zirconium(IV) hybrid oxide [ 26 ], zirconium-coated pumice [ 27 ], Zr/Fe/Al-modified chitosan beads [ 28 ], zirconium modified activated carbon fibers [ 29 ], complexes of zirconium and graphene oxide-zirconium with dicarboxylic acids [ 30 , 31 ], among others. Recently, low-cost carbon-based adsorbents were synthesized [ 32 ].…”